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Modular β‐borylacrylates have been validated as programmable, ambiphilic C3‐synthons in the cascade annulation of 2‐halo‐phenol derivatives to generate structurally and electronically diverse coumarins. Key to this [3+3] disconnection is the BPin unit which serves a dual purpose as both a traceless linker for C(sp2)–C(sp2) coupling, and as a chromophore extension to enable inversion of the alkene geometry via selective energy transfer catalysis. Mild isomerisation is a pre‐condition to access 3‐substituted coumarins and provides a handle for divergence. The method is showcased in the synthesis of representative natural products that contain this venerable chemotype. Facile entry into π‐expanded estrone derivatives modified at the A‐ring is disclosed to demonstrate the potential of the method in bioassay development or in drug repurposing., Modular β‐borylacrylates are validated as programmable, ambiphilic C3‐synthons for the annulation of 2‐halo‐phenol derivatives to generate diverse coumarins. Key to this [3+3] disconnection is the BPin unit which serves a dual purpose as both a traceless linker for C(sp2)–C(sp2) coupling, and as a chromophore extension to enable E → Z alkene isomerisation. Inverting alkene geometry is a pre‐condition to access 3‐susbtituted derivatives. This approach capitalises upon the abundance of 2‐halophenols in biology and may facilitate natural product/drug re‐purposing and the development of imaging tools.

A novel N,N’‐allyl‐bridged bisimidazolium salt and a novel dinuclear Ag(I) and a Au(I) NHC complex are reported. Both metallacyclic complexes have a twisted structural shape due to the rigid allylic system and form two different isomers relating to the position of the double bonds. The allyl‐group shows photoisomerisation, but no reactivity towards bases for the additional coordination of Pd(II)., Building bridges: A novel N,N’‐allyl‐bridged bisimidazolium salt and a novel dinuclear Ag(I) and a Au(I) NHC complex are reported. Both metallacyclic complexes have a twisted structural shape due to the rigid allylic system and form two different isomers relating to the position of the double bonds. The allyl‐group shows photoisomerisation, but no reactivity towards bases for the additional coordination of Pd(II).

While the use of visible light in conjunction with transition metal catalysis offers powerful opportunities to switch between on/‐off states of catalytic activity, the next frontier would be the ability to switch the actual function of the catalyst and resulting products. Here we report such an example of multi‐dimensional catalysis. Featuring an easily prepared, bench‐stable cobalt(I) hydride complex in conjunction with pinacolborane, we can switch the reaction outcome between two widely employed transformations, olefin migration and hydroboration, with visible light as the trigger., Night and day: A rare example of switching product outcome depending on light‐dark is reported. Using a cobalt(I) hydride complex, hydroborated products are obtained under visible‐light irradiation whereas, in contrast, alkene isomerisation occurs in the dark. This dual‐function catalysis results from alteration of the coordination sphere surrounding the metal centre.

This work investigates the effect of ultrasound on switching of cis azobenzene isomers to their trans counterparts in solid films of methyl methacrylate and methacryloyloxyazobenzene copolymers [P(MMA/MOAB)]. Ultraviolet–visible and 1H nuclear magnetic resonance spectroscopies demonstrate that 46% of the cis isomer converts to the trans form purely by ultrasonic agitation and 46% converts to the trans isomer by localized ultrasound-induced heating effects. Comparative studies of isomerization by ultrasound wave, heat, and visible irradiation show that ultrasound exposure requires a longer time to switch the cis-to-trans conformation. The estimated activation energy for the cis-to-trans conversion in solid polymer films is shown to be comparable to previous values of azobenzene isomerization, indicating that incorporation of the chromophore in a polymeric system affects the kinetics of transition but not the barriers to conformational change.

