A novel series of pyridothieno-1,2,3-triazines with potent antifungal activity against Erysiphe graminis f. sp. tritici has been discovered. Two complementary synthetic routes to compounds of this type have been developed and used to efficiently explore the structure-activity relationships around the lead compound. The incorporation of oxygen atoms into the side chains of the molecules has allowed the solubility of the compounds to be increased 10-fold whilst retaining biological activity.