An improved procedure for the synthesis of 3-amino-9-arylsubstituted-thieno[3,2-b]benzothiazine S,S-dioxide 2-decarboxylated is reported. Thieno-[3,2-b]benzothiazine S,S-dioxide derivatives were investigated for their abilities to inhibit beta-hematin formation, hemoglobin hydrolysis and in vivo for their efficacy in rodent Plasmodium berghei. Compounds 5j-o were the most promising as inhibitors of