Synthesis of Thieno[2,3-d]oxazines and Thieno[2,3-d]thiazines as Subtype Specific Kainate Receptor Antagonists

For the development of new antiepileptics the kainate receptors, GluR6 and GluR5, are important targets. Based on the anticonvulsant effects of chinazolines and thieno[2,3-d]pyrimidines that are known from the literature, thieno[2,3-d][1.3]oxazines were synthesized and studied for their inhibitory properties at GluR6 and GluR5 receptors. The strongest inhibitor activity was observed with 5-methyl-6-phenyl-thieno[2,3-d][1.3]oxazines with C1 or C3-substituents in position 2 (3b-f). The 2-trihalide-methyl-substituted compounds 3c and 3d were the most active inhibitors at the GluR5- receptor (IC50=23.4 μmol, 16 μl). The 2-isopropyl-substituted compound 3f displayed the strongest activity at the GluR6- receptor (IC50=8.7 μmol). A number of thieno[2,3-d][1.3]thiazines and thieno[2,3-d]pyrimidines that were synthesized from the thieno[2,3][1.3]oxazines did not show any activity.