Abstract Diamines (6)–(8) and (11) act as acceptable substrates for diamine oxidase (DAO) and the novel phenacyl derivatives (2) are obtained in satisfactory preparative yield; no enantioselectivity is observed with (11) as an enzyme substrate. Remarkably, the triamines (9) and (13) are not oxidized and, moreover,(9) acts as a notable inhibitor for the DAO catalysed oxidation of (4) and (5). Kinetic evidence relevant to the mechanism of DAO ...