Abstract
Cyclization of 5-iodo-1-(β-D-xylofuranosyl) uracil and -cytosine with sodium methoxide afforded 6, 3'-O-cyclouridine (IIa) and -cytidine (IIc), respectively. The rate of cyclization of 5-iodopyrimidine nucleosides is greatly dependent on the ring size formed on cyclization. Introduction of a trityl group at the 5'-position of the nucleoside brought about a decrease in the rate of cyclization. The ease with which ring-opening of 6-O-cyclouracil nucleoside isomers was effected with diluted sulfuric acid was in the opposite order to that of cyclization. The ultraviolet, circular dichroism and mass spectra of 6-O-cyclopyrimidine nucleosides and their isomers were compared.
