[{"from": "human", "value": "Synthesize a molecule that matches the given characteristics. The molecule is an optically active form of 4-hydroxy-2-oxopentanoic acid having 4S-configuration. It is a conjugate acid of a (S)-4-hydroxy-2-oxopentanoate."}, {"from": "gpt", "value": "[C][C@@H1][Branch1][O][C][C][=Branch1][C][=O][C][=Branch1][C][=O][O][O]"}]