Stereoisomeric separation of the chiral herbicide profoxydim and residue method development in rice by QuEChERS and LC-MS/MS

A method for the simultaneous determination of the four stereoisomers of the chiral herbicide profoxydim in rice and husk was developed using the QuEChERS method and LC-tandem mass spectrometry. Four polysaccharide-based chiral stationary phase columns were evaluated. All four stereoisomers were successfully separated on a Chiracel OJ-3R column. The effects of mobile phase, modifiers, mobile phase flow rate and temperature on the separation were also investigated. Different QuEChERS methods were compared for the development of an optimized sample preparation procedure. The method, following SANTE guidelines, showed excellent linearity (R2 ≥ 0.99), the LODs were below 4.0 µg kg-1, and the LOQs did not exceed 12.5 µg kg-1. The overall average recoveries at three levels (12.5, 25.0 and 250 µg kg-1) ranged from 76.77 % to 106.53 %, with RSD values less than 7 %. The method is demonstrated to be convenient and reliable for the routine monitoring of profoxydim stereoisomers in rice and husk.

The first LC-MS/MS stereoselective bioanalytical methods to quantitatively detect 9R- and 9S-hexahydrocannabinols and their metabolites in human blood, oral fluid and urine

A sensitive LC-MS/MS method for the simultaneous quantification of the (9 R)- and (9 S)- hexahydrocannabinols (HHCs), and their metabolites, in human urine, oral fluid (OF) and blood samples were developed, validated and used to the biological samples of volunteers. The analytes were extracted from 100 μL human samples. An isocratic elution mode with methanol was used for chromatographic separation of (9 R)- and (9 S)-HHC on an immobilized amylose tris(3-chloro-5-methylphenylcarbamate)-based chiral column Lux i-Amylose-3. The flow-rate of the mobile phase was 0.5 mL/min. An isocratic elution mode of methanol and water (80/20, v/v) was used for chromatographic separation of metabolites of (9 R)- and (9 S)-HHC on a Lux AMP chiral column (with a proprietary chiral selector) at a flow rate of 0.5 mL/min. MS/MS analysis was performed in positive ionization mode for HHC epimers, while in negative ionization mode was used for metabolites of HHCs. The calibration curves for HHCs and their metabolites in human samples ranged from 0.25- 240 ng mL-1 and 1 - 100 ng mL-1, respectively, with determination coefficients (r2) of ≥ 0.99. All analytes were stable at room temperature, 4 °C, in the autosampler (+10 °C) and -20 °C for 24 h, after three freeze/thaw cycles, and when stored at -20 °C up to one week after quality control (QC) sample preparation (concentration differences less than 20% with respect to time zero response), in blood, urine and OF.

Preclinical characterisation of gallium-68 labeled ferrichrome siderophore stereoisomers for PET imaging applications

BACKGROUND

Siderophores are small iron-binding molecules produced by microorganisms to facilitate iron acquisition from the environment. Radiolabelled siderophores offer a promising solution for infection imaging, as they can specifically target the pathophysiological mechanisms of pathogens. Gallium-68 can replace the iron in siderophores, enabling molecular imaging with positron emission tomography (PET). Stereospecific interactions play a crucial role in the recognition of receptors, transporters, and iron utilisation. Furthermore, these interactions have an impact on the host environment, affecting pharmacokinetics and biodistribution. This study examines the influence of siderophore stereoisomerism on imaging properties, with a focus on ferrirubin (FR) and ferrirhodin (FRH), two cis-trans isomeric siderophores of the ferrichrome type.

RESULTS

Tested siderophores were labelled with gallium-68 with high radiochemical purity. The resulting complexes differed in their in vitro characteristics. [68Ga]Ga-FRH showed less hydrophilic properties and higher protein binding values than [68Ga]Ga-FR. The stability studies confirmed the high radiochemical stability of both [68Ga]Ga-siderophores in all examined media. Both siderophores were found to be taken up by S. aureus, K. pneumoniae and P. aeruginosa with similar efficacy. The biodistribution tested in normal mice showed rapid renal clearance with low blood pool retention and fast clearance from examined organs for [68Ga]Ga-FR, whereas [68Ga]Ga-FRH showed moderate retention in blood, resulting in slower pharmacokinetics. PET/CT imaging of mice injected with [68Ga]Ga-FR and [68Ga]Ga-FRH confirmed findings from ex vivo biodistribution studies. In a mouse model of S. aureus myositis, both radiolabeled siderophores showed radiotracer accumulation at the site of infection.

CONCLUSIONS

The 68Ga-complexes of stereoisomers ferrirubin and ferrirhodin revealed different pharmacokinetic profiles. In vitro uptake was not affected by isomerism. Both compounds had uptake with the same bacterial culture with similar efficacy. PET/CT imaging showed that the [68Ga]Ga-complexes accumulate at the site of S. aureus infection, highlighting the potential of [68Ga]Ga-FR as a promising tool for infection imaging. In contrast, retention of the radioactivity in the blood was observed for [68Ga]Ga-FRH. In conclusion, the stereoisomerism of potential radiotracers should be considered, as even minor structural differences can influence their pharmacokinetics and, consequently, the results of PET imaging.

