Beta-substituted ethylamine derivatives as suicide inhibitors of lysyl oxidase

Lysyl oxidase initiates the covalent cross-linking of elastin and collagen, converting lysyl residues in these proteins to peptidyl aldehyde residues. The present study explored structural and electron withdrawing features required to generate mechanism-based inhibitors of this enzyme with antifibrotic potential. It was found that the electron withdrawing nitrile moiety of beta-aminopropionitrile (BAPN), a naturally occurring syncatalytic inhibitor of lysyl oxidase, can be replaced by chlorine, bromine, or the nitro function to yield 2-haloamines or nitroethylamine compounds which also act as mechanism-based irreversible inhibitors of this enzyme. BAPN and 2-bromo- and 2-chloroethylamine exhibit similar KI values of 6-10 microM. However, the enzyme becomes irreversibly inactivated significantly faster by either of the 2-haloamines than by BAPN. 2-Nitroethylamine has by far the poorest affinity for the enzyme and inactivates much more slowly than the other amines of this series, consistent with interference with optimal enzyme-inhibitor interactions by the anionic nitro group. Unlike BAPN, 2-bromoethylamine is processed to a detectable aldehyde product upon incubation with enzyme, showing a partition ratio of 1.2 mol of acetaldehyde formed per mol of 2-bromo-ethylamine which becomes covalently incorporated in the enzyme. The results are consistent with the processing of 2-bromo-ethylamine to an enzyme-ethyleneamine Schiff base subject to hydrolysis to acetaldehyde or to covalent attack at carbon 2 by an enzyme nucleophile. Thus, beta-haloamines represent a new series of suicide inhibitors of lysyl oxidase which can inactivate the enzyme faster than BAPN and hence may have antifibrotic potential.