Structure-Activity Relationships in a Novel Series of 7-Substituted-Aryl Quinolines and 5-Substituted-Aryl Benzothiazoles at the Metabotropic Glutamate Receptor Subtype 5

Abstract

The metabotropic glutamate receptor subtype 5 (mGluR5) has been implicated in numerous neuropsychiatric disorders including addiction. We have discovered that the rigid diaryl alkyne template, derived from the potent and selective noncompetitive mGluR5 antagonist 2-methyl-6-(phenylethynyl)pyridine (MPEP), can serve to guide the design of novel quinoline analogues and pharmacophore optimization has resulted in potent mGluR5 noncompetitive antagonists (EC₅₀ range 60–100 nM) in the quinoline series.

Introduction

Glutamate is the most abundant excitatory neurotransmitter in the brain. It regulates the body homeostasis through ionotropic (iGluRs) and metabotropic glutamate receptors (mGluRs). There are at least eight subtypes of the mGluRs, which have been identified and partitioned into three groups based on their localization, function, signaling pathway, and structural homology. mGluR5 belongs to group I, along with mGluR1. Accumulating evidence suggests that mGluR5 antagonists have therapeutic potential in the treatment of anxiety, depression, pain, gastro-esophageal acid reflux disease (GERD), Parkinson’s disease, epilepsy, and Fragile X Syndrome (FXS).¹ To date, several mGluR5 antagonists are being tested in clinical trials for GERD, pain, and FXS.² In addition, mGluR5s have been implicated in drug abuse.^3–6

mGluR5s are located on postsynaptic glutamatergic synapses of the limbic cortex, hippocampus, amygdala, and basal ganglia (including nucleus accumbens, striatum and olfactory tubercle).¹ The mGluR5 functions as a dimer, coupled to phospholipase C through Gq, and modulates the phosphatidylinositol signaling pathway. Activation of the mGluR5 increases cytosolic calcium concentrations, which initiates other signaling pathways.⁷

As a member of the G-protein coupled receptor (GPCR) family C, mGluR5 has a seven-transmembrane alpha-helical domain (7TM) and a large “bilobed” N-terminal domain, which contains the orthosteric binding site.⁸ Competitive antagonists binding to the orthosteric site have at least two disadvantages including low brain penetration and low selectivity across the different subtypes.^{1, 9}

MPEP (2-methyl-6-(phenylethynyl)pyridine) and MTEP (3-((2-methyl-1,3-thiazol-4-yl)ethynyl)pyridine) are the two prototypic noncompetitive mGluR5 antagonists, which bind to the allosteric binding site located in the 7TM region.¹⁰ They are potent and selective over other mGluR subtypes.¹ However, off-target actions (e.g., MPEP also acts as an inhibitor of NMDA receptor and a positive modulator of mGluR4, while MTEP is an inhibitor of cytochrome P450)² and potential for rapid metabolic degradation (e.g., MTEP)² have led to significant synthetic efforts to modify and improve the pharmacological and drug-like profile of these parent drugs.^{2, 7, 11–15} One approach has been to replace the ethynylpyridine moiety of MPEP (or ethynylthiazole moiety of MTEP) with a quinoline (or benzothiazole) structure,¹⁶ toward the discovery of new mGluR5 antagonists with a novel structural template.

Previous structure-activity relationship (SAR) studies exemplified the challenge of optimizing the mGluR5 allosteric antagonists with a parent structure that differs from the diaryl alkynes, as binding affinities to the allosteric site are sensitive to small structural changes.^16–19 Typically, chemical modification of the diarylalkynyl analogues of MPEP or MTEP are better tolerated at mGluR5 than alternative templates.^{1, 2, 7, 19–21}

In our previous SAR studies of quinoline and benzothiazole analogues, compounds 3 and 4 were discovered to bind with moderate affinity to mGluR5 by introducing the 3-cyano group into the phenyl rings at the 7-position of the quinoline or the 5-position of the benzothiazole.¹⁶ The addition of a cyano group improved the binding affinity of 3 to 110 nM from the parent compound that only displaced [³H]MPEP by 50% at 10 M.¹⁷ Milbank, et al. also published this compound in their series of quinoline analogues and showed that the addition of a 5-fluoro substitution (shown as structure 5 in Figure 1) further increased the potency ~10 fold.¹⁴ Recently, we discovered that addition of a cyano and/or fluoro group in a series of MPEP and MTEP analogues (e.g., 6 and 7 in Figure 1) also resulted in an increase in potency.¹⁹ Thus, our strategy was to use SAR derived from the MPEP and MTEP analogues to direct the design and synthesis of quinoline and benzothiazole analogues.

Figure 1.

mGluR5 antagonist structural templates.

Among our previous SAR results, we demonstrated that an additional aryl ring appended to the 4′-position of ring ‘b’ was well tolerated, shown as structure 8a–8d in Figure 1.¹⁹ Hence, using 3 and 4 as the parent structures, we incorporated additional aryl ring modifications, and designed a novel series of analogues as shown in Structure I.

Chemistry

One of the synthetic strategies toward the designed quinolines (in Structure I) is shown in Scheme 1, starting from the boronic ester 9a, which was made from commercially available 7-chloro-2-methylquinoline, under Miyaura borylation conditions.¹⁶ 5-Bromo-2-hydroxybenzonitrile was coupled with 9a under modified Suzuki coupling conditions to give 10, and the free hydroxyl group of 10 was converted to the corresponding triflate 12 with trifluoromethanesulfonic anhydride in an overall 17% yield. Attempts to introduce the aryl ring by treating the triflate 12 with various substituted aryl boronic acids was undertaken using Suzuki coupling conditions, but this strategy proved to be difficult as described below. The same strategy was also applied to the benzothiazole compounds starting from 9b. This strategy was hampered by low yields in steps a to c. To improve the yield of the phenolic intermediates (10 and 11), a protection-deprotection strategy was applied as shown in Scheme 2. However, deprotection of the MOM group in compound 16, or the benzyl group in compound 17 and 18, were either low yielding or incomplete. Hence, higher yields were obtained via the direct coupling condition (step a in Scheme 1) with 5-bromo-2-hydroxybenzonitrile, on a small scale (< 2 mmol). The triflates 12 and 13, from the phenols (step b in Scheme 1) also proceeded in low yield. Triflates 12 and 13 were also easily hydrolyzed under the coupling condition of step c in Scheme 1, especially when these reactions were scaled up (>2 mmol). Utilization of a weaker base such as KF was also tried, but it did not improve the yield. Hence, only compound 14 was synthesized using this strategy.

Scheme 1^a.

^a Reagents and conditions: (a) Na₂CO₃, Pd(OAc)₂, dioxane, H₂O, 50 °C, overnight; (b) Trifluoromethanesulfonic anhydride, pyridine, CH₂Cl₂, RT, 2–5 h; (c) K₃PO₄, Pd(PPh₃)₄, Dioxane, 85 °C, overnight.

Scheme 2^a.

^a Reagents and conditions: (a) Na₂CO₃, Pd(PPh₃)₄, DME, H₂O, 80 °C, overnight; (b) CF₃COOH, CH₂Cl₂, RT, 3 h; (c) H₂, 40 psi, Pd/C, ethanol, overnight.

