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1,1,7-Trihydrododecafluoroheptanol is a promising solvent for the development of strontium-selective extractants based on individual stereoisomers of dicyclohexano-18-crown-6 (DCH18C6). In this study the distribution of DCH18C6 between organic and aqueous phases was determined and the effect of macrocycle stereoisomerism was revealed. Extractability of nitric acid depended on the acidity of initial aqueous phase and did not on DCH18C6 stereoisomerism. Based on the structure of radiolytic intermediates, the main channels of radiation destruction of the macrocycle and the solvent were proposed. The obtained data highlights the potentiality of the DCH18C6/1,1,7-trihydrododecafluoroheptanol for designing a technological process for the selective strontium extraction. [ABSTRACT FROM AUTHOR]

This study investigates the complexation of mefloquine hydrochloride by cyclodextrins to improve its solubility in order to design an oral solution. This approach may enhance the effectiveness of mefloquine, a drug which can be used for malaria prophylaxis and treatment in children. Mefloquine hydrochloride's solubility was assessed in different buffer solutions, and its quantification was achieved through high-performance liquid chromatography. The complexation efficiency with cyclodextrins was evaluated, and nuclear magnetic resonance (NMR) methods were employed to determine the interactions between mefloquine and cyclodextrins. Mefloquine's solubility increased when combined with hydroxypropyl-β-cyclodextrin (HP-β-CD) and randomly methylated β-cyclodextrin (RAMEB), with RAMEB being more effective. The drug's solubility varied across different pH buffers, being higher in acidic buffers. Interestingly, mefloquine's solubility decreased with a citrate buffer, possibly due to precipitation. The NMR studies highlighted non-covalent interactions between RAMEB, HP-β-CD, and mefloquine, explaining the solubilizing effect via complexation phenomena. Furthermore, the NMR experiments indicated the complexation of mefloquine by all the studied cyclodextrins, forming diastereoisomeric complexes. Cyclodextrin complexation improved mefloquine's solubility, potentially impacting its bioavailability. [ABSTRACT FROM AUTHOR]

Series of linear tridentate PNPhPR‐ligands (R=Me, Et, Pln, Ph, Cyp, iPr, Cy, tBu) and molybdenum tricarbonyl complexes [Mo(CO)3PNPhPR] (R=Ph, Et, Cyp, iPr, Cy,) were synthesized and characterized using NMR‐, IR‐, and Raman spectroscopy as well as X‐ray crystallography. The influence of the different phosphine donor groups of the PNPhPR ligands on the bonding and activation of CO ligands is investigated. Importantly, all complexes are found to adopt a fac geometry, both in solution and in the solid state. This is in contrast to analogous complexes supported by PNHP ligands. DFT calculations reveal that the phenyl ring at the central amine function is the cause of the preferred geometry, hindering isomerization to a mer geometry. [ABSTRACT FROM AUTHOR]

The relationship between extractant stereochemistry and their extraction performance has only poorly been established. In order to address a part of this concern, we investigated the Pu(IV) liquid‐liquid extraction (LLE) by using the N,N‐di‐(2‐ethylhexyl)butyramide (DEHBA), as well as those of its position isomers. DEHBA (ββ‐isomer) and N‐(2‐ethylhexyl)‐N‐(oct‐3‐yl)butyramide (EHOBA or αβ‐isomer) were synthesized as a mixture of stereoisomer or stereoenriched (R,S)‐ and (S,S)‐diastereoisomers, and were all assessed for PuIV LLE. The results showed that both the position and the stereoisomerism of the aliphatic substituents affect PuIV complexation and extraction. We found that Pu extraction is lowered by factor 2 to 4 when the ethyl branching group is closer to the complexing site. UV‐vis spectroscopy showed that this extraction decrease was affected by steric hindrance inducing a deprivation of Pu inner sphere complex. Effect of stereoisomerism is highlighted for branching closer to the complexing site (α‐position). Enantiopure DEHBA stereoisomers provided similar Pu extraction, whereas a slight decrease could be noticed for the more cluttered stereoenriched (αβ)‐isomers, which was also concomitant with a smaller population of inner sphere complex. In contrast, the stereoisomers mixture led to a strong decrease of Pu extraction because of an antagonistic association in the mixed complexes. [ABSTRACT FROM AUTHOR]

5‐[(Dimethylamino)methylidene]‐4‐{[3‐(trifluoromethyl)phenyl]amino}‐1,3‐thiazol‐2(5H)‐one and the [4‐(trifluoromethyl)phenyl]amino derivative, both C13H12F3N3OS, with the trifluoromethyl group substituted at the arene ring at the meta and para positions, were synthesized to study the structural changes associated with proton tautomerism of the amidine system. The studied compounds were found to be in the amine tautomeric form in both the solid and the liquid (dimethyl sulfoxide solutions) phase. In both isomers, the [(trifluoromethyl)phenyl]amino residue assumes a synperiplanar conformation with respect to the thiazolone system, while the 5‐[(dimethylamino)methylidene] residue adopts the Z configuration. Density functional theory (DFT) calculations correctly predicted that the synperiplanar arrangement is favoured in both isomers. In the crystal, the whole independent molecule of the para compound is disordered over two alternative positions, with occupancy factors of 0.926 (3) and 0.074 (3). [ABSTRACT FROM AUTHOR]

This article documents enu, a freely-downloadable, open-source and stand-alone program written in C++ for the enumeration of the constitutional isomers and stereoisomers of a molecular formula. The program relies on graph theory to enumerate all the constitutional isomers of a given formula on the basis of their canonical adjacency matrix. The stereoisomers of a given constitutional isomer are enumerated as well, on the basis of the automorphism group of this matrix. The isomer list is then reported in the form of canonical SMILES strings within files in XML format. The specification of the molecule family of interest is very flexible and the code is optimized for computational efficiency. The algorithms and implementations underlying enu are described, and simple illustrative applications are presented. The enu code is freely available on GitHub at https://github.com/csms-ethz/CombiFF. [ABSTRACT FROM AUTHOR]

