TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Process: The step (a4) is carried out in presence of N-bromosuccinimide, N-iodosuccinimide, calcium hypochlorite or sodium hypochlorite. Preferred Components: The reagent is N,N'-carbonyldiimidazole, alkyl chloroformates or dialkyl carbonates. ACTIVITY - Hepatotropic; Virucide; Antiinflammatory.    MECHANISM OF ACTION - Hepatitis C virus non-structural protein 3/4A protease inhibitor.    EXAMPLE - Tert-leucine methyl ester hydrochloride (10 g) and tetrahydrofuran (150 ml) were charged in to a round bottom flask and stirred for 5-10 minutes. The mixture was cooled to 0-5 degrees C, triethylamine (8.4 ml) was added to the mixture and maintained for 10-15 minutes. Then 1,1'-carbonyldiimidazole (8.9 g) was added to the reaction mixture at 0-5 degrees C and maintained at the same temperature for 3 hours. Then tert-butylamine (11.6 ml) was added to the above reaction mixture at 5-10 degrees C. The reaction mixture was maintained at 25-35 degrees C for 2-3 hours, then filtered and the resultant filtrate was subjected to distillation at 40-45 degrees C under reduced pressure. The reaction mass was washed with water (100 ml) and chloroform (100 ml). The aqueous and organic layers were separated, and the aqueous layer was extracted with chloroform (100 ml) and combined organic layers were washed with water (100 ml). The organic layer was dried over sodium sulfate (2 g) and solvent was evaporated completely at 45 degrees C under reduced pressure. The obtained reaction mass was subjected to column chromatography by using 3 vol.% methanol/chloroform. The collected fractions were evaporated completely under reduced pressure at 45-50 degrees C to give (S)-2-(3-tert-butyl-ureido)-3,3-dimethyl-butyric acid methyl ester. The obtained (S)-2-(3-tert-butyl-ureido)-3,3-dimethyl-butyric acid methyl ester (2 g) and tetrahydrofuran (10 ml) were charged into a round bottom flask and stirred for 5-10 minutes at 25-35 degrees C. A solution of lithium hydroxide monohydrate (2.5 N, 20 ml) was added to the mixture at 25-35 degrees C and maintained for 24-25 hours. Then unreacted starting material was extracted with ethyl acetate (50 ml). The aqueous layer pH was adjusted to 2 with hydrochloric acid (1.5 ml) and extracted with ethyl acetate. The organic layer solvent was evaporated completely at below 45 degrees C under reduced pressure. The obtained reaction mass was subjected to column chromatography by using ethyl acetate/hexane (2:8). The collected fractions were evaporated completely under reduced pressure at 45-50 degrees C to give (S)-2-(3-tert-butyl-ureido)-3,3-dimethyl-butyric acid (yield 300 mg).