^1H NMR选择检测新技术用于新三萜皂苷的结构研究

从中药川续断根部的乙醇提取物中分得1个新的三萜皂苷,经过测定,其结构为:3-O-α-L-吡喃鼠李糖(1--3)-β-D-吡喃葡萄糖(1--3)-β-L-吡喃鼠李糖(1--2)-β-L-吡喃阿拉伯糖-常春藤苷元(1).研究表明,采用一维SEMDY和三照射NOE差谱NMR新技术相结合能以"拼凑"方式,测定糖链结构.方法简便、快速、测定结果可靠,重叠的信号可以指认,并且对样品不必进行化学降解或衍生化.本方法也可以用于其他类型的寡糖结构测定。

Application of novel selective ^1H NMR techniques to the structural determination of a new trierpenoid glycoside

A new triterpenoid saponin was isolated from the ethanolic extract of the root of Dipsacus asperoids C.Y.Cheng et T.M. A. The structure was elucidated as 3-O-α-L-rhamnopyranosyl (1--3)-β-D-ghycopyranosyl (1--3)-α-L-rhamnopyranosyl (1--2)-β-L- arabinopyranosyl-hederagenin. In the present study, 1D-SEMDY in combination with triple irradiation NOE difference spectroscopy has been successfully used for determining the glycosidation position in an aglycome moiety and the sequence of sugar moiety in the compound 1.The results obtained showed that The efficiency of magnetization transfer among the sugar residue of glycoside is much better for 1D-SEMDY than that for conventional 1D-HOHAHA and 1D-multiple relay COSY experiments. For example, for sugar residues such as arabinose which have coupling of 1-1.5 Hz between 4-H and 5-H proton, complete ^1H NMR subspectra can be obtained. This technique provides the. possibility to acquire pure- phase subspectra without the use of the Z-filter, thus allowing for identification of individual sugar components and spectra assignments in complex overlapping proton spectra. Triple irradiation NOE Difference Spectroscopy is based on the simultaneous irradiation of both lines in a doublet of the sugar] anomeric proton with a low decoupling power during the preirradiation time, by which SPT and Bloch-Siegert shift effects can be removed from difference spectra.