Ring closure of 5-amino-1-β-D-ribofuranosylimidazole-4-carboxamide (AICA-riboside) with phenyl isothiocyanate afforded 2-mercaptoinosine (I) in good yield. Similarly, the ring closure of AICA-riboside 5'-phosphate (AICAR) led to the formation of 2-mercaptoinosine 5'-phosphate (II). Various 2-substituted inosine 5'-phosphates were prepared from I and II or starting with AICA-riboside. It was found that 2-furfuryl-thioinosine 5'-phosphate possessed a flavor enhancing activity of about 17-times that of inosine 5'-phosphate. The chemical structure-flavor enhancing activity relationship was presented.
