Pyrrolopyrimidine nucleosides II. the total synthesis of 7-β-D-ribofuranosylpyrrolo[2,3-d]pyrimidines related to toyocamycin

The first synthesis of a 7-β-D-ribofuranosylpyrrolo2,3-d]pyrimidine by direct ribosidation of a preformed pyrrolo2,3-d]pyrimidine has now been accomplished via the fusion procedure. Subsequent functional group transformations furnished the 6-methyl-thio derivative of the nucleoside antibiotic toyocamycin. Preparation of the 1-, 3- and 7-methyl isomers of 4-amino-5-cyano-6-methylthiopyrrolo2,3-d]pyrimidine was accomplished and has provided an unequivocal assignment for the actual site of ribosidation by a comparison of ultraviolet absorption spectra. Factors utilized for the assignment of anomeric configuration are discussed.