An ortho C-methylation/O-glycosylation motif on a hydroxy-coumarin scaffold, selectively installed by biocatalysis

作者：Gutmann Alexander; Schiller Margaretha; Gruber Khadjawi Mandana; Nidetzky Bernd^*

来源：Organic and Biomolecular Chemistry, 2017, 15(37): 7917-7924.

DOI：10.1039/c7ob01513e

Various bioactive natural products, like the aminocoumarin antibiotics novobiocin and coumermycin, exhibit an aromatic C-methyl group adjacent to a glycosylated phenolic hydroxyl group. Therefore, tailoring of basic phenolic scaffolds to contain the intricate C-methyl/O-glycosyl motif is of high interest for structural and functional diversification of natural products. We demonstrate site-selective 8-C-methylation and 7-O-beta-D-glucosylation of 4,5,7-trihydroxy-3-phenyl-coumarin (1) by S-adenosyl-L-methionine dependent C-methyltransferase (from Streptomyces niveus) and uridine 5'-diphosphate glucose dependent glycosyltransferase from apple (Malus x domestica). Both enzymes were characterized and shown to react readily with underivatized 1. However, glucosylation of the ortho-hydroxyl group prevented C-methylation, probably by precluding an essential substrate activation through deprotonation of 7- OH. Therefore, dual modification was only feasible when C-methylation occurred strictly before O-glucosylation. The target product was synthesized in near quantitative yield (98% conversion) from 500 mu M 1 and its structure was confirmed by NMR. Combination of C-methyltransferase and O-glycosyltransferase reactions for synthetic tailoring of a natural product through biocatalysis was demonstrated for the first time.

• 出版日期2017-10-7