N-Thiolated beta-lactam antibacterials: effects of the N-organothio substituent on anti-MRSA activity

A study on the structure-activity profiles of N-thiolated beta-lactams 1 is reported which demonstrates the importance of the N-organothio moiety on antibacterial activity. Our results indicate that elongation of the N-alkylthio residue beyond two carbons, or extensive branching within the organothio substituent, diminishes antibacterial effects. Of the derivatives we examined, the N-sec-butylthio beta-lactam derivative 5g possesses the strongest growth inhibitory activity against methicillin-resistant Staphylococcus aureus strains. Sulfur oxidation state is important, as the N-sulfenyl and N-sulfinyl groups provide for the best antibacterial activity, while lactams bearing the N-sulfonyl or N-sulfonic acid functionalities have much weaker or no anti-MRSA properties. Stereochemistry within the organothio chain does not seem to be a significant factor, although for N-sec-butylthio beta-lactams 15a-d, the 3R,4S-lactams 15c, d are more active than the 3S,4R-stereoisomers 15a, b in agar diffusion experiments. The N-methylthio lactams are the most sensitive to the presence of glutathione, followed by N-ethylthio and N-sec-butylthio lactams, which indicates that bioactivity and perhaps bacterial selectivity of the lactams may be related to the amount of organothiols in the bacterial cell. These results support the empirical model for the mechanism of action of the compounds in which the lactam transverses the bacterial membrane to deliver the organothio moiety to its cellular target.     

N-Thiolated beta-lactam antibacterials: defining the role of unsaturation in the C4 side chain

N-Methylthio beta-lactams represent a novel family of antibacterial agents for methicillin-resistant Staphylococcus aureus (MRSA). The structure-activity functions and mechanism of action of these compounds, although still largely undefined, differ dramatically from those of all previously reported beta-lactam antibiotics. Prior work has established that the N-alkylthio moiety is required for antibacterial activity, and that a variety of unsaturated groups can be tolerated at C(4) of the lactam ring. This report describes the effect that unsaturation within the C(4) substituent has on antibacterial activity of these interesting new N-thiolated beta-lactams.     

Effect of different C3-aryl substituents on the antioxidant activity of 4-hydroxycoumarin derivatives

The antioxidant activity of 4-hydroxycoumarin synthetic derivatives and 4-methylumbelliferone were determined taking 4-hydroxycoumarin as the reference compound. Six 3-aryl-4-hydroxycoumarin derivatives were synthesized from 4-hydroxycoumarin as precursor in order to evaluate changes in their antioxidant properties due to C3-aryl substituent nature. Free radical scavenging capacities of these compounds against two different species DPPH(·) and ABTS(·+) and the protecting ability towards the β-carotene-linoleic acid co-oxidation enzymatically induced by lipoxygenase were measured. In addition, the relationship between the activities of these molecules against DPPH radical and the bond dissociation energy of O-H (BDE) calculated using methods of computational chemistry was evaluated.     

Pyrazolopyridines with potent activity against herpesviruses: effects of C5 substituents on antiviral activity

Synthesis of a series of 5-substituted as well as 5,7-disubstituted 3-[2-(cyclopentylamino)-4-pyrimidinyl]-2-phenylpyrazolo[1,5-a]pyridin-7-amines with potent activity against herpes simplex viruses is described. Synthetic approaches allowing for variation of the substitution pattern are outlined and resulting changes in antiviral activity are highlighted. Several compounds with in vitro antiviral activity similar to or better than acyclovir are described.     

Syntheses and anti-MRSA activities of the C3 analogs of mansonone F, a potent anti-bacterial sesquiterpenoid: insights into its structural requirements for anti-MRSA activity

Syntheses and excellent anti-MRSA activities of the mansonone F analogs are reported. In addition, the minimal structural requirements for its anti-MRSA activities as well as its structure-activity relationship including the C3 substituents effects on anti-MRSA activity are also described. In particular, this study revealed that both ortho-quinone and tricyclic systems of mansonone F are essential for anti-MRSA activities.     

