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Ajuga remota is the most frequently used medicinal herb for malaria treatment in Kenya. Its two known isolates ajugarin-1 (1) and ergosterol-5,8-endoperoxide (3) and a new isolate 8-O-acetylharpagide (2) were evaluated for their in vitro antiplasmodial activity. Ajugarin-1 was moderately active, with an IC₅₀ of 23.0 ± 3.0 μM, as compared to chloroquine (IC₅₀ = 0.041 ± 0.003 μM) against the chloroquine-sensitive (FCA 20/GHA) strain of Plasmodium falciparum. Ergosterol-5,8-endoperoxide was about 3× as potent (IC₅₀ = 8.2 ± 1.1 μM), while 8-O-acetylharpagide, whose structure was established by spectroscopic evidence, was inactive. Both ajugarin-1 and ergosterol-5,8-endoperoxide did not exhibit cytotoxicity against A431 (skin carcinoma) cell line, but 8-O-acetylharpagide was significantly cytotoxic. This iridoid glucoside, which has been formerly isolated from Ajuga decumbens, was identified in A. remota for the …