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. 2020 Dec 11;5(50):32724–32737. doi: 10.1021/acsomega.0c05117

Enhanced Affinity for 3-Amino-Chromane-Derived σ1 Receptor Ligands

Matthew R Porter †, Haiyan Xiao ‡,§, Sanjay Maity †, Nora Vail †, Sylvia B Smith ‡,§,∥, Joseph J Topczewski †,*
PMCID: PMC7758967  PMID: 33376910

Abstract

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The σ1 receptor is implicated in regulating a diverse range of physiology and is a target for developing therapies for cancer, pain management, neural degradation, and COVID-19. This report describes 36 phenethylamine-containing 3-amino-chromane ligands, which bind to σ1 with low nM affinities. The family consists of 18 distinct compounds and each enantiomer was independently assayed. Three compounds with the greatest affinity bind in the 2 nM Ki range (∼8.7 pKi). Furthermore, ligands with the (3R,4R) absolute stereochemistry on the 3-amino-chromane core have a higher affinity and greater σ1 versus TMEM97 selectivity. The most promising ligands were assayed in 661W cells, which did not show significant protective effects.

Introduction

The σ1 receptor is a membrane-bound chaperone protein located primarily at the endoplasmic reticulum.1 Initially thought to be an opioid receptor,2,3 the σ1 receptor is now understood to be a nonopioid chaperone protein.1 Although its primary function is regulating intracellular calcium levels,1 it also plays a role in opioid receptor potentiation4 and regulating opioid receptors,4 apoptosis,5 kinases,6 TRPV1,7 cellular potassium levels,8,9 and dopamine receptors.10 Recently, the σ1 receptor has become a target for managing diseases.11−13 Modulating the σ1 receptor is implicated in treating cancer,14−16 analgesia,4,17,18 retinal neural degradation,19,20 and COVID-19.21 The first σ1 receptor ligand passed phase 1 clinical trials and is now in phase II trials for pain management (E-52862, Figure 1).22,23

Figure 1.

Figure 1

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Select σ1 receptor ligands.

Our labs disclosed phenethylamine-containing heterocycles that were potent and selective G protein-coupled receptor (GPCR) ligands.24 These heterocycles were synthesized via tandem Friedel–Crafts alkylation (Scheme 1a).25 The compounds’ activity was investigated due to the phenethylamine backbone.26 Initial assays, using racemic samples, identified three selective ligands for the 5-HT2B, 5-HT7, or σ1 receptors (Scheme 1, compounds 5–7, respectively). The ligand (±)-7’s activity was supported by cellular assays.24 This inspired a more focused study aiming to improve the σ1 ligand. Here, a family of 36 σ1 receptor ligands was synthesized in a nonracemic form. Several ligands demonstrated improved affinity. The lead compound’s activity was assessed by oxidative stress assays for neuroprotection.

Scheme 1. 3-Amino-Chromane σ1 Ligands.

Scheme 1

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Results and Discussion

Prior data indicated that 3-amino-chromane was the key pharmacophore (Scheme 2).24 Being mindful of these results, an approach was developed enabling a divergent analogue synthesis from a common intermediate. Azide (±)-8 was synthesized in an excellent overall yield and >20:1 dr.25 Deprotection of the methyl ether was performed with AlCl3, yielding phenol (±)-9. Resolution of racemic (±)-9 was accomplished via semipreparative high-performance liquid chromatography (HPLC), affording (+)-9 and (−)-9, with >98:2 er and >99:1 er, respectively. The absolute stereochemistry of these compounds was determined (see Supporting Information for crystallography). Compound 10r was synthesized from (R)-1-phenylethanol via a Mitsunobu reaction (SN2 inversion assumed). The analysis is consistent with the intermediate (+)-9 having the (3R,4R) absolute stereochemistry. Diversification of the resolved enantiomers was accomplished by etherification. This afforded ethers (3R,4R)- and (3S,4S)-10a–r, which were exposed to HBCy2 to afford the target pyrrolidines (3R,4R)- and (3S,4S)-3a–r (36 analogues in total). The chemical purity of each analogue was determined by reverse-phase HPLC. All had a UV area percentage purity of >90% at 220 nm).

Scheme 2. Ligand Synthesis.

Scheme 2

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Reagents and conditions: (a) 4.5 equiv. AlCl3, DMS, 0 °C to rt, 2 h, 92%; (b) Chiralcel-OD 10 μm semipreparative HPLC column (10 × 250 mm), 30% IPA in hexane, 40 °C, 9.45 mL/min; (c) 2 equiv. R-X, 4 equiv K2CO3, rt–60 °C, 18 h, 55–89%; and (d) HBCy2, DCM, 0 °C to rt., 18 h, 37–99%.

The binding affinity was assayed through the Psychoactive Drug Screening Program (PDSP)27 via two stages. A primary assay was performed at 10 μM concentration of the ligand. The pKi value was obtained for compounds that displaced more than 50% of the radioligand at the 10 μM concentration. The 5-HT2B, σ1, and TMEM97 (σ2)28 receptor affinities were determined (all cloned human proteins). The σ1 receptor was the primary target. The TMEM97 receptor was included to determine the σ1 versus TMEM97 selectivity. Finally, the 5-HT2B receptor was included because other compounds from this family demonstrated some 5-HT2B affinity (Scheme 1). The 5-HT2B receptor is a prominent antitarget.29,30 Compounds with 5-HT2B receptor affinity would be deprioritized.

The initial assay results with compound (3R,4R)-3a were promising (Table 1). Compound (+)-3a demonstrated excellent σ1 binding affinity (pKi = 8.7, Ki = 2.1 nM), good selectivity versus the TMEM97 receptor (36-fold selectivity), and minimal binding to the 5-HT2B receptor (Ki > 10 μM). The binding affinities of other compounds with substituted benzyl groups were then investigated. Polar, nonpolar, and halogen substituents were systematically incorporated into the ortho, meta, and para positions of benzyl ether. All had a measured pKi value between 7.8 and 8.8 against the σ1 receptor. This demonstrates the relative flexibility in the aryl substituent. However, all had either increased 5-HT2B binding or decreased σ1 versus TMEM97 selectivity. Naphthyl analogues (3R,4R)-3k and (3R,4R)-3l were investigated but suffered a similar decrease in selectivity.

Table 1. Affinities for Compounds (3R,4R)-3a–3la.

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a

Ligand affinity assays are conducted by the PDSP. For pKi values reported as <5, the compound did not demonstrate ≥50% binding in an initial assay at 10 μM concentration. These data reflect triplicate measurements of a single experiment. Error values reflect the error in the sigmoidal curve fit. Values highlighted in bold are noted for readers’ convenience.

The enantiomeric series of benzyl ethers universally displayed an inferior activity profile (Table 2, (3S,4S)-3a–(3S,4S)-3l). All of these compounds displayed weaker affinity for σ1 (7.5 to 6.3 pKi). Furthermore, the enantiomers showed decreased selectivity between σ1 and TMEM97 and an increase in 5-HT2B affinity. For example, compared to compound (3R,4R)-3a, compound (3S,4S)-3a exhibited a ∼50-fold decrease in σ1 binding activity, a 9-fold decrease in σ1 to TMEM97 selectivity (36-fold to 4-fold selectivity), and an increase in affinity for the 5-HT2B receptor (>10,000 nM vs 400 nM). These results indicated that SAR (structure activity relationship) should focus on the (3R,4R) enantiomeric series.

Table 2. Affinities for Additional Compoundsa.

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a

See notes from Table 1.

A few additional analogues were synthesized and investigated (Table 3). Compounds (3R,4R)-3m and (3R,4R)-3n contained saturated ether chains. The ether cyclohexylmethyl (3R,4R)-3n gave one of the strongest σ1 binding values with a Ki of 1.5 nM (pKi 8.8). Two analogues were synthesized with shorter (3o) and longer (3p) linkers. Phenyl ether ether (3R,4R)-3o demonstrated high σ1 affinity and enhanced σ1 versus TMEM97 selectivity without significantly increasing the affinity for 5-HT2B. This flexibility in SAR likely indicates that many lipophilic substituents at this site would be appropriate. Compound (3R,4R)-3p demonstrated reduced affinity and selectivity, indicating that longer linkers with more degrees of freedom do not offer an advantage. A stereochemically defined 1-phenylethyoxy substituent was investigated.31 Both diastereomers were synthesized. Data indicated that the (R)-1-phenylethyl substituent was optimal, with affinities comparable to compound (3R,4R)-3a. The (3S,4S) enantiomeric series was again inferior (Table 4).

Table 3. Ki Data for Additional Compounds Continueda.

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a

See notes from Table 1.

Table 4. Ki Data for Additional Compounds Continueda.

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a

See notes from Table 1.

When taken together, these SAR data indicate the relative flexibility in the distal ether linkage with respect to the σ1 binding affinity. The compounds with the highest affinity all feature a lipophilic group in the para position to chromane oxygen.

The σ1 receptor is a target for protecting retinal cells from neural degeneration.19,20 A primary cause of retinal neural degeneration is diabetic retinopathy (DR), also known as diabetic eye disease. DR is one of the major complications associated with diabetes32,33 and is a major cause of vision impairment and blindness worldwide.34 Over 45% of diabetics over the age of 40 in the United States (>5 million people) are believed to suffer from DR.35 Current treatment options for the disease include laser photocoagulation and surgical removal of the vitreous humor. DR can also be treated by an intraocular injection of either steroids or vascular endothelial growth factor inhibitors.36,37 Other retinal degenerative diseases, such as retinitis pigmentosa, have severely limited treatment options. Photoreceptor cells are frequently lost in these diseases, and preventing loss is of interest.38

A σ1 ligand could be used to treat retinal neural degradation. The compound (+)-pentazocine ((+)-PTZ) is currently the most studied compound.39,40 Unfortunately, PTZ is an opioid receptor ligand and is probably not clinically suited for treating retinopathy.41 For perspective, (+)-PTZ has a reported σ1Ki ranging from 1.8 to 23 nM.17,42−47 Potential protective effects of compounds (3R,4R)-3a, (3R,4R)-3o, and (3R,4R)-3q were examined using the well-characterized cone photoreceptor cell line 661W.48 Initially, compounds were screened for cytotoxicity. The treatment of 661W cells resulted in decreased cell viability above 50 μM (Figure 2). Further assays were limited to a 10 μM maximum concentration.

Figure 2.

Figure 2

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Cytotoxicity assay data. 661W cells were treated with compounds (3R,4R)-3a, (3R,4R)-3o, and (3R,4R)-3q at (12.5, 25, 50, and100 μM) for 24 h. Cell viability was assessed using the MTT assay. Data are presented as mean ± standard error of the mean (SEM) of quadruplicate measurements; ***p < 0.001; ****p < 0.0001; ns = not significant as compared to the nontreatment control. The loss of cell viability was observed at 100 μM for (3R,4R)-3o and (3R,4R)-3q and above 50 μM for (3R,4R)-3a.

Exposure of 661W cells to tert-butyl hydroperoxide (tBHP, 55 μM) for 24 h induces oxidative stress, which decreases the cell viability to approximately 50% of the untreated control. Cotreatment with σ1 receptor ligands leads to enhanced cell viability.39,40 In these assays, (+)-PTZ was used as a positive control.39,40,49 Cotreatment with compounds (3R,4R)-3a (Figure 3A), (3R,4R)-3o (Figure 3B), and (3R,4R)-3q (Figure 3C) at concentrations ranging from 0.1 to 10.0 μM did not produce a statistically significant increase in cell viability.

Figure 3.