The performance of magnesium-impregnated NaY zeolite catalysts for the glucose isomerisation into fructose at 100 °C has been evaluated. Although crystallinity and textural properties of the zeolites are reduced through Mg addition, glucose conversion improves (6–49%) by increasing magnesium content (0–15 wt.%) due to an increase of the number of basic sites. Conversely, selectivity to fructose drops (96–66%). Nevertheless, good fructose yields were still reached with 10 and 15 wt.% of magnesium (about 32%), being similar or even higher than those found for a commercial hydrotalcite and a pure magnesium oxide. Catalysts lose performance through carbon retention and cations leaching. Deactivation of magnesium-based zeolites was further investigated by consecutive reaction runs. If no regeneration of the catalyst is performed, the activity of the zeolites decreases mainly as a result of cations leaching, the effect reducing with the number of runs. Regeneration allows the catalyst to recover almost totally its initial activity. Interestingly, used samples show higher fructose selectivity due to the additional pore opening resulting from cations leaching and/or carbon removal. Cations leaching results in a homogeneous catalytic reaction which is most significant for the highest magnesium content. Magnesium-based NaY zeolites are revealed as potential catalysts for glucose isomerisation into fructose with high fructose productivities and good performance in consecutive reactions combined with intermediate regeneration.

The first bis(σ-zincane) complexes, heterotri- metallic species [M(CO)4 (η2 -HZnBDI)2 ], have been prepared (BDI=κ2 -{2,6-(iPr)2 C6 H3 NCMe}2 CH). For M=Cr, a single stereoisomer is observed in solution and the solid-state. For M=Mo and W, cis and trans isomers were found to reversibly interconvert at 297 K. Despite the huge steric demands of the ligand on zinc, the cis isomer was found to be the most thermodynamically stable in all cases. The activation parameters for the isomerisation when M=Mo are ΔH≠ =20.8 kcal mol-1 and ΔS≠ =-12.8 cal K-1 mol-1 . In combination with DFT calculations, the negative activation entropy suggests an intramolecular rotation mechanism for isomerisation.

Dunaliella salina is a rich source of 9-cis &beta, carotene, which has been identified as an important biomolecule in the treatment of retinal dystrophies and other diseases. We previously showed that chlorophyll absorption of red light photons in D. salina is coupled with oxygen reduction and phytoene desaturation, and that it increases the pool size of &beta, carotene. Here, we show for the first time that growth under red light also controls the conversion of extant all-trans &beta, carotene to 9-cis &beta, carotene by &beta, carotene isomerases. Cells illuminated with red light from a light emitting diode (LED) during cultivation contained a higher 9-cis &beta, carotene content compared to cells illuminated with white or blue LED light. The 9-cis/all-trans &beta, carotene ratio in red light treated cultures reached &gt, 2.5 within 48 h, and was independent of light intensity. Illumination using red light filters that eliminated blue wavelength light also increased the 9-cis/all-trans &beta, carotene ratio. With norflurazon, a phytoene desaturase inhibitor which blocked downstream biosynthesis of &beta, carotene, extant all-trans &beta, carotene was converted to 9-cis &beta, carotene during growth with red light and the 9-cis/all-trans &beta, carotene ratio was ~2. With blue light under the same conditions, 9-cis &beta, carotene was likely destroyed at a greater rate than all-trans &beta, carotene (9-cis/all-trans ratio 0.5). Red light perception by the red light photoreceptor, phytochrome, may increase the pool size of anti-oxidant, specifically 9-cis &beta, carotene, both by upregulating phytoene synthase to increase the rate of biosynthesis of &beta, carotene and to reduce the rate of formation of reactive oxygen species (ROS), and by upregulating &beta, carotene isomerases to convert extant all-trans &beta, carotene.

