Synthesis of Boron-containing Fluorescent Probes

3’-PT-Amino-Modifier C6 CPG, 5′,N-protected 2′-O-TBDMS-ribo- (A and G), 5′,N-protected 2’-deoxyribophosphoramidites, Spacer Phosphoramidite 18, and 3’-PT-Amino-Modifier C6 polymer support were purchased from Glen Research Inc (Sterling, VA, USA). 5′,N-Protected 2’-deoxy-2’-fluoro pyrimidine phosphoramidites were purchased from ChemGene Corp (Wilmington, MA, USA). N,N-Diisopropylethylamine (DIPEA), and propargylamine were purchased from Sigma-Aldrich (St. Louis, MO, USA), N,N′-disuccinimidyl carbonate (DSC) was purchased from Acros Organics (Geel, Belgium), Sulfo-Cyanine 5 NHS ester, 10 mM Cu(II)-Tris(benzyltriazolylmethyl)amine (Cu(II)-TBTA) stock in 55% dimethyl sulfoxide (DMSO), ascorbic acid were purchased from Lumiprobe (Russia), and sodium dodecaborate Na₂[B₁₂H₁₂] was from AviaBor (Dzerzhinsk, Russia). ¹⁰B-enriched (>99%) BPA) was purchased from Katchem spol. s r. o. (Czech Republic), and converted into fructose 1:1 complex for increasing solubility [29 (link)]. All solvents (tetrahydrofuran, DMSO, CH₃CN (various vendors)) were dried by 3 Å molecular sieves or by distillation and stored over CaH₂. Bis-tetrabutylammonium-(4-azidobuthoxy)-undecahydro-closo-dodecaborate (closoB12-azide) was synthesized as described in [22 (link)] and kindly provided by Dr. V.N. Silnikov (ICBFM SB RAS).