Synthesis of FMOC-protected S-arylcysteines and modified keratin sequence peptides as specific epitopes as immunogens

Abstract

The sulfhydryl group of cysteine residues is a site for the adduction of ultimate carcinogenic arene oxide metabolites to the proteins keratin I and keratin 10, dominant proteins of the squame. The putative cysteine adducts are: S-phenylcysteine from benzene oxide and S-(1-naphthyl)- and S-(2-naphthyl)cysteine from naphthalene-1,2-oxide. In developing ELISAs for monitoring dermal exposures, we have embarked on synthesis of adducted head sequences GGRFSS(C*)GG (keratin 1) and GGGG(C*)GGGGG (keratin 10) by 9-fluorenyl-methoxycarbonyl chemistry to use in raising epitope-specific antibodies. Synthesis of the FMOC-protected cysteines was based on addition of arylthiols to 2-acetamidoacrylic acid, to give S-arylmercapturic acids. Removal of the N-acetyl group was accomplished quantitatively by extended refluxing in 1:1 t-butanol/concentrated HCl. FMOC derivatization of the S-arylcysteines vas accomplished by a published procedure, modified because of the low solubility. The oligopeptides (C* = S-phenylcysteinyl residue) have been synthesized and characterized.