― The major site of purine synthesis is in the liver. Synthesis of the purine nucleotides begins with PRPP and leads to the first fully formed nucleotide, inosine 5'-monophosphate (IMP). This pathway is diagrammed below. Stage 1: The purine base without the attached ribose moiety is hypoxanthine. The purine base is built upon the ribose by several amidotransferase and transformylation reactions. The synthesis of IMP requires five moles of ATP, two moles of glutamine, one mole of glycine, one mole [...].