Figure 3

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Ligand effect on 661W cells treated with tBHP. a661W cells were treated with tBHP (55 μM) in the presence or absence of increasing concentrations (0.1–10 μM) of compounds (3R,4R)-3a (A), (3R,4R)-3o (B), (3R,4R)-3q (C), or (+)-PTZ (25 and 50 μM, positive control) for 24 h before cell viability assessment. Cell viability was assessed using the MTT assay. Data are presented as mean ± standard error of the mean (SEM) of quadruplicate measurements; ****p < 0.0001; ns = not significant as compared to the tBHP treatment (tBHP = tert-butyl hydroperoxide; PTZ = (+)-pentazocine).

Given the increased affinity of the new ligands to the σ1 receptor (Tables 1 and 3) and the prior success with compound (±)-7 at rescuing tBHP-insulted 661W cells,24 the lack of an increase in cell viability was surprising. A CellROX assay was conducted to quantify the presence of reactive oxygen species (ROS) in tBHP-insulted 661W cells with compounds (3R,4R)-3a, (3R,4R)-3o, (3R,4R)-3q, and (+)-PTZ (positive control). Cells without tBHP (control) exhibited minimal fluorescence, while cells exposed to tBHP exhibited strong fluorescence (Figure 4). All compounds assayed inhibited fluorescence compared to the tBHP control (Figure 4B). This indicated that the ligands do suppress ROS (Figure 4); however, this effect does not appear sufficient to rescue cells using the MTT assay (Figure 3). It is unclear if the encouraging results from the CellROX assay but a minimal effect on cell viability (Figure 4 vs Figure 3) is the result of increased cytotoxicity of ligands (3R,4R)-3a, (3R,4R)-3o, and (3R,4R)-3q relative to compound (±)-7, limited solubility, cell penetration, or a change in the functional behavior. Regrettably, functional assays are not readily available for σ1 as they are for many other GPCR ligands. Additional solubility and PAMPA data are included, which indicate that sufficient solubility and cell permeability are expected (see Supporting Information). Furthermore, the ligand affinity was corroborated by a second source, and additional off-target data are likewise included (see Supporting Information).

Figure 4.

Figure 4

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tBHP-induced attenuated oxidative stress assay. a661W cells were seeded on coverslips for 18 h. Cells either were or were not (control) exposed for 2 h to tBHP (55 μM) in the presence/absence of compound (3R,4R)-3a (5, 10 μM), (3R,4R)-3o (5 μM), (3R,4R)-3q (5, 10 μM), or PTZ (25 μM). (A) Representative immunofluorescent images of cells incubated with CellROX green reagent to detect ROS; green fluorescent signals indicated ROS as visualized by epifluorescence. DAPI was used to label nuclei (blue). (B) Quantification of fluorescent intensity reflecting ROS levels of data shown in panel A. Data are presented as mean ± SEM. Data represent three independent experiments performed in duplicate. Significant differences are indicated: ****p < 0.0001 as compared to the tBHP treatment (tBHP = tert-butyl hydroperoxide; PTZ = (+)-pentazocine).

Conclusions

In conclusion, the σ1, TMEM97, and 5-HT2B receptor affinities were investigated for 36 new 3-amino-chromanes. Ligands derived from phenol (3R,4R)-9 had higher affinity and selectivity. Compounds (3R,4R)-3a, (3R,4R)-3o, and (3R,4R)-3q suppressed ROS in 661W cells. However, the effect was insufficient to increase the 661W cell viability.

Experimental Section

Azide Precautions

Organic and inorganic azides are known to be high-energy materials and explosions have been reported with their use.50 All of the azides reported herein were synthesized without incident; however, several precautions were taken. First, all azides synthesized herein have a C/N ratio of ≥3:1. Second, reaction mixtures with more than 1 mmol of azide were placed behind safety shields both in the fume hood and during rotary evaporation. Third, all waste solutions (both organic and aqueous) that could be contaminated by azides were segregated into specially labeled containers and were kept strictly free of acids to prevent incidental formation of HN3. More information on azide safety are available.51,52

General Chemical Synthesis

All reactions sensitive to air or moisture were carried out in oven-dried glassware using standard Schlenk line techniques or were conducted using a glovebox (details are provided below). All reactions were carried out by magnetic stirring (100–600 rpm). All reactions conducted at elevated temperatures used aluminum block heating with an external thermocouple. Dry DCM and THF were obtained from a commercial solvent purification system using activated alumina columns and stored under a positive pressure of argon. Other reagents and solvents were purchased from commercial suppliers and were used as received. Reactions were monitored by gas chromatography or thin-layer chromatography using precoated plastic plates impregnated with a fluorescent indicator (254 nm). Visualization was carried out with UV light (254 nm), KMnO4, or PMA stains. Column chromatography was performed using a Teledyne Isco CombiFlash Rf purification system utilizing normal-phase precolumn load cartridges and gold high-performance columns.

Instrumentation for Chemical Synthesis

All proton (1H) nuclear magnetic resonance (NMR) spectra were recorded at 400 or 500 MHz using a Bruker spectrometer. All carbon (13C) NMR spectra were recorded at either 101 or 126 MHz using a Bruker spectrometer. Chemical shifts are expressed in ppm and are referenced to a residual solvent as an internal standard (1H: CHCl3, 7.27 ppm, 13C: CDCl3, 77.2 ppm). Infrared (IR) spectra were recorded as a film on NaCl plates using a Nexus 670 FT-IR and are reported in cm–1.

Note

The precursor compound 8 was reported in a previous study. The synthetic route to and characterization for that compound can be found in ref (25).

Biological Activity Assay

Compounds were assayed for receptor affinity at the PDSP via a two-tiered system: an initial screening against receptors at 10 μM concentration followed by a secondary assay to determine Ki values for compounds that exhibited over 50% activity in the primary assay.27 Compounds were shipped to the PDSP as neat oils or solids. All ligand affinities reported at the PDSP were determined against cloned human proteins.

Compound Preparation for Cellular Assays

Solutions of compounds (3R,4R)-3a, (3R,4R)-3o, and (3R,4R)-3q were prepared in dimethyl sulfoxide (DMSO). A (+)-pentazocine (Sigma-Aldrich, St. Louis, MO) solution was prepared in 10% DMSO in 0.01 M phosphate buffered saline (PBS) and 6% 1 M HCl. tBHP [5.5 M in decane] (Sigma-Aldrich, St. Louis, MO) was dissolved in 0.01 M PBS.

Cell Culture and Cell Viability

The 661W cells, obtained from Dr. M. Al-Ubaidi (Univ. of Houston), express blue and green cone pigments, transducin and cone arrestin, characteristic of cone photoreceptor cells. They were cultured in Dulbecco’s modified Eagle’s medium (DMEM, Thermo Fisher Scientific) supplemented with 5% FBS for regular culture or 1% FBS in treatment, along with 100 U/mL penicillin and 100 μg/mL streptomycin. The cells were treated in the presence/absence of compounds (3R,4R)-3a, (3R,4R)-3o, (3R,4R)-3q, or (+)-PTZ, with or without tBHP [55 μM] for 24 h before the cell viability was assessed. Viability was assessed using the Vybrant MTT cell proliferation assay kit (Thermo Fisher), which measures the reduction of yellow 3-(4,5-dimethythiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) by mitochondrial succinate dehydrogenase. In metabolically active cells, MTT enters cells and passes into the mitochondria where it is reduced to formazan, an insoluble, dark purple product. Cells were solubilized in DMSO and released, and the solubilized formazan reagent was measured spectrophotometrically using a Synergy H1 Hybrid Multi-Mode plate reader (Winooski, VT) at 540 nm. The assay was performed in triplicate. tBHP [5.5 M in decane] (Sigma-Aldrich, St. Louis, MO) was dissolved in 0.01 M PBS; tBHP is an inducer of oxidative stress.

Assessment of Oxidative Stress

To assess the effects of compounds (3R,4R)-3a, (3R,4R)-3o, and (3R,4R)-3q on oxidative stress, 661W cells were seeded on coverslips and were exposed to media containing tBHP [55 μM] for 2 h. In companion studies, cells were treated with (3R,4R)-3o [5 μM], (3R,4R)-3a [5, 10 μM], (3R,4R)-3q [5, 10 μM], or (+)-PTZ [25 μM] and tBHP [55 μM] for 2 h or were treated with (3R,4R)-3o, (3R,4R)-3a, (3R,4R)-3q, or (+)-PTZ alone. Control experiments were conducted in parallel in which tBHP and those compounds were omitted from the media. Following treatments, the cells were rinsed with PBS and intracellular ROS were detected in cells using 5 μM CellROX green reagent (Thermo Fisher Scientific; 30 min incubation followed by fixation). CellROX detects hydroxyl, peroxyl, peroxynitrite, and hydroxyl radicals. DAPI was used to stain nuclei. Green fluorescent signals representing ROS were visualized using an Axioplan-2 fluorescence microscope. Fluorescence intensity was quantified using the NIH ImageJ 1.48v software.

Statistical Analysis

The data were analyzed using the GraphPad Prism statistical analysis program (La Jolla, California, USA). Significance was established as p < 0.05. Data were analyzed by one-way ANOVA followed by Tukey’s post hoc test.

(±)-9: In a glovebox, an oven-dried vial was charged with AlCl3 (1.7 g, 12.8 mmol). The vial was sealed and removed from the glovebox. The vial was then cooled to 0 °C and charged with dimethyl sulfide (DMS, 5 mL). Chromane (±)-8 (700 mg, 2.9 mmol) was then transferred into the vial as a DMS solution (2 × 2 mL). After 5 min, the vial was removed from the ice bath. After an additional 2 h, the reaction mixture was slowly poured into the slurry of ice. The resulting solution was then extracted with EtOAc (3 × 15 mL), and the combined organic phases were washed with brine, dried (MgSO4), and concentrated under reduced pressure, affording phenol (±)-9 (640 mg, 2.8 mmol 97%) as a white solid; 1H NMR (400 MHz, CD3CN) δ 6.70 (d, J = 8.7 Hz, 1H), 6.65–6.61 (m, 1H), 6.55–6.53 (m, 2H), 5.78 (ddd, J = 17.1, 10.1, 9.1 Hz, 1H), 5.45 (dd, J = 10.1, 2.0 Hz, 1H), 5.34 (ddd, J = 17.0, 2.0, 0.7 Hz, 1H), 4.20 (d, J = 11.6 Hz, 1H), 3.93 (dd, J = 11.6, 0.8 Hz, 1H), 3.46 (br d, J = 9.2 Hz, 1H), 1.36 (s, 3H); 13C NMR (101 MHz, CD3CN) δ 150.9, 146.4, 135.7, 122.9, 120.4, 116.8, 115.2, 115.1, 70.5, 58.9, 50.2, 19.7; IR (NaCl, thin film, cm–1) 3368, 2109, 1659, 1494, 1450, 1275, 1257, 1216, 1178, 1052, 818, 748; HRMS (ESI-TOF) m/z calcd for C12H13N3O2Na + (M + Na) + 254.0900, found 254.0902.

Semiprep HPLC

A 20 mL vial was charged with compound (±)-9 (640 mg) and heated to 35 °C. To this vial, HPLC-grade IPA and MTBE (1:1, 3 mL total) were added in 100 μL increments and vigorously stirred. The solution was then filtered using a 20 μmsyringe filter into two 2 mL HPLC vials. The vials were transferred directly to the instrument vial rack, which was preheated to 40 °C. HPLC Method: 30% IPA in hexane, 40 °C, 9.45 mL/min, Diacel Chiralcel-OD 10 μm HPLC semiprep column (10 × 250 mm), 100 μL injections. Note: To prevent precipitation on the column, the column should be reversed and flushed with 100% EtOH at 2 mL/min and 40 °C for 2 h following the completion of a semiprep session (20–25 injections).