Aims: Chirality of drugs might be associated with safety issues through pharmacokinetic or pharmacodynamic variations, interactions, or direct toxicological responses. We aimed to compare chiral status of the available drugs to that of drugs withdrawn due to adverse drug reactions (ADRs). Methods: We searched the literature regarding withdrawn drugs due to safety‐related issues (n = 391) to compare them with all available small‐molecule drugs (n = 1633). We examined their chiral status and assigned as achiral compound, chiral mixture or pure enantiomer. We compared the mean survival (i.e., nonwithdrawal) time and withdrawal rates of drugs by their chirality, with further stratification by the launch year, ATC‐1 (Anatomical Therapeutic Chemical) level and ADR. Results: We identified higher withdrawal rate in achiral drugs (hazard ratio 2.1, 95% CI: 1.6–2.7) and chiral mixtures (hazard ratio 2.6, 95% CI: 1.9–3.5) compared to that in pure enantiomers. Pure enantiomers had the longest mean survival time (62.4 ± 0.8 years), followed by achiral drugs (55.4 ± 0.9 years, P <.01) and chiral mixtures (52.4 ± 1.4 years, P <.01). Pure enantiomers had higher survival rates than chiral mixtures if launched before 1941 (P =.02), in 1961–1980 (P <.001) or 1981–2000 (P <.001). Pure enantiomers had lower withdrawal rate (18.2%) vs. chiral mixtures (35.1%, P =.02) in nervous system drugs. Pure enantiomers had lower withdrawal rate than chiral mixtures in hepatotoxic (P <.01) and cardiovascular ADRs (P <.01). Conclusion: Our study showed lower likelihood of withdrawal for pure enantiomers compared to that in chiral mixtures and achiral drugs, which was more remarkable for those launched in certain time periods and several ADRs, including hepatotoxicity and cardiovascular toxicity. [ABSTRACT FROM AUTHOR]

Biomacromolecules are known to feature complex three‐dimensional shapes that are essential for their function. Among natural products, ambiguous molecular shapes are a rare phenomenon. The hexapeptide tryptorubin A can adopt one of two unusual atropisomeric configurations. Initially hypothesized to be a non‐ribosomal peptide, we show that tryptorubin A is the first characterized member of a new family of ribosomally synthesized and posttranslationally modified peptides (RiPPs) that we named atropopeptides. The sole modifying enzyme encoded in the gene cluster, a cytochrome P450 monooxygenase, is responsible for the atropospecific formation of one carbon‐carbon and two carbon‐nitrogen bonds. The characterization of two additional atropopeptide biosynthetic pathways revealed a two‐step maturation process. Atropopeptides promote pro‐angiogenic cell functions as indicated by an increase in endothelial cell proliferation and undirected migration. Our study expands the biochemical space of RiPP‐modifying enzymes and paves the way towards the chemoenzymatic utilization of atropopeptide‐modifying P450s. [ABSTRACT FROM AUTHOR]

Biomacromolecules are known to feature complex three‐dimensional shapes that are essential for their function. Among natural products, ambiguous molecular shapes are a rare phenomenon. The hexapeptide tryptorubin A can adopt one of two unusual atropisomeric configurations. Initially hypothesized to be a non‐ribosomal peptide, we show that tryptorubin A is the first characterized member of a new family of ribosomally synthesized and posttranslationally modified peptides (RiPPs) that we named atropopeptides. The sole modifying enzyme encoded in the gene cluster, a cytochrome P450 monooxygenase, is responsible for the atropospecific formation of one carbon‐carbon and two carbon‐nitrogen bonds. The characterization of two additional atropopeptide biosynthetic pathways revealed a two‐step maturation process. Atropopeptides promote pro‐angiogenic cell functions as indicated by an increase in endothelial cell proliferation and undirected migration. Our study expands the biochemical space of RiPP‐modifying enzymes and paves the way towards the chemoenzymatic utilization of atropopeptide‐modifying P450s. [ABSTRACT FROM AUTHOR]

For the effective valorization of lignin, which is a significant component in agricultural residues, its reactivity needs to be understood in detail. Selective acid-catalysed depolymerisation of the lignin β-O-4 linking motif with stabilization of the formed aldehydes by diols is a promising approach to obtain phenolic monomers in high yields. However, the lignin β-O-4 linking motif exists in both the erythro and threo isomeric forms, and very little information is available on the influence of stereochemistry on the efficiency of the lignin diol-stabilised acidolysis. This is especially true for the set of intermediates in which the presence of stereochemistry persists. In this study, the stereoisomer ratios of two key intermediates, namely the diol (here ethylene glycol) adducts and C2-vinyl ethers, are monitored carefully in ytterbium(III) trifluoromethanesulfonate [Yb(OTf)3]-catalysed conversion of an erythro β-O-4 model compound. The reactions showed the preferential formation and consumption of the ethylene glycol adduct in the erythro configuration, and the favored formation of trans C2-vinyl ether. Multiscale computational methods (including classical reactive molecular dynamics simulations and quantum chemistry calculations) were applied to elucidate the catalytic origins of the observed stereo-preferences and suggested that a proto-trans intermediate complex is stabilised by a hydrogen bond network connecting the carbocation, ethylene glycol, and the anionic [OTf]− species. The synergistic combination of experiments and computational studies disclosed the stereo-preference and the underlying mechanism in triflate-catalysed acidolysis, especially the catalytic role of [OTf]−, which can be helpful for a further improvement of the chemical process. [ABSTRACT FROM AUTHOR]

Both trans and cis iron–CTMC complexes, namely, trans‐dichlorido[(5SR,7RS,12RS,14SR)‐5,7,12,14‐tetramethyl‐1,4,8,11‐tetraazacyclotetradecane]iron(III) tetrachloridoferrate, [Fe(C14H32N4)Cl2][FeCl4] (1a), the analogous chloride methanol monosolvate, [Fe(C14H32N4)Cl2]Cl·CH3OH (1b), and cis‐dichlorido[(5SR,7RS,12SR,14RS)‐5,7,12,14‐tetramethyl‐1,4,8,11‐tetraazacyclotetradecane]iron(III) chloride, [Fe(C14H32N4)Cl2]Cl (2), were successfully synthesized and structurally characterized using X‐ray diffraction. The coordination geometry of the macrocycle is dependent on the stereoisomerism of CTMC. The packing of these complexes appears to be strongly influenced by extensive hydrogen‐bonding interactions, which are in turn determined by the nature of the counter‐anions (1aversus1b) and/or the coordination geometry of the macrocycle (1a/1bversus2). These observations are extended to related ferric cis‐ and trans‐dichloro macrocyclic complexes. [ABSTRACT FROM AUTHOR]

