Application of lipase-catalyzed regioselective esterification in the preparation of digitonin derivatives

The oligosaccharide chain of the monodesmosidic haemolytic saponin digitoni n (1) undergoes an efficient and regioselective acylation in organic solven t by use of Novozym 435 (lipase B from Candida antarctica supported on acry lic resin) in the presence of an activated ester. With vinyl acetate, acety lation occurs at C-6 OH of glucose(II) and C-4 OH of xylose to afford the p reviously unreported diacetyl derivative 2 and the monoacetyl derivatives 3 and 4. With vinyl laurate only the monolauryl derivative 5 is formed. The structures of these acylated digitonins have been established using modern 2D NMR techniques, which allowed complete assignments of all proton resonan ces. The hemolytic activity of derivatives 2-5 is significantly reduced com pared to that of digitonin.