Conformation Analysis and Stereodynamics of Symmetrically ortho-Disubstituted Carvacrol Derivatives.

The design and synthesis of analogs of natural products can be a valuable source of medicinal preparations for the pharmaceutical industry. In the present study, the structural elucidation of eleven derivatives of 2,4-dihalogeno substituted synthetic analogues of the natural compound carvacrol was carried out by means of NMR experiments, and of another thirteen by DFT calculations. By selective NOE experiments and the irradiation of CH signals of the isopropyl group, individual conformers were assigned as syn and anti. By comparing GIAO/B3LYP/6-311++G(d,p)-calculated and experimentally measured vicinal 3JCH spin-spin constants, this assignment was confirmed. An unusual relationship is reported for proton-carbon vicinal couplings: 3JCH (180°) < 3JCH (0°). The conformational mobility of carvacrols was studied by 2D EXSY spectra. The application of homonuclear decoupling technique (HOBS) to these spectra simplifies the spectra, improves resolution without reducing the sensitivity, and allows a systematic examination of the rotational barrier of all compounds via their CH signals of the isopropyl group in a wider temperature interval. The rate constants of the isopropyl rotation between syn and anti conformers were determined and the corresponding energy barriers (14-17 kcal/mol) were calculated. DFT calculations of the energy barriers in carvacrol derivatives allowed the determination of the steric origin of the restricted isopropyl rotation. The barrier height depends on the size of the 2- and 4-position substituents, and is independent of the derivatization of the OH group.

Marrubiin Inhibits Peritoneal Inflammatory Response Induced by Carrageenan Application in C57 Mice.

Marrubiin is a diterpene with a long history of a wide range of biological activities. In this study, the anti-inflammatory effects of marrubiin were investigated using several in vitro and in vivo assays. Marrubiin inhibited carrageenan-induced peritoneal inflammation by preventing inflammatory cell infiltration and peritoneal mast cell degranulation. The anti-inflammatory activity was further demonstrated by monitoring a set of biochemical parameters, showing that the peritoneal fluid of animals treated with marrubiin had lower levels of proteins and lower myeloperoxidase activity compared with the fluid of animals that were not treated. Marrubiin exerted the most pronounced cytotoxic activity towards peripheral mononuclear cells, being the main contributors to peritoneal inflammation. Additionally, a moderate lipoxygenase inhibition activity of marrubiin was observed.

Bioisosteric ferrocenyl 1,3-thiazolidine-4-carboxylic acid derivatives: In vitro antiproliferative and antimicrobial evaluations.

To improve the antiproliferative effect of ALC67 (diastereomeric mixture of ethyl 2-phenyl-3-propioloyl-1,3-thiazolidine-4-carboxylate), its structure was modified via (i) bioisosteric substitution of the phenyl ring by the ferrocene unit and (ii) replacing the propiolamide side-chain in ACL67 with other acyl groups having differing electrophilicities. In this way, a small library of methyl N-acyl-2-ferrocenyl-1,3-thiazolidine-4-carboxylates (13 compounds in total) was created and characterized by spectral and crystallographic means. The last N-acylation step was highly diastereoselective toward the cis-diastereomer. In solution, most of the obtained compounds existed as a mixture of two rotamers and displayed a preference for the syn-orientation around the CN bond. A twisted 5T4 envelope conformation was adopted by the derivative containing the N-phenoxyacetyl group in the crystalline state. Two derivatives with chloroacetyl and bromoacetyl groups in the N-3 side chain were cytotoxic to fibroblasts and hepatocellular cancer cells in the low micromolar range (IC50(MRC5) = 9.0 and 11.8 µM, respectively, and IC50(HepG2) = 10.6 and 18.4 µM, respectively) causing an effect similar to the lead compound (IC50(HepG2) = 10.0 µM) and cisplatin (IC50(MRC5) = 4.0 µM and IC50(HepG2) = 7.7 µM). Several derivatives also manifested modest antimicrobial effects against the studied microbial strains (MICs in the range from 0.44 to 4.0 µmol/mL). Our findings demonstrated that the introduction of a ferrocene core facilitated the preparation of optically pure analogs of ALC67 and that the cytotoxicity of compounds may be enhanced by adding proper electrophilic centers to the N-acyl side-chain.

Synthesis of Small Libraries of Natural Products: Part II: Identification of a New Natural Product from the Essential Oil of Pleurospermum austriacum (L.) Hoffm. (Apiaceae).