Serotonin-induced stereospecific formation and bioactivity of the eicosanoid 17,18-epoxyeicosatetraenoic acid in the regulation of pharyngeal pumping of C. elegans

17,18-Epoxyeicosatetraenoic acid (17,18-EEQ), the most abundant eicosanoid generated by cytochrome P450 (CYP) enzymes in C. elegans, is a potential signaling molecule in the regulation of pharyngeal pumping activity of this nematode. As a chiral molecule, 17,18-EEQ can exist in two stereoisomers, the 17(R),18(S)- and 17(S),18(R)-EEQ enantiomers. Here we tested the hypothesis that 17,18-EEQ may function as a second messenger of the feeding-promoting neurotransmitter serotonin and stimulates pharyngeal pumping and food uptake in a stereospecific manner. Serotonin treatment of wildtype worms induced a more than twofold increase of free 17,18-EEQ levels. As revealed by chiral lipidomics analysis, this increase was almost exclusively due to an enhanced release of the (R,S)-enantiomer of 17,18-EEQ. In contrast to the wildtype strain, serotonin failed to induce 17,18-EEQ formation as well as to accelerate pharyngeal pumping in mutant strains defective in the serotonin SER-7 receptor. However, the pharyngeal activity of the ser-7 mutant remained fully responsive to exogenous 17,18-EEQ administration. Short term incubations of well-fed and starved wildtype nematodes showed that both racemic 17,18-EEQ and 17(R),18(S)-EEQ were able to increase pharyngeal pumping frequency and the uptake of fluorescence-labeled microspheres, while 17(S),18(R)-EEQ and also 17,18-dihydroxyeicosatetraenoic acid (17,18-DHEQ, the hydrolysis product of 17,18-EEQ) were ineffective. Taken together, these results show that serotonin induces 17,18-EEQ formation in C. elegans via the SER-7 receptor and that both the formation of this epoxyeicosanoid and its subsequent stimulatory effect on pharyngeal activity proceed with high stereospecificity confined to the (R,S)-enantiomer.

Iridium-Catalyzed Chemo-, Diastereo-, and Enantioselective Allyl-Allyl Coupling: Accessing All Four Stereoisomers of (E)-1-Boryl-Substituted 1,5-Dienes by Chirality Pairing

Here, we report a highly chemo-, diastereo-, and enantioselective allyl-allyl coupling between branched allyl alcohols and α-silyl-substituted allylboronate esters, catalyzed by a chiral iridium complex. The α-silyl-substituted allylboronate esters can be chemoselectively coupled with allyl electrophiles, affording a diverse set of enantioenriched (E)-1-boryl-substituted 1,5-dienes in good yields, with excellent stereoselectivity. By permuting the chiral iridium catalysts and the substrates, we efficiently and selectively obtained all four stereoisomers bearing two consecutive chiral centers. Mechanistic studies via density functional theory calculations revealed the origins of the diastereo- and chemoselectivities, indicating the pivotal roles of the steric interaction, the β-silicon effect, and a rapid desilylation process. Additional synthetic modifications for preparing a variety of enantioenriched compounds containing contiguous chiral centers are also included.

Natural Vitamin E Supplementation during Pregnancy in Rats Increases RRR-α-Tocopherol Stereoisomer Proportion and Enhances Fetal Antioxidant Capacity, Compared to Synthetic Vitamin E Administration

INTRODUCTION

Low dietary intake of vitamin E is a global public health issue. RRR-α-tocopherol (RRR-αT) is the only naturally occurring vitamin E stereoisomer, but the equimolecular mixture of all eight stereoisomers, synthetic vitamin E (S-αT), is commonly consumed. The objective of this study was to evaluate bioavailability and antioxidant activity of RRR-αT versus S-αT, in both mother and fetus, after maternal supplementation during pregnancy.

METHODS

Female rats (7 weeks of age) received a modified AIN-93G diet supplemented with 75 IU/kg of RRR-αT (NVE, n = 20) or S-αT (SVE, n = 17). At delivery, the levels of αT, stereoisomer distribution, and antioxidant capacity were analyzed in maternal and fetal plasma.

RESULTS

NVE administration significantly increased the proportion of RRR-αT stereoisomer in maternal and fetal plasma. The percentage of RRR-αT increased from 32.76% to 88.33% in maternal plasma, and 35.25% to 97.94% in fetal plasma, in the NVE group compared to SVE. Fetal plasma from the NVE group was found to have higher total antioxidant capacity compared to SVE. Lastly, fetal plasma RRR-αT stereoisomer percentage was positively associated with expression levels of scavenger receptor class B type 1 (SR-B1) in the placenta.

CONCLUSIONS

Both natural and synthetic sources of vitamin E showed similar bioavailability. Still, NVE supplementation increased the proportion of RRR-αT and promoted higher antioxidant activity in fetal plasma at birth. Placental SR-B1 might be involved in the stereoselective transfer of RRR-αT stereoisomer across the placenta and may improve αT bioactivity in the fetus.

