From L-Ascorbic Acid to Protease Inhibitors: Practical Synthesis of Key Chiral Epoxide Intermediates for Aspartyl Proteases

Abstract

Efficient synthetic routes were developed to prepare a sizable amount (4-15 grams) of the chiral epoxides 4-6 as versatile intermediates for the synthesis of aspartyl protease inhibitors of therapeutic interest such as HIV protease and <TEX>${\beta}$</TEX>-secretase. Oxidative cleavage of the C(2)-C(3) double bond of L-ascorbic acid followed by functional group manipulation led to the preparation of the epoxide 10, which was opened with an azide to yield a common aziridine intermediate 12. Through opening of the aziridine ring of 12 with either a carbon or a sulfur nucleophile, chiral epoxide precursors 4-6 could be prepared for various HIV protease inhibitors. Except for the final low melting epoxides 5 and 6, all intermediates were obtained as crystalline solids, thus the synthetic pathway can be easily applied to a large-scale synthesis of the chiral epoxides.