Although the strategy in Scheme 2 was not successful toward the synthesis of the designed final products, several 7-substituted quinoline and 5-substituted benzothiazole analogues were obtained using this synthesis, and evaluated for mGluR5 activity.

The targeted compounds with Structure I were successfully synthesized by the strategy shown in Scheme 3. Selective bromination of 3-chlorobenzonitrile by 1,3-dibromo-5,5-dimethylhydantoin (DBH) gave 2-bromo-5-chlorobenzonitrile 19 as reported previously.²² Compound 19 was treated with various substituted aryl boronic acids under the Suzuki coupling condition to give a set of intermediates 20a-c, and final product 21. The desired compounds 22 to 26 were then synthesized by Suzuki-Miyaura coupling with quinoline boronic ester 9a or benzothiazole boron ester 9b, which were made according to our previously reported procedure.¹⁶

Scheme 3^a.

^a Reagents and conditions: (a) DBH, H₂SO₄, TFA;²² (b) Na₂CO₃, Pd(PPh₃)₄, DME, H₂O, 70 °C, overnight; (c) K₃PO₄, Pd(OAc)₂, ligand 1L, dioxane, H₂O, 105 °C, 16–20 h

These novel quinoliness and benzothiazoles, compand 14 and 22–26, were assessed for mGluR5 activity in a binding assay and in a functional assay measuring mGluR5 activity via calcium mobilization.¹⁹ The resulting SAR led us to the synthesis of 7-pyridylquinolines, such as compound 32. The details will be discussed in the SAR section. At the same time, alkyne 28 and quinoline 30¹⁴ were synthesized for comparison.

Alkyne 28 was synthesized following the procedure in Scheme 4, in which, synthon 27 was prepared according to a literature procedure.²¹ Compound 27 was coupled with 5-bromonicotinonitrile under the Sonogashira coupling condition to give the target alkyne 28.

Scheme 4^a.

^a Reagents and conditions: (a) Pd(PPh₃)₂Cl₂, CuI, NEt₃, RT, overnight;²¹ (b) Pd(PPh₃)₄, CuI, Et₃N, DMF, TBAF, 70 °C.

The corresponding quinolines were synthesized according to Scheme 5, starting from either the commercially available 5-bromonicotinonitrile 29a or 5-bromo-2-chloronicotinonitrile 29b, which was made from a literature procedure.²³ The Suzuki-Miyaura coupling reactions with boronic ester 9a gave the desired compounds 30 and 31. A Suzuki coupling reaction of 31 gave compound 32.

Scheme 5^a.

^a Reagents and conditions: (a) POCl₃, PCl₅, reflux overnight;²³ (b) Na₂CO₃, PdCl₂(dppf), dioxane, H₂O, MW, 140 °C, 30 min; (c) K₃PO₄, Pd(OAc)₂, ligand 1L, dioxane, H₂O, MW 140 °C, 90 min.

All the compounds synthesized were purified by flash column chromatography, analytically characterized as the free bases, and then converted to the HBr salts for biological testing, unless otherwise described in the experimental methods.

In Vitro Pharmacology

All the compounds synthesized were assessed in a radioligand displacement binding assay for mGluR5, using [³H]MPEP as the radioligand in rat brain membranes or HEK293-T cells transfected with cloned rat mGluR5 cDNA (National Institute of Mental Health s Psychoactive Drug Screening Program).²⁴ An assay utilizing calcium fluorescence was employed to test functional activity of compounds by measuring receptor-induced intracellular release of calcium with a kinetic imaging plate reader that makes simultaneous measurements of calcium levels in each well of a 384-well plate.¹⁹ The results of these in vitro tests for the designed quinolines, benzothiazoles and related MPEP or MTEP analogues are listed in Table 1.

Table 1.

In Vitro Data for Quinolines, Benzothiazoles and MPEP or MTEP-like Alkynyl mGluR5 Antagonists^a

Compound ID	template	Y	R	mGluR5 binding affinity Ki±SEM(nM)	mGluR5 function(Ca+2 flux) IC50±SEM(nM)	clogPb
1, MPEP	A	CH	H, 3-Hc	13±1d	3.54±1.39d	3.8
2, MTEP	C	N	H, 3-Hc	16e	13.6±2.09d	2.1
3	B	CH	H	110±20f	29±5f	3.9
4	D		H	2100±580f	NT	3.9
6	A	CH	H	1.3±0.09d	0.415±0.10d	3.2
7	C	CH	3-CN-5-F	0.9±0.2d	0.813±0.11d	3.2
8a	A	CH	Ph	4.0±0.6d	3.08±0.61d	5.1
8b	A	CH	4 -F-Ph	3.0±0.5d	7.19±1.53d	5.3
8c	C	N	4-Ph	5.49±1.43d	1.21± 1.15d	4.2
8d	C	CH	3-F-4-3 -Py	11.4±3d	3.43±0.51d	3.0
10	B	CH	4-OH	>10,000	>10,000	3.9
13	D		OTf	862±200	7840±1250	5.4
14	D		4-F-Ph	4679±1185	>10,000	5.9
16	B	CH	4-OCH2OCH3	596±109	294+21	3.6
17	B	CH	4-OBz	1040±206	>10,000	5.9
18	D		OBz	7134±2026	>10,000	5.9
21	B	CH	3-Hc-2-CN-4-Cl	4720±913	9150±1540	4.6
22	B	CH	4-Ph	97±20	1250±261	5.7
23	B	CH	4-4 -F-Ph	64±16	692±64	5.9
24	B	CH	4-3 -Py	730±190	1340±41	4.3
25	D		Ph	483±98	6890±1250	5.8
26	D		3-Py	>10,000	>10,000	4.3
28	A	N	H	1.5±0.3	13±2.3	1.9
30g	B	N	H	100±21	68±5.3	2.5
31h	B	N	4-Cl	>10,000	3310±384	3.2
32	B	N	4-Ph	97±19	81±8.1	4.7

^aMethods for binding (http://pdsp.med.unc.edu/pdspw/binding.php) and functional assays¹⁹ have been previously published;

^bDetermined with ChemDraw Ultra 10.0;

^c3-H, no CN group on the 3-position of structure;

^dData reported previously in literature.¹⁹;

^eData reported previously in literature.²⁵;

^fData reported previously in literature.¹⁶;

^gCompound reported previously in literature¹⁴;

^hPartial antagonist; NT = not tested.

All the compounds were full antagonists, thereby inducing a complete inhibition of glutamate-induced mGluR5 activity, with the exception of 31, which exhibited partial antagonist activity reaching only 50% inhibition of the EC₈₀ glutamate response (Figure 2)

Figure 2.

