SELECTIVE ACETYLENIC ‘SUICIDE’ AND REVERSIBLE INHIBITORS OF MONOAMINE OXIDASE TYPES A AND B

Abstract

A number of aromatic‐N‐propargyl (acetylenic) compounds and indoleamines were tested for their inhibitory action on monoamine oxidase (MAO) type A and type B using the substrates 5‐hydroxytryptamine (5‐HT), β‐phenylethylamine (PEA) and dopamine. Structure activity studies with aromatic‐N‐propragyl (acetylenic) derivatives have shown that MAO inhibitory potency is least dependent on the aromatic portion of the compounds. N‐methylated propargyl derivatives are the most active and replacement of the methyl group with a higher alkyl or aromatic group results in significant reduction of activity. The triple bond in the N‐propargyl portion is absolutely essential for activity and must be β‐to the nitrogen. It is the acetylenic group that gives these compounds their irreversible MAO inhibitory property. The present study has indicated that since the acetylenic compounds resemble the enzyme substrates the distance between the aromatic ring and the N‐propargyl terminal is crucial in designating the type A or type B MAO inhibitory property. For MAO type A inhibition, a distance equivalent to at least three carbon units is required, while for the inhibition of the B type enzyme this distance can be 1 or 2 carbon units. The compounds AGN‐1133 and AGN‐1135 show most promise in Parkinson's disease or as anti‐depressants because of their irreversible selective type B MAO inhibition in vitro and in vivo. A number of indoleamine derivatives were found to be reversible selective type A inhibitors. 1981 British Pharmacological Society