Two New 5-Deoxyflavonoids from Calliandra inermis

Calliandra inermis (Leguminosae) is an herbaceous plant distributed in the Rayalaseema region of Andhra Pradesh, South India. 1) In continuation of our search for new flavonoids, 2) we have examined the whole plant of C. inermis, and report here the isolation and structure elucidation of two new 5-deoxyflavonoids, 7,2Ј,3Ј,4Ј-tetramethoxyflavone (1) and 7,2Ј,3Ј,4Ј-tetramethoxyflavanone (2) in addition to a known flavone, 7,4Ј-dimethoxy-3Ј-hydroxyflavone (3). Results and DiscussionCompound 1, was isolated as an amorphous powder.The high resolution electron impact mass spectrum (HR-EI-MS) of 1 showed the [M] ϩ peak at m/z 342.1061 in agreement with the molecular formula C 19 H 18 O 6 (Calcd 342.1058).This was corroborated by the decoupled 13 C-NMR spectrum which showed signals for all the nineteen carbons of the molecule.The UV absorption in MeOH (254, 330 nm) suggested compound 1 to be a flavone.3) The IR absorption bands at 1650, 1625 and 1596 cm Ϫ1 and negative ferric chloride test indicated compound 1 to be a non-phenolic flavone.The 1 H-NMR spectrum of 1 showed four methoxyl singlets at d 3.95, 3.93, 3.92 and 3.89 and a sharp one-proton singlet at d 6.92 ascribed to H-3.The eletron impact mass spectrometry (EI-MS) of 1 showed two retro-Diels Alder fragments 4) at m/z 151 [A 1 ϩH] ϩ and m/z 192 [B 1 ] ϩ indicating the presence of one methoxyl group in ring-A and three methoxyl groups in ring-B, respectively.The 1 H-NMR sepectrum of 1 further showed a ABX spin coupled system at d 8.11 (1H, d, Jϭ8.8 Hz), 6.94 (1H, dd, Jϭ8.8, 2.3 Hz) and 6.88 (1H, d, Jϭ2.3 Hz) was assigned to H-5, H-6 and H-8, respectively, as the H-6 and H-8 protons showed nuclear Overhauser enhancement spectroscopy (NOESY) correlation with the methoxyl group at C-7 position.Two ortho coupled protons at d 7.50 and 6.77 were assigned to H-6Ј and H-5Ј respectively.The three methoxyl groups in ring-B at d 3.93, 3.92 and 3.89 were assigned to C-2Ј, C-3Ј and C-4Ј positions as these three methoxyl protons and H-5Ј and H-6Ј protons showed heteronuclear multiple bond connectivity (HMBC) correlations with these carbons at 152.7 (C-2Ј), 142.5 (C-3Ј) and 156.0 (C-4Ј) ppm, 5) respectively (Fig. 1).Thus from the foregoing spectral studies the structure of compound 1 was characterised as 7,2Ј,3Ј,4Ј-tetramethoxyflavone.Compound 2, was isolated as an amorphous powder.Comparison of the 1 H-NMR data of 2 with those of 1, revealed that compound 2 was the 2,3-dihydro derivative of 1, based on the appearance of new signals at d 5.65 (dd, J 2ax. 3ax ϭ12.