Isopropanol → Sitagliptin

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In a 25 mL round bottom flask Isopropanol (1.25 mL) and Dibenzoyl-L-tartaric acid monohydrate (0.462 g) were taken. It was heated to 60-65° C. 4-oxo-4-[3-(trifluoromethyl)-5,6-dihydro[1,2,4]triazolo[4,3-a]pyrazin-7(8H)-yl]-1-(2,4,5-trifluorophenyl)butan-2-amine (0.5 g) dissolved in methanol (1.0 mL) was added into reaction mixture at 60-65° C. over a period of 15 min. It was stirred for 15-30 min. at 60-65° C. Solid salt was precipitated. It was gradually cooled to room temperature and stirred for 30-60 min. The salt was filtered and washed with a mixture of IPA: MeOH (2:1, 3 mL). An enantiomerically enriched desired Dibenzoyl-L-tartaric acid salt off (2R)-4-oxo-4-[3-(trifluoromethyl)-5,6-dihydro[1,2,4]triazolo[4,3-a]pyrazin-7(8H)-yl]-1-(2,4,5-trifluorophenyl)butan-2-amine was obtained (Wt.-0.358 g, % Y-37.8%, Purity by HPLC-97.5%, % Chiral purity by HPLC of R-isomer 99.6%). % of weight loss by TGA-4.7%. m.p.-156-160° C.

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