Homocysteic acid is the organosulfur compound with the formula HO3SCH2CH2CH(NH2)CO2H.

A white solid, it is sulfonic acid-containing non-proteinogenic amino acid.

It is aanalog of glutamic acid and is a potent NMDA receptor agonist.

[1][2] It is related to homocysteine, a by-product of methionine metabolism.

Homocysteic acid is prepared by the oxidation of homocystine with aqueous bromine.