Chemical‐ and cuticular phenoloxidase‐ mediated synthesis of cysteinyl–catechol adducts

Abstract

N‐Acetylcysteine adducts of o‐benzoquinones derived from catechol, 4‐methylcatechol, and N‐acetyldopamine were chemically synthesized and characterized by a combination of UV, IR, and NMR spectral studies. Oxidation of catechol, 4‐methylcatechol, and N‐acetyldopamine by cuticle‐bound phenoloxidase from Sarcophaga bullata in the presence of N‐acetylcysteine resulted in the formation of covalent adducts between catecholic compounds and N‐acetylcysteine. Structural identities of these adducts were established by comparison of their HPLC retention time and UV spectra with those of synthetic adducts and by cochromatography with authentic samples. Although insect cuticle is known to contain only trace amounts of cysteine, the in vitro synthesis of quinone cysteine adducts mediated by cuticular phenoloxidase strongly indicates the occurrence of similar reactions in vivo as well and is in support of Pryor's quinone tanning hypothesis.