Synthesis of protected 2-pyrrolylalanine for Peptide chemistry and examination of its influence on prolyl amide isomer equilibrium

Protected enantiopure 2-pyrrolylalanine was synthesized for application in peptide science as an electron-rich arylalanine (histidine) analog with π-donor capability. (2S)-N-(Boc)-N'-(Phenylsulfonyl)-, (2S)-N,N'-bis-(phenylsulfonyl)-, and (2S)-N,N'-bis-(Boc)-3-(2-pyrrolyl)alanines (10, 3, and 14, respectively) were made in 13-17% overall yields and six to seven steps from oxazolidine β-methyl ester 4. Homoallylic ketone 5 was prepared by a copper-catalyzed cascade addition of vinylmagnesium bromide to ester 4 and converted to pyrrolyl amino alcohol 7 by olefin oxidation and Paal-Knorr condensation. Protecting group shuffle and oxidation of the primary alcohol enabled the synthesis of pyrrolylalanines. The bis-Boc analog 14 proved useful in peptide chemistry and was employed to make N-acetyl-pyrrolylalaninyl-proline N'-methylamide 25. A study of the influence of the pyrrole moiety on the prolyl amide isomer equilibrium of 25 using (1)H NMR spectroscopy in chloroform, DMSO, and water demonstrated that the pyrrolylalanine peptide exhibited behavior and conformations different from those of other arylalanine analogs.     

Synthesis and Biological Evaluation of the Novel Growth Inhibitor Streptol Glucoside,Isolated from an Obligate Plant Symbiont

The plant Psychotria kirkii hosts an obligatory bacterial symbiont, Candidatus Burkholderia kirkii, in nodules on their leaves. Recently, a glucosylated derivative of (+)-streptol, (+)-streptol glucoside, was isolated from the nodulated leaves and was found to possess a plant growth inhibitory activity. To establish a structure–activity relationship study, a convergent strategy was developed to obtain several pseudosugars from a single synthetic precursor. Furthermore, the glucosylation of streptol was investigated in detail and conditions affording specifically the α or β glucosidic anomer were identified. Although (+)-streptol was the most active compound, its concentration in P. kirkii plant leaves extract was approximately ten-fold lower than that of (+)-streptol glucoside. These results provide compelling evidence that the glucosylation of (+)-streptol protects the plant host against the growth inhibitory effect of the compound, which might constitute a molecular cornerstone for this successful plant-bacteria symbiosis.     

Stabilization of the Oxidation State +IV in Siloxide-Supported Terbium Compounds

The synthesis of lanthanides other than cerium in the oxidation state +IV has remained a desirable but unmet target until recently, when two examples of Tb^IV with saturated coordination spheres were isolated. Here we report the third example of an isolated molecular complex of terbium(IV), where the supporting siloxide ligands do not saturate the coordination sphere. The fully characterized six-coordinate complex [Tb^IV(OSiPh₃)₄(MeCN)₂], 2 -Tb^Ph, shows high stability and the labile MeCN ligands can be replaced by phosphinoxide ligands. Computational studies suggest that the stability is due to a strong π(O−Tb) interaction which is stronger than in the previously reported Tb^IV complexes. Cyclic-voltammetry experiments demonstrate that non-binding counterions contribute to the stability of Tb^IV in solution by destabilizing the +III oxidation state, while alkali ions promote Tb^IV/Tb^III electron transfer.     

Heterologous Expression,Biosynthetic Studies,and Ecological Function of the Selective Gq‐Signaling Inhibitor FR900359

The cyclic depsipeptide FR900359 (FR), isolated from the tropical plant Ardisia crenata, is a strong and selective inhibitor of Gq proteins, making it an indispensable pharmacological tool to study Gq‐related processes, as well as a promising drug candidate. Gq inhibition is a novel mode of action for defense chemicals and crucial for the ecological function of FR, as shown by in vivo experiments in mice, its affinity to insect Gq proteins, and insect toxicity studies. The uncultured endosymbiont of A. crenata was sequenced, revealing the FR nonribosomal peptide synthetase (frs) gene cluster. We here provide a detailed model of FR biosynthesis, supported by in vitro enzymatic and bioinformatic studies, and the novel analogue AC‐1, which demonstrates the flexibility of the FR starter condensation domains. Finally, expression of the frs genes in E. coli led to heterologous FR production in a cultivable, bacterial host for the first time.     

