Flavonoids from blue flowers of Nymphaea caerulea

Seven flavonols including the novel 3-(2''-acetylrhamnosides) of myricetin and quercetin (2 and 6), the rare kaempferol 3-(2''- acetylrhamnoside) and quercetin 3-(3''-acetylrhamnoside), in addition to the 3-rhamnosides of kaempferol, quercetin and were isolated from blue flowers of the African water lily Nymphaea caerulea (= Nymphaea capensis). Their structures were elucidated by a combination of chromatography and homo- and heteronuclear two-dimensional NMR techniques and electrospray MS for compound 2.