New monoamine oxidase inhibitors were synthesized as indole analogues of a previously reported pyrrole series. Several compounds were potent MAO-A (12, 17, 19–22, 31, 36, and 37) or MAO-B (14, 20, 24, 38, 44, and 46) inhibitors, and had Ki values in the nanomolar concentration range. In particular, 22 (Ki= 0.00092 μM, and SI= 68,478) was exceptionally potent and selective as MAO-A inhibitor. In molecular modeling studies, compounds 22, ...