Analytical Chiral HPLC

Diacel Chiralcel-OD 10 μm column; hexane:iPrOH = 90:10 at 2.0 mL/min, 40 °C, λ = 211 nm: tmajor = 5.10 min, tminor = 9.50 min: er = 98.6:1.4, 98.5:1.5. The average of 98.5:1.5 is reported. Specific Rotation: [α]D23 = +28.4 ± 3.9 (c = 2.2, DCM).

Chiral HPLC

Diacel Chiralcel-OD 10 μm column; hexane:iPrOH = 90:10 at 2.0 mL/min, 40 °C, λ = 211 nm: tmajor = 9.50 min, tminor = 5.10 min: er = 99.8:0.2, 99.7:0.3. The average of 99.7:0.3 is reported. Specific Rotation: [α]D23 = −24.3 ± 2.9 (c = 2.0, DCM).

General Procedure 1: Alkylation of Phenolic Chromane

Example given for RX = BnBr. (±)-10a: To a vial of (±)-9 (18 mg, 0.078 mmol) at rt was sequentially added acetonitrile (0.10 mL), BnBr (18 μL, 0.16 mmol), and solid K2CO3 (43 mg, 0.32 mmol). After 18 h, the resulting heterogeneous mixture was loaded directly onto a column load cartridge. Vacuum was then applied to the column cartridge for 10 min before final purification by column chromatography (0 to 20% gradient, EtOAc in hexane) to afford (±)-10a (21 mg, 0.066 mmol, 85%) as a white solid: 1H NMR (400 MHz, CDCl3) δ 7.48–7.36 (m, 4H), 7.39–7.31 (m, 1H), 6.84–6.79 (m, 1H), 6.78–6.72 (m, 2H), 5.85 (ddd, J = 17.1, 10.1, 9.0 Hz, 1H), 5.46 (dd, J = 10.1, 1.8 Hz, 1H), 5.30 (ddd, J = 17.0, 1.8, 0.7 Hz, 1H), 5.00 (s, 2H), 4.19 (d, J = 11.4 Hz, 1H), 3.89 (dd, J = 11.4, 0.8 Hz, 1H), 3.37 (br d, J = 9.0 Hz, 1H), 1.41 (s, 3H); 13C NMR (101 MHz, CDCl3) δ 153.3, 147.2, 137.3, 135.7, 128.7, 128.1, 127.7, 122.4, 120.9, 117.2, 115.7, 115.3, 70.82, 70.77, 58.9, 51.1, 20.8; IR (NaCl, thin film, cm–1) 3033, 2976, 2928, 2872, 2109, 1639, 1614, 1494, 1274, 1256, 1219, 1178, 1053, 1025, 927, 804, 736, 696; HRMS (ESI-TOF) m/z calcd for C19H19N3O2Na+ (M + Na)+ 344.1369, found 344.1363.

(3R,4R)-10b

General procedure 1 was used and the product was isolated in 87% (26 mg) as a white solid: 1H NMR (500 MHz, CDCl3) δ 7.64 (d, J = 8.1 Hz, 2H), 7.53 (d, J = 8.0 Hz, 2H), 6.82 (d, J = 9.0 Hz, 1H), 6.80 (dd, J = 9.0, 2.7 Hz, 1H), 6.69 (d, J = 2.5 Hz, 1H), 5.81 (ddd, J = 17.0, 10.1, 8.9 Hz, 1H), 5.43 (dd, J = 10.1, 1.8 Hz, 1H), 5.27 (dt, J = 17.0, 1.4, 0.9 Hz, 1H), 5.04 (s, 2H), 4.18 (d, J = 11.4 Hz, 1H), 3.88 (dd, J = 11.4, 0.8 Hz, 1H), 3.35 (br d, J = 9.0 Hz, 1H), 1.40 (s, 3H); 13C NMR (126 MHz, CDCl3) δ 152.9, 147.5, 141.5, 135.7, 130.2 (q, JC–F = 32.3 Hz), 127.6, 125.7 (q, JC–F = 3.7 Hz), 124.0 (q, JC–F = 272.5 Hz). 122.6, 121.1, 117.4, 115.7, 115.3, 70.9, 70.0, 58.9, 51.2, 20.8; 19F NMR (376 MHz, CDCl3) δ −62.53; IR (NaCl, thin film, cm–1) 3079, 2975, 2928, 2875, 2110, 1621, 1494, 1418, 1326, 1274, 1256, 1220, 1163, 1124, 1066, 1018, 928, 825; HRMS (ESI-TOF) m/z calcd for C20H18F3N3O2Na+ (M + Na)+ 412.1243, found 412.1252.

(3R,4R)-10c

General procedure 1 was used and the product was isolated in 73% (22 mg) as a clear oil: 1H NMR (500 MHz, CDCl3) δ 7.70 (s, 1H), 7.61 (d, J = 7.9 Hz, 1H), 7.59 (d, J = 7.7 Hz, 1H), 7.50 (t, J = 7.7 Hz, 1H), 6.85–6.81 (m, 2H), 6.73–6.69 (m, 1H), 5.82 (dt, J = 17.1, 9.5 Hz, 1H), 5.45 (dd, J = 10.3, 1.6 Hz, 1H), 5.28 (dd, J = 17.1, 1.7 Hz, 1H), 5.03 (s, 2H), 4.18 (d, J = 11.4 Hz, 1H), 3.89 (d, J = 11.4 Hz, 1H), 3.36 (d, J = 9.0 Hz, 1H), 1.40 (s, 3H); 13C NMR (126 MHz, CDCl3) δ 152.9, 147.5, 138.4, 135.6, 131.1 (q, JC–F = 32.3 Hz), 130.9, 129.2, 124.9 (q, JC–F = 3.8 Hz), 124.4 (q, JC–F = 3.8 Hz), 123.6 (q, JC–F = 272.4 Hz), 122.6, 121.1, 117.4, 115.7, 115.4, 70.9, 70.1, 58.9, 51.2, 20.8; 19F NMR (376 MHz, CDCl3) δ −62.63; IR (NaCl, thin film, cm–1) 3081, 2978, 2930, 2875, 2110, 1495, 1331, 1274, 1219, 1165, 1125, 1074, 1055, 927, 801, 701; HRMS (ESI-TOF) m/z calcd for C20H18F3N3O2Na+ (M + Na)+ 412.1243, found 412.1234.

(3R,4R)-10d

General procedure 1 was used and the product was isolated in 76% (23 mg) as a clear oil: 1H NMR (500 MHz, CDCl3) δ 7.74 (d, J = 7.8 Hz, 1H), 7.69 (d, J = 7.8 Hz, 1H), 7.57 (t, J = 7.6 Hz, 1H), 7.42 (t, J = 7.7 Hz, 1H), 6.84–6.79 (m, 2H), 6.71–6.68 (m, 1H), 5.80 (ddd, J = 16.9, 10.0, 9.0 Hz, 1H), 5.42 (dd, J = 10.1, 1.7 Hz, 1H), 5.27 (dd, J = 17.1, 1.7 Hz, 1H), 5.20 (s, 2H), 4.17 (d, J = 11.4 Hz, 1H), 3.88 (d, J = 11.4 Hz, 1H), 3.35 (d, J = 9.0 Hz, 1H), 1.40 (s, 3H); 13C NMR (126 MHz, CDCl3) δ 152.8, 147.5, 136.1, 135.6, 132.3, 128.9, 127.8, 127.5 (q, JC–F = 31.1 Hz), 126.0 (q, JC–F = 5.7 Hz), 127.9–121.2 (m); 122.6, 121.0, 117.4, 115.8, 115.3, 70.9, 66.9 (q, JC–F = 3.1 Hz), 58.9, 51.2, 20.8; 19F NMR (471 MHz, CDCl3) δ −60.28; IR (NaCl, thin film, cm–1) 3079, 2977, 2931, 2875, 2110, 1609, 1495, 1456, 1315, 1257, 1220, 1166, 1120, 1056, 1034, 928, 769; HRMS (ESI-TOF) m/z calcd for C20H18F3N3O2Na+ (M + Na)+ 412.1243, found 412.1256.

(3R,4R)-10e

General procedure 1 was used and the product was isolated in 77% (21 mg) as a white solid: 1H NMR (500 MHz, CDCl3) δ 7.35 (s, 4H), 6.82 (d, J = 8.8 Hz, 1H), 6.79 (dd, J = 8.9, 2.6 Hz, 1H), 6.69 (d, J = 2.6 Hz, 1H), 5.82 (dt, J = 17.2, 9.5 Hz, 1H), 5.44 (dd, J = 10.1, 1.7 Hz, 1H), 5.28 (dd, J = 17.1, 1.7 Hz, 1H), 4.95 (s, 2H), 4.17 (d, J = 11.4 Hz, 1H), 3.88 (d, J = 11.4 Hz, 1H), 3.35 (d, J = 9.0 Hz, 1H), 1.40 (s, 3H); 13C NMR (126 MHz, CDCl3) δ 153.1, 147.4, 135.9, 135.7, 133.9, 129.0, 128.9, 122.5, 121.0, 117.3, 115.8, 115.4, 70.9, 70.1, 58.9, 51.2, 20.9; IR (NaCl, thin film, cm–1) 2974, 2928, 2871, 2110, 1494, 1255, 1220, 1178, 1054, 1014, 928, 809; HRMS (ESI-TOF) m/z calcd for C19H18ClN3O2Na+ (M + Na)+ 378.0980, found 378.0998.

(3R,4R)-10f

General procedure 1 was used and the product was isolated in 86% (24 mg) as a clear oil: 1H NMR (500 MHz, CDCl3) δ 7.45–7.41 (m, 1H), 7.33–7.27 (m, 3H), 6.82 (d, J = 8.7 Hz, 1H), 6.79 (dd, J = 8.9, 2.7 Hz, 1H), 6.69 (d, J = 2.6 Hz, 1H), 5.82 (ddd, J = 17.1, 10.1, 9.0 Hz, 1H), 5.45 (dd, J = 10.1, 1.8 Hz, 1H), 5.28 (ddd, J = 17.1, 1.8, 0.6 Hz, 1H), 4.95 (s, 2H), 4.17 (d, J = 11.4 Hz, 1H), 3.88 (d, J = 11.4 Hz, 1H), 3.35 (br d, J = 9.0 Hz, 1H), 1.40 (s, 3H); 13C NMR (126 MHz, CDCl3) δ 153.0, 147.4, 139.5, 135.7, 134.6, 130.0, 128.2, 127.7, 125.6, 122.5, 121.1, 117.4, 115.8, 115.3, 70.9, 70.0, 58.9, 51.2, 20.8; IR (NaCl, thin film, cm–1) 2967, 2922, 2871, 2110, 1495, 1256, 1220, 1178, 1053, 808, 684; HRMS (ESI-TOF) m/z calcd for C19H18ClN3O2Na+ (M + Na)+ 378.0980, found 378.0983.

