A series of coumarin-3-acyl derivatives have been synthesized and investigated for the ability to inhibit selectively monoamine oxidases. The coumarin-3-carboxylic acids, 2a–e, proved to be reversible and selective inhibitors of the MAO-B isoform, displaying pIC50 values of particular interest: 2a shows pIC50 7.76 and a selectivity index (pS. I.) 2.94 and 2b shows pIC50 7.72 and a pS. I. of 2.80. The coumarin-3-acyl chlorides 3a–e showed high ...