Stereoselective Chiral Molecular Carbon Imides Featuring 12-Fold [5]helicenes Around Four Cores

Despite the great progress in research on molecular carbons containing multiple helicenes around one core, realizing the stereoselectivity of carbons containing multiple helicenes around more cores is still a great challenge. Herein, molecular carbon C₂₀₄ featuring 12-fold [5]helicenes around four cores was successfully constructed by using nine perylene diimide (PDI) units, and exhibits good solubility and stability. Despite 256 possible stereoisomers caused by the 12-fold [5]helicenes, we only obtained one pair of enantiomers with D₃ symmetry. There are four possible pairs of enantiomers with D₃ symmetry, namely 7A, 7B, 7C and 7D. Theoretical and experimental results verify that the obtained structure belongs to 7C, which has the lowest energy. The enantiomers can also be separated by chiral HPLC. These results suggest that choosing PDIs as building blocks can not only improve the solubility and stability but also realize the stereoselectivity and chirality of molecular carbons.

Chiroptical and potential in vitro anti-inflammatory properties of viniferin stereoisomers from grapevine (Vitis vinifera L.)

Determination of stereochemistry and enantiomeric excess in chiral natural molecules is a research of great interest because enantiomers can exhibit different biological activities. Viniferin stilbene dimers are natural molecules present in grape berries and wine but also, in larger amount, in stalks of grapevine. Four stereoisomers of viniferin stilbene dimers (7aS,8aS)-E-ε-viniferin (1a), (7aR,8aR)-E-ε-viniferin (1b), (7aS,8aR)-E-ω-viniferin (2a), and (7aR,8aS)-E-ω-viniferin (2b) were isolated from grapevine stalks of Cabernet Sauvignon, Merlot and Sauvignon Blanc, using a combination of centrifugal partition chromatography (CPC), preparative and chiral HPLC. The structure elucidation of these molecules was achieved by NMR whereas the absolute configurations of the four stereoisomers were investigated by vibrational circular dichroism spectroscopy in combination with density functional theory (DFT) calculations. This study unambiguously established the (+)-(7aS,8aS) and (+)-(7aR,8aS) configurations for E-ε-viniferin and E-ω-viniferin, respectively. Finally, we show that Cabernet Sauvignon provided the quasi enantiopure (+)-(7aS,8aS)-E-ε-viniferin compound which presents the best anti-inflammatory and anti-oxidant activities.

Directing Multivalent Aptamer-Receptor Binding on the Cell Surface with Programmable Atom-Like Nanoparticles

Multivalent interactions of biomolecules play pivotal roles in physiological and pathological settings. Whereas the directionality of the interactions is crucial, the state-of-the-art synthetic multivalent ligand-receptor systems generally lack programmable approaches for orthogonal directionality. Here, we report the design of programmable atom-like nanoparticles (aptPANs) to direct multivalent aptamer-receptor binding on the cell interface. The positions of the aptamer motifs can be prescribed on tetrahedral DNA frameworks to realize atom-like orthogonal valence and direction, enabling the construction of multivalent molecules with fixed aptamer copy numbers but different directionality. These directional-yet-flexible aptPAN molecules exhibit the adaptability to the receptor distribution on cell surfaces. We demonstrate the high-affinity tumor cell binding with a linear aptPAN oligomer (≈13-fold improved compared to free aptamers), which leads to ≈50 % suppression of cell growth.

Stereoselective effects of fungicide difenoconazole and its four stereoisomers on gut barrier, microbiota, and glucolipid metabolism in male mice

Difenoconazole is a commonly used triazole fungicide that consists of four stereoisomers [(2S,4S)-, (2S,4R)-, (2R,4R)-, and (2R,4S)-isomers] with different bioactivity. For example, the toxicity of the (2R,4S)-isomer to fish is approximately seven times higher than that of the (2S,4S)-isomer. However, the stereoselective toxic effects of difenoconazole stereoisomers on mammals have received little attention. In the present study, adult male mice were orally treated with a mixture of the four stereoisomers or each stereoisomer individually (0, 30, or 100 mg/kg/d) by gavage for 28 days. Pathological staining of the liver sections showed that the (2R,4R)-isomer caused lipid droplet accumulation. The mixture or each individual stereoisomers decreased the levels of amino acids and acyl-carnitine in serum. Moreover, the (2S,4R)-, (2R,4R)-, and (2R,4S)-isomers affected intestinal permeability, causing decreases in mucus secretion and tight junction protein expression in colon. Analysis of the gut microbiota composition showed that the stereoisomers caused decreases of OTU numbers and observed species at different levels. Interestingly, difenoconazole and its four stereoisomers reduced the relative abundance of Bacteroidetes at the phylum level and some short-chain fatty acid (SCFA)-producing bacteria. Taking the findings together, 2R-difenoconazole with strong bioactivity against pathogenic fungi also had significant effects in mammals, disrupting hepatic lipid metabolism, intestinal permeability, and gut microbiota. It is concluded that the health risks of the four difenoconazole stereoisomers to mammals should not be overlooked.

