Uncovering the Structure of Human Red Hair Pheomelanin: Benzothiazolylthiazinodihydroisoquinolines As Key Building Blocks

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• 作者：Giorgia Greco ; Lucia Panzella ; Luisella Verotta ; Marco d鈥橧schia ; Alessandra Napolitano
• 刊名：Journal of Natural Products
• 出版年：2011
• 出版时间：April 25, 2011
• 年：2011
• 卷：74
• 期：4
• 页码：675-682
• 全文大小：883K
• 年卷期：v.74,no.4(April 25, 2011)
• ISSN：1520-6025

文摘

Biomimetic oxidation of the pheomelanin precursor 5-S-cysteinyldopa in the presence of Zn²⁺ 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.