(3R,4R)-10g

General procedure 1 was used and the product was isolated in 89% (25 mg) as a clear oil: 1H NMR (500 MHz, CDCl3) δ 7.55 (dd, J = 7.2, 2.1 Hz, 1H), 7.40 (dd, J = 7.4, 1.8 Hz, 1H), 7.32–7.24 (m, 2H), 6.86–6.79 (m, 2H), 6.74–6.72 (m, 1H), 5.83 (dt, J = 16.9, 9.5 Hz, 1H), 5.44 (dd, J = 10.0, 1.7 Hz, 1H), 5.28 (dd, J = 17.0, 1.7 Hz, 1H), 5.09 (s, 2H), 4.17 (d, J = 11.4 Hz, 1H), 3.88 (d, J = 11.4 Hz, 1H), 3.36 (d, J = 9.0 Hz, 1H), 1.40 (s, 3H); 13C NMR (126 MHz, CDCl3) δ 153.1, 147.4, 135.7, 135.1, 132.9, 129.5, 129.2, 129.1, 127.1, 122.6, 121.0, 117.3, 115.9, 115.3, 70.9, 68.0, 58.9, 51.2, 20.9; IR (NaCl, thin film, cm–1) 3075, 2968, 2928, 2873, 2109, 1494, 1256, 1219, 1178, 1058, 928, 755; HRMS (ESI-TOF) m/z calcd for C19H18ClN3O2Na+ (M + Na)+ 378.0980, found 378.0988.

(3S,4S)-10h

A variation of general procedure 1 was used, where the reaction was run at 60 °C for 24 h. The product was isolated in 66% (19 mg) as a white solid: 1H NMR (500 MHz, CDCl3) δ 7.34 (d, J = 8.4 Hz, 2H), 6.92 (d, J = 8.5 Hz, 2H), 6.81 (s, 2H), 6.71 (s, 1H), 5.83 (dt, J = 17.0, 9.5 Hz, 1H), 5.43 (dd, J = 10.1, 1.7 Hz, 1H), 5.27 (dd, J = 17.1, 1.7 Hz, 1H), 4.91 (s, 2H), 4.17 (d, J = 11.4 Hz, 1H), 3.88 (d, J = 11.4 Hz, 1H), 3.83 (s, 3H), 3.36 (d, J = 9.0 Hz, 1H), 1.40 (s, 3H); 13C NMR (126 MHz, CDCl3) δ 159.6, 153.4, 147.2, 135.8, 129.5, 129.4, 122.4, 120.9, 117.2, 115.8, 115.4, 114.2, 70.9, 70.6, 58.9, 55.5, 51.2, 20.9; IR (NaCl, thin film, cm–1) 2968, 2932, 2908, 2837, 2110, 1613, 1514, 1494, 1251, 1218, 1174, 1052, 1035, 1021, 933, 822, 802; HRMS (ESI-TOF) m/z calcd for C20–H21N3O3Na+ (M + Na)+ 374.1475, found 374.1484.

(3S,4S)-10i

A variation of general procedure 1 was used, where the reaction was run at 60 °C for 24 h. The product was isolated in 82% (23 mg) as a clear oil: 1H NMR (500 MHz, CDCl3) δ 7.29 (t, J = 7.8 Hz, 1H), 7.00 (d, J = 7.6 Hz, 1H), 6.98 (d, J = 2.9 Hz, 1H), 6.87 (dd, J = 8.3, 2.5 Hz, 1H), 6.81 (s, 2H), 6.73–6.71 (m, 1H), 5.83 (dt, J = 17.0, 9.5 Hz, 1H), 5.43 (dd, J = 10.1, 1.8 Hz, 1H), 5.28 (dd, J = 17.1, 1.7 Hz, 1H), 4.96 (s, 2H), 4.17 (d, J = 11.4 Hz, 1H), 3.88 (d, J = 11.4 Hz, 1H), 3.83 (s, 3H), 3.36 (d, J = 9.0 Hz, 1H), 1.40 (s, 3H); 13C NMR (101 MHz, CDCl3) δ 160.0, 153.3, 147.2, 139.0, 135.8, 129.8, 122.5, 120.9, 119.9, 117.3, 115.8, 115.3, 113.7, 113.1, 70.9, 70.7, 58.9, 55.4, 51.2, 20.9; IR (NaCl, thin film, cm–1) 2932, 2873, 2109, 1602, 1587, 1494, 1268, 1219, 1179, 1054, 802; HRMS (ESI-TOF) m/z calcd for C20H21N3O3Na+ (M + Na)+ 374.1475, found 374.1482.

(3S,4S)-10k

General procedure 1 was used and the product was isolated in 84% (24 mg) as a clear oil: 1H NMR (500 MHz, CDCl3) δ 8.09–8.06 (m, 1H), 7.93–7.89 (m, 1H), 7.87 (d, J = 8.3 Hz, 1H), 7.59 (dd, J = 7.0, 1.1 Hz, 1H), 7.57–7.53 (m, 2H), 7.48 (dd, J = 8.3, 7.0 Hz, 1H), 6.91 (dd, J = 8.8, 3.0 Hz, 1H), 6.86 (d, J = 8.8 Hz, 1H), 6.81 (d, J = 2.9 Hz, 1H), 5.84 (ddd, J = 17.1, 10.1, 8.9 Hz, 1H), 5.46–5.40 (m, 1H), 5.42 (s, 2H), 5.28 (ddd, J = 17.1, 1.8, 0.7 Hz, 1H), 4.19 (d, J = 11.4 Hz, 1H), 3.89 (d, J = 11.4 Hz, 1H), 3.37 (br d, J = 9.0 Hz, 1H), 1.41 (s, 3H); 13C NMR (126 MHz, CDCl3) δ 153.4, 147.4, 135.7, 134.0, 132.7, 131.8, 129.2, 128.8, 126.9, 126.6, 126.1, 125.5, 124.0, 122.5, 121.0, 117.3, 115.9, 115.4, 70.9, 69.5, 58.9, 51.2, 20.9; IR (NaCl, thin film, cm–1) 3047, 2973, 2919, 2872, 2108, 1494, 1256, 1218, 1178, 1053, 793, 776; HRMS (ESI-TOF) m/z calcd for C23H21N3O2Na+ (M + Na)+ 394.1526, found 394.1536.

(3R,4R)-10l

General procedure 1 was used and the product was isolated in 75% (22 mg) as a white solid: 1H NMR (500 MHz, CDCl3) δ 7.87 (d, J = 8.0 Hz, 2H), 7.85 (dd, J = 4.9, 2.3 Hz, 2H), 7.54 (dd, J = 8.2, 1.7 Hz, 1H), 7.52–7.48 (m, 2H), 6.87 (dd, J = 8.8, 2.9 Hz, 1H), 6.83 (d, J = 8.9 Hz, 1H), 6.77 (d, J = 2.9 Hz, 1H), 5.83 (dt, J = 16.9, 9.5 Hz, 1H), 5.43 (dd, J = 10.1, 1.7 Hz, 1H), 5.27 (dd, J = 17.1, 1.7 Hz, 1H), 5.16 (s, 2H), 4.18 (d, J = 11.4 Hz, 1H), 3.88 (d, J = 11.4 Hz, 1H), 3.35 (d, J = 9.0 Hz, 1H), 1.40 (s, 3H); 13C NMR (126 MHz, CDCl3) δ 153.4, 147.3, 135.8, 134.9, 133.5, 133.3, 128.5, 128.1, 127.9, 126.6, 126.4, 126.2, 125.6, 122.5, 120.9, 117.3, 115.9, 115.5, 71.0, 70.9, 58.9, 51.2, 20.9; IR (NaCl, thin film, cm–1) 2917, 2849, 2114, 1494, 1255, 1222, 1182, 1051, 828; HRMS (ESI-TOF) m/z calcd for C23H21N3O2Na+ (M + Na)+ 394.1526, found 394.1524.

(3S,4S)-10m

A variation of general procedure 1 was used, where the reaction was run at 60 °C for 24 h. The product was isolated in 70% (14 mg) as a white solid: 1H NMR (500 MHz, CDCl3) δ 6.80 (d, J = 8.9 Hz, 1H), 6.74 (dd, J = 8.9, 3.0 Hz, 1H), 6.64 (d, J = 2.9 Hz, 1H), 5.83 (dt, J = 17.0, 9.5 Hz, 1H), 5.43 (dd, J = 10.1, 1.7 Hz, 1H), 5.28 (dd, J = 17.1, 1.7 Hz, 1H), 4.16 (d, J = 11.4 Hz, 1H), 3.87 (d, J = 11.3 Hz, 1H), 3.72 (d, J = 6.9 Hz, 2H), 3.35 (d, J = 9.0 Hz, 1H), 1.39 (s, 3H), 1.30–1.18 (m, 1H), 0.67–0.60 (m, 2H), 0.36–0.30 (m, 2H); 13C NMR (126 MHz, CDCl3) δ 153.6, 147.0, 135.9, 122.4, 120.9, 117.2, 115.5, 115.1, 73.5, 70.8, 59.0, 51.2, 20.9, 10.6, 3.3; IR (NaCl, thin film, cm–1) 3007, 2973, 2917, 2872, 2106, 1494, 1403, 1278, 1259, 1219, 1180, 1049, 1029, 1006, 932, 812, 744; HRMS (ESI-TOF) m/z calcd for C16H19N3O2Na+ (M + Na)+ 308.1369, found 308.1376.

(3S,4S)-10n

A variation of general procedure 1 was used, where the reaction was run at 60 °C for 24 h. The product was isolated in 55% (14 mg) as a white solid: 1H NMR (500 MHz, CDCl3) δ 6.79 (d, J = 8.9 Hz, 1H), 6.73 (dd, J = 8.9, 2.7 Hz, 1H), 6.61 (dd, J = 3.0, 1.1 Hz, 1H), 5.84 (ddd, J = 17.1, 10.1, 9.0 Hz, 1H), 5.44 (dd, J = 10.1, 1.8 Hz, 1H), 5.28 (ddd, J = 17.1, 1.8, 0.7 Hz, 1H), 4.16 (d, J = 11.4 Hz, 1H), 3.87 (dd, J = 11.3, 0.8 Hz, 1H), 3.67 (d, J = 6.4 Hz, 2H), 3.35 (br zd, J = 9.0 Hz, 1H), 1.89–1.81 (m, 2H), 1.80–1.73 (m, 3H), 1.73–1.67 (m, 1H), 1.39 (s, 3H), 1.34–1.15 (m, 3H), 1.03 (qd, J = 12.3, 3.4 Hz, 2H); 13C NMR (126 MHz, CDCl3) δ 153.9, 146.8, 135.9, 122.4, 120.9, 117.2, 115.3, 114.9, 74.2, 70.8, 59.0, 51.2, 38.0, 30.1, 26.7, 26.0, 20.9; IR (NaCl, thin film, cm–1) 2925, 2852, 2110, 1494, 1385, 1278, 1259, 1218, 1179, 1051, 1029, 929, 817; HRMS (ESI-TOF) m/z calcd for C19H25N3O2Na+ (M + Na)+ 350.1839, found 350.1835.

