An efficient approach to asymmetric synthesis of dipeptide β-turn mimetics: Indolizidinone amino acids

Azabicyclo[X.Y.0] alkane amino acids are rigid dipeptide β-turn mimetics with great potential applications for drug discovery. The lack of efficient methods to synthesize these compounds is a major bottleneck in this field. Herein we report an efficient approach to the enantiopure synthesis of (3S,6S,9S) and (3R,6R,9R) methyl 2-oxo-3-[N-(Boc/Cbz)amino]-1-azabicyclo[4.3.0]nonane-9-carboxylates 1. In this approach, the key intermediates 5a and 5b with different stereochemical configurations were efficiently constructed from the same precursor in high stereoselectivity via asymmetric hydrogenations using (S,S) or (R,R) Et-DUPHOS, Rh(I)-based catalysts. The process, starting from inexpensive diethyl 1,3-acetonedicarboxylate 2, can allow for the practical synthesis of this class of compounds.