ISOLATION AND STRUCTURE ELUCIDATION OF A HIGHLY HEMOLYTIC SAPONIN FROM THE MERCK SAPONIN EXTRACT USING HIGH-FIELD GRADIENT-ENHANCED NMR TECHNIQUES

Saponins SAPO50 and SAPO30, of which SAPO50 is highly haemolytic, have been isolated from the commercial Merck Saponin. Their structures hav e been determined exclusively by high-field gradient-enhanced NMR meth ods. The H-1 and C-13 NMR spectra of these saponins in pyridine-deuter ium oxide have been assigned by homonuclear and heteronuclear correlat ion experiments. Anomeric configurations were obtained by combined use of (1)J(CH), (3)J(H-1,H-2), and 1D-NOESY data. Sugar residues were id entified by use of (3)J(HH) values obtained from their subspectra reco rded using an optimized 1D-z-TOCSY sequence. Linkage assignments were made using the ge-HMBC and 1D-NOESY spectra. This study shows that SAP O50 represents a hitherto undescribed saponin with the following struc ture: 3-O-beta-D-xylopyranosyl-(1 --> 3)-[beta-D-galactopyranosyl-(1 - -> 2)]-beta-D-glucuronopyranosyl gypsogenin 28-O-(6-deoxy-beta-D-gluco pyranosyl)-(1 --> 4)-[beta-D-xylopyranosyl-(1 --> 3)-beta-D-xylopyrano syl-(1 --> 4)]-alpha-L-rhamnopyranosyl-(1 --> 2)-beta-D-fucopyranoside . SAPO30, however, corresponds to a saponin previously described [D. F rechet, B. Christ, B. Monegier du Sorbier, H. Fischer, and M. Vuilhorg ne, Phytochemistry, 30 (1991) 927-931]. (C) 1997 Elsevier Science Ltd.