It is known that epoxide-bearing compounds display pronounced pharmacological activities, and the epoxidation of natural metabolites can be a promising strategy to improve their bioactivity. Here, we report the design, synthesis and evaluation of biological properties of αO-SM and βO-SM, novel epoxides of soloxolone methyl (SM), a cyanoenone-bearing derivative of 18βH-glycyrrhetinic acid. We demonstrated that the replacement of a double-bound within the cyanoenone pharmacophore group of SM with α- and β-epoxide moieties did not abrogate the high antitumor and anti-inflammatory potentials of the triterpenoid. It was found that novel SM epoxides induced the death of tumor cells at low micromolar concentrations (IC50(24h) = 0.7–4.1 µM) via the induction of mitochondrial-mediated apoptosis, reinforced intracellular accumulation of doxorubicin in B16 melanoma cells, probably by direct interaction with key drug efflux pumps (P-glycoprotein, MRP1, MXR1), and the suppressed pro-metastatic phenotype of B16 cells, effectively inhibiting their metastasis in a murine model. Moreover, αO-SM and βO-SM hampered macrophage functionality in vitro (motility, NO production) and significantly suppressed carrageenan-induced peritonitis in vivo. Furthermore, the effect of the stereoisomerism of SM epoxides on the mentioned bioactivities and toxic profiles of these compounds in vivo were evaluated. Considering the comparable antitumor and anti-inflammatory effects of SM epoxides with SM and reference drugs (dacarbazine, dexamethasone), αO-SM and βO-SM can be considered novel promising antitumor and anti-inflammatory drug candidates. [ABSTRACT FROM AUTHOR]

The first examples of 1,10-phenanthroline-2,9-diamides bearing CF3-groups on the side amide substituents were synthesized. Due to stereoisomerism and amide rotation, such complexes have complicated behavior in solutions. Using advanced NMR techniques and X-ray analysis, their structures were completely elucidated. The possibility of the formation of complex compounds with lanthanoids nitrates was shown, and the constants of their stability are quantified. The results obtained are explained in terms of quantum-chemical calculations. [ABSTRACT FROM AUTHOR]

Compounds that contain (R)-3-amino-4-(2,4,5-trifluorophenyl)butanoic acid substituted with bicyclic amino moiety (2-aza-bicyclo[2.2.1]heptane) were designed using molecular modelling methods, synthesised, and found to be potent DPP-4 (dipeptidyl peptidase-4) inhibitors. Compound 12a (IC50 = 16.8 ± 2.2 nM), named neogliptin, is a more potent DPP-4 inhibitor than vildagliptin and sitagliptin. Neogliptin interacts with key DPP-4 residues in the active site and has pharmacophore parameters similar to vildagliptin and sitagliptin. It was found to have a low cardiotoxic effect compared to sitagliptin, and it is superior to vildagliptin in terms of ADME properties. Moreover, compound 12a is stable in aqueous solutions due to its low intramolecular cyclisation potential. These findings suggest that compound 12a has unique properties and can act as a template for further type 2 diabetes mellitus drug development. [ABSTRACT FROM AUTHOR]

Introduction: Cisatracurium is a new non depolarising, Neuromuscular Blocking Drug (NMBD) with fast onset and short duration of action. It is a stereoisomer of atracurium with a potency of approximately 3 to 4 times greater than that of atracurium. As it is devoid of histamine release, it reduces the chances of adverse effects during operative procedures. However, the optimum intubating dosage needs to be established in patients. This warrants the need for studies focusing on the efficacy of different doses of cisatracurium and their outcomes. Aim: To study the efficacy of three different doses of cisatracurium {2x Effective dose (ED) 95, 4x ED95, and 6x ED95} for the time of onset of action, duration and haemodynamic stability offered for intubation. Materials and Methods: A double-blind, randomised clinical study was conducted from December 2017 to July 2019 at a tertiary care hospital and research center, Kolhapur, Maharashtra, India. Total 90 patients, undergoing surgeries under general anaesthesia were allocated into three groups, group A received 0.1 mg/kg, group B received 0.2 mg/kg and group C received 0.3 mg/kg of cisatracurium. Time taken for Train Of Four (TOF) to reach 0 was taken as the onset of action, and appearance of TOF 2/3 or patient's attempt to breathe was taken as duration of action. Haemodynamic changes were also assessed preoperatively and postintubation immediately after confirmation of placement of ETT. Results: Mean age 33.23±6.26 years in group A, 37.70±10.80 years in group B, 38.23±8.764 years in group C (p-value=0.06). Least time was required for the TOF to become zero by group C (5.10±1.01 minutes) as compared to groups A and B (9.91±1.39 and 7.48±1.45 minutes) which was statistically significant (p-value <0.001). The duration of action was also more in group C (49.83±5.33) compared to group A (27.23±6.97) and group B (36.17±7.62) (p-value=0.00001). Group C had better haemodynamic stability as the heart rate remained more stable than group A and group B. Conclusion: Higher dose of cisatracurium provides faster onset, longer duration of action with better cardiovascular stability. This predictable recovery from non depolarising muscle relaxation makes it a good choice of muscle relaxant agent for intubation. [ABSTRACT FROM AUTHOR]

A network of tetrahedral vertices can fill three-dimensional (3D) spaces in a beautiful and isotropic manner, which is found as diamonds with sp3-hybridized carbon atoms. Although a network of trigonal vertices (i.e., another form of carbon atoms with sp2- hybridization) naturally results in a lower-dimensional two-dimensional network of graphenes, an isotropic 3D arrangement of trigonal vertices has been of theoretical and mathematical interest, which has materialized as a proposal of a "diamond twin." We herein report the synthesis and optical resolution of a minimal cage of a chiral diamond-twin network. With triangular phenine units at 14 vertices, triply fused decagonal rings were assembled by forming 15 biaryl edges via coupling. A unique chirality of the network has been disclosed with the minimal cage, which may stimulate explorations of chiral carbonaceous materials. [ABSTRACT FROM AUTHOR]

Tetragallium(III) complex in [Ga4(L4‐Py)2(dpm)6] ⋅ EtOH, with H3L4‐Py=2‐(hydroxymethyl)‐2‐(pyridin‐4‐yl)propane‐1,3‐diol and Hdpm=dipivaloylmethane, was investigated as a diamagnetic analogue of tetrametallic, propeller‐like single‐molecule magnets (SMMs). The chiral molecular structure partitions the six CH2 protons of each tripodal (L4‐Py)3− ligand into two diastereotopic sets. The two signals were clearly detected by 1H NMR spectroscopy in C6D6, proving that Λ and Δ enantiomers interconvert slowly over NMR timescale. Density functional theory calculations provided quantitative agreement with the observed values of chemical shifts and scalar coupling constants across both geminal and long‐range interaction pathways. The solid‐state structure suggests the occurrence of a lower symmetry stereoisomer (27 mol%), which was clearly identified in the NMR spectra. Since high spin Fe3+ forms distinctly more inert complexes than Ga3+, comparable or greater configurational stability is expected for the isostructural FeIII4, FeIII3CrIII, and FeIII3VIII SMMs, which are difficult to investigate by solution NMR because of the strong paramagnetism. [ABSTRACT FROM AUTHOR]

