NOVELTY - Preparation of 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 (I) or its salts involves reacting corresponding butan-2-one or its metal ion salt with enzyme to obtain 3-hydroxy-1-(3-(trifluoromethyl)-5,6-dihydro-(1,2,4)triazolo(4,3-a)pyrazin-7(8H)-yl)-4-(2,4,5-trifluorophenyl)butan-1-one (IV); reacting with reagents that activates hydroxyl group to obtain (1,2,4)triazolo(4,3-a)pyrazines (III); converting (III) to (1,2,4)triazolo(4,3-a)pyrazines (II) by using amine equivalent; and deprotecting (II).    USE - For preparation of 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 (claimed) used as DPP-IV inhibitor; and in the preparation of pharmaceutical composition.    ADVANTAGE - The method improves the overall chemical, optical and stereoisomeric yield of compound (I). The method avoids use of diastereoselective catalysts that are difficult to prepare and very expensive. The method produces compound (I) at low cost; is easy to handle at large scale; and is environmentally friendly. The method provides compound in high yield and purity and properly stated configuration. The method is applicable on commercial scale and is inexpensive; is efficient, cost effective and does not result in impure product thus making the process amenable for commercial scale use.    DETAILED DESCRIPTION - A process for the preparation of 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 (I) or its salts either in its racemic (R/S) form or any of its optically active (S) or (R) forms or enantiomeric excess mixture of any of the forms involves: a) reacting 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-one (V) or its metal ion salt with an enzyme or its variants that reduce a ketone to form an alcohol, to obtain 3-hydroxy-1-(3-(trifluoromethyl)-5,6-dihydro-(1,2,4)triazolo(4,3-a)pyrazin-7(8H)-yl)-4-(2,4,5-trifluorophenyl)butan-1-one (IV) in racemic (R/S) form or any of its optically active (S) or (R) forms or their enantiomerically excess mixtures; b) reacting 3-hydroxy-1-(3-(trifluoromethyl)-5,6-dihydro-(1,2,4)triazolo(4,3-a)pyrazin-7(8H)-yl)-4-(2,4,5-trifluorophenyl)butan-1-one (IV) either in its racemic (R/S) form or any of its optically active (S) or (R) forms or enantiomeric excess mixture of any of the forms with reagents that activates the hydroxyl group to obtain 5,6,7,8-tetrahydro-(1,2,4)triazolo(4,3-a)pyrazine compound of formula (III) with retention of configuration; c) optionally isolating the compound (III); d) converting compound (III) to compound of formula 5,6,7,8-tetrahydro-(1,2,4)triazolo(4,3-a)pyrazine (II) with inversion of configuration, by using amine equivalent, optionally with additives in solvents; and e) deprotecting or reducing the compound (II) or employing chemistry to obtain compound (I) with retention of configuration.    R=leaving group such as caboxylate, sulfonate, phosphate or oxyphosphonium ion;    R1=azide, cyclic imido, aralkylamino, or sulfonamido.    INDEPENDENT CLAIMS are included for the following:    (1) new compound (III) in racemic (R/S) form or any of its optically active (S) or (R) forms or their enantiomerically excess mixtures, where R is alkyl carboxylate selected from -OCOCH3; haloalkyl carboxylate selected from -OCOCF3; aryl carboxylate selected from optionally substituted -OCOPh; alkoxy carboxylate group selected from -OC(O)OCH2CH3; alkyl sulfonates group selected from -OSO2CH2CH3; haloalkyl sulfonate group selected from -OSO2CF3, -OSO2CH2CF3; aryl sulfonates group selected from optionally substituted -OSO2Ph; substituted OSO2Ph selected from OO2S-1,4-phenylene-NO2, alkoxy phosphates group selected from -OP(O)(OEt)2; an oxyphosphonium ion leaving group selected from -O-P+(X)3; and    (2) new compound (II) in racemic (R/S) form or any of its optically active (S) or (R) forms or their enantiomerically excess mixtures, where R1 is araalkyamino group selected from -NHCH2(4-OCH3Ph), -NHCH(CH3)Ph, or -NHCH(Ph)3; sulfonamido group selected from -NHSO3H, -HNO2S-1,4-phenylene-CH3 or phenyl (substituted on 4-position by -SO2-NH-COOC(CH3)3); or imido group selected from pyrrolidine-2,5-dione-1-yl.    X=alkyl, aryl or cycloalkyl.