From dopamine 4 to sigma 1: Synthesis, SAR and biological characterization of a piperidine scaffold of σ1 modulators

Abstract

The sigma 1 receptor is a multifunctional receptor with wide distribution in the nervous system and its function has been implicated with a number of neurological disorders including dementia and Alzheimer’s disease (AD) and other neurodegenerative disorders. In addition, modulators of σ1 have been advanced into clinical trials for the treatment of pain. Starting from our previously disclosed piperidine scaffold, we have identified a class of potent sigma 1 modulators. This work highlights the key SAR components that lead to the divergence in D₄ and σ1 activity. In addition, we further profile lead compounds in a panel of off-target receptors, in vitro and in vivo pharmacokinetic studies. This has culminated in the discovery of multiple σ1 receptor modulators with properties that will allow for study in animal models.

1. Introduction

The dopamine receptors (DR) were first characterized in the 1980s as members of the Class A G-protein-coupled receptors (GPCRs) super-family [1–4]. They were later subdivided into five subtypes, D_1–5; which are further subdivided into two families of distinct receptor types (D₁-like and D₂-like) [4,5]. The dopamine receptors garnered much attention due to the dopamine hypothesis of schizophrenia and much of the work centered on the D₂ and D₃ receptors, specifically due to the activity of the typical and atypical antipsychotics [6–11]. In addition, the dopamine 4 receptor subtype garnered quite a bit of interest in the early 1990s as a potential therapeutic target for schizophrenia, as it was shown the atypical antipsychotic clozapine was more active at D₄ compared to the other dopamine receptor subtypes [12,13]. One of the first compounds that progressed into clinical trials for the treatment of schizophrenia was L745,870, 1; however, the compound failed to show efficacy, although it was well tolerated (Fig. 1) [14,15]. In addition to 1, other D₄ antagonists that were progressed to clinical trials failed to show any efficacy. After these failures, many of the D₄ receptor antagonists and modulators were sidelined in favor of the other subtypes. Recently there have been several reports linking D₄ to addiction [16], Parkinson’s disease (PD) [17], and cancer [18,19], and as such, there has been a resurging interest in D₄ antagonists [20].

Fig. 1.

Reported D₄ antagonists.

l-DOPA is the hallmark therapeutic treatment for PD; however, chronic treatment with l-DOPA can lead to the development of abnormal involuntary movements (dyskinesia). These l-DOPA-induced dyskinesias (PD-LIDs) can lead to significant loss of quality of life. D₄ receptors are present in the basal ganglia, and it has been postulated that treatment with D₄ antagonists can lead to a reduction in PD-LIDs. Again, 1 was the lead compound, and it was reported to have activity in rodent and non-human primate models of l-DOPA induced dyskinesias [21,22]. However, 1 failed to improve rotarod performance, suggesting that it would have a narrow therapeutic window for PD-LIDs. Our laboratory reported the discovery of morpholine and 4,4-difluoropiperidine scaffolds, 2 and 3 [23,24], and showed that 2 was active in an in vivo mouse model of PD-LIDs and was devoid of the rotarod issue associated with 1 [25].

During this, and subsequent SAR work, we performed selectivity studies using the Psychoactive Drug Screening Program (PDSP) to gauge the relative selectivity of these tool compounds against a wide panel of CNS receptors [26]. We noticed a common off-target receptor, sigma 1, that was consistently active when tested against our compounds. Most of our original compounds maintained high potency against the D₄ receptor (K_i < 10 nM) and had modest selectivity against σ1 (~10-fold) (Table 1). However, we did notice a distinct change in the selectivity profile with only a modest change to the compound. The 5-indole southern analog, 4, was potent at D₄ (K_i = 3.3 nM) and ~13-fold selective versus σ1; however, moving to the 5-benzimidazole moiety reversed this selectivity (5, σ1, K_i = 18 nM vs. D₄, K_i = 426 nM). This was the first time in this morpholine scaffold that we saw this switch, and we wanted to further investigate the σ1 activity in our newly reported piperidine D₄ scaffolds [27].

Table 1.

Dopamine 4 and sigma 1 receptor binding values of previously disclosed compounds.

Cmpd	Structure	σ1	LEb/LLEb/MPO	D4
		Ki (nM); pKia		Ki (nM); pKia
1		101; 7.00	0.43 3.49 4.9	0.6; 9.26
2		41; 7.39	0.43 4.00 4.7	5.0; 8.30
3		52; 7.28	0.38 1.60 2.5	3.5; 8.45
4		44; 7.36	0.43 3.86 4.8	3.3; 8.48
5		18; 7.74	0.42 4.77 5.4	426; 6.37

^aK_i values determined by competitive inhibition of [³H]N-methylspiperone (D4R) or [³H] Pentazocine (S1R) binding in membranes harvested from HEK293 cells. All K_i are run in triplicate.

^bLigand efficiency (LE) and ligand-lipophilicity (LLE) measurements based on the σ1 receptor.

The sigma (σ) receptors were identified in the 1970s as opioid receptors but were later accepted as a separate and distinct family of receptors, which is comprised of two subtypes, the sigma 1 (σ1) and sigma 2 (σ2) receptors [28,29]. Although the structural and functional aspects of the sigma receptors are not fully elucidated, the σ1 receptor has recently been implicated in a variety of CNS disorders and cancer, including Parkinson’s disease [30,31], pain [32–34], Alzheimer’s disease [30,31,35], depression [36], and addiction [37,38]. Much of the information regarding the σ1 receptor and its role in pain modulation is due to the use of σ1 knockout (KO) [39–41] experiments and σ1 antagonists, showing its effects of analgesia without the known side effects of opioids (constipation and tolerance). Recently, σ1 receptor antagonists have been advanced to clinical trials for pain [42,43]. The X-ray crystallographic structures of the human σ1 receptor in complex with known modulators have been recently published, and this has paved the way for additional SAR studies [44]. The X-ray crystallographic work also showed a common SAR motif that overlapped with our knowledge of the D₄ receptor pharmacophore work. We were able to dock our compounds using the Schrödinger Drug Discovery Suite (Maestro, Release 2022–3) and generate poses using Glide [45,46]. Both receptors have scaffolds with basic nitrogens (e.g., piperidine, morpholine, pyrazole) that make key interactions (σ1: Glu172; D₄: Asp115) with additional aromatic or benzylic groups participating in π-π stacking (Fig. 2) [47,48]. Due to this overlap, and the availability of both the σ1 and D₄ structural information, we embarked on an effort to characterize a set of 3- and 4-hydroxypiperidine compounds [27] as potent σ1 modulators and detail where the SAR diverges with respect to D₄.

Fig. 2.

Docking studies of 5 in the (A) D4 receptor (5WIU) and (B) s1 receptor (5HK1).

2. Chemistry

The synthesis of the 3- and 4-oxypiperidine scaffolds is shown in Scheme 1. Starting with the commercially available tert-butyl (S)-3-hydroxy or 4-hydroxypiperidine-1-carboxylates, 6 or 7, which were alkylated with NaH and the respective BnBr to form the benzyl ethers, followed by deprotection to yield the amines 8 or 9. Next, the final targets, 10–23, were realized by either direct N-alkylation (Cs₂CO₃ and BnBr), reductive amination protocols (Et₃N, ArCHO, NaHB(OAc)₃), or polymer-supported reductive amination (ArCHO, PS-NaBH₃CN, AcOH, CH₂Cl₂) [27].

Scheme 1.

Synthesis of 3- and 4-hydroxypiperidine analogs.

^aReagents and conditions: a) NaH, DMF, BnBr; b) 4 N HCl, dioxane; c) Cs₂CO₃, DMF, BnBr; d) ArCHO, Et₃N, CH₂Cl₂, NaHB(OAc)₃; e) CH₂Cl₂, ArCHO, AcOH, PS-NaBH₃CN, μW, 110 °C, 10 min.

In addition to the piperidine scaffolds, we had wanted to explore other alternative scaffolds that may introduce new chemical matter into the D₄ realm. For this, we thought the commercially available diazaspiro [4.4]nonanes or diazaspiro[4.5]decanes might be of interest. These racemic spirocyclic compounds, 24 or 25, were synthesized in a similar fashion to the piperidine analogs (Scheme 2). The phenyl acetamides, 22, were synthesized by direct N-alkylation of the requisite spirocyclic amines, 20, with the chloroacetamides, 21, under basic conditions (Et₃N, NaI, THF), followed by N-Boc deprotection (4 N HCl, dioxane) to yield 22. The heteroaryl southern analogs, 25, were made via reductive amination (R₂CHO, Et₃N, DCE, NaBH(OAc)₃) followed by deprotection to yield 23. Both 23 and 24 were alkylated with the 3,4-difluorobenzyl bromide (iPr₂EtN, DCE or Cs₂CO₃, CH₃CN) to yield the desired final targets 24 or 25 [27].

Scheme 2.

Synthesis of spirocyclic analogs.

^aReagents and conditions: a) Et₃N, NaI, THF; b) 4 N HCl, dioxane; c) R₂CHO, Et₃N, DCE, NaBH(OAc)₃; d) iPr₂EtN, DCE; e) Cs₂CO₃, CH₃CN, 3,4-difluorobenzyl bromide.

3. Results and discussion

3.1. Evaluation of pharmacological activity

Recently, we have disclosed a series of 3- and 4-hydroxypiperidine compounds, that had moderate D₄ activity [27]; however, over the course of the selectivity screening, we noticed that the divergence in D₄/σ1 activity was exemplified even more dramatically with the benzimidazole (10a, σ1, K_i = 8.3 nM; D₄, K_i = 4,280 nM vs. 5, σ1, K_i = 18 nM; D₄, K_i = 426 nM) in this series compared to the morpholine scaffold (Table 2). This trend continued with the additional 5-benzimidazole derivatives 10b (σ1, K_i = 3.1 nM; D₄, K_i = 1,158 nM) and 10c (σ1, K_i = 27 nM; D₄, K_i = 1,803 nM). To confirm the activity against the sigma 1 receptor, we had 10a and 10b run at Eurofins in their cell-based assay utilizing Jurkat cells. The K_i values were confirmed in this assay (10a, K_i = 12 nM; 10b, K_i = 3.9 nM). The trifluoromethylbenzyl compound, 10c, had a diminished selectivity but that was due to a slight loss of σ1 activity. Adding a methyl group to the benzimidazole nitrogen resulted in compounds that retained the σ1 activity (11a-c); however, the D₄ activity was better for 11a and 11c and slightly worse for 11b. Moving the nitrogen from the benzimidazole into the indazole moiety led to more potent compounds against both σ1 and D₄, 12a-c (e.g., 12a, σ1, K_i = 1.8 nM; D₄, K_i = 1,730 nM); which resulted in excellent selectivity (σ1:D₄ > 950). The 4-chloro-3-fluoro indazole analog, 12b, is the most potent σ1 modulator identified in this study (K_i = 0.7 nM) with an excellent selectivity profile (σ1:D₄ = 828). The NH-indazole analogs, 12a-c, have excellent ligand efficiency (LE > 0.45) [49], ligand-lipophilicity efficiency (LLE >5)⁵⁰, and the CNS multiparameter optimization (CNS MPO) scores (>4.6)^{51, 52}, all measures of drug-like molecules. The LE parameter is an estimate of efficiency of binding, the LLE parameter estimates lipophilicity efficiency and the CNS MPO is a scoring set that utilizes a set of six physicochemical properties to predict CNS-like compounds. Adding a methyl to the nitrogen of the indazole produced a similar pattern as the methylated benzimidazole, similar potency against σ1, but more D₄ activity (13a-c). We compared these compounds with the morpholine scaffold, and the selectivity for σ1 over D₄ was completely lost in this scaffold (13d-e), with the thiazole analog, 13e, losing significant activity against both receptors compared to the 3, 4-difluorophenyl, 13d. Moving to the (S)-3-oxopiperidine with the N-methyl-5-indazole produced compounds with varying σ1 activity. The 2-pyridine, 13f, lost activity against σ1 (Kι = 1,283 nM), which was analogous to the thiazole, 13e. However, the 2-methylphenyl, 13g, regained the activity against σ1 (K_i = 37 nM) and was significantly less active against D₄ (65% inhibition at 10 μM), maintaining high selectivity.

Table 2.

Dopamine 4 and sigma 1 receptor binding values of piperidine-based scaffold.

Cmpd	Structure	σ1	LEb/LLEb/MPO	D4
		Ki (nM); pKia		Ki (nM); pKia
5		18; 7.74	0.42 4.77 5.4	426; 6.37
10a		8.3; 8.08	0.44 4.91 5.4	4,280; 5.37
10b		3.1; 8.51	0.46 4.88 4.8	1,158; 5.94
10c		27; 7.57	0.38 3.81 4.7	1,803; 5.74
11a		11; 7.95	0.41 4.55 4.8	1,400; 5.85
11b		31; 7.51	0.39 3.65 4.3	48%; ND
11c		12; 7.91	0.38 3.92 4.0	640; 6.19
12a		1.8; 8.74	0.48 5.75 5.4	1,730; 5.76
12b		0.7; 9.15	0.47 5.11 4.9	580; 6.24
12c		1.2; 8.92	0.46 5.71 4.6	860; 6.07
13a		1.8; 8.74	0.45 5.41 5.2	276; 6.56
13b		1.3; 8.89	0.46 5.10 4.3	170; 6.77
13c		1.7; 8.76	0.42 4.83 4.1	201; 6.70
13d		23; 7.65	0.40 4.52 5.3	28; 7.55
13e		1,326; 5.88	0.33 3.56 4.9	557; 6.25
13f		1,283; 5.89	0.32 3.39 5.9	23%; ND
13g		37; 7.66	0.40 3.42 4.2	65%; ND

^aK_i values determined by competitive inhibition of [³H]N-methylspiperone (D4R) or [³H] Pentazocine (S1R) binding in membranes harvested from HEK293 cells. All K_i are run in triplicate.

^bLigand efficiency (LE) and ligand-lipophilicity (LLE) measurements based on the σ1 receptor.

Next, we expanded the SAR for the southern portion of the molecule to include additional heteroaryl 5,6- and 6,5-moieties (Table 3). The 6-chloro-2-indole analogs (14a-e) all lost selectivity for the σ1 receptor versus D₄ predominantly due to increased D₄ activity (e.g., 14a, σ1, K_i =8.1 nM; D₄, K_i = 149 nM); however, reduced σ1 activity was also to blame for some compounds (e.g., 14d, σ1, K_i = 52 nM; D₄, K_i = 319 nM); although the 2-pyridine, 14d, did retain activity compared to 13f, above. As was seen above, the morpholine analog, 14e, reversed the selectivity and was more active against D₄ (14e, σ1, K_i = 388 nM; D₄, K_i = 169 nM). Moving to the imidazo[1,5-a]pyridine southern portion also continued the above trend that showed a diminished σ1:D₄ selectivity compared to the previously shown 5-benzimidazole and 5-indazole compounds (Table 1). Specifically, the 3-imidazo[1,5-a]pyridine analogs, 15a-e, showed a loss of σ1 activity, which led to the diminished selectivity (σ1:D₄, 1–5); with the exception of 15d, which lost all activity against D₄ (40% inhibition of D₄ at 10 μM). The 3-methyl-1-imidazo [1,5-a]pyridine analogs, 16a-c, were also less selective, and had more significant D₄ activity, with selectivity ratios of 9–12 (σ1:D₄). However, the activity against σ1 could be regained by moving to the 2-imidazo [1,2-a]pyridine compounds (17a-c) on the 4-oxypiperidine scaffold. Thus, these compounds have excellent binding against σ1 (Ki = 2.3–5.2 nM); however, they also do have D₄ activity (Ki = 134–338 nM), leading to better selectivities compared to the imidazo[1,5-a]pyridines. In addition, these three compounds retain excellent LE (>0.45) [49], LLE (>5.4) [50], and CNS MPO (>5) scores [51,52]. The northern 2-pyridine substituents lost activity, which was seen previously as well (17d-e). When this southern fragment was included on the 3-oxopiperidine scaffold, nearly all the activity was lost – at both the σ1 and D₄ receptor, with the notable exception of 17g (σ1, K_i = 34.7 nM; D₄, K_i = 646 nM). Similar to what we’ve seen, the thiazole substituted morpholine scaffold, 17j, lost activity while the aryl substituted morpholine retained the D₄ activity while not being active against σ1, 17k (σ1, K_i = 1,093 nM; D₄, K_i = 91 nM). Lastly, we evaluated a series of N-arylacetamides on the southern portion of the molecule (18a-d). These compounds also lost potency on σ1 while retaining activity against D₄, which again eroded the selectivity seen in other compounds (e.g., 18a, σ1, K_i = 131 nM; D₄, K_i = 299 nM).

Table 3.

Additional Dopamine 4 and sigma 1 receptor binding values of piperidine-based scaffold.

Cmpd	Structure	σ1	LEb/LLEb/MPO	D4
		Ki (nM); pKia		Ki (nM); pKia
14a		8.1; 8.09	0.42 3.58 3.4	149; 6.83
14b		29; 7.54	0.39 2.57 2.9	323; 6.49
14c		14; 7.84	0.38 2.74 2.8	211; 6.68
14d		52; 7.28	0.39 3.60 4.8	319; 6.50
14e		388; 6.41	0.36 2.91 4.7	169; 6.77
15a		143; 6.84	0.37 4.44 5.4	215; 6.67
15b		31; 7.25	0.35 3.25 5.1	158; 6.80
15c		175; 6.76	0.34 3.77 4.9	208; 6.68
15d		55; 7.26	0.35 3.26 4.2	40%; NA
15e		15%; NA	NA NA 6.0	19%; NA
16a		40; 7.40	0.38 4.87 5.4	478; 6.32
16b		12; 7.94	0.41 4.95 5.0	96; 7.02
16c		35; 7.46	0.36 4.34 4.8	309; 6.52
17a		5.2; 8.29	0.45 5.54 5.2	338; 6.47
17b		2.3; 8.65	0.47 5.78 5.1	134; 6.87
17c		3.5; 8.46	0.42 5.11 4.6	175; 6.76
17d		180; 6.74	0.32 4.27 6.0	320; 6.49
17e		170; 6.77	0.34 4.50 6.0	2,290; 5.64
17f		490; 6.31	0.37 3.47 5.0	1,210; 5.92
17g		35; 7.46	0.36 3.10 3.9	646; 6.19
17h		39%; NA	NA NA 6.0	23%; NA
17i		503; 6.30	0.35 2.87 4.7	60%; NA
17j		6%; NA	NA NA 6.0	1,559; 5.80
17k		1,093; 5.96	0.32 3.41 5.7	91; 7.04
18a		131; 6.88	0.34 2.69 3.9	299; 6.52
18b		358; 6.45	0.30 1.7 3.4	1,156; 5.94
18c		97; 7.01	0.5 2.36 3.5	441; 6.36
18d		81; 7.09	0.35 3.36 4.4	121; 6.92

^aK_i values determined by competitive inhibition of [³H]N-methylspiperone (D4R) or [³H] Pentazocine (S1R) binding in membranes harvested from HEK293 cells. All K_i are run in triplicate.

