Synthesis of novel monomeric and homodimeric cyanine dyes based on oxazolo[4,5-b]pyridinium and quinolinium end groups for nucleic acid detection

Twelve novel di-, tri- and tetracationic monomeric and homodimeric monomethine cyanine dyes based on oxazolo[4,5-b]pyridinium and quinolinium end groups were synthesized by condensation of 4-methyl-2-methylmercapto-oxazolo[4,5-b]pyridinium methosulfate and 1-(ω-iodopropyl)-4-methylquinolinium or appropriate 1-(ω-bromoalkyl)-4-methylquinolinium compounds and subsequent quaternization with pyridine, 1-methyl-4-aza-1-azonia-bicyclo[2.2.2]octanium iodide, 4,4′-trimethylenebis(1-methylpiperidinium)methyl iodide, N,N,N,N′,N′-pentamethyl-1,3-propandiammonium iodide, or bisquaternization with N,N,N′,N′-tetramethyl-1,3-propanediamine, 4,4′-trimethylenebis(1-methylpiperidine). All dyes absorb at 521-522 nm in methanol and have a high molar absorptivity of about 106 000 (monomeric dyes) and 240 000 L mol−1 cm−1 (homodimeric dyes). The products were characterized by 1H NMR spectra and elemental analysis. In the presence of nucleic acid a strong enhancement of the fluorescence was observed.