The effects of 4'-alkyl substituents on the mutagenic activity of 4-amino- and 4-nitrostilbenes in Salmonella typhimurium

Six derivatives of trans-4-aminostilbene bearing different alkyl groups in the 4'-position and six of the corresponding nitro compounds were synthesized and tested for their mutagenic potency in Salmonella typhimurium strains TA98 and TA100. Regarding the test series in presence of S9-mix, maximum activity was observed for those trans-4-aminostilbenes and trans-4-nitrostilbenes bearing small alkyl substituents like methyl and ethyl. More bulky substituents reduced the mutagenic potential in the order iso-propylethyl>iso-propyl>sec-butyl>tert-butyl). These trends have been compared with quantitative structure activity relationship (QSAR) model predictions, leading to the conclusion that steric demand is an important factor for mutagenicity of substituted aminostilbenes and nitrostilbenes. The unexpected result for the tert-butyl nitrostilbene tested with metabolic activation may be attributed to a different metabolic pathway.     

3-Phenyl-5-methyl-2H,5H-furan-2-ones: tuning antifungal activity by varying substituents on the phenyl ring

A series of racemic 3-phenyl-5-methyl-2H,5H-furan-2-ones related to a natural product, (-)incrustoporine, was synthesized, and their antifungal activity evaluated. The key structural feature, furanone ring, was closed via H2SO4-mediated cyclization of 2-phenylpent-4-enoic acids. The compounds displayed antifungal activity, especially against filamentous fungi. Expressed as the minimum inhibition concentration (MIC) in micromol/L, the activity of the most promising derivative against Absidia corymbifera matched that of ketoconazole (31.25 micromol/L). In terms of microg/mL, the substance was more active (7.6 microg/mL) than this standard antifungal drug (16.6 microg/mL).     

Novel BK channel openers containing dehydroabietic acid skeleton: structure-activity relationship for peripheral substituents on ring C

A series of dehydroabietic acid (DHAA, 2) derivatives was synthesized and evaluated as BK channel openers in an assay system of CHO-K1 cells expressing hBKalpha channels. Systematic modifications of the peripheral functionality of ring C of DHAA showed that the introduction of a nitro or (thio)urea group in ring C greatly enhanced the BK channel-opening activity.     

Studies on plant growth-regulating substances: XXXIII. The influence of ring substituents on the plant growth-regulating activity of phenylacetic acid

A comprehensive range of phenylacetic acids substituted with nitro, halogen, methyl, amino, hydroxyl and N-acetylamino groups have been synthesized and their growth-regulating activities assessed in the wheat cylinder, pea curvature and pea segment tests. The influence of substituents on molecular shape is shown to be more important in determining activity than their effects on electron distribution. Studies with 2,6-disubstituted phenylacetic acids have indicated that the most active compounds can attain a certain spatial configuration in which one surface of the molecule, including the plane of the ring system, is flat and the carboxyl group is above with its axis of rotation perpendicular to this surface. Positional requirements for growth-regulating activity in phenylacetic acids are shown to be less important than in the phenoxyacetic and benzoic acids.     

Synthesis and SAR of potent inhibitors of the Hepatitis C virus NS3/4A protease: Exploration of P2 quinazoline substituents

Novel NS3/4A protease inhibitors comprising quinazoline derivatives as P2 substituent were synthesized. High potency inhibitors displaying advantageous PK properties have been obtained through the optimization of quinazoline P2 substituents in three series exhibiting macrocyclic P2 cyclopentane dicarboxylic acid and P2 proline urea motifs. For the quinazoline moiety it was found that 8-methyl substitution in the P2 cyclopentane dicarboxylic acid series improved on the metabolic stability in human liver microsomes. By comparison, the proline urea series displayed advantageous Caco-2 permeability over the cyclopentane series. Pharmacokinetic properties in vivo were assessed in rat on selected compounds, where excellent exposure and liver-to-plasma ratios were demonstrated for a member of the 14-membered quinazoline substituted P2 proline urea series.     

Effects of irradiance and temperature on photosynthesis in C3, C4 and C3/C4 Panicum species

