Example 125
Methyl 4-((5-(benzyloxy)-2-methoxyphenyl)(ethyl)amino)butanoate (184). 5-(Benzyloxy)-N-ethyl-2-methoxyaniline (146) (0.681 g, 2.65 mmol), DIEA (0.92 mL, 5.3 mmol), and methyl 4-iodobutyrate (0.72 mL, 5.3 mmol) in DMF (5 mL) were stirred at 70° C. for 5 days. The reaction mixture was cooled to rt, diluted with EtOAc (60 mL), washed with water (4×50 mL), brine (75 mL), dried over Na2SO4 and evaporated. The residue was purified by chromatography on a silica gel column (2.5×30 cm bed, packed with CHCl3), eluant: 5% MeOH in CHCl3 to get compound 184 (0.72 g, 76%) as a dark amber oil.
Methyl 4-(ethyl(5-hydroxy-2-methoxyphenyl)amino)butanoate (186). Ester 184 (0.72 g, 2.0 mmol) was stirred under reflux with 6 mL of water and 6 mL of conc HCl for 1.5 hrs and then evaporated to dryness to give acid 185 as a brown gum. The crude acid was dissolved in 50 mL of methanol containing 1 drop (cat.) of methanesulfonic acid ant the solution was kept for 2 hrs at rt. After that the mixture was concentrated in vacuum and the residue was mixed with 20 mL of saturated NaHCO3. The product was extracted with EtOAc (3×40 mL). The extract was washed with brine (40 mL), dried over Na2SO4 and evaporated. The residue was purified by chromatography on a silica gel column (2.5×30 cm bed, packed with CHCl3), eluant: 5% MeOH in CHCl3 to get compound 186 (0.444 g, 83%) as a brown oil.
N-(6-(dimethylamino)-9-(4-(ethyl(4-methoxy-4-oxobutyl)amino)-2-hydroxy-5-methoxyphenyl)-3H-xanthen-3-ylidene)-N-methylmethanaminium chloride (187). To a stirred suspension of tetramethylrhodamine ketone 101 (0.234 g, 0.830 mmol) in 10 mL of dry chloroform was added oxalyl chloride (72 μL, 0.82 mmol) upon cooling to 0-5° C. The resulting red solution was stirred for 0.5 h at 5° C., and the solution of compound 186 (0.222 g, 0.831 mmol) in dry chloroform (5 mL) was introduced. The reaction was allowed to heat to rt, stirred for 72 h, diluted with CHCl3 (100 mL and washed with sat. NaHCO3 solution (2×30 mL) The organic layer was extracted with 5% HCl (3×25 mL). The combined acid extract was washed with CHCl3 (2×15 mL; discarded), saturated with sodium acetate and extracted with CHCl3 (5×30 mL). The extract was washed with brine (50 mL), dried over Na2SO4 and evaporated. The crude product was purified by chromatography on silica gel column (2×50 cm bed, packed with CHCl3/MeOH/AcOH/H2O (100:20:5:1)), eluant: CHCl3/MeOH/AcOH/H2O (100:20:5:1) to give the product 187 (0.138 g, 29%) as a purple solid.
4-((4-(6-(dimethylamino)-3-(dimethyliminio)-3H-xanthen-9-yl)-5-hydroxy-2-methoxyphenyl)(ethyl)amino)butanoate (188). Methyl ester 187 (0.136 g, 0.240 mmol) was dissolved in 5 mL of 1M KOH (5 mmol). The reaction mixture was kept at rt for 1.5 hrs and the acetic acid (1 mL) was added. The mixture was extracted with CHCl3 (4×30 mL), and combined extract was washed with brine (20 mL), filtered through the paper filter and. The crude product was purified by chromatography on silica gel column (2×50 cm bed, packed with MeCN/H2O (4:1)), eluant: MeCN/H2O/AcOH/(4:1:1) to give the product 188 (0.069 g, 98%) as a purple solid.
N-(6-(dimethylamino)-9-(4-((4-(2,5-dioxopyrrolidin-1-yloxy)-4-oxobutyl)(ethyl)amino)-2-hydroxy-5-methoxyphenyl)-3H-xanthen-3-ylidene)-N-methylmethanaminium chloride (189). To a solution of the acid 188 (69 mg, 0.12 mmol) in DMF (2 mL) and DIEA (58 μL, 0.33 mmol) was added N-hydroxysuccinimide trifluoroacetate (70 mg, 0.33 mmol). The reaction mixture was stirred for 30 min, diluted with chloroform (100 mL) and washed with water (5×50 mL), brine (50 mL), filtered through paper and concentrated in vacuum. The crude product was purified by precipitation from CHCl3 solution (5 mL) with ether (20 mL) to give compound 189 (55 mg, 67%) as a purple powder.
