4-Hydroxy-5,6-dihydropyrones as inhibitors of HIV protease: the effect of heterocyclic substituents at C-6 on antiviral potency and pharmacokinetic parameters.

Due largely to the emergence of multi-drug-resistant HIV strains, the development of new HIV protease inhibitors remains a high priority for the pharmaceutical industry. Toward this end, we previously identified a 4-hydroxy-5,6-dihydropyrone lead compound (CI-1029, 1) which possesses excellent activity against the protease enzyme, good antiviral efficacy in cellular assays, and promising bioavailability in several animal species. The search for a suitable back-up candidate centered on the replacement of the aniline moiety at C-6 with an appropriately substituted heterocyle. In general, this series of heterocyclic inhibitors displayed good activity (in both enzymatic and cellular tests) and low cellular toxicity; furthermore, several analogues exhibited improved pharmacokinetic parameters in animal models. The compound with the best combination of high potency, low toxicity, and favorable bioavailabilty was (S)-3-(2-tert-butyl-4-hydroxymethyl-5-methyl-phenylsulfanyl)-4-hydroxy-6-isopropyl-6-(2-thiophen-3-yl-ethyl)-5,6-dihydro-pyran-2-one (13-(S)). This thiophene derivative also exhibited excellent antiviral efficacy against mutant HIV protease and resistant HIV strains. For these reasons, compound 13-(S) was chosen for further preclinical evaluation.

5,6-Dihydropyran-2-ones possessing various sulfonyl functionalities: potent nonpeptidic inhibitors of HIV protease.

On the basis of previous SAR findings and molecular modeling studies, a series of compounds were synthesized which possessed various sulfonyl moieties substituted at the 4-position of the C-3 phenyl ring substituent of the dihydropyran-2-one ring system. The sulfonyl substituents were added in an attempt to fill the additional S(3)' pocket and thereby produce increasingly potent inhibitors of the target enzyme. Racemic and enantiomerically resolved varieties of selected compounds were synthesized. All analogues in the study displayed decent binding affinity to HIV protease, and several compounds were shown to possess very good antiviral efficacy and safety margins. X-ray crystallographic structures confirmed that the sulfonamide and sulfonate moieties were filling the S(3)' pocket of the enzyme. However, the additional substituent did not provide improved enzymatic inhibitory or antiviral activity as compared to the resolved unsubstituted aniline. The addition of the sulfonyl moiety substitution does not appear to provide favorable pharamacokinectic parameters. Selected inhibitors were tested for antiviral activity in clinical isolates and exhibited similar antiviral activity against all of the HIV-1 strains tested as they did against the wild-type HIV-1. In addition, the inhibitors exhibited good antiviral efficacies against HIV-1 strains that displayed resistance to the currently marketed protease inhibitors.

Nonpeptidic HIV protease inhibitors: 6-alkyl-5,6-dihydropyran-2-ones possessing a novel and achiral 3-(2-t-butyl-5-methyl-4-sulfamate)phenylthio moiety.

Dihydropyran-2-ones possessing a sulfamate moiety at the 4-position of the thiophenyl ring were designed to reach S3' pocket of the HIV protease. Synthetic routes for the preparation of thiotosylates possessing 3-(2-t-butyl-5-methyl-4-sulfamate) phenylthio moiety were established. SAR of various sulfamate analogs including HIV protease binding affinities, antiviral activities and therapeutic indices will be described.

Nonpeptidic HIV protease inhibitors: 6-alkyl-5,6-dihydropyran-2-ones possessing achiral 3-(4-amino/carboxamide-2-t-butyl,5-methylphenyl thio) moiety: antiviral activities and pharmacokinetic properties.

Dihydropyran-2-ones possessing amino and carboxamide functionalities on 3-SPh (2-tert-butyl, 5-methyl) ring were synthesized and evaluated for their antiviral activities. Both the enantiomers of inhibitor 15 were synthesized. The in vitro resistance profile, inhibitory activities against cytochrome P450 isozymes and pharmacokinetic properties of inhibitor 15S will be discussed.

Nonpeptidic HIV protease inhibitors possessing excellent antiviral activities and therapeutic indices. PD 178390: a lead HIV protease inhibitor.

