Studies on the biosynthesis of bacterial and viral pyrimidines. II. Dihydrouracil and dihydrothymine nucleosides.

In Paper I (l), it was shown that, in Escherichia co&, exogenous uracil can be converted to nucleic acid thymine and that the methyl group of methionine does not serve as a precursor of either bacterial thymine or bacteriophage thymine and hydroxymethylcytosine. Considerations as to the nature of the l-carbon precursor of the thymine methyl group and of possible biosynthetic mechanisms have led us to propose dihydrohydroxymethylpyrimidine derivatives as possible intermediates in the biosynthesis of thymine (1). To test this hypothesis further, we have investigated the synthesis of dihydropyrimidine derivatives. This paper describes the synthesis of dihydrouracil and dihydrothymine nucleosides and some of their chemical and metabolic properties.