Protecting agents, acyl azides

A-Acyl-benzotriazoles, which are stable and easily handled (cf. acid chlorides or anhydrides) and can be prepared from a large variety of acids, including A-protected a-amino acids, have been widely used as N-, 0-, S- and C-acylating agents, for example to make acyl azides. ° The benzotriazole derivatives of A-protected-a-amino acids have been extensively developed as agents for peptide coupling. ... 

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