The acid group is protected by transforming it into an ester by reaction with an alcohol. Methyl, ethyl or tert -butyl esters are prepared by esterification and hydrolyzed (deprotected) in a basic medium.


Protection of alanine with tert-butanol in an acid medium.
proteccion-grupo-acido
Deprotection can be performed with acid or base hydrolysis of the ester.
proteccion-grupo-acido
Another very interesting protecting group is benzyl alcohol. When reacting with the acid it forms an ester that can be cleaved by hydrogenation with H 2 /Pd. If the amino group is protected with CBZ-Cl and the acid with benzyl alcohol, both can be simultaneously deprotected by hydrogenation.
proteccion-grupo-acido
Deprotection by hydrogenation of the CO bond
proteccion-grupo-acido