TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Method: In the method, the compound (X) is prepared by (i) introducing an amine protecting group into L-aspartic acid to prepare (S)-N-(benzyloxycarbonyl)aspartic acid of formula (IV); (ii) converting the compound (IV) into an anhydride form to prepare (S)-benzyl(2,5-dioxotetrahydrofuran-3-yl)carbamate of formula (V); (iii) reacting the compound (V) with alcohol to prepare (S)-3-((benzyloxycarbonyl)amino)-4-methoxy-4-oxobutanoic acid of formula (VI); (iv) reacting the compound (VI) with 3-(trifluoromethyl)-5,6,7,8-tetrahydro-(1,2,4)triazolo(4,3-a)pyrazine hydrochloride of formula (III) to prepare (S)-2-((benzyloxycarbonyl)amino)-4-oxo-4-(3-(trifluoromethyl)-5,6,7,8-tetrahydro-(1,2,4)triazolo(4,3-a)pyrazine)butanoic acid methylester (VII); (v) hydrolyzing the compound (VII) to prepare (S)-2-((benzyloxycarbonyl)amino)-4-oxo-4-(3-(trifluoromethyl)-5,6,7,8-tetrahydro-(1,2,4)triazolo(4,3-a)pyrazine)butanoic acid (VIII); (vi) reacting the compound (VIII) with O,N-dimethyl-hydroxylamine of formula (XVI) to prepare (S)-benzyl(1-(methoxy(methyl)amino)-1,4-dioxo-4-(3-(trifluoromethyl)-5,6,7,8-tetrahydro-(1,2,4)triazolo(4,3-a)pyrazin-7-yl)butan-2-yl) carbamate (IX); and reacting the compound (IX) with 1,2,4-trifluoro-5-methyl-benzene of formula (XVII) to prepare the compound (X). The compound (X) is prepared by (ia) allowing monoesterification of L-aspartic acid to prepare (S)-2-amino-4-methoxy-4-oxobutanoic acid of formula (XI); (iia) introducing an amine protecting group into the compound (XI) to prepare (S)-2-(benzyloxycarbonyl)amino-4-methoxy-4-oxobutanoic acid (XII); (iiia) reacting the compound (XII) with the compound (XVI) to prepare (S)-3-((benzyloxycarbonyl)amino)-4-(methoxy(methyl)amino)-4-oxobutanoic acid methylester (XIII); (iva) reacting the compound (XIII) with the compound (XVII) to prepare (S)-3-((benzyloxycarbonyl)amino)-4-(2,4,5-trifluoro)-4-oxobutanoic acid methylester (XIV); (va) hydrolyzing the compound (IV) to prepare (S)-3-((benzyloxycarbonyl)amino)-4-(2,4,5-trifluoro)-4-oxobutanoic acid (XV); and reacting the compound (XV) with the compound (III) to prepare the compound (X). The step (iv), (vi), (iiia) and (via) are performed using at least one selected from 1,1'-carbonyldiimidazole (CDI), O-(benzotriazol-1-yl)-1,1,3,3-tetramethyluronium hexafluorophosphate (HBTU), O-(7-azabenzotriazol-1-yl)-1,1:3,3-tetramethyluronium hexafluorophosphate (HATU), 1,3-dicyclohexyl carbodiimide (DCC), diisopropylcarbodiimide (DIC), 1-Hydroxybenzotriazole (HOBT) and 1-ethyl-3-(dimethylaminopropyl) carbodiimide (EDC) as the coupling agent for amide bond. The step (v) and (va) are performed using at least one selected from sodium hydroxide, lithium hydroxide, and potassium hydroxide as the catalyst of the hydrolysis reaction. The compound (XVII) is prepared by reacting 1-bromo-2,4,5-trifluoro-benzenethe (II) with a compound of formula (XVIII), where the reaction is performed under a nitrogen atmosphere.R'=1-4C alkyl;X'=Cl, Br or I.Preferred Components: The amine protecting group is benzyl, benzyl oxycarbonyl, or formyl. The removal agent of amine protecting group is any one selected from Na, NH3 and MeCONH2; Li and NH3-EtOH; HBr and AcOH; TFA and PhSMe; Pd(O), N-Me-morpholine and EtOH; 1,4-cyclohexadiene and Pd/C; Pd/C and H2; Pd(OH)2 and H2; Pd(OH)2/C and H2; H2, Pd/C and H+; Na and NH3; and Li and NH3. The carbonyl reducing agent is at least one selected from H2 and Pd/C; H2, Pd/C and H+; H2 and PtO2; cyclohexene, Pd/C and FeCl3; Raney Ni and EtOH; HI, P and I2; Li, NH3 and NH4Cl; BH3, pyridine and TFA; BH3 and BF3-OEt2; NaBH4 and BF3-OEt2; NaBH4 and TFA; NaBH4 and PdCl2; and LiAlH4 and AlCl3. The alcohol is 1-4C alcohol. ACTIVITY - Antidiabetic. No biological data given.    MECHANISM OF ACTION - Dipeptidyl peptidase-4 (DPP-4) inhibitor.    EXAMPLE - Sodium borohydride (NaBH4) (3.4 g) was added to tetrahydrofuran (THF) (200 ml) and was cooled to less than or equal to -10 degrees C. BF3-OEt2 (9.96 ml) was slowly added to it and then stirred for 1 hour maintaining temperature from 0 to -10 degrees C. (S)-benzyl(1,4-dioxo-4-(3-(trifluoromethyl)-5,6,7,8-tetrahydro-(1,2,4)triazolo(4,3-a)pyrazin-7-yl)-1-(2,4,5-triflurophenyl)butan-2-yl)carbamate (10 g) was added to it. Then, the temperature was raised to room temperature and the reactant was stirred for 2 hours. Then, the reactant was cooled to methanol (0-100 ml) was added slowly dropwise. 1N Hydrochloric acid (100 ml) was added to it and the temperature was raised to 40 degrees C followed by stirring for 1 hour. Dichloromethane (200 ml) was added to it followed by a phase-separation. After phase-separation, the organic layer was dried over magnesium sulfate followed by concentration under reduced pressure. Dichloromethane (100 ml) and 1N hydrochloric acid (100 ml) was added to residual concentrate and then stirred for phase-separation. After phase-separation, the organic layer was discarded. Dichloromethane (100 ml) was put in the water layer followed by neutralization with 5% aqueous sodium hydroxide solution. After phase-separation, the water layer was discarded. The organic layer was washed with saturated sodium hydrogen carbonate. The resultant was dried over magnesium sulfate, concentrated under reduced pressure, and dissolved in dichloromethane (10 ml) followed by adding diisopropylether (100 ml) to produce crystals. The crystals were filtered, and dried under vacuum to obtain sitagliptin (4.2 g, yield: 57%).