Monitoring the hepatic residues of cis- and trans-diastereoisomers of second generation anticoagulant rodenticides reveals a different bioaccumulation of diastereoisomers in the food chain of the Réunion harrier (Circus maillardi)

The Réunion harrier is an endangered raptor and endemic species to the Réunion Island. Second generation anticoagulant rodenticides (SGARs) are widely used pesticides on the island in order to control rodent populations. The latter are responsible for the transmission of leptospirosis to humans, the damage of sugarcane crops, and the decline of endemic endangered birds. SGARs are very persistent chiral pesticides and consequent secondary exposure or poisoning of the Réunion harrier has been observed (73% of prevalence in a group of 58 harriers). Commercial formulations of SGARs are a mixture of trans- and cis-diastereoisomers. Both diastereoisomers of all SGARs have been shown to inhibit coagulation function with the same potency. On the other hand, they have been shown to have a significant difference in terms of tissue-persistence. This difference has led to residue levels in rats with a significantly lower proportion of one of the isomers compared to the bait composition. In this study, residue levels of the diastereoisomers of all SGARs were evaluated in the livers of 58 harrier carcasses. The respective concentrations and proportions of cis- and trans- diastereoisomers of all SGARs are presented. cis-Brodifacoum and trans-bromadiolone had the highest concentrations (up to 438 and 573 ng/g ww respectively), while trans-brodifacoum was less than 46 ng/g and cis-bromadiolone was barely detected. cis-Difenacoum showed the highest prevalence and the highest concentration was 82 ng/g ww, while trans-difenacoum was never detected. This study demonstrated that only cis-brodifacoum and trans-bromadiolone (and cis-difethialone, but with a low prevalence) had hepatic concentrations above a toxic threshold. The cis- and trans-diastereoisomers of SGARs had differential bioaccumulation in the food chain of the Réunion harrier compared to commercial baits. This suggests that a change of the proportions of SGARs diastereoisomers in baits could reduce the risk of secondary poisoning of predators, but maintain primary toxicity.

Chiral liquid chromatography-tandem mass spectrometry analysis of superwarfarin rodenticide stereoisomers - Bromadiolone, difenacoum and brodifacoum - In human plasma

Superwarfarins are second-generation long-acting anticoagulant rodenticides that can cause unintended human and wildlife toxicity due, in part, to their prolonged half-lives. Commercially available superwarfarin rodenticides are synthesized as racemates with two asymmetric carbons, producing four stereoisomers. To support studies of human plasma half-lives of individual superwarfarin stereoisomers, a method was developed based on LC-MS/MS to separate and quantify stereoisomers of the commercially important superwarfarins bromadiolone, difenacoum and brodifacoum. Human plasma samples were prepared using protein precipitation and centrifugation. Chiral-phase HPLC separation was carried out on-line with tandem mass spectrometric quantitative analysis of the eluting stereoisomers using selected-reaction monitoring with positive ion electrospray on a triple quadrupole mass spectrometer. All four stereoisomers of each superwarfarin were resolved within 12.5 min with calibration curves spanning 2-3 orders of magnitude and lower limits of quantitation between 0.87 and 2.55 ng/mL. This method was used to determine the half-lives of superwarfarin stereoisomers in plasma from patients who had inhaled synthetic cannabinoid products contaminated with superwarfarins. These data may be used to guide the development of safer next generation anticoagulant rodenticides stereoisomers.

Preparative separation of high-purity trans- and cis-ferulic acid from wheat bran by pH-zone-refining counter-current chromatography

Ferulic acid stereoisomers are the most abundant phenolic acids in cereal bran. However, it is challenging to separate them because of the similar structures and properties. In this study, a preparative separation method of ferulic acid stereoisomers from the crude extract of wheat bran was successfully developed. The method contained a two-step separation, the traditional counter-current chromatography (CCC, hexane: ethyl acetate: methanol: water = 2:5:2:4) was followed with a pH-zone-refining CCC (hexane: ethyl acetate: acetonitrile: water = 2:5:2:2, 10 mmol L^-1 trifluoroacetic acid in organic stationary phase and 10 mmol L^-1 ammonia in aqueous mobile phase). Trans-ferulic acid and cis-ferulic acid with HPLC high purity over than 99% and 98% can be yielded in large-scale separation. Moreover, it is found that different proton affinity, deprotonation ability and interaction site of hydrogen bond result in distinct partition behavior of stereoisomers, which is illustrated by quantitative analysis of molecular surface. This contributes to our in-depth understanding of the separation mechanism toward pH-zone refining CCC. The developed method can be applied in the exploitation of ferulic acids and related phenolic acids from other resources.

The relationship between stereochemical and both, pharmacological and ADME-Tox, properties of the potent hydantoin 5-HT7R antagonist MF-8

This study concerns synthesis and evaluation of pharmacodynamic and pharmacokinetic profile for all four stereoisomers of MF-8 (5-(4-fluorophenyl)-3-(2-hydroxy-3-(4-(2-methoxyphenyl)piperazin-1-yl)propyl)-5-methylimidazolidine-2,4-dione), the previously described, highly potent 5-HT₇R ligand with antidepressant activity on mice. The combination of DFT calculations of ¹H NMR chemical shifts with docking and dynamic simulations, in comparison to experimental screening results, provided prediction of the configuration for one of two present stereogenic centers. The experimental data for stereoisomers (MF-8A-MF-8D) confirmed the significant impact of stereochemistry on both, 5-HT₇R affinity and antagonistic action, with K_i and K_b values in the range of 3-366 nM and 0.024-99 μM, respectively. We also indicated the stereochemistry-dependent influence of the tested compounds on P-glycoprotein efflux, absorption in Caco-2 model, metabolic pathway as well as CYP3A4 and CYP2C9 activities.

