The first 6′-O-sulfated phenylanthraquinones: isolation from Bulbine frutescens, structural elucidation, enantiomeric purity, and partial synthesis
- 作者：Joan Mutanyatta ; Merhatibeb Bezabih ; Berhanu M. Abegaz ; Michael Dreyer ; Reto Brun ; Nikolaus Kocher and Gerhard Bringmann
- 关键词：Bulbine frutescens ; Sulfated phenylanthraquinones ; Axial chirality ; Enantiomeric resolution ; LC– ; CD coupling ; Crystal structure
- 刊名：Tetrahedron
- 出版年：2005
- 期刊代码：107_00404020
- 类别：ch
- 出版时间：2005
- 卷：61
- 期：35
- 页码：8475-8484
- 文件大小：425 K
摘要
From the roots of Bulbine frutescens, the first sulfated phenylanthraquinones were isolated, together with their known sulfate-free analogs. Their structures were elucidated by spectroscopic and chiroptical methods, by acid hydrolysis or by partial synthesis. The new compounds have the usual stereo-orientation at the biaryl axis (i.e., with the acetyl portion above the anthraquinone plane) except for sodium ent-knipholone 6′-O-sulfate (and thus, also its hydrolysis product, ent-knipholone), which exhibit an opposite axial configuration. We also describe the first stereoanalysis of natural phenylanthraquinones, some of which were found to be not enantiomerically pure, some even near-racemic. We furthermore, report on the first X-ray structure analysis of a phenylanthraquinone, viz. 4′-O-demethylknipholone.