A fragment-based drug design approach on dengue virus methyltransferase. Optimization of new non-nucleosidique methyltransferase inhibitors by fragment-linking. Synthesis of Phenyl [(phenylcarbamoyl)amino]benzene-1-sulfonate and -sulfonamide derivatives. Crystal structures of dengue virus methyltransferase in complex with new inhibitors. Validation of dengue virus and West Nile virus methyltransferases inhibition.