Identification and Synthesis of Putative Pheromone Components of the Threatened Salt Marsh Bagworm Moth, Whittleia retiella (Lepidoptera: Psychidae)

Whittleia retiella (Newman, 1847) is a threatened salt marsh species of the bagworm moth family Psychidae. For its preservation it is necessary to develop efficient tools to survey its distribution and habitat requirements in order to use appropriate conservation methods. Such tools may be pheromone-based monitoring systems, which have documented efficacy in establishing the occurrence of cryptic insect species in nature. By using gas chromatography combined with electroantennographic detection (GC-EAD), we found two compounds in female W. retiella headspace samples and whole-body extracts that elicited electrophysiological activity in male antennae. Gas chromatograpy coupled with mass spectrometry (GC-MS) operating in electron impact (EI) mode and comparison of the analytical data with those of synthetic reference compounds showed the chemical structures of these putative pheromone components to be (1S)-1-methylpropyl (5Z)-dec-5-enoate and 1-methylethyl (5Z)-dec-5-enoate. Field assays using baits loaded with synthetic compounds revealed that conspecific males were attracted to (1S)-1-methylpropyl (5Z)-dec-5-enoate alone or in combination with 1-methylethyl (5Z)-dec-5-enoate, whereas 1-methylethyl (5Z)-dec-5-enoate neither attracted nor repelled males in the field assays when tested alone. This study shows the potential of using (1S)-1-methylpropyl (5Z)-dec-5-enoate for monitoring W. retiella to gather more detailed information about the geographic distribution and habitat needs of this rare moth.

Comparative biological properties of the four stereoisomers of difethialone, a second-generation anticoagulant rodenticide, in rats: development of a model allowing to choose the appropriate stereoisomeric ratio

The current management of rodent pest populations is based on second-generation anticoagulant rodenticides (SGAR). These molecules, of which difethialone is part, are much more efficient than the first generation. Nevertheless, this efficiency comes with a major drawback, SGARs are tissue persistent that increases the exposure of rodent predators to them. According to its chemical structure, difethialone has four stereoisomers, whose specific inhibition potency and pharmacokinetic have never been described and might be useful to design new eco-friendly rodenticides. The study aimed to investigate the ability to inhibit anticoagulant target enzyme (VKORC1) and the pharmacokinetics in rats of the four difethialone stereoisomers in rats. We show that stereoisomers are all highly efficient to inhibit VKORC1 activity, but they have distinct initial half-life with 6.0 h, 25.4 h, 69.3 h, and 82.3 h for, respectively, E4-trans, E2-cis, E1-trans, and E3-cis stereoisomer. These results open the way of the development of eco-friendly and efficient rodenticide by mixing some of these stereoisomers. Preferential incorporation of the E4-trans stereoisomer (high inhibitory VKORC1 potency, relatively shorter liver half-life) into difethialone rodenticides baits might result in a more eco-friendly product than current commercially available difethialone formulations. In addition, we put forward modelling to help design bait according to the circumstance of use (presence of non-target species, food competition, etc.) by modulating the theorical AUC and and the theorical concentration of the product at the death of the rodent pest. Thus, this modeling might allow to diminish the use of laboratory animal in assay.

Isolation of Inositol Hexakisphosphate from Soils by Alkaline Extraction and Hypobromite Oxidation

Inositol hexakisphosphates are extracted from soil in strong alkali and isolated from other organic phosphates by hypobromite oxidation. The procedure yields the four stereoisomeric forms of inositol hexakisphosphate in a form suitable for spectroscopic or chromatographic identification.

Discrimination of Regioisomeric and Stereoisomeric Saponins from Aesculus hippocastanum Seeds by Ion Mobility Mass Spectrometry

Modern mass spectrometry methods provide a huge benefit to saponin structural characterization, especially when combined with collision-induced dissociation experiments to obtain a partial description of the saponin (ion) structure. However, the complete description of the structures of these ubiquitous secondary metabolites remain challenging, especially since isomeric saponins presenting small differences are often present in a single extract. As a typical example, the horse chestnut triterpene glycosides, the so-called escins, comprise isomeric saponins containing subtle differences such as cis-trans ethylenic configuration (stereoisomers) of a side chain or distinct positions of an acetyl group (regioisomers) on the aglycone. In the present paper, the coupling of liquid chromatography and ion mobility mass spectrometry has been used to distinguish regioisomeric and stereoisomeric saponins. Ion mobility arrival time distributions (ATDs) were recorded for the stereoisomeric and regioisomeric saponin ions demonstrating that isomeric saponins can be partially separated using ion mobility on a commercially available traveling wave ion mobility (TWIMS) mass spectrometer. Small differences in the ATD can only be monitored when the isomeric saponins are separated with liquid chromatography prior to the IM-MS analysis. However, gas phase separation between stereoisomeric and regioisomeric saponin ions can be successfully realized, without any LC separation, on a cyclic ion mobility-enabled quadrupole time-of-flight (Q-cIM-oaToF) mass spectrometer. The main outcome of the present paper is that the structural analysis of regioisomeric and stereoisomeric natural compounds that represents a real challenge can take huge advantages of ion mobility experiments but only if increased ion mobility resolution is attainable.