Compound 31 as a partial antagonist

All alkyne, quinoline and benzothiazole analogues were functionally inactive (<50% inhibition at 10 μM) at all the other mGluR subtypes and did not bind to NMDA receptors at a concentration of 10 μM.²⁴

Structure-Activity Relationships

For the MPEP analogues (template A) in Table 1, the aryl ring systems introduced into the 4-position of ring b, were well tolerated (e.g., phenyl group in 8a (Ki = 4 nM) and 4-fluorophenyl group in 8b (Ki = 3 nM) as compared to their parent structure 6 (Ki = 1.3 nM).¹⁹ As predicted, the same modification on the ring ‘b’ system of the quinoline analogues (template B), 22 (Ki = 97 nM) and 23 (Ki = 64 nM) showed comparably high binding affinities to their parent structure 3 (Ki = 110 nM), which demonstrated the same SAR trend as the MPEP analogues.

In general, mGluR5 binding affinity (Ki) values were comparable to functional potency (IC₅₀) values in the calcium fluorescence assay. However, in the case of these two quinolines, 22 and 23, their functional potencies were lower than expected (e.g., 22 (IC₅₀ = 1250 nM) and 23 (IC₅₀ = 692 nM) v. 3 (IC₅₀ = 29 nM)). Considering this and their high cLogP values (e.g., 22, cLogP =5.7 and 23, cLogP = 5.9), we reasoned that addition of the third aromatic ring system may be problematic for future in vivo investigation. Hence, we introduced the heteroatom “N” into the ring systems of our target compound, including the 3^rd additional aryl ring and ring ‘b’, to give compounds 24, 30–32. This modification lowered the cLogP values below 5. The corresponding alkyne was also synthesized for comparison (e.g., 28 v. 6).

The cLogP value of alkyne 28 was decreased to 1.9; high binding affinity (Ki = 1.5 nM) and functional activity (IC₅₀ = 13 nM) were retained. The same trend was observed in quinoline 30 (Ki = 100 nM, IC₅₀ = 68 nM) compared to its parent compound 3 (Ki = 110 nM, IC₅₀ = 29 nM). Importantly, the additional heteroaryl ring was well tolerated (32 v. 30) in both binding affinity (32 (Ki = 97 nM) v. 30 (Ki = 100 nM)), and functional activity (32 (IC₅₀ = 81 nM) v. 30 (IC₅₀ = 68 nM)).

On the other hand, the relatively low binding affinity of 24 implied that the “N” introduced to the third ring system was detrimental to the binding affinity (Ki = 730 nM) and the functional activity (IC₅₀ = 1340 nM), although its cLogP value is comparable to compound 32 (4.3 v. 4.7). This suggested the 4–3 -pyridyl substituent was not favored for the template B structure.

3D-superimposition comparison of 8a and 32, shown in Figure 3,²⁶ demonstrated that with the additional phenyl ring, alkyne 8a and quinoline 32 aligned quite well. Conversely, 3D-superimposition of 8d and 26, showed that the benzothiazole 26 did not align well with alkyne 8d (Figure 4),²⁶ which may explain why the benzothiazoles (template D) did not have comparable binding affinities as seen in the quinoline series. However, although they only showed moderate potencies, improved tolerability for the additional ring system was observed for compound 25 (Ki = 483 nM), which showed ~4-fold increase in binding affinity compared to its parent structure 4 (Ki = 2100 nM). This corresponds to the trend observed in the alkyne series (template C) 8c (Ki = 5.49 nM) v. 2, MTEP (Ki = 16 nM).¹⁹ Other aryl-substituted benzothiazoles, such as 14, only showed low binding affinity (Ki = 4679 nM) and compound 26 was completely inactive at mGluR5.

Figure 3. 3D-superimposition of 8a (alkyne) and 32 (quinoline).²⁶.

Note: Compound 32 is shown in turquoise blue and 8a in orange on right side for clarity.

Figure 4. 3D-superimposition of 8d (alkyne) and 26 (benzothiazole).²⁶.

Note: Compound 8d is shown in turquoise blue and 26 in orange on right side for clarity.

The SAR results of other 7-aryl-substituted quinoline analogues with structural template B also provided additional SAR for mGluR5. In Figure 5,²⁶ the small substitutions on the 4-position of ring b in template B (e.g., OH in compound 10 and Cl in compound 31) were not favored for binding or functional potency. This also corresponded to our previously reported results.¹⁶ Compound 31 was observed to be a weak partial antagonist. Similar conversions of functional efficacy from mGluR5 antagonists to partial antagonists, or even to the positive allosteric modulators has been reported recently.^{2, 27, 28} Hence, we provide additional evidence suggesting that mGluR5 intrinsic activities are very sensitive to small structural modifications.

Figure 5.

3D-superimposition of quinoline analogues.²⁶

The flexibility of this 4-position on ring ‘b’ in template B is also limited to the size of the substitution. For example, compound 17 extends the phenyl ring away from the quinoline, which decreased binding affinity (Ki =1040 nM) ~10 fold compared to compound 22 (Ki = 97 nM). A similar 15-fold decrease in potency was also observed in the 6-aryl substituted benzothiazole (18 (Ki = 7134 nM) v. 25 (Ki = 483nM)) in template D.

In addition to these in vitro pharmacological results, computational toxicology analyses²⁹ predicted that these quinoline compounds would not show toxicity, adding promise to the development of quinoline compounds as mGluR5 antagonist.

Summary

A series of quinoline and benzothiazole analogues of the parent compounds 3 and 4 were synthesized as selective mGluR5 antagonists using the SAR results we obtained for MPEP and MTEP analogues.¹⁹ As hypothesized, the mGluR5 binding affinity and functional results of these analogues demonstrated overlapping SAR between the quinolines and their corresponding MPEP analogues. The additional ring modifications on ring ‘b’ were tolerated in both alkyne and quinoline structures, with the alkynes showing higher potencies, uniformly, than the quinolines. This suggests that the SAR results of MPEP analogues can be used to direct the further investigation of novel quinoline analogues. In vivo evaluation of the lead compounds herein will provide valuable direction toward future drug design.

Experimental Methods

Reaction conditions and yields were not optimized, and spectroscopic data refer to the free base unless otherwise described in each compound. Microwave reactions were performed using a CEM Corp. (Matthews, NC) Discover LabMate system using the standard 10 mL reaction vessel. Flash chromatography was performed using silica gel (EMD Chemicals, Inc.; 230–400 mesh, 60 Å). ¹H and ¹³C NMR spectra were acquired using a Varian Mercury Plus 400 spectrometer. Chemical shifts are reported in parts-per-million (ppm) and referenced according to deuterated solvent for ¹H spectra (CDCl₃, 7.26; (CD₃)₂SO, 2.50), ¹³C spectra (CDCl₃, 77.2; (CD₃)₂SO, 39.5), ¹⁹F spectra (CFCl₃, 0). Infrared spectra were recorded as a KBr pellet using a Perkin-Elmer Spectrum RZ I FT-IR spectrometer or recorded as powder using an Avatar 370 FT-IR thermo Nicolet spectrometer. Gas chromatography-mass spectrometry (GC/MS) data were acquired using an Agilent Technologies (Santa Clara, CA) 6890N GC equipped with an HP-5MS column (cross-linked 5% PH ME siloxane, 30 m × 0.25 mm i.d. × 0.25 μM film thickness) and a 5973 mass-selective ion detector in electron-impact mode. Ultrapure grade helium was used as the carrier gas at a flow rate of 1.2 mL/min. The injection port and transfer line temperatures were 250 and 280 °C, respectively, and the oven temperature gradient used was as follows: the initial temperature (100 °C) was held for 3 min and then increased to 295 °C at 15 °C/min over 13 min, and finally maintained at 295 °C for 10 min. Combustion analysis was performed by Atlantic Microlab, Inc. (Norcross, GA) and agrees within 0.5% of calculated values. Melting point determination was conducted using a Thomas-Hoover melting point apparatus and are uncorrected. Anhydrous solvents were purchased from Aldrich or J. T. Baker and were used without further purification, except for tetrahydrofuran, which was freshly distilled from sodium-benzophenone ketyl. All other chemicals and reagents were purchased from Aldrich Chemical Co., Combi-Blocks, TCI, America., Matrix Scientific, Lancaster Synthesis, Inc. (Alfa Aesar) and AK Scientific, Inc. The final products were converted into HBr salts, typically by treating the free base with methanolic HBr followed by precipitation from a combination of organic solvents. On the basis of NMR, GC-MS, and combustion data, all final compounds are >95% pure. Methods for binding affinity and functional assay for mGluR5 have been previously reported.¹⁹

