title: Uncovering the structure of human red hair pheomelanin: benzothiazolylthiazinodihydroisoquinolines as key building blocks.
abstract: Biomimetic oxidation of the pheomelanin precursor 5-S-cysteinyldopa in the presence of Zn(2+) ions led to the isolation of two isomeric products, one of which could be identified as the benzothiazolylthiazinodihydroisoquinoline 5, while the other proved too unstable for a complete characterization. Both these products were converted into more stable oxidized forms, which after ethylchloroformate derivatization were characterized as the ethyl ester/ethoxycarbonyl isoquinolines 8 and 9. Compound 5 exhibited absorption characteristics similar to those of red hair pheomelanin, including a main band around 400 nm in acids. Similarly to red hair pheomelanin and synthetic pigments, 5 afforded on chemical degradation a thiazolylpyridinecarboxylic acid fragment. Model chemical studies allowed the proposal of a formation mechanism for the benzothiazole and dihydroisoquinoline systems in compound 5.
authors.affiliation: Department of Organic Chemistry and Biochemistry, University of Naples Federico II, Via Cintia 4, I-80126 Naples, Italy.
authors.forename: Giorgia
authors.initials: G
authors.lastname: Greco
authors.forename: Lucia
authors.initials: L
authors.lastname: Panzella
authors.forename: Luisella
authors.initials: L
authors.lastname: Verotta
authors.forename: Marco
authors.initials: M
authors.lastname: d'Ischia
authors.forename: Alessandra
authors.initials: A
authors.lastname: Napolitano
mesh_terms: D052160:Benzothiazoles / Q000737:chemistry / Q000378:metabolism*; D003548:Cysteinyldopa / Q000096:biosynthesis* / Q000737:chemistry; D006197:Hair / Q000737:chemistry / Q000378:metabolism; D006200:Hair Color / Q000502:physiology*; D006801:Humans; D007546:Isoquinolines / Q000737:chemistry / Q000378:metabolism*; D008543:Melanins / Q000096:biosynthesis* / Q000737:chemistry* / Q000502:physiology; D008956:Models, Chemical; D015394:Molecular Structure; D010084:Oxidation-Reduction; D010860:Pigments, Biological / Q000096:biosynthesis* / Q000737:chemistry; D013237:Stereoisomerism; D015032:Zinc / Q000737:chemistry
chemical_list: D052160:Benzothiazoles; C109853:G 1617; D007546:Isoquinolines; D008543:Melanins; D010860:Pigments, Biological; C018362:pheomelanin; D003548:Cysteinyldopa; C005465:benzothiazole; D015032:Zinc