(3R,4R)-10p

A variation of general procedure 1 was used, where the reaction was run at 60 °C for 24 h. The product was isolated in 64% (17 mg) as a white solid: 1H NMR (500 MHz, CDCl3) δ 7.30 (ddq, J = 27.7, 15.1, 6.9 Hz, 5H), 6.81 (d, J = 8.8 Hz, 1H), 6.75 (dd, J = 8.9, 3.0 Hz, 1H), 6.63 (d, J = 2.9 Hz, 1H), 5.83 (dt, J = 17.3, 9.5 Hz, 1H), 5.44 (dd, J = 10.1, 1.6 Hz, 1H), 5.28 (dd, J = 17.0, 1.5 Hz, 1H), 4.17 (d, J = 11.4 Hz, 1H), 4.11 (t, J = 7.2 Hz, 2H), 3.87 (d, J = 11.4 Hz, 1H), 3.35 (d, J = 8.9 Hz, 1H), 3.08 (t, J = 7.2 Hz, 2H), 1.40 (s, 3H); 13C NMR (126 MHz, CDCl3) δ 153.3, 147.1, 138.5, 135.8, 129.2, 128.7, 126.6, 122.4, 120.9, 117.3, 115.27, 115.26, 70.8, 69.5, 58.9, 51.2, 36.1, 20.9; IR (NaCl, thin film, cm–1) 3065, 3026, 2929, 2874, 2108, 1615, 1495, 1419, 1385, 1255, 1219, 1180, 1054, 928, 815, 744, 698; HRMS (ESI-TOF) m/z calcd for C20H21N3O2Na+ (M + Na)+ 358.1526, found 358.1529.

General Procedure 2: Formation of Aryl Ethers via the Mitsunobu Reaction

Example given for R = o-OMe: A variation of a known procedure was performed.53 To a solution of chromane (3S,4S)-9 (18.0 mg, 78 μmol), o-methoxy benzyl alcohol (10.0 μL, 74 μmol), and PPh3 (21 mg, 82 μmol) in THF (0.15 mL) was added DIAD (16 μmol, 82 μmol) in an ice bath. After 5 min, the ice bath was removed and the solution was allowed to gradually warm to room temperature. After 18 h, the reaction mixture was loaded directly onto a column load cartridge. Final purification by column chromatography (0 to 40% gradient, EtOAc in hexane) afforded (3S,4S)-10j (16.0 mg, 48 μmol 65%) as a clear oil: 1H NMR (500 MHz, CDCl3) δ 7.45 (dd, J = 7.5, 1.8 Hz, 1H), 7.30 (td, J = 7.8, 1.8 Hz, 1H), 7.01–6.95 (m, 1H), 6.91 (d, J = 8.3 Hz, 1H), 6.84 (dd, J = 8.9, 2.9 Hz, 1H), 6.81 (d, J = 8.8 Hz, 1H), 6.74 (d, J = 2.8 Hz, 1H), 5.84 (ddd, J = 17.0, 10.1, 9.0 Hz, 1H), 5.43 (dd, J = 10.1, 1.8 Hz, 1H), 5.27 (ddd, J = 17.1, 1.8, 0.7 Hz, 1H), 5.03 (s, 2H), 4.17 (d, J = 11.4 Hz, 1H), 3.90–3.84 (m, 1H), 3.86 (s, 3H), 3.36 (br d, J = 8.9 Hz, 1H), 1.40 (s, 3H); 13C NMR (126 MHz, CDCl3) δ 157.1, 153.6, 147.1, 135.9, 129.1, 129.1, 125.7, 122.4, 120.80, 120.76, 117.2, 115.9, 115.3, 110.5, 70.8, 65.8, 59.0, 55.6, 51.2, 20.9; IR (NaCl, thin film, cm–1) 2933, 2108, 1604, 1494, 1463, 1247, 1218, 1178, 1053, 1030, 928, 750; HRMS (ESI-TOF) m/z calcd for C20H21N3O3Na+ (M + Na)+ 374.1475, found 374.1465.

(3R,4R)-10r

A variation of general procedure 2 was performed, with (R)-1-phenylethanol used instead of o-methoxy benzyl alcohol. The product was isolated in 73% (19 mg) as a white solid: 1H NMR (500 MHz, CDCl3) δ 7.37–7.31 (m, 4H), 7.28–7.24 (m, 1H), 6.71 (d, J = 8.8 Hz, 1H), 6.67 (dd, J = 8.9, 2.9 Hz, 1H), 6.61 (d, J = 2.9, 1H), 5.68 (ddd, J = 17.1, 10.1, 8.9 Hz, 1H), 5.35 (d, J = 10.1 Hz, 1H), 5.21 (dd, J = 17.1, 2.2 Hz, 1H), 5.18 (q, J = 6.5 Hz, 1H), 4.12 (d, J = 11.4 Hz, 1H), 3.83 (d, J = 11.4 Hz, 1H), 3.29 (d, J = 9.0 Hz, 1H), 1.61 (d, J = 6.5 Hz, 3H), 1.37 (s, 3H); 13C NMR (101 MHz, CDCl3) δ 152.4, 147.0, 143.5, 135.7, 128.7, 127.6, 125.9, 122.3, 120.7, 117.2, 117.0, 116.2, 76.8, 70.8, 58.9, 51.1, 24.5, 20.8; IR (NaCl, thin film, cm–1) 3081, 3031, 2976, 2928, 2874, 2110, 1491, 1451, 1425, 1372, 1274, 1256, 1220, 1179, 1068, 1052, 1013, 928, 807, 760, 700, 641; HRMS (ESI-TOF) m/z calcd for C20H21N3O2Na+ (M + Na)+ 358.1526, found 358.1535.

(3S,4S)-10q

A variation of general procedure 2 was performed, with (R)-1-phenylethanol used instead of o-methoxy benzyl alcohol. The product was isolated in 61% yield (16 mg) as a clear oil: 1H NMR (400 MHz,CDCl3) δ 7.38–7.30 (m, 4H), 7.26 (d, J = 6.7 Hz, 1H), 6.74–6.64 (m, 2H), 6.60 (d, J = 2.6 Hz, 1H), 5.79 (ddd, J = 17.0, 10.1, 9.0 Hz, 1H), 5.41 (dd, J = 10.1, 1.8 Hz, 1H), 5.27–5.09 (m, 2H), 4.12 (d, J = 11.4 Hz, 1H), 3.82 (d, J = 11.4 Hz, 1H), 3.26 (d, J = 9.0 Hz, 1H), 1.60 (d, J = 6.5 Hz, 3H), 1.36 (s, 3H); 13C NMR (126 MHz, CDCl3) δ 152.3, 146.9, 143.4, 135.6, 128.6, 127.4, 125.7, 122.1, 120.6, 116.9, 116.8, 116.4, 76.8, 70.7, 58.7, 50.9, 24.3, 20.7; IR: 3067, 3032, 2978, 2929, 2876, 2109, 1637, 1612, 1492, 1452, 1422, 1491, 1257, 1220, 1180, 1068, 1054, 760, 700, 630; HRMS (ESI-TOF) m/z calcd for C20H21N3O2Na+ (M + Na)+ 358.1526, found 358.1535.

(3R,4R)-10o

To a vial charged with alcohol (3R,4R)-9 (30 mg, 0.13 mmol) were sequentially added 3 Å molecular sieve beads (200 mg), PhB(OH)2 (32 mg, 0.26 mmol), Cu(OAc)2 (24 mg, 0.13 mmol), DCM (1.3 mL), and TEA (91 μL, 0.65 mmol). The vial was then sealed and allowed to stir under air. After 18 h, the resulting solution was then transferred using DCM directly onto a column load cartridge. Final purification by column chromatography (0–20% gradient EtOAc in hexane) afforded (3R,4R)-10o (30 mg, 0.10 mmol, 75%) as a clear oil. 1H NMR (500 MHz, CDCl3) δ 7.37–7.33 (m, 1H), 7.32–7.28 (m, 1H), 7.05 (tt, J = 7.2, 1.1 Hz, 1H), 6.96–6.90 (m, 2H), 6.86–6.85 (m, 2H), 6.83–6.81 (m, 1H), 5.81 (ddd, J = 17.0, 10.1, 9.0 Hz, 1H), 5.41 (dd, J = 10.1, 1.7 Hz, 1H), 5.25 (ddd, J = 17.0, 1.6, 0.7 Hz, 1H), 4.21 (d, J = 11.5 Hz, 1H), 3.92 (dd, J = 11.5, 0.8 Hz, 1H), 3.37 (br d, J = 8.9 Hz, 1H), 1.41 (s, 3H); 13C NMR (126 MHz, CDCl3) δ 158.5, 150.4, 149.3, 135.3, 129.9, 129.8, 123.0, 122.6, 121.3, 120.9, 120.1, 117.7, 71.0, 58.8, 51.0, 20.8; IR (NaCl, thin film, cm–1) 2968, 2926, 2877, 2111, 1590, 1487, 1457, 1252, 1217, 1173, 1052, 691; HRMS (ESI-TOF) m/z calcd for C18H17N3O2Na+ (M + Na)+ 330.1213, found 330.1220.

General Procedure 3: Pyrrolidine Synthesis

Example given for R = H. Compound (3R,4R)-3a: In a glovebox, a 4 mL vial was charged with HBCy2 (121 mg, 0.68 mmol). The vial was sealed with a septa cap and removed from the glovebox. The vial was then placed in an ice bath and charged with DCM (0.5 mL). A solution of azide (3R,4R)-10a in DCM (104 mg, 0.34 mmol, 0.2 M) was added and rinsed with additional DCM (0.2 mL). After 5 min, the ice bath was removed and the solution was allowed to gradually warm to room temperature. After 18 h, the reaction was quenched by the addition of solid sodium fluoride (270 mg, 6.8 mmol) and water (61 μL, 3.4 mmol). After 1 h, the solution was filtered through a short plug of silica gel, rinsed (2% NEt3 in DCM), and the filtrate was concentrated under reduced pressure. Final purification by column chromatography (0 to 70% gradient, iPrOH in 99:1 hexane:NEt3) afforded pyrrolidine (3R,4R)-3a (72 mg, 0.26 mmol, 76%) as a clear oil: 1H NMR (400 MHz, CDCl3) δ 7.46–7.37 (m, 4H), 7.36–7.31 (m, 1H), 6.84–6.79 (m, 1H), 6.79–6.74 (m, 2H), 5.01 (s, 2H), 3.76 (d, J = 10.9 Hz, 1H), 3.69 (d, J = 10.9 Hz, 1H), 3.09 (dt, J = 10.5, 7.6 Hz, 1H), 3.00 (ddd, J = 10.6, 7.9, 4.7 Hz, 1H), 2.88 (t, J = 7.7 Hz, 1H), 2.47 (dtd, J = 12.6, 7.8, 4.7 Hz, 1H), 2.04 (br s, 1H), 1.86 (dq, J = 12.8, 7.7 Hz, 1H), 1.25 (s, 3H); 13C NMR (101 MHz, CDCl3) δ 153.5, 148.1, 137.4, 128.7, 128.1, 127.7, 127.2, 117.6, 116.0, 114.2, 71.8, 70.8, 58.4, 45.9, 44.8, 36.1, 24.5; IR (NaCl, thin film, cm–1) 3360, 2960, 2927, 2869, 1660, 1612, 1495, 1454, 1379, 1267, 1210, 1027, 817, 735, 697; HRMS (ESI-TOF) m/z calcd for C19H21NO2+ (M + H)+ 296.1645, found 296.1635; HPLC purity (percent peak area, 220 nm) 99.5%.

(3S,4S)-3a

General procedure 3 was used and the compound was isolated in 68% (8.5 mg) as a white solid. The compound provided an identical 1H NMR spectrum as (3R,4R)-3a: HPLC purity (percent peak area, 220 nm) 99.0%.