^bLigand efficiency (LE) and ligand-lipophilicity (LLE) measurements based on the σ1 receptor.

Utilizing the (S)-3-oxopiperidine scaffold, we had evaluated several southern benzyl substituents, and although they did possess D₄ activity, they were not as potent as the morpholine scaffold. We were pleased to see that these compounds did, however, possess significant binding activity against σ1 (Table 4). The initial compound, 19a, showed single-digit nanomolar activity with good selectivity against D₄ (σ1, K_i = 2.4 nM; D₄, K_i = 135 nM). During the course of the D₄ project we knew that the activity primarily resides in the (S)-enantiomer, and this was also confirmed in this study (e.g., 19a vs. 19b, D₄, K_i = 135 nM vs. 1,054 nM, respectively). The slight reduction of activity was also seen against the σ1 receptor (19a vs. 19b, σ1, K_i = 2.4 vs. 8.8 nM), although the loss was not quite as dramatic as in the D₄ receptor (3.7 vs. 8-fold), and 19b still retained significant activity. Further study is warranted to fully understand the enantiopreference in the sigma 1 receptor binding. Nearly all of the compounds in this series that were tested showed excellent binding against the σ1 receptor (K_i’s = 2.4–45 nM); with some compounds, such as 19h, being fully selective against D₄ (46% inhibition at 10 μM). Although these compounds were potent σ1 binders and had good selectivity against D₄, they did suffer from poor CNS MPO (~3)^{51, 52} and LLE (~3)⁵⁰, which was primarily due to the higher cLogP and cLogD values of these lipophilic analogs.

Table 4.

3-Oxypiperidine analogs.

Cmpd	Structure	σ1	LEb/LLEb/MPO	D4
		Ki (nM); pKia		Ki (nM); pKia
19a		2.4; 8.63	0.46 3.93 3.2	135; 6.87
19b		8.8; 8.06	0.42 3.11 3.2	1,054; 5.98
19c		4.3; 8.37	0.47 4.19 3.6	206; 6.69
19d		8.7; 8.06	0.45 3.50 3.3	343; 6.46
19e		5.5; 8.26	0.46 3.70 3.3	241; 6.62
19f		14; 7.86	0.46 3.43 4.2	1,014; 5.99
19g		19; 7.73	0.47 3.02 3.1	33%; NA
19h		5.2; 8.28	0.46 3.72 3.3	46%; NA
19i		6.5; 8.19	0.48 2.96 2.7	165; 6.78
19j		45; 7.43	0.45 2.72 3.1	29%; NA

^aK_i values determined by competitive inhibition of [³H]N-methylspiperone (D4R) or [³H] Pentazocine (S1R) binding in membranes harvested from HEK293 cells. All K_i are run in triplicate.

^bLigand efficiency (LE) and ligand-lipophilicity (LLE) measurements based on the σ1 receptor.

A variety of spirocyclic scaffold analogs were tested with the 3,4-difluorobenzyl derivative as the common northern moiety and various southern substituents (Table 5). All of the compounds tested were inactive against the D₄ receptor (or significantly reduced in activity), with the exception of 25b, the 6-chloro-1H-indol-2-yl)methyl)-1,7-diazaspiro[4.4]nonane derivative (D₄, K_i = 268 nM). However, these compounds all possessed significant σ1 receptor binding. The spirocyclic compounds imparted improved binding with the N-phenylacetamide derivatives (e.g., 24b vs. 18a, σ1, K_i = 14.2 nM vs. 131 nM). Coupling the improved σ1 binding and the loss of D₄ binding, these compounds exhibited a much-improved selectivity profile. Unfortunately, these compounds suffered from poor LLE and CNS MPO scores that are attributed to several factors: the presence of a H-bond donor, higher MW, and higher cLogP’s. Moving from the acetamides to the 2-imidazo [1,2-a]pyridine produced a potent σ1 binder with selectivity over D₄ of 65 (25a, σ1, K_i = 3.6 nM; D₄, K_i = 337 nM). Introducing this southern group also improved the drug-like properties (LLE = 5.54 and MPO = 5.2). The 6-chloro-2-indole group also brought the σ1 binding activity (25b, σ1, K_i = 5.5 nM; 25c, σ1, K_i = 7.1 nM) into the single-digit nanomolar range and had varying D₄ receptor activity (25b, D₄, K_i = 268 nM; 25c, D₄, K_i = 39% inhibition at 10 μM); however, due to the presence of the H-bond donor and higher cLogP values, the drug-like properties were worse than for 25a.

Table 5.

Spirocyclic analogs.

Cmpd	Structure	σ1	LEb/LLEb/MPO	D4
		Ki (nM); pKia		Ki (nM); pKia
24a		83; 7.08	0.46 3.93 3.2	4%; NA
24b		14; 7.85	0.42 3.11 3.2	1,704; 5.77
24c		19; 7.72	0.47 4.19 3.6	23%; NA
24d		27; 7.57	0.45 3.50 3.3	25%; NA
24e		16; 7.79	0.46 3.70 3.3	14%; NA
24f		11; 7.97	0.46 3.43 4.2	11%; NA
25a		3.6; 8.45	0.47 3.02 3.1	−0.7%; NA
25b		5.5; 8.27	0.46 3.72 3.3	268; 6.57
25c		7.1; 8.15	0.48 2.96 2.7	39%; NA

^aK_i values determined by competitive inhibition of [³H]N-methylspiperone (D4R) or [³H] Pentazocine (S1R) binding in membranes harvested from HEK293 cells. All K_i are run in triplicate.

^bLigand efficiency (LE) and ligand-lipophilicity (LLE) measurements based on the σ1 receptor.

3.2. Off-target selectivity and functional activity

Our initial selectivity filter was for the σ1 and D₄ receptors, but we wanted to expand this to the other members of those receptor families (i.e., σ2, D1,2–5), and those results are shown in Table 6. The selectivity versus the σ2 receptor was significantly reduced compared to the D₄ receptor; this was expected as the σ1:σ2 selectivity has been difficult to obtain for previously published scaffolds [26]. The selectivity ranged from ~1.4 (18d) to a high of 31 (19g), with most compounds in the 3–6 range. Two compounds with the highest selectivity (19f,g) were from the (S)-3-oxopiperidine scaffold with the substituted benzyl moieties on the southern portion; these compounds were also selective against the dopamine receptor family (>74-fold). Another highly selective compound was 10a (σ1:σ2 = 20) which was the initial benzimidazole compound and had high selectivity against the dopamine family (>490). The only spirocycle with high selectivity versus the dopamine family was 25a, although the σ2 selectivity was less (6-fold). In addition to selectivity versus the sigma and dopamine receptor families, we evaluated 10a, 19f, 19g, and 25a against the Psychoactive Drug Screening Panel (PDSP) at the University of North Carolina, Chapel Hill [26]. This panel consists of 45 receptors and transporters that are important in the CNS (Supplemental Table S2). Compound 10a was selective against the panel with only SERT (K_i = 163 nM, selectivity = 20) and α_2C (K_i = 853 nM, selectivity = 103) having activity under 1 μM. Both 19f and 19g were highly selective with only DAT showing any activity (both >300-fold selective); although the activity was weak (19f, DAT K_i = 4, 087 nM, selectivity = 300; 19g, DAT K_i = 8,815 nM, selectivity = 473). Finally, 25a was also selective against the panel, with only α_2A (K_i = 697 nM, selectivity = 194) having activity under 1 μM.

Table 6.

Selectivity versus sigma 2 and dopamine 1–5 receptors.

Cmpd	σ1	D4	σ2	D1	D2	D3	D5
	Ki (nM)
10a	8.3	4,280	166	>10,000		4,079	>10,000
10b	3.1	1,517	70	>10,000
10c	27	1,803	73	>10,000		948	>10,000
13a	1.8	276	10	>10,000
13g	37	1,663	239	>10,000
18a	131	81	299	>10,000		2,463	>10,000
18d	81	121	123	>10,000
19a	2.4	135	123	>10,000
19b	8.8	1,054	206	>10,000
19f	14	1,014	248	>10,000
19g	19	>10,000	574	>10,000
19h	5.2	>10,000	40	>10,000
19i	6.5	165	76	>10,000
24a	83	>10,000	121	>10,000
24b	14	1,704	43	>10,000
24e	16	>10,000	47	>10,000		512	>10,000
24f	11	>10,000	45	>10,000		376	>10,000
25a	3.6	>10,000	23	>10,000
25b	5.4	268	23	2,373	>10,000	118	>10,000
25c	7.1	>10,000	30	1,527	>10,000	345	>10,000

^aK_i values determined by competitive inhibition of [³H]N-methylspiperone (D2R, D3R, D4R), [³H]SCH23390 (D1R, D5R), [³H] Pentazocine (S1R) or [³H] DTG (S2R) binding in membranes harvested from HEK293 cells. All K_i are run in triplicate.

3.3. In vitro PK evaluation

Having identified several compounds that were potent σ1 binders, we profiled select compounds in in vitro DMPK assays to assess their human and mouse liver microsomal intrinsic clearance and plasma protein binding (Table 7) [53,54]. In human liver microsomes, there were a number of stable compounds (10a, 11b, 17a; CL_INT < 20 mL/min/kg) and others that displayed low clearance (12b, 14a; CL_INT < 30 mL/min/kg). However, there was a species difference seen in these compounds, with some displaying moderate stability in mouse liver microsomes (MLM) (CL_INT < 90 mL/min/kg), except for 11b, which was stable in MLM (CL_INT < 20 mL/min/kg). The benzyl southern substituted compounds (19) and the spirocyclic compounds (24, 25) all displayed high clearance in both species. From a metabolite identification study (unpublished results), the compounds showed oxidation as the primary metabolism product. Using equilibrium dialysis, the plasma protein binding of the selected compounds was determined in human and mouse plasma. Most of the compounds tested showed moderate free fraction in both human and mouse (%f_u > 3%); however, there were some notable exceptions in the human protein binding (see Table 7). A few compounds showed a high free fraction in mouse plasma (10a, 11b, 17a, 25a; %f_u >30%); however, this was not due to plasma instability.

Table 7.

In vitro PK parameters of selected compounds.

Cmpd	Intrinsic clearance (mL/min/kg)a,d				Plasma protein binding (% fu)b,d
	hCLINT	hCLHEP	mCLINT	mCLHEP	hPPB	mPPB
10a	<20	<10	93.9	46.0	22.9	40.1
10b	48.3	14.2	90.4	45.1	7.7	17.1
11b	<20	<10	<20	<16	13.0	75.0
12b	26.8	11.5	72.0	40.0	7.0	6.5
13a	32.8	12.5	103.7	48.2	3.6	16.6
13b	42.7	13.7	85.3	43.8	0.9	5.2
13c	63.3	15.3	85.2	43.8	1.0	5.7
13g	334.1	19.0	545.1	77.3	4.3	8.8
14a	23.5	10.8	83.2	43.3	<0.3	0.4
16b	130.1	17.4	198.7	62.0	8.3	9.0
17a	<20	<10	158.3	57.4	6.2	42.8
17b	44.1	13.8	96.8	46.7	1.8	22.4
17c	69.3	15.6	149.8	56.3	2.2	8.8
17k	42.1	13.6	320.8	70.3	2.4	14.3
18a	144.7	17.6	287.1	68.6	0.3	1.5
18d	49.5	14.3	306.2	69.6	0.5	c
19a	963.8	19.7	>2,400	86.8	0.6	1.2
19b	673.9	19.5	960.8	82.4	c	1.0
19e	1,127.9	19.7	1,187.7	83.7	1.3	2.5
19f	842.2	19.6	484.6	76.0	1.2	2.4
19g	1,401.5	19.8	>2,400	86.8	0.3	1.4
24f	602.1	19.5	855.3	81.5	0.02	c
25a	223.2	18.4	695.5	79.8	2.7	30.2

^aPredicted hepatic clearance based on intrinsic clearance in mouse and human liver microsomes using the well-stirred organ CL model (binding terms excluded).

^bf_u = fraction unbound.

^cUnstable in plasma.

^dIn vitro DMPK studies performed at Q2 Solutions, Indianapolis, IN.

3.4. In vivo pharmacokinetic study

Based on the totality of the properties of the evaluated compounds, we chose to progress 10a and 10b into a discrete mouse in vivo PK study (IP dosing, 5 mg/kg) (Table 8). The study was done in order to determine the plasma and brain concentrations over a 24 h time period. Both 10a and 10b displayed good plasma half-life (t_1/2 = 2.1 h and 3.7 h, respectively) and each had significantly longer half-life in brain (t_1/2 = 9.1 h and 6.9 h, respectively). In addition, each compound had total plasma and brain concentrations significantly higher than the σ1 K_i, and the compounds showed excellent brain penetration. This brain penetration can be seen in both the high K_p (10a, 2.8 and 10b, 4.9) and K_p,uu (10a, 1.6 and 10b, 2.4) at 1 h; and due to the longer brain t_1/2 even higher or equivalent K_p (10a, 6.4 and 10b, 4.9) and K_p,uu (10a, 3.7 and 10b, 2.4) at 5 h. The free plasma and brain concentrations that are greater than the K_i’s are maintained over a 10 h time span, making these compounds good in vivo probes. Overall, 10a and 10b show the appropriate properties (K_i < 10 nM; >20-fold selectivity vs. a panel of receptors; high K_p,uu) to be used as σ1 in vivo tool compounds to probe the mechanistic role of σ1 in a variety of CNS disorders.

Table 8.

In vivo mouse PK.

PK Parametersa,b	10a		10b
	Plasma	Brain	Plasma	Brain
T1/2 (h)	2.14 ± 0.5	9.11 ± 0.29	3.68 ± 0.98	6.88 ± 2.32
MRT (h)	2.12 ± 0.21	8.43 ± 0.91	4.54 ± 0.21	8.3 ± 1.9
Tmax (h)	0.28 ± 0.19	0.56 ± 0.42	0.67 ± 0.29	1.67 ± 1.15
Cmax (ng/mL or ng/g)	527 ± 52	860 ± 38	401 ± 45	1893 ± 313
AUCinf (h*ng/mL or h*ng/g)	952 ± 163	4561 ± 965	2225 ± 331	13871 ± 532
B:P	Kpc	Kp,uud,e	Kpc	Kp,uud,e
1 h	2.78	1.59	4.94	2.43
5 h	6.44	3.68	4.88	2.40

^aPK studies performed at Pharmaron, Inc. (Louisville, KY).

^bIP dosing (5 mg/kg); Formulation (10%DMSO/10% Cremphor EL/30% PEG400/50% water); PK parameters were estimated by non-compartmental model using WinNonlin 8.3.

^cKp is the ratio of total brain concentration to total plasma concentration.

^dK_p,uu is the ration of the free brain concentration to free plasma concentration. ^eBased on f_u (mPPB) = 0.358; f_u (mBHB) = 0.205.

^eBased on f_u (mPPB) = 0.189; f_u (mBHB) = 0.093.

4. Conclusions

In conclusion, we have identified a series of oxopiperidine compounds as new σ1 modulators. This work highlights the divergence in the SAR between the D₄ and σ1 receptors. Starting with a scaffold with modest selectivity for the σ1 receptor, our SAR efforts identified compounds with high selectivity against the dopamine receptors (D_1–5), and modest selective against the sigma 2 receptor and against a panel of important CNS receptors. Our compound SAR and design generally follow the pharmacophore outlined in previous studies [55,56]. In vitro PK studies have identified compounds that have high human liver microsome stability; however, these compounds also show species differentiation with moderate-low stability in mice and rats. Lastly, selected compounds have high brain penetration when assessed in a discrete mouse PK assay. Coupling the in vivo PK study with the high σ1 binding and excellent selectivity make these compounds ideal probe compounds. Further studies aimed at improving clearance, determining functional activity and in vivo animal studies are on-going and will be reported in due course.

5. Experimental procedures

5.1. Chemistry

5.1.1. General experimental methods

All ¹H & ¹³C NMR spectra were recorded on Bruker AV-400 (500 MHz) instrument. Chemical shifts are reported in ppm relative to residual solvent peaks as an internal standard set to δ¹H 3.31 or δ¹³C 49.0 (CD₃OD) or δ¹H 2.50 or δ¹³C 39.5 ((CD₃)₂SO) or δ¹H 7.26 or δ¹³C 77.2 (CDCl₃). Data are reported as follows: chemical shift, multiplicity (br = broad, s = singlet, d = doublet, t = triplet, q = quartet, m = multiplet), coupling constant (Hz), and integration. Low resolution mass spectra were obtained on an Agilent 1260 LCMS with electrospray ionization, with a gradient of 5–95% MeCN in 0.1% formic acid water over 4 min. Analytical thin layer chromatography was performed on LuxPlate silica gel 60 F254 plates. Visualization was accomplished with UV light, and/or the use of ninhydrin, anisaldehyde and ceric ammonium molybdate solutions followed by charring on a hotplate. Chromatography on silica gel was performed using Silica Gel 60 Å (230–400 mesh) from Sorbent Technologies. Solvents for extraction, washing and chromatography were HPLC grade. All reagents were purchased from Aldrich Chemical Co. (or similar) and were used without purification. All reagents and solvents were commercial grade and purified prior to use when necessary.

