Synthesis of Reactive Pegylated Indocyanine Dyes

Objective: The aim of this study was synthesis and selection of conditions for isolation and purification of fluorescently labeled polyethylene glycol with a reactive carboxyl group for labeling biomolecules. Pegylated nucleotides, which are part of drugs, allow targeted drug delivery to specific organ, prolong the half-life, reduce immunogenicity, and increase stability. Methods: The reaction product was isolated using three-stage chromatographic purification: reverse-phase column chromatography with C18-RP sorbent, ion exchange chromatography on DEAE-cellulose DE52 sorbent, and column chromatography on silica gel. Results and Discussion: An activated derivative of an indocarbocyanine dye was preliminarily synthesized and then used to obtain fluorescently labeled polyethylene glycol with a reactive carboxyl group. The conjugation reaction of the activated indocyanine dye ester with a 10-fold excess of polyethylene glycol was performed in DMF in the presence of DIPEA at 50°C for 12 h. The reaction in hexametapol resulted in the formation of only a by-product with a quantitative yield. Conducting the conjugation reaction of PEG with indocarbocyanine dye in one stage without isolating the intermediate activated ester of the dye in an aqueous organic solvent led to the formation of the target product in trace amounts. Conclusions: The synthesis of fluorescently labeled polyethylene glycol with a reactive carboxyl group for subsequent modification of single-stranded DNA molecules was carried out, and conditions for its isolation and purification were selected. The availability of an effective and feasible method for producing reactive pegylated indocyanine dyes, which provides a possibility to control the quality of intermediates at each stage of the synthesis, will expand the screening of therapeutic drugs with specified characteristics.