. "The chemical reactions and pathways resulting in the formation of xanthine, 2,6-dihydroxypurine, a purine formed in the metabolic breakdown of guanine but not present in nucleic acids." . . . "xanthine synthesis" . "xanthine biosynthetic process" . "xanthine anabolism" . "xanthine biosynthesis" . "xanthine formation" . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .