Enzymatic preparation of (S)-3-amino-3-(o-tolyl)propanoic acid, a key intermediate for the construction of Cathepsin inhibitors

Abstract

• ( S )-3-Amino-3-( o -tolyl)propanoic acid was prepared in high ee (>98%). • Burkholderia cepacia lipase catalysed enantioselectively ( E > 200) the acylation of N -hydroxymethylated β-lactam and hydrolysis of β-amino ester. • Ring cleavage of β-lactam by using Candida antarctica lipase B showed excellent E (>200). Enantiomerically pure ( S )-3-amino-3-( o -tolyl)propanoic acid [( S )- 6 ], identified as the preferred enantiomeric form for the construction of novel β-amino acid derivatives as inhibitors of Cathepsin, was prepared through both indirect and direct enzymatic strategies. Resolution of hydroxymethylated β-lactam (±)- 1 through Burkholderia cepacia lipase PSIM-catalysed R -selective butyrylation ( E > 200) was first carried out in t -BuOMe. Treatment of the unreacted ( S )-1 with 18% HCl then furnished the desired ( S )- 6 ·HCl. Next, Candida antarctica lipase B catalysed the ring cleavage of racemic 4-( o -tolyl)azetidin-2-one [(±)- 2 ] with excellent R enantioselectivity ( E > 200), either in t -BuOMe with added H 2 O as nucleophile or in H 2 O at 60 °C. Hydrolysis of the less reactive β-lactam enantiomer [( S )- 2 ] with 18% HCl afforded ( S )-6·HCl. A direct enzymatic route to enantiomeric ( S )- 6 was finally optimized through the lipase PSIM-catalysed S -enantioselective ( E > 200) hydrolysis of racemic ethyl 3-amino-3-( o -tolyl)propanoate [(±)- 3 ] in t -BuOMe with added H 2 O at 45 °C or in H 2 O at 3 °C.