Indian Journal of Chemistry Vol. 46B, February 2007, pp. 366-369 Note A new prenylated isoflavone from Tephrosia tinctoria B Anil Kumar Reddy, S Ibrahim Khalivulla & D Gunasekar* Natural Products Division, Department of Chemistry, Sri Venkateswara University, Tirupati 517 502, India E-mail: duvvurusekarg@rediffmail.com Received 9 May 2006; accepted (revised) 20 September 2006 A new prenylated isoflavone, 7-O-geranylbiochanin A 1 has been isolated from the roots of Tephrosia tinctoria, together with three previously known compounds, 7-O-methylglabranin 2, flemichapparin B 3 and dehydrodeguelin 4. The structures of the compounds, 1 - 4 have been established by spectroscopic methods, including analysis by 2D NMR spectroscopy. Keywords: Tephrosia tinctoria, Isoflavone IPC: Int.Cl. 8 C07D Tephrosia PERS. (Fam: Leguminosae, Sub fam: Papilionoideae) is a large tropical and sub-tropical genus estimated to contain 300 species 1 . The genus Tephrosia is known to elaborate a rich variety of flavonoids and isoflavonoids 2 . Tephrosia tinctoria Pers. is an erect undershrub widely distributed in Talakona forest of Andhra Pradesh, South India 3 . As there is no record of any phytochemical work on T. tinctoria, we have examined the roots of this species and report herein the isolation and structure elucidation of a new prenylated isoflavone, 7-O- geranylbiochanin A 1 together with three known compounds, 7-O-methylglabranin 2, flemichapparin B 3 and dehydrodeguelin 4. Results and Discussion Compound 1, obtained as pale yellow amorphous powder, showed [M + H] + peak at m/z 421 in the positive ion FABMS corresponding to the molecular formula C 26 H 28 O 5 . This was corroborated by the 13 C NMR spectrum, which showed signals for all the 26 carbons present in the molecule. The UV spectrum showed absorption maxima at 262 and 327 nm, characteristic of an isoflavone derivative 4 . The 1 H NMR spectrum of 1 showed a sharp signal at δ 7.90 (1H, s), typical of the proton at C-2 of an isoflavonoid skeleton. Addition of NaOAc caused no shift in band II UV absorption maximum indicating the absence of a free hydroxyl at C-7. A bathochromic shift of 11 nm in band I UV absorption maximum with AlCl 3 and a downfield 1 H NMR signal at δ 12.82 in 1, suggested the presence of a chelated hydroxyl at C-5. The IR spectrum exhibited absorption bands for chelated hydroxyl (3376 cm -1 ), conjugated carbonyl (1646 cm -1 ), olefin (1415 cm -1 ) and ether (1179 cm -1 ) functionalities. The 1 H NMR spectrum of 1 showed two singlet signals at δ 6.12 and 6.29, which correlated to carbons at 99.6 (C-6) and 94.4 ppm (C-8), in the HSQC spectrum, were characteristic of H-6 and H-8 protons of ring A. It also showed two sets of ortho-coupled doublets (J = 8.8 Hz) at δ 6.95 and 7.44, integrating for two protons each, correlating with C-3′ and C-5′ (114.0 ppm) and C-2′ and C-6′ signals (130.1 ppm), respectively in the HMBC spectrum (Figure 1), were assigned to H-3′, 5′ and H-2′, 6′ protons of ring B. A sharp three-proton singlet at δ 3.82 was attributed to a methoxyl group and was placed at C-4′ as it showed 3 J correlation with this carbon at 159.7 ppm in the HMBC spectrum. The 1 H NMR spectrum of 1 further showed three olefinic methyl singlets δ (1.57, 1.65, 1.81), two multiplet methylene signals (2.06, 2.08), an oxygenated doublet methylene signal (4.54) and two triplet vinyl proton signals (5.03, 5.234) assignable to either geranyl or neryl moiety. The 13 C NMR data, particularly the chemical shifts of the methyl at C-3′′ and the C-4′′ methylene, aid in distinguishing geranyl from neryl side chain. The chemical shifts at 16.1 and 39.6 ppm observed for methyl and methylene groups, respectively, confirmed the presence of a geranyl side chain 5 in 1. The geranyl moiety was placed at C-7 as the geranyloxy methylene protons at C-1′′ correlated to C-7 of the isoflavone nucleus in the HMBC spectrum. Moreover, the interactions observed in the 2D phase-sensitive NOESY (Figure 1) experiment between the methylene protons at C-1′′ and H-6 and H-8 aromatic protons unambiguously confirms the presence of an O-geranyl moiety at C-7 position. On the basis of the foregoing spectral studies, the structure of 1 was elucidated as 5-hydroxy-4′- methoxy-7-O-geranyl isoflavone (or 7-O-geranyl- biochanin A). Incidentally, the isolation of 1