Abstract: The present disclosure provides a method for preparing a pyrazine compound of formula (I). In the present disclosure, 3-hydroxyl-6-bromopyrazine-2-amide is subjected to a reaction in the presence of phosphorus oxychloride and DIEA, during which adding an organic inorganic chloride makes the content of impurities greatly decreased, thereby obtaining 3,6-dichloropyrazine-2-carbonitrile with high-purity. 3,6-dichloropyrazine-2-carbonitrile prepared in the present disclosure is high in purity, low in production cost and suitable for industrial scale-up production and is very helpful for follow-on production of favipiravir API.

Abstract: The present disclosure discloses a compound 1,1,3,3-tetramethylguanidine (R)-(tert-butoxycarbonyl)(2-(5-(2-fluoro-3-methoxyphenyl)-3-(2-fluoro-6-(trifluoromethyl)benzyl)-4-methyl-2,6-dicarbonyl-3,6-dihydropyrimidine-1(2H)-yl)-1-phenylethyl) sulfamate (of structural formula I) and a preparation method thereof.

Abstract: The present disclosure provides an image-based search method, which is applied to a server. Said method comprises: according to image content in an image to be searched, extracting a target set from an index library; according to the attribute of each target in the target set, determining the number of targets corresponding to the attribute of each target; and according to the number of targets corresponding to the attribute of each target, sending a display target and the attribute of the display target to a terminal.