6-Methoxy-2-phenyl-2,7a-dihydro-7-oxa-8-thia-1,2-diazacyclopenta[fg]naphthacene AIDS-138898 AIDS138898 Methyl 2-phenyl-2,7a-dihydro-7-oxa-8-thia-1,2-diazacyclopenta[fg]naphthacen-6-yl ether NSC646496