STRUCTURE OF ISOCORYDINE

C20H23NO4, M(r) = 341.41, orthorhombic, P2(1)2(1)2(1), a = 7.536 (5), b = 9.926 (8), c = 23.397 (16) angstrom, V = 1750 (2) angstrom3, Z = 4, D(x) = 1.296 Mg m-3, lambda(Mo K-alpha) = 0.7107 angstrom, mu = 0.084 mm-1, F(000) = 728, T = 293 (1) K, R = 0.038 for 1570 reflections with I > 3.5 sigma(I). Both B and C rings have a screw-boat conformation and the latter is almost perfect. The C-N-C angles indicate sp3 hybridization of the N atom. Bonds O1-C17 and O4-C19 are in the planes of rings A and D, respectively, as indicated by the corresponding torsion angles, while O2-C18 is perpendicular to the plane of ring A. The C20 methyl group is in an equatorial position, as indicated by the torsion angles. The hydroxyl group forms a strong intramolecular hydrogen bond [O3-H3 0.80 (5), H3...O2 1.78 (5), O3...O2 2.547 (4) A, O3-H3...O2 160 (5)-degrees]. Molecules are held together by van der Waals contacts.