Triethylamine → tert-butyl (3S,4R)-3-(2-tert-butylsilyloxypropan-2-yl)-4-[[[1-(3-methoxypropyl)-3-methylindole-6-carbonyl]-propan-2-ylamino]methyl]pyrrolidine-1-carboxylate

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Reaction Steps

A mixture of (3S,4R)-3-(tert-butyl-dimethyl-silanyloxymethyl)-4-(isopropylamino-methyl)-pyrrolidine-1-carboxylic acid tert-butyl ester (8.5 g, 22 mmol), 1-(3-methoxy-propyl)-3-methyl-1H-indole-6-carboxylic acid (7.6 g, 30.8 mmol), bis(2-oxo-3-oxazolidinyl)phosphinic chloride (7.84 g, 30.8 mmol) and triethylamine (12.3 mL, 88 mmol) in CH2Cl2 (425 mL) is refluxed overnight under a nitrogen atmosphere and then quenched by the addition of an aqueous saturated solution of NaHCO3. The organic layer is separated, and the aqueous phase is extracted 3 times with AcOEt. The combined organic extracts are concentrated in vacuo. The residual oil is taken up in a mixture of THF and MeOH, NaOH 1N is added to cleave the anhydride side product and the mixture stirred for 3 h. The solvents are concentrated, CH2Cl2 is added and the layers are separated. The aqueous one is then back extracted twice with CH2Cl2 and the combined organic extracts are washed with brine, dried over Na2SO4, filtered and concentrated. The crude product is used in the next step without further purification. TLC, Rf (AcOEt)=0.6. MS (LC-MS): 516.3 [M-Boc+H]+; tR (HPLC, Macherey-Nagel Nucleosil C18 column, 10-100% CH3CN/H2O/5 min, 100% CH3CN/3 min, CH3CN an H2O containing 0.1% TFA, flow: 1.5 mL/min): 8.60 min.

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