Twenty-two pyrazoline derivatives were synthesized and tested for their human MAO (hMAO) inhibitory activity. Twelve molecules with unsubstituted ring A and substituted ring C (5-16) were found to be potent inhibitors of hMAO-A isoform with SI(MAO-A) in the order 10(3) and 10(4). Ten molecules with unsubstituted ring A and without ring C (21-30), in which eight molecules (21, 23-26, and 28-30) were selective for hMAO-A, one for hMAO-B (22) and the other one non-selective (27). Presence of ring C increases potency as well as SI towards hMAO-A; however its absence decreases both potency and SI towards hMAO-A and hMAO-B. (C) 2011 Elsevier Ltd. All rights reserved.