Cl.Cl.[NH:3]1[CH2:8][CH2:7][NH:6][CH2:5][CH:4]1[C:9]([OH:11])=[O:10].[OH-].[Na+].[C:14](OC([O-])=O)([O:16][C:17]([CH3:20])([CH3:19])[CH3:18])=[O:15].Cl>O1CCOCC1.O>[C:17]([O:16][C:14]([N:6]1[CH2:7][CH2:8][NH:3][CH:4]([C:9]([OH:11])=[O:10])[CH2:5]1)=[O:15])([CH3:20])([CH3:19])[CH3:18]
A mixture of piperazine-2-carboxylic acid dihydrochloride in dioxan (1000 ml) and water (500 ml), at 10–15° C., was treated with aqueous sodium hydroxide solution (50%) over 15 minutes to adjust the pH to 9.1. This mixture was then treated portionwise (0.1 equivalent portions) with tert-butyl dicarbonate (114.6 g) over a period of 1 hour whilst maintaining the temperature at 5° C. and the pH around 8.8. After stirring at room temperature overnight the reaction mixture was cooled to 10° C., then the pH of the mixture was adjusted to 2 by the addition of hydrochloric acid (37%) and then the mixture was concentrated at 40° C. under reduced pressure. The resulting solid was treated with methanol (1500 ml) and this mixture was heated at reflux temperature and then filtered to remove the insoluble inorganics. The filtrate was evaporated to give the title compound (126 g) as an off white solid. MS: 231 [MH]+.
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