Shawn D. Walker,* Christopher J. Borths, Evan DiVirgilio, Liang Huang, Pingli Liu, Henry Morrison, Kiyoshi Sugi, Masahide Tanaka, Jacqueline C. S. Woo, and Margaret M. Faul
Org. Process Res. Dev., 2011, 15, 570–580
Summary: AMG 837 is a novel GPR40 receptor agonist developed at Amgen. The end game of the synthesis involved an alkylative coupling between (S)-3-(4-hydroxyphenyl)hex-4-ynoic acid (1) and 3-(bromomethyl)-4′-(trifluoromethyl)biphenyl (2). The chiral non-racemic acid (1) (bottom left) was prepared in 35% overall yield via a classical resolution utilizing the amino alcohol, (1S,2R)-1-amino-2-indanol . The racemic acid (1) was prepared by a telescoped sequence which included the conjugate 1,4-addition of the Grignard reagent (resulting in the installation of the alkyne moiety) to the Meldrum’s acid derived substrate. Additionally, the formation of (3) was monitored by react-IR. The biaryl bromide (2) was prepared in short order utilizing a 2-step sequence involving (i) Suzuki−Miyaura coupling and (ii) a benzylic bromination. Key to the success of the process was application of a chemoselective alkylation (of a phenol derivative) mediated by tetrabutylphosphonium hydroxide that provided AMG 837 via direct coupling of (1) and (2). Ultimately, the more stable crystalline hemicalcium salt dihydrate form was used as the final salt form. In summary, the synthesis of AMG 837 was developed into an efficient 9-step route furnishing the desired target molecule in 25% overall yield.