Final compounds were purified on a Gilson preparative reversed-phase HPLC system comprised of a 322 aqueous pump with solvent-selection valve, 334 organic pump, GX-271 liquid hander, two column switching valves, and a 159 UV detector. UV wavelength for fraction collection was user-defined, with absorbance at 254 nm always monitored. Column: Phenomenex Axia-packed Luna C18, 50 × 21.2 mm, 5 μm. For Acidic Method: Mobile phase: CH₃CN in H₂O (0.1% formic acid). Gradient conditions: 2.0 min equilibration, followed by user-defined gradient (starting organic percentage, ending organic percentage, duration, typically 15 min), hold at 95% CH₃CN in H₂O (0.1% TFA) for 2 min, 20 mL/min, 23 °C. Final compounds were confirmed to be >95% purity based on HPLC and measured at 215 and 254 nm.

There were no unexpected or unusually high safety hazards encountered for the synthesis of these compounds.

5.1.1.1. General synthetic procedure

5.1.1.1.1. General procedure A.

To tert-butyl (S)-3-hydroxypiperidine-1-carboxylate, 6, (1 eq) in DMF (10 mL) was slowly added sodium hydride (3 eq) at rt and stirred for 1h then the benzyl bromide (1 eq) was added and the reaction was stirred at 60 °C for 48 h. The reaction was quenched with distilled water (100 mL), extracted with ethyl acetate (30 mL × 3), combined organic phases washed with brine (20 mL), dried with magnesium sulfate, concentrated in vacuo, and purified by normal phase chromatography (0–100% hexane/ethyl acetate).

HCl in dioxane was added dropwise at rt and the reaction was stirred overnight at 60 °C, concentrated in vacuo, and taken to the next step without further purification. Compound 8 (1 eq) was dissolved in DMF (10 mL) in a 30 mL glass vial, then Cs₂CO₃ (2.5 eq) was added followed by benzyl bromide (1.4 eq). The reaction was heated in a microwave at 120 °C for 1 h then quenched with distilled water (100 mL), extracted with ethyl acetate (30 mL × 3), washed with brine (20 mL), dried over MgSO₄ and then concentrated in vacuo. The final compound was purified by normal phase chromatography (0–100% hexane/ethyl acetate) and (0–100% DCM/MeOH) to yield the desired compounds.

5.1.1.1.2. General procedure B.

General Procedure B. To the piperidine hydrogen chloride, 8 or 9, (1 eq) in anhydrous DCE (4 mL) was added Et₃N (2 eq) dropwise at rt and the mixture was stirred at room temperature for 1 h then 1-methyl-1H-indazole-5-carbaldehyde (0.9 eq) in anhydrous DCE (5 mL) was added followed by a slow addition of sodium triacetoxyborohydride (2 eq). The reaction was stirred at rt under argon for 72 h then quenched with saturated Na₂CO₃ (40 mL), extracted with ethyl acetate (20 mL × 3), washed with brine (15 mL), dried with magnesium sulfate, concentrated in vacuo, and purified via normal phase (0–100% DCM/MeOH) and reverse phase chromatography (0–100% ACN/water) to yield the desired compounds.

5.1.1.1.3. General Procedure C.

A microwave vial containing piperidine starting material, 9, (1 eq), aldehyde (1 eq), polymer supported sodium cyanoborohydride (2 eq), acetic acid (20 mL), and dichloromethane (500 mL) was reacted for 10 min at 110 °C. The reaction was quenched with saturated sodium bicarbonate solution and product was extracted with dichloromethane. Product was purified on flash chromatography 0–15% MeOH (0.01% TEA):CH₂Cl₂ and reverse-phase chromatography 0–100% water:CH₃CN to yield the desired compounds.

5.1.1.1.4. (S)-4-((1H-benzo[d]imidazole-5-yl)methyl)-2-((3,4-difluorophenoxy)methyl)morpholine (5).

Prepared using General Procedure outlined in Ref. 23. Yield = 15.6 mg (50%, red oil). LCMS: R_T = 1.649 min, ESI-MS: m/z [M + H]⁺, calc’d 360.15 for C₁₉H₂₀F₂N₃O₂, found 360.1. ¹H NMR (500 MHz, CDCl₃) δ 8.30 (s, 1H), 8.12 (s, 1H), 7.67 (s, 1H), 7.63 (d, J = 8.3 Hz, 1H), 7.30 (d, J = 8.3 Hz, 1H), 7.03 (q, J = 9.3 Hz, 1H), 6.71 (ddd, J = 11.8, 6.5, 3.0 Hz, 1H), 6.61–6.53 (m, 1H), 3.94 (dd, J = 9.6, 5.2 Hz, 3H), 3.87 (dd, J = 9.7, 4.2 Hz, 1H), 3.83–3.71 (m, 3H), 2.96 (d, J = 11.1 Hz, 1H), 2.82 (d, J = 11.4 Hz, 1H), 2.35 (t, J = 11.2 Hz, 1H), 2.21 (t, J = 10.4 Hz, 1H). ¹³C NMR (125 MHz, CDCl₃) δ 155.0, 151.4, 149.4, 146.2, 144.2, 140.9, 132.3, 124.4, 117.1, 116.0, 115.3, 109.9, 104.3, 73.9, 70.1, 66.8, 63.5, 55.0, 52.9, 40.9.

*Additional carbon peaks due to C–F coupling peaks however, these are overlapping with other aromatic peaks.

5.1.1.1.5. 5-((4-((3,4-difluorobenzyl)oxy)piperidin-1-yl)methyl)-1H-benzo[d]imidazole (10a).

Prepared using General Procedure B. Yield = 18.5 mg (15%, yellow oil). LCMS: R_T = 1.968 min; ESI-MS: m/z [M + H]⁺, calc’d 358.17 for C₂₀H₂₂F₂N₃O, found 358.1. ¹H NMR (500 MHz, CDCl₃) δ 8.08 (s, 1H), 7.71 (s, 1H), 7.58 (d, J = 8.2 Hz, 1H), 7.28 (d, J = 8.2 Hz, 1H), 7.17–7.05 (m, 2H), 7.01 (d, J = 3.8 Hz, 1H), 4.45 (d, J = 9.7 Hz, 2H), 3.84 (s, 2H), 3.53 (s, 1H), 2.90 (t, J = 8.2 Hz, 2H), 2.57 (s, 2H), 2.13–2.02 (m, 2H), 1.80 (s, 2H). ¹³C NMR (125 MHz, CDCl₃) δ 151.3, 150.9, 149.5, 148.9, 141.9, 135.4, 124.9, 123.2, 123.2, 117.2, 116.3, 71.6, 68.9, 62.4, 49.3, 29.0.

5.1.1.1.6. 5-((4-((4-chloro-3-fluorobenzyl)oxy)piperidin-1-yl)methyl)-1H-benzo[d]imidazole (10b).

Prepared using General Procedure C. Yield: 16.2 mg (21%, yellow oil). LCMS: R_T = 1.866 min; ESI-MS: m/z [M + H]⁺, calc’d 374.14 for C₂₀H₂₂ClFN₃O, found 374.1. ¹H NMR (500 MHz, CDCl₃) δ 8.07 (s, 2H), 7.68 (s, 2H), 7.58 (d, J = 8.2 Hz, 2H), 7.37–7.29 (m, 2H), 7.27 (d, J = 10.4 Hz, 3H), 7.12 (d, J = 9.8 Hz, 2H), 7.02 (t, J = 10.8 Hz, 2H), 5.29 (s, 1H), 4.51–4.40 (m, 4H), 3.79 (s, 4H), 3.50 (s, 2H), 2.95–2.80 (m, 4H), 2.48 (s, 4H), 2.12–1.94 (m, 5H), 1.77 (d, J = 7.9 Hz, 2H).¹³C NMR (125 MHz, CDCl₃) δ 159.1, 157.1, 141.8, 139.5, 139.5, 130.5, 124.8, 123.4, 123.4, 120.0, 119.9, 115.5, 115.3, 72.2, 68.8, 62.5, 49.5, 29.3.

5.1.1.1.7. 5-((4-((3-(trifluoromethyl)benzyl)oxy)piperidin-1-yl) methyl)-1H-benzo[d]imidazole (10c).

Prepared using General Procedure B. Yield = 28.6 mg (21%, yellow oil). LCMS: R_T = 2.083 min; ESI-MS: m/z [M + H]⁺, calc’d 390.18 for C₂₁H₂₃F₃N₃O, found 390.1. ¹H NMR (500 MHz, CDCl₃) δ 8.10 (s, 1H), 7.74 (s, 1H), 7.60–7.54 (m, 2H), 7.52 (d, J = 7.6 Hz, 1H), 7.48 (d, J = 7.5 Hz, 1H), 7.43 (t, J = 7.6 Hz, 1H), 7.27 (d, J = 7.0 Hz, 1H), 4.55 (d, J = 16.4 Hz, 2H), 3.88 (s, 2H), 3.57 (s, 1H), 2.95 (t, J = 8.4 Hz, 2H), 2.65 (d, J = 14.2 Hz, 2H), 2.09 (s, 2H), 1.95–1.69 (m, 2H). ¹³C NMR (125 MHz, CDCl₃) δ 142.2, 139.3, 130.9, 130.7, 130.6, 129.0, 125.2, 124.9, 124.5, 124.0, 123.0, 117.7, 115.9, 71.4, 69.5, 62.3, 49.2, 28.8.

5.1.1.1.8. 5-((4-((3,4-difluorobenzyl)oxy)piperidin-1-yl)methyl)-1-methyl-1H-benzo[d]imidazole (11a).

Prepared using General Procedure C. Yield = 10.0 mg (9%, orange oil). LCMS: R_T = 2.176 min; ESI-MS: m/z [M + H]⁺, calc’d 372.19 for C₂₁H₂₄F₂N₃O, found 372.1. ¹H NMR (500 MHz, CDCl₃) δ 7.86 (s, 1H), 7.70 (d, J = 1.5 Hz, 1H), 7.49 (d, J = 8.8 Hz, 1H), 7.38 (d, J = 8.2 Hz, 1H), 7.33 (t, J = 7.8 Hz, 1H), 7.11 (dd, J = 9.9, 1.9 Hz, 1H), 7.03–6.99 (m, 1H), 4.47 (s, 2H), 3.84 (s, 3H), 3.80 (s, 2H), 3.49 (s, 1H), 2.85 (s, 2H), 2.04 (s, 2H), 1.77 (s, 2H). ¹³C NMR (125 MHz, CDCl₃) δ 159.1, 157.1, 144.0, 143.7, 139.9, 130.5, 125.0, 123.4, 121.4, 119.8, 115.4, 115.3, 109.5, 74.4, 68.6, 62.8, 50.1, 31.1, 29.7.

5.1.1.1.9. 5-((4-((4-chloro-3-fluorobenzyl)oxy)piperidin-1-yl)methyl)-1-methyl-1H-benzo[d]imidazole (11b).

Prepared using General Procedure C. Yield = 17.2 mg (14%, orange oil). LCMS: R_T = 2.252 min; ESI-MS: m/z [M + H]⁺, calc’d 388.16 for C₂₁H₂₄ClFN₃O, found 388.1. ¹H NMR (500 MHz, CDCl₃) δ 7.85 (s, 1H), 7.70 (d, J = 1.5 Hz, 1H), 7.41 (d, J = 8.6 Hz, 1H), 7.35 (d, J = 8.2 Hz, 1H), 7.16–7.06 (m, 2H), 7.01 (ddt, J = 6.9, 4.6, 1.9 Hz, 1H), 4.45 (s, 2H), 3.83 (s, 3H), 3.72 (s, 2H), 3.45 (s, 1H), 2.87–2.77 (m, 2H), 2.32 (s, 2H), 1.98 (s, 2H), 1.77–1.66 (m, 2H). ¹³C NMR (125 MHz, CDCl₃) δ 151.3, 150.6, 149.3, 148.7, 143.8, 136.0, 134.1, 124.7, 123.1, 121.1, 117.1, 116.3, 109.3, 74.1, 68.6, 62.9, 50.4, 31.1, 30.7.

5.1.1.1.10. 1-Methyl-5-((4-((3-(trifluoromethyl)benzyl)oxy)piperidin-1-yl)methyl)-1H-benzo[d]imidazole (11c).

Prepared using General Procedure C. Yield = 13.4 mg (11%, orange oil). LCMS: RT = 2.291 min; m/z [M + H]⁺, calc’d 404.19 for C₂₂H₂₅F₃N₃O, found 404.1. ¹H NMR (500 MHz, CDCl₃) δ 7.85 (s, 1H), 7.70 (d, J = 1.5 Hz, 1H), 7.58 (s, 1H), 7.51 (t, J = 6.8 Hz, 2H), 7.43 (dd, J = 14.6, 7.1 Hz, 2H), 7.36 (d, J = 8.2 Hz, 1H), 4.56 (s, 2H), 3.83 (s, 3H), 3.73 (s, 2H), 3.48 (s, 1H), 2.88–2.79 (m, 2H), 2.33 (s, 2H), 1.78–1.67 (m, 2H). ¹³C NMR (125 MHz, CDCl₃) δ 143.9, 143.8, 139.9, 134.1, 130.8, 130.6, 128.8, 125.2, 124.8, 124.3, 124.0, 123.1, 121.1, 109.3, 74.5, 69.1, 63.0, 50.5, 31.1, 30.7, 29.7.

5.1.1.1.11. 5-((4-((3,4-difluorobenzyl)oxy)piperidin-1-yl)methyl)-1H-indazole (12a).

Prepared using General Procedure C. Yield = 13.8 mg (18%, yellow oil). LCMS: R_T = 2.169 min; ESI-MS: m/z [M + H]⁺, calc’d 358.17 for C₂₀H₂₂F₂N₃O, found 358.1. ¹H NMR (500 MHz, CDCl₃) δ 8.01 (s, 1H), 7.70 (s, 1H), 7.48–7.40 (m, 2H), 7.21–7.04 (m, 2H), 7.01 (ddt, J = 8.3, 3.9, 1.6 Hz, 1H), 4.46 (s, 2H), 3.76 (s, 2H), 3.51 (s, 1H), 2.92–2.77 (m, 2H), 2.47 (s, 2H), 2.04 (d, J = 10.7 Hz, 2H), 1.79 (dd, J = 13.2, 7.8 Hz, 2H). ¹³C NMR (125 MHz, CDCl₃) δ 151.3, 150.7, 149.4, 148.7, 139.8, 135.8, 134.7, 128.8, 123.3, 123.1, 121.8, 117.1, 116.3, 109.9, 73.4, 68.7, 62.7, 50.1, 30.2.

5.1.1.1.12. 5-((4-((4-chloro-3-fluorobenzyl)oxy)piperidin-1-yl) methyl)-1H-indazole (12b).

Prepared using General Procedure C. Yield = 17.1 mg (22%, yellow oil). LCMS: R_T = 2.261 min; ESI-MS: m/z [M + H]⁺, calc’d 374.14 for C₂₀H₂₂ClFN₃O, found 374.1. ¹H NMR (500 MHz, CDCl₃) δ 8.03 (s, 1H), 7.68 (s, 1H), 7.43 (s, 2H), 7.33 (t, J = 7.8 Hz, 1H), 7.14 (dd, J = 9.8, 1.9 Hz, 1H), 7.03 (dd, J = 8.2, 1.9 Hz, 1H), 4.48 (s, 2H), 3.69 (s, 2H), 3.48 (d, J = 9.5 Hz, 1H), 2.81 (q, J = 6.3, 5.1 Hz, 2H), 2.33 (s, 2H), 1.74 (qd, J = 11.4, 9.4, 5.2 Hz, 2H). ¹³C NMR (125 MHz, CDCl₃) δ 159.1, 157.1, 140.0, 139.7, 134.8, 130.4, 128.7, 123.4, 123.3, 121.3, 119.7, 115.5, 115.3, 109.7, 74.3, 68.5, 62.8, 50.5, 30.7.

5.1.1.1.13. 5-((4-((3-(trifluoromethyl)benzyl)oxy)piperidin-1-yl) methyl)-1H-indazole (12c).

Prepared using General Procedure C. Yield = 17.8 mg (24%, yellow oil). LCMS: R_T = 2.322 min; ESI-MS: m/z [M + H]⁺, calc’d 390.18 for C₂₁H₂₃F₃N₃O, found 390.1. ¹H NMR (500 MHz, CDCl₃) δ 8.02 (s, 1H), 7.69 (s, 1H), 7.59 (s, 1H), 7.52 (t, J = 8.3 Hz, 2H), 7.45 (d, J = 7.6 Hz, 3H), 4.57 (s, 2H), 3.72 (s, 2H), 3.51 (dt, J = 8.2, 4.4 Hz, 1H), 2.85 (ddd, J = 11.5, 6.9, 3.5 Hz, 2H), 2.39 (s, 2H), 2.03 (t, J = 10.0 Hz, 2H), 1.79 (td, J = 9.0, 8.4, 4.1 Hz, 2H). ¹³C NMR (125 MHz, CDCl₃) δ 139.9, 139.7, 134.7, 130.9, 130.6, 128.8, 128.8, 125.2, 124.3, 124.0, 123.3, 123.1, 121.5, 109.8, 74.0, 69.2, 62.8, 50.4, 30.5.

5.1.1.1.14. 5-((4-((3,4-difluorobenzyl)oxy)piperidin-1-yl)methyl)-1-methyl-1H-indazole (13a).