Species in the Laxa and Grandia groups of the genus Panicum are adapted to low, wet areas of tropical and subtropical America. Panicum milioides is a species with C₃ photosynthesis and low apparent photorespiration and has been classified as a C₃/C₄ intermediate. Other species in the Laxa group are C₃ with normal photorespiration. Panicum prionitis is a C₄ species in the Grandia group. Since P. milioides has some leaf characteristics intermediate to C₃ and C₄ species, its photosynthetic response to irradiance and temperature was compared to the closely related C₃ species, P. laxum and P. boliviense and to P. prionitis. The response of apparent photosynthesis to irradiance and temperature was similar to that of P. laxum and P. boliviense, with saturation at a photosynthetic photo flux density of about 1 mmol m^-2 s^-1 at 30°C and temperature optimum near 30°C. In contrast, P. prionitis showed no light saturation up to 2 mmol m^-2 s^-1 and an optimum temperature near 40°C. P. milioides exhibited low CO₂ loss into CO₂-free air in the light and this loss was nearly insensitive to temperature. Loss of CO₂ in the light in the C₃ species, P. laxum and P. boliviense, was several-fold higher than in P. milioides and increased 2- to 5-fold with increases in temperature from 10 to 40°C. The level of dark respiration and its response to temperature were similar in all four Panicum species examined. It is concluded that the low apparent photorespiration in P. milioides does not influence its response of apparent photosynthesis to irradiance and temperature in comparison to closely related C₃ Panicum species.Abbreviations AP apparent photosynthesis - I CO₂ compensation point - gl leaf conductance; gm, mesophyll conductance - PPFD photosynthetic photon flux density - PR apparent photorespiration rate - RuBPC sibulose bisphosphate carboxylase     

Studies on galactose oxidase active site model complexes: effects of ring substituents on Cu(II)-phenoxyl radical formation

Copper(II) complexes of new N₃O- and N₂O₂-donor tripodal ligands bearing one or two o-substituted phenol moieties have been synthesized as models for the galactose oxidase active site. The complexes of 2-[N-(1-methyl-2′-imidazolylmethyl)-N-(6″-methyl-2″-pyridylmethyl)-aminomethyl)]-4-methyl-6-methylthiophenol (MeSL), [Cu(MeSL)Cl], and N-(6-methyl-2-pyridylmethyl)-N,N-bis(2′-hydroxy-3′,5′-di-tert-butylbenzyl)amine (t-buL2mepy), [Cu(t-buL2mepy)(H₂O)], have been revealed by X-ray structural analysis to have a square-pyramidal structure with one and two phenolate oxygens in the basal plane, respectively. [Cu(MeSL)Cl] was converted into a Cu(II)-o-methylthiophenoxyl radical species by electrochemical or Ce(IV) oxidation. An o-methoxyphenoxyl radical in a similar complex was considerably more stable than the 2,4-di(tert-butyl)phenoxyl radical. While t-buL2mepy reacted with Cu(ClO₄)₂ to give [Cu(t-buL2mepy)(H₂O)] without disproportionation, an N2O2-donor ligand containing an o-methoxyphenol, a 2,4-di(tert-butyl)phenol, and an N-methylimidazole moiety gave a phenoxyl radical complex exhibiting the characteristic absorption peak at 478 nm as a reddish powder by the reaction with Cu(ClO₄)₂ as a result of spontaneous disproportionation. It exhibited a quasi-reversible redox wave at E_1/2=0.34 V (vs. Ag/AgCl) in CH₃CN, which is lower than the potentials of the copper complexes of various N₃O-donor ligands, and oxidized ethanol to acetaldehyde with a low turnover number.     

Synthesis and insecticidal activity of N-oxydihydropyrroles: 4-hydroxy-3-mesityl-5,5-dimethyl derivatives with various substituents at the 1-position

A new series of N-oxydihydropyrrole derivatives was synthesized and evaluated for insecticidal activity against Nilaparvata lugens and Myzus persicae. Various substituents were introduced to the 1-position of the dihydropyrrole ring, and the derivatives obtained exhibited systemic and/or contact insecticidal activity. The structure-activity relationship revealed that small alkyoxy and alkoxyalkoxy groups were more favorable than alkylcarbonyloxy, alkoxycarbonyloxy, or sulfonyloxy groups as substituents at the 1-position.     

Pyrazolo[1,5-a]pyridine antiherpetics: effects of the C3 substituent on antiviral activity

A recently disclosed series of pyrazolo[1,5-a]pyridine inhibitors of herpes virus replication has been closely examined herein for effects of the C3 substituent on antiviral activity. Significant changes in activity are observed by alterations of the heteroatom basicity and orientation of the group at C3. These results in combination with previous studies have served to further elaborate the minimal pharmacophore required for potency of this novel series of antiviral agents. During the course of these studies, several novel synthetic approaches were developed and are described.     

