(2S)-4-Oxo-2-oxetanecarboxylic Acid Ethyl Ester is the S-isomer of 4-Oxo-2-oxetanecarboxylic Acid Ethyl Ester (O858475); the ethyl ester derivative of 4-Oxo-2-oxetanecarboxylic Acid (O858455) which is a building block in copolymers which are used as coating materials for medical devices.