Two enzymatic reactions convert this triphosphate to the cyclic phosphate of pyranopterin.

XendoU is a U-specific metal dependent enzyme that produces products with a 2'-3' cyclic phosphate termini.

Antiviral activity is retained for acetate and phosphate derivation of the ribose hydroxyls, including the triphosphate and 3', 5' cyclic phosphates, but these compounds are no more active than the parent molecule, reflecting the high efficiency of esterase and kinase activity in the body.