Red hot compounds from the red hot poker plant, kniphofia, and related taxa

Abstract

Knipholone, the first 4 - arylanthraquinone was discovered from the stem of Kniphofia foliosa (Asphodelaceae) in 1984 1 . Since then a number of 4 - arylanthraquinones have been isolated from this plant 2,3 and other members of the Asphodelaceae, namely from Bulbine 4 and from Bulbinela species 5 . Compounds belonging to this class of anthraquinones have rotationally hind ered biaryl linkages. The absolute configuration of knipholone and the other members was established by the use of advanced quantum chemical CD calculations 6 . Recently the first dimeric arylanthraquinones, named joziknipholones A and B, have been discovere d from the roots of Bulbine frutescens 7 . We have now reinvestigated Kniphofia foliosa and Bulbine frutescens and identified novel phenylanthraquinones, including joziknipholone A and knipholone cyclooxanthrone, and anthraquinone dimmers with remarkable bio logical activities 8,9 . The roots of Bulbine frutescens also gave a new xanthone, 8 - hydroxy - 6 - methylxanthone - 1 - carboxylic acid, whose structure was confirmed through X - ray crystallography and then used as a reference to propose the revision of six seco - anth raquinones into xanthones 10 . The structures, antiprotozoal activities and cytotoxicity of these compounds will be discussed.