Herein, comprehensive data of NMR, MS, IR, and gas chromatography (RI) obtained by GC-MS on commonly used capillary columns of different polarity (non-polar DB-5MS and polar HP-Innowax) of a series of esters of all constitutional isomers of hexanoic acid with a homologous series of ω-phenylalkan-1-ols (phenylmethanol, 2-phenylethanol, 3-phenylpropan-1-ol, 4-phenylbutan-1-ol, and 5-phenylpentan-1-ol) and phenol, in total 48 chemical entities, were collected. The created synthetic library allowed the identification of a new constituent of the P. austriacum essential oil (3-phenylpropyl 2-methylpentanoate). The accumulated spectral and chromatographical data, as well as the established correlation between RI values and structures of regioisomeric hexanoates, provide (phyto)chemists with a tool that will make future identification of related natural compounds a straightforward task.

Wax Composition of Serbian Dianthus spp. (Caryophyllaceae): Identification of New Metabolites and Chemotaxonomic Implications.

Although ethnopharmacologically renowned, wax constituents of Dianthus species were sporadically studied. A combination of GC-MS analysis, synthesis, and chemical transformations enabled the identification of 275 constituents of diethyl-ether washings of aerial parts and/or flowers of six Dianthus taxa (Dianthus carthusianorum, D. deltoides, D. giganteus subsp. banaticus, D. integer subsp. minutiflorus, D. petraeus, and D. superbus) and one Petrorhagia taxon (P. prolifera) from Serbia. Seventeen of these constituents (nonacosyl benzoate, additional 12 benzoates with anteiso-branched 1-alkanols, eicosyl tiglate, triacontane-14,16-dione, dotriacontane-14,16-dione, and tetratriacontane-16,18-dione) and two additional synthesized eicosyl esters (angelate and senecioate) represent completely new compounds. The structures of the tentatively identified ß-ketones were confirmed by analysis of the mass fragmentation of the corresponding pyrazoles and silyl enol ethers obtained by transformations of crude extracts and extract fractions. Silylation allowed the identification of 114 additional constituents, including a completely new natural product (30-methylhentriacontan-1-ol). The results obtained by multivariate statistical analyses showed that the chemical profile of Dianthus taxa's surface waxes is subject to both genetic and ecological factors, whereas the latter seemingly takes a more important role for the studied Dianthus samples.

The potential of lemon balm (Melissa officinalis L.) essential oil as an anti-anxiety agent - is the citronellal the activity carrier?

ETHNOPHARMACOLOGICAL RELEVANCE: Among the fewest drugs discovered are those belonging to the class of anxiolytics. Although some drug targets for anxiety disorders are established, it is hard to modify and selectively choose the active principle for those targets. Thus, the ethnomedical approach to treating anxiety disorders remains one of the most prevalent ways for (self)managing the symptoms. Melissa officinalis L. (lemon balm) has been extensively used as an ethnomedicinal remedy for the treatment of different psyche-related symptoms, especially dose related to restlessness. AIM OF THE STUDY: This work aimed to evaluate the anxiolytic activity, in several in vivo models, of the essential oil extracted from Melissa officinalis (MO) and its main constituent citronellal, a widespread plant utilized for managing anxiety. MATERIALS AND METHODS: In the present study several animal models were used to assess MO anxiolytic potential in mice. The effect of the MO essential oil applied in doses ranging from 12.5 to 100 mg/kg was estimated in light/dark, hole board, and marble burying tests. In parallel doses of citronellal corresponding to the ones in the MO essential oil were applied to animals to determine if this is the activity carrier. RESULTS: The results indicate that the MO essential oil exerts anxiolytic potential in all three experimental settings by significantly altering the traced parameters. The effects of citronellal are somewhat inconclusive and should not be interpreted only as anxiolytic but rather as a combination of anti-anxiety and motor-inhibiting effects. CONCLUSIONS: In conclusion, we could say that the results of the present study provide a base for future mechanistic studies that would evaluate the activity of M. officinalis essential oil on various neurotransmitter systems involved in the generation, propagation, and maintenance of anxiety.

On the configuration and occurrence of 2,6-cyclocuparan-3-ols: Resolving a lasting discrepancy.

2,6-Cyclocuparan-3-ols are chemical markers and major volatiles of several liverwort species. Conflicting reports on the structures of these cyclocuparanols can be found in the literature-different research groups assigned the same spectral data to different structures, yet these inconsistencies were never addressed, let alone satisfactorily explained. Following the isolation of all four diastereoisomeric cyclocuparanols from Marchantia polymorpha, their relative and absolute configurations were extensively studied by chemical and spectroscopic methods and definite stereostructures were proposed.

