Antje Hüfner

Design, synthesis and antimycobacterial activities of 1-methyl-2-alkenyl-4(1H)-quinolones

Graphical abstract A series of new 1-methyl-2-alkenyl-4(1H)-quinolones lacking carboxyl, fluorine and piperazinyl at position-3, -6 and -7, respectively, have been synthesized and tested in vitro against fast growing species of mycobacteria.

In vitro metabolism and disposition of honokiol in rat and human livers

The biotransformation of honokiol, a major constituent of the bark of Magnolia officinalis, was investigated in rat and human livers. When isolated, rat livers were perfused with 10 µM honokiol and two metabolites, namely hydroxylated honokiol conjugated with glucuronic and sulfuric acid (M1) and honokiol monoglucuronide (M2), were quantified in bile and perfusate by high-performance liquid chromatography. The hepatic extraction ratio and clearance of honokiol was very high in rat liver (E: 0.99 ± 0.01 and 35.8 ± 0.04 mL/min, respectively) leading to very low bioavailability (F = 0.007 ± 0.001). M2 formation was also highly efficient in human liver microsomes [V(max) /K(m) = 78.1 ± 6.73 µL/(min mg)], which appeared to be catalyzed mainly by UDP-glucuronosyltransferases 1A1, A3, 1A8, and 1A10, indicating hepatic and extrahepatic glucuronidation. Monosulfation of honokiol to the minor metabolite honokiol monosulfate [V(max) /K(m) = 27.9 ± 4.33 µL/(min mg)] by human liver cytosol was less pronounced and is mediated by sulfotransferases 1A1* 1, 1A1* 2, 1A2, 1A3, 1B1, and 1E1. P450-mediated oxidation of honokiol by liver microsomes, however, was below detection limit. In summary, this study established that glucuronidation and sulfation are the main metabolic pathways for honokiol in rat and human liver, suggesting their major contribution to clearance in vivo.

Interaction of N-methyl-2-alkenyl-4-quinolones with ATP-dependent MurE ligase of Mycobacterium tuberculosis: antibacterial activity, molecular docking and inhibition kinetics

Objectives The aim of this study was to comprehensively evaluate the antibacterial activity and MurE inhibition of a set of N-methyl-2-alkenyl-4-quinolones found to inhibit the growth of fast-growing mycobacteria. Methods Using the spot culture growth inhibition assay, MICs were determined for Mycobacterium tuberculosis H37Rv, Mycobacterium bovis BCG and Mycobacterium smegmatis mc2155. MICs were determined for Mycobacterium fortuitum, Mycobacterium phlei, methicillin-resistant Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa using microplate dilution assays. Inhibition of M. tuberculosis MurE ligase activity was determined both by colorimetric and HPLC methods. Computational modelling and binding prediction of the quinolones in the MurE structure was performed using Glide. Kinetic experiments were conducted for understanding possible competitive relations of the quinolones with the endogenous substrates of MurE ligase. Results The novel synthetic N-methyl-2-alkenyl-4-quinolones were found to be growth inhibitors of M. tuberculosis and rapid-growing mycobacteria as well as methicillin-resistant S. aureus, while showing no inhibition for E. coli and P. aeruginosa. The quinolones were found to be inhibitory to MurE ligase of M. tuberculosis in the micromolar range (IC50 ∼40–200 μM) when assayed either spectroscopically or by HPLC. Computational docking of the quinolones on the published M. tuberculosis MurE crystal structure suggested that the uracil recognition site is a probable binding site for the quinolones. Conclusions N-methyl-2-alkenyl-4-quinolones are inhibitors of mycobacterial and staphylococcal growth, and show MurE ligase inhibition. Therefore, they are considered as a starting point for the development of increased affinity MurE activity disruptors.

Synthesis of N-substituted 2-[(1E)-alkenyl]-4-(1H)-quinolone derivatives as antimycobacterial agents against non-tubercular mycobacteria

In an effort to improve biological activities and to examine antimycobacterial-lipophilicity relationships of 2-[(1E)-alkenyl)]-4-(1H)-quinolones, we have synthesized a series of 30 quinolones by introducing several alkyl groups, an alkenyl and an alkynyl group at N-1. All synthetic compounds were first tested in vitro against Mycobacterium smegmatis and the most active compounds (MIC values ∼3.0–7.0 μM) were further examined against three other rapidly growing strains of mycobacteria using a microtiter broth dilution assay. The Clog P values of the synthetic compounds were calculated to provide an estimate of their lipophilicity. Compounds 18e, 19a and 19b displayed the most potent inhibitory effect against M. smegmatis mc2155 with an MIC value of ∼1.5 μM, which was twenty fold and thirteen fold more potent than isoniazid and ethambutol, respectively. On the other hand, compounds 17e, 18e and 19a were most active against Mycobacterium fortuitum and Mycobacterium phlei with an MIC value of ∼3.0 μM. In the human diploid embryonic lung cell line MRC-5 cytotoxicity assay, the derivatives showed moderate to strong cytotoxic activity. Although the antimycobacterial activity of our synthetic compounds could not be correlated with the calculated log P values, an increase in lipophilicity enhances the antimycobacterial activity and C13–C15 total chain length at positions 1 and 2 is required to achieve optimal inhibitory effect against the test strains.

Synthesis and antibacterial evaluation of a new series of N-Alkyl-2-alkynyl/(E)-alkenyl-4-(1H)-quinolones.

