Four new pterocarpanoids crotafurans A (1), B (2), C (3), and D (4) were isolated from the bark of Crotalaria pallida and the seeds of the C. assamica, respectively. The structures, including relative configurations were elucidated by spectroscopic data.
In the 1 H-NMR spectrum of 1, signals at d 3.66 (dd, J 10.4, 10.4 Hz, 1 H), 3.73 (ddd, J 11.0, 7.2, 4.8 Hz, 1 H), 4.33 (dd, J 10.4, 4.8 Hz, 1 H), and 5.69 (d, J 7.2 Hz, 1 H) were assigned to H b ÀC(6), H a ÀC(6a), H a ÀC(6), and H a ÀC(11a) protons of the pterocarpan ( 6a,11a-dihydro-6H-benzofuro[3,2-c]benzopyran) moiety, suggesting a cis arrangement of H a ÀC(6a) and H a ÀC(11a) . The 13 C-NMR signals at d 40.8, 67.3, and 80.4 were in agreement with the signals assigned to C(6a), C(6), and C(11a) of the pterocarpan moiety . The 1 H-and 13 C-NMR spectra revealed signals due to a trisubstituted and a tetrasubstituted benzene moiety, a trisubstituted furan moiety [3], as well as an exocyclic methylene, tertiary Me, and phenolic OH group. The position of the trisubstituted benzene moiety (ring A) of 1, i.e., its fusion at C(1a)ÀC(4a), was established by COSY90, HMQC, and the HMBC correlations HÀC(2)/C(1a), HÀC(4)/C(4a), HÀC(4)/C(1a), H b ÀC(6)/ C(4a), HÀC(11a)/C(4a), HÀC(11a)/C(1) (Table ). Similarly, the fusion of the tetrasubstituted benzene moiety (ring D) at C(7a)ÀC(10a) was suggested by COSY90, HMQC, and the HMBC correlations HÀC(7)/ C(10a) and HÀC(8)/C(7a). The attachment of the methyl and exocyclic methylene groups at C( ) was confirmed by the HMBC correlations Me(16)/C(14), Me(16)/C(15), HÀC(15)/C(16), and HÀC(15)/C(14). The HMBC correlations HÀC(15)/C(13), HÀC(12)/C(13), HÀC(12)/C(10), HÀC(8)/C(10), and HÀC(7)/ C(9) established the connectivity of the 1-methylethenyl moiety at the trisubstituted furan (ring E) moiety through the C(13)ÀC( ) bond and the fusion site of the trisubstituted furan (ring E) moiety at C(9)ÀC(10) of ring D.
The presence of characteristic peaks at m/z 303 ([320 À OH] ), 277 ([M À a À 2 H] ), and 186 ([M À b 2 H] ) in the EI-MS of 1 (Fig. ) supported the proposed structure. The relative configurations at C(6a) and