Preparation techniques alter the mineral and organic fractions of fish otoliths: insights using Raman micro-spectrometry

The high spatial resolution analysis of the mineral and organic composition of otoliths using Raman micro-spectrometry involves rigorous protocols for sample preparation previously established for microchemistry and trace elements analyses. These protocols often include otolith embedding in chemically neutral resin (i.e., resins which do not contain, in detectable concentration, elements usually sought in the otoliths). Such embedding may however induce organic contamination. In this paper, Raman micro-spectrometry reveals the presence of organic contamination onto the surface obtained from the use of epoxy resin, specifically Araldite. This contamination level varies depending on otolith structures. Core and checks, known as structural discontinuities, exhibit the most important level of contaminations. Our results suggest that otolith embedding with resin affects the organic matrix of the otolith, probably through an infiltration of the resin in the crystalline structure. The interpretation of chemical otolith signatures, especially Raman otolith signatures, and stable isotope analyses should then be revised in light of these results. In this respect, we propose a method for the correction of Raman otolith signatures for contamination effects.     

Dual Responsive Regulation of Host–Guest Complexation in Aqueous Media to Control Partial Release of the Host

The regulation of the concentration of a wide range of small molecules is ubiquitous in biological systems because it enables them to adapt to the continuous changes in the environmental conditions. Herein, we report an aqueous synthetic system that provides an orchestrated, temperature and pH controlled regulation of the complexation between the cyclobis(paraquat-p-phenylene) host ( BBox ) and a 1,5-dialkyloxynaphthalene ( DNP ) guest attached to a well-defined dual responsive copolymer composed of N-isopropylacrylamide as thermoresponsive monomer and acrylic acid as pH-responsive monomer. Controlled, partial release of the BBox , enabling control over its concentration, is based on the tunable partial collapse of the copolymer. This colored supramolecular assembly is one of the first synthetic systems providing control over the concentration of a small molecule, providing great potential as both T and pH chromic materials and as a basis to develop more complex systems with molecular communication.     

Rapid analysis of Na,Mg, Ca,Fe, and Zn in breakfast cereals (granola type) by energy dispersive-X-ray fluorescence

Energy dispersive-X-ray fluorescence (ED-XRF) is a well spread near-line analytical technique, suitable for easy and rapid measurement of major elements and/or trace elements especially in many different food matrices. This study demonstrates the fitness for purpose of this method to ensure the correct addition of minerals during breakfast cereal production. Indeed, variations in process and in raw material compositions may lead to values out of legal tolerance, and thus quality controls need to be regularly performed to meet the release compliance criteria. Using such analytical technique close to production lines can allow controls that are more systematic as well as avoiding the shipment of numerous samples for reference method analyses often done to external laboratories. Thus, ED-XRF allows to ensure finished products compliance with product declarations. A commercial ED-XRF device was used during this study. Within 7 min of analytical time for two replicates/sample, the developed method gave accurate results for the quantification of Na, Mg, Ca, Fe, and Zn in breakfast cereals without any proportional biases between ED-XRF and reference method (inductively coupled plasma-atomic emission spectrometry) results.     

Targeted multidimensional gas chromatography using a heart-cutting device and cryogenic focusing for the determination of benzophenone derivatives in foodstuffs

Photoinitiators are used to promote the polymerization process during the curing of varnishes or inks on cartonboard packaging. Depending on storage conditions and shelf life, these substances are able to migrate through the packaging layer into the foodstuff. This type of contamination phenomenon is therefore becoming a critical issue in terms of food safety. In order to tackle this problem, a fast and selective method was developed for the determination of benzophenone and three methylbenzophenone isomers in cereal-based foodstuffs and their cardboard packaging. Food samples or packages were efficiently extracted by pressurized liquid extraction using acetonitrile, and the extracts were directly injected onto the analytical system. The analysis was performed by multidimensional gas chromatography–mass spectrometry using a heart-cutting approach to reduce the background noise from complex matrices. The strategy employed two distinct cuts each containing its proper deuterated internal standard leading to accurate quantification. By integrating a cryofocusing effect, an enhancement in signal/noise ratio was achieved by a factor >10, which markedly decreased the sensitivity threshold. Moreover, baseline separation of the critical isomers allowed their unequivocal determination. The method was fully validated on cereal-based foodstuffs based upon an analysis of variance, and excellent performances were obtained at the decision limit making this method well suited for official food controls.     

New D-π-A-conjugated organic sensitizers based on α-pyranylidene donors for dye-sensitized solar cells

A series of new push-pull organic dyes incorporating a cyanoacrylic acid group as electron acceptor unit and α-chalcogenopyranylidene group (X = S; O) as electron donor unit has been synthesized, characterized and used as sensitizer for dye-sensitized solar cells (DSSCs). For the first time, α-pyranylidene and thiopyranylidene groups, have been evaluated in DSSC. To obtain the thermodynamic values of the solar cell, an investigation of their electrochemical (CV) and optical properties (UV–vis absorption spectroscopy) is also reported.