Prepared using General Procedure B. Yield = 32.9 mg (28%, yellow oil). LCMS: R_T = 1.919 min; ESI-MS: m/z [M + H]⁺, calc’d 372.19 for C₂₁H₂₄F₂N₃O, found 372.1. ¹H NMR (500 MHz, CDCl₃) δ 7.95 (d, J = 0.9 Hz, 1H), 7.63 (s, 1H), 7.43 (dd, J = 8.6, 1.5 Hz, 1H), 7.37 (d, J = 8.6 Hz, 1H), 7.19 (ddd, J = 11.1, 7.7, 2.1 Hz, 1H), 7.12 (dt, J = 10.2, 8.1 Hz, 1H), 7.04 (ddt, J = 8.2, 3.8, 1.7 Hz, 1H), 4.49 (s, 2H), 4.08 (s, 3H), 3.63 (s, 2H), 3.44 (tt, J = 8.6, 3.9 Hz, 1H), 2.79 (dt, J = 10.6, 4.5 Hz, 2H), 2.21 (t, J = 10.8 Hz, 2H), 1.94 (dd, J = 12.4, 5.1 Hz, 2H), 1.70 (dtd, J = 12.8, 9.0, 3.6 Hz, 2H). ¹³C NMR (125 MHz, CDCl₃) δ 151.3, 150.6, 149.4, 148.7, 139.5, 136.1, 132.5, 130.6, 128.1, 124.0, 123.1, 121.1, 117.0, 116.3, 108.7, 74.9, 68.5, 63.0, 50.9, 35.6, 31.2.

5.1.1.1.15. 5-((4-((4-chloro-3-fluorobenzyl)oxy)piperidin-1-yl) methyl)-1-methyl-1H-indazole (13b).

Prepared using General Procedure C. Yield = 24.9 mg (8%, yellow oil). LCMS: R_T = 2.115 min; ESI-MS: m/z [M + H]⁺, calc’d 388.16 for C₂₁H₂₄ClFN₃O, found 388.1. ¹H NMR (500 MHz, CDCl₃) δ 8.62 (s, 1H), 7.94 (s, 3H), 7.65 (s, 3H), 7.44 (dd, J = 8.6, 0.7 Hz, 3H), 7.38–7.30 (m, 6H), 7.12 (dd, J = 9.8, 1.3 Hz, 3H), 7.03 (t, J = 9.7 Hz, 3H), 4.47 (s, 6H), 4.06 (s, 9H), 3.76 (s, 6H), 3.49 (s, 3H), 2.89–2.75 (m, 6H), 2.44 (s, 5H), 2.03–1.92 (m, 6H), 1.82–1.67 (m, 6H). ¹³C NMR (125 MHz, CDCl₃) δ 159.1, 157.1, 139.9, 139.6, 132.6, 130.4, 128.3, 124.0, 123.3, 121.8, 119.7, 115.3, 108.9, 73.9, 68.5, 62.6, 50.1, 35.6, 30.4.

5.1.1.1.16. 1-Methyl-5-((4-((3-(trifluoromethyl)benzyl)oxy)piperidin-1-yl)methyl)-1H-indazole (13c).

Prepared using General Procedure B. Yield = 27.6 mg (22%, yellow oil). LCMS: R_T = 2.169 min; ESI-MS: m/z [M + H]⁺, calc’d 404.19 for C₂₂H₂₅F₃N₃O, found 404.1. ¹H NMR (500 MHz, CDCl₃) δ 7.93 (s, 1H), 7.61 (d, J = 7.1 Hz, 2H), 7.52 (d, J = 7.7 Hz, 2H), 7.43 (dd, J = 16.0, 8.3 Hz, 2H), 7.35 (d, J = 8.6 Hz, 1H), 4.57 (s, 2H), 4.06 (s, 3H), 3.61 (s, 2H), 3.49–3.41 (m, 1H), 2.85–2.71 (m, 2H), 2.20 (s, 2H), 1.94 (d, J = 10.2 Hz, 2H), 1.71 (ddd, J = 17.2, 10.9, 3.4 Hz, 2H). ¹³C NMR (125 MHz, CDCl₃) δ 140.0, 139.5, 132.6, 130.8, 130.6, 128.8, 128.2, 125.2, 124.2, 124.0, 123.0, 121.3, 108.8, 74.8, 69.1, 62.9, 50.7, 35.6, 30.9.

5.1.1.1.17. (S)-2-((3,4-Difluorophenoxy)methyl)-4-((1-methyl-1H-indazol-5-yl)methyl)morpholine (13d).

Prepared following the procedure outlined in Ref. 23. Yield = 10.4 mg (32%, pink oil). LCMS: R_T = 2.012 min; ESI-MS: m/z [M + H]⁺, calc’d 374.17 for C₂₀H₂₂F₂N₃O₂, found 374.1. ¹H NMR (500 MHz, CDCl₃) δ 7.94 (s, 1H), 7.63 (s, 1H), 7.39 (dd, J = 27.5, 8.6 Hz, 2H), 7.03 (q, J = 9.4 Hz, 1H), 6.71 (ddd, J = 11.9, 6.5, 3.0 Hz, 1H), 6.62–6.53 (m, 1H), 4.07 (s, 3H), 3.98–3.82 (m, 4H), 3.74 (td, J = 11.3, 2.2 Hz, 1H), 3.67–3.59 (m, 2H), 2.84 (d, J = 11.2 Hz, 1H), 2.71 (d, J = 11.3 Hz, 1H), 2.26 (td, J = 11.4, 3.2 Hz, 1H), 2.13–2.01 (m, 1H). ¹³C NMR (125 MHz, CDCl₃) δ 154.9, 151.3, 149.3, 146.2, 144.3, 139.6, 132.6, 128.1, 124.0, 117.2, 109.9, 109.0, 104.4, 73.7, 69.9, 66.3, 63.2, 55.2, 52.7, 35.6.

5.1.1.1.18. (S)-4-((1-methyl-1H-indazol-5-yl)methyl)-2-(((4-methylthiazol-2-yl)oxy)methyl)morpholine (13e).

Prepared following the procedure outlined in Ref. 23. Yield = 23.9 mg (29%, white solid). LCMS: R_T = 2.008 min; ESI-MS: m/z [M + H]⁺, calc’d 359.15 for C₁₈H₂₃N₄O₂S, found 359.1. ¹H NMR (500 MHz, CDCl₃) δ 7.93 (s, 1H), 7.62 (s, 1H), 7.41 (dd, J = 8.7, 1.5 Hz, 1H), 7.35 (d, J = 8.6 Hz, 1H), 6.20 (d, J = 1.5 Hz, 1H), 4.37 (d, J = 4.9 Hz, 2H), 4.06 (s, 3H), 4.01–3.94 (m, 1H), 3.91 (ddd, J = 11.4, 3.4, 1.8 Hz, 1H), 3.79–3.70 (m, 1H), 3.65 (s, 2H), 2.86–2.68 (m, 2H), 2.27 (td, J = 11.3, 3.3 Hz, 1H), 2.22 (s, 3H), 2.12 (t, J = 10.7 Hz, 1H). ¹³C NMR (125 MHz, CDCl₃) δ 168.4, 151.4, 150.8, 149.4, 148.8, 137.0, 135.6, 134.7, 127.2, 125.4, 123.2, 119.7, 117.2, 116.3, 73.6, 68.9, 62.1, 51.6, 31.6, 14.3.

5.1.1.1.19. (S)-1-methyl-5-((3-((6-methylpyridin-2-yl)methoxy)piperidin-1-yl)methyl)-1H-indazole (13f).

Prepared using general Procedure B. Yield = 23.3 mg (14%, viscous orange oil). LCMS: R_T = 1.645 min; ESI-MS: m/z [M + H]⁺, calc’d 351.22 for C₂₁H₂₇N₄O, found 351.1. ¹H NMR (500 MHz, CDCl₃) δ 7.92 (s, 1H), 7.61 (s, 1H), 7.53 (t, J = 7.7 Hz, 1H), 7.41 (d, J = 8.6 Hz, 1H), 7.34 (d, J = 8.6 Hz, 1H), 7.22 (d, J = 7.7 Hz, 1H), 7.00 (d, J = 7.6 Hz, 1H), 4.63–4.56 (m, 2H), 4.06 (s, 3H), 3.73–3.66 (m, 2H), 3.64–3.58 (m, 1H), 3.02 (d, J = 9.2 Hz, 1H), 2.73 (d, J = 10.8 Hz, 1H), 2.50 (s, 3H), 2.17–2.11 (m, 2H), 2.05–1.99 (m, 1H), 1.80–1.74 (m, 1H), 1.58 (dd, J = 24.5, 11.0 Hz, 1H), 1.37 (dd, J = 23.3, 13.9 Hz, 1H). ¹³C NMR (125 MHz, CDCl₃) δ 157.7, 157.3, 139.8, 137.1, 132.9, 128.7, 124.3, 124.0, 123.4, 122.2, 118.6, 109.4, 72.9, 71.6, 61.4, 55.2, 51.9, 35.6, 29.1, 24.1, 20.8.

5.1.1.1.20. (S)-1-methyl-5-((3-((2-methylbenzyl)oxy)piperidin-1-yl) methyl)-1H-indazole (13g).

Prepared using General Procedure B. Yield = 54.2 mg (32%, viscous orange oil). LCMS: R_T = 2.295 min; ESI-MS: m/z [M + H]⁺, calc’d 350.22 for C₂₂H₂₈N₃O, found 350.1. ¹H NMR (500 MHz, CDCl₃) δ 7.96 (s, 1H), 7.64 (s, 1H), 7.43 (d, J = 8.5 Hz, 1H), 7.36 (d, J = 8.5 Hz, 1H), 7.30 (d, J = 7.0 Hz, 1H), 7.18 (dt, J = 13.0, 6.3 Hz, 3H), 4.53 (q, J = 11.5 Hz, 2H), 4.09 (s, 3H), 3.70 (q, J = 13.0 Hz, 2H), 3.62–3.55 (m, 1H), 3.07 (d, J = 8.9 Hz, 1H), 2.76 (d, J = 10.6 Hz, 1H), 2.32 (s, 3H), 2.15–2.02 (m, 3H), 1.77 (dd, J = 9.8, 3.6 Hz, 1H), 1.59 (dd, J = 24.1, 11.9 Hz, 1H), 1.34 (td, J = 12.5, 3.9 Hz, 1H). ¹³C NMR (125 MHz, CDCl₃) δ 139.2, 136.4, 136.3, 132.3, 130.2, 129.9, 128.3, 127.9, 127.5, 125.5, 123.8, 120.9, 108.4, 74.4, 68.6, 63.0, 57.9, 53.1, 35.3, 30.3, 23.1, 18.6.

5.1.1.1.21. 6-chloro-2-((4-((3,4-difluorobenzyl)oxy)piperidin-1-yl) methyl)-1H-indole (14a).

Prepared using General Procedure B. Yield = 16.8 mg (20%, brown oil). LCMS: R_T = 2.337 min; ESI-MS: m/z [M + H]⁺, calc’d 391.14 for C₂₁H₂₂ClF₂N₂O, found 391.1. ¹H NMR (500 MHz, CDCl₃) δ 8.65 (s, 1H), 7.48–7.38 (m, 2H), 7.19–7.07 (m, 2H), 7.04 (td, J = 7.4, 6.3, 1.8 Hz, 2H), 6.40 (s, 1H), 4.46 (s, 2H), 3.96 (s, 2H), 3.64 (s, 1H), 2.97–2.85 (m, 2H), 2.73 (s, 2H), 2.13–2.03 (m, 2H), 1.89 (s, 2H). ¹³C NMR (125 MHz, CDCl₃) δ 151.4, 150.7, 149.4, 148.7, 136.5, 135.9, 127.4, 126.9, 123.1, 121.0, 120.3, 117.1, 116.3, 110.8, 101.6, 74.2, 68.7, 55.6, 51.0, 31.0.

5.1.1.1.22. 6-chloro-2-((4-((4-chloro-3-fluorobenzyl)oxy)piperidin-1-yl)methyl)-1H-indole (14b).

Prepared using General Procedure B. Yield = 44.0 mg (39%, brown oil). LCMS: R_T = 2.510 min; ESI-MS: m/z [M + H]⁺, calc’d 407.11 for C₂₁H₂₂Cl₂FN₂O, found 407.0. ¹H NMR (500 MHz, CDCl₃) δ 9.18 (s, 1H), 7.44 (d, J = 8.4 Hz, 1H), 7.37–7.31 (m, 3H), 7.15 (dd, J = 9.8, 1.9 Hz, 1H), 7.04 (dt, J = 8.3, 2.1 Hz, 3H), 6.33 (d, J = 2.0 Hz, 1H), 4.48 (s, 3H), 3.70 (s, 3H), 3.49 (dp, J = 8.1, 3.7 Hz, 1H), 2.79 (ddd, J = 11.3, 6.8, 3.4 Hz, 3H), 2.35 (d, J = 10.6 Hz, 2H), 1.96 (ddt, J = 13.8, 7.1, 3.5 Hz, 3H), 1.73 (dtd, J = 12.4, 8.3, 3.5 Hz, 3H). ¹³C NMR (125 MHz, CDCl₃) δ 170.0, 159.1, 157.1, 139.9, 136.7, 135.5, 130.5, 127.5, 126.8, 123.4, 121.0, 120.3, 119.8, 115.4, 110.9, 102.1, 73.8, 68.6, 55.4, 50.6, 30.6.

5.1.1.1.23. 6-chloro-2-((4-((3-(trifluoromethyl)benzyl)oxy)piperidin-1-yl)methyl)-1H-indole (14c).

Prepared using General Procedure B. Yield = 20.6 mg (25%, yellow oil). LCMS: R_T = 2.564 min; ESI-MS: m/z [M + H]⁺, calc’d 423.15 for C₂₂H₂₃ClF₃N₂O, found 423.0. ¹H NMR (500 MHz, CDCl₃) δ 8.74 (s, 1H), 7.63 (s, 1H), 7.56 (t, J = 7.3 Hz, 2H), 7.48 (dd, J = 15.2, 8.0 Hz, 2H), 7.35 (s, 1H), 7.07 (dd, J = 8.4, 1.9 Hz, 1H), 6.34 (d, J = 2.0 Hz, 1H), 4.61 (s, 2H), 3.68 (s, 2H), 3.52 (tt, J = 8.2, 3.8 Hz, 1H), 2.81 (dt, J = 11.0, 4.7 Hz, 2H), 2.29 (t, J = 10.6 Hz, 2H), 1.99 (ddd, J = 13.4, 6.7, 3.6 Hz, 2H), 1.75 (dtd, J = 12.6, 8.7, 3.6 Hz, 2H). ¹³C NMR (125 MHz, CDCl₃) δ 139.9, 136.5, 130.6, 128.9, 127.4, 126.9, 125.3, 124.3, 124.0, 123.1, 120.9, 120.3, 110.8, 101.6, 74.5, 69.2, 55.6, 51.0, 31.1.

5.1.1.1.24. (S)-6-chloro-2-((3-((6-methylpyridin-2-yl)methoxy)piperidin-1-yl)methyl)-1H-indole (14d).

Prepared using General Procedure B. Yield = 12.0 mg (9%, viscous brown oil). LCMS: R_T = 2.509 min; ESI-MS: m/z [M + H]⁺, calc’d 370.17 for C₂₁H₂₅ClN₃O, found 370.1. ¹H NMR (500 MHz, CDCl3) δ 8.47 (s, 1H), 7.54 (t, J = 7.7 Hz, 1H), 7.46–7.41 (m, 2H), 7.17 (d, J = 7.7 Hz, 1H), 7.07–7.00 (m, 2H), 6.41 (s, 1H), 4.58 (q, J = 12.5 Hz, 2H), 4.14 (dd, J = 32.9, 13.5 Hz, 2H), 3.84 (dt, J = 10.7, 3.5 Hz, 1H), 3.04 (d, J = 12.4 Hz, 1H), 2.94 (s, 1H), 2.73 (d, J = 7.0 Hz, 2H), 2.51 (s, 3H), 2.05–1.91 (m, 2H), 1.77 (ddd, J = 12.1, 9.0, 4.9 Hz, 1H), 1.67 (d, J = 8.2 Hz, 1H). ¹³C NMR (125 MHz, CDCl3) δ 157.7, 156.2, 137.8, 128.9, 127.2, 125.8, 122.8, 121.3, 120.8, 119.2, 112.1, 106.0, 71.4, 71.3, 54.0, 53.6, 51.9, 27.8, 23.6, 18.9.

5.1.1.1.25. (S)-4-((6-chloro-1H-indol-2-yl)methyl)-2-(((4-methylthiazol-2-yl)oxy)methyl)morpholine (14e).

Prepared following the procedure outlined in Ref. 23. Yield = 49.6 mg (56%, yellow solid). LCMS: R_T = 2.231 min; ESI-MS: m/z [M + H]⁺, calc’d 378.10 for C₁₈H₂₁ClN₃O₂S, found 378.0. ¹H NMR (500 MHz, CDCl₃) δ 8.90 (s, 1H), 7.46 (d, J = 8.4 Hz, 1H), 7.36–7.33 (m, 1H), 7.07 (dd, J = 8.4, 1.8 Hz, 1H), 6.37 (d, J = 2.0 Hz, 1H), 6.23 (d, J = 1.4 Hz, 1H), 4.41 (d, J = 4.8 Hz, 2H), 4.01–3.92 (m, 2H), 3.75 (td, J = 11.4, 2.4 Hz, 1H), 3.70 (s, 2H), 2.85 (dt, J = 11.5, 2.0 Hz, 1H), 2.75–2.69 (m, 1H), 2.32 (td, J = 11.4, 3.4 Hz, 1H), 2.25 (d, J = 1.2 Hz, 3H), 2.18 (t, J = 10.7 Hz, 1H). ¹³C NMR (125 MHz, CDCl₃) δ 173.6, 146.6, 136.7, 135.0, 127.6, 126.8, 121.1, 120.5, 110.9, 105.4, 102.4, 73.4, 71.7, 66.4, 55.8, 54.5, 52.7, 17.7.

5.1.1.1.26. 3-((4-((3,4-difluorobenzyl)oxy)piperidin-1-yl)methyl)imidazo[1,5-a]pyridine (15a).