Discrimination between polyunsaturated fatty acid isomers with three double bonds is a great challenge, due to structural similarities and similar polarities. In this study, we report the identification of four minor geometrical isomers of α-linolenic acid (ALA) present in linseed oil samples: (9E,12Z,15E)-, (9Z,12Z,15E)-, (9Z,12E,15Z)- and (9E,12Z,15Z)-octadeca-9,12,15-trienoic acids, chromatographically resolved by gas chromatography (GC) using a new and highly polar ionic phase column (SLB-IL111). Gas chromatography-electron ionisation mass spectrometry (GC-EIMS) determined that the four unknown compounds were C18:3 n-3 isomers. The positional 9-12-15 C18:3 configuration was achieved by covalent adduct chemical ionisation tandem mass spectrometry (CACI-MS/MS) while geometrical configuration was established with analytical standards based on relative retention. We hypothesised that these isomers are formed during linseed oil deodorisation and postulate preferred and unfavoured isomerisation pathways of ALA., This work was supported by U.S. National Institutes of Health (NIH) Grant R01 AT007003 from the National Center for Complementary and Integrative Health and the Office of Dietary Supplements. P. Gómez-Cortés gratefully acknowledges receipt of a postdoctoral grant from the Alfonso Martín Escudero Foundation (Madrid, Spain).

Hopanoids are pentacyclic triterpenoids produced by a wide range of bacteria. Within modern settings, hopanoids mostly occur in the biological 17β,21β(H) configuration. However, in some modern peatlands, the C31 hopane is present as the thermally-mature 17α,21β(H) stereoisomer. This has traditionally been ascribed to isomerisation at the C-17 position catalysed by the acidic environment. However, recent work has argued that temperature and/or hydrology also exert a control upon hopane isomerisation. Such findings complicate the application of geohopanoids as palaeoenvironmental proxies. However, due to the small number of peats that have been studied, as well as the lack of peatland diversity sampled, the environmental controls regulating geohopanoid isomerisation remain poorly constrained. Here, we undertake a global approach to investigate the occurrence, distribution and diagenesis of geohopanoids within peat, combining previously published and newly generated data (n = 395) from peatlands with a wide temperature (-1 to 27°C) and pH (3 to 8) range. Our results indicate that peats are characterised by a wide range of geohopanoids. However, the C31 hopane and C32 hopanoic acid (and occasionally the C32 hopanol) typically dominate. C32 hopanoic acids occur as αβ- and ββ-stereoisomers, with the ββ-isomer typically dominating. In contrast, C31 hopanes occur predominantly as the αβ-stereoisomer. These two observations collectively suggest that isomerisation is not inherited from an original biological precursor (i.e. biohopanoids). Using geohopanoid ββ/(αβ+ββ) indices, we demonstrate that the abundance of αβ-hopanoids is strongly influenced by the acidic environment, and we observe a significant positive correlation between C31 hopane isomerisation and pH (n = 94, r2 = 0.64, p < 0.001). Crucially, there is no correlation between C31 hopane isomerisation and temperature. We therefore conclude that within peats, αβ-hopanoids are acid-catalysed diagenetic products and their occurrence at shallow depths indicates that this isomerisation is rapid. This shows that geohopanoid ββ/(αβ+ββ) indices can be used to reconstruct pH within modern and ancient peat-forming environments. However, we only recommend using ββ/(αβ+ββ) indices to interrogate large amplitude (> 1 pH unit) and longer-term (> 1 kyr) variation. Overall, our findings demonstrate the potential of geohopanoids to provide unique new insights into understanding depositional environments and interpreting terrestrial organic matter sources in the geological record.

Various chemical compounds in green coffee beans are precursors of coffee beverage sensory attributes. The hypothesis was that those chemical compounds would vary with microclimate over the vertical plant profile of coffee plants. The plants of the cultivar IAPAR 59 were grown in two high plant densities (6000 and 10,000 plants ha−1) under rectangular and square planting patterns. Coffee beans were collected from three canopy strata. Chemical compounds and chlorogenic acid isomer (CGA) contents were determined by near infrared spectroscopy and ultra-performance liquid chromatography, respectively. The free-choice profile technique was employed to estimate the sensory attributes of coffee beverage. Brightness, transparency appearance, typical coffee color and aroma, tastes as sweet, acid, astringent and bitter, and full-bodied texture were attributes detected by panelists. Plants cultivated under lower plant density had lower leaf area index indicating lower self-shading than under higher plant density. Coffee beans originated from the inferior stratum of higher density had the lowest concentrations of 5-caffeoylquinic acid (5-CQA), while the inverse situation occurred in their upper strata. Strata of lower planting density were associated to high levels of all CGA isomers. The coffees cultivated under higher density showed high lipids and CGA isomers contents. Under lower density, beans had low concentration of sucrose, proteins, and caffeine and high of CGA isomer contents. The beverage sensory attributes depended on the concentration of proteins, lipids, and sucrose in combination to CQA isomers in beans, varying over the vertical profile and planting designs of coffee plants.

