The Complestatins as HIV-1 Integrase Inhibitors. Efficient Isolation, Structure Elucidation, and Inhibitory Activities of Isocomplestatin, Chloropeptin I, New Complestatins, A and B, and Acid-Hydrolysis Products of Chloropeptin I

From the screening of a microbial extract library, isocomplestatin (<BO>1</BO>), a new axial-chiral isomer of complestatin (<BO>2</BO>) which is a known rigid bicyclic hexapeptide, was identified as a potent natural product inhibitor of HIV-1 integrase, a unique enzyme responsible for viral replication. Isocomplestatin showed inhibitory activities (IC<INF>50</INF>) in coupled 3‘-end processing/strand transfer (200 nM), strand transfer (4 μM), and HIV-1 replication (200 nM) in virus-infected cells. Attempted large-scale isolation of <BO>1</BO> by the literature method, used for the isolation of complestatin, led to lower yield and limited availability. We have developed several new, two-step, high-yielding absorption/elution methods of isolation based on reverse-phase chromatography at pH 8 that are applicable to scales from one gram to potential industrial quantities. We have also discovered and determined the structure of two new congeners of <BO>1</BO>, namely, complestatins A (<BO>4</BO>) and B (<BO>5</BO>), with almost equal HIV-1 integrase activity. They differ from <BO>1</BO> at C2‘ and C3‘ of the tryptophan moiety (residue F). Selective acid hydrolysis of chloropeptin I (<BO>3</BO>), itself a known acid-catalyzed rearranged isomer of <BO>1</BO> and <BO>2</BO> (8‘- vs 7‘-substitution in tryptophan residue F, respectively), an isomer of complestatin, and isocomplestatin resulted in a number of fragments (<BO>6</BO>−<BO>10</BO>) with retention of most of the HIV-1 integrase activity. The structure−activity relationship as revealed by these compounds could possibly lead to the design of better inhibitors or understanding of the HIV-1 integrase target.