The copper-containing amine oxidases, like bovine plasma amine oxidase (BPAO), carry out a transaminative oxidation of primary amines to aldehydes via use of an active site Tyr-derived 2,4,5-trihydroxyphenylalanine quinone (TPQ) cofactor. Propargylamine is a potent inactivator of BPAO (IC50 = 3 µM), possibly through active-site modification by the a, ß-unsaturated aldehyde turnover product, but the simple structure is expected to confer low selectivity. On the basis of the finding by previous students that certain extended conjugation analogs such as 1,6-diamino-2,4- hexadiyne and 3-cyanopropargylamine preserve strong inactivation potency, other extended conjugation analogs of propargylamine were evaluated. In particular, 1-amino-2,4-hexadiynes with a 6-OH rather than 6-NH2 group were found to be potent inhibitors.