[Display omitted] • ENDO-PNC and EXO-PNC with different spatial configurations are synthesized. • The stereoisomerism effect on energy storage of polymer dielectrics is explored. • ENDO-PNC with flexural configuration delivers higher E b , U d and η than EXO-PNC. • The universality of stereoisomerism strategy is proved in PNC, FPNI and PNI. Developing dielectric polymers with different stereoisomers may provide a novel strategy to improve electrostatic energy storage performance under harsh environments. However, there is still little research about the effect of polymer stereoisomerism on capacitive energy storage so far. Here, we report a new class of cycloaliphatic polynorbornene-imide (PNC) dielectric with two different spatial configurations and demonstrate that flexural configuration significantly improves the energy storage performance at room temperature and high temperature. ENDO-PNC with flexural configuration possesses slightly higher dielectric constant, comparably large bandgap and dramatically improved thermal properties with respect to EXO-PNC with near-planar configuration. Notedly, ENDO-PNC exhibits dramatically inhibited leakage current density and hopping distance, substantially improved activation energy, electrical resistivity and breakdown strength. Consequently, ENDO-PNC exhibits an ultrahigh discharged energy density (U d) of 11.10 J/cm3, 9.11 J/cm3 and 6.77 J/cm3 at 25 °C, 150 °C and 200 °C respectively, as high as 1.4 times, 2.0 times and 2.8 times that of EXO-PNC. Moreover, ENDO-PNC delivers a maximum U d of 6.0 J/cm3 and 3.3 J/cm3 above 90 % efficiency respectively at 150 °C and 200 °C, superior to neat polymers and highly competitive in reported polymer composites. The stereoisomerism effect on dielectric energy storage is further demonstrated in other dielectric polymers, revealing this strategy is universally applicable and particularly meaningful to design and exploit polymer dielectrics working under harsh environments. [ABSTRACT FROM AUTHOR]

• New isomeric 4-(methoxyphenyl)amino-1,3-thiazol-2(5 H)-one derivatives were synthesized. • The phenomena of proton tautomerism and stereoisomerism were investigated. • Compounds were characterized by X-ray analysis, FT-IR, and NMR spectroscopy. • A theoretical analysis of the intermolecular interactions was performed. In this article, we have reported the most recent results of our systematic studies of phenyl-ring substituent effect on proton tautomerism and stereoisomerism in 4-phenylamino-1,3-thiazol-2(5 H)-one derivatives. The work concerns the synthesis, analysis of 1H and 13C NMR and FT-IR spectra, and X-ray crystal studies of three isomeric compounds, i.e. 5-dimethylaminomethylidene-4-(o -, m -, p -methoxyphenyl)amino-1,3-thiazol-2(5 H)-ones. All three isomers were found to solely exist in the amino tautomeric form, both in the DMSO solution and the solid phase. In the molecules of all the title compounds, the o -, m -, p -methoxyphenylamine residue has synperiplanar disposition with respect to the thiazolone system, while the 5-dimethylaminomethylidene residue adopts the Z -configuration. DFT calculations correctly predict that the synperiplanar arrangement is favored in all investigated materials [ABSTRACT FROM AUTHOR]

Introduction: Unusual amino acids play vital roles in biology, serving as bioactive molecules, scaffolds, and building blocks for drug discovery. The asymmetric synthesis of chiral molecules, especially amino acids, is crucial in pharmaceutical research due to the distinct behaviour of individual enantiomers. Aim: This study aims to asymmetrically synthesize a novel class of enantiomerically enriched α-amino acids with heterocyclic substituents in the side-chain radical. We seek to investigate their biological activity and potential applications in drug delivery systems. Material and methods: Using a chiral niII complex of Schiff's base derived from dehydroalanine and dehydroamonobutyric acid, along with the chiral auxiliary (S)-2-n-(n'-benzylprolyl)aminobenzo-phenone, we synthesized amino acids with high optical purity (ee>95%). Biological examination involved UV analysis, fluorescence studies, dynamic light scattering (DLS), molecular docking, and cell vitality assays. Results: Our findings reveal the significant impact of synthesised amino acids on alpha-helix formation, supramolecular networks, and structural changes in serum albumin, as elucidated through CD and UV (HT(V)) spectra. Molecular docking highlighted unique subdomain interactions, showcasing diverse modulatory effects on serum albumin. Conclusions: This study lays the foundation for further exploration into protein-drug interactions and the development of innovative drug delivery systems. The potential of artificial amino acids offers promising avenues for patient-centric therapies and advancements in pharmaceutical research. [ABSTRACT FROM AUTHOR]

The role of molecular models in teaching chemistry is well-known. It is widely used in explaining the shape of molecules. Several authors have reported the difficulty in teaching stereochemistry/chirality. Some researchers have pleaded that the students face difficulty in solving stereochemistry problems because of poor visualization of three-dimensional structure of molecules. The present paper describes herewith the use of simple and inexpensive ball-stick molecular models in teaching stereoisomerism (conformation, configuration, and chirality in allenes) of organic molecules at undergraduate introductory organic chemistry course. It specially describes the use of simplified molecular models in determining the configuration (R or S) of the molecule. [ABSTRACT FROM AUTHOR]

Herein, we report a comprehensive study on the lanthanide‐directed coordination self‐assembly with two bis‐tetradentate acylhydrazone ligands H4L1 and H4L2. Multifarious outcomes, which are base‐ and metal‐dependent, were revealed by NMR, ESI‐TOF‐MS and X‐ray crystallography. In the absence of base, bent H4L1 was assembled into dinuclear double‐strand helicate Ln2(H2L1)2 by partially‐deprotonated assembly with La, Sm or Eu, while trinuclear Ln3(H2L1)3 with Yb or Lu. For linear H4L2, infinite 1D zig‐zag metal‐organic polymeric chain (Ln2H2L2)n was obtained. However, complete deprotonated L1 and L2 assembled into discrete trinuclear Ln3(L1/2)3 and tetranuclear Ln4(L1/2)4 macrocyclic structures under the basic condition. For these, there are multiple possible isomers coexisting in the solution which were enumerated and simulated with molecular mechanic modeling. Visible‐light sensitized NIR emissions on the Yb complexes have been observed, endowing them potential application in photofunctional materials. [ABSTRACT FROM AUTHOR]