General Procedure A: Coupling of heteroaryl bromides with boronic ester or acid

To a suspension of boronic ester (0.6 equiv.) or boronic acid (1.2 equiv.), heteroaryl bromide (1 equiv.), and Na₂CO₃ or KF (3 equiv.) in a mixture of solvents DME/H₂O (3/1, 4 mL for 1 mmol scale reaction) was added Pd(PPh₃)₄ (5 mol%) under Argon. The mixture was warmed to 70–80 °C for 3 h to overnight with TLC monitoring. The solvent was then removed under reduced pressure, and the residue was extracted with EtOAc. The organic layer was dried over MgSO₄ and concentrated to crude product, which was then purified by flash column chromatography to give the pure product.

General Procedure B: Coupling of heteroaryl chlorides with boronic ester or acid

To a suspension of boronic ester (1 equiv.) or boronic acid (1.2 equiv.), heteroaryl chloride (1 equiv.), biphenyl phosphine ligand (1L, 4 mol %) and K₃PO₄ (3 equiv.) in a solvent mixture of dioxane/H₂O (10/1, 4 mL for 1 mmol scale reaction) was added Pd(OAc)₂ (2 mol %) under Argon. The mixture was warmed to 105 °C and kept stirring overnight. Solvents were then removed under reduced pressure, and the residue was extracted with EtOAc. The organic layer was dried over MgSO₄ and concentrated to dryness. The crude product was purified by flash column chromatography to give the pure product.

2-Hydroxy-5-(2-methylquinolin-7-yl)benzonitrile (10)

A suspension of 5-bromo-2-hydroxybenzonitrile (0.24 g, 1.2 mmol), 9a (0.3 g, 1.1 mmol), Na₂CO₃ (0.32 g, 3 mmol), and Pd(OAc)₂ (0.011 g, 5%) in a mixture of dioxane (4 mL) and water (0.4 mL) was degassed and heated at 50 °C overnight, under Argon protection. Solvent was removed under vacuum. The residue was dissolved in methanol and filtered. The filtrate was concentrated and purified by a flash chromatography eluting with EtOAc to provide the solid product (0.19 g) in 60% yield; ¹H NMR (400 MHz, DMSO-d₆) δ 8.24 (d, J = 8.4 Hz, 1H), 8.14 (s, 1H), 8.10 (s, 1H), 7.98 (m, 2H), 7.84 (d, J = 8.0 Hz, 1H), 7.39 (d, J = 8.0 Hz, 1H), 7.12 (d, J = 8.8 Hz, 1H), 2.65 (s, 3H); ¹³C NMR (100MHz, DMSO-d₆) δ 160.6, 160.2, 151.8, 136.7, 134.1, 132.2, 129.2, 126.0, 125.3, 125.3, 122.8, 117.6, 110.0, 100.4, 25.3; HBr salt precipitated from MeOH; mp 225–226 °C; IR (powder) 3463, 2226 cm⁻¹; Anal. (C₁₇H₁₂N₂O·HBr·1/2 H₂O) C, H, N.

2-Hydroxy-5-(2-methylbenzo[d]thiazol-5-yl)benzonitrile (11)

A suspension of 5-bromo-2-hydroxybenzonitrile (0.24 g, 1.2 mmol), 9b (0.3 g, 1 mmol), Na₂CO₃ (0.32 g, 3 mmol), and Pd(OAc)₂ (0.011 g, 5%) in a mixture of dioxane (4 mL) and water (0.4 mL) was degassed and heated at 50 °C overnight, under Argon protection. Solvent was removed under vacuum. The residue was dissolved in methanol and filtered. The filtrate was concentrated and purified using a flash chromatography eluting with EtOAc to provide the solid product (0.11 g) in 40% yield; mp 195–197 °C (dec); ¹H NMR (400 MHz, DMSO-d₆) δ 11.2 (br, 1H), 8.15 (s, 1H), 8.06 (d, J = 8.4 Hz, 1H), 8.01 (s, 1H), 7.90 (d, J = 8.8 Hz, 1H), 7.66 (d, J = 8.8 Hz, 1H), 7.12 (d, J = 8.8 Hz, 1H), 2.80 (s, 3H); ¹³C NMR (100 MHz, DMSO-d₆) δ 168.7, 160.4, 154.4, 137.2, 134.8, 134.0, 132.0, 131.9, 123.9, 123.1, 120.0, 117.6, 117.5, 100.2, 20.5; IR (powder) 3096, 2232 cm⁻¹; Anal. (C₁₅H₁₀N₂OS·5/8 H₂O) C, H, N.

2-Cyano-4-(2-methylquinolin-7-yl)phenyl triflate (12)

To a suspension of 10 (0.6 g, 1.7 mmol) in 8 mL CH₂Cl₂ on an ice bath, pyridine (0.6 mL, 7.4 mmol) and trifloromethanesulfonic anhydride (0.6 mL, 3.4 mmol) were added successively. The reaction mixture was stirred at RT for 2 h. The reaction mixture was extracted with CH₂Cl₂. The organic layer was concentrated and purified by flash chromatography eluting with hexane/EtOAc (4:1) to give the product as syrup (0.2 g) in 30% yield. ¹H NMR (400 MHz, CDCl₃) δ 8.23 (s, 1H), 8.10 (d, J = 8.8 Hz, 1H), 8.10 (s, 1H), 8.05 (d, J = 8.8 Hz, 1H), 7.92 (d, J = 8.8Hz, 1H), 7.67 (d, J = 8.8 Hz, 1H), 7.62 (d, J = 8.4 Hz, 1H), 7.37 (d, J = 8.4 Hz, 1H), 2.79 (s, 3H); ¹³C NMR (100 MHz, CDCl₃) δ 162.1, 159.5, 149.2, 145.5, 134.8, 133.5, 129.5, 129.2, 126.8, 126.5, 123.8, 123.6, 123.5, 109.8, 29.5; GC-MS (EI) m/z 392 (M⁺)

2-Cyano-4-(2-methylbenzo[d]thiazol-5-yl)phenyl triflate (13)

