Carboxybenzyl

Carboxybenzyl (abbreviated as Cbz or Z) is a carbamate which is often used as an amine protecting group in organic synthesis. It is commonly used in peptide synthesis where the carboxybenzyl protection group is introduced by reacting the amine functionality with benzyl chloroformate in the presence of a weak base:

File:Cbz-Protection V1.svg

Benzyl chloroformate 1 reacts with an amino acid 2 to give a Cbz-protected amino acid 3.

Alternatively, as in the Curtius rearrangement, it is made by the trapping of an isocyanate with benzyl alcohol.

It is used to protect amines from electrophiles. The protected amine can be deprotected by catalytic hydrogenation or treatment with HBr, yielding a terminal carbamic acid that then readily decarboxylates to yield the free amine.

The method was first used by Max Bergmann and Leonidas Zerwas in 1932 for the synthesis of peptides. The abbreviation Z is in honor of Zerwas.