Selective progesterone receptor modulators are promising therapeutic options for the treatment of uterine fibroids. Vilaprisan, a new chemical entity that was discovered at Bayer is currently in clinical development. In this study we provide a combined experimental and quantum chemical approach providing the data that allowed to present hydroxyestradienone as an acceptable starting material for drug substance synthesis. Hydroxyestradienone has four stereogenic centers leading to 8 diastereomers and 16 enantiomers of which only six diastereomers were synthetically accessible but two not. A computational multistep protocol resulting in density functional P2PLYP-D3(BJ)/dev2-TZVPP Gibbs free energies and SMD solvation free energies led to a clear separation between the existing and the synthetically not accessible enantiomers, whereas multiple geometry-based and cheminformatic descriptors were not able to explain experimental findings. [ABSTRACT FROM AUTHOR]

Out-of-plane deformations of metalloporphyrin skeletons have been well documented as playing important roles in relevant biological processes. In contrast, out-of-plane binding to the Ncore of large metal cations as period 6 post-transition elements has remained poorly investigated. We describe herein monometallic complexes of Pb(II) and Bi(III) with 5,10 single strapped porphyrin ligands bearing a carboxylic acid group with two possible "in/out" orientations, in which the metal ions are bound to the N-core of the macrocycle either from the strap side or from the naked side. In the case of Pb(II), both the kinetics of insertion and resulting OOP stereoselectivity are influenced by the "in/out" stereoisomerism of the overhanging COOH. Remarkably, Bi(III) insertion proceeded quasi-instantaneously at RT owing to the transmetalation of its Pb(II) counterpart. The addition of a cyano group in α position of the carboxylic acid group generates a ligand exhibiting an increased stereoselectivity in the metalation processes with Pb(II) and Bi(III): these cations are coordinated exclusively from the naked and strap side of the macrocycle, respectively. This difference in behavior is likely explained by steric hindrance for the divalent cation, which is counterbalanced by the establishment of the second sphere of coordination with the strap for the trivalent cation. Such a behavior is thought of interest for the further design of adaptable supramolecular coordination assemblies. [ABSTRACT FROM AUTHOR]

The conversion of the 1 : 1‐complex of Cisplatin with 1‐methyluracil (1MeUH), cis‐[Pt(NH3)2(1MeU‐N3)Cl] (1 a) to the aqua species cis‐[Pt(NH3)2(1MeU‐N3)(OH2)]+ (1 b), achieved by reaction of 1 a with AgNO3 in water, affords a mixture of compounds, the composition of which strongly depends on sample history. The complexity stems from variations in condensation patterns and partial loss of NH3 ligands. In dilute aqueous solution, 1 a, and dinuclear compounds cis‐[(NH3)2(1MeU‐N3)Pt(μ‐OH)Pt(1MeU‐N3)(NH3)2]+(3) as well as head‐tail cis‐[Pt2(NH3)4(μ‐1MeU‐N3,O4)2]2+ (4) represent the major components. In addition, there are numerous other species present in minor quantities, which differ in metal nuclearity, stoichiometry, stereoisomerism, and Pt oxidation state, as revealed by a combination of 1H NMR and ESI‐MS spectroscopy. Their composition appears not to be the consequence of a unique and repeating coordination pattern of the 1MeU ligand in oligomers but rather the coexistence of distinctly different condensation patterns, which include μ‐OH, μ‐1MeU, and μ‐NH2 bridging and combinations thereof. Consequently, the products obtained should, in total, be defined as a heterogeneous mixture rather than a mixture of oligomers of different sizes. In addition, a N2 complex, [Pt(NH3)(1MeU)(N2)]+ appears to be formed in gas phase during the ESI‐MS experiment. In the presence of Na+ ions, multimers n of 1 a with n=2, 3, 4 are formed that represent analogues of non‐metalated uracil quartets found in tetrastranded RNA. [ABSTRACT FROM AUTHOR]

[Display omitted] • Novel copper(II) complexes with Schiff-base ligands derived from 2-formylphenoxyacetic acid (fphaa) and DL-α-alanine, β-alanine, taurine, and γ-aminobutanoic acid. • New type of stereoisomerism arising from a different molecular arrangement of the apical ligand in square-pyramidal or square-bipyramidal complexes with respect to the conformation of a multidentate equatorial ligand. • Complexes with excellent inhibitory properties against jack bean urease. Enzyme urease plays a significant role in the pathogenesis of several diseases and has practical implications in fields such as agriculture and chemical analysis. Four new copper(II) complexes with Schiff-base ligands obtained from the template synthesis of 2-formylphenoxyacetic acid (fphaa) with DL-α-alanine, β-alanine, taurine, and γ-aminobutanoic acid were synthesized in addition to the previously described [Cu(fphaa-gly)(H 2 O)] derived from glycine. Crystallographic study of two solvates of Cu(fphaa-α-ala)⋅S (where S = H 2 O or DMSO) showed similarity of these complexes with the one derived from glycine. In addition, an E / Z isomerism originating in a different molecular arrangement of the aqua ligand with respect to the methyl group from alanine was described in the aqua complex. Only Z isomers were found in the complex with DMSO. All prepared complexes showed excellent inhibitory properties against jack bean urease (IC 50 = 0.53–0.71 μmol/dm3), considerably better than the standard inhibitor acetohydroxamic acid (IC 50 = 185 μmol/dm3). [ABSTRACT FROM AUTHOR]

The article titled "Front Cover: Molybdenum Tricarbonyl Complexes Supported by Linear PNP Ligands: Influence of P- and N-Substituents on Relative Stability, Stereoisomerism and on the Activation of Small Molecules" explores the influence of P- and N-substituents on the stability, stereoisomerism, and activation of small molecules in molybdenum tricarbonyl complexes supported by linear PNP ligands. The front cover of the journal features a scenic image of the seaside in Schleswig-Holstein, Germany, with a lighthouse and marram grass. The two conformations of the PNP ligands, represented by seagulls, illustrate the meridional and facial coordination modes. The paper concludes that due to the phenylamine function of these ligands, only facial complexes are obtained. The research was conducted by T. A. Engesser, F. Tuczek, and their colleagues. [Extracted from the article]

[Display omitted] The conditions and reasons for the stereoselective transformation of the rac form of 2,2'-(methylene)- dicyclohexanone into the meso- or rac-diastereomer of tetracyclic dispiro ozonide (1,2,4-trioxolane) in the reaction with 30% aqueous H 2 O 2 in the presence of acid have been determined. A mechanism for the stereoisomerization of ozonides was proposed, and the stereochemistry of diastereomeric ozonides was established by NMR data. [ABSTRACT FROM AUTHOR]

With the current interest in multicomponent crystals containing chiral residues, a wide variety of studies could benefit from a comprehensive inventory of chirality in multicomponent crystals. We combined computational approaches for identifying chiral carbon atoms and methods for identifying residue types in order to make such an inventory for all organic multicomponent entries in the Cambridge Structural Database (CSD). [Groom et al., Acta Cryst. B, 2016, 72, 171–179] This inventory provides a new and extended view on multicomponent classification by including chirality. We classified 66 355 multicomponent CSD-entries into one of seven multicomponent classes and one of seven stereoisomerism classes, based on the residue type and the presence of chirality in each entry. We present refcode lists of the 49 resulting subclasses, and examples of applications of the combined classification. [ABSTRACT FROM AUTHOR]

