Exploring and applying the substrate promiscuity of a C-glycosyltransferase in the chemo-enzymatic synthesis of bioactive C-glycosides

Kebo Xie,Fei Ye,Songyang Sui,Jungui Dai,Xiaolin Zhang

doi:10.1038/s41467-020-18990-9

Abstract

Bioactive natural C-glycosides are rare and chemical C-glycosylation faces challenges while enzymatic C-glycosylation catalyzed by C-glycosyltransferases provides an alternative way. However, only a small number of C-glycosyltransferases have been found, and most of the discovered C-glycosyltransferases prefer to glycosylate phenols with an acyl side chain. Here, a promiscuous C-glycosyltransferase, AbCGT, which is capable of C-glycosylating scaffolds lacking acyl groups, is identified from Aloe barbadensis. Based on the substrate promiscuity of AbCGT, 16 C-glycosides with inhibitory activity against sodium-dependent glucose transporters 2 are chemo-enzymatically synthesized. The C-glycoside 46a shows hypoglycemic activity in diabetic mice and is biosynthesized with a cumulative yield on the 3.95 g L‒1 scale. In addition, the key residues involved in the catalytic selectivity of AbCGT are explored. These findings suggest that AbCGT is a powerful tool in the synthesis of lead compounds for drug discovery and an example for engineering the catalytic selectivity of C-glycosyltransferases.

Highlights

Bioactive natural C-glycosides are rare and chemical C-glycosylation faces challenges while enzymatic C-glycosylation catalyzed by C-glycosyltransferases provides an alternative way
Enzymatic C-glycosylation catalyzed by specific C-glycosyltransferases (CGTs) can alleviate these disadvantages and is considered to be a prospective approach to synthesize C-glycosides14–16
Mining CGTs with catalytic stereospecificity and promiscuity toward other structurally different substrates and further establishing a green and economical biosynthesis route for bioactive C-glycosides are significant for drug design and discovery

Summary

Introduction

Bioactive natural C-glycosides are rare and chemical C-glycosylation faces challenges while enzymatic C-glycosylation catalyzed by C-glycosyltransferases provides an alternative way. A promiscuous C-glycosyltransferase, AbCGT, which is capable of C-glycosylating scaffolds lacking acyl groups, is identified from Aloe barbadensis. Based on the substrate promiscuity of AbCGT, 16 C-glycosides with inhibitory activity against sodium-dependent glucose transporters 2 are chemo-enzymatically synthesized. GgCGT could efficiently catalyze C-glycosylation of substrates containing a flopropione unit These discovered CGTs function primarily on C-glycosylating flavonoids and other phenols with acyl groups. Mining CGTs with catalytic stereospecificity and promiscuity toward other structurally different substrates and further establishing a green and economical biosynthesis route for bioactive C-glycosides are significant for drug design and discovery. The unusual catalytic property of AbCGT was further used to design and economically synthesize a series of unnatural C-glycosides with the aim of finding SGLT2 inhibitors

Methods

Results

Conclusion