(3R,4R)-3b

General procedure 3 was used and the product was isolated in 54% (10 mg) as a white solid: 1H NMR (500 MHz, CDCl3) δ 7.65 (d, J = 8.0 Hz, 2H), 7.55 (d, J = 8.0 Hz, 2H), 6.82 (d, J = 8.4 Hz, 1H), 6.77–6.73 (m, 2H), 5.07 (s, 2H), 3.80 (d, J = 10.9 Hz, 1H), 3.72 (d, J = 11.0 Hz, 1H), 3.13 (dt, J = 10.8, 7.6 Hz, 1H), 3.02 (ddd, J = 10.9, 7.8, 4.8 Hz, 2H), 2.91 (t, J = 7.7 Hz, 1H), 2.49 (dtd, J = 12.7, 7.8, 4.8 Hz, 1H), 1.87 (dq, J = 12.6, 7.5 Hz, 1H), 1.28 (s, 3H); 13C NMR (126 MHz, CDCl3) δ 153.1, 148.4, 141.5, 130.8–129.8 (m), 127.6, 127.1, 125.7 (q, JC–F = 3.8 Hz), 127.6–121.4 (m), 117.9, 115.9, 114.3, 71.6, 70.0, 58.7, 45.9, 44.7, 35.9, 24.2; 19F NMR (471 MHz, CDCl3) δ −62.55; IR (NaCl, thin film, cm–1) 3340, 2962, 2873, 1621, 1496, 1326, 1209, 1164, 1124, 1066, 1018, 824; HRMS (ESI-TOF) m/z calcd for C20H21F3NO2+ (M + H)+ 364.1519, found 364.1528; HPLC purity (percent peak area, 220 nm) 94.2%.

(3S,4S)-3b

General procedure 3 was used and the compound was isolated in 55% (9.4 mg) as a white solid. The compound provided an identical 1H NMR spectrum as (3R,4R)-3b: HPLC purity (percent peak area, 220 nm) 99.1%.

(3R,4R)-3c

General procedure 3 was used and the product was isolated in 65% (14 mg) as a clear oil: 1H NMR (500 MHz, CDCl3) δ 7.71 (s, 1H), 7.62 (d, J = 7.6 Hz, 1H), 7.59 (d, J = 7.8 Hz, 1H), 7.51 (t, J = 7.7 Hz, 1H), 6.82 (dd, J = 7.7, 1.7 Hz, 1H), 6.79–6.75 (m, 2H), 5.06 (s, 2H), 3.78 (d, J = 11.0 Hz, 1H), 3.71 (d, J = 10.9 Hz, 1H), 3.11 (dt, J = 10.7, 7.5 Hz, 1H), 3.01 (ddd, J = 10.7, 7.9, 4.7 Hz, 1H), 2.90 (t, J = 7.7 Hz, 1H), 2.65 (br s, 1H), 2.49 (dtd, J = 12.7, 7.8, 4.7 Hz, 1H), 1.87 (dq, J = 12.9, 7.6 Hz, 1H), 1.26 (s, 3H); 13C NMR (126 MHz, CDCl3) δ 153.1, 148.4, 138.5, 131.1 (q, JC–F = 32.3 Hz), 130.83–130.78 (m), 129.2, 127.2, 124.9 (q, JC–F = 3.8 Hz), 124.3 (q, JC–F = 3.9 Hz), 127.3–120.9 (m), 117.8, 116.0, 114.3, 71.7, 70.1, 58.5, 45.9, 44.7, 36.0, 24.3; 19F NMR (471 MHz, CDCl3) δ −62.64; IR (NaCl, thin film, cm–1) 3321, 2962, 2871, 1612, 1496, 1331, 1210, 1164, 1124, 1073, 1041, 801, 701; HRMS (ESI-TOF) m/z calcd for C20H21F3NO2+ (M + H)+ 364.1519, found 364.1527; HPLC purity (percent peak area, 220 nm) 96.4%.

(3S,4S)-3c

General procedure 3 was used and the compound was isolated in 65% (14 mg) as a clear oil. The compound provided an identical 1H NMR spectrum as (3R,4R)-3c: HPLC purity (percent peak area, 220 nm) 96.6%.

(3R,4R)-3d

General procedure 3 was used and the product was isolated in 45% (11 mg) as a clear oil: 1H NMR (400 MHz, CDCl3) δ 7.77 (d, J = 7.8 Hz, 1H), 7.70 (d, J = 7.8 Hz, 1H), 7.58 (t, J = 7.6 Hz, 1H), 7.42 (t, J = 7.6 Hz, 1H), 6.84–6.79 (m, 1H), 6.79–6.73 (m, 2H), 5.22 (s, 2H), 3.75 (d, J = 10.9 Hz, 1H), 3.69 (d, J = 10.9 Hz, 1H), 3.09 (dt, J = 10.6, 7.6 Hz, 1H), 3.00 (ddd, J = 10.6, 7.8, 4.6 Hz, 1H), 2.88 (t, J = 7.7 Hz, 1H), 2.47 (dtd, J = 12.6, 7.8, 4.6 Hz, 1H), 1.91 (br s, 1H), 1.85 (dq, J = 12.7, 7.7 Hz, 1H), 1.24 (s, 3H); 13C NMR (126 MHz, CDCl3) δ 153.0, 148.4, 136.2, 132.3, 128.9, 127.8, 127.9–127.0 (m), 127.4, 126.0 (q, JC–F = 5.7 Hz), 127.4–121.0 (m), 117.8, 115.9, 114.4, 71.9, 66.9 (q, JC–F = 3.2 Hz), 58.3, 45.9, 44.8, 36.1, 24.5; 19F NMR (376 MHz, CDCl3) δ −60.28; IR (NaCl, thin film, cm–1) 3298, 2963, 2875, 1496, 1456, 1315, 1212, 1167, 1119, 1050, 1035, 768; HRMS (ESI-TOF) m/z calcd for C20H21F3NO2 (M + H)+ 364.1519, found 364.1524; HPLC purity (percent peak area, 220 nm) 97.1%.

(3S,4S)-3d

General procedure 3 was used and the compound was isolated in 37% (8.4 mg) as a clear oil. The compound provided an identical 1H NMR spectrum as (3R,4R)-3d: HPLC purity (percent peak area, 220 nm) 91.9%.

(3R,4R)-3e

General procedure 3 was used and the product was isolated in 50% (7 mg) as a white solid: 1H NMR (500 MHz, CDCl3) δ 7.36 (s, 4H), 6.81 (d, J = 8.5 Hz, 1H), 6.77–6.72 (m, 2H), 4.97 (s, 2H), 3.78 (d, J = 10.9 Hz, 1H), 3.70 (d, J = 10.9 Hz, 1H), 3.11 (dt, J = 10.8, 7.5 Hz, 1H), 3.01 (ddd, J = 10.9, 8.0, 4.7 Hz, 1H), 2.89 (t, J = 7.7 Hz, 1H), 2.48 (dtd, J = 12.6, 7.8, 4.7 Hz, 1H), 2.11 (br s, 1H), 1.87 (dq, J = 12.8, 7.6 Hz, 1H), 1.26 (s, 3H); 13C NMR (126 MHz, CDCl3) δ 153.3, 148.3, 135.9, 133.9, 129.0, 128.9, 127.2, 117.8, 116.0, 114.3, 71.7, 70.1, 58.6, 45.9, 44.8, 36.0, 24.3; IR (NaCl, thin film, cm–1) 3331, 2962, 2926, 2869, 1496, 1461, 1377, 1266, 1210, 1091, 1047, 1014, 811, 634; HRMS (ESI-TOF) m/z calcd for C19H21ClNO2+ (M + H)+ 330.1255, found 330.1254; HPLC purity (percent peak area, 220 nm) 95.3%.

(3S,4S)-3e

General procedure 3 was used and the compound was isolated in 54% (9.0 mg) as a waxy solid. The compound provided an identical 1H NMR spectrum as (3R,4R)-3e: HPLC purity (percent peak area, 220 nm) 97.2%.

(3R,4R)-3f

General procedure 3 was used and the product was isolated in 50% (7 mg) as a clear oil: 1H NMR (500 MHz, CDCl3) δ 7.45–7.42 (m, 1H), 7.32–7.29 (m, 3H), 6.84–6.79 (m, 1H), 6.77–6.71 (m, 2H), 4.98 (s, 2H), 3.76 (d, J = 10.8 Hz, 1H), 3.70 (d, J = 10.8 Hz, 1H), 3.10 (dt, J = 10.5, 7.5 Hz, 1H), 3.00 (ddd, J = 10.6, 7.9, 4.7 Hz, 1H), 2.88 (t, J = 7.7 Hz, 1H), 2.48 (dtd, J = 12.6, 7.8, 4.7 Hz, 1H), 2.26 (br s, 1H), 1.86 (dq, J = 12.8, 7.7 Hz, 1H), 1.25 (s, 3H); 13C NMR (126 MHz, CDCl3) δ 153.2, 148.4, 139.6, 134.7, 130.0, 128.2, 127.6, 127.3, 125.6, 117.8, 116.1, 114.3, 71.8, 70.0, 58.4, 46.0, 44.8, 36.1, 24.4; IR (NaCl, thin film, cm–1) 3341, 2963, 2872, 1600, 1576, 1496, 1430, 1377, 1266, 1210, 1042, 780, 682; HRMS (ESI-TOF) m/z calcd for C19H21ClNO2+ (M + H)+ 330.1255, found 330.1264; HPLC purity (percent peak area, 220 nm) 97.3%.

(3S,4S)-3f

General procedure 3 was used and the compound was isolated in 53% (11 mg) as a clear oil. The compound provided an identical 1H NMR spectrum as (3R,4R)-3f: HPLC purity (percent peak area, 220 nm) 96.2%.

(3R,4R)-3g

General procedure 3 was used and the product was isolated in 73% (16 mg) as a clear oil: 1H NMR (500 MHz, CDCl3) δ 7.57 (dd, J = 7.2, 2.0 Hz, 1H), 7.40 (dd, J = 7.6, 1.7 Hz, 1H), 7.30 (td, J = 7.4, 1.7 Hz, 1H), 7.30–7.23 (m, 1H), 6.85–6.79 (m, 1H), 6.79–6.75 (m, 2H), 5.11 (s, 2H), 3.76 (d, J = 10.9 Hz, 1H), 3.70 (dd, J = 11.0, 0.8 Hz, 1H), 3.10 (dt, J = 10.6, 7.6 Hz, 1H), 3.00 (ddd, J = 10.6, 7.9, 4.6 Hz, 1H), 2.89 (br t, J = 7.7 Hz, 1H), 2.48 (dtd, J = 12.5, 7.8, 4.6 Hz, 1H), 1.87 (dq, J = 12.7, 7.7 Hz, 2H), 1.25 (s, 3H); 13C NMR (126 MHz, CDCl3) δ 153.2, 148.3, 135.2, 132.8, 129.5, 129.11, 129.07, 127.3, 127.1, 117.7, 116.0, 114.4, 71.9, 68.0, 58.4, 46.0, 44.9, 36.2, 24.5; IR (NaCl, thin film, cm–1) 3327, 2962, 2923, 2871, 1612, 1495, 1444, 1378, 1267, 1212, 1151, 1035, 817, 749; HRMS (ESI-TOF) m/z calcd for C19H21ClNO2+ (M + H)+ 330.1255, found 330.1258; HPLC purity (percent peak area, 220 nm) 96.5%.

(3S,4S)-3g

General procedure 3 was used and the compound was isolated in 43% (10 mg) as a clear oil. The compound provided an identical 1H NMR spectrum as (3R,4R)-3g: HPLC purity (percent peak area, 220 nm) 96.2%.