Isomerisation of n-hexane was studied in the presence of acid and bifunctional metal-acid catalysts based on Keggin-type heteropoly acids (HPA), in particular focusing on Cs2.5H0.5PW12O40 (CsPW) and Pt/CsPW as the catalysts, using a fixed-bed microreactor under differential conditions (n-hexane conversion ≤ 10%) at 180–220 °C, ambient pressure and a ratio of n-hexane and H2 partial pressures of 0.06–0.24. The turnover rate of HPA-catalysed isomerisation was found to correlate with the acid strength of HPA (initial enthalpy of ammonia adsorption). Bifunctional Pt-HPA catalysts were more efficient than monofunctional HPA catalysts. In the isomerisation over Pt/CsPW bifunctional catalyst, n-hexane dehydrogenation step was found to equilibrate at a molar ratio of Pt and H+ surface sites Pts/H+ ≥ 0.8, corresponding to a Pt loading ≥6%. Bimetallic PtAu/CsPW catalyst showed higher activity in n-hexane isomerisation than Pt/CsPW, although the Au alone without Pt was inert. In the presence of Au, the turnover rate at Pt sites increased more than twofold. The effect of Au is attributed to PtAu alloying. Scanning transmission electron microscopy–energy dispersive X-ray spectroscopy (STEM-EDX) and X-ray diffraction (XRD) analyses of PtAu/CsPW indicated the presence of bimetallic PtAu nanoparticles with a wide range of Pt/Au atomic ratios.

A range of cyclopropyl‐fused N‐tosyl piperidines have been synthesised and shown to undergo ring‐opening isomerisation on treatment with platinum(II) catalysts. The products can have either an endo‐cyclic or exo‐cyclic double bond. The selectivity is influenced by reaction temperature, solvent and, most significantly, the catalyst. A mechanism involving C−C bond activation and β‐hydride elimination is proposed. When β‐hydride elimination is blocked, a stereospecific platinum‐driven Wagner–Meerwein shift is observed. MOE (Min. of Education, S’pore) Accepted version

International audience; Two novel cycloruthenated compounds, 2 and 3, derived from cycloruthenated 2-phenyl pyridine(Ru(PhPy)) have been synthesized by adding one equivalent of 2,20;60,200-terpyridine (terpy) to [Ru(2-C6H4-20-C5H4N-kC,N)(MeCN)4]PF6 in MeOH/MeCN (16:1) at reflux temperature as a mixture of 1:1 isomers. The structures of both compounds that were formed under kinetic and thermodynamic control respectively, differ by the position of the central pyridine unit of terpy that was found trans or cis to the C-Ru bond of the Ru(PhPy) unit for 2 and 3 respectively. Whereas 2 did not afford substitution reactions when treated with any ligand, the substitution by MeOH or H2O of the MeCN trans to C in 3 could be followed by UV-vis spectroscopy. Moreover, the reaction in MeOH between 3 and imidazoles afforded new cycloruthenated compounds, 6a and 6b whose cytotoxicities, together with that of 2 and 3, against HCT116 and AGS cancer cells were determined.