To a solution of 11 (0.4 g, 1.5 mmol) in 20 mL CH₂Cl₂ on an ice bath, pyridine (0.3 mL, 3.7 mmol) and trifloromethanesulfonic anhydride (0.3 mL, 1.7 mmol) were added successively. The reaction mixture was stirred at RT for 5 h and then extracted with CH₂Cl₂. The organic layer was concentrated and purified by flash chromatography eluting with hexane/EtOAc (4:1) to give the product as a solid (0.1 g) in 18% yield; mp 87–89 °C (dec); ¹H NMR (400 MHz, CDCl₃) δ 8.10 (d, J = 1.6 Hz, 1H), 8.00 (d, J = 2.0 Hz, 1H), 7.96 (s, 1H), 7.94 (s, 1H); 7.59 (d, J = 8.4 Hz, 1H), 7.53 (dd, J = 8.4, 2.0 Hz, 1H), 2.87 (s, 3H); ¹³C NMR (100 MHz, CDCl₃) δ 169.2, 163.8, 159.1, 149.8, 143.8, 142.3, 138.4, 135.5, 133.5, 133.0, 123.9, 123.4, 122.6, 121.1, 20.28; ¹⁹F NMR (376 MHz, CDCl₃) δ -72.9; IR (powder) 2232 cm⁻¹; GC-MS (EI) m/z 398 (M⁺); Anal. (C₁₆H₉F₃N₂O₃S₂) C, H, N.

2-(4-Fluorophenyl)-4-(2-methylbenzo[d]thiazol-5-yl)benzonitrile (14)

A suspension of 13 (0.4 g, 0.75 mmol), 4-fluorophenylboronic acid (0.135 g, 1 mmol), K₃PO₄ (0.64 g, 3 mmol), and Pd(PPh₃)₄ (0.06 g, 0.05 mmol) in dioxane (5 mL) was degassed and heated at 85 °C overnight, under Argon protection. Solvent was removed under vacuum. The residue was extracted with CH₂Cl₂ and washed with brine. The organic layer was dried over magnesium sulfate and concentrated to give a crude product. It was purified by flash chromatography eluting with hexane/EtOAc (6:1, 4:1) to give the product (50 mg) in 25% yield; mp 101–103 °C; ¹H NMR (400 MHz, CDCl₃) δ 8.18 (s, 1H), 8.04 (s, 1H), 7.93 (dd, J = 8.4, 8.8 Hz, 2H), 7.60 (m, 4H), 7.22 (dd, J = 8.4, 8.8 Hz, 2H), 2.89 (s, 3H); ¹³C NMR (100 MHz, CDCl₃) δ 168.7, 154.4, 143.4, 140.8, 136.9, 136.1, 132.6, 131.9, 130.9, 130.8, 130.8, 123.9, 122.4, 120.9, 118.8, 116.2, 116.0, 112.1, 20.5; ¹⁹F NMR (376 MHz, CDCl₃) δ -113.3; IR (powder) 2232 cm⁻¹; GC-MS (EI) m/z 44 (M⁺); Anal. (C₂₁H₁₃FN₂S) C, H, N. HBr salt precipitated from MeOH. Anal.(C₂₁H₁₃FN₂S·HBr) C, H, N.

2-Benzoxy-5-bromobenzonitrile (15a)

A suspension of 5-bromo-2-hydroxybenzonitrile (10 g, 50 mmol), benzyl bromide (6 mL, 50 mmol), and K₂CO₃ (7.6 g, 55 mmol) in acetone (100 mL) was refluxed for 5 h. The reaction mixture was filtered. The filtrate was concentrated and solidified to give crude product. It was washed with hexane to give the pure product (12 g) in 83% yield; mp 74–76 °C. ¹H NMR (400 MHz, CDCl₃) δ 7.68 (s, 1H), 7.57 (d, J = 9.2 Hz, 1H), 7.44–7.33 (m, 5H), 6.88 (d, J = 9.2 Hz, 1H) 5.21 (s, 2H); ¹³C NMR (100 MHz, CDCl₃) δ 159.6, 137.3, 136.2, 135.3, 129.3, 29.1, 128.7, 128.1, 127.2, 115.2, 114.9, 112.9, 104.5, 71.2,; IR (powder) 2232, 1135 cm⁻¹; GC-MS (EI) m/z 287, 289 (M⁺).

5-Bromo-2-methoxymethoxylbenzonitrile (15b)

To a suspension of 5-bromo-2-hydroxybenzonitrile (1 g, 5 mmol) and K₂CO₃ (0.76 g, 5.5 mmol) in DMF (10 mL) was added methoxymethyl chloride (4.18 mL, 5.5 mmol). The reaction mixture was kept at RT overnight and extracted with ether. The organic layer was concentrated to give the product (0.93 g) in 77% yield; mp 65–67 °C; ¹H NMR (400 MHz, CDCl₃) δ 7.68 (m, 1H), 7.65 (m, 1H), 7.16 (m, 1H), 5.29 (s, 2 H), 3.53 (s, 3H); ¹³C NMR (100 MHz, CDCl₃) δ 158.5, 137.5, 135.9, 116.9, 115.1, 113.9, 104.9, 95.2, 57.0; IR (powder) 2236, 1129 cm⁻¹; GC-MS (EI) m/z 241, 243 (M⁺).

2-Methoxymethoxy-5-(2-methylquinolin-7-yl)benzonitrile (16)

Prepared by following the general procedure A using 9a (0.27 g, 1 mmol) and 15b (0.24 g, 1 mmol), eluting with hexane/EtOAc (4:1) to give the product (0.18 g) in 59% yield; mp 97–99 °C; ¹H NMR (400 MHz, CDCl₃) δ 8.18 (d, J = 2.4 Hz, 1H), 8.08 (d, J = 8.4 Hz, 1H), 7.94 (d, J = 2.4 Hz, 1H), 7.91 (dd, J = 8.8, 2.4 Hz, 1H), 7.88 (d, J = 8.8 Hz, 1H), 7.67 (dd, J = 8.4, 2.0 Hz, 1H), 7.37 (d, J = 8.4 Hz, 1H), 7.32 (d, J = 8.4 Hz, 1H), 5.35 (s, 2H), 3.57 (s, 3H), 2.78 (s, 3H); ¹³C NMR (100 MHz, CDCl₃) δ 160.2, 158.9, 148.3, 139.6, 136.1, 134.8, 133.4, 132.4, 128.6, 126.3, 126.0, 124.7, 122.6, 115.7, 103.7, 95.1, 57.0, 25.6; IR (powder) 2232, 1258 cm⁻¹; GC-MS (EI) m/z 304 (M⁺); Anal. (C₁₉H₁₆N₂O₂·1/4 H₂O) C, H, N.

