(3R,5R)-TETRAHYDRO-2H-1,4-THIAZINE-3,5-DICARBOXYLIC ACID MONOHYDRATE

(3R,5R)-Tetrahydro-2H-1,4-thiazine-3,5-dicarboxylic acid monohydrate, which is in the zwitterionic form in the crystal, shows a puckered chair conformation of the six-membered ring with S(1) and N(4) out of the C(2), C(3), C(5), C(6) mean plane by 0.972 and 0.648 angstrom, respectively. The ionized carboxyl group is axially oriented.