We report the synthesis of a mixed methyl- and hydro-substituted cyclosilane (1) possessing cis/trans stereoisomerism. Each diastereomer of 1 possesses distinct symmetry elements (cis-1: Cs-symmetric; trans-1: C2-symmetric). Cyclosilane 1 is a model system to probe configuration- and conformation-dependent long-range proton–proton coupling. Extensive NMR spectroscopic characterization is reported, including one-dimensional 1H NMR and 29Si DEPT and INEPT+ spectra and two-dimensional 1H–29Si and 1H–1H correlated spectroscopy (HSQC, HMBC, COSY). On the basis of these experiments, molecular connectivity consistent with four-bond 1H–1H coupling is confirmed. [ABSTRACT FROM AUTHOR]

Glycans are ubiquitous in biology, but their complex structure and biosynthesis have challenged research of their wide-ranging roles. Here, the authors comment on current trends on the role of chemical methodologies in the field of glycobiology. [ABSTRACT FROM AUTHOR]

To study the radiolysis of the extractant composition based on solutions of dicyclohexano-18-crown-6 (DCH18C6) in ionic liquids containing the bis(trifluoromethylsulfonyl)imide anion (NTf2−), we synthesized stereoisomeric DCH18C6•Sr(NTf2)2 complexes as a model of the strontium-containing macrocyclic component of this system and studied the mechanism of their destruction in the solid phase. Three main stages of radiation-chemical transformations were found. At the initial stage of radiolysis after ionization of the complex components, a positive charge is transferred from the macrocycle to the anion, which is induced by the lower ionization potential of NTf2− as compared to the crown ether. This results in the radiation protection of the macrocycle due to the blockage of the polyether ring cleavage, which is observed under radiolysis of "free" DCH18C6. The next stage consists in the accumulation of the —O—•CH—CH2— radicals caused by the reaction of the dissociation products of the NTf2− anion with the crown ether. It intensifies the radiation destruction of the polyether ring. At the final stage, the macrocyclic radicals efficiently scavenge SO2, the molecular product of dissociation of the NTf2− anion, with the formation of sulfonyl-type radicals. The discovered channels of radiation-chemical transformations of the macrocycle in the systems including the NTf2− anion should be considered in the design of new radiation-resistant extractants. [ABSTRACT FROM AUTHOR]

We report on triethylene glycol‐based orthoformate cryptands, which adapt their bridgehead configurations in response to metal templates and intramolecular hydrogen bonding in a complex manner. In contrast to smaller 1.1.1‐orthoformate cryptands, the inversion from out,out‐2.2.2 to in,in‐2.2.2 occurs spontaneously by thermal homeomorphic isomerization, i. e. without bond breakage. The global thermodynamic minimum of the entire network, which includes an unprecedented third isomer (in,out‐2.2.2), could only be reached under conditions that facilitate dynamic covalent exchange. Both inversion processes were studied in detail, including DFT calculations and MD simulations, which were particularly helpful for explaining differences between equilibrium compositions in solvents chloroform and acetonitrile. Unexpectedly, the system could be driven to the in,out‐2.2.2 state by using a metal template with a size mismatch with respect to the out,out‐2.2.2 cage. [ABSTRACT FROM AUTHOR]

Background: The stereochemical aspects of drugs are generally recognized as fundamentally important influencers of drug action and disposition. Nevertheless, the nonproprietary names of the vast majority of stereochemically relevant therapeutic agents in the USP Dictionary of United States Adopted Names (USAN) and International Drug Names and in the WHO Drug Information listings provide no information on the stereochemical aspects. Objective: In view of the importance of stereochemistry in drug action and disposition, it is desirable to have a nonproprietary drug nomenclature system that provides basic information on the stereochemical identity and composition of drugs. Methods: The USP Dictionary of USAN and International Drug Names, the WHO Drug Information listings, and the chemical literature were examined for stereochemical information on drugs as a basis for proposing a new stereochemically informative nonproprietary drug name system. Results: A new system of stereochemically informative nonproprietary nomenclature system was designed that provides a "flag" alerting to the presence of stereochemical elements in the drug structure and includes basic information on the stereoisomerism of the drug. One of five prefixes would be added to the name: [dex]- (dextrorotatory single chiral stereoisomer); [lev]- (levorotatory single chiral stereoisomer); [rac]- (racemic mixture); [uni]-, (single achiral stereoisomer); and [mix]-, (mixture of stereoisomers other than racemic). Conclusions: The proposed system would be useful in the various domains of drug information, therapy, and research. [ABSTRACT FROM AUTHOR]

Information accumulated over the past decades on the physiological functions and metabolic pathways of biosynthesis and degradation of D-amino acids has led to a renewed interest in their study. These isomers are known to form both in nature and during the chemical synthesis of L-amino acids for feeding and pharmacological purposes, as well as in the industrial processing of some raw materials. This article discusses the positive and negative effects of D-amino acids on the human body, animals and the environment. In addition, the scientific data concerning the mechanisms of cytotoxic action of D-amino acids and their industrial and biomedical potential are summarized. [ABSTRACT FROM AUTHOR]

The chemical structure of a yellow dye present in Mirabilis jalapa L., miraxanthin I, was characterized by NMR spectroscopy. The extract of M. jalapa was analysed by a high-performance liquid chromatographic system (LC-DAD-FL-ESI-MS/MS) and the presence of miraxanthin I among other betaxanthins was confirmed. This dye was synthesized from previously generated methionine-betaxanthin by oxidation with 10% H2O2. The E/Z stereoisomers of miraxanthin I were found by NMR analysis to occur in a 50 : 33 : 10 : 7 ratio in aqueous solution (7E,9E : 7Z,9E : 7E,9Z : 7Z,9Z configurations, respectively). Comparison of NMR data with chemical shifts obtained from quantum chemical calculations strongly suggests the presence of intramolecular hydrogen bonds which may favour a more rigid structure of the dye. This explains the highest fluorescence quantum yield among betaxanthins. The observed changes in the 1H NMR spectra during the measurements indicate on miraxanthin I hydrolysis for which a mechanism is proposed. The first step during the hydrolysis process is protonation of the nitrogen atom within the central bridge bond system which is observed in the ZE stereoisomer by NMR. [ABSTRACT FROM AUTHOR]

