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8-Chloro-3-methyl-1,2,4-triazolo[4,3-a]pyrazine is used as a reagent to synthesize derivatives of Formycin, a C-nucleoside antibiotic that inhibits the influenza A virus and is also known to replace adenosine during transcription.

Step 2: Synthesis of 8-chloro-3-methyl-[1,2,4]triazolo[4,3-a]pyrazine [0197] To a stirred solution of 2-chloro-3-hydrazinopyrazine (2.0 g, 14 mmol) in xylene (20 mL) was slowly added triethyl orthoacetate (5.8 mL, 32 mmol). The reaction mixture was heated under reflux conditions overnight and subsequently cooled to room temperature. The precipitate precipitated was collected by filtration to afford the target compound 8-chloro-3-methyl-[1,2,4]triazolo[4,3-a]pyrazine as a brown powder (2.0 g, 87% yield). Mass Spectrometry (ESI): Calculated value C6H5ClN4 [M+H]+: 168.0; Measured value: 169.2. 1H NMR (400MHz, CDCl3) δ: 7.80 (d, J=4.8Hz, 1H), 7.71 (d, J=4.8Hz, 1H), 2.83 (s, 3H).

[1] Bioorganic and Medicinal Chemistry Letters, 2017, vol. 27, # 20, p. 4606 - 4613
[2] Patent: WO2016/100349, 2016, A2. Location in patent: Paragraph 0197