Purine studies. XXIII. Conformational aspects of N-(6-amino-2,4-dioxo-1,2,3,4-tetrahydropyrimidin-5-y1)formamides and related N-benzyl derivatives

Abstract

The occurrence of 'Z' and 'E' conformers in 5-formamidouracil derivatives has been investigated by ¹H n.m.r. and the effect of the nature and size of the substituents on the isomer ratio studied. Also considered was the relative steric competition between the benzyl and uracil moieties. As it is known that cyclic substituents with groups located ortho to the formamido group can induce rotation of the plane of the latter group into an orthogonal position to the plane of the ring, evidence for a corresponding effect in the case of the 6- aminouracil derivatives was sought. Similar but more restricted studies have been made with related 5-thioureidouracil analogues.