(2S)-2-(4-Ethyl-2,3-dioxopiperazine-1-carboxamido)-2-(4-hy­droxy­phen­yl)acetic acid

There are two mol­ecules in the asymmetric unit of the title compound, C(15)H(17)N(3)O(6). The 2,3-dioxopiperazine ring adopts a half-chair conformation with torsion angles of −7.6 (4) and 35.1 (4)° in one mol­ecule, and 5.3 (4) and 45.4 (4)° in the other mol­ecule. In the crystal structure, the carb­oxy groups are involved in classical inversion-related O—H⋯O hydrogen bonds, which link the mol­ecules into centrosymmetric dimers. These dimers are further linked by inter­molecular O—H⋯O and C—H⋯O hydrogen bonds. Each independent mol­ecule also exhibits an intra­molecular N—H⋯O hydrogen bond. The H atoms of the carb­oxy groups are disordered over two positions, with refined site-occupancy factors of 0.5.