Diisopropylethylamine → (5S)-2,2-dimethyl-5-((1S)-3-methyl-1-{[(2R)-2-methyl-4-(2-pyridinyl)piperazinyl]carbonyl}butyl)-1,3-dioxolan-4-one

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Reaction Steps

To a cold (0° C.) solution of (2R)-2-[(4S)-2,2-dimethyl-5-oxo-1,3-dioxolan-4-yl]-4-methylpentanoic acid (prepared according to WO 94/0244 or similarly to Seebach et al., 1990, Org. Syntheses, Coll. Vol. III, p 153-159; 7; 755.0 mg; 3.28 mmol; 1.0 eq.) and DIEA (1.18 mL; 6.89 mmol; 2.1 eq.) in DMF (4 mL) was added HATU (1.37 g; 3.61 mmol; 1.1 eq.) and the resulting reaction mixture was stirred for 2 min at 0° C. (3R)-3-methyl-1-pyridin-2-ylpiperazine (Intermediate 3, 639.3 mg; 3.61 mmol; 1.1 eq.) was then added and the resulting reaction mixture was stirred for 14 h at RT. Water was added and the mixture was extracted with Et2O (3×). The combined organic layers were washed with an aqueous saturated solution of NaCl, dried over MgSO4, filtered and evaporated to give an oil. This residue was purified by chromatography (gradient from 33% EtOAc in c-hex up to 50% EtOAc in c-hex in about 30 min) to give the title product as a white solid (625 mg, 49%) as a mixture of 2 diastereoisomers (HPLC (Condition D): Rt major: 13.7 min; Rt minor: 13.8 min.; major/minor: 55/45). M+(ESI): 390.3. HPLC (Condition A), Rt: 2.3 min (HPLC purity: 97.4%).

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