Prepared using General Procedure B. Yield = 24.0 mg (31%, brown oil). LCMS: R_T = 2.036 min; ESI-MS: m/z [M + H]⁺, calc’d 358.17 for C₂₀H₂₂F₂N₃O, found 358.1. ¹H NMR (500 MHz, CDCl₃) δ 8.22 (d, J = 7.1 Hz, 1H), 7.40 (d, J = 9.1 Hz, 1H), 7.33 (s, 1H), 7.15 (ddd, J = 10.4, 7.7, 2.1 Hz, 1H), 7.09 (dt, J = 10.2, 8.2 Hz, 1H), 7.01 (ddd, J = 8.5, 4.1, 1.9 Hz, 1H), 6.70 (dd, J = 9.2, 6.3 Hz, 1H), 6.58–6.50 (m, 1H), 4.45 (s, 2H), 3.94 (s, 2H), 3.42 (tt, J = 8.5, 4.0 Hz, 1H), 2.73 (dt, J = 10.8, 4.6 Hz, 2H), 2.27–2.19 (m, 2H), 1.90 (dt, J = 12.5, 4.0 Hz, 2H), 1.63 (dtd, J = 13.0, 9.2, 3.6 Hz, 2H). ¹³C NMR (125 MHz, CDCl₃) δ 151.3, 150.6, 149.3, 148.7, 136.0, 135.1, 131.4, 123.1, 122.5, 118.6, 118.4, 118.2, 117.0, 116.3, 112.0, 74.6, 68.6, 55.2, 51.0, 31.2.

5.1.1.1.27. 3-((4-((4-chloro-3-fluorobenzyl)oxy)piperidin-1-yl) methyl)imidazo[1,5-a]pyridine (15b).

Prepared using General Procedure B. Yield = 12.6 mg (16%, brown oil). LCMS: R_T = 2.316 min; ESI-MS: m/z [M + H]⁺, calc’d 374.14 for C₂₀H₂₂ClFN₃O, found 374.1. ¹H NMR (500 MHz, CDCl₃) δ 8.24 (d, J = 7.1 Hz, 1H), 7.41 (d, J = 9.2 Hz, 1H), 7.34 (q, J = 8.0 Hz, 2H), 7.16–7.10 (m, 1H), 7.03 (d, J = 7.8 Hz, 1H), 6.75–6.67 (m, 1H), 6.55 (q, J = 6.7 Hz, 1H), 4.48 (s, 2H), 3.96 (s, 2H), 3.50–3.37 (m, 1H), 2.80–2.69 (m, 2H), 2.25 (s, 2H), 1.90 (t, J = 16.5 Hz, 2H), 1.65 (dt, J = 13.8, 6.2 Hz, 2H). ¹³C NMR (125 MHz, CDCl₃) δ 159.1, 157.1, 140.1, 131.4, 130.4, 123.4, 122.5, 119.7, 118.6, 118.5, 118.2, 115.4, 112.0, 75.2, 68.5, 55.2, 50.9, 31.1.

5.1.1.1.28. 3-((4-((3-(trifluoromethyl)benzyl)oxy)piperidin-1-yl) methyl)imidazo[1,5-a]pyridine (15c).

Prepared using General Procedure B. Yield: 20.7 mg (28%, brown oil). LCMS: R_T = 2.328 min; ESI-MS: m/z [M + H]⁺, calc’d 390.18 for C₂₁H₂₃F₃N₃O, found 390.0. ¹H NMR (500 MHz, CDCl₃) δ 8.24 (d, J = 7.1 Hz, 1H), 7.59 (s, 1H), 7.51 (t, J = 6.5 Hz, 2H), 7.46–7.39 (m, 2H), 7.34 (s, 1H), 6.70 (dd, J = 9.1, 6.3 Hz, 1H), 6.54 (t, J = 6.8 Hz, 1H), 4.56 (s, 2H), 3.95 (s, 2H), 3.45 (tt, J = 8.5, 3.9 Hz, 1H), 2.75 (dt, J = 10.6, 4.5 Hz, 2H), 2.25 (t, J = 10.9 Hz, 2H), 1.94 (dt, J = 13.8, 4.0 Hz, 2H), 1.66 (dtd, J = 13.1, 9.3, 3.6 Hz, 2H). ¹³C NMR (125 MHz, CDCl₃) δ 139.9, 135.1, 131.4, 130.8, 130.6, 128.8, 124.3, 124.0, 122.5, 118.6, 118.4, 118.2, 112.0, 74.8, 69.1, 55.2, 51.0, 31.2.

5.1.1.1.29. (S)-3-((3-((3-(trifluoromethoxy)benzyl)oxy)piperidin-1-yl)methyl)imidazo[1,5-a]pyridine (15d).

Prepared using General Procedure B. Yield = 36.7 mg (19%, brown viscous oil). LCMS: R_T = 2.558 min; ESI-MS: m/z = 406.1 [M + H]⁺, calc’d 406.17 for C₂₁H₂₃F₃N₃O₂, found 406.1. ¹H NMR (500 MHz, CDCl₃) δ 8.20 (d, J = 7.1 Hz, 1H), 7.41 (d, J = 10.2 Hz, 1H), 7.35 (s, 1H), 7.31 (t, J = 7.9 Hz, 1H), 7.18 (d, J = 7.7 Hz, 1H), 7.15 (s, 1H), 7.09 (d, J = 8.2 Hz, 1H), 6.69 (ddd, J = 9.1, 6.4, 0.7 Hz, 1H), 6.51–6.46 (m, 1H), 4.50–4.43 (m, 2H), 4.01–3.94 (m, 2H), 3.49 (ddd, J = 12.2, 8.2, 3.7 Hz, 1H), 2.87 (d, J = 9.7 Hz, 1H), 2.60–2.53 (m, 1H), 2.21 (dd, J = 17.5, 7.8 Hz, 2H), 1.93 (dd, J = 11.7, 3.8 Hz, 1H), 1.76 (ddd, J = 12.2, 8.2, 3.9 Hz, 1H), 1.53–1.44 (m, 1H), 1.39 (td, J = 12.4, 3.7 Hz, 1H). ¹³C NMR (125 MHz, CDCl₃) δ 149.3, 141.3, 135.1, 131.3, 129.5, 125.4, 122.4, 121.4, 119.6, 119.4, 118.5, 118.3, 118.1, 111.9, 74.5, 69.2, 57.6, 55.4, 53.2, 30.0, 22.9.

5.1.1.1.30. (S)-3-((3-((6-methylpyridin-2-yl)methoxy)piperidin-1-yl) methyl)imidazo[1,5-a]pyridine (15e).

Prepared using General Procedure B. Yield = 150.8 mg (30%, brown viscous oil). LCMS: R_T = 1.480 min; ESI-MS: m/z [M + H]⁺, calc’d 337.20 for C₂₀H₂₅N₄O, found 337.1. ¹H NMR (500 MHz, CDCl₃) δ 8.22 (d, J = 7.1 Hz, 1H), 7.54 (t, J = 7.7 Hz, 1H), 7.41 (d, J = 9.1 Hz, 1H), 7.34 (s, 1H), 7.23 (d, J = 7.7 Hz, 1H), 7.01 (d, J = 7.6 Hz, 1H), 6.73–6.66 (m, 1H), 6.49 (t, J = 6.7 Hz, 1H), 4.59 (q, J = 13.4 Hz, 2H), 3.98 (s, 2H), 3.58–3.51 (m, 1H), 2.94 (d, J = 9.9 Hz, 1H), 2.58 (d, J = 11.0 Hz, 1H), 2.51 (s, 3H), 2.26–2.14 (m, 2H), 1.99 (d, J = 8.2 Hz, 1H), 1.75 (d, J = 13.1 Hz, 1H), 1.49 (dd, J = 23.8, 10.6 Hz, 1H), 1.40 (dd, J = 21.1, 10.1 Hz, 1H). ¹³C NMR (125 MHz, CDCl₃) δ 158.4, 157.4, 136.7, 135.0, 131.3, 122.5, 121.7, 118.4, 118.4, 118.1, 118.0, 111.9, 74.9, 71.3, 57.9, 55.4, 53.2, 30.1, 24.3, 23.0.

5.1.1.1.31. 1-((4-((3,4-difluorobenzyl)oxy)piperidin-1-yl)methyl)-3-methylimidazo[1,5-a]pyridine (16a).

Prepared using General Procedure B. Yield = 37.0 mg (45%, red oil). LCMS: R_T = 2.038 min; ESI-MS: m/z [M + H]⁺, calc’d 372.19 for C₂₁H₂₄F₂N₃O, found 372.1. ¹H NMR (500 MHz, CDCl₃) δ 7.62 (d, J = 7.1 Hz, 1H), 7.58 (d, J = 9.2 Hz, 1H), 7.09 (ddt, J = 13.2, 10.2, 5.1 Hz, 2H), 6.98 (ddd, J = 8.5, 4.2, 1.9 Hz, 1H), 6.69 (dd, J = 9.2, 6.3 Hz, 1H), 6.58–6.53 (m, 1H), 4.42 (s, 2H), 3.98 (s, 2H), 3.49 (s, 1H), 2.97 (ddd, J = 11.9, 7.9, 3.4 Hz, 2H), 2.61 (s, 5H), 2.12–2.00 (m, 2H), 1.86–1.75 (m, 2H). ¹³C NMR (125 MHz, CDCl₃) δ 151.3, 150.6, 149.3, 148.7, 135.8, 134.5, 129.5, 123.1, 120.7, 118.3, 118.0, 117.1, 116.2, 112.5, 68.6, 54.2, 49.5, 29.7, 12.5.

5.1.1.1.32. 1-((4-((4-chloro-3-fluorobenzyl)oxy)piperidin-1-yl) methyl)-3-methylimidazo[1,5-a]pyridine (16b).

Prepared using General Procedure B. Yield = 44.5 mg (37%, red oil). LCMS: R_T = 2.326 min; ESI-MS: m/z [M + H]⁺, calc’d 388.16 for C₂₁H₂₄ClFN₃O, found 388.1. ¹H NMR (500 MHz, CDCl₃) δ 7.59 (t, J = 6.2 Hz, 1H), 7.52 (d, J = 9.2 Hz, 1H), 7.31–7.24 (m, 1H), 7.06 (d, J = 9.7 Hz, 1H), 6.97 (d, J = 8.0 Hz, 1H), 6.65 (dd, J = 9.2, 6.3 Hz, 1H), 6.52 (q, J = 6.6 Hz, 1H), 4.41 (d, J =7.0 Hz, 2H), 3.91 (d, J = 8.2 Hz, 2H), 3.45 (s, 1H), 3.43–3.36 (m, 1H), 2.91 (ddt, J = 13.8, 9.7, 4.9 Hz, 2H), 2.57 (d, J = 7.5 Hz, 3H), 2.51 (s, 2H), 2.01 (ddd, J = 13.2, 8.7, 4.3 Hz, 2H), 1.81–1.71 (m, 2H). ¹³C NMR (125 MHz, CDCl₃) δ 159.0, 157.0, 139.9, 134.4, 130.4, 129.3, 123.3, 120.7, 119.6, 119.5, 118.2, 117.9, 117.9, 115.3, 112.5, 73.2, 68.5, 54.2, 49.7, 29.9, 12.4.

5.1.1.1.33. 3-methyl-1-((4-((3-(trifluoromethyl)benzyl)oxy)piperidin-1-yl)methyl)imidazo[1,5-a]pyridine (16c).

Prepared using General Procedure B. Yield = 34.4 mg (44%, red oil). LCMS: R_T = 2.364 min; ESI-MS: m/z [M + H]⁺, calc’d 404.19 for C₂₂H₂₅F₃N₃O, found 404.1. ¹H NMR (500 MHz, CDCl₃) δ 7.61 (d, J = 7.2 Hz, 1H), 7.58 (d, J = 9.1 Hz, 1H), 7.54 (s, 1H), 7.49 (dd, J = 14.8, 7.7 Hz, 2H), 7.42 (t, J = 7.6 Hz, 1H), 6.69 (dd, J = 9.2, 6.3 Hz, 1H), 6.58–6.52 (m, 1H), 4.53 (s, 2H), 3.97 (s, 2H), 3.52 (s, 1H), 2.97 (ddd, J = 11.7, 7.8, 3.5 Hz, 2H), 2.60 (s, 3H), 2.58–2.37 (m, 1H), 2.13–2.03 (m, 2H), 1.87–1.77 (m, 2H). ¹³C NMR (125 MHz, CDCl₃) δ 139.8, 134.5, 130.8, 130.5, 128.8, 125.2, 124.3, 123.9, 123.0, 120.7, 118.2, 118.0, 112.5, 72.8, 69.1, 54.3, 49.7, 29.9, 12.5.

5.1.1.1.34. 2-((4-((3,4-difluorobenzyl)oxy)piperidin-1-yl)methyl)imidazo[1,2-a]pyridine (17a).

Prepared using General Procedure B. Yield = 47.0 mg (60%, brown oil). LCMS: R_T = 1.890 min; ESI-MS: m/z [M + H]⁺, calc’d 358.17 for C₂₀H₂₂F₂N₃O, found 358.1. ¹H NMR (500 MHz, CDCl₃) δ 8.06 (dt, J = 6.8, 1.3 Hz, 1H), 7.59–7.48 (m, 2H), 7.19–7.05 (m, 3H), 7.01 (ddd, J = 8.2, 4.0, 2.1 Hz, 1H), 6.74 (td, J = 6.8, 1.2 Hz, 1H), 4.45 (s, 2H), 3.75 (s, 2H), 3.44 (tt, J = 8.3, 3.8 Hz, 1H), 2.96–2.84 (m, 2H), 2.35 (d, J = 10.8 Hz, 2H), 1.96 (ddd, J = 13.6, 6.5, 3.4 Hz, 2H), 1.73 (dtd, J = 12.7, 8.8, 3.6 Hz, 2H). ¹³C NMR (125 MHz, CDCl₃) δ 151.3, 150.6, 149.3, 148.6, 145.0, 143.3, 136.1, 125.5, 124.3, 123.1, 117.4, 117.0, 116.2, 112.2, 111.3, 74.3, 68.5, 56.4, 51.0, 30.9.

5.1.1.1.35. 2-((4-((4-chloro-3-fluorobenzyl)oxy)piperidin-1-yl) methyl)imidazo[1,2-a]pyridine (17b).

Prepared using General Procedure B. Yield = 28.6 mg (37.4%, red oil). LCMS: R_T = 2.019 min; ESI-MS: m/z [M + H]⁺, calc’d 374.14 for C₂₀H₂₂ClFN₃O, found 374.1. ¹H NMR (500 MHz, CDCl₃) δ 8.05 (dd, J = 6.8, 1.3 Hz, 1H), 7.58 (s, 1H), 7.53 (d, J = 9.1 Hz, 1H), 7.31 (t, J = 7.8 Hz, 1H), 7.16–7.09 (m, 2H), 7.01 (dd, J = 8.3, 1.9 Hz, 1H), 6.74 (td, J = 6.7, 1.2 Hz, 1H), 4.47 (s, 2H), 3.77 (s, 2H), 3.45 (dq, J = 8.4, 3.9 Hz, 1H), 2.93 (ddd, J = 11.2, 6.4, 3.7 Hz, 2H), 2.40 (s, 2H), 1.97 (ddt, J = 13.7, 7.0, 3.6 Hz, 2H), 1.75 (ddd, J = 12.7, 8.4, 3.7 Hz, 2H). ¹³C NMR (125 MHz, CDCl₃) δ 159.1, 157.1, 145.1, 140.0, 130.4, 125.6, 124.4, 123.4, 119.7, 117.5, 115.4, 115.3, 112.3, 73.9, 68.5, 56.2, 50.7, 30.5.

5.1.1.1.36. 2-((4-((3-(trifluoromethyl)benzyl)oxy)piperidin-1-yl) methyl)imidazo[1,2-a]pyridine (17c).

Prepared using General Procedure B. Yield = 36.0 mg (48%, red oil). LCMS: R_T = 2.063 min; ESI-MS: m/z [M + H]⁺, calc’d 390.18 for C₂₁H₂₃F₃N₃O, found 390.1. ¹H NMR (500 MHz, CDCl₃) δ 8.05 (d, J = 6.7 Hz, 1H), 7.58 (d, J = 3.5 Hz, 2H), 7.52 (dd, J = 16.2, 8.4 Hz, 3H), 7.42 (t, J = 7.7 Hz, 1H), 7.12 (ddd, J = 8.9, 6.8, 1.3 Hz, 1H), 6.73 (td, J = 6.8, 1.2 Hz, 1H), 4.55 (s, 2H), 3.77 (s, 2H), 3.47 (tt, J = 8.1, 3.7 Hz, 1H), 2.97–2.89 (m, 2H), 2.40 (d, J = 11.2 Hz, 2H), 1.99 (ddd, J = 13.0, 6.9, 3.6 Hz, 2H), 1.76 (dtd, J = 12.6, 8.6, 3.6 Hz, 2H). ¹³C NMR (125 MHz, CDCl₃) δ 145.0, 142.6, 140.0, 130.8, 130.6, 128.8, 125.6, 125.2, 124.4, 124.2, 124.0, 123.1, 117.4, 112.3, 111.6, 74.1, 69.1, 56.2, 50.7, 30.6.

5.1.1.1.37. 2-((4-((6-methylpyridin-2-yl)methoxy)piperidin-1-yl) methyl)imidazo[1,2-a]pyridine (17d).

