Environment-friendly Simple, and Straightforward Approach Towards the C-4 functionalization of (2S)-5-oxoproline Methyl Ester

Abstract

4-Substituted- 5-oxo-prolinates (pyroglutamates) are important components in various natural products, e.g. (-)-bulgecinine, (-)-anatoxin, salinosporamide, as well as ACE inhibitors. These also act as important intermediates in the synthesis of many of the bioactive molecules. Due to these reasons, the synthesis of 4-substituted-(2S)-5-oxo-prolinates has received much attention over the globe in the last three decades. However, most of the synthetic strategies available in the literature describe either the use of expensive lithium enolate-derived lowtemperature chemistry or the rigorous reaction conditions, and therefore, a simple, environmentfriendly, and cost-effective approach was truly demanding. In our ongoing research program, we required different 4-substituted pyroglutamates as intermediates, and with that very basic objective, we were looking for an alternate strategy which should be simple, requiring cheap reagents and consequently, in the process, it was thought to attempt proline catalyzed aldol/alkylation reactions on pyroglutamates, and the idea provided excellent outcome. Herein we wish to report the L-proline catalyzed asymmetric functionalization at C-4 of (2S)-5-oxoproline methyl ester, which furnished desired products at room temperature at the same time, not requiring expensive reagents and, therefore, in turn, cost-effective. This new strategy explored for synthesizing 4-substituted pyroglutamates could be useful for researchers across the globe working in the area and requiring substitution at C-4 of pyroglutamates for synthesizing bioactive molecules/natural products.