Aminoethylation in model peptides reveals conditions for maximizing thiol specificity

Control of pH in aminoethylation reactions is critical for maintaining high selectivity towards cysteine modification. Measurement of aminoethylation rate constants by liquid chromatography mass spectrometry demonstrates reaction selectivity of cysteine>>amino-terminus>>histidine. Lysine and methionine were not reactive at the conditions used. For thiol modification, the acid/base property of the gamma-thialysine residue measured by NMR results in a 1.15 decrease in pK(a) (relative to a lysine residue). NMR confirms ethylene imine is the reactive intermediate for alkylation of peptide nucleophiles with bromoethylamine. Conversion of bromoethylamine into ethylene imine prior to exposure to the target thiol, provides a reagent that promotes selectivity by allowing precise control of reaction pH. Reaction selectivity plots of relative aminoethylation rates for cysteine, histidine, and N-terminus imine demonstrate increasing alkaline conditions favors thiol modification. When applied to protein modification, the conversion of bromoethylamine into ethylene imine and buffering at alkaline pH will allow optimal cysteine residue aminoethylation.

A convenient S-2-aminoethylation of cysteinyl residues in reduced proteins

The cysteinyl residues in proteins had been S-2-aminoethylated with ethylenimine quantitatively. However, ethylenimine is now listed as a carcinogen and is no longer commercially available. A method of converting cysteinyl residues to S-2-aminoethyl derivatives quantitatively using 2-bromoethylamine under mild conditions was developed here.

Binary ethylenimine as an inactivant for foot-and-mouth disease virus and its application for vaccine production

Foot-and-mouth disease virus was inactivated with binary ethylenimine formed apart from or directly in the virus suspension by the cyclization of 2-bromoethylamine hydrobromide or 2-chloroethylamine hydrochloride under alkaline conditions. The inactivation rates with binary ethylenimine prepared apart from the virus suspension in dilute sodium hydroxide with either 2-bromoethylamine hydrobromide or 2-chlorethylamine hydrochloride were higher than with pure ethylenimine. When binary ethylenime was prepared directly in the virus suspension only 2-bromoethylamine hydrobromide gave acceptable inactivation rates. The reduced inactivation rates for binary ethylenimine directly prepared in the virus suspension are due to the different cyclization rates of 2-bromoethylamine hydrobromide and 2-chloroethylamine hydrochloride and to the interference of bicarbonate in the cyclization reaction. The complement fixing antigen of foot-and-mouth disease virus was not affected by binary ethylenimine inactivation. Vaccines prepared with foot-and-mouth disease virus inactivated by binary ethylenimine were comparable in their immunogenicity to vaccines prepared with ethylenimine or N-acetylethylenimine used as inactivants. Application of binary ethylenimine in the preparation of foot-and-mouth disease vaccines considerably reduces the potential danger associated with handling pure ethylenimine and other aziridines.