With the insight generated by the availability of X-ray crystal structures of various 5,6-dihydropyran-2-ones bound to HIV PR, inhibitors possessing various alkyl groups at the 6-position of 5,6-dihydropyran-2-one ring were synthesized. The inhibitors possessing a 6-alkyl group exhibited superior antiviral activities when compared to 6-phenyl analogues. Antiviral efficacies were further improved upon introduction of a polar group (hydroxyl or amino) on the 4-position of the phenethyl moiety as well as the polar group (hydroxymethyl) on the 3-(tert-butyl-5-methyl-phenylthio) moiety. The polar substitution is also advantageous for decreasing toxicity, providing inhibitors with higher therapeutic indices. The best inhibitor among this series, (S)-6-[2-(4-aminophenyl)-ethyl]-(3-(2-tert-butyl-5-methyl-phenylsulfa nyl)-4-hydroxy-6-isopropyl-5,6-dihydro-pyran-2-one (34S), exhibited an EC50 of 200 nM with a therapeutic index of > 1000. More importantly, these non-peptidic inhibitors, 16S and 34S, appear to offer little cross-resistance to the currently marketed peptidomimetic PR inhibitors. The selected inhibitors tested in vitro against mutant HIV PR showed a very small increase in binding affinities relative to wild-type HIV PR. Cmax and absolute bioavailability of 34S were higher and half-life and time above EC95 were longer compared to 16S. Thus 34S, also known as PD 178390, which displays good antiviral efficacy, promising pharmacokinetic characteristics and favorable activity against mutant enzymes and CYP3A4, has been chosen for further preclinical evaluation.

Discovery and optimization of nonpeptide HIV-1 protease inhibitors.

Several small, achiral nonpeptide inhibitors of HIV-1 protease with low micromolar activity were identified by mass screening of the Parke-Davis compound library. Two of the compounds, structurally similar, were both found to be competitive and reversible inhibitors [compound 1, 4-hydroxy-3-(3-phenoxypropyl)-1-benzopyran-2-one: Ki = 1.0 microM; compound 2, 4-hydroxy-6-phenyl-3-(phenylthio)-pyran-2-one: Ki = 1.1 microM]. These inhibitors were chosen as initial leads for optimization of in vitro inhibitory activity based on molecular modeling and X-ray crystallographic structural data. While improvements in inhibitory potency were small with analogues of compound 1, important X-ray crystallographic structural information of the enzyme-inhibitor complex was gained. When bound, 1 was found to displace H2O301 in the active site while hydrogen bonding to the catalytic Asps and Ile50 and Ile150. The pyranone group of compound 2 was found to bind at the active site in the same manner, with the 6-phenyl and the 3-phenylthio occupying P1 and P1', respectively. The structural information was used to develop design strategies to reach three or four of the internal pockets, P2-P2'. This work led to analogues of diverse structure with high potency (IC50 < 10 nM) that contain either one or no chiral centers and remain nonpeptide. The highly potent compounds possess less anti-HIV activity in cellular assays than expected, and current optimization now focuses on increasing cellular activity. The value of the HIV-1 protease inhibitors described is their potential as better pharmacological agents with a different pattern of viral resistance development, relative to the peptide inhibitors in human clinical trials.

A novel nonpeptide HIV-1 protease inhibitor: elucidation of the binding mode and its application in the design of related analogs.

HIV-1 protease has been identified as a significant target enzyme in AIDS research. While numerous peptide-derived inhibitors have been described, the identification of a nonpeptide inhibitor remains an important goal. Using an HIV-1 protease mass screening technique, 4-hydroxy-3-(3-phenoxypropyl)-2H-1-benzopyran-2-one (1) was identified as a nonpeptide competitive inhibitor of the enzyme. Employing a Monte Carlo-based docking procedure, the coumarin was docked in the active site of the enzyme, revealing a binding mode that was later confirmed by the X-ray crystal analysis. Several analogs were prepared to test the binding interactions and improve the overall binding affinity. The most active compound in the study was 4,7-dihydroxy-3-[4-(2-methoxyphenyl)butyl]-2H-1-benzopyran-2-one (31).

Synthesis and antibacterial activity of new quinolones containing a 7-[3-(1-amino-1-methylethyl)-1-pyrrolidinyl] moiety. Gram-positive agents with excellent oral activity and low side-effect potential.

A series of the R and S isomers of 7-[3-(1-amino-1-methylethyl)-1-pyrrolidinyl]-1,4-dihydro-4-oxoquinoline- and 1,8-naphthyridine-3-carboxylic acids was prepared to determine the effect on potency of the two methyl groups adjacent to the distal nitrogen in the pyrrolidinyl moiety. The antibacterial efficacy of these dimethylated derivatives was compared to the relevant 7-[3-(aminomethyl)-1-pyrrolidinyl] parent compounds and, to a lesser extent, the 7-[3-(1-aminoethyl)-1-pyrrolidinyl] analogues. The activity of the title and reference compounds was assayed in vitro using an array of Gram-negative and Gram-positive organisms and in vivo using a mouse infection model. Selected derivatives were then screened for potential side effects in a phototoxicity mouse model and an in vitro mammalian cell cytotoxicity protocol. The results showed that the R isomer displayed a 2-20-fold advantage in activity in vitro and a 2-15-fold advantage in vivo over the S isomer. Although equipotent to the 7-[3-(aminomethyl)-1-pyrrolidinyl] parent compounds in vitro, the R isomers of the 7-[3-(1-amino-1-methylethyl)-1-pyrrolidinyl] analogues showed a dramatic increase in in vivo potency, especially via the oral route of administration. These same R isomers also appeared to possess a reduced risk of phototoxicity and cytotoxicity. This combination of superior in vivo performance with a low degree of phototoxicity and mammalian cell cytotoxicity recommends these agents for further study. Of these agents, naphthyridine 16-R represents the optimal blend of potency and safety.

