Enhancement of Antibiotic Activity by 1,8-Naphthyridine Derivatives against Multi-Resistant Bacterial Strains.

The search for new antibacterial agents has become urgent due to the exponential growth of bacterial resistance to antibiotics. Nitrogen-containing heterocycles such as 1,8-naphthyridine derivatives have been shown to have excellent antimicrobial properties. Therefore, the purpose of this study was to evaluate the antibacterial and antibiotic-modulating activities of 1,8-naphthyridine derivatives against multi-resistant bacterial strains. The broth microdilution method was used to determine the minimum inhibitory concentration (MIC) of the following compounds: 7-acetamido-1,8-naphthyridin-4(1H)-one and 3-trifluoromethyl-N-(5-chloro-1,8-naphthyridin-2-yl)-benzenesulfonamide. The antibiotic-modulating activity was analyzed using subinhibitory concentrations (MIC/8) of these compounds in combination with norfloxacin, ofloxacin, and lomefloxacin. Multi-resistant strains of Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus were used in both tests. Although the compounds had no direct antibacterial activity (MIC ≥ 1.024 µg/mL), they could decrease the MIC of these fluoroquinolones, indicating synergism was obtained from the association of the compounds. These results suggest the existence of a structure-activity relationship in this group of compounds with regard to the modulation of antibiotic activity. Therefore, we conclude that 1,8-naphthyridine derivatives potentiate the activity of fluoroquinolone antibiotics against multi-resistant bacterial strains, and thereby interesting candidates for the development of drugs against bacterial infections caused by multidrug resistant strains.

Discovery of novel 2-substituted-4-phenoxypyridine derivatives as potential antitumor agents.

A series of 2-substituted-4-phenoxypyridine derivatives were designed, synthesized, and evaluated for their antiproliferative activity against 4 cancer cell lines (A549, HT-29, H460, and U87MG) in vitro. Most compounds showed moderate to excellent potency. Nine tyrosine kinases (c-Met, Flt-3, ALK, VEGFR-2, VEGFR-3, PDGFR-α, PDGFR-ß, c-Kit, and EGFR) were used to evaluate the inhibitory activities with the most promising analogue 39, which showed the Flt-3/c-Met IC50 values of 2.18/2.61 nM. Structure-activity relationship studies indicated that n-Pr served as R1 group showed a higher preference, and stronger mono-EWGs on the phenyl ring (such as R2 = 4-F) was benefited to the potency.

Hydroxy tricyclic 1,5-naphthyridinone oxabicyclooctane-linked novel bacterial topoisomerase inhibitors as broad-spectrum antibacterial agents-SAR of RHS moiety (Part-3).

Novel bacterial topoisomerase inhibitors (NBTIs) are a new class of broad-spectrum antibacterial agents targeting bacterial Gyrase A and ParC and have potential utility in combating antibiotic resistance. (R)-Hydroxy-1,5-naphthyridinone left-hand side (LHS) oxabicyclooctane linked pyridoxazinone right-hand side (RHS) containing NBTIs showed a potent Gram-positive antibacterial profile. SAR around the RHS moiety, including substitutions around pyridooxazinone, pyridodioxane, and phenyl propenoids has been described. A fluoro substituted pyridoxazinone showed an MIC against Staphylococcus aureus of 0.5 µg/mL with reduced functional hERG activity (IC50 333 µM) and good in vivo efficacy [ED90 12 mg/kg, intravenous (iv) and 15 mg/kg, oral (p.o.)]. A pyridodioxane-containing NBTI showed a S. aureus MIC of 0.5 µg/mL, significantly improved hERG IC50 764 µM and strong efficacy of 11 mg/kg (iv) and 5 mg/kg (p.o.). A phenyl propenoid series of compounds showed potent antibacterial activity, but also showed potent hERG binding activity. Many of the compounds in the hydroxy-tricyclic series showed strong activity against Acinetobacter baumannii, but reduced activity against Escherichia coli and Pseudomonas aeruginosa. Bicyclic heterocycles appeared to be the best RHS moiety for the hydroxy-tricyclic oxabicyclooctane linked NBTIs.

