A series of pyridines, pyrimidinones, oxazinones and their derivatives were synthesized as antimicrobial agents using citrazinic acid (2,6-dihydroxyisonicotinic acid) as a starting material. α,β-Unsaturated ketones 3a-c were condensed with cyanothio-acetamide in the presence of ammonium acetate to give 2-cyanopyridinethiones 4a-c, which were reacted with ethyl chloroacetate to yield the corresponding cyano esters 5a-c. The esters 5a-c were cyclized by action of sodium methoxide to aminoesters 6a-c, which were aminolyzed with ammonia to corresponding aminoamide derivatives 7a-c. Also, the esters 6a-c were hydrolyzed with NaOH to the corresponding sodium salt 8a-c, which were treated with acetic anhydride to afford 2-methyloxazinones 9a-c. The latter compounds were treated with ammonium acetate to afford 2-methylpyrimidinones 10a-c, followed by methylation with methyl iodide to yield 2,3-dimethyl-pyrimidinones 11a-c. The antimicrobial screening showed that many of these compounds have good antibacterial and antifungal activities comparable to streptomycin and fusidic acid used as reference drugs.