2-Benzoxy-5-(2-methylquinolin-7-yl)benzonitrile (17)

Prepared by following the general procedure A using 9a (0.27 g, 1 mmol) and 15a (0.35 g, 1.1 mmol), eluting with hexane/EtOAc (4:1) to give the solid product (0.14 g) in 40% yield. HBr salt precipitated from MeOH/Acetone. mp 190–191 °C; ¹H NMR (400 MHz, DMSO-d₆) δ 8.86 (m, 1H), 8.31 (m, 3H), 8.17 (dd, J = 7.2, 9.2 Hz, 2H), 7.82 (d, J = 8.8 Hz, 1H), 7.54 (d, J = 9.2 Hz, 1H), 7.52 (m, 2H), 7.43 (dd, J = 8.0, 7.2 Hz, 2H), 7.37 (d, J = 6.4 Hz, 1H), 5.37 (s, 2H), 2.84 (s, 3H); ¹³C NMR (100 MHz, DMSO-d₆) δ 160.6, 159.5, 136.6, 134.6, 133.3, 132.0, 130.2, 129.3, 129.0, 128.3, 127.7, 126.5, 124.1, 116.7, 115.2, 102.6, 71.2, 22.8; IR (powder) 2349, 1135 cm⁻¹; GC-MS (EI) m/z 350 (M⁺); Anal. (C₂₄H₁₈N₂O·HBr·2/3 H₂O) C, H, N.

2-Benzoxy-5-(2-methylbenzo[d]thiazol-5-yl)benzonitrile (18)

Prepared by following the general procedure A using 9b (0.48 g, 1.8 mmol) and 15a (0.65 g, 2.7 mmol), eluting with hexane/EtOAc (5:2) to give the solid product (0.6 g) in 94% yield; mp 102–103 °C; ¹H NMR (400 MHz, CDCl₃) δ 8.06 (s, 1H), 7.89 (s, 1H), 7.86 (d, J = 9.2 Hz, 1H), 7.76 (d, J = 7.2 Hz, 1H), 7.5–7.4 (m, 5H), 7.36 (d, J = 7.2 Hz, 1H), 7.12 (d, J = 9.2 Hz, 1H), 5.29 (s, 2 H), 2.87 (s, 3 H); ¹³C NMR (100 MHz, CDCl₃) δ 168.5, 159.9, 154.3, 137.2, 135.8, 135.3, 134.4, 133.3, 132.6, 129.0, 128.5, 127.2, 123.8, 122.2, 120.5, 116.6, 113.7, 103.2, 71.1, 20.5; IR (powder) 2232, 1170 cm⁻¹; GC-MS (EI) m/z 356 (M⁺); Anal. (C₂₂H₁₆N₂OS) C, H, N.

2-Bromo-5-chloro-benzonitrile (19)²²

Yield: 4.45 g (76%). ¹H NMR (400 MHz, CDCl₃) δ7.64 (s, 1H), 7.63 (d, J = 10.8 Hz, 1H), 7.44 (d, J = 10.8 Hz, 1H); GC-MS (EI) m/z 217 (M⁺).

5-Chloro-2-phenylbenzonitrile (20a)

Prepared by following the general procedure A using 19 (1 g, 5 mmol) and phenyl boronic acid (0.67 g, 5.5 mmol), eluting with hexane/EtOAc (6:1) to give the product (0.52 g) in 50% yield; mp 87–89 °C; ¹H NMR (400 MHz, CDCl₃) δ 7.75 (s, 1H), 7.64 (d, J = 8.4 Hz, 1H), 7.48 (m, 6H); ₁₃C NMR (100 MHz, CDCl₃) δ 144.2, 137.2, 133.9, 133.4, 131.6, 129.3, 129.1, 128.9, 117.7, 112.9; IR (powder) 2226 cm⁻¹; GC-MS (EI) m/z 213 (M⁺).

5-Chloro-2-(4-fluorophenyl)benzonitrile (20b)

Prepared by following the general procedure A using 19 (0.54 g, 2.5 mmol) and 4-fluorophenyl boronic acid (0.27 g, 2.7 mmol). The crude product was solidified by adding MeOH and filtered to give the pure product (0.22 g) in 40% yield; mp 101–102 °C; ¹H NMR (400 MHz, CDCl₃) δ 7.74 (s, 1H), 7.62 (d, J = 8.4 Hz, 1H), 7.51 (dd, J = 8.8, 8.8 Hz, 2H), 7.43 (d, J = 8.8 Hz, 1H), 7.19 (dd, J = 8.4, 8.8 Hz, 2H); ¹³C NMR (100 MHz, CDCl₃) δ 158.3, 139.2, 130.6, 130.5, 130.2, 129.5, 127.6, 126.9, 126.8, 124.4, 119.7, 112.4, 112.2; ¹⁹F NMR (376 MHz, CDCl₃) δ -112.8; IR (powder) 2226 cm⁻¹; GC-MS (EI) m/z 231 (M⁺).

5-Chloro-2-(pyridin-3-yl)benzonitrile (20c)

Prepared by following the general procedure A using 19 (0.44 g, 2 mmol) and 3-pyridylboronic acid (0.27 g, 2.2 mmol), eluting with hexane/EtOAc (1:1) to give the product (0.35 g) in 75% yield; mp 137–139 °C. ¹H NMR (400 MHz, CDCl₃) δ 8.76(s, 1H), 8.73 (d, J = 7.2 Hz, 1H), 7.95 (d, J = 7.6 Hz, 1H), 7.80 (s, 1H), 7.69 (d, J = 7.6 Hz, 1H), 7.48 (m, 2H); ¹³C NMR (100 MHz, CDCl₃) δ 150.4, 149.4, 140.5, 136.2, 135.1, 133.8, 133.7, 133.1, 131.5, 123.7, 117.1, 113.3; IR (powder) 2232 cm⁻¹; GC-MS (EI) m/z 214 (M⁺).

5-Chloro-2-(2-methylquinolin-7-yl)benzonitrile (21)

Prepared by following the general procedure A using 9a (0.19 g, 0.7 mmol) and 19 (0.2 g, 0.7 mmol), eluting with hexane/EtOAc (4:1) to provide the product (0.1 g) in 36% yield; mp 98–100 °C; ¹H NMR (400 MHz, CDCl₃ δ 8.15(s, 1H), 8.12 (d, J = 8.0 Hz, 1H), 7.91 (d, J = 8.4 Hz, 1H), 7.79 (s, 1H), 7.69 (dd, J = 8.4, 8.8 Hz, 2H), 7.59 (d, J = 8.8 Hz, 1H), 7.36 (d, J = 8.4 Hz, 1H), 2.78 (s, 3H); ¹³C NMR (100MHz, CDCl₃) δ 160.4, 152.7, 147.8, 143.6, 138.2, 136.3, 133.6, 133.7, 131.8, 129.1, 128.4, 126.0, 123.3, 117.5, 113.2, 25.6; IR (powder) 2232 cm⁻¹; GC-MS (EI) m/z 278 (M⁺); HBr salt precipitated from MeOH/Acetone/ether. Anal. (C₁₇H₁₁ClN₂·HBr·1/3H₂O) C, H, N.

