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Application of lipase-catalyzed regioselective esterification in the preparation of digitonin derivatives
B Danieli1, M Luisetti, S Steurer
1Dipartimento di Chimica Organica e Industriale, Università degli Studi di Milano, Centro CNR di Studio per le Sostanze Organiche Naturali, via Venezian 21, 20133 Milano, Italy. danieli@icil64.cilea.it
Abstract:
The oligosaccharide chain of the monodesmosidic haemolytic saponin digitonin (1) undergoes an efficient and regioselective acylation in organic solvent by use of Novozym 435 (lipase B from Candida antarctica supported on acrylic resin) in the presence of an activated ester. With vinyl acetate, acetylation occurs at C-6 OH of glucose(II) and C-4 OH of xylose to afford the previously 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 resonances. The hemolytic activity of derivatives 2-5 is significantly reduced compared to that of digitonin.
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