Synthesis of Mitomycin C and decarbamoylmitomycin C N6 deoxyadenosine-adducts

Mitomycin C (MC), an anti-cancer drug, and its analog, decarbamoylmitomycin C (DMC), are DNA-alkylating agents. MC is currently used in the clinics and its cytotoxicity is mainly due to its ability to form Interstrand Crosslinks (ICLs) which impede DNA replication and, thereby, block cancer cells proliferation. However, both MC and DMC are also able to generate monoadducts with DNA. In particular, we recently discovered that DMC, like MC, can form deoxyadenosine (dA) monoadducts with DNA. The biological role played by these monoadducts is worthy of investigation. To probe the role of these adducts and to detect them in enzymatic digests of DNA extracted from culture cells treated by both drugs, we need access to reference compounds i.e. MC and DMC dA-mononucleoside adducts. Previous biomimetic methods used to generate MC and DMC mononucleoside adducts are cumbersome and very low yielding. Here, we describe the diastereospecific chemical synthesis of both C-1 epimers of MC and DMC deoxyadenosine adducts. The key step of the synthesis involves an aromatic substitution reaction between a 6-fluoropurine 2'-deoxyribonucleoside and appropriately protected stereoisomeric triaminomitosenes to form protected-MC-dA adducts with either an S or R stereochemical configuration at the adenine-mitosene linkage. Fluoride-based deprotection methods generated the final four reference compounds: the two stereoisomeric MC-dA adducts and the two stereoisomeric DMC-dA adducts. The MC and DMC-dA adducts synthesized here will serve as standards for the detection and identification of such adducts formed in the DNA of culture cells treated with both drugs.

Study on the recognition of G-quadruplexes by two stereoisomers of alkaloids

G-quadruplexes have been widely researched as new targets for cancer treatment owing to their non-canonical structure and crucial role in biological processes. Although attention has been paid to the development of selective G-quadruplex ligands, few studies have focused on the binding affinity of stereoisomers towards G-quadruplex, which will be conducive to support the optimal design of G-quadruplex ligands in future studies. Here, tetrandrine and isotetrandrine were used to study the binding affinity and difference of stereoisomers towards G-quadruplex structures. The results showed that tetrandrine had a high possibility of binding to the N-myc and Bcl-2 G-quadruplexes through hydrogen bonding, whereas the possibility of binding of isotetrandrine was low and it seemed to have no possibility of forming hydrogen bonds. Our study shows that optical isomerism of ligand molecules has an important effect on G-quadruplex recognition, which is helpful for the design of G-quadruplex ligands in future studies. Graphical abstract.

Discriminative Stimulus Properties of S(-)-Nicotine: "A Drug for All Seasons"

S(-)-Nicotine is the major pharmacologically active substance in tobacco and can function as an effective discriminative stimulus in both experimental animals and humans. In this model, subjects must detect and communicate the nicotine drug state versus the non-drug state. This review describes the usefulness of the procedure to study nicotine, presents a general overview of the model, and provides some relevant methodological details for the establishment of this drug as a stimulus. Once established, the (-)-nicotine stimulus can be characterized for dose response and time course effects. Moreover, tests can be conducted to determine the similarity of effects produced by test drugs to those produced by the training dose of nicotine. Such tests have shown that the stimulus effects of nicotine are stereoselective [S(-)-nicotine >R(+)-nicotine] and that other "natural" tobacco alkaloids and (-)-nicotine metabolites can produce (-)-nicotine-like effects, but these drugs are much less potent than (-)-nicotine. Stimulus antagonism tests with mecamylamine and DHβE (dihydro-β-erythroidine) indicate that the (-)-nicotine stimulus is mediated via α4β2 nicotinic acetylcholine receptors (nAChRs) in brain; dopamine systems also are likely involved. Individuals who try to cease their use of nicotine-based products are often unsuccessful. Bupropion (Zyban®) and varenicline (Chantix®) may be somewhat effective as anti-smoking medications because they probably produce stimulus effects that serve as suitable substitutes for (-)-nicotine in the individual who is motivated to quit smoking. Finally, it is proposed that future drug discrimination studies should apply the model to the issue of maintenance of abstinence from (-)-nicotine-based products.

13C-1H coupling constants as a conformational tool for structural assignment of quinic and octulosonic acid

A complete set of NMR coupling constants (¹J_C-H, ²J_C-H, ³J_C-H, and ³J_H-H) were calculated for the eight stereoisomers of quinic acid, at the B3LYP/6-311G(d,p)/PCM(methanol) level of theory. The Fermi contact term of the coupling constants was computed with a modified, uncontracted, version of the 6-311G(d,p) basis set, with additional tight polarization functions. ¹H and ¹³C NMR chemical shifts were determined at the same level using the gauge-invariant atomic orbital (GIAO) method. The magnitude of the spin-spin coupling constants was found to be affected by the orientation (axial or equatorial) of the coupling proton and the orientation of the hydroxy group on the coupling carbon, whereas the chemical shifts depend on the presence or absence of electron-withdrawing hydroxy groups attached to the carbon atoms involved. Graphical Abstract Nuclear magnetic resonance coupling constants, computed with density functional theory, can be used to differentiate and identify the different stereoisomers of quinic acid.

