title: New dammarane and malabaricane triterpenes from Caloncoba echinata.
abstract: Three novel triterpenes, (11R,20R)-11,20-dihydroxy-24-dammaren-3-one (1), (17S,20R,24R)-17,25-dihydroxy-20,24-epoxy-14(18)-malabaricen-3-one (2), and (17R,20S,24R)-17,25-dihydroxy-20,24-epoxy-14(18)-malabaricen-3-one (3), were isolated from leaves of Caloncoba echinata. The structures were established using mainly 800 MHz NOESY and HMBC connectivities. The absolute stereochemistry of C-11 in 1 and that of C-17 in 2 were established by the Mosher method. The stereochemistry of the side chains of the malabaricanes is compatible with their biosynthesis by a cascade opening of diepoxides. The isolated triterpenes inhibited growth of Plasmodium falciparum parasites in vitro apparently via incorporation into erythrocyte membrane, as suggested by transformation of erythrocytes into stomatocytes at a concentration level at which the growth inhibition was observed.
authors.affiliation: Department of Medicinal Chemistry, Royal Danish School of Pharmacy, Universitetsparken 2, DK-2100 Copenhagen, Denmark.
authors.forename: Hanne L
authors.initials: HL
authors.lastname: Ziegler
authors.forename: Dan
authors.initials: D
authors.lastname: Staerk
authors.forename: Jette
authors.initials: J
authors.lastname: Christensen
authors.forename: Carl Erik
authors.initials: CE
authors.lastname: Olsen
authors.forename: Archibald A
authors.initials: AA
authors.lastname: Sittie
authors.forename: Jerzy W
authors.initials: JW
authors.lastname: Jaroszewski
mesh_terms: D000818:Animals; D000962:Antimalarials / Q000737:chemistry / Q000302:isolation & purification* / Q000494:pharmacology; D002851:Chromatography, High Pressure Liquid; D004912:Erythrocytes / Q000187:drug effects; D005869:Ghana; D020128:Inhibitory Concentration 50; D015394:Molecular Structure; D019906:Nuclear Magnetic Resonance, Biomolecular; D018515:Plant Leaves / Q000737:chemistry; D010946:Plants, Medicinal / Q000737:chemistry*; D010963:Plasmodium falciparum / Q000187:drug effects*; D031308:Salicaceae / Q000737:chemistry*; D013237:Stereoisomerism; D014315:Triterpenes / Q000737:chemistry / Q000302:isolation & purification* / Q000494:pharmacology; D000097669:Dammaranes
chemical_list: D000962:Antimalarials; D014315:Triterpenes; D000097669:Dammaranes; C473157:11,20-dihydroxy-24-dammaren-3-one; C473158:17,25-dihydroxy-20,24-epoxy-14(18)-malabaricen-3-one