hydro alcoholic phase is cooled down to 0 5 u00b0 c and diluted with ch 2 cl 2 1 u00d7 100 ml under vigorous stirring at 0 5 u00b0 c conc ammonia 3 1 ml nh 4 oh is added dropwise a 1 degree increase of the temperature is obtained up to ph 7 8 the biphasic reaction is stirred at the same temperature for 20 minutes then the phases are separated and the aqueous layer is extracted with ch 2 cl 2 5 u00d7 100 ml the combined organic layers are concentrated under vacuum till 100 ml and at room temperature under stirring the product crystallizes the precipitate is filtered through a glass sintered filter and after drying under vacuum at 40 u00b0 c overnight 7 5 of the title compound are obtained compound i 16 g hplc purity assay 90 57 20 49 mmol is dissolved in a mixture 1 1 of absolute etoh and ch 2 cl 2 320 ml and to the slightly yellowish solution di tert butyl dicarbonate boc 2 o in ch 2 cl 2 24 18 mmol 5 27 g dissolved in 5 ml of ch 2 cl 2 is added at the end of the addition the reaction mixture is stirred for 16 hours at room temperature tlc shows no compound.