Novel isoxazolopyridone derivatives and their use

The invention relates to isoxazolopyridone derivatives of a formula (I-a): 1 wherein R 1a represents an optionally-substituted heteroaryl or phenyl group, R 2a represents an optionally-substituted phenyl or heteroaryl group, and R 3a represents a methyl group, provided that, (1) when R 1a is an unsubstituted phenyl group, then R 2a must not be a para-substituted phenyl group of which the substituent is any of a methoxy group, a chloro group, a methyl group, a trifluoromethyl group, a fluoro group, a bromomethyl group or a dimethylaminomethyl group, and R 2a must not be an unsubstituted heteroaryl group, and (2) when R 1a is a 4-tolyl group or a 4-fluorophenyl group, then R 2a must not be an unsubstituted phenyl group, a 4-methoxyphenyl group or a 4-fluorophenyl group, or their pharmaceutically-acceptable salts. The isoxazolopyridone derivatives or their pharmaceutically-acceptable salts of the invention have a metabotropic glutamic acid receptor-antagonistic effect, and are useful for remedy of, for example, anxiety disorders, psychosomatic disorders, obsessive-compulsive neurosis, bipolar disorders, melancholia, eating disorders, schizophrenia, multi-infarct dementia, Alzheimer disease, epilepsy, Parkinson disease, Huntington's chorea, pain or retrograde neurosis.