[NH2:1][CH2:2][CH:3](N)[CH3:4].ClCC(O[CH2:11][CH3:12])=O.C(=O)([O-])[O-].[K+].[K+].C(OC(OC(C)(C)C)=O)(O[C:22](C)([CH3:24])[CH3:23])=O.[C:34]([O:38][C:39]([N:41]1[CH2:46][C:45](=[O:47])[NH:44][CH:43]([CH3:48])[CH2:42]1)=[O:40])([CH3:37])([CH3:36])[CH3:35]>C(O)C>[C:34]([O:38][C:39]([N:41]1[CH2:46][C:45](=[O:47])[N:44]([CH2:4][CH2:3][CH2:2][N:1]2[CH2:12][CH2:11][CH2:24][CH2:22][CH2:23]2)[CH:43]([CH3:48])[CH2:42]1)=[O:40])([CH3:37])([CH3:35])[CH3:36]A solution of 1,2-diaminopropane (12.1 g, 163 mmol) in ethanol (20 ml) was added at room temperature over 90 min to a solution of ethyl chloroacetate (2.00 g, 16.3 mmol) in ethanol (70 ml), then after 2 h potassium carbonate (2.26 g, 16.3 mmol) was added. After another 2 h, insoluble material was removed by filtration, and the filtrate was evaporated. The residue was suspended in dichloromethane (50 ml) and treated with di-tert-butyl dicarbonate (24.9 g, 114 mmol), and the reaction mixture was stirred at room temperature for 16 h, then evaporated. The residue was chromatographed (SiO2; heptane-ethyl acetate gradient) to afford 984 mg of a 3:2 mixture of the desired 3-methyl-5-oxo-piperazine-1-carboxylic acid tert-butyl ester and the regioisomer 3-methyl-5-oxo-piperazine-1-carboxylic acid tert-butyl ester. 200 mg of this regioisomeric mixture was alkylated with t-(3-chloropropyl)piperidine as described in intermediate 17b to produce the title compound (120 mg) containing 2-methyl-5-oxo-4-(3-piperidin-1-yl-propyl)-piperazine-1-carboxylic acid tert-butyl ester (ca. 20%) as a regioisomeric impurity. Light yellow oil, MS (ISP)=340.3 (M+H)+.
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