Prepared using general Procedure B. Yield = 75.3 mg (19%, viscous pink oil). LCMS: R_T = 0.695 min; ESI-MS: m/z [M + H]⁺, calc’d 337.20 for C₂₀H₂₅N₄O, found 337.1. ¹H NMR (500 MHz, CDCl₃) δ 8.07 (d, J = 6.7 Hz, 1H), 7.66–7.50 (m, 3H), 7.30 (s, 1H), 7.17–7.11 (m, 1H), 7.03 (d, J = 7.6 Hz, 1H), 6.76 (t, J = 6.7 Hz, 1H), 4.63 (s, 2H), 3.75 (s, 2H), 3.55–3.47 (m, 1H), 2.98–2.89 (m, 2H), 2.53 (s, 3H), 2.35 (s, 2H), 2.00 (dd, J = 13.7, 3.0 Hz, 2H), 1.82–1.74 (m, 2H). ¹³C NMR (125 MHz, CDCl₃) δ 158.6, 157.5, 144.9, 143.8, 136.8, 125.4, 124.2, 121.7, 118.0, 117.4, 112.0, 111.0, 74.9, 70.8, 56.5, 51.2, 31.1, 24.3.

5.1.1.1.38. 2-((4-(pyridin-3-ylmethoxy)piperidin-1-yl)methyl)imidazo [1,2-a]pyridine (17e).

Prepared using general Procedure B. Yield = 28.8 mg (8%, viscous pink oil). LCMS: R_T = 0.393 min; m/z [M + H]⁺, calc’d 323.19 for C₁₉H₂₃N₄O, found 323.1. ¹H NMR (500 MHz, CDCl₃) δ 8.55 (d, J = 1.6 Hz, 1H), 8.50 (dd, J = 4.8, 1.6 Hz, 1H), 8.05 (dt, J = 6.8, 1.1 Hz, 1H), 7.66 (dt, J = 7.8, 1.9 Hz, 1H), 7.57–7.50 (m, 2H), 7.24 (dd, J = 8.0, 5.1 Hz, 1H), 7.11 (ddd, J = 9.0, 6.7, 1.2 Hz, 1H), 6.72 (td, J = 6.8, 1.1 Hz, 1H), 4.53 (s, 2H), 3.71 (s, 2H), 3.46–3.40 (m, 1H), 2.93–2.85 (m, 2H), 2.30 (s, 2H), 1.95 (dd, J = 13.1, 3.3 Hz, 2H), 1.75–1.68 (m, 2H). ¹³C NMR (125 MHz, CDCl₃) δ 149.0, 148.9, 145.0, 144.0, 135.2, 134.3, 125.4, 124.1, 123.3, 117.4, 112.0, 110.9, 74.8, 67.2, 56.5, 51.2, 31.1.

5.1.1.1.39. (S)-2-((3-((3-fluorobenzyl)oxy)piperidin-1-yl)methyl)imidazo[1,2-a]pyridine (17f).

Prepared using general Procedure B. Yield = 87.0 mg (21%, viscous pink oil). LCMS: R_T = 2.016 min; ESI-MS: m/z [M + H]⁺, calc’d 340.18 for C₂₀H₂₃FN₃O, found 340.1. ¹H NMR (500 MHz, CDCl₃) δ 8.05 (d, J = 6.8 Hz, 1H), 7.55 (d, J = 9.1 Hz, 1H), 7.51 (s, 1H), 7.25 (dt, J = 13.7, 7.0 Hz, 1H), 7.16–7.10 (m, 1H), 7.05 (t, J = 8.6 Hz, 2H), 6.96–6.88 (m, 1H), 6.74 (t, J = 6.7 Hz, 1H), 4.57–4.47 (m, 2H), 3.77 (s, 2H), 3.62–3.53 (m, 1H), 3.11 (d, J = 9.4 Hz, 1H), 2.84 (d, J = 11.0 Hz, 1H), 2.15 (dd, J = 21.8, 11.6 Hz, 2H), 1.99 (dd, J = 12.2, 3.8 Hz, 1H), 1.79–1.72 (m, 1H), 1.58 (td, J = 15.0, 3.6 Hz, 1H), 1.30 (ddd, J = 22.0, 12.2, 4.2 Hz, 1H). ¹³C NMR (125 MHz, CDCl₃) δ 163.9, 161.9, 145.0, 143.5, 141.6, 129.7, 125.4, 124.2, 122.8, 117.5, 114.2, 112.1, 111.0, 74.6, 69.6, 58.1, 56.6, 53.5, 30.2, 23.1.

5.1.1.1.40. (S)-2-((3-((3-(trifluoromethoxy)benzyl)oxy)piperidin-1-yl)methyl)imidazo[1,2-a]pyridine (17g).

Prepared using General Procedure B. Yield = 39.6 mg (23%, viscous dark red oil). LCMS: R_T = 2.689 min; ESI-MS: m/z [M + H]⁺, calc’d 406.17 for C₂₁H₂₃F₃N₃O₂, found 406.1. ¹H NMR (500 MHz, CDCl₃) δ 8.05 (d, J = 6.8 Hz, 1H), 7.55 (d, J = 9.1 Hz, 1H), 7.53 (s, 1H), 7.30 (t, J = 7.9 Hz, 1H), 7.21 (d, J = 7.7 Hz, 1H), 7.18 (s, 1H), 7.13 (ddd, J = 9.0, 6.7, 1.2 Hz, 1H), 7.08 (d, J = 8.1 Hz, 1H), 6.74 (td, J = 6.8, 1.0 Hz, 1H), 4.58–4.51 (m, 2H), 3.84–3.78 (m, 2H), 3.63–3.56 (m, 1H), 3.15 (d, J = 8.0 Hz, 1H), 2.88 (d, J = 11.2 Hz, 1H), 2.21 (dt, J = 19.1, 10.4 Hz, 2H), 2.02–1.96 (m, 1H), 1.76 (ddd, J = 11.5, 7.6, 3.8 Hz, 1H), 1.65–1.56 (m, 1H), 1.31 (ddd, J = 22.0, 12.2, 4.3 Hz, 1H). ¹³C NMR (125 MHz, CDCl₃) δ 149.3, 145.0, 143.3, 141.4, 129.6, 125.5, 125.4, 124.2, 121.5, 119.7, 119.4, 117.4, 112.1, 111.1, 74.6, 69.5, 57.8, 56.4, 53.4, 30.3, 23.1.

5.1.1.1.41. (S)-2-((3-((6-methylpyridin-2-yl)methoxy)piperidin-1-yl) methyl)imidazo[1,2-a]pyridine (17h).

Prepared using General Procedure B. Yield = 18.3 mg (12%, viscous orange oil). LCMS: R_T = 1.361 min; ESI-MS: m/z = 335.1 [M – H]⁺, calc’d 335.19 for C₂₀H₂₃N₄O, found 335.1. ¹H NMR (500 MHz, CDCl₃) δ 8.07 (d, J = 6.8 Hz, 1H), 7.60 (s, 1H), 7.55 (dd, J = 13.0, 5.4 Hz, 2H), 7.24 (s, 1H), 7.17–7.11 (m, 1H), 7.00 (d, J = 7.6 Hz, 1H), 6.76 (t, J = 6.7 Hz, 1H), 4.66–4.59 (m, 2H), 3.86 (s, 2H), 3.71–3.65 (m, 1H), 3.21 (d, J = 9.6 Hz, 1H), 2.91 (d, J = 10.5 Hz, 1H), 2.50 (s, 3H), 2.27 (d, J = 9.8 Hz, 2H), 2.08–2.01 (m, 1H), 1.80 (dd, J = 9.7, 3.9 Hz, 1H), 1.65 (dd, J = 23.9, 11.5 Hz, 1H), 1.42–1.32 (m, 1H). ¹³C NMR (125 MHz, CDCl₃) δ 158.2, 157.5, 144.9, 142.9, 136.8, 125.5, 124.3, 121.8, 118.3, 117.5, 112.1, 111.3, 74.6, 71.3, 57.7, 56.5, 53.4, 29.9, 24.2, 22.7.

5.1.1.1.42. (S)-2-((3-((2-methylbenzyl)oxy)piperidin-1-yl)methyl) imidazo[1,2-a]pyridine (17i).

Prepared using General Procedure B. Yield = 64.6 mg (37%, viscous orange oil). LCMS: R_T = 2.213 min; ESI-MS: m/z [M + H]⁺, calc’d 336.21 for C₂₁H₂₆N₃O, found 336.1. ¹H NMR (500 MHz, CDCl₃) δ 8.03 (d, J = 6.8 Hz, 1H), 7.54 (d, J = 9.1 Hz, 1H), 7.48 (s, 1H), 7.28 (d, J = 7.4 Hz, 1H), 7.17–7.09 (m, 4H), 6.78–6.67 (m, 1H), 4.52 (q, J = 11.6 Hz, 2H), 3.82–3.72 (m, 2H), 3.63–3.55 (m, 1H), 3.14 (d, J = 8.1 Hz, 1H), 2.85 (d, J = 11.1 Hz, 1H), 2.29 (s, 3H), 2.17–2.08 (m, 2H), 2.01 (dd, J = 12.2, 3.4 Hz, 1H), 1.78–1.71 (m, 1H), 1.63–1.54 (m, 1H), 1.28 (ddd, J = 22.3, 12.3, 4.3 Hz, 1H). ¹³C NMR (125 MHz, CDCl₃) δ 144.7, 143.3, 136.3, 136.3, 129.9, 128.3, 127.4, 125.5, 125.3, 124.0, 117.1, 111.8, 110.8, 74.4, 68.7, 58.1, 56.4, 53.1, 30.0, 23.0, 18.6.

5.1.1.1.43. (S)-4-(imidazo[1,2-a]pyridin-2-ylmethyl)-2-(((4-methylthiazol-2-yl)oxy)methyl)morpholine (17j).

Prepared following the procedure outlined in Ref. 23. Yield = 29.5 mg (37%, red oil). LCMS: R_T = 1.907 min; ESI-MS: m/z [M + H]⁺, calc’d 345.14 for C₁₇H₂₁N₄O₂S, found 345.1. ¹H NMR (500 MHz, CDCl₃) δ 8.10–8.07 (m, 1H), 7.60 (d, J = 9.1 Hz, 1H), 7.57 (s, 1H), 7.18 (ddd, J = 8.9, 6.8, 1.3 Hz, 1H), 6.80 (td, J = 6.8, 1.2 Hz, 1H), 6.20 (d, J = 1.4 Hz, 1H), 4.38 (d, J = 4.9 Hz, 2H), 4.03 (dtd, J = 10.1, 4.9, 2.3 Hz, 1H), 3.94 (ddd, J = 11.5, 3.5, 1.6 Hz, 1H), 3.85–3.76 (m, 3H), 2.99 (dt, J = 11.3, 2.0 Hz, 1H), 2.89 (dq, J = 11.5, 2.1 Hz, 1H), 2.42 (td, J = 11.5, 3.4 Hz, 1H), 2.29–2.22 (m, 4H). ¹³C NMR (125 MHz, CDCl₃) δ 173.9, 146.9, 145.3, 142.2, 125.9, 125.2, 117.6, 112.9, 111.8, 105.5, 73.6, 72.2, 66.7, 56.5, 54.7, 53.0, 17.9.

5.1.1.1.44. (S)-2-((3,4-difluorophenoxy)methyl)-4-(imidazo[1,2-a] pyridin-2-ylmethyl)morpholine (17k).

Prepared following the procedure outlined in Ref. 23. Yield = 6.0 mg (19%, pink oil). LCMS: R_T = 1.923 min; ESI-MS: m/z [M + H]⁺, calc’d 360.15 for C₁₉H₂₀F₂N₃O₂, found 360.1. ¹H NMR (500 MHz, CDCl3) δ 8.07 (dd, J = 6.8, 1.3 Hz, 1H), 7.58 (s, 1H), 7.58–7.55 (m, 1H), 7.16 (ddd, J = 9.1, 6.7, 1.3 Hz, 1H), 7.02 (q, J = 9.3 Hz, 1H), 6.77 (td, J = 6.8, 1.2 Hz, 1H), 6.71 (ddd, J = 12.0, 6.5, 3.0 Hz, 1H), 6.58 (dtd, J = 9.1, 3.2, 1.7 Hz, 1H), 4.02 (dtd, J = 10.4, 5.0, 2.3 Hz, 1H), 3.97–3.90 (m, 2H), 3.90–3.75 (m, 4H), 3.02 (dt, J = 11.3, 2.0 Hz, 1H), 2.89 (dd, J = 11.6, 2.2 Hz, 1H), 2.41 (td, J = 11.5, 3.4 Hz, 1H), 2.26 (t, J = 10.8 Hz, 1H). ¹³C NMR (125 MHz, CDCl₃) δ 155.0, 150.4, 146.1, 145.2, 144.2, 142.3, 125.6, 124.6, 117.5, 117.1, 112.4, 111.5, 109.9, 104.4, 73.7, 70.0, 66.6, 56.6, 55.0, 52.9.

*Additional carbon peaks due to C–F coupling peaks however, these are overlapping with other aromatic peaks.

5.1.1.1.45. N-(3-chloro-2-methylphenyl)-2-(4-((3,4-difluorobenzyl) oxy)piperidin-1-yl)acetamide (18a).

Prepared following the procedure outlined in Ref. 27. Yield = 43.8 mg (46.5%, pale yellow solid). LCMS: R_T = 2.219 min; ESI-MS: m/z [M + H]⁺, calc’d 409.15 for C₂₁H₂₄ClF₂N₂O₂, found 409.1. ¹H NMR (500 MHz, CDCl₃) δ 9.41 (s, 1H), 8.04 (d, J = 4.6 Hz, 1H), 7.22–7.00 (m, 5H), 4.50 (s, 2H), 3.50 (s, 1H), 3.20 (d, J = 24.6 Hz, 2H), 2.91 (s, 2H), 2.46 (s, 2H), 2.34 (s, 3H), 2.00 (s, 2H), 1.75 (d, J = 9.0 Hz, 2H). ¹³C NMR (125 MHz, CDCl₃) δ 168.4, 151.1, 149.1, 137.0, 135.6, 134.7, 127.2, 125.4, 123.2, 119.7, 117.2, 117.1, 116.4, 116.3, 73.6, 68.9, 62.1, 51.6, 31.6, 14.3.

5.1.1.1.46. N-(3-chloro-2-methylphenyl)-2-(4-((3-(trifluoromethyl) benzyl)oxy)piperidin-1-yl)acetamide (18b).

Prepared following the procedure outlined in Ref. 27. Yield = 33.8 mg (33.3%, yellow oil). LCMS: R_T = 2.334 min; ESI-MS: m/z [M + H]⁺, calc’d 441.16 for C₂₂H₂₅ClF₃N₂O₂, found 441.1. ¹H NMR (500 MHz, CDCl₃) δ 9.42 (s, 1H), 8.05 (s, 1H), 7.62 (s, 1H), 7.55 (t, J = 6.5 Hz, 2H), 7.47 (t, J = 7.7 Hz, 1H), 7.19–7.08 (m, 2H), 4.61 (s, 2H), 3.53 (s, 1H), 3.18 (s, 2H), 2.92 (s, 2H), 2.48 (d, J = 7.2 Hz, 2H), 2.35 (s, 3H), 2.03 (d, J = 9.6 Hz, 2H), 1.78 (d, J = 8.7 Hz, 2H). ¹³C NMR (125 MHz, CDCl₃) δ 168.4, 139.6, 137.0, 134.7, 131.0, 130.6, 128.9, 127.2, 125.4, 124.5, 124.1, 123.1, 119.8, 73.8, 69.4, 62.1, 51.6, 31.7, 14.3.

5.1.1.1.47. N-(3-chloro-2-methylphenyl)-2-(4-((4-chloro-3-fluorobenzyl)oxy)piperidin-1-yl)acetamide (18c).

Prepared following the procedure outlined in Ref. 27. Yield = 37.2 mg (37.9%, yellow oil). LCMS: R_T = 2.301 min; ESI-MS: m/z [M + H]⁺, calc’d 425.12 for C₂₁H₂₄Cl₂FN₂O₂, found 425.1. ¹H NMR (500 MHz, CDCl₃) δ 9.41 (s, 1H), 8.04 (d, J = 5.3 Hz, 1H), 7.36 (t, J = 7.8 Hz, 1H), 7.19–7.10 (m, 3H), 7.06 (d, J = 8.1 Hz, 1H), 4.51 (s, 2H), 3.50 (s, 1H), 3.17 (s, 2H), 2.86 (d, J = 43.0 Hz, 2H), 2.48 (d, J = 9.1 Hz, 2H), 2.35 (d, J = 9.7 Hz, 3H), 2.06–1.92 (m, 2H), 1.76 (d, J = 9.0 Hz, 2H). ¹³C NMR (125 MHz, CDCl₃) δ 159.1, 157.1, 139.7, 137.0, 134.7, 130.5, 127.2, 125.4, 123.5, 123.4, 119.9, 115.5, 115.3, 73.7, 68.8, 62.1, 51.6, 31.6, 14.3.

5.1.1.1.48. 2-(4-((3,4-difluorobenzyl)oxy)piperidin-1-yl)-N-(4-fluoro-3-methylphenyl)acetamide (18d).

Prepared following the procedure outlined in Ref. 27. Yield = 57.1 mg (58.5%, white solid). LCMS: R_T = 2.301 min; ESI-MS: m/z [M + H]⁺, calc’d 393.18 for C₂₁H₂₄ClF₃N₂O₂, found 393.1. ¹H NMR (500 MHz, CDCl₃) δ 9.12 (s, 1H), 7.39 (dd, J = 6.8, 2.7 Hz, 1H), 7.33 (ddd, J = 8.7, 4.4, 2.8 Hz, 1H), 7.17 (ddd, J = 10.3, 7.6, 2.1 Hz, 1H), 7.11 (dt, J = 10.2, 8.2 Hz, 1H), 7.03 (ddt, J = 8.2, 3.7, 1.6 Hz, 1H), 6.94 (t, J = 9.0 Hz, 1H), 4.48 (s, 2H), 3.48 (tt, J = 8.2, 3.9 Hz, 1H), 3.11 (s, 2H), 2.85 (dt, J = 10.7, 4.6 Hz, 2H), 2.42 (ddd, J = 12.0, 9.2, 3.1 Hz, 2H), 2.25 (d, J = 2.1 Hz, 3H), 2.03–1.93 (m, 2H), 1.74 (dtd, J = 12.6, 8.8, 3.6 Hz, 2H). ¹³C NMR (125 MHz, CDCl₃) δ 168.3, 158.8, 156.9, 151.3, 150.7, 149.4, 148.7, 135.8, 133.4, 125.4, 123.2, 122.5, 118.4, 117.1, 116.3, 115.2, 73.6, 61.9, 53.5, 51.5, 31.5, 14.6.