Stereoselective synthesis of the four 16-hydroxymethyl-3-methoxy- and 16-hydroxymethyl-3-benzyloxy-13α-estra-1,3,5(10)-trien-17-ol isomers and their antiproliferative activities

The reduction of 16-hydroxymethylene-3-methoxy-13α-estra-1,3,5(10)-trien-17-one (14) and 16-hydroxymethylene-3-benzyloxy-13α-estra-1,3,5(10)-trien-17-one (16) yielded a mixture of two diastereomeric diols, the 16α-hydroxymethyl,17β-hydroxy and 16β-hydroxymethyl,17α-hydroxy isomers (17a-20a) in a ratio of 6:1. We describe a straightforward synthetic route to transform the isomers with trans functional groups attached to ring D (17a-20a) into isomers with cis functional groups (25a-28a). We determined the in vitro antiproliferative activities of compounds 17a-20a and 25a-28a by means of MTT assays against a panel of human adherent cancer cell lines HeLa, A2780, MCF-7, T47D, MDA-MB-231 and MDA-MB-361.

Cis-bromadiolone diastereoisomer is not involved in bromadiolone Red Kite (Milvus milvus) poisoning

Anticoagulant rodenticides (ARs) are widely used pesticides to control rodent populations. Bromadiolone, a second generation anticoagulant rodenticide (SGARs), is authorized in France to control the population of water voles (Arvicola scherman). The persistence of SGARs in rodents is responsible for secondary exposure or poisoning of predators and scavengers, and is of ecological concern for the conservation of endangered species. Commercial formulations are a mixture of two diastereoisomers of bromadiolone: 70-90% is trans-bromadiolone and 10-30% is cis-bromadiolone. Both diastereoisomers have been shown to inhibit coagulation function with the same potency. On the other hand, cis-bromadiolone has been shown to be less tissue-persistent than trans-bromadiolone in rats. This difference led to residue levels in rats with substantially weakened proportion in cis-bromadiolone compared to the composition of baits. In this study, a multi-residue LC-MS/MS method for the quantification of the diastereoisomers of SGARs was used to investigate their proportions in field samples of predators. In 2011, 28 red kites (Milvus milvus) were found dead within a few months of bromadiolone application in grassland to control water vole outbreaks. In this study, we report the concentrations of the two diastereoisomers of bromadiolone measured in the livers of thirteen red kites. Exposure to bromadiolone was apparent in all the kites with hepatic concentrations of trans-bromadiolone ranging from 390 to 870ng/g (89 to 99% of summed SGARs). However, cis-bromadiolone was not detected in 5 of 13 red kites and was present at very low concentrations (below 2.2ng/g) in 8 of 13 kites, demonstrating that cis-bromadiolone is not involved in this red kite poisoning event. The results suggest that a change of the proportions of bromadiolone diastereoisomers in baits could reduce the risk of secondary poisoning of predators, but retain primary toxicity for control rodent outbreaks.

Metabolic profiles of neotuberostemonine and tuberostemonine in rats by high performance liquid chromatography/quadrupole time-of-flight mass spectrometry

Neotuberostemonine (NS) and tuberostemonine (TS), a pair of stereoisomers, are the active components contained in Stemona tuberosa, an antitussive herbal medicine in China. Two isomers have different pharmacological efficacies, which will be related with their in vivo disposition. However, the metabolic fates of NS and TS remain unknown. A method of high performance liquid chromatography/quadrupole time-of-flight mass spectrometry coupled with mass detect filter technique was established to investigate the metabolites in rat plasma, bile, urine, and feces after oral administration of the equal doses of NS and TS. The results showed that NS produced 48 phase I metabolites, including NS, 3 hydrolyzed, 14 hydroxylated, 20 monohydrolyzed+hydroxylated and 10 dihydrolyzed+hydroxylated metabolites. The number of detected NS metabolites was 11, 39, 22 and 30 in plasma, bile, urine and feces. TS yielded 23 phase I metabolites, including TS, 3 hydrolyzed, 7 hydroxylated, 9 monohydrolyzed+hydroxylated and 3 dihydrolyzed+hydroxylated metabolites. Besides, TS yielded 9 phase II metabolites, including 1 glucuronic acid and 2 glutathione conjugates, and the later further degraded and modified into cysteine-glycine, cysteine and N-acetylcysteine conjugates. The number of detected TS metabolites was 9, 24, 24 and 15 in plasma, bile, urine and feces. Different metabolic patterns may be one of the main reasons leading to different pharmacological effects of NS and TS.

A set of interesting sequoiatones stereoisomers from a wetland soil-derived fungus Talaromyces flavus

Four interesting sequoiatones stereoisomers (1–4) were isolated from a wetland soil-derived fungus Talaromyces flavus by chiral HPLC. On the basis of comprehensive NMR and mass analyses, their planar structures were elucidated as the same as that of sequoiatone B. Among them, 1 and 3 (or 2 and 4) were a pair of enantiomers, and 1 and 2 (or 3 and 4) were a pair of stereoisomers with epimerization at C-12, which indicated that sequoiatione-type metabolites exist as enantiomers rather than as optically pure compounds in some strains. With the quantum chemical ECD calculations, the absolute configurations of C-8 in 1–4 were determined, which is the first report to establish the absolute configuration of C-8 in sequoiatones. However, the absolute configurations of C-12 in sequoiatones are still unsolved.

