Antimycobacterial ergosterol-5,8-endoperoxide from Ajuga remota

In a bioassay-guided search for antimycobacterial natural products from hig her plants, we have chemically investigated the methanol extract of aerial parts of Ajuga remote Benth. (Labiatae) for its active constituent(s). Bioa ctive chromatographic fractions of the crude extract provided the known tri terpene ergosterol-5,8-endoperoxide plus the diterpenes clerodin, ajugarin- I, and ajugarin-II, which had been previously isolated from A. remote. This is the first report on the isolation of ergosterol-5,8-endoperoxide from t his plant. The above compounds were tested in a radiorespirometric bioassay for activity against Mycobacterium tuberculosis. Ergosterol-5,8-endoperoxi de showed a minimum inhibitory concentration (MIC) of 1 mu g/ml, while ergo sterol-5,8-endoperoxide acetate, ergosterol, and ergosta-5,7,9(11),22-tetra en-3 beta-ol gave MICs of 8 mu g/ ml, >128 mu g/ml, and 128 mu g/ml, respec tively. Clerodin, ajugarin-I, and ajugarin-II were inactive with MICs of >1 28 mu g/ml.