The first 6′- O-sulfated phenylanthraquinones: isolation from Bulbine frutescens, structural elucidation, enantiomeric purity, and partial synthesis

• Published in: Tetrahedron Vol. 61; no. 35; pp. 8475 - 8484
• Main Authors: Mutanyatta, Joan, Bezabih, Merhatibeb, Abegaz, Berhanu M., Dreyer, Michael, Brun, Reto, Kocher, Nikolaus, Bringmann, Gerhard
• Format: Journal Article
• Language: English
• Published: OXFORD Elsevier Ltd 29.08.2005; Elsevier
• Subjects: Axial chirality; Bulbine frutescens; Chemistry; Chemistry, Organic; Crystal structure; Enantiomeric resolution; LC–CD coupling; Physical Sciences; Science & Technology; Sulfated phenylanthraquinones; Enantiomeric resolution; Bulbine frutescens; LC–CD coupling; Sulfated phenylanthraquinones; Axial chirality; Crystal structure; DIRECTED BIARYL SYNTHESIS; ANTIPLASMODIAL ACTIVITY; FLAVERIA-BIDENTIS; sulfated phenylanthraquinones; KNIPHOLONE; enantiomeric resolution; FLAVONOID SULFATES; axial chirality; QUERCETIN; CENTAUREA-BRACTEATA; LC-CD coupling; AERIAL PARTS; crystal structure; ROOTS; DERIVATIVES
• ISSN: 0040-4020; 1464-5416
• DOI: 10.1016/j.tet.2005.06.055

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. Graphical Abstract