The novel compounds corresponding to the formula ##STR1## wherein R is either H or CX.sub.3, with each X substituent being individually selected from the group consisting of H and X' wherein X' is either F or Cl, are prepared by reacting di(sodiomercapto)methylenemalononitrile with the corresponding 5,6-dihalothiazolo(4,5-b)pyrazine in dimethylformamide as a reaction medium at a temperature between about 0.degree. C and about 60.degree. C until the reaction is substantially complete. The novel compounds of the present invention have antimicrobial activity.
Thiazolopyrazines having growth inhibitory activity against microorganisms are of the formula ##STR1## wherein X is --Br, --Cl or F and R is --H or --CH.sub.3-x Y.sub.x, Y is --Br, --Cl, or F and x is 0, 1, 2 or 3. These compounds also have utility as intermediates for the preparation of three-ring compounds which are highly active against microorganisms.