Antitubercular diterpenoids from Vitex trifolia

A new halimane diterpenoid, 13-hydroxy-5(10),14-halimadien-6-one (1) and two new labdane diterpenoids, 6α,7α-diacetoxy-13-hydroxy-8(9),14-labdadien (2) and 9-hydroxy-13(14)-labden-15,16-olide (3), were isolated for the first time, along with fifteen known compounds, from the hexane soluble fraction of methanolic extract of Vitex trifolia leaves. The structures of these new diterpenoids were elucidated by spectral analysis. Their relative configurations were established using analysis of NOESY correlations and coupling constants observed in 1H NMR. Compounds 2, 3 and another known diterpenoid, isoambreinolide (4) were evaluated for antitubercular activity. 3 and 4 exhibited antitubercular activity (MIC = 100 and 25 μg/ml) against Mycobacterium tuberculosis H37Rv in BACTEC-460 assay.