Cucurbitacin b and isocucurbitacin b: Cytotoxic Components of Helicteres Isora

Abstract

Helicteres isora L. (Sterculiaceae) is one of the best known articles of the Hindu Materia Medica (1, 2). Antitumor screening of the EtOH root extract detected cytotoxicity in the 9KB (human nasopharyngeal carcinoma) cell culture assay (3). The several compounds previously reported (4, 5) from this plant do not account for this activity or the purported medicinal properties. The concentrated EtOH extract of the ground root logs was partitioned and purified through column chromatography and hplc to yield two potent cytotoxic compounds. Analysis of spectral and physical data identified the compounds as curcurbitacin B (ED5O=<10-5 μg/ml) and isocucurbitacin B (ED50=7.6X 10–5μg/ml). Both compounds have been previously isolated (6–8) as natural cytotoxic substances. Cucurbitacins are heretofore unknown in the family Sterculiaceae, but they have been reported from another family (Elaeocarpaceae) in the same order (Malvales) as well as elsewhere (9). © 1985, American Chemical Society. All rights reserved.