Tricyclic 1,5-naphthyridinone oxabicyclooctane-linked novel bacterial topoisomerase inhibitors as broad-spectrum antibacterial agents-SAR of left-hand-side moiety (Part-2).

Novel bacterial topoisomerase inhibitors (NBTIs) represent a new class of broad-spectrum antibacterial agents targeting bacterial Gyrase A and ParC and have potential utility in combating antibiotic resistance. A series of novel oxabicyclooctane-linked NBTIs with new tricyclic-1,5-naphthyridinone left hand side moieties have been described. Compounds with a (R)-hydroxy-1,5-naphthyridinone moiety (7) showed potent antibacterial activity (e.g., Staphylococcus aureus MIC 0.25 µg/mL), acceptable Gram-positive and Gram-negative spectrum with rapidly bactericidal activity. The compound 7 showed intravenous and oral efficacy (ED50) at 3.2 and 27 mg/kg doses, respectively, in a murine model of bacteremia. Most importantly they showed significant attenuation of functional hERG activity (IC50 >170 µM). In general, lower logD attenuated hERG activity but also reduced Gram-negative activity. The co-crystal structure of a hydroxy-tricyclic NBTI bound to a DNA-gyrase complex exhibited a binding mode that show enantiomeric preference for R isomer and explains the activity and SAR. The discovery, synthesis, SAR and X-ray crystal structure of the left-hand-side tricyclic 1,5-naphthyridinone based oxabicyclooctane linked NBTIs are described.

Structure-based design, synthesis and evaluation in vitro of arylnaphthyridinones, arylpyridopyrimidinones and their tetrahydro derivatives as inhibitors of the tankyrases.

The tankyrases are members of the PARP superfamily; they poly(ADP-ribosyl)ate their target proteins using NAD(+) as a source of electrophilic ADP-ribosyl units. The three principal protein substrates of the tankyrases (TRF1, NuMA and axin) are involved in replication of cancer cells; thus inhibitors of the tankyrases may have anticancer activity. Using structure-based drug design and by analogy with known 3-arylisoquinolin-1-one and 2-arylquinazolin-4-one inhibitors, series of arylnaphthyridinones, arylpyridinopyrimidinones and their tetrahydro-derivatives were synthesised and evaluated in vitro. 7-Aryl-1,6-naphthyridin-5-ones, 3-aryl-2,6-naphthyridin-1-ones and 3-aryl-2,7-naphthyridin-1-ones were prepared by acid-catalysed cyclisation of the corresponding arylethynylpyridinenitriles or reaction of bromopyridinecarboxylic acids with ß-diketones, followed by treatment with NH3. The 7-aryl-1,6-naphthyridin-5-ones were methylated at 1-N and reduced to 7-aryl-1-methyl-1,2,3,4-tetrahydro-1,6-naphthyridin-5-ones. Cu-catalysed reaction of benzamidines with bromopyridinecarboxylic acids furnished 2-arylpyrido[2,3-d]pyrimidin-4-ones. Condensation of benzamidines with methyl 1-benzyl-4-oxopiperidine-3-carboxylate and deprotection gave 2-aryl-5,6,7,8-tetrahydropyrido[4,3-d]pyrimidin-4-ones, aza analogues of the known inhibitor XAV939. Introduction of the ring-N in the arylnaphthyridinones and the arylpyridopyrimidinones caused >1000-fold loss in activity, compared with their carbocyclic isoquinolinone and quinazolinone analogues. However, the 7-aryl-1-methyl-1,2,3,4-tetrahydro-1,6-naphthyridin-5-ones showed excellent inhibition of the tankyrases, with some examples having IC50=2nM. One compound (7-(4-bromophenyl)-1-methyl-1,2,3,4-tetrahydro-1,6-naphthyridin-5-one) showed 70-fold selectivity for inhibition of tankyrase-2 versus tankyrase-1. The mode of binding was explored through crystal structures of inhibitors in complex with tankyrase-2.