Pulicaria dysenterica (L.) Bernh.-Rightfully Earned Name? Identification and Biological Activity of New 3-Methoxycuminyl Esters from P. dysenterica Essential Oil.

Motivated by the ethnopharmacological use of Pulicaria dysenterica, in the present study, the antimicrobial potential of the extracted essential oil was investigated against a panel of eighteen microorganism strains. Additionally, anti-acetylcholinesterase and antispasmodic (isolated rat distal colon) activities, general acute toxicity (Artemia salina model), and immunomodulatory properties (cytotoxicity on isolated mouse macrophages) were studied. Detailed analyses of the essential oil led to the identification of 3-methoxycuminyl 2-methylbutanoate (a new natural product) and 3-methoxycuminyl 3-methylbutanoate (a rare natural product). The obtained esters and intermediates in the synthesis of the starting alcohol (3-methoxycuminol) were subjected to a battery of 1D- and 2D-NMR experiments. The synthesized esters were additionally characterized by GC-MS, IR, and UV-Vis. The synthesized compounds (ten in total) were biologically tested in the same way as the extracted P. dysenterica essential oil. The obtained low acute toxicity and promising antimicrobial potential suggest that the P. dysenterica essential oil might partially explain the ethnopharmacological application of P. dysenterica plant material for the treatment of gastrointestinal infections.

An HPLC-based assay for improved measurement of glutamate decarboxylase inhibition/activation.

L-Glutamic acid decarboxylase (GAD) is an enzyme that ensures the balance between the levels of two neurotransmitters, γ-aminobutyric acid (GABA) and L-glutamic acid (L-Glu), necessary for proper brain functioning. A reduction in the concentrations of GABA and/or GAD activity has been implicated in the symptoms associated with epilepsy, which could be plausibly alleviated by the application of GAD activators. As any unnecessary interference in GAD catalytic activity could be detrimental, it is important to study whether CNS (or other) drug candidates act on GAD or not. The ability to identify and reduce this risk early could significantly improve the process of drug development. Although many methods for measuring GAD activity in various biological samples have been described, only few (such as manometric and radiometric) were adopted as in vitro assays for the screening of potential GAD inhibitors/activators. However, these methods require specialized equipment and/or an expensive radiolabeled substrate, and may have sensitivity and/or reliability issues. Therefore, this study aimed to develop an HPLC-DAD-based assay that would allow a simple and more accurate measurement of GAD inhibition or activation using unpurified mice or rat brain homogenates. This assay is based on the quantification of GABA, formed during the enzymatic reaction, after its derivatization with dansyl chloride. Various parameters were evaluated to optimize the assay procedure (e.g. homogenate volume, incubation time, DMSO content, GAD, GABA, and dansyl-GABA stabilities). This assay was validated for pharmacological screenings using 3-mercaptopropionic acid and gallic acid and GAD obtained from different experimental animals.

New neryl esters from Helichrysum italicum (Roth) G. Don (Asteraceae) essential oil.

Helichrysum italicum (immortelle) is a dwarf aromatic shrub native to the Mediterranean region. The typical subspecies (italicum) produces an essential oil rich in neryl acetate and characteristic ß-diketones, italidiones, highly valued in the perfume industry. As esters are an important group of aroma-active volatiles, herein the composition of the ester fraction of this immortelle chemotype essential oil was studied in detail. Chromatographic separation of Corsican immortelle essential oil enabled the discovery of numerous potentially olfactory-interesting esters of nerol and/or angelic acid, undetectable by direct GC-MS analyses of the unfractioned oil. Four esters of nerol and medium-chain branched fatty acids represent new natural products, while several other esters have a rather restricted occurrence in the Plant Kingdom.

Lemon balm (Melissa officinalis L.) essential oil and citronellal modulate anxiety-related symptoms - In vitro and in vivo studies.

