Structure activity relationship of N-1 substituted 1,5-naphthyrid-2-one analogs of oxabicyclooctane-linked novel bacterial topoisomerase inhibitors as broad-spectrum antibacterial agents (Part-9).

Novel bacterial topoisomerase inhibitors (NBTIs) are the newest members of gyrase inhibitor broad-spectrum antibacterial agents, represented by the most advanced member, gepotidacin, a 4-amino-piperidine linked NBTI, which is undergoing phase III clinical trials for treatment of urinary tract infections (UTI). We have extensively reported studies on oxabicyclooctane linked NBTIs, including AM-8722. The present study summarizes structure activity relationship (SAR) of AM-8722 leading to identification of 7-fluoro-1-cyanomethyl-1,5-naphthyridin-2-one based NBTI (16, AM-8888) with improved potency and spectrum (MIC values of 0.016-4 µg/mL), with Pseudomonas aeruginosa being the least sensitive strain (MIC 4 µg/mL).

In Vitro and In Vivo Characterization of the Novel Oxabicyclooctane-Linked Bacterial Topoisomerase Inhibitor AM-8722, a Selective, Potent Inhibitor of Bacterial DNA Gyrase.

Oxabicyclooctane-linked novel bacterial topoisomerase inhibitors (NBTIs) represent a new class of recently described antibacterial agents with broad-spectrum activity. NBTIs dually inhibit the clinically validated bacterial targets DNA gyrase and topoisomerase IV and have been shown to bind distinctly from known classes of antibacterial agents directed against these targets. Herein we report the molecular, cellular, and in vivo characterization of AM-8722 as a representative N-alkylated-1,5-naphthyridone left-hand-side-substituted NBTI. Consistent with its mode of action, macromolecular labeling studies revealed a specific effect of AM-8722 to dose dependently inhibit bacterial DNA synthesis. AM-8722 displayed greater intrinsic enzymatic potency than levofloxacin versus both DNA gyrase and topoisomerase IV from Staphylococcus aureus and Escherichia coli and displayed selectivity against human topoisomerase II. AM-8722 was rapidly bactericidal and exhibited whole-cell activity versus a range of Gram-negative and Gram-positive organisms, with no whole-cell potency shift due to the presence of DNA or human serum. Frequency-of-resistance studies demonstrated an acceptable rate of resistance emergence in vitro at concentrations 16- to 32-fold the MIC. AM-8722 displayed acceptable pharmacokinetic properties and was shown to be efficacious in mouse models of bacterial septicemia. Overall, AM-8722 is a selective and potent NBTI that displays broad-spectrum antimicrobial activity in vitro and in vivo.

Structure activity relationship of pyridoxazinone substituted RHS analogs of oxabicyclooctane-linked 1,5-naphthyridinyl novel bacterial topoisomerase inhibitors as broad-spectrum antibacterial agents (Part-6).

Oxabicyclooctane linked 1,5-naphthyridinyl-pyridoxazinones are novel broad-spectrum bacterial topoisomerase inhibitors (NBTIs) targeting bacterial DNA gyrase and topoisomerase IV at a site different than quinolones. Due to lack of cross-resistance to known antibiotics they present excellent opportunity to combat drug-resistant bacteria. A structure activity relationship of the pyridoxazinone moiety is described in this Letter. Chemical synthesis and activities of NBTIs with substitutions at C-3, C-4 and C-7 of the pyridoxazinone moiety with halogens, alkyl groups and methoxy group has been described. In addition, substitutions of the linker NH proton and its transformation into amide analogs of AM-8085 and AM-8191 have been reported. Fluoro, chloro, and methyl groups at C-3 of the pyridoxazinone moiety retained the potency and spectrum. In addition, a C-3 fluoro analog showed 4-fold better oral efficacy (ED50 3.9 mg/kg) as compared to the parent AM-8085 in a murine bacteremia model of infection of Staphylococcus aureus. Even modest polarity (e.g., methoxy) is not tolerated at C-3 of the pyridoxazinone unit. The basicity and NH group of the linker is important for the activity when CH2 is at the linker position-8. However, amides (with linker position-8 ketone) with a position-7 NH or N-methyl group retained potency and spectrum suggesting that neither basicity nor hydrogen-donor properties of the linker amide NH is essential for the activity. This would suggest likely an altered binding mode of the linker position-7,8 amide containing compounds. The amides showed highly improved hERG (functional IC50 >30 µM) profile.

