From the reaction mixtures of D-ribose or D-xylose and urea, two anomeric pairs of D-ribopyranosyl- and D-xylopyranosylureas were separated by a Celite column. These ureides, after acetylation followed by condensation with 2-methyl-3-methoxyacryloyl chloride, afforded the intermediates, the cyclisation of which produced two anomeric pairs of D-ribopyranosyl- and D-xylopyranosylthymines.
