Synthesis and Structural Studies ofSP andRP Diastereomers of Deoxyxylothymidyl-3′-O-acetylthymidyl (3′,5′)-O-(2-Cyanoethyl)phosphorothioate in Solution and in the Solid State

Abstract

The synthesis and full assignment of the molecular structure of the diastereomers of deoxyxylothymidyl-3′-O-acetylthymidyl (3′,5′)-O-(2-cyanoethyl)phosphorothioate (1) in the liquid phase based on 1 H, 13C, 1D and 2D homo- and heteronuclear PFG (Pulse Field Gradient) NMR spectroscopic experiments are reported. The pseudorotation parameters of deoxyribose and deoxyxylose were analyzed by means of the PSEUROT program. The absolute configuration RP and SP of the phosphorus centers was deduced from 1H ROESY experiment. The 31P CP/MAS technique was used to establish the ratio between the amorphous and crystalline phases, and to test the progress of crystallization. The differences in the 31P δii principal elements of the chemical shift tensor, in particular the δ33 parameter, for crystalline and amorphous phases were calculated. Finally, the X-ray data for the SP diastereomer are reported. The influence of weak C−H···S hydrogen bonding on the molecular packing of both Rp-1 and SP-1, and the significance of this type of intermolecular interaction for phosphorothioate systems is discussed.