Structures of colchicine analogues. I. Allocolchicine.

Methyl 5-acetylamino-6,7-dihydro-9,10,11-trimethoxy-5H-dibenzo[a,c] cycloheptene-3-carboxylate, C22H25NO6, Mr = 399.4, monoclinic, P2(1), a = 7.968 (1), b = 9.482 (1), c = 15.063 (2) A, beta = 112.95 (1) degrees, V = 1047.9 (2) A3, Z = 2, Dm(flotation) = 1.27 (1), Dx = 1.266 Mg m 3, lambda(Cu K alpha) = 1.5418 A, mu = 0.68 mm 1, F(000) = 424, T = 288 (1) K. Final R = 0.050 for 1765 observed data. The seven-membered ring has the expected boat conformation, and the angle between the normals to the phenyl rings is 48.7 (4) degrees. The relative orientations of the three adjacent methoxy groups and the acetamido substituent are similar to those observed in crystals of colchicine. Intermolecular hydrogen bonds between the N and O atoms of the acetamido groups link the molecules into infinite spirals along the b axis.