Abstract
In a bioassay-guided search for antimycobacterial natural products from
higher plants, we have chemically investigated the methanol extract of aerial
parts of Ajuga remota Benth. (Labiatae) for its active
constituent(s). Bioactive chromatographic fractions of the crude extract provided
the known triterpene ergosterol-5,8-endoperoxide plus the diterpenes clerodin,
ajugarin-I, and ajugarin-II, which had been previously isolated from
A. remota. This is the first report on the isolation of ergosterol-5,8-endoperoxide
from this plant. The above compounds were tested in a radiorespirometric bioassay
for activity against Mycobacterium tuberculosis.
Ergosterol-5,8-endoperoxide showed a minimum inhibitory concentration (MIC)
of 1 μg/ml, while ergosterol-5,8-endoperoxide acetate, ergosterol,
and ergosta-5,7,9(11),22-tetraen-3β-ol gave MICs of 8 μg/ml,
> 128 μg/ml, and 128 μg/ml, respectively. Clerodin,
ajugarin-I, and ajugarin-II were inactive with MICs of > 128 μg/ml.
Key words:
Ajuga remota
- Labiatae - ergosterol-5,8-endoperoxide -
Mycobacterium tuberculosis
- antituberculosis - clerodin - ajugarin-I - ajugarin-II
