Synthesis of 2-Alkylthioinosine 5'-Phosphates and N<SUP>2</SUP>-Methylated Guanosine 5'-Phosphates

2-Alkylthioinosine 5'-phosphates and N2-methylated guanosine 5'-phosphates (the minor constituents of transfer RNA) were synthesized via 2', 3'-O-isopropylidene-2-mercaptoinosine (I) from 5-amino-1-β-D-ribofuranosyl-4-imidazolecarboxamide (AICA-riboside). The relationship between their chemical structures and flavoring activity was investigated, and 2-methylthioinosine 5'-phosphate (VII) was found to have an extremely strong flavoring activity.