Heterocyclic compounds based on 3-(4-bromophenyl) azo-5-phenyl-2(3H)-furanone: Anti-avian influenza virus (H5N1) activity / Heterociklički derivati 3-(4-bromfenil) azo-5-fenil-2(3H)-furanona: Djelovanje na virus ptičje gripe (H5N1)