Regioselective methylation of methyl glycopyranosides with diazomethane in the presence of transition-metal chlorides and of boric acid
作者:Evgeny V. Evtushenko
DOI:10.1016/s0008-6215(99)00044-0
日期:1999.3
Abstract Partial methylation of the methyl pyranosides of a number of pentoses, hexoses, 6-deoxyhexoses, methyl uronates and their methyl ethers with diazomethane in the presence of transition-metal chlorides and boric acid was studied. It was found for methyl glycosides of pentoses and 6-deoxyhexoses that tin(II), antimony(III), and titanium(IV) chlorides as well as boric acid promoted substitution
Studies on the constituents of the root of Polygala tenuifolia Willdenow. II. On the structures of onjisaponins A, B and E.
作者:SEIICHI SAKUMA、JUNZO SHOJI
DOI:10.1248/cpb.30.810
日期:——
The structures of three triterpenoidal saponins, onjisaponins A (1), B (2) and E (3), were determined on the basis of spectral and chemical evidence as presenegenin-(3)-β-D-glucopyranosido-(28)-2-O-[β-D-apio-D-furanosyl (1→3)] [β-D-galactopyranosyl (1→4)-β-D-xylopyranosyl (1→4)]-α-L-rhamnopyranosyl}-3-O-(α-L-rhamnopyranosyl)-4-O-(4'-methoxy-cinnamoyl)-β-D-fucopyranoside, presenegenin-(3)-β-D-glucopyranosido-(28)-2-O-[β-D-galactopyranosyl (1→4)-β-D-xylopyranosyl (1→4)-α-L-rhamnopyranosyl]-3-O-(α-L-rhamnopyranosyl)-4-O-(4'-methoxycinnamoyl)-β-D-fucopyranoside (=senegin III) and presenegenin- (3)-O-β-D-glucopyranosido-(28)-2-O-[β-D-galactopyranosyl (1→4)-β-D-xylopyranosyl (1→4)-α-L-rhamnopyranosyl]-4-O-(3', 4', 5'-trimethoxycinnamoyl)-β-D-fucopyranoside, respectively. The 13C nuclear magnetic resonance spectra of onjisaponins A, B, E and their derivatives were investigated and each carbon signal was assigned as shown in Table I.
Abstract A tentative mechanism for complexation, and a possible model of a tin(II)chloride—methyl glycoside intermediate complex, have been established largely from analysis of methyl ethers formed on methylation of methyl α- l -rhamnopyranoside and its monomethyl ethers by diazomethane in the presence of a catalytic amount of tin(II) chloride in selected solvents. The complex is mainly formed through displacement