5-(2-Methylquinolin-7-yl)-2-phenylbenzonitrile (22)

Prepared by following the general procedure B using 9a (0.4 g, 1.5 mmol) and 20a (0.26 g, 1.2 mmol), eluting with hexane/EtOAc (4:1) to provide the product (0.16 g) in 42% yield. ¹H NMR (400 MHz, CDCl₃) δ 8.29 (s, 1H), 8.14 (s, 1H), 8.11 (d, J = 8.4 Hz, 1H), 8.03 (d, J = 8.4 Hz, 1H), 7.91 (d, J = 8.4 Hz, 1H), 7.76 (d, J = 8.4 Hz, 1H), 7.67- 7.46 (m, 6H), 7.35 (d, J = 8.8 Hz, 1H), 2.79 (s, 3H); ¹³C NMR (100 MHz, CDCl₃) δ 160.05, 148.06, 144.49, 140.06, 135.90, 132.45, 131.64, 128.81, 126.72, 124.54, 122.58, 118.66, 111.94, 24.87. GC-MS (EI) m/z 320 (M⁺). HBr salt precipitated from MeOH/Acetone. mp 273–274 °C (dec); IR (powder) 2220 cm⁻¹; Anal. (C₂₃H₁₆N₂·HBr·5/4 H₂O) C, H, N.

5-(2-Methylquinolin-7-yl)-2-(4-fluorophenyl)benzonitrile (23)

Prepared by following the general procedure B using 9a (0.28 g, 1.1 mmol) and 20b (0.27 g, 1 mmol), eluting with hexane/EtOAc (4:1, 2.5:1) to give the product (0.16 g) in 42% yield. HBr salt precipitated from MeOH/Acetone; mp 192–193 °C; ¹H NMR (400 MHz, DMSO-d₆) δ 8.95 (d, J = 6.4 Hz, 1H), 8.48 (s, 1H), 8.40 (s, 1H), 8.36 (d, J = 8.0 Hz, 1H), 8.27 (m, 2H), 7.88 (d, J = 7.6 Hz, 1H), 7.83 (d, J = 9.2 Hz, 1H), 7.72 (m, 2H), 7.42 (m, 2H), 2.79 (s, 3H); ¹³C NMR (100 MHz, DMSO-d₆) δ 165.2, 162.0, 159.8, 144.3, 138.8, 133.3, 132.9, 131.9, 131.8, 131.7, 130.4, 127.0, 124.5, 118.9, 116.7, 116.4, 112.1, 22.8; ¹⁹F NMR (376 MHz, DMSO-d₆) δ -113.0; IR (powder) 2226 cm⁻¹; GC-MS (EI) m/z 338 (M⁺); Anal. (C₂₃H₁₅FN₂·HBr·7/4 H₂O) C, H, N.

5-(2-Methylquinolin-7-yl)-2-(pyridin-3-yl)benzonitrile (24)

Prepared by following the general procedure B using 9a (0.36 g, 1.33 mmol) and 20c (0.28 g, 1.3 mmol), eluting with EtOAc to provide the product (0.14 g) in 33% yield. ¹H NMR (400 MHz, CDCl₃) δ 8.86 (s, 1H), 8.74 (d, J = 6.0 Hz, 1H), 8.30 (s, 1H), 8.18 (s, 1H), 8.11 (d, J = 8.4 Hz, 1H), 8.08 (d, J = 6.0 Hz, 1H), 8.02 (d, J = 8.4 Hz, 1H), 7.93 (d, J = 8.8 Hz, 1H), 7.76 (d, J = 8.8 Hz, 1H), 7.68 (d, J = 8.8 Hz, 1H), 7.48 (m, 1H), 7.36 (d, J = 8.4 Hz, 1H), 2.80 (s, 3H); ¹³C NMR (100 MHz, CDCl₃) δ 160.18, 149.98, 149.31, 141.06, 138.90, 136.08, 132.65, 131.93, 130.71, 128.64, 126.9, 126.28, 124.45, 123.43, 122.73, 112.26, 25.48; GC-MS (EI) m/z 321 (M⁺); Anal. (C₂₂H₁₅N₃·1/2 H₂O) C, H, N. HBr salt precipitated from acetone. mp 171–172 °C; IR (powder) 2220 cm⁻¹; Anal. (C₂₂H₁₅N₃·2HBr·3/2 H₂O) C, H, N.

2-Phenyl-4-(2-methylbenzo[d]thiazol-5-yl)benzonitrile (25)

Prepared by following the general procedure B using 9b (0.38 g, 1.38 mmol) and 20a (0.26 g, 1.26 mmol), eluting with hexane/EtOAc (4:1) to give the solid product (0.1 g) in 24% yield. ¹H NMR (400 MHz, CDCl₃) δ 8.19 (s, 1H), 8.05 (s, 1H), 7.94 (dd, J = 7.2, 7.2 Hz, 2H), 7.65–7.47 (m, 7H), 2.89 (s, 3H); ¹³C NMR (100 MHz, CDCl₃) δ 168.4, 154.2, 140.4, 137.7, 136.8, 132.4, 131.6, 130.7, 128.7, 123.7, 122.1, 120.7, 118.7, 111.9, 20.31; GC-MS (EI) m/z 326 (M⁺). HBr salt precipitated from MeOH/Acetone; mp 234–235 °C (dec); IR (powder) 2226 cm⁻¹; Anal. (C₂₁H₁₄N₂S·HBr) C, H, N.

2-(Pyridin-3-yl)-4-(2-methylbenzo[d]thiazol-5-yl)benzonitrile (26)

Prepared by following the general procedure B using 9b (0.3 g, 1.1 mmol) and 20c (0.21 g, 1 mmol), eluting with EtOAc and MeOH/NH₄OH (trace amount) to give the product (0.18 g) in 55% yield. ¹H NMR (400 MHz, CDCl₃) δ 8.84 (s, 1H), 8.73 (d, J = 6.4 Hz, 1H), 8.19 (d, J = 2.0 Hz, 1H), 8.09 (d, J = 2.0 Hz, 1H), 8.00 (m, 1H), 7.97 (s, 1H), 7.95 (s, 1H), 7.65 (d, J = 8.4 Hz, 1H), 7.61 (m, 1H), 7.49 (dd, J = 8.0, 4.8 Hz, 1H), 2.89 (s, 3H); ¹³C NMR (100 MHz, CDCl₃) δ 168.5, 154.2, 150.0, 149.3, 141.4, 140.5, 136.1, 133.6, 132.6, 131.9, 130.7, 123.4, 122.2, 120.7, 118.2, 112.2, 20.3; GC-MS (EI) m/z 327 (M⁺). HBr salt precipitated from MeOH/Acetone. mp 264–266 °C(dec); IR (powder) 2220 cm⁻¹; Anal. (C₂₀H₁₃N₃S·2HBr·H₂O) C, H, N.

2-Methyl-6-((trimethylsilanyl)ethynyl)pyridine (27)²¹

Yield: 2.35 g (71%). ¹H NMR (400 MHz, CDCl₃) δ 7.54 (m, 1H), 7.30 (m, 1H), 7.10 (m, 1H), 2.55 (s, 3H), 0.26 (s, 9H). GC-MS (EI) m/z 189 (M⁺).

