Compounds of Formula I, its stereoisomers, pharmaceutically acceptable salts, complexes, hydrates, solvates, tautomers, polymorphs, racemic mixtures, optically active forms and pharmaceutically active derivative thereof and pharmaceutical compositions containing them as the active ingredient which can be used as medicaments are provided. The aforementioned substances can also be used in the manufacture of medicaments for treatment, prevention, or suppression of diseases, and conditions mediated by microbes. Methods for the synthesis and characterization of the aforementioned substances are also provided.