MOLECULAR AND CRYSTAL-STRUCTURE OF 1-(3'-C-METHYL-2'-DEOXYRIBOFURANOSYL)THYMINE

The structure of 3'-C-methylthymidine (3'-Me-Thd), a <<functionally competent>> analogue of thymidine, was determined by X-ray analysis. The space group is P2(1). Cell dimensions are: a = 5.100(1), b = 12.489(2), c = 9.202(1) angstrom; beta = 98.47(1)-degrees, V = = 579.7 angstrom 3, Z = 2. The structure was elucidated by direct methods and refined by the full-matrix least square method to R = 2.3%. The moleule of 3'-Me-Thd has anti-conformation with respect to the glycosidic bond (chi(04'-C1'-N1-C2) = -116.6-degrees), C2'-endo-C1'-exo puckering of the sugar moiety and gauche-gauche conformation about exocyclic C4'-C5'-bond (phi(C3'-C4'-C5'-O5') = 50.1-degrees). Using comparative analysis of 3'-Me-Thd and 3'-Me-cytidine [1] it was concluded that 3'-Me-pyrimidines have <<hard>> conformation independent of the sugar and base types.