(1R,2R)-4-Methylurazole-α-D-pyranosyl-2-deoxyriboside from Reaction of 4-Methylurazole with 2-Deoxy-D-ribose

The crystalline nucleoside formed from an aqueous solution of 4-methylurazole and 2-deoxy-D-ribose was identified unequivocally by its X-ray structure as a single diastereomer, (1R,2R)-4-methyl­urazole-α-D– pyranosyl-2-deoxyriboside [IUPAC name: 1-(2-deoxy-α-D-erythro- pentopyranosyl)-1-(R), 2-(R)-4-methyl-4-triazolidine-3,5-dione, C₈H₁₃N₃O₅]. In its urazole ring the two hydrazidic N atoms are pyramidal and confer R chirality, the respective pyranosyl and H-atom substituents being substanti­ally out of the ring plane and trans juxtaposed, while the imidic N atom is trigonal planar, its methyl substituent being essentially coplanar with the ring. The intermolecular hydrogen bonding involves pyranose–pyranose and pyranose–urazole interactions producing one-dimensional cross-linked double chains. From this study and our results from the preparation of three related nucleosides we find that the crystalline nucleosides formed by direct coupling of these nucleobases with 2-deoxy­ribose are consistently diastereospecific.

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