An ent-kaurane diterpene from Mikania laevigata (Asteraceae)

Abstract

The genus Mikania contains more than 450 species and around 150 of them are found in Brazil [1]. This genus is divided in two groups of species, one of them produces preferently sesquiterpene lactones and the other, diterpenic acids. The late compounds seem to play an important role in defense system of plants [2]. Mikania laevigata Schultz Bip. ex Baker („guaco“) is the most abundant Mikania species in Southern Brazil [3]. The leaves are used mainly to treat respiratory diseases, but antiseptic, antiasthmatic and antirheumatic properties have been described. The characteristic smell of Mikania species is due to coumarins and some of their properties are also attributed to these compounds [4]. The plant material was cultivated at Federal University of Santa Catarina. The dried and powdered leaves (281g) were macerated with ethanol during 7 days. The crude extract was treated with MeOH:H2O (9:1), and extracted with petrol (PE), CH2Cl2, ethyl acetate and n-butanol. PE fraction was fractionated by flash chromatography (gradient of PE:CH2Cl2) followed by silica gel column chromatography (PE:ethyl acetate gradient) and Sephadex LH-20 (MeOH), yielding 21mg of compound 1. The NMR-H1, NMR-C13, IR and UV data suggested compound 1 to be ent-15β-benzoyloxy-kaur-16(17)-en-19-oic acid. This compound has been isolated also from other Mikania species [5,6], but it has never been found in M. laevigata, therefore being a new compound of this species.