Exploration of the nicotinamide-binding site of the tankyrases, identifying 3-arylisoquinolin-1-ones as potent and selective inhibitors in vitro.

Tankyrases-1 and -2 (TNKS-1 and TNKS-2) have three cellular roles which make them important targets in cancer. Using NAD(+) as a substrate, they poly(ADP-ribosyl)ate TRF1 (regulating lengths of telomeres), NuMA (facilitating mitosis) and axin (in wnt/ß-catenin signalling). Using molecular modelling and the structure of the weak inhibitor 5-aminoiso quinolin-1-one, 3-aryl-5-substituted-isoquinolin-1-ones were designed as inhibitors to explore the structure-activity relationships (SARs) for binding and to define the shape of a hydrophobic cavity in the active site. 5-Amino-3-arylisoquinolinones were synthesised by Suzuki-Miyaura coupling of arylboronic acids to 3-bromo-1-methoxy-5-nitro-isoquinoline, reduction and O-demethylation. 3-Aryl-5-methylisoquinolin-1-ones, 3-aryl-5-fluoroisoquinolin-1-ones and 3-aryl-5-methoxyisoquinolin-1-ones were accessed by deprotonation of 3-substituted-N,N,2-trimethylbenzamides and quench with an appropriate benzonitrile. SAR around the isoquinolinone core showed that aryl was required at the 3-position, optimally with a para-substituent. Small meta-substituents were tolerated but groups in the ortho-positions reduced or abolished activity. This was not due to lack of coplanarity of the rings, as shown by the potency of 4,5-dimethyl-3-phenylisoquinolin-1-one. Methyl and methoxy were optimal at the 5-position. SAR was rationalised by modelling and by crystal structures of examples with TNKS-2. The 3-aryl unit was located in a large hydrophobic cavity and the para-substituents projected into a tunnel leading to the exterior. Potency against TNKS-1 paralleled potency against TNKS-2. Most inhibitors were highly selective for TNKSs over PARP-1 and PARP-2. A range of highly potent and selective inhibitors is now available for cellular studies.

Naphthyridinone (NTD) integrase inhibitors 4. Investigating N1 acetamide substituent effects with C3 amide groups.

A series of N1 acetamide substituted naphthyridinone HIV-1 integrase inhibitors have been explored to understand structure-activity relationships (SAR) with various C3 amide groups. Investigations were evaluated using integrase enzyme inhibition, antiviral activity and protein binding effects to optimize the sub-structures. Lipophilicity was also incorporated to understand ligand lipophilic efficiency as a function of the structural modifications. Three representative analogs were further examined in a peripheral blood mononuclear cell (PBMC) antiviral assay as well as in vitro and in vivo drug metabolism and pharmacokinetic studies.

New tricyclic systems as photosensitizers towards triple negative breast cancer cells.

Nineteen pyrrolo[1,2-h][1,7]naphthyridinones and pyrido[2,3-c]pyrrolo[1,2-a]azepinones were synthesized as new tricyclic systems in which the pyridine ring is annelated to the 6,7-dihydroindolizin-8(5H)-one and 5,6,7,8-tetrahydro-9H-pyrrole[1,2-a]azepine-9-one moieties to obtain potential photosensitizing agents. They were tested for their photoantiproliferative activity on a triple-negative breast cancer cell line, MDA-MB-231, in the dark and under UVA light (2.0 J/cm2). We demonstrated that their toxicity, only when exposed to light, was primarily due to the generation of reactive oxygen species while their photodegradation products were not responsible for their activity. The most active compounds exhibited photocytotoxicity with IC50 values at low micromolar level inducing a decrease in the intracellular content of thiol, thus triggering cancer cell death through apoptosis. All the pyridone derivatives revealed to be pure photosensitizers with preferential photocytotoxic activity towards cancerous over healthy cells. Altogether, the results obtained confirm pyrrolo[1,2-h][1,7]naphthyridinones and pyrido[2,3-c]pyrrolo[1,2-a]azepinones as promising photosensitisers against triple-negative breast cancer.