Quinolone antibacterials containing the new 7-[3-(1-aminoethyl)-1- pyrrolidinyl] side chain: the effects of the 1-aminoethyl moiety and its stereochemical configurations on potency and in vivo efficacy.

A series of stereochemically pure 7-[3-(1-aminoethyl)-1-pyrrolidinyl]-1, 4-dihydro-4-oxoquinoline and 1,8-naphthyridine-3-carboxylic acids, with varied substituents at the 1-, 5-, and 8-positions, were synthesized to study the effects of the 7-[3-(1-aminoethyl)-1- pyrrolidinyl] moiety on potency and in vivo efficacy relative to the known 7-[3-(aminomethyl)-1- pyrrolidinyl] derivatives. The antibacterial efficacies of the target compounds and their relevant reference agents were determined in vitro using an assortment of Gram-negative and Gram-positive organisms and in vivo using Escherichia coli and Streptococcus pyogenes mouse infection models. The effects of the 7-[3-(1-aminoethyl)-1-pyrrolidinyl] moiety were also examined at the level of the target enzyme by employing a DNA-gyrase supercoiling inhibition assay. Selected compounds were further evaluated for potential phototoxic and clastogenic liabilities using a phototoxicity mouse model and an in vitro mammalian cell cytotoxicity assay. It was found that the differences in in vitro antibacterial activity between the stereoisomers were significantly greater than previously reported for other optically pure 3-substituted pyrrolidinyl side chains. Relative to their 7-[3-(aminomethyl)-1-pyrrolidinyl] analogs, the (3R,1S)-3-(1-aminoethyl)pyrrolidines generally conferred a 2-4-fold increase in Gram-positive in vitro activity and an average of 10-fold improvement in oral efficacy. The level of phototoxicity and cytotoxicity of the product quinolones was ultimately determined by the combined influence of the 7-[3-(1-aminoethyl)-1-pyrrolidinyl] side chains and the other quinolone substituents. From this study, several compounds were identified with outstanding antibacterial activity and low degrees of phototoxicity and mammalian cell cytotoxicity. One such agent, 34F-R,S (PD 140248), showed the best overall blend of safety and efficacy.

New 8-(trifluoromethyl)-substituted quinolones. The benefits of the 8-fluoro group with reduced phototoxic risk.

A series of 8-(trifluoromethyl)-substituted quinolones has been prepared and evaluated for in vitro and in vivo antibacterial activity, and phototolerance in a mouse phototolerance assay. These analogues were compared to the corresponding series of 6,8-difluoro- and 6-fluoro-8H-quinolones (ciprofloxacin type). Although their in vitro antibacterial activities are less than the 6,8-difluoro analogues, the 8-(trifluoromethyl)quinolones are generally equivalent to their 8H analogues. In vivo, they are comparable to the 6,8-difluoro series and show up to 10-fold improvement in efficacy when compared to their ciprofloxacin counterparts vs Streptococcus pyogenes and Streptococcus pneumonia. In the phototolerance model, the 8-(trifluoromethyl)quinolones are comparable to the 8H-quinolones. Both of these series display much higher no effect doses (greater tolerance) than the corresponding 6,8-difluoroquinolones.

Synthesis and biological activity of 5-amino- and 5-hydroxyquinolones, and the overwhelming influence of the remote N1-substituent in determining the structure-activity relationship.

A series of 5-amino- and 5-hydroxyquinolone antibacterials substituted at C7 with a select group of common piperazinyl and 3-aminopyrrolidinyl side chains was prepared. These 5-substituted derivatives were compared to the analogous 5-hydrogen compounds for antiinfective activity by using DNA gyrase inhibition, minimum inhibitory concentrations against a variety of bacteria, and in vivo efficacy in the mouse infection model. The influence on the structure-activity relationships of varied substituents at C8 (H, F, Cl) and N1 (ethyl, cyclopropyl, difluorophenyl) was also studied. The results showed that several of the structure-activity conclusions regarding side-chain bulk at C7, the effect of halogen at C8, and the effect of the C5-amino group were greatly influenced by the choice of the N1-substituent. Several outstanding broad spectrum quinolones were identified in this work. In particular, the spectrum and potency of the 7-piperazinyl quinolones could be greatly enhanced by the judicious choice of C5-, C8-, and N1-substituents.

