The SP Diastereomer of a Dinucleoside Methylphosphonate Methanol Solvate Containing Thymine and N3-Methyl-4-thiothymine Bases

Abstract

The structure of the non-self-complementary di-, Tp(Me)msT, C22H31NaOio-PS.CH40, has been determined and its absolute configuration at the phosphorus centre shown to be S. The 2'-deoxyribose rings of the thymidine and N 3-methyl-4-thiothymidine moieties adopt 3 T2 (C3'-exo/ C2'-endo) and 2T 3 (C2"-endo/CY-exo) conformations, respectively. Both heterocyclic bases are oriented anti relative to the sugar rings. The deoxyribose-phosphonate backbone has an extended conformation with the bases completely unstacked and tilted away from being parallel by 16 (1)°.