Gas Chromatographic and Mass Spectrometric Study of the Bromination of Protein Fibers with N-Bromosuccinimide and Triphenylphosphine

Abstract

Silk fibers were brominated with a 1:1 (mole/mole) mixture of N-bromosuccinimide (NBS) and triphenylphosphine (TPP) in dimethylformamide. β-Bromoalanine (Brala) residues formed by the bromination of serine residues with NBS/TPP were very un stable under acid hydrolysis conditions, and Brala was not detected in the hydrolyzate of the brominated silk by gas chromatography-mass spectrometry of amino acids as their butyl esters of N(Q)-triftuoroacetyl derivatives. The brominated silk fibers were treated with aqueous solutions of ammonia and methyl-, ethyl-, propyl-, and butyl amines. Chromatographic-spectrometric analysis of amino acids of the treated silk samples showed the formation of corresponding β-aminoalanine and β-alkylami noalanines formed by the reaction of Brala residues, by direct condensation, or through the formation of dehydroalanine residues as intermediates. The analysis also showed that monobromotyrosine was formed by the treatment with NBS/TPP. Bromination of tyrosine residues must proceed by electrophilic substitution, probably by the action of free NBS in the reaction mixture.

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