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.