Synthesis of protein-reactive (aminostyryl)pyridinium dyes

Abstract

The synthesis of two protein reactive (aminostyryl)pyridinium fluorescent dyes, N-ethyl-N-[4-[2-[4-(1-methylpyridinio)]ethyl]phenyl]glycine chloride N-hydroxysuccinimide ester (SuASP, 2) and 4-[4-[2-[4-(N,N- dimethylamino)phenyl]ethenyl]pyridinio]butyrate N-hydroxysuccinimide ester (ASPSu, 3), is reported. Both form amide linkage through the activated succinimidyl ester with primary amines. The two analogues differ by the position of the pyridinium positive change relative to the activated ester. SuASP forms an amide linkage that positions the positive charge distal to the protein surface, while ASPSu places the positive charge proximal. The synthesis of SuASP utilizes a palladium coupling reaction for the arylation of 4-vinylpyridine, while the major connection for ASPSu is accomplished through an aldol condensation between 4-(N,N-dimethylamino)benzaldehyde and picoline. Both reagents are shown to label covalently bovine serum albumin.