Inhibitors of bacterial enoyl acyl carrier protein reductase (FabI): 2,9-disubstituted 1,2,3,4-tetrahydropyrido[3,4-b]indoles as potential antibacterial agents.

An SAR study of a screening lead has led to the identification of 2,9-disubstituted 1,2,3,4-tetrahydropyrido[3,4-b]indoles as inhibitors of Staphylococcus aureus enoyl acyl carrier protein reductase (FabI).

Design and characterization of orally active Arg-Gly-Asp peptidomimetic vitronectin receptor antagonist SB 265123 for prevention of bone loss in osteoporosis.

The Arg-Gly-Asp (RGD)-binding integrin alpha(V)beta(3) is highly expressed on osteoclasts and has been proposed to mediate cell-matrix adhesion required for osteoclast-mediated bone resorption. Antagonism of this receptor should prevent stable osteoclast adhesion and thereby inhibit bone resorption. We have generated an orally bioavailable, nonpeptide RGD mimetic alpha(v)beta(3) antagonist, SB 265123, which prevents bone loss in vivo when dosed by oral administration. SB 265123 binds alpha(v)beta(3) and the closely related integrin alpha(v)beta(5) with high affinity (K(i) = 3.5 and 1.3 nM, respectively), but binds only weakly to the related RGD-binding integrins alpha(IIb)beta(3) (K(i) >1 microM) and alpha(5)beta(1) (K(i) >1 microM). The compound inhibits alpha(v)beta(3)-mediated cell adhesion with an IC(50) = 60 nM and more importantly, inhibits human osteoclast-mediated bone resorption in vitro with an IC(50) = 48 nM. In vivo, SB 265123 completely blocks bone resorption in a thyroparathyroidectomized rat model of acute bone resorption when dosed at 2.5 mg/kg/h by continuous i.v. infusion. When dosed orally with 3 to 30 mg/kg b.i.d. , in the ovariectomy-induced rat model of osteoporosis, SB 265123 prevents bone resorption in a dose-dependent fashion. This is the first report of an orally active alpha(v)beta(3) antagonist that is effective at inhibiting bone resorption when dosed in a pharmaceutically acceptable fashion. Such a molecule may provide a novel therapeutic agent for the treatment of postmenopausal osteoporosis.

Preclinical pharmacokinetics and interspecies scaling of a novel vitronectin receptor antagonist.

Allometric scaling may be used in drug development to predict the pharmacokinetics of xenobiotics in humans from animal data. Although allometry may be successful for compounds that are excreted unchanged or that are oxidatively metabolized (with corrections for metabolic capacity), it has been more challenging for compounds excreted primarily as conjugates in bile. (S)-10, 11-Dihydro-3-[3-(pyridin-2-ylamino)-1-propyloxy]-5H-dibenzo[ a, d]cycloheptene-10-acetic acid (SB-265123) is a novel alphavbeta3 ("vitronectin receptor") antagonist. In this study, the in vivo pharmacokinetics and in vitro plasma protein binding of SB-265123 were examined in four species: mice, rats, dogs, and monkeys. In monkeys and dogs, SB-265123 exhibited moderate clearance, whereas low clearance (<20% hepatic blood flow) was observed in the rat, and high clearance (>70% hepatic blood flow) was seen in the mouse. The concentration-time profiles indicated the possibility of enterohepatic recirculation; subsequent studies in bile duct-cannulated rats demonstrated extensive biliary excretion of an acyl-glucuronide of SB-265123. In allometric scaling to predict the disposition of SB-265123 in humans, various standard correction factors were applied, including protein binding, maximum lifespan potential, and brain weight; each failed to produce adequate interspecies scaling of clearance (r(2) < 0.72). Consequently, a novel correction factor incorporating bile flow and microsomal UDP-glucuronosyltransferase activity in each species was applied, demonstrating substantial improvement in the correlation of the allometric plot (r(2) = 0.96). This study demonstrates a novel allometric correction that may be applicable to compounds that undergo conjugation and biliary excretion.

Orally bioavailable nonpeptide vitronectin receptor antagonists with efficacy in an osteoporosis model.

A new series of potent nonpeptide vitronectin receptor antagonists, based on a novel carbocyclic Gly-Asp mimetic, has been discovered. A representative of this series, SB 265123 (4), has 100% oral bioavailability in rats, and is orally active in vivo in the ovariectomized rat model of osteoporosis.

Conformational preferences in a benzodiazepine series of potent nonpeptide fibrinogen receptor antagonists.

Previously, we reported the direct design of highly potent nonpeptide 3-oxo-1,4-benzodiazepine fibrinogen receptor antagonists from a constrained, RGD-containing cyclic semipeptide. The critical features incorporated into the design of these nonpeptides were the exocyclic amide at the 8-position which overlaid the Arg carbonyl, the phenyl ring which maintained an extended Gly conformation, and the diazepine ring which mimicked the gamma-turn at Asp. In this paper, we investigate conformational preferences of the 8-substituted benzodiazepine analogues by examining structural modifications to both the exocyclic amide and the seven-membered diazepine ring and by studying the conformation of the benzodiazepine ring using molecular modeling, X-ray crystallography, and NMR. We found that the directionality of the amide at the 8-position had little effect on activity and the (E)-olefin analogue retained significant potency, indicating that the trans orientation of the amide, and not the carbonyl or NH groups, made the largest contribution to the observed activity. For the diazepine ring, with the exception of the closely analogous 3-oxo-2-benzazepine ring system described previously, all of the modifications led to a significant reduction in activity compared to the potent 3-oxo-1, 4-benzodiazepine parent ring system, implicating this particular type of ring system as a desirable structural feature for high potency. Energy minimizations of a number of the modified analogues revealed that none could adopt the same low-energy conformation as the one shared by the active (S)-isomer of the 3-oxo-1, 4-benzodiazepines and 3-oxo-2-benzazepines. The overall data suggest that the features contributing to the observed high potency in this series are the orientation of the 3-4 amide and the conformational constraint imposed by the seven-membered ring, both of which position the key acidic and basic groups in the proper spatial relationship.

A check on rational drug design: crystal structure of a complex of human immunodeficiency virus type 1 protease with a novel gamma-turn mimetic inhibitor.

We have previously reported (Newlander et al., J. Med. Chem. 1993, 36, 2321-2331) the design of human immunodeficiency virus type 1 (HIV-1) protease inhibitors incorporating C7 mimetics that lock three amino acid residues of a peptide sequence into a gamma-turn. The design of one such compound, SB203238, was based on X-ray structures of reduced amide aspartyl protease inhibitors. It incorporates a gamma-turn mimetic in the P2-P1' position, where the carbonyl of the C7 ring is replaced with an sp3 methylene group yielding a constrained reduced amide. It shows competitive inhibition with Ki = 430 nM at pH 6.0. The three-dimensional structure of SB203238 bound to the active site of HIV-1 protease has been determined at 2.3 A resolution by X-ray diffraction and refined to a crystallographic R-factor (R = sigma magnitude of Fo magnitude of - magnitude of Fc magnitude of /sigma magnitude of Fo magnitude of, where Fo and Fc are the observed and calculated structure factor amplitudes, respectively) of 0.177. The inhibitor lies in an extended conformation in the active site; however, because of the constrained geometry of the C7 ring, it maintains fewer hydrogen bonds with the protein than in most other HIV-1 protease-inhibitor complexes. More importantly, the inhibitor binds to the enzyme differently than predicted in its design, by binding with the P2-P1' alpha-carbon atoms shifted by approximately one-half a residue toward the N-terminus from their presumed positions. This study illustrates the importance of structural information in an approach to rational drug design.

A novel constrained reduced-amide inhibitor of HIV-1 protease derived from the sequential incorporation of gamma-turn mimetics into a model substrate.

C7 mimetics, designed to lock three amino acid residues of a peptide chain into a gamma-turn conformation, were introduced sequentially between the P3 to P2' positions of a model HIV-1 protease substrate I (resulting in compounds II-IV) to probe its conformational requirements in binding to HIV-1 protease. Of these, compound IIIa with the C7 mimetic replacing Asn-Tyr-Pro, corresponding to the P2 through P1' positions of substrate, was found to be an inhibitor with a Ki of 147 microM. Reduction of the amide bond in the C7 mimetic of IIIa resulted in a novel constrained reduced-amide mimetic VIa with a Ki of 430 nM. This corresponds to over a 300-fold improvement in inhibitory activity over the original C7 mimetic. The inhibitory activity of mimetic VIa was in addition found to be 44-fold better than a similar linear reduced-amide containing inhibitor V. The synthesis of these mimetics are described.

A minor modification of residue 1 in potent vasopressin antagonists dramatically reduces agonist activity.

[1-(beta,beta-Pentamethylene-beta-mercaptopropionic acid),2-(O-ethyl)-D- tyrosine,4-valine,9-desglycine]arginine-vasopressin (SK&F 101926, 1), a potent in vivo and in vitro vasopressin V2 receptor antagonist, was recently tested in human volunteers and shown to be a full antidiuretic agonist. A new animal model for vasopressin activity has been developed in dogs that duplicates the clinical agonist findings exhibited with SK&F 101926. In this model we have discovered that substitution of a cis-4'-methyl group on the Pmp moiety at residue 1 of vasopressin antagonists results in substantially reduced agonist activity compared to the unsubstituted molecule (SK&F 101926). The corresponding analogue with a trans-4'-methyl group exhibits more agonist activity than the cis molecule. These findings can be explained by viewing the biological activities of compounds such as 1 as the interaction of the vasopressin receptor with a number of discrete molecular entities, conformers of 1, which present different pharmacophores. Models have been developed to assist in the understanding of these results.