PREPARATION OF UREIDONUCLEOSIDES OF THE THREONINE ISOMERS

The hypermodified ureidonucleoside ranosyl-9H-purine-6-yl)amino)carbon yl]-L-threonine (5) is a constituent of transfer ribonucleic acid (tRN A) and is secreted as a tRNA catabolite in body fluids such as blood, milk and urine. Compound 5 and the isomeric ureidonucleosides bearing D-threonine (9), L-allo- (7) and D-allo-threonine (11) as side chain m oieties were synthesized on a preparative scale. The amido protons of 5 and 9 cause two separate H-1 NMR signals whereas 7 and 11 cause mult iplets. The C-13 NMR signals of all carbon atoms of the allo-amino aci d side chains (7, 11) are shifted downfield of the corresponding signa ls in compounds 5 and 9. The chemically protected intermediate compoun d adenosine urethane (3) is potentially of interest in the analysis of amino acids because it may be converted to nucleosides of the ureido type by reaction with amino acids in biological matrices.