Tephrosia PERS. (Leguminosae, Papilionoideae) is a large tropical and sub-tropical genus estimated to contain 300 species.1) Tephrosia calophylla BEDD. is a perennial undershrub found widely in Talakona forest of Andhra Pradesh, South India.2) The genus Tephrosia is known to elaborate a rich variety of flavonoids and isoflavonoids.3) Phytochemical investigation of the whole plant of this hitherto uninvestigated species has led to the isolation of a new coumestan, tephcalostan (1) together with two known flavonoids, 7-Omethylglabranin (2) and kaempferol-3-O-b-D-glucopyranoside (3).
Results and DiscussionTephcalostan 1, obtained as colourless needles, showed [MϩH] ϩ peak at m/z 363.0945 in its positive electrospray ionisation time of flight mass spectrum (ESI-TOF-MS) consistent with the molecular formula C 21 H 14 O 6 . It was supported by 13 C-NMR spectrum and distortionless enhancement by polarisation transfer (DEPT, 90 and 135) experiments, which showed 21 carbon resonances consisting of one methyl, three methylene, five methine and twelve quaternary carbons. The UV absorption maxima at 248, 313 and 355 nm were typical of a coumestan skeleton.4) The IR spectrum of 1 exhibited strong absorption bands attributable to d-lactone carbonyl (1728 cm (d 3.09, 1H, dd, Jϭ15.8, 7.8 Hz; 3.42, 1H, dd, Jϭ16.4, 9.3 Hz), an oxygenated methine proton signal (d 5.29, 1H, t, Jϭ 8.6 Hz), two olefinic proton signals (d 5.10, 1H, br s; 4.94, 1H, br s) and a methyl signal (d 1.76, 3H, s). Based on heteronuclear multiple bond connectivity (HMBC) correlations (Fig. 1) the aromatic protons at d 7.67, 6.87, 7.42 and 7.06 were assigned to H-1, H-4, H-7, and H-10. Thus from the foregoing spectral studies, two possible structures (1, 1a) could be assigned for tephcalostan.A distinction between two possible structures (1, 1a) for tephcalostan was made by HMBC and nuclear Overhauser enhancement spectroscopy (NOESY) studies. The methylenedioxy group at d 6.02 was placed at C-8/C-9 positions of ring-B as these protons showed HMBC correlations with C-8 (d 145.9) and C-9 (d 147.1) which further showed cross correlations with two para related aromatic protons at d 7.42 (H-7) and 7.06 (H-10) in its HMBC spectrum (Fig. 1)