ETHNOPHARMACOLOGICAL RELEVANCE: Besides psyche-related symptoms, patients with anxiety disorders can have a large number of somatic symptoms as well. Although the treatment of these disorders is mainly focused on resolving their mental component, one cannot neglect the need for the treatment of accompanying somatic symptoms. Melissa officinalis L. (lemon balm), in various formulations, has been extensively used as an ethnomedicinal remedy for the treatment of different psyche-related symptoms, and its use is considered relatively safe. AIM OF THE STUDY: In the present study, the activity of M. officinalis (MO) essential oil was evaluated in several in vitro and in vivo models mimicking or involving anxiety-related somatic symptoms. MATERIALS AND METHODS: To address the effect of MO essential oil on the gastrointestinal and heart-related symptoms accompanying anxiety disorders, in vitro models were utilized that follow the function of the isolated mouse ileum and atria tissues, respectively, after exposure to MO essential oil. Effects of MO essential oil on BALB/c mice motor activity was estimated using the open field, rota-rod, and horizontal wire tests. Additionally, the essential oil was assayed for its potential in inhibiting acetylcholinesterase activity. RESULTS: The performance of mice treated with 25 mg/kg of the oil showed a statistically significant decrease in the motor impairment arising from acute anxiety (open field test), while there was a prolonged latency and a reduction of the frequency of falling from a rotating rod and/or a horizontal wire (signs of muscle weakness/spasms). Concentrations of the essential oil higher than 1 µg/mL were found to inhibit both spontaneous and induced ileum contractions. Moreover, the essential oil and citronellal were found to decrease isolated mouse atria contraction frequency, as well as contraction force. However, the oil was found to be a very weak acetylcholinesterase inhibitor. CONCLUSION: The modulation of anxiety-related symptoms by the oil was found not to be mediated through the inhibition of the acetylcholinesterase, nonetheless, the mechanistic studies involving the ileum and cardiac tissues, revealed that the activity of MO and citronellal might be related to the modification of either voltage-gated Ca2+ channels or muscarinic receptors. Mice locomotion, balance, and muscle strength were not impacted by the essential oil; however, its main constituent, citronellal, was found to exert a certain degree of muscle function inhibition. All these results suggest that the activity of MO essential oil arises from synergistic and/or antagonistic interactions of its constituents, and is not completely dependent on the oil's main constituent.

Methyl and Isopropyl N-Methylanthranilates Affect Primary Macrophage Function - An Insight into the Possible Immunomodulatory Mode of Action.

To complement the knowledge on the anti-inflammatory activity of methyl and isopropyl N-methylanthranilates, two natural products with panacea-like properties, we investigated their effects on thioglycolate-elicited macrophages by evaluating macrophage ability to metabolize MTT, macrophage membrane function, and macrophage myeloperoxidase and phagocytic activities. Moreover, two additional aspects of the inflammatory response of these compounds, their inhibitory activity on xanthine oxidase and catalase, were studied. It was found that these two compounds regulate elicited macrophage functions, most probably by interfering with the function of cell membranes and changing the reducing cellular capacity or enzyme activity of macrophages. Nonetheless, no significant inhibitory action either towards xanthine oxidase or catalase was found, suggesting that the inhibition of these enzymes is not involved in the anti-inflammatory mode of action of these two esters.

Linking the antimicrobial and anti-inflammatory effects of immortelle essential oil with its chemical composition - The interplay between the major and minor constituents.

Immortelle (Helichrysum italicum, Asteraceae) essential oil has been widely used in alternative medicine to accelerate wound healing, as well as in cosmetic products to stimulate skin regeneration and to reduce the appearance of wrinkles. It is also considered a natural and safe culinary spice that could also be applied in the food industry as a preservative in the future. The therapeutic efficacy of this oil changes with the natural variability of the composition. Herein we tested and mutually compared the antimicrobial and anti-inflammatory activities of four commercial immortelle oils differing in the relative amounts of marker compounds, i.e. neryl esters, α-pinene, γ- and ar-curcumenes, and ß-diketones. The anti-inflammatory effect of selected chromatographic fractions, enriched in the aforementioned constituents, was evaluated by studying toxicity toward rat peritoneal macrophages, their nitric oxide production, myeloperoxidase, and arginase activities. Subsequently, the compositional and activity data were subjected to a multivariate statistical treatment to reveal the possible correlation(s) between the percentage of essential-oil constituents and the observed activities. The obtained results imply that immortelle oil efficiency as an antimicrobial and/or anti-inflammatory agent is most plausibly a result of a synergistic action between its constituents, and/or, rather unexpectedly, the presence of some minor constituents.

Analysis of Polycyclic Aromatic Hydrocarbons and Phthalate Esters in Soil and Food Grains from the Balkan Peninsula: Implication on DNA Adduct Formation by Aristolochic Acid I and Balkan Endemic Nephropathy.