Double bond migration in N-allylindoles has been investigated as a method to access N-vinyl derivatives of this heterocycle. The optimal reaction conditions employed t-BuOK or NaH in DMSO as the solvent at room temperature to afford the products in yields ranging from 51 to 99%. Although in some cases a high degree of stereoselectivity was observed, preferential formation of either the Z- or E-isomer was not predictable. The developed methodology was employed in the synthesis of (+/-)-debromoarborescidine B. Supplementary material: [http://cherry.chem.bg.ac.rs/handle/123456789/3501]

International audience; The asymmetric synthesis of gymnastatin H has been achieved by using the photoisomerisation of a conjugated ester to its β,γ-unsaturated isomer through the protonation of a in situ generated dienol as key step. Thanks to diacetone D-glucose used as a chiral alkoxy group, the protonation occurred well onto one of the two diastereotopic faces with very high yields and selectivities. Moreover, by this way the configuration of the C-6 centre of the target molecule was controlled.

Large zeolite crystals of ferrierite have been used to study the deactivation, at the single particle level, of the alkyl isomerisation catalysis of oleic acid and elaidic acid by a combination of visible micro-spectroscopy and fluorescence microscopy (both polarised wide-field and confocal modes). The large crystals did show the desired activity, albeit only traces of the isomerisation product were obtained and low conversions were achieved compared to commercial ferrierite powders. This limited activity is in line with their lower external non-basal surface area, supporting the hypothesis of pore mouth catalysis. Further evidence for the latter comes from visible micro-spectroscopy, which shows that the accumulation of aromatic species is limited to the crystal edges, while fluorescence microscopy strongly suggests the presence of polyenylic carbocations. Light polarisation associated with the spatial resolution of fluorescence microscopy reveals that these carbonaceous deposits are aligned only in the larger 10-MR channels of ferrierite at all crystal edges. The reaction is hence further limited to these specific pore mouths.

Synthetic overcrowded alkene-based molecular motors achieve 360° unidirectional rotary motion of one motor half (rotator) relative to the other (stator) through sequential photochemical and thermal isomerisation steps. In order to facilitate and expand the use of these motors for various applications, it is important to investigate ways to increase the rates and efficiencies of the reactions governing the rotary motion. Here, we use computational methods to explore whether the thermal isomerisation performance of some of the fastest available motors of this type can be further improved by reducing the sizes of the motor halves. Presenting three new redesigned motors that combine an indanylidene rotator with a cyclohexadiene, pyran or thiopyran stator, we first use multiconfigurational quantum chemical methods to verify that the photoisomerisations of these motors sustain unidirectional rotary motion. Then, by performing density functional calculations, we identify both stepwise and concerted mechanisms for the thermal isomerisations of the motors and show that the rate-determining free-energy barriers of these processes are up to 25 kJ mol−1 smaller than those of the original motors. Furthermore, the thermal isomerisations of the redesigned motors proceed in fewer steps. Altogether, the results suggest that the redesigned motors are useful templates for improving the thermal isomerisation performance of existing overcrowded alkene-based motors. Funding agencies: Swedish Research Council [621-2011-4353]; Olle Engkvist Foundation [2014/734]; Carl Trygger Foundation [CTS 15:134]; Linkoping University

International audience; Peptide bonds in protein structures are mainly found in trans conformation with a torsion angle ω close to 180°. Only a very low proportion is observed in cis conformation with ω angle around 0°. Cis-trans isomerization leads to local conformation changes which play an important role in many biological processes. In this paper, we reviewed the recent discoveries and research achievements in this field. First, we presented some interesting cases of biological processes in which cis-trans isomerization is directly implicated. It is involved in protein folding and various aspect of protein function like dimerization interfaces, autoinhibition control, channel gating, membrane binding. Then we reviewed conservation studies of cis peptide bonds which emphasized evolution constraints in term of sequence and local conformation. Finally we made an overview of the numerous molecular dynamics studies and prediction methodologies already developed to take into account this structural feature in the research area of protein modeling. Many cis peptide bonds have not been recognized as such due to the limited resolution of the data and to the refinement protocol used. Cis-trans proline isomerization reactions represents a vast and promising research area that still needs to be further explored for a better understanding of isomerization mechanism and improvement of cis peptide bond predictions.

