A suspension of 4.00 g (12.44 mmol) of 5(S)-[1(S)-(Boc-amino)-2-(p-hydroxyphenyl)-ethyl]dihydrofuran-2-(3H)-one (Example 11f)) in 240 ml of DMF/dioxane, 1:1, is reacted, under an N2 atmosphere, with 8.1 g (24.88 mmol) of Cs2CO3 and 0.77 ml (12.44 mmol) of methyl iodide. After 18 h, the reaction mixture is poured onto 190 ml of ice-water, and this mixture is extracted 3× with methylene chloride. The organic phases are washed with water and saline, dried with Na2SO4 and evaporated. Stirring with hexane in an ultrasonication bath affords the title compound: TLC Rf (C)=0.43; tRet (II)=13.5 min; FAB-MS (M+H)+ =336.
