| Popis: |
Publisher Summary This chapter discusses the synthesis of an oxytocin-type fragment of insulin. S-trityl, S-diphenylmethyl, and S-acyl cysteine derivatives are intermediates for incorporation of cysteine residues in a peptide chain. These S-protecting groups do not hinder the further lengthening of the peptide chain, provided that, in each case, the amino acid to be incorporated, has been properly N-protected. S-protecting groups can be selectively removed without affecting the sensitive parts of the molecule, especially any already existing -S-S-bridge. When N-benzyloxycarbonylglycine is not coupled with S-benzoyl-L-cysteine methyl ester hydrochloride through the relatively slowly reacting carbodi-imide but through the much faster reacting mixed anhydrides, then the N-peptide, N-(N-benzyloxycarbonylglycyl)-S-benzoyl- L-cysteine methyl ester can be obtained in moderate yield instead of the S-peptide. Treatment of the fully protected heptapeptide with mercuric chloride in acetic acid or silver nitrate-pyridine in dimethylformamide yields the corresponding dimercaptides. |
