L-Hydroxyproline → (2s,4r)-4-Hydroxy-1-(naphthalene-2-sulfonyl)pyrrolidine-2-carboxylic acid

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Reaction Conditions

Reaction Steps

11 g (83.9 mmol) L-Hydroxyproline were dissolved in 110 ml hexamethyldisilazane and heated to 120° C. overnight, cooled to room temperature and evaporated. The oily residue was dissolved in 110 ml THF, 16.5 ml (79.7 mmol, 0.95 eq) N-ethyl-morpholine was added, followed by 18.25 g (79.7 mmol, 0.95 eq) 2-naphthalenesulfonyl chloride in 130 ml THF over a period of 60 min. The solution was stirred at RT for 50 h, 15 ml ethanol were added and the solution was stirred for 15 min. At that time 400 ml of Et2O and 250 ml of aqueous saturated NaHCO3 solution were added and the phases were separated. The aqueous layer was acidified and extracted with EtOAc, the combined organic layers were washed with brine, dried over MgSO4 and concentrated. 17.39 g (65%) (2S,4R)-4-hydroxy-1-(naphthalene-2-sulfonyl)-pyrrolidine-2-carboxylic acid isolated as yellow solid, mp 140° C., MS: 321 (MH+).

Provenance & Evidence