Nikolas Fokialakis

Natural Resins and Bioactive Natural Products thereof as Potential Anitimicrobial Agents

Natural products and their derivatives have historically been invaluable as a source of therapeutic agents and have contributed to the discovery of antimicrobial agents. However, today with the development of drug-resistant strains, new scaffolds and new sources of bioactive compounds are needed. To this end, plant derived natural resins are reviewed for their potential application as antimicrobial agents. Natural gums, extracts of the whole resins, as well as specific extracts, fractions, essential oils and isolated compounds from the above resins are discussed in terms of their antifungal, antibacterial, and antiprotozoal activity.

Synthesis and biological evaluation of novel tamoxifen analogues

A collection of compounds, structurally related to the anticancer drug tamoxifen, used in breast cancer therapy, were designed and synthesized as potential anticancer agents. McMurry coupling reaction was used as the key synthetic step in the preparation of these analogues and the structural assignment of E, Z isomers was determined on the basis of 2D-NOESY experiments. The compounds were evaluated for their antiproliferative activity on breast cancer (MCF-7), cervix adenocarcinoma (HeLa) and biphasic mesothelioma (MSTO-211H) human tumor cell lines. The estrogen like properties of the novel compounds were compared with those of the untreated controls using an estrogen responsive element-based (ERE) luciferase reporter assay and compared to 17β-estradiol (E2). Finally, with the aim to correlate the antiproliferative activity with an intracellular target(s), the effect on relaxation activity of DNA topoisomerases I and II was assayed.

The bite of the honeybee: 2-heptanone secreted from honeybee mandibles during a bite acts as a local anaesthetic in insects and mammals.

Honeybees secrete 2-heptanone (2-H) from their mandibular glands when they bite. Researchers have identified several possible functions: 2-H could act as an alarm pheromone to recruit guards and soldiers, it could act as a chemical marker, or it could have some other function. The actual role of 2-H in honeybee behaviour remains unresolved. In this study, we show that 2-H acts as an anaesthetic in small arthropods, such as wax moth larva (WML) and Varroa mites, which are paralysed after a honeybee bite. We demonstrated that honeybee mandibles can penetrate the cuticle of WML, introducing less than one nanolitre of 2-H into the WML open circulatory system and causing instantaneous anaesthetization that lasts for a few minutes. The first indication that 2-H acts as a local anaesthetic was that its effect on larval response, inhibition and recovery is very similar to that of lidocaine. We compared the inhibitory effects of 2-H and lidocaine on voltage-gated sodium channels. Although both compounds blocked the hNav1.6 and hNav1.2 channels, lidocaine was slightly more effective, 2.82 times, on hNav.6. In contrast, when the two compounds were tested using an ex vivo preparation–the isolated rat sciatic nerve–the function of the two compounds was so similar that we were able to definitively classify 2-H as a local anaesthetic. Using the same method, we showed that 2-H has the fastest inhibitory effect of all alkyl-ketones tested, including the isomers 3- and 4-heptanone. This suggests that natural selection may have favoured 2-H over other, similar compounds because of the associated fitness advantages it confers. Our results reveal a previously unknown role of 2-H in honeybee defensive behaviour and due to its minor neurotoxicity show potential for developing a new local anaesthetic from a natural product, which could be used in human and veterinary medicine.

Submerged fermentation of the edible mushroom Pleurotus ostreatus in a batch stirred tank bioreactor as a promising alternative for the effective production of bioactive metabolites

The aim of this study was to investigate the potential of the submerged fermentation procedure in the production of bioactive metabolites of the common edible mushroom Pleurotus ostreatus. The biomass of the mushroom strain was produced by submerged fermentation in a batch stirred tank bioreactor and extracted by solvents of increasing polarity. The dichloromethane and methanol extract were fractioned by different techniques including Adsorption Chromatography and Fast Centrifugal Partition Chromatography (FCPC). The structures of pure compounds were elucidated with 1D/2D NMR-spectroscopic analyses, and chemical correlations combined with GC/MS and LC/MS experiments. Nineteen metabolites (e.g., fatty acids, phenolic metabolites, nucleotides and alkaloids) were isolated. Beyond the production of known metabolites, we report herein the production also of trans-3,4-dihydro-3,4,8-trihydroxynapthalen-1(2H)-one, indolo-3-carboxylic acid, 3-formylpyrrole and 4-hydroxybenzoic acid, that have pharmaceutical interest and are isolated for the first time from Pleurotus strains.This work indicates the great potential of the established bioprocess for the production of P. ostreatus mycelia with enhanced metabolic profile.

