Lecture35outline

Lecture35outline - I. Review Peptide synthesis proceeds...

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I. Review • Peptide synthesis proceeds through a specific amide bond formation between two amino acids in the presence of a coupling agent • Dicyclohexylcarbodiimide (DCC) and other carbodiimides are commonly used as coupling agents • These reactions proceed through proton transfer between the carboxylic acid and the carbodiimide followed by nucleophilic addition to form a mixed anhydride-type intermediate that reacts with amines to form amides • Selective coupling requires that only one amino acid can act as a nucleophile and only one amino acid can act as an electrophile • Conversion of a carboxylic acid to an ester or an amide prevents its reaction with DCC, thereby eliminating its potential to act as an electrophile • Conversion of an amine to a carbamate significantly inhibits its nucleophilicity • The reaction between an amino ester (or amide) and a carbamate-protected amino acid in the presence of a coupling agent leads to selective peptide bond formation • Cleavage of the carbamate (see carbamate section in the amine chapter) provides an
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Lecture35outline - I. Review Peptide synthesis proceeds...

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