Figure 4.

Nitrosylation of AMK to AMMC and oxidative products (dimers, putative vinylaminoindole, tyrosyl adduct) of AMK. Abbreviation: AMMC, 3-acetamidomethyl-6-methoxy-cinnol- inone. The structure of 2-acetamidomethyl-5-methoxy-3-vinylaminoindole is still hypothetic, but consistent with high-resolution MS [127]. Dimerization is indicative of AMK’s potential for nitrogen-dependent adduct formation, as in the interaction with tyrosyl residues. The similarity of the vinylaminoindole to melatonin would suggest possible N-nitrosylation as known for melatonin.