TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Preparation (claimed): The pyrimidine derivative (VI) is prepared by reacting N-(4,6-dichloro-2-(propylsulfanyl)pyrimidin-5-yl)-2,2,2-trifluoroacetamide with cyclopentanamine compound of formula (VII) or its salt. The salt of cyclopentanamine compound (VII) is L-tartrate, D-tartrate, L-dibenzoyl tartrate, D-dibenzoyl tartrate, L-mandelate, D-mandelate, oxalate, maleate or hippurate, more preferably L-tartrate. Preferred Process: The preparation of pyrimidine derivative (VI) further involves removing hydroxy protection group of pyrimidine derivative (VI) in presence of acid to obtain N-(4-(((3aS,4R,6S,6aR)-6-(2-hydroxyethoxy)-2,2-dimethyl-hexahydrocyclopenta(d)(1,3)dioxol-4-yl)amino)-6-chloro-2-(propylsulfanyl)pyrimidin-5-yl)-2,2,2-trifluoroacetamide. The reaction is carried out in presence of alkali (a1) in a solvent (s1) at 0-100?oC. The alkali (a1) is preferably chosen from triethylamine, diisopropylethylamine, pyridine and 2,3,4-monoalkyl-substituted pyridine. 4,6-Dichloro-2-(propylsulfanyl)pyrimidin-5-amine is reacted with trifluoroacetylation reagent in presence of alkali (a2) in a solvent (s2), to obtain N-(4,6-dichloro-2-(propylsulfanyl)pyrimidin-5-yl)-2,2,2-trifluoroacetamide. The pyrimidine derivative (VI) is reacted with alkali (a2) in solvent (s2), to prepare pyrimidine derivative of formula (V). The ticagrelor is prepared by using pyrimidine derivative (V). The pyrimidine derivative (V) is processed to obtain pyrimidine derivative of formula (IV). The pyrimidine derivative (IV) is reacted with (1R,2S)-2-(3,4-difluorophenyl)cyclopropan-1-amine to obtain 5-(propylsulfanyl)-3H-(1,2,3)triazolo(4,5-d)pyrimidin-7-amine of formula (II). The 5-(propylsulfanyl)-3H-(1,2,3)triazolo(4,5-d)pyrimidin-7-amine (II) is processed to obtain (1S,2S,3R,5S)-3-(7-(((1R,2S)-2-(3,4-difluorophenyl)cyclopropyl)amino)-5-(propylsulfanyl)-3H-(1,2,3)triazolo(4,5-d)pyrimidin-3-yl)-5-(2-hydroxyethoxy)cyclopentane-1,2-diol. The N-(4-(((3aS,4R,6S,6aR)-6-(2-hydroxyethoxy)-2,2-dimethyl-hexahydrocyclopenta(d)(1,3)dioxol-4-yl)amino)-6-chloro-2-(propylsulfanyl)pyrimidin-5-yl)-2,2,2-trifluoroacetamide is reacted with strong acid or alkali (a2) in solvent (s2), to prepare (1S,2S,3R,5S)-3-((5-amino-6-chloro-2-(propylsulfanyl)pyrimidin-4-yl)amino)-5-(2-hydroxyethoxy)cyclopentane-1,2-diol. The ticagrelor is prepared using (1S,2S,3R,5S)-3-((5-amino-6-chloro-2-(propylsulfanyl)pyrimidin-4-yl)amino)-5-(2-hydroxyethoxy)cyclopentane-1,2-diol. The (1S,2S,3R,5S)-3-((5-amino-6-chloro-2-(propylsulfanyl)pyrimidin-4-yl)amino)-5-(2-hydroxyethoxy)cyclopentane-1,2-diol is reacted with nitrate of formula: MNO2 (i) or RONO (ii), to obtain (1S,2S,3R,5S)-3-(7-chloro-5-(propylsulfanyl)-3H-(1,2,3)triazolo(4,5-d)pyrimidin-3-yl)-5-(2-hydroxyethoxy)cyclopentane-1,2-diol. The (1S,2S,3R,5S)-3-(7-chloro-5-(propylsulfanyl)-3H-(1,2,3)triazolo(4,5-d)pyrimidin-3-yl)-5-(2-hydroxyethoxy)cyclopentane-1,2-diol is reacted with (1R,2S)-2-(3,4-difluorophenyl)cyclopropan-1-amine or its salt in presence of alkali and solvent, to obtain ticagrelor. The N-(4-(((3aS,4R,6S,6aR)-6-(2-hydroxyethoxy)-2,2-dimethyl-hexahydrocyclopenta(d)(1,3)dioxol-4-yl)amino)-6-chloro-2-(propylsulfanyl)pyrimidin-5-yl)-2,2,2-trifluoroacetamide is reacted with strong acid in solvent (s3) chosen from fatty alcohol with carbon atom number of less than 6, preferably methyl alcohol or ethyl alcohol.M=not defined.Preferred Composition: The solvent (s1) is chosen from methylbenzene, tetrahydrofuran, 2-methyltetrahydrofuran, dioxane, N,N-dimethylformamide, N,N-dimethylacetamide, acetonitrile, dichloromethane, trichloromethane, dichloroethane, dimethylbenzene, trimethylbenzene, methyl tert-butyl ether and cyclopentyl methyl ether. The trifluoroacetylation reagent is chosen from trifluoroacetic acid ethyl ester, trifluoroacetic anhydride, trifluoroacetic acid-succinimide, trifluoroacetyl benzotriazole, trifluoroacetic acid-5 fluorophenol ester and 2-trifluoroacetoxyl pyridine. The alkali (a2) is preferably chosen from triethylamine, diisopropylethylamine, pyridine, 2,3,4-monoalkyl substituted pyridine, anhydrous potassium carbonate, anhydrous sodium carbonate, anhydrous sodium bicarbonate, anhydrous trisodium phosphate and anhydrous potassium phosphate. The solvent (s2) is chosen from methylbenzene, tetrahydrofuran, 2-methyltetrahydrofuran, dioxane, N,N-dimethylformamide, N,N-dimethylacetamide, dichloromethane, trichloromethane, dichloroethane, ethyl acetate, dimethylbenzene, trimethylbenzene, diethyl ether, isopropyl ether, methyl tert-butyl ether and cyclopentyl methyl ether. The strong acid is chosen from hydrochloric acid, methanesulfonic acid, trifluoromethanesulfonic acid, trifluoroacetic acid and sulfuric acid. Preferred Definitions:    R=hydroxy protection group.