International audience; Using easily accessible aromatic alkoxy-arylalkynones, we have investigated the gold-catalyzed intramolecular addition of ethers to alkynes, to give easy access to various substituted chromones. This reaction involves the transfer of the ether substituent via a carbodemetallation process. We also noticed a competing isomerization of several starting materials for which we propose a second gold catalyzed mechanism.

For a spatially restricted excitation volume, the effective modulation of the excitation in time is influenced by the passage times of the molecules through the excitation volume. By applying an additional time-modulated excitation, the buildup of photoinduced reversible dark states in fluorescent molecules can be made to vary significantly with their passage times through the excitation volume. The variations in the dark state populations are reflected by the time-averaged fluorescence intensity, which thus can be used to characterize the mobilities of the molecules. The concept was experimentally verified by measuring the fluorescence response of freely diffusing cyanine fluorophores (Cy5), undergoingtrans-cis isomerization when subject to time-modulated excitation in a focused laser beam. From the fluorescence response, and by applying a simple photodynamic model, the transition times of the Cy5 molecules could be well reproduced when applying different laminar flow speeds through the detection volume. The presented approach puts no constraints on sample concentration, no requirements for high time resolution or sensitivity in the detection, nor requires a high fluorescence brightness of the characterized molecules. This can make the concept useful for a broad range of biomolecular mobility studies. QC 20100617 Uppdaterad från manuskript till artikel (20110110). Tidigare titel: Recovery of Photo-Induced Reversible Dark States Utilized for Molecular Diffusion Measurements

International audience; The palladium hydride-iminium complex generated from Pd/C and triethylamine catalyses the isomerisation of allylic alcohols into carbonyl compounds, and Pd/C catalyses the conjugate reduction of activated double bonds using triethylamine as the source of the two newly incorporated hydrogen atoms via the same complex.

5-thio-D-xylopyranose, a synthon used for the preparation of drugs with antithrombotic activity, was synthesised by an enzymatic isomerisation from the corresponding ketose, 5-thio-D-xylulofuranose, with glucose isomerase. This compound was obtained by two different chemoenzymatic routes, the key step being the stereospecific formation of a C–C bond, catalysed by transketolase or fructose-1,6-bisphosphate aldolase. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Synthesis, isomerisation and structure elucidation of the title compounds 1–6 and its isomers 7–12 by FTIR, 1H, 13C, 15N, 77Se NMR spectroscopy is reported. Ethyl 2–(3–acylselenoureido)thiophene–3–carboxylates and their benzoanalogues (where acyl is benzoyl and pivaloyl) were prepared by addition of ethyl 2–aminothiophene–3–carboxylates and ethyl 2–aminobenzoate on benzoyl– or pivaloylisoselenocyanate in acetone solution. An isomerization of 1–6 to the corresponding 3–acylisoselenoureas 7–12 was obtained. The isomerisation proceeds either by irradiation with light (340–400 nm) or in the case of benzoylderivatives 1, 3, 5 by treatment with acetic acid. On the other hand the acid action in the pivaloyl set inhibited this isomerisation and evoked the retroisomerisation reaction of 8, 10, 12 to 2, 4, 6. Thermal analyses showed that isomerisation can be initiated also by heating. These changes proceed in the solid phase as an exothermic process at an elevated temperature but always below the temperature of melting. The structure 2 was supported by X–ray analysis. Molecular design of 2 and 8 was modeled during application of ab initio quantum chemistry calculation.

Assignment of configuration to the 1,10-double bond in the cis-trans isomeric 3β-acetoxy-5,10-seco-1,10-cholesten-5-ones has been achieved by means of NMR spectrometry. Some reactions of these new compounds have been studied and, as expected from conformational analysis, it was found that only the trans-isomer readily undergoes transannular cyclizations.