Structural Stringency of Cholesterol for Membrane Protein Function Utilizing Stereoisomers as Novel Tools: A Review

Cholesterol is an important lipid in the context of membrane protein function. The function of a number of membrane proteins, including G protein-coupled receptors (GPCRs) and ion channels, has been shown to be dependent on membrane cholesterol. However, the molecular mechanism underlying such regulation is still being explored. In some cases, specific interaction between cholesterol and the protein has been implicated. In other cases, the effect of cholesterol on the membrane properties has been attributed for the regulation of protein function. In this article, we have provided an overview of experimental approaches that are useful for determining the degree of structural stringency of cholesterol for membrane protein function. In the process, we have highlighted the role of immediate precursors in cholesterol biosynthetic pathway in the function of membrane proteins. Special emphasis has been given to the application of stereoisomers of cholesterol in deciphering the structural stringency required for regulation of membrane protein function. A comprehensive examination of these processes would help in understanding the molecular basis of cholesterol regulation of membrane proteins in subtle details.

Quantitative analysis of ceramides using a novel lipidomics approach with three dimensional response modelling

In the outermost layer of the skin, the stratum corneum (SC), ceramides form a diverse and essential pool of lipids. Due to their diversity and the limited availability of synthetic standards it is challenging to quantitatively analyse all SC ceramides independently. We aim to perform a detailed analysis of ceramides on SC harvested from in vivo and ex vivo skin, therefore, a LC/MS method was developed in which all steps from sample acquisition until data analysis were examined and optimized. Improving extraction efficiency of ceramides resulted in an increase in efficiency from 71.5% to 99.3%. It was shown that sample harvesting by tape-stripping in vivo was accurate and precise. A full scan MS method was developed, compatible with all sample types, enabling simultaneously qualitative and quantitative data analysis. A novel three dimensional response model was constructed to quantify all detected ceramides from full scan data using a limited amount of synthetic ceramides. The application is demonstrated on various SC sample types. When ex vivo SC was regenerated during human skin culture, increases are observed in the amount of the ceramide sphingosine subclasses, in mono unsaturated ceramides (which have an cis-double bond in the acyl chain), and ceramides with a short C34 carbon chain (ceramides with a total carbon chain of 34 carbon atoms), compared with native human skin. These changes in ceramide levels are also often encountered in diseased skin.

Assessment of flavanol stereoisomers and caffeine and theobromine content in commercial chocolates

Assessment of the flavanol composition of 41 commercial chocolates was by HPLC-DAD. Among individual flavonols ranged from 0.095 to 3.264mgg(-1), epicatechin was the predominant flavanol accounting for 32.9%. Contrary to catechin, epicatechin was a reliable predictive value of the polyphenol content. Conversely the percentage of theobromine used as a proxy measure for nonfat cocoa solids (NFCS) was not a good predictor of epicatechin or flavanol content. In a further chiral analysis, the naturally occurring forms of cocoa flavanols, (-)-epicatechin and (+)-catechin, was determined joint the occurrence of (+)-epicatechin and (-)-catechin due to the epimerization reactions produced in chocolate manufacture. (-)-Epicatechin, the most bioactive compound and predominant form accounted of 93%. However, no positive correlation was found with% cocoa solids, the most significant quality parameter.

Preferences of the peripheral olfactory system of Western Flower Thrips, Frankliniella occidentalis towards stereoisomers of common plant volatiles

Stereochemistry plays a significant role in structure–activity relationships of messenger chemicals. The ability to distinguish between enantiomers and geometric isomers, however, may be limited to certain stereoisomeric substances, depending on the receiver. In this study, we assessed the preference of the peripheral olfactometry system of Western Flower Thrips, F. occidentalis towards ubiquitously expressed host compounds, with a goal of establishing whether particular stereoisomers enhance host odour recognition. We demonstrate that the peripheral olfactory system of a highly polyphagous thysanopteran insect has evolved to become highly sensitive to a type of green leaf volatile, which is highly ubiquitous in the plant kingdom. We show that there is a significantly greater antennal response to the cis isomer, more so than the isomerisation by-product trans-3-hexen-1-ol. We demonstrate that the antennae of a highly polyphagous insect are capable of detecting common plant secondary metabolites in both enantiomeric forms.

Stereoisomeric profiling of drugs of abuse and pharmaceuticals in wastewaters of Valencia (Spain)

The enantiomeric and diastereomeric profiling of chiral pharmaceuticals (ephedrine, norephedrine, atenolol and venlafaxine) and illicit drugs (amphetamine, methamphetamine, 3,4-methylenedioxyamphetamine (MDA), 3,4-methylenedioxy-N-methylamphetamine (MDMA) and 3,4-methylenedioxy-N-ethylamphetamine (MDEA)) was undertaken over a period of fourteen consecutive days in three wastewater treatment plants (WWTPs) in the city of Valencia, Spain. Degradation efficiency of WWTPs was found to be compound and enantiomer dependent. Selective enantiomer enrichment was observed for several target analytes. Amphetamine and MDMA were enriched with R(-)-enantiomers. 1S,2S(+)-pseudoephedrine was found to be more readily degradable during activated sludge treatment than its diastereomer 1R,2S(-)-ephedrine. Atenolol underwent enrichment with either S(-)- or R(+)-enantiomer in different WWTPs. This unexpected enantiomeric variation in the stereoselective degradation of atenolol could be attributed to different processes utilized during activated sludge treatment. The application of (enantiomeric) profiling of wastewater revealed usage patterns of chiral drugs in the Valencia region.