5′-Phosphoribosylformylglycinamidine (or FGAM) is a biochemical intermediate in the formation of purine nucleotides via inosine-5-monophosphate, and hence is a building block for DNA and RNA.

[1][2] The vitamins thiamine[3][4] and cobalamin[5] also contain fragments derived from FGAM.

[6] The compound is biosynthesized from phosphoribosyl-N-formylglycineamide (FGAR) which is converted to an amidine by the action of phosphoribosylformylglycinamidine synthase (EC 6.3.5.3), transferring an amino group from glutamine in a reaction that also requires ATP: The biosynthesis pathway next converts FGAM to 5-aminoimidazole ribotide (AIR) by the action of AIR synthetase (EC 6.3.3.1) which uses ATP to activate the terminal carbonyl group to attack by the nitrogen atom at the anomeric center: