Mechanistic information and structure-based design methods have been used to design a series of nonpeptide cyclic ureas that are potent inhibitors of human immunodeficiency virus (HIV) protease and HIV replication. A fundamental feature of these inhibitors is the cyclic urea carbonyl oxygen that mimics the hydrogen-bonding features of a key structural water molecule. The success of the design in both displacing and mimicking the structural water molecule was confirmed by x-ray crystallographic studies. Highly selective, preorganized inhibitors with relatively low molecular weight and high oral bioavailability were synthesized.

High-resolution X-ray structures of the complexes of HIV-1 protease (HIV-1PR) with peptidomimetic inhibitors reveal the presence of a structural water molecule which is hydrogen bonded to both the mobile flaps of the enzyme and the two carbonyls flanking the transition-state mimic of the inhibitors. Using the structure−activity relationships of C 2-symmetric diol inhibitors, computed-aided drug design tools, and first principles, we designed and synthesized a novel class of cyclic ureas that incorporates this structural water and preorganizes the side chain residues into optimum binding conformations. Conformational analysis suggested a preference for pseudodiaxial benzylic and pseudodiequatorial hydroxyl substituents and an enantiomeric preference for the RSSR stereochemistry. The X-ray and solution NMR structure of the complex of HIV-1PR and one such cyclic urea, DMP323, confirmed the displacement of the structural water. Additionally, the bound and “unbound” (small-molecule X-ray) ligands have similar conformations. The high degree of preorganization, the complementarity, and the entropic gain of water displacement are proposed to explain the high affinity of these small molecules for the enzyme. The small size probably contributes to the observed good oral bioavailability in animals. Extensive structure-based optimization of the side chains that fill the S2 and S2‘ pockets of the enzyme resulted in DMP323, which was studied in phase I clinical trials but found to suffer from variable pharmacokinetics in man. This report details the synthesis, conformational analysis, structure−activity relationships, and molecular recognition of this series of C 2-symmetry HIV-1PR inhibitors. An initial series of cyclic ureas containing nonsymmetric P2/P2‘ is also discussed.

ABSTRACT

New ruthenium complexes of two tridentate ligands 2,6-bis( benzimidazol-2-yl)pyridine ( L7) and 2,6bis( 1 -methylbenzimidazol-2-yl)pyridine (La) have been synthesised. Proton and 13C NM R spectroscopy served well for their characterization, and the observed change. Proton chemical shift yields information about the electron distribution accompanying deprotonation of the ligands. The [ RuL7Jn+ chelate acts as a tetrabasic acid, with pK, ranging from 2.5 to 10.7, depending on the ruthenium oxidation state. The absorption spectra and oxidation potentials are consequently sensitive to solution pH and to solvent. The proton-coupled oxidative electron-transfer reactions of the complexes afford stable higher oxidation states such as Ru'". The properties of the complexes are discussed in comparison to those of previously reported bis(tridentate 1igand)ruthenium compounds.

The synthesis, in vitro activities, and pharmacokinetics of a series of azepanone-based inhibitors of the cysteine protease cathepsin K (EC 3.4.22.38) are described. These compounds show improved configurational stability of the C-4 diastereomeric center relative to the previously published five- and six-membered ring ketone-based inhibitor series. Studies in this series have led to the identification of 20, a potent, selective inhibitor of human cathepsin K (K(i) = 0.16 nM) as well as 24, a potent inhibitor of both human (K(i) = 0.0048 nM) and rat (K(i,app) = 4.8 nM) cathepsin K. Small-molecule X-ray crystallographic analysis of 20 established the C-4 S stereochemistry as being critical for potent inhibition and that unbound 20 adopted the expected equatorial conformation for the C-4 substituent. Molecular modeling studies predicted the higher energy axial orientation at C-4 of 20 when bound within the active site of cathepsin K, a feature subsequently confirmed by X-ray crystallography. Pharmacokinetic studies in the rat show 20 to be 42% orally bioavailable. Comparison of the transport of the cyclic and acyclic analogues through CaCo-2 cells suggests that oral bioavailability of the acyclic derivatives is limited by a P-glycoprotein-mediated efflux mechanism. It is concluded that the introduction of a conformational constraint has served the dual purpose of increasing inhibitor potency by locking in a bioactive conformation as well as locking out available conformations which may serve as substrates for enzyme systems that limit oral bioavailability.

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A series of N,N'-disubstituted cyclic urea 3-benzamides has been synthesized and evaluated for HIV protease inhibition and antiviral activity. Some of these benzamides have been shown to be potent inhibitors of HIV protease with Ki < 0.050 nM and IC90 < 20 nM for viral replication and, as such, may be useful in the treatment of AIDS. The synthesis and quantitative structure-activity relationship for this benzamide series will be discussed.

The molecular modeling studies, rational design, and synthesis of a novel series of bisphenylamidine carboxylate compounds which are inhibitors of factor Xa in the blood coagulation cascade are described. Inhibition of blood coagulation has been proposed to have several potential therapeutic utilities (Kaiser and Hauptmann, Cardiovasc. Drug Rev. 1994, 12, 225-236). Factor Xa (fXa) holds a central position in the coagulation cascade (Coleman et al. in Hemostasis and Thrombosis: Basic Principles and Clinical Practice, 1994, pp 3-18). Its major role is the generation of thrombin by the proteolytic cleavage of prothrombin. Inhibition of fXa would serve to reduce the formation of platelet clots. The fXa dimer crystal structure (Tulinsky et al., J. Mol. Biol. 1993, 232, 947-966) was used in our molecular modeling studies to design a novel series of fXa inhibitors. We initially docked and minimized isolated small molecule fragments in the S1 and S4 aryl-binding subsites. Subsequently, these fragments were connected with a tether, so as not to disturb the orientation of the fragments in their respective pockets. These modeling studies led to the initial compound (1) which was found to have significant inhibitory potency for fXa (Ki = 34 nM). The synthesis of the core structure, structure-activity relationships (SAR), and proposed binding orientation based on molecular modeling for this novel bis-phenylamidine series of fXa inhibitors are described.