5.1.1.1.49. (S)-3-((4-fluoro-3-methylbenzyl)oxy)-1-(3-fluoro-4-methoxybenzyl)piperidine (19a).

Prepared using General Procedure A. Yield = 166.4 mg (31%, viscous yellow oil). LCMS: R_T = 2.403 min; ESI-MS: m/z [M + H]⁺, calc’d 362.19 for C₂₁H₂₆F₂NO₂, found 362.1. ¹H NMR (500 MHz, CDCl₃) δ 7.15 (d, J = 7.3 Hz, 1H), 7.09 (d, J = 10.9 Hz, 2H), 7.00 (d, J = 8.2 Hz, 1H), 6.95 (t, J = 9.0 Hz, 1H), 6.90 (t, J = 8.4 Hz, 1H), 4.46 (q, J = 11.6 Hz, 2H), 3.90 (s, 3H), 3.58–3.49 (m, 1H), 3.47 (s, 2H), 2.96 (d, J = 9.5 Hz, 1H), 2.68 (d, J = 10.7 Hz, 1H), 2.27 (s, 3H), 2.06–1.95 (m, 3H), 1.75 (dd, J = 9.8, 3.7 Hz, 1H), 1.54 (dd, J = 24.0, 11.9 Hz, 1H), 1.30 (td, J = 12.4, 3.9 Hz, 1H). ¹³C NMR (125 MHz, CDCl₃) δ 161.7, 159.8, 153.2, 151.3, 146.6, 134.2, 130.8, 126.6, 124.6, 116.7, 114.7, 113.0, 74.5, 69.8, 62.1, 57.9, 56.3, 53.3, 30.4, 23.3, 14.5.

5.1.1.1.50. (R)-3-((4-fluoro-3-methylbenzyl)oxy)-1-(3-fluoro-4-methoxybenzyl)piperidine (19b).

Prepared using General Procedure A. Yield = 14.0 mg (11%, viscous yellow oil). LCMS: R_T = 2.525 min; ESI-MS: m/z [M + H]⁺, calc’d 362.19 for C₂₁H₂₆F₂NO₂, found 362.1. ¹H NMR (500 MHz, CDCl₃) δ 7.12 (d, J = 7.4 Hz, 1H), 7.07 (dt, J = 5.5, 3.3 Hz, 2H), 6.97 (d, J = 8.2 Hz, 1H), 6.96–6.91 (m, 1H), 6.88 (t, J = 8.4 Hz, 1H), 4.44 (q, J = 11.5 Hz, 2H), 3.88 (s, 3H), 3.49 (td, J = 9.1, 4.3 Hz, 1H), 3.45 (s, 2H), 2.93 (d, J = 9.0 Hz, 1H), 2.66 (d, J = 10.9 Hz, 1H), 2.25 (s, 3H), 2.04–1.92 (m, 3H), 1.76–1.70 (m, 1H), 1.58–1.47 (m, 1H), 1.28 (ddd, J = 22.1, 12.2, 4.2 Hz, 1H). ¹³C NMR (125 MHz, CDCl₃) δ 13C NMR (126 MHz, CDCl3) δ 161.7, 159.8, 153.2, 151.3, 146.6, 134.1, 130.9, 126.6, 124.6, 116.7, 114.7, 112.9, 74.5, 69.8, 62.1, 58.0, 56.3, 53.3, 30.4, 23.3, 14.5.

5.1.1.1.51. (S)-1-(3-fluoro-4-methoxybenzyl)-3-((3-fluorobenzyl)oxy) piperidine (19c).

Prepared using General Procedure A. Yield = 65.1 mg (43%, viscous yellow oil). LCMS: R_T = 2.152 min; ESI-MS: m/z [M + H]⁺, calc’d 348.18 for C₂₀H₂₄F₂NO₂, found 348.1. ¹H NMR (500 MHz, CDCl₃) δ 7.27 (dd, J = 13.8, 7.9 Hz, 1H), 7.06 (t, J = 9.8 Hz, 3H), 6.98 (d, J = 8.3 Hz, 1H), 6.94 (td, J = 8.6, 2.4 Hz, 1H), 6.88 (t, J = 8.4 Hz, 1H), 4.52 (q, J = 12.3 Hz, 2H), 3.87 (s, 3H), 3.50 (td, J = 9.0, 4.4 Hz, 1H), 3.46 (d, J = 13.9 Hz, 2H), 2.92 (d, J = 9.1 Hz, 1H), 2.64 (d, J = 11.0 Hz, 1H), 2.00 (d, J = 13.3 Hz, 3H), 1.74 (ddt, J = 11.4, 7.7, 4.0 Hz, 1H), 1.56–1.46 (m, 1H), 1.31 (ddd, J = 16.2, 12.3, 4.2 Hz, 1H). ¹³C NMR (125 MHz, CDCl₃) δ 163.8, 161.9, 153.2, 151.2, 146.5, 141.6, 131.3, 129.7, 124.5, 122.7, 116.5, 114.1, 112.9, 74.7, 69.5, 62.0, 57.9, 56.2, 53.2, 30.3, 23.2.

5.1.1.1.52. (S)-1-(3-fluoro-4-methoxybenzyl)-3-((2-methylbenzyl) oxy)piperidine (19d).

Prepared using general Procedure A. Yield = 63.0 mg (41%, viscous yellow oil). LCMS: R_T = 2.173 min; ESI-MS: m/z [M + H]⁺, calc’d 344.20 for C₂₁H₂₇FNO₂, found 344.1. ¹H NMR (500 MHz, CDCl₃) δ 7.34–7.29 (m, 1H), 7.22–7.14 (m, 3H), 7.09 (dd, J = 12.2, 1.8 Hz, 1H), 6.99 (d, J = 8.3 Hz, 1H), 6.90 (t, J = 8.4 Hz, 1H), 4.53 (q, J = 11.6 Hz, 2H), 3.89 (s, 3H), 3.56–3.50 (m, 1H), 3.46 (q, J = 13.2 Hz, 2H), 2.98 (d, J = 8.6 Hz, 1H), 2.67 (d, J = 11.0 Hz, 1H), 2.34 (s, 3H), 2.07–1.97 (m, 3H), 1.75 (ddt, J = 11.1, 7.4, 3.9 Hz, 1H), 1.58–1.49 (m, 1H), 1.31 (ddd, J = 21.6, 12.0, 3.9 Hz, 1H). ¹³C NMR (125 MHz, CDCl₃) δ 153.2, 151.2, 146.5, 136.5, 131.4, 130.1, 128.5, 127.6, 125.7, 124.5, 116.5, 112.9, 74.5, 68.8, 62.1, 58.0, 56.0, 53.2, 30.3, 23.3, 18.7.

5.1.1.1.53. (S)-1-(3-fluoro-4-methoxybenzyl)-3-((4-methylbenzyl) oxy)piperidine (19e).

Prepared using General Procedure A. Yield = 20.6 mg (8%, orange viscous yellow oil). LCMS: R_T = 2.230 min; ESI-MS: m/z [M + H]⁺, calc’d 344.20 for C₂₁H₂₇FNO₂, found 344.1. ¹H NMR (500 MHz, CDCl₃) δ 7.20 (d, J = 7.9 Hz, 2H), 7.13 (d, J = 7.9 Hz, 2H), 7.07 (dd, J = 12.2, 1.8 Hz, 1H), 6.98 (d, J = 8.3 Hz, 1H), 6.89 (t, J = 8.4 Hz, 1H), 4.49 (q, J = 11.7 Hz, 2H), 3.88 (s, 3H), 3.52–3.47 (m, 1H), 3.46 (d, J = 8.7 Hz, 2H), 2.95 (d, J = 8.6 Hz, 1H), 2.65 (d, J = 11.0 Hz, 1H), 2.33 (s, 3H), 1.98 (dd, J = 17.7, 8.8 Hz, 3H), 1.73 (ddt, J = 11.2, 7.6, 3.9 Hz, 1H), 1.55–1.46 (m, 1H), 1.28 (qd, J = 12.3, 4.2 Hz, 1H). ¹³C NMR (125 MHz, CDCl₃) δ 153.2, 151.3, 146.5, 137.1, 135.7, 129.0, 127.7, 124.6, 116.6, 112.9, 74.2, 70.2, 62.1, 58.1, 56.3, 53.2, 30.4, 23.3, 21.1.

5.1.1.1.54. (S)-4-((3-((4-methylbenzyl)oxy)piperidin-1-yl)methyl) benzonitrile (19f).

Prepared using General Procedure A. Yield = 10.6 mg (7%, viscous orange oil). LCMS: R_T = 2.361 min; ESI-MS: m/z [M + H]⁺, calc’d 321.20 for C₂₁H₂₅N₂O, found 321.1. ¹H NMR (500 MHz, CDCl₃) δ 7.60 (d, J = 8.1 Hz, 2H), 7.43 (d, J = 8.0 Hz, 2H), 7.19 (d, J = 7.9 Hz, 2H), 7.13 (d, J = 7.9 Hz, 2H), 4.49 (q, J = 11.7 Hz, 2H), 3.56 (s, 2H), 3.53–3.47 (m, 1H), 2.90 (d, J = 9.1 Hz, 1H), 2.62 (d, J = 9.9 Hz, 1H), 2.34 (s, 3H), 2.03 (dt, J = 17.1, 5.9 Hz, 3H), 1.78–1.72 (m, 1H), 1.52 (dd, J = 23.4, 11.7 Hz, 1H), 1.31 (ddd, J = 15.9, 12.5, 4.2 Hz, 1H). ¹³C NMR (125 MHz, CDCl₃) δ 137.2, 135.6, 131.9, 129.4, 129.0, 127.6, 119.0, 110.8, 74.0, 70.2, 62.5, 58.2, 53.5, 30.2, 23.1, 21.1.

5.1.1.1.55. (S)-1-(3-fluorobenzyl)-3-((4-methylbenzyl)oxy)piperidine (19g).

Prepared using General Procedure A. Yield = 26.2 mg (25%, viscous orange oil). LCMS: R_T = 2.266 min; ESI-MS: m/z [M + H]⁺, calc’d 314.19 for C₂₀H₂₅FNO, found 314.1. ¹H NMR (500 MHz, CDCl₃) δ 7.30–7.27 (m, 1H), 7.22 (d, J = 7.9 Hz, 2H), 7.15 (d, J = 7.9 Hz, 2H), 7.08 (t, J = 8.3 Hz, 2H), 6.99–6.94 (m, 1H), 4.52 (q, J = 11.7 Hz, 2H), 3.59–3.50 (m, 3H), 2.99 (d, J = 8.5 Hz, 1H), 2.69 (d, J = 10.9 Hz, 1H), 2.36 (s, 3H), 2.04 (dd, J = 15.5, 11.4 Hz, 3H), 1.79–1.72 (m, 1H), 1.55 (tt, J = 15.1, 3.8 Hz, 1H), 1.35–1.27 (m, 1H). ¹³C NMR (125 MHz, CDCl₃) δ 163.8, 161.9, 137.1, 135.7, 129.5, 129.0, 127.7, 124.5, 115.7, 113.9, 74.1, 70.2, 62.4, 58.1, 53.3, 30.4, 23.2, 21.1.

5.1.1.1.56. (S)-3-((3-fluoro-4-methoxybenzyl)oxy)-1-(3-methylbenzyl)piperidine (19h).

Prepared using General Procedure A. Yield = 4.1 mg (3%, viscous yellow oil). LCMS: R_T = 2.218 min; ESI-MS: m/z [M + H]⁺, calc’d 344.20 for C₂₁H₂₇FNO₂, found 344.1. ¹H NMR (500 MHz, CDCl₃) δ 7.22 (t, J = 7.4 Hz, 1H), 7.15 (s, 1H), 7.10 (dd, J = 16.4, 9.2 Hz, 3H), 7.02 (d, J = 8.3 Hz, 1H), 6.91 (t, J = 8.4 Hz, 1H), 4.51–4.42 (m, 2H), 3.89 (s, 3H), 3.53 (q, J = 12.3 Hz, 3H), 2.99 (d, J = 9.1 Hz, 1H), 2.71 (d, J = 8.9 Hz, 1H), 2.37 (s, 3H), 2.04 (d, J = 8.7 Hz, 3H), 1.76 (d, J = 13.1 Hz, 1H), 1.56 (d, J = 10.7 Hz, 1H), 1.34–1.26 (m, 1H).¹³C NMR (125 MHz, CDCl₃) δ 153.3, 151.4, 148.0, 137.8, 132.0, 129.9, 128.0, 127.8, 126.3, 123.3, 115.5, 113.2, 74.3, 69.4, 63.1, 57.9, 56.3, 53.3, 30.4, 23.2, 21.4.

5.1.1.1.57. (S)-3-((4-fluoro-3-methylbenzyl)oxy)-1-(4-methylbenzyl) piperidine (19i).

Prepared using General Procedure A. Yield = 20.7 mg (8%, viscous yellow oil). LCMS: R_T = 2.555 min; ESI-MS: m/z [M + H]⁺, calc’d 328.21 for C₂₁H₂₇FNO, found 328.1. ¹H NMR (500 MHz, CDCl₃) δ 7.19 (d, J = 7.9 Hz, 2H), 7.13 (d, J = 7.8 Hz, 3H), 7.08 (ddd, J = 7.3, 4.9, 2.0 Hz, 1H), 6.96–6.91 (m, 1H), 4.45 (q, J = 11.6 Hz, 2H), 3.55–3.48 (m, 3H), 2.99 (d, J = 8.2 Hz, 1H), 2.69 (d, J = 11.0 Hz, 1H), 2.35 (s, 3H), 2.26 (d, J = 1.7 Hz, 3H), 1.99 (dd, J = 17.4, 10.3 Hz, 3H), 1.73 (qd, J = 7.6, 4.0 Hz, 1H), 1.58–1.48 (m, 1H), 1.32–1.23 (m, 1H). ¹³C NMR (125 MHz, CDCl₃) δ 161.6, 159.8, 136.6, 134.9, 134.2, 130.9, 129.1, 128.8, 126.6, 124.6, 114.7, 74.5, 69.8, 62.9, 58.0, 53.3, 30.5, 23.3, 21.1, 14.5.

5.1.1.1.58. (S)-3-((3-fluorobenzyl)oxy)-1-(2-methylbenzyl)piperidine (19j).

Prepared using General Procedure A. Yield = 59.6 mg (35%, viscous orange oil). LCMS: R_T = 2.181 min; ESI-MS: m/z [M + H]⁺, calc’d 314.19 for C₂₀H₂₅FNO, found 314.1. ¹H NMR (500 MHz, CDCl₃) δ 7.28 (dt, J = 14.1, 7.3 Hz, 2H), 7.21–7.13 (m, 3H), 7.07 (t, J = 8.5 Hz, 2H), 7.00–6.91 (m, 1H), 4.55–4.48 (m, 2H), 3.52 (dd, J = 8.8, 4.4 Hz, 1H), 3.48 (d, J = 14.1 Hz, 2H), 3.00 (d, J = 9.2 Hz, 1H), 2.70 (d, J = 10.9 Hz, 1H), 2.37 (s, 3H), 2.05 (dd, J = 20.3, 10.8 Hz, 3H), 1.78–1.71 (m, 1H), 1.52 (dd, J = 24.5, 11.6 Hz, 1H), 1.39–1.28 (m, 1H). ¹³C NMR (125 MHz, CDCl₃) δ 163.9, 161.9, 141.7, 137.3, 136.6, 130.2, 129.7, 129.6, 126.9, 125.4, 122.7, 114.2, 114.1, 74.9, 69.4, 60.8, 58.0, 53.3, 30.6, 23.4, 19.2.

5.1.1.1.59. General Procedure D.

To spirocycle, 20, starting material (1.0 eq.) in THF (2 mL) was added the substituted 2-chloro-N-phenylacetamide, 21, (1.0 eq.), Et₃N (2.0 eq.), and NaI (5 mg). The reaction was stirred overnight at room temperature. The reaction was then quenched with saturated sodium bicarbonate solution and product was extracted into ethyl acetate. The product was purified by flash chromatography 0–65% EtOAc:hexanes.

5.1.1.1.60. General Procedure E.

To the spirocycle, 20, (1.1 eq.) in dichloroethane (2 mL) was added 4 Å molecular sieves, aldehyde (1.0 eq.) and Et₃N (2.0 eq.). The reaction was stirred at room temperature for 2 h. Next, sodium triacetoxyborohydride (2.0 eq.) was added and the reaction was stirred overnight at room temperature. The reaction was quenched with saturated sodium bicarbonate solution and product was extracted in dichloromethane. Product was purified on flash chromatography 0–10% MeOH (0.01% Et₃N):DCM and reverse-phase chromatography 0–100% water:ACN when necessary. Boc deprotection was done using 4 N HCl in dioxane. The reaction was stirred for 2 h before it was concentrated in vacuo.

5.1.1.1.61. General Procedure F.

To a vial with deprotected intermediate spirocycle, 22 or 23, (1.1 eq.) in dichloroethane was slowly added 3,4-difluorobenzyl bromide (1 eq) and iPr₂EtN (2 eq.). The reaction was stirred for 20 h at room temperature. The reaction was quenched with water and the product was extracted with dichloromethane. The DCM layers were collected and washed with brine and dried with sodium sulfate. The product was purified with flash chromatography 0–10% MeOH:DCM.

5.1.1.1.62. General Procedure G.

To a vial with deprotected intermediate spirocycle, 22 or 23, (1 eq.) in acetonitrile at 0 °C was slowly added cesium carbonate (2 eq.). The mixture was stirred for 1 h and allowed to warm to room temperature. The vial was cooled in an ice bath before adding the substituted benzyl bromide (1.1 eq.). The reaction was allowed to come to room temperature and was stirred for 20 h. The reaction was quenched with water and the product was extracted with EtOAc. The EtOAc layers were collected and washed with brine and dried with sodium sulfate. The product was purified with flash chromatography 0–15% EtOAc:hexanes.