Synthesis and biological activity of 5-alkyl-1,7,8-trisubstituted-6-fluoroquinoline-3-carboxylic acids.

A series of 5-alkyl-1,7,8-trisubstituted-6-fluoro-1,4-dihydro-4-oxo-3- quinolinecarboxylic acids was prepared and evaluated for in vitro and in vivo antibacterial activity. When compared to the 5-hydrogen analogues, the presence of the 5-methyl group enhanced in vitro potency for those compounds containing a cyclopropyl moiety at N1 but decreased potency for those containing an ethyl group at N1. Replacing the 5-methyl with a 5-ethyl significantly reduced the efficacy. In general, the 5-methyl and 5-hydrogen analogues were equipotent in vivo. Several of the 5-methyl-1-cyclopropylquinolones displayed excellent in vitro and in vivo activity, warranting further development.

New quinolone antibacterial agents. Synthesis and biological activity of 7-(3,3- or 3,4-disubstituted-1-pyrrolidinyl)quinoline-3-carboxylic acids.

A series of 7-(3-amino- or 3-aminomethyl-1-pyrrolidinyl)-1-cyclopropyl-6,8-difluoro-1,4-dihydro-4-o xo-3-quinolinecarboxylic acids was synthesized and tested for antibacterial activity. Unique to these quinolones was the presence of a methyl or phenyl group in the pyrrolidine ring. Although the in vitro activity of these agents was usually equal to or less than that of their unsubstituted counterparts, one quinolone, 7-[3-(aminomethyl)-3-methyl-1-pyrrolidinyl]-1-cyclopropyl-6,8-difluoro-1 ,4-dihydro-4-oxo-3-quinolinecarboxylic acid, displayed exceptional potency both in vitro and in vivo, particularly against Gram-positive organisms.

Quinolone antibacterial agents. Synthesis and structure-activity relationships of 8-substituted quinoline-3-carboxylic acids and 1,8-naphthyridine-3-carboxylic acids.

A series of 7,8-disubstituted 1-cyclopropyl-6-fluoroquinoline-3-carboxylic acids, 7-substituted 1-cyclopropyl-6-fluoro-1,8-naphthyridine-3-carboxylic acids, and 10-substituted 9-fluoropyridobenzoxazine-6-carboxylic acids has been prepared and evaluated for antibacterial activity. The side chains examined at the 7-position (benzoxazine 10-position) included piperazinyl (g), 3-aminopyrrolidinyl (a), 3-(aminomethyl)pyrrolidinyl (b), and alkylated 3-(aminomethyl)pyrrolidinyl (c-f). Variations at C-8 of the quinolone ring system included hydrogen, nitro, amino, fluorine, and chlorine. The relative enhancement of in vitro activities by the side chains on the 8-hydrogen quinolone and 1,8-naphthyridine against Gram-negative organisms was a greater than b greater than g greater than c-f. The activity imparted to the substituted quinolone nucleus by the 8-substituent was in the order F greater than Cl greater than naphthyridine greater than H greater than benzoxazine greater than NH2 greater than NO2. These trends were retained in vivo.

5-Amino-7-(3-amino-1-pyrrolidinyl)-1-cyclopropyl-6,8-difluoro-1,4- dihydro-4-oxo-3-quinolinecarboxylic acid (PD 124,816). Synthesis and biological evaluation of a new class of quinolone antibacterials.

A series of 5-amino-1-cyclopropyl-6,8-difluoro-1,4-dihydro-4-oxo-3- quinolinecarboxylic acids with piperazinyl or pyrrolidinyl side-chains appended at C7 were prepared to test the effect of the 5-amino group on the biological and physicochemical properties of these quinolones. The target compounds were synthesized from 2-nitro-3,4,5,6-tetrafluorobenzoic acid and were tested against a variety of Gram-negative and Gram-positive bacteria and the bacterial enzyme DNA gyrase, using standard microtitration techniques. The results are compared to reference quinolones such as ciprofloxacin. The 5-amino derivatives were significantly more potent (2-16 times) than their non-amino analogues. Alkylation or acylation of the 5-amino group reduced potency dramatically. The 5-amino group was neither basic nor nucleophilic. 5-Amino-7-(3-amino-1-pyrrolidinyl)-1-cyclopropyl- 6,8-difluoro-1,4-dihydro-4-oxo-3-quinolinecarboxylic acid (PD 124,816) was selected as the best compound in this study.