Flavonoids bearing an O-arabinofuranosyl-(1-->3)-rhamnoside moiety from Cladocolea micrantha: inhibitory effect on human melanoma cells.

Eleven known triterpenes (alpha-amyrin, beta-amyrin, lupeol, and their respective acetates, 3-O-acetyl derivatives of betulinic, oleanolic, and ursolic acids, cycloartenol, and tirucall-7,24-dicnol), two new flavonols presenting an uncommon interglycosidic O-[1 -> 3) linkage (kaempferol 3-O-alpha-L-arabinofuranosyl-(1 -> 3)-alpha-L-rhamnoside and quercetin 3-O-alpha-L-arabinofuranosyl-(1 -> 3)-alpha-L-rhamnoside), beta-sitosterol, stigmasterol, quercetin, and gallic acid were isolated from the Amazonian medicinal mistletoe, Cladocolea micrantha Kuijt (Loranthaceae). Their structures were established by spectral methods and eventual chromatographic comparisons. The quercetin derivative was not cytotoxic to MV3 human melanoma cells, but was able, when administered at 1 mu g/mL, to promote a twofold inhibition of the migration of the cells through the transwell system when compared with paclitaxel at 5 mu M.