Crystal and molecular structure of triacanthine, 6-amino-3-dimethylallylpurine,a naturally occurring N(3)-substituted purine

The crystal and molecular structures of the naturally occurring, N(3)-substituted purine triacanthine (6-amino-3-dimethylallylpurine) are presented. Triacanthine crystallizes, from a saturated DMSO solution, in the monoclinic system, space groupP2₁/c. Crystallographic data are as follows:a = 12.451(4),b = 8.508(4),c = 11.365(3) Å, = 122.74(2) °,V_c = 1012.66 ų,Z = 4,D_m = 1.335(1),D_x= 1.333 g cm^–3. The structural solution was obtained by direct methods and has been refined, based on full-matrix least squares with 2124 observedF_o data, to a finalR value of 0.075. The principal molecular features are (1) the occurrence of the substituted purine as the amino tautomer, (2) a nearly planar purine ring system, and (3) a highly planar dimethylallyl group oriented approximately orthogonally to the purine ring system. The crystal packing is dominated by intermolecular hydrogen bonds involving the exocyclic amino group and the acceptor sites N(1) and N(9). Sheets of such hydrogen-bonded molecules are stacked along [10¯1]. Two distinct types of molecular overlaps are observed within these stacks.