Disclosed is a compound of formula (E2) that have a three ring fused system such as a pyrimido[1,2-b]indazole core. An example of a compound of formula E2 is 2-(2-methyl-4-p-tolylpyrimido[1,2-b]indazol-3-yl)pentanoic acid, which is useful for treating HIV. Also disclosed are compounds consisting of other three ringed fused systems having antiviral activity, more specifically HIV (Human Immunodeficiency Virus) replication inhibiting 5 properties. Further disclosed are pharmaceutical compositions comprising an effective amount of such compounds as active ingredients. The use of such compounds, optionally combined with one or more other drugs having antiviral activity, for the treatment of animals suffering from viral infections, in particular HIV infection is also disclosed.