5.1.1.1.63. N-(3-chloro-2-methylphenyl)-2-(1-(3,4-difluorobenzyl)-1,8-diazaspiro[4.5]decan-8-yl)acetamide (24a).

Using General Procedure D and F, N-(3-chloro-2-methylphenyl)-2-(1,8-diazaspiro[4.5]decan-8-yl)acetamide (50.0 mg; 0.156 mmol), 3,4-difluorobenzyl bromide (18.1 μL; 0.141 mmol), DIPEA (49.1 μL, 0.282 mmol) were reacted. Yield = 56.6 mg (44.7%, white solid). LCMS: R_T = 1.890 min; ESI-MS: m/z [M + H]⁺, calc’d 448.20 for C₂₄H₂₉ClF₂N₃O, found 448.1. ¹H NMR (500 MHz, CDCl₃) δ 9.43 (s, 1H), 8.01 (dd, J = 7.0, 2.4 Hz, 1H), 7.23–7.00 (m, 5H), 3.59 (s, 2H), 3.18 (s, 2H), 3.00–2.92 (m, 2H), 2.64 (t, J = 6.4 Hz, 2H), 2.45 (td, J = 12.1, 2.4 Hz, 2H), 2.34 (s, 3H), 1.77 (d, J = 13.9 Hz, 6H), 1.49 (d, J = 12.6 Hz, 2H). ¹³C NMR (125 MHz, CDCl₃) δ 168.5, 151.3, 149.3, 137.9, 137.0, 134.7, 127.3, 125.7, 125.4, 123.8, 119.9, 116.9, 62.1, 60.7, 52.5, 51.2, 50.6, 34.2, 32.7, 31.6, 22.7, 20.9, 14.4.

5.1.1.1.64. N-(3-chloro-2-methylphenyl)-2-(1-(3,4-difluorobenzyl)-1,7-diazaspiro[4.4]nonan-7-yl)acetamide (24b).

Using General Procedure D and F, N-(3-chloro-2-methylphenyl)-2-(1,7-diazaspiro[4.4]nonan-7-yl)acetamide (50.0 mg; 0.163 mmol), 3,4-difluorobenzyl bromide (18.9 μL; 0.148 mmol), DIPEA (51.5 μL, 0.296 mmol) were reacted. Yield = 30.8 mg (40.8%, yellow oil). LCMS: R_T = 2.199 min; ESI-MS: m/ z [M + H]⁺, calc’d 434.18 for C₂₃H₂₇ClF₂N₃O, found 434.1. ¹H NMR (500 MHz, CDCl₃) δ 9.15 (s, 1H), 8.00 (dd, J = 7.4, 2.0 Hz, 1H), 7.20 (t, J = 7.0 Hz, 1H), 7.19–7.12 (m, 2H), 7.12–7.01 (m, 2H), 3.81–3.70 (m, 1H), 3.70–3.63 (m, 1H), 3.41–3.25 (m, 2H), 3.07–2.99 (m, 1H), 2.93 (td, J = 8.7, 4.7 Hz, 1H), 2.81–2.72 (m, 1H), 2.62 (dd, J = 14.7, 9.0 Hz, 2H), 2.30 (s, 3H), 2.15 (dq, J = 14.7, 7.8, 6.5 Hz, 1H), 1.98 (qd, J = 12.2, 11.7, 5.4 Hz, 2H), 1.83–1.76 (m, 3H). ¹³C NMR (125 MHz, CDCl₃) δ 168.4, 151.4, 151.3, 149.5, 149.4, 136.9, 134.7, 127.2, 125.6, 123.8, 120.3, 117.1, 116.9, 70.7, 61.4, 59.9, 54.6, 52.5, 51.2, 40.2, 32.4, 20.9, 14.3.

5.1.1.1.65. N-(3-chloro-2-methylphenyl)-2-(7-(3,4-difluorobenzyl)-2,7-diazaspiro[4.5]decan-2-yl)acetamide (24c).

Using General Procedure D and F, N-(3-chloro-2-methylphenyl)-2-(2,7-diazaspiro[4.5]decan-2-yl)acetamide (50.0 mg; 0.156 mmol), 3,4-difluorobenzyl bromide (18.1 μL; 0.141 mmol), DIPEA (49.1 μL, 0.282 mmol) were reacted. Yield = 52.9 mg (54.4%, pale yellow oil). LCMS: R_T = 1.852 min; ESI-MS: m/z [M + H]⁺, calc’d 448.20 for C₂₄H₂₉ClF₂N₃O, found 448.1. ¹H NMR (500 MHz, CDCl₃) δ 9.24 (s, 1H), 8.03 (dd, J = 6.8, 2.6 Hz, 1H), 7.20–7.13 (m, 3H), 7.08–6.99 (m, 2H), 3.81–3.74 (m, 1H), 3.69–3.62 (m, 1H), 3.42 (q, J = 13.6 Hz, 2H), 3.29 (q, J = 16.6 Hz, 2H), 2.86–2.76 (m, 2H), 2.71 (q, J = 8.0 Hz, 1H), 2.53 (d, J = 9.4 Hz, 1H), 2.18 (s, 3H), 1.80–1.72 (m, 1H), 1.66 (ddd, J = 13.8, 8.5, 5.9 Hz, 2H), 1.61–1.51 (m, 2H), 1.51–1.42 (m, 1H). ¹³C NMR (125 MHz, CDCl₃) δ 168.7, 151.3, 150.4, 149.3, 148.4, 137.0, 136.1, 134.6, 127.2, 125.3, 124.3, 119.9, 117.2, 116.9, 65.2, 64.0, 62.0, 59.5, 54.1, 53.9, 42.6, 36.6, 36.2, 23.4, 14.0.

5.1.1.1.66. 2-(1-(3,4-difluorobenzyl)-1,8-diazaspiro[4.5]decan-8-yl)-N-(4-fluoro-3-methylphenyl)acetamide (24d).

Using General Procedure D and F, N-(4-fluoro-3-methylphenyl)-2-(1,8-diazaspiro[4.5]decan-8-yl) acetamide (61.7 mg; 0.202 mmol), 3,4-difluorobenzyl bromide (23.5 μL; 0.183 mmol), DIPEA (63.7 μL, 0.366 mmol) were reacted. Yield = 10.2 mg (12.9%, pale yellow oil). LCMS: R_T = 2.121 min; ESI-MS: m/z [M + H]⁺, calc’d 432.23 for C₂₄H₂₉F₃N₃O, found 432.2. ¹H NMR (500 MHz, CDCl₃) δ 9.06 (s, 1H), 7.41 (dd, J = 6.7, 2.7 Hz, 1H), 7.31 (ddd, J = 8.8, 4.4, 2.8 Hz, 1H), 7.21 (s, 1H), 6.95 (t, J = 9.0 Hz, 1H), 3.64 (s, 2H), 3.14 (s, 2H), 2.93 (d, J = 11.5 Hz, 2H), 2.65 (s, 2H), 2.40 (t, J = 12.0 Hz, 2H), 2.26 (d, J = 1.9 Hz, 3H), 1.78 (s, 6H). ¹³C NMR (125 MHz, CDCl₃) δ 168.4, 158.9, 157.0, 151.4, 149.4, 138.0, 133.3, 125.4, 123.8, 122.7, 118.6, 116.9, 115.2, 62.1, 60.8, 52.4, 51.4, 50.6, 34.1, 32.5, 31.7, 22.7, 20.9, 14.7.

5.1.1.1.67. 2-(1-(3,4-difluorobenzyl)-1,7-diazaspiro[4.4]nonan-7-yl)-N-(4-fluoro-3-methylphenyl)acetamide (24e).

Using General Procedure D and F, N-(4-fluoro-3-methylphenyl)-2-(1,7-diazaspiro[4.4]nonan-7-yl) acetamide (62.5 mg; 0.214 mmol), 3,4-difluorobenzyl bromide (25.0 μL; 0.195 mmol), DIPEA (67.9 μL, 0.390 mmol) were reacted. Yield = 18.1 mg (22.2%, yellow oil). LCMS: R_T = 2.340 min; ESI-MS: m/z [M + H]⁺, calc’d 418.21 for C₂₃H₂₇F₃N₃O, found 418.2. ¹H NMR (500 MHz, CDCl₃) δ 8.93 (s, 1H), 7.29 (td, J = 8.4, 3.2 Hz, 2H), 7.21 (d, J = 9.8 Hz, 1H), 7.12–7.01 (m, 2H), 6.92 (t, J = 8.9 Hz, 1H), 3.73 (q, J = 12.8 Hz, 2H), 3.31 (d, J = 16.4 Hz, 1H), 3.19 (d, J = 16.4 Hz, 1H), 3.02 (s, 1H), 2.87 (s, 1H), 2.69 (q, J = 8.4 Hz, 1H), 2.57 (t, J = 7.5 Hz, 2H), 2.45 (d, J = 10.0 Hz, 1H), 2.22 (d, J = 2.1 Hz, 3H), 2.18–2.07 (m, 1H), 2.02–1.90 (m, 2H), 1.86–1.71 (m, 3H). ¹³C NMR (125 MHz, CDCl₃) δ 168.3, 158.9, 156.9, 151.4, 149.4, 137.1, 133.3, 125.5, 123.7, 122.3, 118.2, 117.0, 115.2, 70.9, 61.4, 59.7, 54.3, 52.6, 51.2, 40.0, 32.7, 21.0, 14.6.

5.1.1.1.68. 2-(7-(3,4-difluorobenzyl)-2,7-diazaspiro[4.5]decan-2-yl)-N-(4-fluoro-3-methylphenyl)acetamide (24f).

Using General Procedure D and F, N-(4-fluoro-3-methylphenyl)-2-(2,7-diazaspiro[4.5]decan-2-yl) acetamide (55.2 mg; 0.181 mmol), 3,4-difluorobenzyl bromide (21.0 μL; 0.164 mmol), DIPEA (57.1 μL, 0.328 mmol) were reacted. Yield = 20.8 mg (24.7%, clear oil). LCMS: R_T = 2.194 min; ESI-MS: m/z [M + H]⁺, calc’d 432.23 for C₂₄H₂₉F₃N₃O, found 432.2. ¹H NMR (500 MHz, CDCl₃) δ 8.97 (s, 1H), 7.36 (dd, J = 6.8, 2.7 Hz, 1H), 7.23 (dt, J = 7.8, 3.5 Hz, 1H), 7.19–7.12 (m, 1H), 7.09–7.00 (m, 2H), 6.95 (t, J = 9.0 Hz, 1H), 3.44 (q, J = 13.6 Hz, 2H), 3.26 (t, J = 13.0 Hz, 2H), 2.89–2.62 (m, 3H), 2.49 (d, J = 9.5 Hz, 1H), 2.35 (d, J = 34.9 Hz, 2H), 2.26 (d, J = 2.0 Hz, 3H), 2.23–2.09 (m, 1H), 1.70–1.60 (m, 2H), 1.60–1.50 (m, 2H), 1.50–1.40 (m, 1H). ¹³C NMR (125 MHz, CDCl₃) δ 168.5, 158.9, 156.9, 150.8, 148.8, 136.1, 133.3, 125.4, 124.2, 122.4, 118.3, 117.3, 116.8, 115.2, 64.9, 63.9, 62.1, 59.3, 53.9, 53.7, 42.6, 36.4, 36.2, 23.4, 14.6.

5.1.1.1.69. 1-(3,4-difluorobenzyl)-7-(imidazo[1,2-a]pyridin-2-ylmethyl)-1,7-diazaspiro[4.4]nonane (25a).

Using General Procedure E and F, 7-(imidazo[1,2-a]pyridin-2-ylmethyl)-1,7-diazaspiro[4.4]nonane (74.3 mg; 0.289 mmol), 3,4-difluorobenzyl bromide (40.6 μL; 0.318 mmol), DIPEA (100.6 μL, 0.578 mmol) were reacted. Yield = 20.2 mg (18.3%, yellow oil). LCMS: R_T = 2.749 min; ESI-MS: m/z [M + H]⁺, calc’d 383.20 for C₂₂H₂₅F₂N₄, found 383.1. ¹H NMR (500 MHz, CDCl₃) δ 8.14–8.09 (m, 1H), 7.97 (s, 1H), 7.52 (dd, J = 9.1, 1.2 Hz, 1H), 7.20 (ddd, J = 9.1, 6.7, 1.3 Hz, 1H), 7.11 (ddd, J = 11.4, 7.7, 2.0 Hz, 1H), 7.06–6.96 (m, 2H), 6.81 (td, J = 6.8, 1.2 Hz, 1H), 4.21 (q, J = 13.5 Hz, 2H), 3.81 (d, J = 13.8 Hz, 1H), 3.59 (d, J = 13.7 Hz, 1H), 3.40–3.30 (m, 2H), 3.12 (q, J = 7.3 Hz, 1H), 2.99 (d, J = 11.6 Hz, 1H), 2.63 (ddd, J = 9.6, 7.9, 5.9 Hz, 1H), 2.51 (dt, J = 9.5, 7.1 Hz, 1H), 2.25 (dt, J = 13.3, 8.7 Hz, 1H), 2.10–2.01 (m, 1H), 1.96 (dt, J = 12.6, 7.6 Hz, 1H), 1.82 (ddd, J = 13.3, 6.9, 3.9 Hz, 1H), 1.79–1.72 (m, 2H), 1.41 (t, J = 7.3 Hz, 1H). ¹³C NMR (125 MHz, CDCl₃) δ 150.8, 148.7, 145.1, 138.0, 136.4, 126.1, 125.5, 123.9, 117.4, 117.0, 116.8, 113.7, 113.0, 70.6, 58.4, 53.1, 52.7, 52.1, 51.3, 46.0, 39.7, 20.9.

5.1.1.1.70. 7-((6-chloro-1H-indol-2-yl)methyl)-1-(3,4-difluorobenzyl)-1,7-diazaspiro[4.4]nonane (25b).

Using General Procedure E and G, 7-((6-chloro-1H-indol-2-yl)methyl)-1,7-diazaspiro[4.4]nonane (83.8 mg; 0.215 mmol), 3,4-difluorobenzyl bromide (30.3 μL; 0.237 mmol), Cs₂CO₃ (140.3 mg, 0.431 mmol) were reacted. Yield = 11.6 mg (12.9%, yellow oil). LCMS: R_T = 2.564 min; ESI-MS: m/z [M + H]⁺, calc’d 416.17 for C₂₃H₂₅ClF₂N₃, found 416.1. ¹H NMR (500 MHz, CDCl₃) δ 11.54 (s, 1H), 8.48 (s, 1H), 7.49–7.44 (m, 2H), 7.14–7.09 (m, 1H), 7.06 (ddd, J = 8.2, 5.8, 3.9 Hz, 2H), 7.01–6.95 (m, 1H), 6.46 (s, 1H), 4.27 (s, 2H), 3.73 (d, J = 13.6 Hz, 1H), 3.56 (d, J = 13.6 Hz, 1H), 3.32 (ddd, J = 11.8, 8.3, 4.3 Hz, 1H), 3.18 (dt, J = 17.6, 11.3 Hz, 2H), 2.95 (d, J = 12.2 Hz, 1H), 2.70–2.62 (m, 1H), 2.52 (ddd, J = 9.5, 8.3, 6.6 Hz, 1H), 2.34–2.26 (m, 1H), 2.04 (qdd, J = 12.5, 8.5, 6.6 Hz, 2H), 1.91–1.76 (m, 3H). ¹³C NMR (125 MHz, CDCl₃) δ 168.1, 151.0, 148.9, 138.0, 135.9, 128.9, 128.8, 125.8, 123.8, 121.3, 120.9, 117.0, 112.1, 104.9, 70.2, 57.8, 52.9, 52.7, 51.7, 51.2, 40.0, 30.3, 20.9.

5.1.1.1.71. 2-((6-chloro-1H-indol-2-yl)methyl)-7-(3,4-difluorobenzyl)-2,7-diazaspiro[4.5]decane (25c).

Using General Procedure E and G, 2-((6-chloro-1H-indol-2-yl)methyl)-2,7-diazaspiro[4.5]decane (93.4 mg; 0.232 mmol), 3,4-difluorobenzyl bromide (32.6 μL; 0.255 mmol), Cs₂CO₃ (151.2 mg, 0.464 mmol) were reacted. Yield = 17.8 mg (17.9%, pale yellow oil). LCMS: R_T = 2.246 min; ESI-MS: m/z [M + H]⁺, calc’d 430.19 for C₂₄H₂₇ClF₂N₃, found 430.1. ¹H NMR (500 MHz, CDCl₃) δ 11.73 (s, 1H), 8.48 (s, 1H), 7.53–7.46 (m, 2H), 7.15–7.06 (m, 3H), 6.99 (ddd, J = 8.3, 4.0, 2.0 Hz, 1H), 6.45 (s, 1H), 4.30–4.19 (m, 2H), 3.44 (s, 2H), 3.25 (s, 1H), 3.14 (s, 2H), 2.98 (d, J = 11.9 Hz, 1H), 2.21 (s, 2H), 2.02 (s, 1H), 1.92 (dt, J = 13.6, 7.7 Hz, 1H), 1.64 (dd, J = 9.8, 5.4 Hz, 2H), 1.57–1.43 (m, 2H). ¹³C NMR (125 MHz, CDCl₃) δ 168.2, 150.9, 148.9, 138.0, 135.3, 128.9, 128.5, 125.7, 124.6, 121.1, 117.5, 117.0, 112.2, 104.8, 62.3, 61.7, 61.4, 53.2, 52.4, 52.2, 42.5, 35.2, 34.5, 23.1.

Appendix A. Supplementary data

Supplementary data to this article can be found online at https://doi.org/10.1016/j.ejmech.2022.114840.

Data availability

Data will be made available on request.