(3R,5S)-5(3)-Carboxy-3,4,5,6-tetrahydro-2H-1,4-thiazin-4-ium-3(5)-carboxylate

The molecule of the zwitterionic title compound, C6H9NO4S, which lies on a mirror plane, shows a puckered chair conformation of the six-membered ring with the S and N atoms out of the mean plane of the other four C atoms by 0.929 (2) and 0.647 (2) A ° , respectively. The ionized carboxyl group is equatorially oriented. The hydrogen-bonding network includes very short O—H...O [2.470 (2) A ° ] and N—H...S [3.471 (2) and 3.416 (2) A ° ] intermolecular contacts