Balkan endemic nephropathy (BEN) is a chronic tubulointerstitial nephropathy affecting residents of rural farming areas in many Balkan countries. Although it is generally believed that BEN is an environmental disease caused by multiple geochemical factors with much attention on aristolochic acids (AAs), its etiology remains controversial. In this study, we tested the hypothesis that environmental contamination and subsequent food contamination by polycyclic aromatic hydrocarbons (PAHs) and phthalate esters are AA toxicity factors and important to BEN development. We identified significantly higher concentrations of phenanthrene, anthracene, diethyl phthalate (DEP), dibutyl phthalate (DBP), and benzyl butyl phthalate (BBP) in both maize and wheat grain samples collected from endemic villages than from nonendemic villages. Other PAHs and phthalate esters were also detected at higher concentrations in the soil samples from endemic villages. Subsequent genotoxicity testing of cultured human kidney cells showed an alarming phenomenon that phenanthrene, DEP, BBP, and DBP can interact synergistically with AAs to form elevated levels of AA-DNA adducts, which are associated with both the nephrotoxicity and carcinogenicity of AAs, further increasing their disease risks. This study provides direct evidence that prolonged coexposure to these environmental contaminants via dietary intake may lead to greater toxicity and accelerated development of BEN.

Thymol regulates the functions of immune cells in the rat peritoneal cavity after l-arginine-induced pancreatitis.

AIMS: The present study aimed to evaluate the protective action of thymol towards l-arginine-induced acute pancreatitis (AP) by studying the function of rat peritoneal immune cells. MAIN METHODS: Rat peritoneal exudate cells (PECs), obtained 24 h after the injection of l-arginine (350 mg/100 g of b.w.), were evaluated for mitochondrial activity (MTT assay), adherence capacity (methylene-blue assay), and phagocyte enzyme activity (myeloperoxidase, MPO, assay). The activity of α-amylase and free MPO, as well as the concentration of reactive oxygen species (ROS, i.e. O2-), were determined in the peritoneal exudate fluid. Also, serum α-amylase activity determination and pancreatic tissue pathohistological analysis were performed. KEY FINDING: The administered thymol (50 and 100 mg/kg, per os) caused a significant decrease in the PEC mitochondrial activity and adherence capacity when compared with these functions of PECs isolated from rats with AP. A decrease in cellular MPO activity, as well as in the levels of ROS, α-amylase, and free MPO in peritoneal exudates was found in animals treated with thymol compared to the control animals with AP. Additionally, thymol administration prevented an increase in serum α-amylase activity, accompanied by the decrease in pancreatic tissue damage that follows l-arginine application. SIGNIFICANCE: The present results showed that thymol exerts significant immunomodulatory properties and a potential to silence PEC functions in inflammatory conditions such as the AP induced by l-arginine.

A series of esters of diastereomeric menthols: Comprehensive mass spectral libraries and gas chromatographic data.

A comprehensive data collection of mass spectral and gas chromatographic data of a series of esters of diastereomeric menthols (menthol, isomenthol, neomenthol, and neoisomenthol), in total 150 chemical entities, obtained by GC-MS on commonly used capillary columns of different polarity (non-polar HP-5MS and polar HP-Innowax), was created. Also, MS libraries containing electron ionization MS recorded on single quadrupole as well as on quadrupole ion-trap mass detectors together with the RIs on non-polar and polar columns were compiled (available as supplementary materials). The results point out to frequent misidentification of neoisomenthyl acetate as isomenthyl acetate in the literature, and the means of how to resolve this issue was suggested. The outcomes of this study provide chemists and food technologists with a useful tool in the field of food analysis of compounds with important food aroma properties.

Very-Long-Chain Wax Constituents from Primula veris and P. acaulis: Does the Paradigm of Non-Branched vs. Branched Chain Dominance Universally Hold in all Plant Taxa?

Herein n-, iso- and anteiso-series of very-long-chained (VLC) alkanes (C21 -C35 ), fatty acid benzyl esters (FABEs; C20 -C32 ), and 2-alkanones (C23 -C35 ) were identified in the wax of Primula veris L. and P. acaulis (L.) L. (Primulaceae). For the very first time in a sample of natural origin, the presence of iso- and anteiso-VLC FABEs and 2-alkanones was unequivocally confirmed by synthetic work, derivatization, and NMR. It should be noted that the studied species produced unusually high amounts of branched wax constituents (e. g., >50 % of 2-alkanones were branched isomers). The domination of iso-isomers, probably biosynthesized from leucine-derived starters, is a unique feature in the Plant Kingdom. The plant organ distribution of these VLC compounds in P. acaulis samples (different habitats and phenological phases) pointed to their possible ecological value. This was supported by a eutectic behavior of binary blends of FABEs and alkanes, as well as by high UV-C absorption by FABEs.

