A NEW METHOD FOR THE SYNTHESIS OF HEPTAMETHINE CYANINE DYES - SYNTHESIS OF NEW NEAR-INFRARED FLUORESCENT LABELS

A new uncatalyzed synthesis of heptamethine cyanine dyes is described. The reaction involves heating a mixture of N-alkyl-substituted quaternary salts derived from 2,3,3-trimethylindole or 2,3,3-trimethylbenzindole and 2-chloro-1-formyl-3-(hydroxymethylene)cyclohex-1-ene to reflux in a mixture of 1-butanol and benzene (7:3) as solvent. No catalyst is used, and water is removed as an azeotrope. The resulting chloro compounds possess strong absorption and fluorescence properties in the near-infrared region and are converted to dyes bearing reactive functionalities such as hydroxy and isothiocyanate groups useful as fluorescent tags for nucleic acids and proteins. Several symmetric and nonsymmetric dyes have been synthesized in high yields.