Compounds represented by the general formula (1) ##STR00001## wherein R.sup.1 and R.sup.3 are each independently hydrogen or a carboxyl group and R.sup.2 and R.sup.4 are each independently hydrogen or a hydroxyl group, or pharmaceutically acceptable salts thereof, which exhibit semaphorin-inhibitory activity and are useful as preventives or remedies for neuropathic and neurodegenerative diseases are provided.