This invention relates to racemic and optically active N-(2-chloro-5-methylthiophenyl)-N′-(3-methylsulfinylphenyl)-N′-methylguanidine, N-(2-chloro-5-methylsulfinylphenyl)-1-(7-trifluoromethyl- 1,2,3,4-tetrahydroquinolinyl)carboximidamide, and N-(3-methylsulfinylphenyl)-N-methyl-N′-(2-chloro-5-methoxyphenyl)guanidine and pharmaceutically acceptable salts thereof, and pharmaceutical compositions and therapeutic methods of treatment that comprise such compounds. Compounds of the invention are particularly useful for the treatment or prophylaxis of neurological injury and neurodegenerative disorders.