To gain further insight into the structural requirements of the aliphatic group at position 2 for their antimycobacterial activity, some N-alkyl-4-(1H)-quinolones bearing position 2 alkynyls with various chain length and triple bond positions were prepared and tested for in vitro antibacterial activity against rapidly-growing strains of mycobacteria, the vaccine strain Mycobacterium bovis BCG, and methicillin-resistant Staphylococcus aureus strains, EMRSA-15 and -16. The compounds were also evaluated for inhibition of ATP-dependent MurE ligase of Mycobacterium tuberculosis. The lowest MIC value of 0.5 mg/L (1.2–1.5 µM) was found against M. fortuitum and M. smegmatis. These compounds displayed no or only weak toxicity to the human lung fibroblast cell line MRC-5 at 100 µM concentration. The quinolone derivatives exhibited pronounced activity against the epidemic MRSA strains (EMRSA-15 and -16) with MIC values of 2–128 mg/L (5.3–364.7 µM), and M. bovis BCG with an MIC value of 25 mg/L (66.0–77.4 µM). In addition, the compounds inhibited the MurE ligase of M. tuberculosis with moderate to weak activity showing IC50 values of 200–774 µM. The increased selectivity towards mycobacterial bacilli with reference to MRC-5 cells observed for 2-alkynyl quinolones compared to their corresponding 2-alkenyl analogues serves to highlight the mycobacterial specific effect of the triple bond. Exploration of a terminal bromine atom at the side chain of N-alkyl-2-(E)-alkenyl-4-(1H)-quinolones showed improved antimycobacterial activity whereas a cyclopropyl residue at N-1 was suggested to be detrimental to antibacterial activity.

Flavon- and flavonolglycosides from Achillea pannonica Scheele.

The detailed investigation of a methanolic extract of aerial parts of Achillea pannonica SCHEELE. within a chemotaxonomic study led to the isolation of 6 flavonoid glycosides. Besides rutin, apigenin-7-O-glucopyranoside, luteolin-7-O-glucopyranoside, apigenin-7-O-rutinoside and acacetin-7-O-rutinoside, an unusual flavondiglucoside was isolated. Its structure was established by UV, 1HNMR and 13C NMR spectroscopic methods including 2D-NMR techniques and ESI-MS as luteolin-7,4′-O-β-diglucoside. This substance is reported for the first time in the genus Achillea. Chemotaxonomic aspects are discussed briefly

Synthetic Transformations of Abietic Acid IV [1]. B- and C-Ring Oxidation

Summary. Selective oxidations at the B- or C-ring of abietic acid are described. The products can be used as educts for the synthesis of higher terpenes. Carbon side chains are attached to the B-ring via Michael additions and Reformatzky reactions.Zusammenfassung. Es werden selektive Oxidationsreaktionen am Abietinsäuregerüst beschrieben, die zur Einführung von Sauerstoffunktionen am B-bzw. C-Ring führen. Die Oxidationsprodukte können zur Synthese höherer Terpenderivate verwendet werden. An einzelnen Verbindungen werden Aufbaureaktionen beschrieben (Michael-Addition, Reformatzky-Reaktion), die es gestatten, Kohlenstoffketten an den B-Ring zu knüpfen.

1,2-substituted 4-(1H)-quinolones : synthesis, antimalarial and antitrypanosomal activities in vitro

A diverse array of 4-(1H)-quinolone derivatives bearing substituents at positions 1 and 2 were synthesized and evaluated for antiprotozoal activities against Plasmodium falciparum and Trypanosoma brucei rhodesiense, and cytotoxicity against L-6 cells in vitro. Furthermore, selectivity indices were also determined for both parasites. All compounds tested showed antimalarial activity at low micromolar concentrations, with varied degrees of selectivity against L-6 cells. Compound 5a was found to be the most active against P. falciparum, with an IC50 value of 90 nM and good selectivity for the malarial parasite compared to the L-6 cells. Compound 10a, on the other hand, showed a strong antitrypanosomal effect with an IC50 value of 1.25 µM. In this study side chain diversity was explored by varying the side chain length and substitution pattern on the aliphatic group at position-2 and a structure-antiprotozoal activity study revealed that the aromatic ring introduced at C-2 contributed significantly to the antiprotozoal activities.

Reduction of Diene Adducts ofLaevopimaric Acid

Summary. Diene adducts of laevopimaric acid with maleic anhydride or fumaric acid were reduced with LiAIH4. Besides a triol, a monoacid and the corresponding lactone were obtained from the maleic acid adduct. The fumaric acid adduct afforded two triols with different configuration at C-16. Regioselective reduction of the maleic anhydride adduct with NaBH4 gave a lactone.Zusammenfassung. Bei der Reduktion mit LiAlH4 gingen die Addukte der Lävopimarsäure mit Maleinsäureanhydrid bzw. Fumarsäure in ein Triol, eine Monocarbonsäure und das entsprechende Lacton über. Das Fumarsäureaddukt lieferte zwei Triole mit unterschiedlicher Konfiguration an C-16. Regioselektive Reduktion des Maleinsäureanhydridaddukts mit NaBH4 ergab ein Lacton.

Chemical and pharmacological investigations of Metaxya rostrata.

In a bioassay-guided approach the chemical composition of rhizomes of Metaxya rostrata (Kunth C. Presl) was studied for the first time. Investigations of the cytotoxicity of extracts and fractions on SW480 colorectal carcinoma cells resulted in the isolation of two polyphenols D cinnamtannin B-1 and aesculitannin B. The structures of the compounds were elucidated by different NMR experiments. Additionally, sugars, common sterols, such as sitosterol, stigmasterol and campesterol, as well as chlorogenic acid and caffeic acid were identified in Metaxya rostrata.