(3S,4S)-3h

General procedure 3 was used and the product was isolated in 58% (10 mg) as a white solid: 1H NMR (500 MHz, CDCl3) δ 7.35 (d, J = 8.4 Hz, 2H), 6.92 (d, J = 8.6 Hz, 2H), 6.80 (d, J = 9.0 Hz, 1H), 6.78–6.74 (m, 2H), 4.93 (s, 2H), 3.83 (s, 3H), 3.75 (d, J = 10.9 Hz, 1H), 3.69 (d, J = 10.8 Hz, 1H), 3.09 (dt, J = 10.7, 7.6 Hz, 1H), 3.00 (ddd, J = 10.6, 9.4, 4.6 Hz, 1H), 2.88 (t, J = 7.7 Hz, 1H), 2.47 (dtd, J = 12.5, 7.8, 4.7 Hz, 1H), 1.93 (br s, 1H), 1.86 (dq, J = 12.6, 7.6 Hz, 1H), 1.24 (s, 3H); 13C NMR (126 MHz, CDCl3) δ 159.6, 153.56148.1, 129.5, 129.4, 127.2, 117.6, 116.0, 114.3, 114.2, 71.9, 70.6, 58.4, 55.5, 46.0, 44.9, 36.2, 24.5; IR (NaCl, thin film, cm–1) 3357, 2959, 2928, 2868, 1612, 1514, 1495, 1466, 1248, 1209, 1173, 1031, 823, 729; HRMS (ESI-TOF) m/z calcd for C20H24NO3+ (M + H)+ 326.1751, found 326.1762; HPLC purity (percent peak area, 220 nm) 97.5%.

(3R,4R)-3h

General procedure 3 was used and the compound was isolated in 59% (8.3 mg) as a white solid. The compound provided an identical 1H NMR spectrum as (3S,4S)-3h: HPLC purity (percent peak area, 220 nm) 96.5%.

(3S,4S)-3i

General procedure 3 was used and the product was isolated in 48% (10 mg) as a clear oil: 1H NMR (500 MHz, CDCl3) δ 7.30 (t, J = 7.9 Hz, 1H), 7.03–6.98 (m, 2H), 6.87 (dd, J = 8.3, 2.6 Hz, 1H), 6.81 (d, J = 9.8 Hz, 1H), 6.78–6.73 (m, 2H), 4.99 (s, 2H), 3.83 (s, 3H), 3.76 (d, J = 10.9 Hz, 1H), 3.69 (d, J = 10.9 Hz, 1H), 3.09 (dt, J = 10.6, 7.6 Hz, 1H), 3.00 (ddd, J = 10.6, 7.9, 4.7 Hz, 1H), 2.88 (t, J = 7.7 Hz, 1H), 2.47 (dtd, J = 12.6, 7.8, 4.7 Hz, 1H), 2.08 (br s, 1H), 1.86 (dq, J = 12.7, 7.7 Hz, 1H), 1.24 (s, 3H); 13C NMR (126 MHz, CDCl3) δ 160.0, 153.5, 148.2, 139.0, 129.8, 127.2, 119.9, 117.7, 116.0, 114.2, 113.6, 113.1, 71.8, 70.7, 58.4, 55.4, 45.9, 44.8, 36.1, 24.5; IR (NaCl, thin film cm–1) 3362, 2959, 2925, 2870, 1602, 1587, 1495, 1462, 1377, 1267, 1209, 1154, 1037, 777, 693; HRMS (ESI-TOF) m/z calcd for C20H24NO3+ (M + H)+ 326.1751, found 326.1763; HPLC purity (percent peak area, 220 nm) 98.5%.

(3R,4R)-3i

General procedure 3 was used and the compound was isolated in 68% (12 mg) as a clear oil. The compound provided an identical 1H NMR spectrum as (3S,4S)-3i: HPLC purity (percent peak area, 220 nm) 98.5%.

(3S,4S)-3j

General procedure 3 was used and the product was isolated in 71% (10 mg) as a clear glassy oil: 1H NMR (500 MHz, CDCl3) δ 7.47 (dd, J = 7.5, 1.7 Hz, 1H), 7.30 (td, J = 7.9, 1.7 Hz, 1H), 6.99 (t, J = 7.4 Hz, 1H), 6.92 (d, J = 8.2 Hz, 1H), 6.82–6.77 (m, 3H), 5.06 (s, 2H), 3.87 (s, 3H), 3.77 (d, J = 10.9 Hz, 1H), 3.70 (d, J = 10.9 Hz, 1H), 3.10 (dt, J = 10.7, 7.6 Hz, 1H), 3.01 (ddd, J = 10.6, 7.9, 4.8 Hz, 1H), 2.89 (t, J = 7.7 Hz, 1H), 2.48 (dtd, J = 12.7, 7.8, 4.7 Hz, 1H), 2.16 (br s, 1H), 1.88 (dq, J = 12.6, 7.6 Hz, 1H), 1.25 (s, 3H); 13C NMR (126 MHz, CDCl3) δ 157.0, 153.7, 148.0, 129.1, 128.9, 127.1, 125.8, 120.8, 117.6, 115.9, 114.4, 110.5, 71.8, 65.8, 58.5, 55.6, 46.0, 44.8, 36.1, 24.4; IR (NaCl, thin film cm–1) 3349, 2960, 2925, 2872, 1604, 1590, 1495, 1463, 1379, 1244, 1210, 1047, 1030, 814, 754; HRMS (ESI-TOF) m/z calcd for C20H24NO3+ (M + H)+ 326.1751, found 326.1762; HPLC purity (percent peak area, 220 nm) 96.7%.

(3R,4R)-3j

General procedure 3 was used and the compound was isolated in 74% (12 mg) as a clear glassy oil. The compound provided an identical 1H NMR spectrum as (3S,4S)-3j: HPLC purity (percent peak area, 220 nm) 98.8%.

(3S,4S)-3k

General procedure 3 was used and the product was isolated in 53% (12 mg) as a yellow solid: 1H NMR (500 MHz, CDCl3) δ 8.08 (d, J = 8.0 Hz, 1H), 7.91 (d, J = 7.8 Hz, 1H), 7.87 (d, J = 8.2 Hz, 1H), 7.60 (d, J = 7.0 Hz, 1H), 7.58–7.51 (m, 2H), 7.48 (t, J = 7.6 Hz, 1H), 6.88–6.82 (m, 3H), 5.44 (s, 2H), 3.78 (d, J = 10.9 Hz, 1H), 3.71 (d, J = 10.9 Hz, 1H), 3.10 (dt, J = 11.0, 7.6 Hz, 1H), 3.01 (ddd, J = 10.7, 9.4, 4.8 Hz, 1H), 2.89 (t, J = 7.7 Hz, 1H), 2.48 (dtd, J = 12.4, 7.7, 4.5 Hz, 1H), 1.93 (br s, 1H), 1.88 (dq, J = 12.5, 7.7 Hz, 1H), 1.26 (s, 3H); 13C NMR (126 MHz, CDCl3) δ 153.6, 148.3, 134.0, 132.8, 131.8, 129.2, 128.3, 127.3, 126.8, 126.6, 126.1, 125.5, 124.0, 117.7, 116.1, 114.4, 71.9, 69.5, 58.4, 46.0, 44.9, 36.2, 24.5; IR (NaCl, thin film, cm–1) 3348, 3044, 2959, 2923, 2870, 1495, 1263, 1208, 1152, 1030, 792, 776, 731, 723; HRMS (ESI-TOF) m/z calcd for C23H24NO2+ (M + H)+ 346.1802, found 346.1798; HPLC purity (percent peak area, 220 nm) 97.9%.

(3R,4R)-3k

General procedure 3 was used and the compound was isolated in 56% (14 mg) as a yellow solid. The compound provided an identical 1H NMR spectrum as (3S,4S)-3k: HPLC purity (percent peak area, 220 nm) 97.7%.

(3S,4S)-3l

General procedure 3 was used and the product was isolated in 73% (15 mg) as a clear glassy oil: 1H NMR (500 MHz, CDCl3) δ 7.91–7.86 (m, 3H), 7.85 (d, J = 4.7 Hz, 1H), 7.55 (d, J = 8.4 Hz, 1H), 7.52–7.47 (m, 2H), 6.85–6.79 (m, 3H), 5.18 (s, 2H), 3.79 (d, J = 10.9 Hz, 1H), 3.71 (d, J = 10.9 Hz, 1H), 3.11 (dt, J = 10.6, 7.5 Hz, 1H), 3.01 (ddd, J = 10.8, 7.9, 4.8 Hz, 1H), 2.90 (t, J = 7.7 Hz, 1H), 2.52 (br s, 1H), 2.48 (dtd, J = 12.7, 7.8, 4.9 Hz, 1H), 1.87 (dq, J = 12.4, 7.6 Hz, 1H), 1.27 (s, 3H); 13C NMR (126 MHz, CDCl3) δ 153.6, 148.2, 134.9, 133.5, 133.2, 128.5, 128.1, 127.9, 127.1, 126.5, 126.4, 126.2, 125.5, 117.7, 116.1, 114.4, 71.7, 71.0, 58.6, 45.9, 44.8, 36.0, 24.3; IR (NaCl, thin film, cm–1) 3341, 3053, 2961, 2924, 2870, 1611, 1493, 1466, 1427, 1377, 1267, 1210, 1153, 1032, 855, 817, 738; HRMS (ESI-TOF) m/z calcd for C23H24NO2+ (M + H)+ 346.1802, found 346.1806; HPLC purity (percent peak area, 220 nm) 96.4%.

(3R,4R)-3l

General procedure 3 was used and the compound was isolated in 79% (15 mg) as a clear glassy oil. The compound provided an identical 1H NMR spectrum as (3S,4S)-3l: HPLC purity (percent peak area, 220 nm) 97.9%.

(3S,4S)-3m

General procedure 3 was used and the product was isolated in 66% yield (9 mg) as a white solid: 1H NMR (400 MHz, CDCl3) δ 6.79 (dd, J = 6.3, 2.4 Hz, 1H), 6.73–6.66 (m, 2H), 3.77–3.73 (m, 3H), 3.68 (dd, J = 10.8, 0.8 Hz, 1H), 3.09 (dt, J = 10.2, 7.8 Hz, 1H), 3.00 (ddd, J = 10.4, 9.6, 4.7 Hz, 1H), 2.87 (br t, J = 7.7 Hz, 1H), 2.48 (dtd, J = 12.6, 7.7, 4.7 Hz, 1H), 1.94 (br s, 1H), 1.87 (dq, J = 12.7, 7.7 Hz, 1H), 1.32–1.17 (m, 1H), 1.24 (s, 3H), 0.68–0.56 (m, 2H), 0.34 (dt, J = 6.2, 4.6 Hz, 2H); 13C NMR (101 MHz, CDCl3) δ 153.5, 147.7, 127.0, 117.4, 115.5, 113.8, 73.4, 71.6, 58.3, 45.8, 44.7, 36.0, 24.3, 10.4, 3.2; IR (NaCl, thin film, cm–1) 3353, 3080, 2961, 2918, 2871, 1611, 1497, 1469, 1267, 1209, 1034; HRMS (ESI-TOF) m/z calcd for C16H22NO2+ (M + H)+ 260.1645, found 260.1648; HPLC purity (percent peak area, 220 nm) 95.9%.

(3R,4R)-3m

General procedure 3 was used and the compound was isolated in 68% (9.2 mg) as a white solid. The compound provided an identical 1H NMR spectrum as (3S,4S)-3m: HPLC purity (percent peak area, 220 nm) 96.9%.

