The invention provides biologically active compounds that may be reacted with macromolecules, such as albumin, to form covalent linked complexes wherein the resulting complexes exhibit a desired biological activity in vivo. More specifically, the complexes are isolated complexes comprising a biologically active moiety covalently bound to a linking group and a protein. The complexes are prepared by conjugating a biologically active moiety, for example, a renin inhibitor or a viral fusion inhibitor peptide, with purified and isolated protein. The complexes have extended lifetimes in the bloodstream as compared to the unconjugated molecule, and exhibit biological activity for extended periods of time as compared to the unconjugated molecule. The invention also provides anti-viral compounds that are inhibitors of viral infection and/or exhibit anti-fusiogenic properties. In particular, this invention provides compounds having inhibiting activity against viruses such as human immunodeficiency virus (HIV), respiratory syncytial virus (RSV), human parainfluenza virus (HPV), measles virus (MeV), and simian immunodeficiency virus (SIV) and that have extended duration of action for the treatment of viral infections.