16α-Hydroxy-(–)-kauranoic Acid: A Selectively Cytotoxic Diterpene from Annona bullata

Abstract
Using brine shrimp lethality to direct fractionation, extracts of the bark of Annona bullata Rich. (Annonaceae) have yielded 16α-hydroxy-(–)-kauranoic acid as a bioactive plant constituent. This previously known diterpene showed significant (ED50 8.25 × 10−2 µg/ml) and selective cytotoxicity against A-549 (lung) cells in our panel of human tumor cells.