A new family of strap porphyrins exhibiting out/in overhanging carboxylic acid stereoisomerism, has been synthesized and investigated for its coordination properties. Their 5,10 linkage allows a significant flexibility of the strap which exhibits various degrees of angulation relatively to the mean porphyrin plane, making the ligand adjustable to the metal it binds. Notably, in the case of Bi(III), a second sphere of coordination plays a crucial role for the side selective insertion of the large metal ion. As a result, inward and outward orientation of the overhanging carboxylic acid function can be tuned, which is of interest for supramolecular coordination assemblies. [ABSTRACT FROM AUTHOR]

Abstract Asymmetrical side chains were widely used in conjugated molecules, but related stereoisomeric phenomenan is rarely investigated. Herein, two stereoisomers based on ladder-type acceptor IDT-BT-R with asymmetrical side chains were synthesized and their properties were studied. Compared to cis -IDT-BT-R, trans -IDT-BT-R with centrosymmetrical structure showed stronger crystallinity and more ordered molecular packing. As a result, trans -IDT-BT-R based photovoltaic devices exhibited higher charge transport properties and superior power conversion efficiency (PCE) up to 9.43%. Graphical abstract Two stereoisomers of ladder-type acceptor molecules were obtained and their aggregation behaviors and photovoltaic performance were investigated. Image 1 Highlights • Two stereoisomers with asymmetrical side chains based on IDT-BT-R were successfully synthesized. • Centrosymmetric trans -IDT-BT-R showed enhanced crystallinity and denser intermolecular packing. • OSCs based on trans -IDT-BT-R showed high PCE of 9.43%. [ABSTRACT FROM AUTHOR]

Abstract The intramolecular rotation of several C O and C C bonds of a set of aliphatic ethers were studied using quantum-chemical calculations at the RB3LYP 6-311++G(3df,3pd) level of theory. For molecules of di-n-propyl (I) , diisopropyl (II) , methyl-n-propyl (III) and methyl isopropyl (IV) ether, the most stable conformations were found, geometric parameters and rotational constants were optimized, relative energies were estimated, and fundamental vibrations were simulated for each of them. The rotational (conformational) isomerism of these flexible aliphatic ethers with carbon and oxygen atoms in an sp3 hybridized state are examined. Thermodynamic functions for di-n-propyl (I) , diisopropyl (II) , methyl-n-propyl (III) and methyl isopropyl (IV) ethers in the ideal gas state in the temperature range T = (50–1500 K) were calculated for the first time using molecular and spectral data. [ABSTRACT FROM AUTHOR]

Some peculiarities of the effect of enantiomers of the monodentate ligand on the stereoisomerism of the mixed octahedral tetrafluoride complexes of d0-transition metals are established by the 19F{1Н} and 31Р{1Н} NMR methods for the complex formation of TiF4 with Ph2P(O)CH2CH(OH)Me (L) having the asymmetric carbon atom in the aliphatic hydrocarbon radical and being a racemic mixture of enantiomers in СН2Сl2. The compositions of the complexes formed in solutions are determined. The conclusion about the relative stereochemical configuration of the chiral and meso-stereoisomers of the geometric isomers of the TiF4L2 octahedral complex is based on an analysis of the 19F NMR spectra using the heterotropic concept. [ABSTRACT FROM AUTHOR]

The objective of this work was to bring the students closer to a real and three-dimensional structure of the matter, relating this characteristic with the physical and chemical properties of stereoisomeric molecules with chiral centers and checking the didactic transposition through molecular models made in origami. For the methodological development of the research, 101 Colombian students from the Pedagogical and Technological University from Colombia and the University from Boyacá participated, from the academic programs in Chemistry, Biology, Bachelor of Natural Sciences and Environmental Education and Physiotherapy. The results obtained show that the implementation of molecular models in origami strengthens visuospatial skills; in addition, the conceptual appropriation of stereoisomers and molecular representations. [ABSTRACT FROM AUTHOR]

The first examples of diboron complexes of the tetrapyrroles octaethylporphyrazine (OEPz) and 2,9,16,23‐tetra‐t‐butyl‐phthalocyanine (Pc) are reported, counterpoints to the better known monoboron tripyrroles, subporphyrazine and subphthalocyanine. Two stereochemical possibilities are observed, with cisoid‐B2OF2(OEPz), both cisoid‐B2OPh2(OEPz) and transoid‐B2OPh2(OEPz), transoid‐B2OF2(Pc) and cisoid‐B2OPh2(Pc) having been isolated and characterised, including structure determinations for the OEPz complexes. This variation in stereochemistry, which can be extended to include the previously reported transoid‐B2OF2(porphyrin), cisoid‐[B2OF2(corrole)]−, and both transoid‐ and cisoid‐B2OF2(calixphyrin), prompted a wider DFT study to elucidate the factors influencing the stereochemical preferences. This shows that the cisoid/transoid preference is correlated to the ease with which the macrocycle accommodates a rectangularly distorted N4 cavity. Fully characterised boron complexes of porphyrazine and phthalocyanine contain FBOBF and PhBOBPh moieties in both cisoid and transoid geometries. A DFT study, extended to include the previously reported FBOBF porphyrin, corrole, and calixphyrin complexes shows that the stereochemical preferences correlate with the ease with which each macrocycle can accommodate a rectangularly distorted N4 cavity. [ABSTRACT FROM AUTHOR]

Abstract Herein, we present the primary results on two valuable E-Z stereoisomers containing ferrocene scaffold [(E)-5,5-dimethyl-3-oxo-2-(2-phenyl-2-ferrocenyl-vinyl)cyclohex-1-en-1-yl acetate (E-FerCycAc) and its Z-stereoisomer (Z-FerCycAc)]. These compounds were both prepared from 1-phenylvinyl-ferrocene and 5,5-dimethyl-1,3-cyclohexanedione under catalysis of manganese(III) acetate according to the radical addition mechanism. The prominent spectroscopic data of the target stereoisomers were provided by FT-IR, LC-MS, 1H NMR, 13C NMR techniques, and their stereochemical identification was made primarily by NOESY analysis. The corresponding data (absorbance, transmittance and optical and transport energy gap) were collected from UV– vis studies. The optical properties of the glass slides coated with E-FerCycAc and Z-FerCycAc films were examined and consequently, the optical and transport energy band gap values of the E-FerCycAc were found significantly lower than Z-FerCycAc. The physicochemical and spectroscopic findings (HOMO-LUMO energies, bandgap values, UV– vis , FT-IR, 1H, and 13C NMR spectra) were also compared and supported with the acquired DFT calculations. Graphical abstract Image 1 Highlights • Two newly designed E/Z-stereoisomers containing ferrocene subunit were successfully prepared. • The optical properties of the stereoisomers were evaluated via experimental and theoretical UV– vis studies. • The E-isomer has shown better than Z-isomer optical performance and can be considered a suitable candidate for further studies as photovoltaic material. [ABSTRACT FROM AUTHOR]