Long-chain syn-1-phenylalkane-1,3-diyl diacetates, related phenylalkane derivatives, and sec-alcohols, all possessing dominantly iso-branched chain termini, and 2/3-methyl-branched fatty acids from Primula veris L. (Primulaceae) wax.

Herein, the results of the first study of non-flavonoid constituents of aboveground surface-wax washings of Primula veris L. (Primulaceae) are presented. Chromatography of the washings yielded a minor fraction composed of n-, iso-, and anteiso-series of long-chained syn-1-phenylalkane-1,3-diyl diacetates, 3-oxo-1-phenylalkan-1-yl acetates, 1-phenylalkane-1,3-diones, 1-hydroxy-1-phenylalkan-3-ones, sec-alcohols (2- to 10-alkanols), and n-, iso-, anteiso-, 2-methylalkanoic and 3-methylalkanoic acids; 118 of these constituents represent up to now unreported natural compounds. The structural/stereochemical elucidation was accomplished by the synthesis of authentic standards, derivatization reactions, the use of gas chromatographic retention data and detailed 1D and 2D-NMR analyses of the obtained complex chromatographic fraction. Primula veris produces unusually high amounts of branched long-chained metabolites (>60%) except for the fatty acids where the percentage of branched isomers is comparable to the ones with n-chains. Noteworthy is the fact that long-chained α- and ß-methyl substituted fatty acids were detected herein for the first time in the kingdom Plantae.

An Impact of Psychological Stress on the Interplay between Salivary Oxidative Stress and the Classic Psychological Stress-Related Parameters.

Both oxidative and psychological (mental) stress are the likely culprits for several acute and chronic health disturbances, and adequate tests mimicking that are needed. Herein, in controlled laboratory surroundings, a PEBL (Psychology Experiment Building Language) test battery was used to evoke stress-related biological responses followed by tracking changes in saliva parameters. The study objectives were to determine the impact of psychological stress on selected salivatory parameters and to assess the correlation between the determined oxidative and stress parameters. The study was conducted on 36 healthy young subjects, mainly females (n = 24). Before and following the completion of a battery of four PEBL tests, subjects' saliva samples were collected. Stress-evoking changes in total antioxidant capacity and nitrite/nitrate levels, as oxidative stress parameters, and cortisol and immunoglobulin A (IgA), as parameters of psychological stress, were established and mutually correlated by comparing the values of the evaluated parameters pre- and post-PEBL test. The results showed that there is no change in the total salivary antioxidant capacity (p > 0.05); however, there was a significant increase in nitrites/nitrates levels after the PEBL test (p = 0.007). On the other hand, the determined cortisol levels after the test battery were found to be statistically significantly increased (p = 0.025) when compared to the values obtained before the test, while the levels of IgA were found to be statistically significantly decreased (p < 0.001). The only statistically significant correlation between the changes in the studied parameters was found to be the one between cortisol and IgA levels (Spearman's Rö = -0.4). These results suggest that the short-term stress induced by the PEBL test does evoke changes in the salivary mental stress-related parameters (an increase in cortisol and nitrite/nitrate levels, and a decrease in IgA), but not in the total antioxidant capacity. They also indicate that the constructed PEBL four-test battery might represent an adequate laboratory stress-inducing paradigm.

Synthesis and antimicrobial activity of (-)-cleistenolide and analogues.

Using the "chiral pool" approach, two modified total syntheses of the biologically active δ-lactone cleistenolide (1) have been achieved starting from d-glucose. These approaches also enabled the preparation of novel analogues and derivatives of natural product 1. The applied strategy for the synthesis of 1 involves: the initial degradation of the chiral precursor for a single C-atom, C2-fragment chain extension using Z-selective Wittig reaction, and the final δ-lactonization. All tested cleistenolide analogues displayed antimicrobial activity against a panel of nine microbial strains, most of them superseding the activity of cleistenolide itself, and, in some cases, coming close in value to the observed minimal inhibitory concentrations of chloramphenicol. Increased lipophilicity of the derivatives and the non-sterically congested conjugated lactone moiety were a prerequisite for analogues with high inhibitory activity against S. aureus and, in general, Gram-positive bacteria.