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With sodium hydroxide; sodium acetate; In methanol; water;
Step 1: 2-Amino-5,6-dimethylpyrazine. Glycine amidine dihydrobromide (620 mg, 2.64 mmol) was stirred in 6 mL of MeOH at -30 C (acetonitrile/CO2 bath) in a capped flask. Butanedione (232 μL, 2.64 mmol) was stirred separately in 6 mL H2O with sodium acetate (700 mg) until homogeneous. The diketone was added to the amidine solution by pipet followed by 2.5 mL of 3.6 M NaOH. The yellow solution was allowed to warm slowly to RT and was then stirred overnight. MeOH was removed by rotovap and the aqueous solution extracted 3*30 mL with EtOAc. The combined organic extracts were dried (MgSO4), filtered and concentrated to a yellow solid which contained some impurities. The solid was triturated with EtOAc/Et2O and filtered to give pure compound (55 mg, 17%). 1H-NMR (400 MHz, CDCl3) δ7.76 (s, 1H), 4.25 (br s, 2H), 2.40 (s, 3H), 2.37 (s, 3H)
410 mg
With sodium acetate; sodium hydride; In methanol; water; at 0℃; for 0.5h;
An aqueous solution (40.0 mL) of 2,3-butanedione (1.55 g) and sodium acetate (4.72 g) was added to a methanol solution (40.0 mL) of 2-aminoacetamidine dihydrobromide (4.24 g) at - 30C over 10 min. Furthermore, 3.6 mol/L aqueous sodium hydroxide solution (17.0 mL) was added, and the reaction mixture was stirred at 0C for 30 min and at room temperature overnight. Methanol was evaporated under reduced pressure, water was added, and the mixture was extracted 3 times with ethyl acetate. The organic layer was dried over anhydrous sodium sulfate, filtered and concentrated, and the obtained residue was purified by silica gel column chromatography (solvent; hexane/ethyl acetate=50/50 - 0/100) to give the title compound (410 mg). MS(ESI)m/z; 124[M+H]+
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