Evolution of C4 phosphoenolpyruvate carboxylase in the genus Alternanthera: gene families and the enzymatic characteristics of the C4 isozyme and its orthologues in C3 and C3/C4 Alternantheras

Phosphoenolpyruvate carboxylase (PEPCase, EC 4.1.1.3) is a key enzyme of C₄ photosynthesis. It has evolved from ancestral non-photosynthetic (C₃) isoforms and thereby changed its kinetic and regulatory properties. We are interested in understanding the molecular changes, as the C₄ PEPCases were adapted to their new function in C₄ photosynthesis and have therefore analysed the PEPCase genes of various Alternanthera species. We isolated PEPCase cDNAs from the C₄ plant Alternanthera pungens H.B.K., the C₃/C₄ intermediate plant A. tenella Colla, and the C₃ plant A. sessilis (L.) R.Br. and investigated the kinetic properties of the corresponding recombinant PEPCase proteins and their phylogenetic relationships. The three PEPCases are most likely derived from orthologous gene classes named ppcA. The affinity constant for the substrate phosphoenolpyruvate (K _0.5 PEP) and the degree of activation by glucose-6-phosphate classified the enzyme from A. pungens (C₄) as a C₄ PEPCase isoform. In contrast, both the PEPCases from A. sessilis (C₃) and A. tenella (C₃/C₄) were found to be typical C₃ PEPCase isozymes. The C₄ characteristics of the PEPCase of A. pungens were accompanied by the presence of the C₄-invariant serine residue at position 775 reinforcing that a serine at this position is essential for being a C₄ PEPCase (Svensson et al. 2003). Genomic Southern blot experiments and sequence analysis of the 3′ untranslated regions of these genes indicated the existence of PEPCase multigene family in all three plants which can be grouped into three classes named ppcA, ppcB and ppcC.     

Effect of substituents of the benzoquinone ring on electron-transfer activities of ubiquinone derivatives

The effect of substituents on the 1,4-benzoquinone ring of ubiquinone on its electron-transfer activity in the bovine heart mitochondrial succinate-cytochrome c reductase region is studied by using synthetic ubiquinone derivatives that have a decyl (or geranyl) side-chain at the 6-position and various arrangements of methyl, methoxy and hydrogen in the 2, 3 and 5 positions of the benzoquinone ring. The reduction of quinone derivatives by succinate is measured with succinate-ubiquinone reductase and with succinate-cytochrome c reductase. Oxidation of quinol derivatives is measured with ubiquinol-cytochrome c reductase. The electron-transfer efficacy of quinone derivatives is compared to that of 2,3-dimethoxy-5-methyl-6-decyl-1,4-benzoquinone. When quinone derivatives are used as the electron acceptor for succinate-ubiquinone reductase, the methyl group at the 5-position is less important than are the methoxy groups at the 2- and 3-positions. Replacing the 5-methyl group with hydrogen causes a slight increase in activity. However, replacing one or both of 2- and 3-methoxy groups with a methyl completely abolishes electron-acceptor activity. Replacing the 3-methoxy group with hydrogen results in a complete loss of electron-acceptor activity, while replacing the 2-methoxy with hydrogen results in an activity decrease by 70%, suggesting that the methoxy group at the 3-position is more specific than that at the 2-position. The structural requirements for quinol derivatives to be oxidized by ubiquinol-cytochrome c reductase are less strict. All 1,4-benzoquinol derivatives examined show partial activity when used as electron donors for ubiquinol-cytochrome c reductase. Derivatives that possess one unsubstituted position at 2, 3 or 5, with a decyl group at the 6-position, show substrate inhibition at high concentrations. Such substrate inhibition is not observed when fully substituted derivatives are used. The structural requirements for quinone derivatives to be reduced by succinate-cytochrome c reductase are less specific than those for succinate-ubiquinone reductase. Replacing one or both of the 2- and 3-methoxy groups with a methyl and keeping the 5-position unsubstituted (plastoquinone derivatives) yields derivatives with no acceptor activity for succinate-Q reductase. However, these derivatives are reducible by succinate in the presence of succinate-cytochrome c reductase. This reduction is antimycin-sensitive and requires endogenous ubiquinone, suggesting that these (plastoquinone) derivatives can only accept electrons from the ubisemiquinone radical at the Qi site of ubiquinol-cytochrome c reductase, and cannot accept electrons from the QPs of succinate-ubiquinone reductase.