Synthesis of PEG derivatives bearing aminophenyl and their application for liquid-phase synthesis of water-soluble unsymmetrical cyanine dyes

The synthesis and NMR characterization of soluble PEG-supported polymers were described, and their subsequent application for liquid-phase synthesis of water-soluble cyanine dyes was also studied. Nucleophilic substitution of tosylation of PEG 16 with 1,3-bis(4-nitrophenoxy)-2-propanol 15 under basic conditions, followed by nitro group reduction, gave PEG-bound aminophenyl 18. Another PEG-bound aminophenyl 28 was prepared by condensation reaction of PEG-bound pentaerythritol 25 and 4-aminobenzoic acid followed by the cleavage of BOC group. Subsequent loading and activation of sulfoindoleninium to PEG derivatives 18 or 28 were achieved via simple strategies. Cyanine dyes were released by the attack of heterocyclic carbon nucleophile and the cleavage of PEG-bound hemicyanine without the chromatographic separation. The efficient, facile, and practical approaches appear to be robust and versatile strategies to deliver not only indocyanine dyes but also benzoindocyanine dyes.