Methanol → methylphosphonothioic acid O-[3-(1H-indol-2-yl)-1H-indazol-5-yl]ester O-methyl ester

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The compound methylphosphonothioic acid O-[3-(1H-indol-2-yl)-1H-indazol-5-yl]ester O-methyl ester is prepared according to procedure F using 200 mg of 3-(1H-indol-2-yl)-H-indazole-5-ol (intermediate B) in solution with 284 mg of methylphosphonothioic acid O,O—bis-(4-nitrophenyl)ester in 6 ml of dichloromethane (stabilized with amylene), to which 120 μl of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in solution in 1 ml of dichloromethane are added. After stirring at ambient temperature for 4 h 30 min, 325 μl of methanol and 120 μl of DBU in solution in 1 ml of dichloromethane are added. The mixture is left at ambient temperature overnight and the solvent is then evaporated off and the crude is purified by flash chromatography on 35-70 μm silica, eluent: cyclohexane/ethyl acetate 90/10 to 50/50. The fractions obtained are concentrated and purified by preparative LC/MS to obtain 47.7 mg of methylphosphonothioic acid O-[3-(1H-indol-2-yl)-1H-indazol-5-yl]ester O-methyl ester.

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