Spectres de R.M.N.-13C de disaccharides et trisaccharides contenant du d-glucose, d-galactose et l-rhamnose

Osteosaponins 1 and 2: two new saponin glycosides from Osteospermum vaillantii

Osteospermum vaillantii (Decne) T. Norl., collected from southern Saudi Arabia, yielded two new saponins characterised as 3-O-beta-D-glucopyranosyl-(2' --> 1'')-beta-D-glucopyranosyl-(3' --> 1''')-O-beta-D-galactopyranosyl-oleanolic acid, designated as osteosaponin, and 3-O-beta-D-glucopyranosyl-(2' --> 1'')-beta-D-glucopyranosyl-(2''-1''''')-beta-D-glucopyranosyl-(3' --> 1''')-O-beta-(-D-galactopyranosyl-oleanolic-acid-28-C(O)-O-beta-D-(1'''')-glucopyranosyl ester, designated as osteosaponin. The sugar attachments and configurations were confirmed by spectroscopic methods, that is, 1H, 13C-NMR, COSY, HSQC and HMBC-NMR experiments.

Synthesis and characterisation of methyl 2-O-(beta-D- glucopyranosyl)-6-O-(alpha-L-rhamnopyranosyl)-alpha-D-glucopyranoside

The branched trisaccharide, 2-O-(beta-D-glucopyranosyl)-6-O-(alpha-L-rhamnopyranosyl)-D-glucopyranos e (2), is regarded as the sugar moiety of an anthocyanin pigment isolated from the fruits and flowers of certain Begonia, Clivia, Rubus, Prunus, and Ribis species. The cyanidin-3-glycoside of 1 has been identified as one of the major pigments of Montmorency cherries (Prunus cerasus). It has also been isolated as quercetin and kaempherol glycosides from the flowers of potato (Solanum tuberosum). Synthesis of the methyl glycoside of 1, methyl 2-O-(beta-D-glucopyranosyl)-6-O-(alpha-L-rhamnopyranosyl)-alpha-D-glucop yranoside (2) is reported.

Determination of the structures of trisaccharides by 13C-n.m.r. spectroscopy

A literature survey of the 13C-n.m.r. chemical-shift data for aqueous solutions of monosaccharides, disaccharides, oligosaccharides, and their methyl derivatives is reported. Analysis of these data reveals a set of empirical rules which may be used in the elucidation of the structure of trisaccharides of known monosaccharide composition, and an example is reported. However, it is not possible to extend the rules to tetrasaccharides and higher saccharides without additional chemical-shift data for related model compounds.

Cell-wall lipopolysaccharide of the urinary-tract-infective Escherichia coli 04:K12:H-. Structure of the polysaccharide chain

The O-specific polysaccharide moiety (04 polysaccharide) of the 04 antigen (lipopolysaccharide) from Escherichia coli 04:K12:H- was isolated in pure form by degradation of the lipopolysaccharide and chromatography on Sephadex G-50. The primary structure of the 04 polysaccharide was elucidated by composition, Smith degradation, nuclear magnetic resonance spectroscopy, methylation and oligosaccharide analysis. Oligosaccharides were obtained by deaminating fragmentation of partially and completely de-N-acetylated polysaccharides. The polysaccharide consists of repeating units of the pentasaccharide (formula; see text) which are joined in the polymer through alpha-1, 4-linkages. The 04 polysaccharide has a mean molecular mass of 13800 Da and consists of the core oligosaccharide and about 14 pentasaccharide repeating units.

Structural studies of the O-specific polysaccharide from Serratia marcescens N.C.T.C. 1377

The putative O-specific polysaccharide of Serratia marcescens N.C.T.C. 1377 is a partially acetylated glucorhamnan. By means of 1H- and 12C-n.m.r. spectroscopy, methylation analysis, and periodate oxidation, it was shown that the polymer has a disaccharide repeating-unit for which the following structure is proposed: leads to 4)-alpha-D-Glcp-(1 leads to 3)-beta-L-Rhap-(1-leads. O-Acetyl groups are probably located at C-2 of the rhamnopyranosyl residues. Except for the extent of O-acetylation, the polysaccharide is identical with the corresponding product from S. marcescens Bizio (A.T.C.C. 264), for which a different structure has previously been proposed.

[Structure of chrysantellin B, a new saponin isolated from Chrysanthellum procumbens Rich (author's transl)]

A new saponin, chrysantellin B, has been found in a tropical plant Chrysanthellum procumbens Rich as a minor companion of chrysantellin A which was previously studied. The structure of chrysantellin B was determined by mass spectrometry, proton and 13C nuclear-magnetic resonance. The aglycone part is a triterpene: 3 beta, 16 alpha, 23-trihydroxy-olean-12-en-28-oic acid or caulophyllogenin. Carbohydrate components are D-glucose, D-oxylose and L-rhamnose in a molar ratio 1:2:2. The structure of chrysantellin B was established as 3-O-beta-D-glucopyranosyl[L-rhamnopyranosyl-(alpha 1 leads to 3)-D-xylopyranosyl-(beta 1 leads to 4)-L-rhamnopyranosyl-(alpha 1 leads to 2)-D-xylopyranosyl-(beta 1 leads to 28)]caulophyllogenin.