(2S,1'R,2'R,3'R)-2-(2,3-dicarboxycyclopropyl)-glycine (DCG-I) and (2S,1'S,2'S,3'S)-2-(2,3-dicarboxycyclopropyl)glycine (DCG-II), as well as methods for synthesizing these compounds are provided. Studies on L-glutamate receptors with the use of DCG-I and DCG-II, which are agonists for NMDA receptors, contribute to the development of remedies for various nervous disorders. Further, DCG-I and DCG-II selectively inhibit monosynaptic reflex even at a low concentration, which makes them useful as a remedy for spastic palsy, an anesthetic and an analgesic.