Synthetic small molecule GLP-1 secretagogues prepared by means of a three-component indole annulation strategy

Rational assembly of small molecule libraries for purposes of drug discovery requires an efficient approach in which the synthesis of bioactive compounds is enabled so that numerous structurally related compounds of a similar basic formulation can be derived. Here, we describe (4 + 3) and (3 + 2) indole annulation strategies that quickly generate complex indole heterocycle libraries that contain novel cyclohepta- and cyclopenta[b]indoles, respectively. Screening of one such library comprised of these indoles identifies JWU-A021 to be an especially potent stimulator of glucagon-like peptide-1 (GLP-1) secretion in vitro. Surprisingly, JWU-A021 is also a potent stimulator of Ca2+ influx through TRPA1 cation channels (EC50 ca. 200 nM), thereby explaining its ability to stimulate GLP-1 release. Of additional importance, the available evidence indicates that JWU-A021 is one of the most potent non-electrophilic TRPA-1 channel agonists yet to be reported in the literature.


S1
General Information 1 H NMR data were recorded on a Bruker Avance III 500 MHz spectrometer (TBI probe) and Bruker Avance III 600 MHz (BBFO probe) with calibration spectra to CHCl3 (7.26 ppm) and CH2Cl2 (5.32 ppm) at ambient temperature. Multiplicities are indicated as s (singlet), d (doublet), t (triplet), and m (multiplet). 13 C NMR data were recorded at 125 MHz on Bruker Avance III 600 MHz spectrometer (BBFO probe) at ambient temperature and expressed in ppm using solvent as the internal standard CD2Cl2 (53.84 ppm) and CDCl3 (77.16 ppm). IR spectra were recorded on Jasco FT-IR 4100 Series spectrophotometer, vmax (cm -1 ) are partially reported. Analytical thin layer chromatography (TLC) was performed on SILICYCLE pre-coated TLC plates (silica gel 60 F-254, 0.25mm). Flush column chromatography was performed on silica gel 60 (SILICYCLE 230−400 mesh). Visualization was accomplished with UV light and ceric ammonium molybdate (CAM). High-resolution mass spectroscopy data were acquired from Mass Spectrometry Laboratory of the University of Illinois (Urbana-Champaign, IL).
All reactions were carried out in oven-dried glassware with magnetic stirring. Solvents were freshly distilled. All reagents and starting materials were purchased from commercial vendors and used without further purification.

General Procedure A for the Synthesis of Cyclohepta[b]indoles
A round-bottom flask was charged with indole (0.66 mmol, 1 equiv), aldehyde or ketone (1.32 mmol, 2 equiv), and diene (3.30 mmol, 5 equiv). Then, CH2Cl2 (2.0 mL) was added followed by GaBr3 (0.07 mmol, 0.1 equiv). The reaction was stirred at room temperature until it was complete as judged by thin layer chromatography. The volatiles were concentrated in vacuo and the residue was purified via silica gel flash chromatography (EtOAc/Hexanes) to yield the desired products.

General Procedure B for the Synthesis of Cyclopenta[b]indoles
A round-bottom flask was charged with indole (0.66 mmol, 1 equiv), aldehyde or ketone (1.32 mmol, 2 equiv), and styrene (3.30 mmol, 5 equiv). Then, dichloroethane (2.0 mL) was added followed by TfOH (0.13 mmol, 0.2 equiv). The reaction was stirred at room temperature until it was complete as judged by thin layer chromatography. The volatiles were concentrated in vacuo and the residue was purified via silica gel flash chromatography (EtOAc/Hexanes) to yield the desired products.

Characterization of Cyclohepta[b]indole products
The preparation of JWU-A001 through JWU-A021 were carried out as previously described. 1 All characterization data were identical to those previously reported. 1

FIG. S1
By following the general procedure A described above, JWU-A029 was prepared in 43%

FIG. S8
By following the general procedure B described above, a 1:1 diastereomeric mixture of

FIG. S9
By following the general procedure B described above, JWU-B014 was prepared in 25% SHELXL-97 5 , which are incorporated in OLEX2. 6 The structure was solved in the space group P2 1 (# 4). All non-hydrogen atoms are refined anisotropically. Hydrogens were calculated by geometrical methods and refined as a riding model. The Flack 7 parameter is used to determine chirality of the crystal studied, the value should be near zero, a value of one is the other enantiomer and a value of 0.5 is racemic. The Flack parameter was refined to -0.017(9), confirming the absolute stereochemistry. Determination of absolute structure using Bayesian statistics on Bijvoet differences using the program within Platon 8 also report that we have the correct enantiomer based on this comparison. 9 The crystal used for the diffraction study showed no decomposition during data collection. All drawings are done at 50% ellipsoids.

The following are 50% thermal ellipsoidal drawings of one molecule (c) in the asymmetric cell with various amount of labeling.
This is a drawing of the packing along the b-axis; hydrogen atoms have been omitted for clarity.