naphthoquinones and rubimaillin

[reaction: see text] A total synthesis of the bioactive naphthohydroquinone mollugin and the related naphthoquinone dimer microphyllaquinone is described. Both syntheses exploit the propensity of prenylated quinones to undergo tautomerization/oxa 6pi-electrocyclizations.

Topics: Cyclization; Molecular Structure; Naphthoquinones; Plants, Medicinal; Pyrans; Rubia; Stereoisomerism

Several quinone type compounds were isolated from the hexane, dichloromethane, and ethyl acetate extracts of the roots of Pentas longiflora. The hexane extract afforded two new compounds, [(3alpha,3'alpha,4beta,4'beta)-3,3']-dimethoxy-cis-[4,4'-bis(3,4,5,10-tetrahydro-1H-naphtho[2,3-c]pyran)]-5,5',10,10'-tetraone (1) and cis-3,4-dihydroxy-3,4-dihydromollugin (2), together with six known compounds, namely, pentalongin, mollugin, trans-3,4-dihydroxy-3,4-dihydromollugin, methyl-2,3-epoxy-3-prenyl-1,4-naphthoquinone-2-carboxylate, tectoquinone, and 3-hydroxymollugin. From the dichloromethane extract were isolated the three known compounds 3-methoxymollugin, methyl-3-prenyl-1,4-naphthoquinone-2-carboxylate, and scopoletin, while the ethyl acetate extract afforded the known 2-methoxy-3-methylanthraquinone.

Topics: Chromatography, Thin Layer; Kenya; Mass Spectrometry; Molecular Structure; Naphthoquinones; Nuclear Magnetic Resonance, Biomolecular; Plant Roots; Plants, Medicinal; Pyrans; Rubiaceae; Scopoletin; Stereoisomerism