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To a 48percent aqueous hydrogen bromide solution (0.893 mL) and water (9 mL), 2-bromo-1, 1-diethoxyethane (5.98 mL, 38.5 mmol) was added, and stirred for one hour while heating under reflux. To the reaction solution, water and ethyl ether were added to separate phases. The water phase was extracted with ethyl ether and organic phases were combined, dried over magnesium sulfate, filtrated and concentrated under reduced pressure. To the resultant residue and a dimethoxyethane (22 mL) solution of 3-chloropyrazine-2-amine (2.0 g, 15.4), a 48percent aqueous hydrogen bromide solution (0.3 mL) was added, stirred for 3 hours while heating under reflux. The resultant solid substance was obtained by filtration and washed with ether to obtain 8-chloroimidazo[1, 2-a]pyrazine (2.07 g, 88percent) as a black solid substance.MS (ESI) m/z=154 (M+H)8-Chloroimidazor 1 , 2-alpyrazine[00237] 2-Bromo-l, l-diethoxyethane (6.21 mL, 0.041 mmol) was added to a mixture of 48percent HBr (aq.) solution (1.64 mL) and water (20 mL) and the resulting mixture was stirred under reflux for 1 hour. The reaction mixture was then allowed to cool and washed with brine (2 x 30 mL), dried (MgSO4) and carefully concentrated in vacuo. The resulting oil was dissolved in 1 , 2-dimethoxoethane (20 mL) and added to a suspension of 2-amino-3 -chloro- pyrazine (2.142 g, 0.016 mmol) in 1 , 2-dimethoxoethane (30 mL). 48 percent HBr (aq.) solution (0.313 mL) was then added and the resulting mixture was stirred under reflux for 1 hour. Upon cooling a precipitate formed which was collected by filtration and washed with diethyl ether to give the crude HBr salt. This was dissolved in NaHCO3 (aq.) and extracted into DCM. Drying of the organic layer (MgSO4) followed by concentration in vacuo provided the title compound (1.9 g, 75percent) as a yellow/pale brown solid. 1H NMR (d6-DMSO): 8.68-8.64 (IH, br m), 8.30-8.26 (IH, br m), 7.88-7.85 (IH, br m), 7.75-7.70 (IH, br m).Bromoacetaldehyde diethyl acetal (17.4 ml, 115.8 mmol) was added dropwise to a 48percent aqueous solution of hydrobromic acid (4.45 ml, 38.6 mmol) at RT. The mixture was stirred at reflux temperature for 2 h. and then poured onto a suspension of sodium hydrogen carbonate (74.5 g, 0.88 mol) in isopropanol (220 ml). The mixture was stirred for a further 30 min. and then filtered off. 3-Chloro-pyrazin-2-ylamine (5 g, 38.6 mmol) was added to the filtrate and the mixture was stirred at 85 °C for 4 h. The solvent was evaporated in vacuo and the crude product suspended in a saturated solution of sodium hydrogen carbonate and extracted with DCM. The organic layer was dried (NaExample A3Step B: Preparation of 8-chloro-imidazo[ 1 , 2-a]pyrazine To a stirred suspension of 3-chloropyrazin-2-amine (107.5 g, 129.6mmol) in water (2500 mL) and THF (236 mL) at rt was added ethyl 2-bromo-1 , 1 -diethoxyethane (375 mL, 197 mmol) in one portion. After stirring at reflux for 4 h and 5 h at rt, the solution was adjusted to pH 8 by potassium carbonate, extracted with DCM (4 x 1000 mL9, dried over sodium sulphate, filtered and evaporated. Yield 132.9 g (104 percent) 8-chloro-imidazo[1 , 2-a]pyrazine: Bromoacetaldehyde diethyl acetal (45 ml, 0.29 mol) was treated with water (33 ml) and 48percent hydrobromic acid (33 ml) and this mixture was heated at 95°C for 90 min. The reaction was cooled, diluted with propan-2-ol (300 ml) and treated with sodium hydrogencarbonate (33 g) added in portions. This mixture was stirred for 30 min then filtered. The filtrate was treated with 2-amino-3- chloropyrazine (25 g, 0.19 mol) and then heated at 90°C for 16 h. The reaction was cooled to ambient temperature, concentrated to about one-third volume and then treated with 48percent hydrobromic acid (25 ml). More propan-2-ol (300 ml) was added and the mixture aged for 1 h. The resulting solid was collected by filtration, washed with propan-2-ol and then dissolved in water (500 ml). This solution was made basic by adding solid sodium hydrogencarbonate and then extracted with chloroform (3 x 250 ml). The organics were combined, dried over anhydrous magnesium sulphate, filtered and concentrated to give a solid. Trituration with diethyl ether afforded 8-CHLOROIMIDAZO [1, 2-A] PYRAZINE as an off- white solid (18.6 g, 63percent)Second generation imidazo[1, 2-a]pyrazineinhibitors, variants at 2- and 6-positions.8-Chloroimidazo[1, 2-a]pyrazine 2-Amino-3-chloropyrazine (200 mg, 1.54mmol) and NaHCOA mixture of bromoacetaldehyde diethyl acetal (29 ml, 192.77 mmol) and 48percent aqueous hydrogen bromide solution (7 ml)was stirred at reflux temperature for 1.5 h. After cooling back toroom temperature it was poured onto a suspension of sodiumhydrogen carbonate (14.50 g, 172.62 mmol) and 2-propanol(230 ml) and stirred until the gas evolution ceased. The formedprecipitate was filtered, then 2-amino-3-chloropyrazine (8) (7.51 g, 58 mmol) was added to the filtrate and stirred at reflux temperaturefor 3 h. The reaction mixture was allowed to cool down toroom temperature, the resulting solid was collected by filtrationand washed with 2-propanol. The solid was partitioned betweenchloroform and 10percent aqueous sodium hydrogen carbonate solution.The layers were separated and the aqueous layer was extractedwith chloroform (2). The combined organic layers were dried oversodium sulphate, filtered and concentrated under reduced pressure.The crude product was triturated with diisopropyl ether andfiltered to give the title compound (6.48 g)