Specific compounds of formula (Ia): and pharmaceutically acceptable salts thereof. Pharmaceutical compositions of the specific compounds of formula (Ia) and pharmaceutically acceptable salts thereof. A method for inhibiting tumor growth in a subject that includes administering to the subject an effective amount of a compound selected from the specific compounds of formula (Ia) and pharmaceutically acceptable salts thereof. A method for modulating semicarbazide-sensitive amine oxidase activity in a subject that includes administering to the subject an effective amount of a compound selected from the specific compounds of formula (Ia) and pharmaceutically acceptable salts thereof.