The application of the desyl or 2-oxo-1,2-diphenylethyl moiety as a photolabile ligand for the release of phosphates such as cAMP and inorganic phosphate (Pi)1,2 is extended to include selected excitatory amino acids. The synthesis and photochemical studies of N- and O-desyl-caged versions of the endogenous amino acid neurotransmitters glutamate and γ-aminobutyric acid (GABA) are reported. Photolysis at 350 nm of solutions of γ-O-desyl glutamate (11) and O-desyl GABA (14) in 1:1 H2O−acetonitrile cleanly produced free glutamate and GABA, respectively, with rate constants of ca. 107 s-1; 2-phenylbenzo[b]furan (2) was the only photobyproduct detected by HPLC. Photolysis quantum efficiencies for the disappearance of O-desyl amino acid esters were in the range of 0.29−0.31, and the appearance efficiencies of furan 2 (and the corresponding amino acid) were 0.14. The photolysis of 14 was efficiently quenched with sodium 2-naphthalenesulfonate, yielding a triplet lifetime of ca. 10 ns. Photolysis of 11 in mammali...