(3R,4R)-3n

General procedure 3 was used and the product was isolated in 69% (8.2 mg) as a clear oil: 1H NMR (500 MHz, CDCl3) δ 6.79 (d, J = 8.5 Hz, 1H), 6.70–6.64 (m, 2H), 3.75 (d, J = 10.9 Hz, 1H), 3.70–3.66 (m, 3H), 3.09 (dt, J = 10.7, 7.6 Hz, 1H), 3.00 (ddd, J = 10.6, 7.9, 4.7 Hz, 1H), 2.87 (t, J = 7.7 Hz, 1H), 2.48 (dtd, J = 12.6, 7.7, 4.6 Hz, 1H), 1.93–1.83 (m, 4H), 1.80–1.68 (m, 4H), 1.36–1.16 (m, 3H), 1.24 (s, 3H), 1.04 (qd, J = 12.2, 3.4 Hz, 2H); 13C NMR (126 MHz, CDCl3) δ 154.0, 147.7, 127.1, 117.6, 115.4, 113.9, 74.3, 71.9, 58.4, 46.0, 44.9, 38.0, 36.2, 30.15, 30.13, 26.7, 26.0, 24.5; IR (NaCl, thin film, cm–1) 3360, 2922, 2852, 1496, 1467, 1449, 1267, 1209, 1040; HRMS (ESI-TOF) m/z calcd for C19H28NO2+ (M + H)+ 302.2115, found 302.2115; HPLC purity (percent peak area, 220 nm) 99.3%.

(3S,4S)-3n

General procedure 3 was used and the compound was isolated in 68% (8.8 mg) as a clear oil. The compound provided an identical 1H NMR spectrum as (3R,4R)-3n: HPLC purity (percent peak area, 220 nm) 94.2%.

(3S,4S)-3o

General procedure 3 was used and the product was isolated in 76% yield (18 mg) as a clear oil: 1H NMR (500 MHz, CDCl3) δ 7.35–7.28 (m, 2H), 7.06 (td, J = 7.3, 1.2 Hz, 1H), 6.99–6.94 (m, 2H), 6.90–6.83 (m, 2H), 6.80 (dd, J = 8.7, 2.9 Hz, 1H), 3.79 (d, J = 10.9 Hz, 1H), 3.74 (d, J = 11.0 Hz, 1H), 3.10 (dt, J = 10.6, 7.6 Hz, 1H), 3.01 (ddd, J = 10.6, 7.9, 4.6 Hz, 1H), 2.88 (t, J = 7.8 Hz, 1H), 2.45 (dtd, J = 12.6, 7.8, 4.7 Hz, 1H), 2.13 (br s, 1H), 1.86 (dq, J = 12.7, 7.7 Hz, 1H), 1.26 (s, 3H); 13C NMR (126 MHz, CDCl3) δ 158.3, 150.6, 149.9, 129.6, 127.4, 122.5, 120.7, 118.8, 117.9, 117.7, 71.6, 58.1, 45.6, 44.6, 35.9, 24.2; IR (NaCl, thin film, cm–1) 3348, 3039, 2963, 2929, 2870, 1591, 1486, 1257, 1212, 1166, 1025, 820, 754, 692; HRMS (ESI-TOF) m/z calcd for C18H20NO2+ (M + H)+ 282.1489, found 282.1483; HPLC purity (percent peak area, 220 nm) 97.7%.

(3R,4R)-3o

General procedure 3 was used and the compound was isolated in 99% (27 mg) as a clear oil. The compound provided an identical 1H NMR spectrum as (3S,4S)-3o: HPLC purity (percent peak area, 220 nm) 95.7%.

(3S,4S)-3p

General procedure 3 was used and the product was isolated in 79% (13 mg) as a clear oil: 1H NMR (500 MHz, CDCl3) δ 7.37–7.22 (m, 5H), 6.79 (d, J = 8.7 Hz, 1H), 6.74–6.63 (m, 2H), 4.13 (t, J = 7.2 Hz, 2H), 3.75 (d, J = 10.8 Hz, 1H), 3.68 (d, J = 10.9 Hz, 1H), 3.09 (t, J = 7.0 Hz, 3H), 3.03–2.97 (m, 1H), 2.86 (t, J = 7.7 Hz, 1H), 2.47 (dtd, J = 12.6, 7.7, 4.6 Hz, 1H), 1.91–1.81 (m, 2H), 1.24 (s, 3H); 13C NMR (126 MHz, CDCl3) δ 153.5, 148.0, 138.5, 129.2, 128.7, 127.2, 126.6, 117.7, 115.6, 114.1, 71.8, 69.5, 58.4, 46.0, 44.8, 36.2, 36.1, 24.5; IR (NaCl, thin film, cm–1) 3356, 3028, 2960, 2927, 2870, 1612, 1495, 1472, 1453, 1429, 1380, 1266, 1211, 1044, 816, 749, 700; HRMS (ESI-TOF) m/z calcd for C20H24NO2+ (M + H)+ 310.1802, found 310.1797; HPLC purity (percent peak area, 220 nm) 93.1%.

(3R,4R)-3p

General procedure 3 was used and the compound was isolated in 65% (10 mg) as a clear oil. The compound provided an identical 1H NMR spectrum as (3S,4S)-3p: HPLC purity (percent peak area, 220 nm) 91.8%.

(3R,4R)-3q

General procedure 3 was used and the product was isolated in 53% (13 mg) as a clear glassy oil: 1H NMR (500 MHz, CDCl3) δ 7.38 (t, J = 6.8 Hz, 3H), 7.34 (d, J = 7.6 Hz, 1H), 7.30–7.23 (m, 1H), 6.71 (d, J = 9.0 Hz, 1H), 6.66–6.61 (m, 2H), 5.19 (q, J = 6.5 Hz, 1H), 3.71 (d, J = 10.9 Hz, 1H), 3.65 (d, J = 10.9 Hz, 1H), 3.06 (dt, J = 10.6, 7.6 Hz, 1H), 2.97 (ddd, J = 10.5, 7.7, 4.6 Hz, 1H), 2.79 (t, J = 7.7 Hz, 1H), 2.43 (dtd, J = 12.6, 7.8, 4.7 Hz, 1H), 2.00 (br s, 1H), 1.82 (dq, J = 12.6, 7.6 Hz, 1H), 1.61 (d, J = 6.4 Hz, 3H), 1.20 (s, 3H); 13C NMR (126 MHz, CDCl3) δ 152.7, 148.0, 143.6, 128.8, 127.6, 127.1, 125.8, 117.5, 117.4, 115.4, 77.0, 71.8, 58.4, 45.8, 44.8, 36.1, 24.5, 24.4; IR (NaCl, thin film, cm–1) 3359, 3029, 2960, 2925, 2870, 1610, 1493, 1451, 1265, 1211, 1068, 1029, 699; HRMS (ESI-TOF) m/z calcd for C20H24NO2+ (M + H)+ 310.1802, found 310.1810; HPLC purity (percent peak area, 220 nm) 97.4%.

(3S,4S)-3q

General procedure 3 was used and the compound was isolated in 42% (7.5 mg) as a clear glassy oil. The compound provided an identical 1H NMR spectrum as (3R,4R)-3q: HPLC purity (percent peak area, 220 nm) 96.0%.

(3R,4R)-3r

General procedure 3 was used and the product was isolated in 64% (11 mg) as a clear glassy oil: 1H NMR (500 MHz, CDCl3) δ 7.39–7.31 (m, 4H), 7.28–7.22 (m, 1H), 6.73–6.67 (m, 1H), 6.66–6.59 (m, 2H), 5.20 (q, J = 6.4 Hz, 1H), 3.77 (d, J = 10.9 Hz, 1H), 3.69 (dd, J = 10.9, 0.8 Hz, 1H), 3.09 (dt, J = 10.7, 7.5 Hz, 1H), 2.97 (ddd, J = 10.8, 7.9, 5.1 Hz, 1H), 2.86 (br t, J = 7.5 Hz, 1H), 2.83 (br s, 1H), 2.38 (dtd, J = 12.9, 7.8, 5.0 Hz, 1H), 1.73 (dq, J = 12.9, 7.4 Hz, 1H), 1.62 (d, J = 6.5 Hz, 3H), 1.26 (s, 3H); 13C NMR (126 MHz, CDCl3) δ 152.6, 147.8, 143.5, 128.7, 127.6, 126.6, 125.8, 117.5, 117.2, 115.4, 76.8, 71.3, 59.1, 45.7, 44.7, 35.6, 24.5, 24.1; IR (NaCl, thin film, cm–1) 3367, 3028, 2970, 2928, 1612, 1493, 1451, 1265, 1210, 1070, 1029, 734, 700; HRMS (ESI-TOF) m/z calcd for C20H24NO2+ (M + H)+ 310.1802, found 310.1803; HPLC purity (percent peak area, 220 nm) 93.2%.

(3S,4S)-3r

General procedure 3 was used and the compound was isolated in 43% (7.7 mg) as a clear glassy oil. The compound provided an identical 1H NMR spectrum as (3R,4R)-3r: HPLC purity (percent peak area, 220 nm) 94.0%.

Acknowledgments

The National Institute of Mental Health’s Psychoactive Drug Screening Program (NIMH-PDSP) is acknowledged for the determination of the Ki values in this paper. The PDSP is directed by Bryan L. Roth, MD, PhD, the University of North Carolina at Chapel Hill and Project Officer Jamie Driscoll at NIMH, Bethesda, MD. For more details on the PDSP, as well as experimental details on binding assays, see the PDSP website at https://pdsp.unc.edu/pdspweb/. N.V. acknowledges support from the UMN NSF-LANDO undergraduate research program (supported by the National Science Foundation under Grant CHE-1851990).

Glossary

Abbreviations

PDSP

Psychoactive Drug Screening Program

(+)-PTZ

(+)-pentazocine

DR

diabetic retinopathy

tBHP

tert-butyl hydroperoxide

ROS

reactive oxygen species

PAMPA

parallel artificial membrane permeability assay

Supporting Information Available

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.0c05117.

  • Crystallographic data for compound (3R,4R)-3e (CIF)

  • Crystallographic data for compound (3R,4R)-10r (CIF)

  • PAMPA Assay Data (XLSX)

  • Solubility Assay Data (XLSX)

  • Experimental procedures, characterization data, and additional assay data (PDF)

Author Contributions

The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. M.R.P., S.M., and N.V. are responsible for the chemical synthesis and characterization of new ligands. H.X. conducted assays with 661W cells.

This research was supported by the National Institute of General Medical Sciences of the National Institutes of Health under Award Number R35GM124718, the National Institutes of Health under award number R01EY028103, and the Foundation Fighting Blindness award number TA-NMT-0617-021-AUG.

The authors declare the following competing financial interest(s): M.R.P. and J.J.T. filed US patent No. 16/428,343, submitted 5/31/2019.

Notes

The authors declare the following competing financial interest(s): a provisional patent has been filed by the University of Minnesota on the substructure disclosed in this report; M.R.P. and J.J.T. filed US patent No. 16/428,343, submitted on 5/31/2019.

Supplementary Material

ao0c05117_si_001.cif (579.3KB, cif)
ao0c05117_si_002.cif (1MB, cif)
ao0c05117_si_003.xlsx (39KB, xlsx)
ao0c05117_si_004.xlsx (32.8KB, xlsx)
ao0c05117_si_005.pdf (14.1MB, pdf)

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Supplementary Materials

ao0c05117_si_001.cif (579.3KB, cif)
ao0c05117_si_002.cif (1MB, cif)
ao0c05117_si_003.xlsx (39KB, xlsx)
ao0c05117_si_004.xlsx (32.8KB, xlsx)
ao0c05117_si_005.pdf (14.1MB, pdf)

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