Caesalpinia pulcherrima (Leguminosae) is a small size plant distributed in the hill tracks of Tirumula Hills, Andhra Pradesh, South India. 1) In traditional Indian Medicine C. pulcherrima is used in the treatment of tridosha, fever, ulcer, abortifacient, emmenagogue, asthma, tumors, vata and skin diseases.2) Previous studies on this plant have resulted in the isolation of several diterpenoids, [3][4][5][6] flavanoids, 7) peltogynoids 8) and homoisoflavonoids.[7][8][9] In continuation of our search for new plant secondary metabolites, 10) we have investigated the whole plant of C. pulcherrima, and report here the isolation, structure elucidation and antimicrobial activity of two new homoisoflavanoids, (E)-7-methoxy-3-(4Ј-methoxybenzylidene)chroman-4-one (1) and (E)-7-hydroxy-3-(3Ј,4Ј,5Ј-trimethoxybenzylidene)chroman-4-one (5), together with three known homoisoflavonoids, (Z)-7-hydroxy-3-(4Јmethoxybenzylidene)chroman-4-one (isobonducellin) (2), (E)-7-hydroxy-3-(4Ј-methoxybenzylidene)chroman-4-one (bonducellin) (3) and (E)-7-hydroxy-3-(2Ј,4Ј-dimethoxybenzylidene)chroman-4-one (4). Results and DiscussionCompound 1, was isolated as an amorphous powder.Its molecular formula was assigned as C 18 H 16 O 4 from its mass spectrum (M ϩ at m/z 296), elemental analysis and 13 C-NMR spectrum, with eleven degree of unsaturation.The strong IR absorptions at 1659 (CϭO), 1604 (CϭC), 829 cm Ϫ1 (para substituted benzene ring), UV absorption maxima at 356 and 320 nm and negative ferric chloride test indicated that 1 was a non-phenolic unsaturated homoisoflavanone.8)The 1 H-NMR spectrum of 1 revealed the presence of two methoxyl groups as a singlet at d 3.82 integrating for 6 pro-tons.The EI-MS of 1 showed two retro-Diels-Alder fragments at m/z 151 and m/z 146 indicating the presence of one methoxyl group in ring-A and another methoxyl group in ring-B, respectively.The correlations observed in the NOESY spectrum of 1 (Fig. 3) indicated that the two methoxyl groups in 1 were placed at C-7 and C-4Ј position.The 1 H-NMR spectrum of 1 showed an ABX spin coupled system at d 7.79 (1H, d, Jϭ8.8 Hz), 6.68 (1H, dd, Jϭ8.8, 1.9 Hz) and 6.54 (1H, d, Jϭ1.9 Hz) was assigned to H-5, H-6 and H-8, respectively.Further it also revealed the presence of AAЈ XXЈ spin coupled system with two protons centered at d 7.42 (d, Jϭ8.5 Hz) and another two protons at d 7.04 (d, Jϭ8.5 Hz), which were assigned to the H-2Ј, 6Ј and H-3Ј, 5Ј protons, respectively.The E-geometry of the double bond at C-3 and C-9 in 1 was clearly indicated by d values of the methylene protons at d 5.40 for C-2 and the vinylic proton at
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Maheswara et al. (2006) studied this question.