Preparation of labeled probes with aminohexanoylextended hydroxyprolinol linker (FI 4, Table 1) 3 0 -Hydroxyprolinol modified probe precursor was synthesized using a modified CPG support (18) , and 3 0 -DNAphosphoramidites and Eclipse Quencher phosphoramidite on a 0.2 mmol scale. The probe was purified by reversephase HPLC using a gradient of acetonitrile in 0.1 M triethylammonium bicarbonate buffer (pH 8-9) followed by drying in a SpeedVac evaporator. The probe precursor was redissolved in 50 ml of dry DMSO and treated with 10 mmol of pentafluorophenyl N-FMOC-6-aminohexanoate (19) for 10 h. The FMOC-aminohexanoyl modified probe was isolated by reverse-phase HPLC and deprotected by treatment with concentrated ammonium hydroxide for 1 h at room temperature. The deprotected oligonucleotide was further purified by reverse-phase HPLC using the triethylammonium bicarbonate buffer as described above, dried and re-dissolved in 50 ml of dry DMSO. To this solution, 10 mmol compound 8c (Scheme 2) and 1 ml triethylamine were added. After being kept at room temperature for 10 h the reaction was combined with 1 ml of 2% solution of NaClO 4 in acetone. The precipitated crude conjugate was further purified by reverse-phase HPLC, dried and reconstituted in 1· TE buffer. An additional molar absorbance (e 260 ) of 28 500 M À1 cm À1 was used in the probe concentration calculation to correct for the presence of the dye.