Herein we report the discovery of AM
Herein, we report the discovery of AM-3189 (). AM-3189 maintains the in vivo efficacy of AMG 837 while displaying a superior pharmacokinetic profile and minimal CNS exposure. As we reported previously, activity on the GPR40 receptor varies significantly with substitution at the β-carbon relative to the carboxylate. We hoped to modify the beta-substitution of AMG 837 in order to improve potency and desired physiochemical properties. The racemate of AMG 837 ( in the ) displayed the expected twofold decrease in potency on GPR40 compared to the active enantiomer AMG 837 and its activity crossed over to the rat and mouse forms of GPR40. Due to the lack of an efficient method for the asymmetric synthesis of β-substituted 2-phenylpropanoates at the time, racemic compounds were assayed for structure–activity relationship (SAR) studies and early screening purposes. Using the tail group from AMG 837 as a probe, the synthetic route for modification of the beta-substitutions of the carboxylic acids is shown in . Treatment of aldehydes with (4-((tetrahydro-2-pyran-2-yl)oxy)phenyl) magnesium bromide afforded secondary alcohols , which were oxidized by pyridinium chlorochromate (PCC) to yield ketones . The ketones were converted to α,β-unsaturated esters through Peterson-olefination followed by hydrogenation to afford beta-substituted 3-arylpropanoates . After removing the THP protecting group with TFA, the resulting para-substituted phenols were alkylated with 3-(bromomethyl)-4′-(trifluoromethyl)-1,1′-biphenyl in the presence of cesium carbonate to afford the esters , which were hydrolyzed under basic conditions to yield the desired carboxylic acids . Since GPR40 is a G-coupled GPCR, compounds were assayed for GPR40 activity in a chemiluminescent system (aequorin) monitoring calcium flux in CHO M871 transiently transfected with GPR40 as reported previously ()., In the later stage of the project, a CHO cell line stably transfected with human GPR40 was developed. GPR40 aequorin assay was then run in buffer containing 0.01% human serum albumin or in 100% human serum to test activity of compounds in the absence or presence of plasma proteins (). AMG 837 was included with all assays as a positive control and as a reference compound for benchmarking SAR. The SAR of the β-substituted 3-phenylpropanoate lead series with AMG 837 tail group is shown in . Activity on the GPR40 receptor varied significantly with substitution at the β-carbon of the carboxylate. Simple phenyl () reduces GPR40 potency 10-fold relative to the methyl acetylene compound (, racemate of AMG 837). Introducing a nitrogen to the phenyl ring in various positions does not restore the lost potency, thus pyridin-2-yl and pyridin-3-yl compounds (, ) are equally potent to the simple phenyl analog (), while the pyridin-4-yl compound () is slightly more potent. Five-membered ring heterocycles retain potency slightly more than the phenyl analogs, as evidenced by 2-thiophenyl () compared to the simple phenyl (). Replacing the thiophene ring with a thiazole ring or 2-methylimidazole ring also showed slightly improved potency ( vs. and ). In an attempt to quantify the likely improvement in the balance between physiochemical properties and potency, the lipophilic efficiency (LipE) of this set of compounds was calculated and shown in . was revealed to be the best of replacements in terms of lipophilic efficiency among the set shown in and it was comparable to that of (racemate of AMG 837). By incorporating both acidic and basic functional groups, analogs derived from should be less likely to penetrate the BBB. Therefore, the imidazole arylpropionate was used as the scaffold for the next set of compounds. In designing our analogs, emphasis was placed on increasing polarity and conformational rigidity. We had established in previous work that meta-biaryls yielded the most potent molecules so we excluded ortho- and para-biaryls from our designs. The synthesis of meta-biaryl analogs of is depicted in . Compound was synthesized as a racemic mixture, using the commercially available 1-methyl-1-imidazole-2-carbaldehyde with the procedure described in . The separated single enantiomer (compound ), which yielded more potent compounds, was advanced through the synthesis. The absolute configuration of the compound was later determined by comparison of experimental and calculated vibrational circular dichroism (VCD) spectra and optical rotations to be in the -configuration, which is consistent with the finding from the discovery of AMG 837. The enantiomerically pure material (ee>98%) was alkylated with substituted 3-bromobenzyl bromides or chlorides in the presence of cesium carbonate to afford ethers , which were converted to compounds using Suzuki cross coupling. The desired carboxylic acids were obtained by hydrolysis of esters under basic conditions. The ee value of compound was found to be preserved during these transformations as all final products had ee%>98%.