Biocatalytic Generation of Molecular Diversity: Modification of Ginsenoside Rb1 by β-1,4-Galactosyltransferase and Candida antarctica Lipase, Part 4 For Part 3, see [1].

A series of specific derivatives of the complex protopanaxadiol glycoside ginsenoside Rb1 (1) were prepared by catalysis of two unrelated enzymes: the β-1,4-galactosyltransferase from bovine colostrum (GalT) and the lipase B from Candida antarctica (Novozym ® 435). Both of the enzymes showed the expected regioselectivity towards specific glucose OH groups (i.e., OHC(4) for GalT and preferentially the primary OHC(6) for Novozym ® 435), accompanied by a nonpredictable ‘site selectivity' for the gentiobiose disaccharide unit linked at C(20) of the dammarane skeleton. The galactosylated products 1a–e and the acetylated products 1f–h were isolated by HPLC and fully characterized by extensive MS and NMR analysis.