In our biological screening of higher plants, an aqueous and an 80 % E
tOH extract from the root bark of Cryptolepis sanguinolenta showed pot
ent antibacterial, anticomplementary, and moderate antiviral activitie
s, but no antifungal effect could be detected. Bioassay-guided fractio
nation of the 80 % EtOH extract led to the isolation of three alkaloid
s: quindoline (1), hydroxycryptolepine (2), cryptolepine HCl (3), and
the corresponding base cryptolepine (4). All compounds strongly inhibi
ted the growth of Gram-positive bacteria (MIC less than or equal to 10
0 mu g/ml) and showed a moderate (MIC = 125 or 250 mu g/ml), a weak (M
IC = 500 mu g/ml), or no activity (MIC > 500 mu g/ml) against selected
Gram-negative bacteria. They also possessed a bactericidal effect dep
ending on the bacterial strain. Compounds 1, 2, and 3 displayed a dose
-dependent inhibitory effect on the classical pathway of the complemen
t system while compounds 2 and 3 activated the alternative pathway, ex
cept for compound 1. Compound 3 was found to possess an antiherpetic a
ctivity. Compounds 1 and 4 showed no antiviral effect, but were quite
cytotoxic in the antiviral test system down to a concentration of 1 mu
g/ml.