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Iridoid Glycosides from Underground P arts of Ajuga remota

Lawrence Onyango A. Manguro, Peter Lemmen and Pang Hao

Maseno University, Chemistry Department, P. O. Box 333, Maseno, Kenya

Technische Universitaet Muenchen, Institut Fuer Organische Chemie und Biochemie, Lichtenbergstrasse 4, 85747, Garching, Germany;

Guangzhou Institute of Geochemistry, Department of Organic Chemistry of Natural Products, Guangzhou, 540640, Guangdong, Peoples Republic of China

Abstract:Fractionation of EtOAc and aqueous MeOH extracts of Ajuga remota underground part has led to the isolation of four new iridoid glycosides identified as 2', 3'-diacetyharpagide (1), 6'-O-rhamnosylharpagide (2), 6'-O-galloyl-7,8-dehydroharpagide (3) and 6-O-xylosylharpagoside-B (4). Together with these were known compounds 8-O-acetylharpagide(5), harpagide (6), cyasterone (7), 20-hydroecdysone (8), sengosterone (9), 3-O-β-glucopyranosylstigmasta-5, 25-diene (10), stigmasterol (11) and ergosterol-5, 8-endoperoxide (12). Their structures were determined using spectroscopic methods as well as comparison with data from known compounds. In the in vitro larvicidal tests using 2 nd instar Aedes aegypti larvae, the EtOAc extract was found to be toxic with LC 50 of 5.30 ± 1.3 µg/mL, while the MeOH extract exhibited weak toxicity with an LC 50 value of 65.94 ± 0.4 µg/mL. Among the pure isolates tested, compound 12 associated with EtOAc extract was the active principal with LC 50 value of 4.40 ± 0.2.

Keywords: Ajuga remota ; iridoid glycosides; phytoecdysteroids; sterol glycoside; larvicidal activity.