2-Methoxy-5H-pyrido[3',2':5,6][1,4]thiazino[2,3-b]quinoxaline 74396-45-5 AIDS-129803 AIDS129803 Methyl 5H-pyrido[3',2':5,6][1,4]thiazino[2,3-b]quinoxalin-2-yl ether NSC367416