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.

Stereoselective synthesis of cis-2-fluorocyclopropanecarboxylic acid.

A rhodium-catalyzed cyclopropanation of 1-fluoro-1-(phenylsulfonyl)ethylene and diazo esters is described as an effective method for the stereoselective synthesis of cis-2-fluorocyclopropanecarboxylic acid. This process provides an example of the cyclopropanation of electron-deficient olefin and diazoacetates.

Synthesis and biological evaluation of tubulysin D analogs related to stereoisomers of tubuvaline.

The synthesis and biological evaluation of stereoisomers in tubulysin D are described. The stereoselective synthesis of all possible stereoisomers of C-11 and C-13 positions in tubulysin D was achieved by employing 1'-epi-Tuv-Me, 3'-epi-Tuv-Me, and ent-Tuv-Me and their biological properties were evaluated. It is clear that the stereochemistries of the C-11 and C-13 positions in tubulysin D have no practical impact on the inhibition of tubulin polymerization but play a role in the potent antiproliferative activities.

Total syntheses of tubulysins.

The total syntheses of tetrapeptides tubulysins D (1 b), U (1 c), and V (1 d), which are potent tubulin polymerization inhibitors, are described. The synthesis of Tuv (2), an unusual amino acid constituent of tubulysins, includes an 1,3-dipolar cycloaddition reaction of chiral nitrone D-6 derived from D-gulose with N-acryloyl camphor sultam (-)-9 employing the double asymmetric induction, whereas the synthesis of Tup (20), another unusual amino acid, involves a stereoselective Evans aldol reaction of (Z)-boron enolate generated from (S)-4-isopropyl-3-propionyl-2-oxazolidinone with N-protected phenylalaninal and a subsequent Barton deoxygenation protocol. We accomplished the total syntheses of tubulysins U (1 c) and V (1 d) by using these methodologies, in which the isoxazolidine ring was used as the effective protective group for γ-amido alcohol functionality. Furthermore, to understand the structure-activity relationship of tubulysins, we synthesized tubulysin D (1 b) and cyclo-tubulysin D (1 e) from 2-Me and 20, and ent-tubulysin D (ent-1 d) from ent-2-Me and ent-20, respectively. The preliminary results regarding their biological activities are also reported.

Synthesis and structure-activity relationship studies of highly potent novel oxazolidinone antibacterials.

Novel antibacterial biaryl oxazolidinones bearing an aza-, an oxa-, or a thiabicyclo[3.1.0]hex-6-yl ring system were synthesized, and their in vitro antibacterial activity and structure-activity relationships (SAR) were evaluated. Most of the synthesized biaryl bicyclo[3.1.0]hex-6-yl oxazolidinones showed good antibacterial activity against the Gram-positive and -negative bacteria tested. Regarding SAR trends among the C-ring subtypes, the pyridyl ring was preferable to the phenyl ring. The results showed that the structural variety of the C-ring has a greater impact on antibacterial activity than that of the B-ring. A cyano group at the D-ring C-6 position plays an important role in the highly potent antibacterial activity.

Structures, biological activities, and total syntheses of 13-hydroxy- and 13-acetoxy-14-nordehydrocacalohastine, novel modified furanoeremophilane-type sesquiterpenes from Trichilia cuneata.

[reaction: see text] 13-Hydroxy-14-nordehydrocacalohastine (2) and 13-acetoxy-14-nordehydrocacalohastine (3), two novel modified furanoeremophilane-type sesquiterpenes isolated from Trichilia cuneata, showed inhibitory activities for membrane lipid peroxidation in mitochondria and microsomes. The first, highly convergent total syntheses of new compounds 2 and 3 have also been achieved via a palladium-mediated three-component coupling reaction between 2-iodotoluene (7), 1-penten-4-yn-3-ol (8), and diethyl ethoxymethylenemalonate (9).