Antioxidant and Cytotoxic Activity of the Wild Edible Mushroom Gomphus clavatus

The fruiting bodies of the edible mushroom Gomphus clavatus (Family Gomphaceae) were collected from the wild and extracted with solvents of increasing polarity. Crude extracts were evaluated for their total phenolic content, their antioxidant capacity, and their cytotoxic activity against MCF-7 and PC-3 cancer cell lines. Concerning total phenolics and antioxidant activity, the methanol extract showed the most potent radical scavenging activity with inhibition of 45.5% of 1,1-diphenyl-2-picrylhydrazyl at 3 mg/mL. Further chemical investigation of the methanol extract led to the isolation and identification of nine compounds, among them four ergosterol derivatives. Concerning cytotoxicity, the dichloromethane (DCM) extract showed the most interesting activity, with half-maximal inhibitory concentration (IC(50)) values of 55.3 and 49.0 μg/mL in the MCF-7 and PC-3 cell lines, respectively. Further investigation of the DCM extract lead to the identification of methyl esters of fatty acids and the isolation of four fatty acids and three ergosterol derivatives. Ergosterol peroxide (compound 6) was one of the most active constituents, with IC(50) values of 35.8 μM and 30.6 μM for MCF-7 and PC-3 cells, respectively, suggesting that the cytotoxic activity of the crude extract could be at least partly attributed to the presence of ergostan derivatives. Those findings suggest that G. clavatus can be considered as a medicinal food with antioxidant and chemopreventive activities.

Cyclomegistine, the first alkaloid with the new cyclobuta[b]quinoline ring system from Sarcomelicope megistophylla

Abstract A new quinolone, cyclomegistine, was isolated from the bark of Sarcomelicope megistophylla. This alkaloid possesses the cyclobuta[b]quinoline ring system that has not been previously described either from natural or from synthetic origin. Biogenetically, cyclomegistine could arise from the oxidative aromatic ring cleavage of an acridone precursor, followed by photoisomerization of the resulting butadiene into the isomeric cyclobutene.

The raputindoles: novel cyclopentyl bisindole alkaloids from Raputia simulans.

A novel class of bisindole alkaloids is established by the isolation and structural determination of raputindoles A-D (1-4) from the Amazonian plant Raputia simulans Kallunki (Rutaceae). Complete spectroscopic characterization was accomplished by means of NMR spectroscopy and APCI (+) HRMS. Raputindoles A-D possess a cyclopentyl moiety fused on the benzene part of the indole ring, originating from the combination of prenylated indole monomers.

Essential Oil Constituents of Valeriana italica and Valeriana tuberosa. Stereochemical and Conformational Study of 15-Acetoxyvaleranone

The chemical composition of the essential oils obtained by hydrodistillation of roots, stems with leaves and inflorescences of Valeriana italica Lam. and Valeriana tuberosa L. were studied by GC/MS. Seventy-three and fourty-one constituents were identified from each plant, respectively. The major constituent of the oil obtained from the roots of V. italica was isolated and identified as 15-acetoxyvaleranone. Its stereochemistry and conformation has been studied using NMR spectroscopy and molecular modelling. The oils obtained from V. tuberosa completely lacked the characteristic valerane or kessane sesquiterpenes. Running title: Essential oils of Valeriana italica and V. tuberosa

Deoxybenzoins are novel potent selective estrogen receptor modulators

Deoxybenzoins are plant compounds with similar structure to isoflavones. In this study, we evaluated the ability of two synthesized deoxybenzoins (compound 1 and compound 2) (a) to influence the activity of the estrogen receptor subtypes ERalpha and ERbeta in HeLa cells co-transfected with an estrogen response element-driven luciferase reporter gene and ERalpha- or ERbeta-expression vectors, (b) to modulate the IGFBP-3 and pS2 protein in MCF-7 breast cancer cells, (c) to induce mineralization of KS483 osteoblasts and (d) to affect the cell viability of endometrial (Ishikawa) and breast (MCF-7, MDA-MB-231) cancer cells. Docking and binding energy calculations were performed using the mixed Monte Carlo/Low Mode search method (Macromodel 6.5). Compound 1 displayed significant estrogenic activity via ERbeta but no activity via ERalpha. Compound 2 was an estrogen-agonist via ERalpha and antagonist via ERbeta. Both compounds increased, like the pure antiestrogen ICI182780, the IGFBP-3 levels. Compound 2 induced, like 17beta-estradiol, significant mineralization in osteoblasts. The cell viability of Ishikawa cells was unchanged in the presence of either compound. Compound 1 increased MCF-7 cell viability consistently with an increase in pS2 levels, whereas compound 2 inhibited the cell viability. Molecular modeling confirmed the agonistic or antagonistic behaviour of compound 2 via ER subtypes. Compound 2, being an agonist in osteoblasts, an antagonist in breast cancer cells, with no estrogenic effects in endometrial cancer cells, makes it a potential selective estrogen receptor modulator and a choice for hormone replacement therapy.

Furomegistines I and II, two furanopyridine alkaloids from the bark of Sarcomelicope megistophylla

Two alkaloids, furomegistine I (1) and furomegistine II (2), were isolated from the bark of Sarcomelicope megistophylla. Their structures have been elucidated on the basis of MS and NMR data. Both belong to the category of furanopyridine alkaloids and should be considered as oxidation products of a furo[2,3-b]quinoline precursor. The two alkaloids exhibited moderate cytotoxic activity.