Natural geiparvarin 1 and a number of its analogues were prepared and tested as inhibitors of both monoamine oxidase isoforms, MAO-B and MAO-A. The desmethyl congener 6 of geiparvarin, proved potent and selective MAO-B inhibitor (PIC50 = 7.55 vs 4.62). X-ray crystallography and molecular modelling studies helped the understanding of the observed structure-activity relationships. (C) 2002 Elsevier Science Ltd. All rights reserved.