Abstract Bisazo Tröger base analogs are claw-looking molecules that carry two identical but independent photoswitching groups. These bisazo compounds, like dual switches, can be at EE , EZ , and ZZ photoisomerization states while the ∧-shape void of Tröger base scaffold may also introduce an additional possibility of stereoisomerism by holding the photoisomerizable groups in endo or exo positions. To date, the exact molecular geometries of the isomerizable analogs of Tröger's base have not been elaborated. Owing to the special features and potential applications of these molecules, herein their photoisomerization is probed. The gleaned data from 15N isotope labeling and a variety of spectroscopic, spectrophotometric, crystallographic, and computational techniques have revealed the structure of the studied photoisomers and suggested their use in the design of molecular pull and push mechanisms, light driven actuators, and artificial muscles. Graphical abstract Image 1 Highlights • Bisazo Tröger base analogs as dual switches have EE , EZ , and ZZ states. • X-ray analysis of the EE revealed an extended ∧-shape structure of Tröger base. • TLC and 1H NMR confirmed the stepwise conversion of EE–EZ and EZ–ZZ. • FT-IR, 15N NMR and UV–vis displayed photonic E–Z and thermal Z–E conversions. • QM calculations showed that the EE contraction to ZZ is about 60% lengthwise. [ABSTRACT FROM AUTHOR]

In this work we present one of the rare cases of single‐crystal‐to‐single‐crystal (SCSC) linear polymerizations, resulting in a novel ladder‐type polymer. The polymerization is based on the photoinduced [4+4]‐cycloaddition reactions between trifunctional anthracene‐based monomers. The careful design of the monomer anthraphane‐tri(OMe), results in perfectly stacked anthracene pairs in the crystal structure, with Schmidt's distances d=3.505–3.666 Å and shift s=1.109 Å, allowing a selective linear polymerization in quantitative yields and in a matter of minutes, without compromising the integrity of the single crystals. The obtained polyanthraphane‐tri(OMe), reveals moreover a very interesting and unprecedented case of stereoisomerism, which is characteristic for polyanthraphanes. The crystal, the packing, and the polymer: A desymmetrized anthraphane was synthesized and crystallized from different solvents. One specific crystal packing upon photoirradiation resulted in a very efficient single‐crystal‐to‐single‐crystal (SCSC) polymerization, affording a new kind of polyanthraphane and highlighting an interesting case of stereoisomerism typical of these polymers. [ABSTRACT FROM AUTHOR]

Effect of enantiomers of a monodentate ligand on the stereoisomerism of mixed octahedral cis-tetrafluoro complexes of d0 transition metals has been studied by 19F{1H} and 31P{1H} NMR by the example of TiF4 complexation in CH2Cl2 with Ph2P(O)CH2CH(OH)Me (L) containing asymmetric carbon atom in the aliphatic hydrocarbon group that constitutes a racemic mixture of enantiomers. Composition of complexes formed in solution has been determined, conclusion has been drawn on the relative stereochemical configuration of the chiral and meso stereoisomers of octahedral complex cis-TiF4L2 on the basis of analysis of 19F NMR spectra, using the heterotropism concept. [ABSTRACT FROM AUTHOR]

Abstract: We report an asymmetric synthesis of enantioenriched gem‐bis(boryl)alkanes in an enantioselective diborylation of 1,1‐disubstituted alkenes catalyzed by Co(acac)2/(R)‐DM‐segphos. A range of activated and unactivated alkenes underwent this asymmetric diborylation in the presence of cyclooctene as a hydrogen acceptor, affording the corresponding gem‐bis(boryl)alkanes with high enantioselectivity. The synthetic utility of these chiral organoboronate compounds was demonstrated through several stereospecific derivatizations and the synthesis of sesquiterpene and sesquiterpenoid natural products. [ABSTRACT FROM AUTHOR]

The group hierarchy for each skeleton of ligancy 6 is formulated to be: point group (PG Gσ) ⊆RS-stereoisomeric group (RS-SIG Gσσ~I^) ⊆ stereoisomeric group (SIG G~σσ~I^) ⊆ isoskeletomeric group (ISG G~~σσ~I^ = SσI^[6]), where we start from the PG Gσ = D6h for the Kekulé benzene skeleton, from the PG Gσ = D3h for the Ladenburg benzene skeleton, from the PG Gσ = C2v for the Dewar benzene skeleton, or from the PG Gσ = C2v for the benzvalene skeleton. After these groups are constructed as combined-permutation representations, the calculation of the respective cycle indices with chirality fittingness (CI-CFs) and the introduction of ligand-inventory functions are conducted to give generation functions for 3D-based enumerations (for PGs and RS-SIGs) and 2D-based enumerations (for SIGs and ISGs). The enumeration results are discussed by means of isomer-classification diagrams, in which equivalence classes under enantiomerism (for PGs), RS-stereoisomerism (for RS-SIGs), stereoisomerism (for SIGs), and isoskeletomerism (for ISGs) are illustrated schematically. The implicit connotations of the conventional terms “skeletal isomerism”, “positional isomerism”, and “constitutional isomerism” are discussed, where the effects of the concept of isoskeletomerism are emphasized. [ABSTRACT FROM AUTHOR]

Pyrethroids are chiral insecticides characterized by stereoisomerism, which occurs due to the presence of one to three asymmetric (chiral) carbons, generating one or two pairs of cis/trans diastereomers, and two or four pairs of enantiomers. Diastereomers have equal chemical properties and different physical properties, while enantiomer pairs, have the same physicochemical properties, with exception by the ability to deviate the plane of polarized light to the right or to the left. However, stereoisomers exhibit different toxicities at the metabolic level, presenting enzyme and receptor selectivity in biological systems. Studies in aquatic organisms have shown that toxic effects are caused by specific enantiomers (1R-cis and 1R-trans) and that those cause potential estrogenic effects (1S-cis and 1Strans). In this context, the same compound can have wide-ranging effects in organisms. Therefore, several studies have highlighted pyrethroid stereochemical selectivity in different environmental matrices. The analytical ability to distinguish the diastereomeric and enantiomeric patterns of these compounds is fundamental for understanding the processes of biotransformation, degradation environmental behavior and ecotoxicological impacts. In this context, a pyrethroid stereochemical approach is recommended and therefore should be included in future risk assessments and regulatory decisions. [ABSTRACT FROM AUTHOR]