CARBONYL-2-METHYL-1,2-ISOXAZOLIDINE]-RIBOTHYMIDINE

The title compound, C15H21N3O7, is a thymidine derivative with a tetra hydroisoxazole (THI) ring fused to the sugar ring at the 2'- and 3'-C atoms, The thymine base is in an anti conformation [chi = -122.5 (3)de grees] while the ribose moiety has a C2'-exo,C3'-endo (T-3(2)) conform ation with a highly flattened sugar ring [P = -5.8, tau(m) = 13.1 degr ees], The molecule contains a pseudo-twofold axis on the C2'-C3' bond with the ethyl ester group acting as the base and the N-methyl group a cting as the 5'-hydroxyl group in a nucleoside. The THI ring fused to the furanose has a C3'-endo,C4'-exo (T-3(4)) conformation [P = 41.8, t au(m) = 19.3 degrees]. The ethyl ester moiety is disordered with respe ct to two conformations, the population of the major form being 87.4 ( 8)% and that of the minor form 12.6(8)%.