Amino acid amides, deamidation

Another screening method has been described for the enzymatic deamidation of (rac)-N-carbamoyl amino acid amides to enantiopure /V-carbamoyl-i.-amino acids.413... 

A second type of deamidation reaction for glutamine and asparagine exists. Early work by Greenstein and co-workers demonstrated the existence of an a-keto acid-activated glutaminase and aspart nase in liver 43). It was own later by Meister and associates ( 44, 4 ) that these enzymes catalyze a transamination reaction between the amino acid amides and a-keto acids followed by the hydrolysis of the a-ketoglutaramic or a-ketosuccinamic acids with the release of ammoiua. These reactions will be considered in Section IV, 2. 

Enfuvirtide (Fuzeon , T-20, Ro 29-9800, Hoffmann-La Roche) is a 36-amino acid synthetic peptide with a molecular weight of 4492 Da. It selectively inhibits human immunodeficiency virus (HIV) fusion to the host cell membranes [73]. The N-terminus of the molecule is acetylated and the C-terminus is amidated. A metabolite, M-20, is deamidated at the C-terminus. An ELISA method was initially used during drug development of this compound, but the decision was made to develop and validate an LC-ESI-MS/MS method for the simultaneous determination of enfuvirtide and M-20 for PK studies to support the NDA submission of this product [53]. Some of the issues of LC-ESI-MS/MS application for peptide bioanalysis are highlighted in the following. 

Deamidation The hydrolysis of the side chain amide linkage of an amino acid residue leading to the formation of a free carboxylic acid. 

A common structural modification of recombinant proteins is the deamidation of asparagine (Asn) residues [85]. Deamidation occurs under physiological conditions that can be taken as a measure for protein half-life in blood. It occurs along with the loss of a functional amide residue of asparagine, which is metabolized to the respective acidic amino acid ... 

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