The objective of the proposed work is to test the hypothesis that divalent molecules - molecules presenting two copies of a suitable ligand - will be more potent inhibitors of HIV-1 than the corresponding monovalent inhibitors. In particular, we will synthesize divalent antagonists of the chemokine receptor CCR5. Given the high mutation rate of HIV-1, it is desirable to explore alternative strategies for inhibiting HIV-1. The chemokine receptor CCR5 is a particularly promising target for AIDS therapy. While molecules have been identified that inhibit HIV-1 entry via the CCR5 co-receptor, there are challenges involved in designing inhibitors that have a higher affinity for CCR5 than existing drugs, and that exhibit greater stabilities and are less expensive than peptide-based therapeutics. We have already synthesized monovalent derivatives of known CCR5 antagonists that have reactive "handles" (free amino groups) and retain the ability to inhibit the CCR5-mediated infection of target cells by HIV-I. Several studies have shown that divalent ligands can be several orders of magnitude more potent than the corresponding monovalent ligands. It should therefore be feasible to design divalent inhibitors that will bind to two CCR5 molecules simultaneously, and with high affinity. We will utilize two strategies for the synthesis of divalent inhibitors. The first strategy involves the synthesis of compounds in which two copies of the CCR5 antagonist are connected by flexible oligo (ethylene glycol) linkers. The second strategy involves connecting two copies of the CCR5 antagonist by oligoglycine linkers. These linkers are more rigid than the oligo (ethylene glycol) linkers, and will allow us to determine the influence of the flexibility of the linker on the potency of the divalent molecule. We will test the efficacy of these inhibitors in a cell culture system, and test their immunogenicity in BALB/c mice. Divalent HIV-1 entry inhibitors with a higher affinity for CCR5 may play an important role in preventing or delaying the emergence of drug resistant viral strains. The ability of these inhibitors to dimerize CCR5 on the surface of the target cell may further enhance their ability to inhibit HIV-1 entry. The administration of these potent inhibitors in a 'cocktail' along with protease and reverse transcriptase inhibitors could have a major impact on AIDS therapy.