The present invention relates to a process for preparing a compound comprising an α,γ amide linkage between a cysteine moiety and a glutamic acid moiety, such as γ-glutamylcysteine or a γ-glutamylcysteine derivative, the process comprising providing a cysteine derivative, a γ-glutamyl donor and an enzyme capable of transferring the γ-glutamyl group to said cysteine derivative in a reaction environment promoting transfer of the γ-glutamyl group to said cysteine derivative. The invention also relates to compounds comprising an α,γ amide linkage between a cysteine moiety and a glutamic acid moiety, such as γ-glutamylcysteine or a γ-glutamylcysteine derivative, when obtained by processes of the invention, and uses thereof.