To a solution of (±)-1-(5-chloro-2-hydroxy-phenyl)-3,4-dihydro-1H-isoquinoline-2-carboxylic acid benzyl ester (192 mg, 0.30 mmol, 1.0 eq.) in MeCN (1 mL), (S)-2-(toluene-4-sulfonyloxy)-propionic acid methyl ester (80 mg, 0.30 mmol, 1.0 eq.) and potassium carbonate anhydrous (83 mg, 0.60 mmol, 2.0 eq.) were added and the mixture was heated to 65° C. for 18 hours. (S)-2-(Toluene-4-sulfonyloxy)-propionic acid methyl ester (40 mg, 0.15 mmol, 0.5 eq.) was added again and the mixture was heated at 90° C. for 4 hours. The mixture was allowed to cool to r.t. and extracted with Et2O (2×), dried over MgSO4, filtered, and concentrated in vacuo. To a solution of the crude ester in THF (1.3 mL), 1M aq. NaOH soln. (0.38 mL) was added. The solution was stirred at r.t. for 18 hours. The solution was diluted with water (2 mL) and 1M aq. HCl soln. (0.38 mL) followed by DCM. The mixture was shaked then the layers were separated and the aq. phase was extracted with DCM (2×). The comb. org. phases were concentrated in vacuo. The crude mixture, redissolved in DMF (1.2 mL), was purified by prep. HPLC (column: Atlantis, 19×50 mm, 5 um, UV/MS, acidic conditions) to give the desired acid.
