To a suspension of (±)-(S*)-(3,5-dimethoxy-phenoxy)-((1S*)-1-phenyl-1,2,3,4-tetrahydro-isoquinolin-1-yl)-acetic acid (200 mg, 0.477 mmol, Example 1) in THF (5 ml) Hünig's base (327 μl, 1.91 mmol) followed by chlorotrimethylsilane (72 μl, 0.572 mmol) is added. The mixture is stirred at 55° C. for 3 h before methyliodide (30 μl, 0.477 mmol) is added. Stirring at 55° C. is continued for another 16 h. The mixture is diluted with EA and extracted with water. The aqueous phase is acidified with 2 N HCl and extracted with EA. The EA-phase is dried over Na2SO4 and evaporated. The crude product is purified by prep. HPLC on Rp-C18-silica gel to give (±)-(S*)-(3,5-dimethoxy-phenoxy)-((1S*)-2-methyl-1-phenyl-1,2,3,4-tetrahydro-isoquinolin-1-yl)-acetic acid (139 mg) as a white powder. LC-MS2: tR=4.03 min, [M+1]+=434.34, [M−1]−=432.32.
