Synthesis of selenopeptides: an alternative way of incorporating selenocystine.

Selenocysteine (Sec) residue cannot be directly attached to a peptide sequence unless the selenol form is protected beforehand and several problems have been reported in the preparation of Sec building blocks. In this article a series of selenocystine, the oxidized form of Sec, containing peptides has been synthesized using a new methodology, where Boc-NH-chloroalanine is coupled with methyl ester protected residues (Ala, Met, Phe) using DCC/HOBt as the coupling reagents providing di- and tripeptides. Further, the treatment of disodium diselenide with chloroalanine peptides (Boc-ClAla-Ala-OMe, Boc-ClAla-Met-OMe and Boc-ClAla-Ala-Phe-OMe) afforded the respective selenocystine-containing peptides (Boc-Sec-Ala-OMe, Boc-Sec-Met-OMe and Boc-Sec-Ala-Phe-OMe).