title: Characterization of products from the reactions of N-acetyldopamine quinone with N-acetylhistidine.
abstract: When insects harden or sclerotize their exoskeletons, quinones of N-acetylated catecholamines such as N-acetyldopamine (NADA) undergo nucleophilic addition reactions with amino acids such as histidine in cuticular proteins. To determine the products that might form when this type of reaction occurs during cuticle sclerotization, the reactions between electrochemically prepared NADA quinone and N-acetylistidine (NAcH), a protein model nucleophile, have been investigated at pH 7. Two major products, 6-[N-(N-acetylhistidyl)]-N-acetyldopamine and 2-[N-(N-acetylhistidyl)]-N-acetyldopamine, were purified by semipreparative reversed-phase liquid chromatography and identified by mass spectrometry and nuclear magnetic resonance spectroscopy. The relative molar ratio of the C(6) mono-addition adduct to the C(2) mono-addition adduct is 87:13. UV/vis spectroscopic analysis shows that both products have an absorption maximum at 284 nm. Cyclic voltammetry shows that these adducts are oxidized less readily than NADA.
authors.affiliation: Department of Chemistry, Kansas State University, Manhattan 66506, USA.
authors.forename: R
authors.initials: R
authors.lastname: Xu
authors.forename: X
authors.initials: X
authors.lastname: Huang
authors.forename: T D
authors.initials: TD
authors.lastname: Morgan
authors.forename: O
authors.initials: O
authors.lastname: Prakash
authors.forename: K J
authors.initials: KJ
authors.lastname: Kramer
authors.forename: M D
authors.initials: MD
authors.lastname: Hawley
mesh_terms: D016227:Benzoquinones / Q000737:chemistry*; D002853:Chromatography, Liquid; D006639:Histidine / Q000031:analogs & derivatives* / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D009682:Magnetic Resonance Spectroscopy; D013056:Spectrophotometry, Ultraviolet
chemical_list: D016227:Benzoquinones; D006639:Histidine; C061419:N-acetyldopamine quinone; C023495:N-acetylhistidine