5-((6-Methylpyridin-2-yl)ethynyl)nicotinonitrile (28)

To a suspension of 5-bromonicotinonitrile (0.5 g, 2.5 mmol), 27 (0.5 g, 2.6 mmol), CuI (0.05 g, 0.25 mmol), Et₃N (1.47 mL) and Pd(PPh)₄) (0.15 g) in degassed DMF (8 mL) was added tributylamonium fluoride (TBAF, 2.64 mL, 2.6 mmol) in THF (1.0 M) dropwise at 55°C for 30 min. The reaction mixture was kept at 70°C overnight, then extracted with ether and washed with brine. The organic layer was dried over magnesium sulfate and concentrated to give the crude product. It was purified by flash chromatography eluting with hexane/EtOAc (1:1) to provide the pure product (0.3 g) in 52% yield; mp 162–164 °C; ¹H NMR (400 MHz, CDCl₃) δ 8.99 (s, 1H), 8.83 (s, 1H), 8.13 (d, J = 2.0 Hz, 1H), 7.64 (m, 1H), 7.41 (d, J = 7.6 Hz, 1H), 7.21 (d, J = 8.0 Hz, 1H), 2.61 (s, 3H); ¹³C NMR (100 MHz, CDCl₃) δ 155.6, 151.3, 149.0, 144.4, 141.7, 136.9, 133.4, 126.7, 125.1, 124.0, 114.7, 20.59; IR (powder) 2226 cm⁻¹; GC-MS (EI) m/z 219 (M⁺); Anal. (C₁₄H₉N₃) C, H, N.

5-Bromo-2-chloronicotinonitrile (29b)²³

A solution of 5-bromo-2-hydroxynicotinonitrile (0.2 g, 1 mmol) and PCl₅ (0.21 g, 1 mmol) in POCl₃ (3 mL) was refluxed overnight. Aqueous NaOH solution (1 M) was added slowly to quench the reaction with an ice bath. Product was extracted with ether. The solvent was removed to give crude product, which was used in the followed reaction without further purification. ¹H NMR (400 MHz, CDCl₃) δ 8.67 (s, 1H), 8.12 (s, 1H); GC-MS (EI) m/z 216, 218 (M⁺).

5-(2-Methylquinolin-7-yl)nicotinonitrile (30)¹⁴

A suspension of 5-bromonicotinonitrile (0.09 g, 0.5 mmol), 9a (0.2 g, 0.5 mmol), Na₂CO₃ (0.16 g, 1.5 mmol), and PdCl₂(dppf) (0.02 g) in DME (4.5 mL) and H₂O (0.75 mL) was degassed and reacted under microwave condition at 140 °C for 30 min. Solvent was removed under vacuum. The residue was extracted with EtOAc and washed with brine. The organic layer was dried over magnesium sulfate and evaporated to give the crude product. It was purified by flash chromatography eluting with hexane/EtOAc (1:1) to give the product (0.1 g) in 80% yield; mp 195–196 °C; ¹H NMR (400 MHz, CDCl₃) δ 9.19 (s, 1H), 8.91 (s, 1H), 8.28 (d, J = 2.0 Hz, 1H), 8.26 (s, 1H), 8.12 (d, J = 8.4 Hz, 1H), 7.95 (d, J = 8.4 Hz, 1H), 7.70 (d, J = 8.4 Hz, 1H), 7.38 (dd, J = 8.4, 2.0 Hz, 1H), 2.81 (s, 3H); ¹³C NMR (100 MHz, CDCl₃) δ 162.1, 160.5, 151.8, 151.2, 137.5, 136.3, 129.1, 127.9, 124.5, 123.5, 110.2, 100.5, 25.9; GC-MS (EI) m/z 245 (M⁺); Anal. (C₁₆H₁₁N₃) C, H, N. HBr salt precipitated from MeOH/Acetone. Anal. (C₁₆H₁₁N₃·2HBr·3/4 H₂O) C, H, N.

2-Chloro-5-(2-methylquinolin-7-yl)nicotinonitrile (31)

Prepared by following the general procedure A using 9a (0.11 g, 0.4 mmol) and 29 (0.1 g, 0.4 mmol), eluting with hexane/EtOAc (4:1, 1:1) to provide the product (70 mg) in 65% yield; mp 187–189 °C (dec); ¹H NMR (400 MHz, CDCl₃) δ 8.96 (s, 1H), 8.32 (s, 1H), 8.24 (s, 1H), 8.12 (d, J = 8.0 Hz, 1H), 7.95 (d, J = 8.4 Hz, 1H), 7.66 (d, J = 8.4 Hz, 1H), 7.39 (d, J = 8.0 Hz, 1H), 2.79 (s, 3H); ¹³C NMR (100 MHz, CDCl₃) δ 165.3. 152.8, 141.5, 140.0, 139.9, 134.3, 131.7, 129.8, 128.5, 120.5, 115.4, 30.3; IR (powder) 2232 cm⁻¹; GC-MS (EI) m/z 279 (M⁺); Anal. (C₁₆H₁₀ClN₃·1/8 H₂O) C, H, N. HBr salt precipitated from MeOH/Acetone. Anal. (C₁₆H₁₀ClN₃·HBr·5/4 H₂O) C, H, N.

5-(2-Methylquinolin-7-yl)-2-phenylnicotinonitrile (32)

To a microwave reaction vessel was added 31 (0.28g, 1 mmol), phenylboronic acid (0.13 g, 1.05 mmol), Pd(OAc)₂ (0.045g, 0.20 mmol, 3mol%), ligand 1L (0.17g, 0.40 mmol, 6 mol%), K₃PO₄ ( 0.64 g, 3 mmol), dioxane (5mL). The reaction mixture was degassed, protected under Argon, and reacted under microwave condition at 140°C for 90 min, followed the same work-up procedure in general procedure B, eluting with hexane/EtOAc (4:1, 2.5:1) to provide the product (70 mg) in 30% yield; mp 105–107 °C (dec); ¹H NMR (400 MHz, CDCl₃) δ 9.26 (t, J = 2.8 Hz, 1H), 8.40 (t, J = 2.8 Hz, 1H), 8.32 (s, 1H), 8.12 (dd, J = 8.0, 2.8 Hz, 1H), 8.02 (m, 2H), 7.96 (dd, J = 8.0, 2.8 Hz, 1H), 7.55 (dt, J = 8.4, 2.0 Hz, 1H), 7.56 (m, 3H), 7.38 (dd, J = 6.8, 2.8 Hz, 1H), 2.80 (s, 3H); ¹³C NMR (100 MHz, CDCl₃) δ 160.7, 159.9, 151.5, 148.2, 140.2, 137.0, 136.2, 134.4, 130.6, 129.7, 129.2, 129.1, 129.0, 127.3, 126.7, 124.4, 123.3, 117.9, 107.8, 25.7; IR (powder) 2226 cm⁻¹; GC-MS (EI) m/z 321 (M⁺); Anal. (C₂₂H₁₅N₃·1/8 H₂O) C, H, N. HBr salt precipitated from MeOH/Acetone. Anal. (C₂₂H₁₅N₃·2HBr·H₂O) C, H, N.

Abbreviations

mGluR

metabotropic glutamate receptor

iGluR

ionotropic glutamate receptor

MPEP

2-methyl-6-(phenylethynyl)pyridine

MTEP

3-((2-Methyl-4-thiazolyl)ethynyl)pyridine