Antifungal activity of naphthoquinones and triterpenes isolated from the root bark of Euclea natalensis

Euclea natalensis A. DC. belonging to the family Ebenaceae, is widely used for curing bronchitis, pleurisy, chronic asthma and urinary tract infections by the Zulus, in South Africa. Four triterpenes namely lupeol, betulin, β-sitosterol, 20(29)-lupene-3β-isoferulate and two naphthoquinones shinanolone and octahydroeuclein isolated from the ethanolic extract of E. natalensis root bark were investigated for their antifungal activity against Aspergillus flavus, Aspergillus niger, Cladosporium cladosporioides, and Phytophthora sp. A. niger was significantly inhibited by β-sitosterol, 20(29)-lupene-3β-isoferulate and shinanolone at 0.01 mg ml− 1. Of all the compounds tested, only octahydroeuclein was found to be significantly effective against Phytophthora sp. at 0.1 mg ml− 1. β-Sitosterol and octahydroeuclein inhibited the growth of C. cladosporioides significantly at 0.01 mg ml− 1. None of the isolated compounds exhibited significant activity against A. flavus at 0.01 mg ml− 1.