ent-kaurene diterpenoids from Blepharispermum hirtum

The twigs and leaves of Blepharispermum hirtum Oliver (Asteraceae) were investigated for their larvicidal and antimicrobial activity. Fractionation of the extracts of the twigs, directed by brine shrimp test and antibacterial activities, led to the isolation of compounds 1-4; two of which are new ent-kaurene diterpenoids, blepharispins A and B (1 and 2, resp.). The structures of compounds 1 and 2 were established from spectral data. The absolute configuration at C(15) in 1 was inferred from Mosher ester analysis and relative configurations were suggested by a NOESY experiment. Compound 4 was significantly larvicidal to newly hatched naupleii of Artemia salina L. (BST LC ₅₀=1.3 (3.7 -0.0) μg/ml), but the blepharispins were not (BST LC ₅₀>500 μg/ml). Nevertheless, compound 1 inhibited the growth of Staphylococcus aureus and Bacillus subtilis at a MIC value of 62.5 μg/ml. The significance of the bioactivity results and the presence of ent-kaurene diterpenoids in B. hirtum are discussed from biosynthetic and local utilization viewpoints.