Archive for the ‘Organic’ Category

Bioinspired catalysis for eco-friendly chemical transformations in water

One challenge that today’s chemists face is making large-scale processes more economical and environmentally friendly. Within this area, there has been a surge of interest in the development of bioinspired catalytic systems which, relative to traditional catalysis, have the potential to reduce chemical waste by 85% by performing efficient reactions in pure water.

Prof. Normand Voyer and coworkers from Laval University have recently published an eco-friendly methodology for the preparation of chiral a,b-epoxyketones in pure water using the supramolecular catalyst, homo-oligopeptide poly-L-leucine (PLL).

Achieving enantioselectivity in organic reactions carried out in water poses challenges but peptide derived catalysts have shown great promise in this regard. The best example of this is the Juliá-Colonna epoxidation which has been studied and improved since its discovery in the early 1980’s. While significant progress in this area has been made, most transformations using natural homo-oligopeptides have required the use of an organic co-solvent to improve reaction efficiency.

Professor Voyer shows the new, eco-friendly process begins with several homo-oligopeptides being synthesised from their corresponding amino acid N-carboxyanhydrides and used to catalyse the Juliá-Colonna epoxidation of an electron deficient olefin in water. Of all the catalysts, PLL provided the highest conversion and enantioselectivity (Table) however, the generality of the reaction appeared to be dependent on the sterics and electronics of the substrates.

Computational analysis was used to model the PLL supramolecular catalyst and rationalise the observed reaction trends. PLL adopts a helical conformation with hydrophobic grooves distributed along the helical axis. When modelled with substrate 1 (Table), it was observed that the chalcone moiety fits perfectly within the PLL groove and forms a stable complex. It is this complexation that also aids in solubility of the ketone, removing the need for an organic co-solvent.

Epoxidation is proposed to take place through a “groove sliding” mechanism, where the substrate slides into the hydrophobic pocket generated by the leucine side chains until it reaches the N-terminal of PLL where a hydroperoxide anion is waiting (Figure). This mechanistic proposal lends to the enantioselectivity of the reaction and explains the observed electronic and steric constraints.

While the scope of PLL remains limited, this study underscores the fact that conformation and the hydrophobic nature of the oligopeptide catalysts are critical for carrying out environmentally benign organic reactions and has set a precedent for the development of future biomimetic supramolecular catalysts.

To find out more see:

Revisiting the Juliá–Colonna enantioselective epoxidation: supramolecular catalysis in water
Christopher Bérubé, 
DOI:10.1039/C7CC01168G


Victoria Corless is currently completing her Ph.D. in organic chemistry with Prof. Andrei Yudin at The University of Toronto. Her research is centred on the synthesis of kinetically amphoteric molecules which offer a versatile platform for the development of chemoselective transformations with particular emphasis on creating novel biologically active molecules.

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Opening the door to poly(ionic liquid)s with enhanced properties

Poly(ionic liquid)s, or PILs, are polyelectrolytes whose potential uses are being investigated for a variety of technologies, such as batteries, membranes, solar cells and switchable surfaces. In this ChemComm communication, Professor Eric Drockenmuller and co-workers at the Université de Lyon, University of Liège and the Institut Universitaire de France describe a new family of PILs based on poly(vinyl ester 1,2,3-triazolium)s, which should give rise to new properties and application possibilities. 

The materials are prepared from a multistep route making use of `click chemistry´(copper(I) catalysed azide alkyne Huisgen cycloaddition reaction), palladium catalyzed vinyl group exchange, and cobalt mediated radical polymerisation. This route yields a neutral polymer, which is transformed into the poly(ionic liquid) using N-methyl bis[(trifluoromethyl)sulfonyl]imide. This useful reagent alkylates the triazole group present, and delivers the bis[(trifluoromethyl)sulfonyl]imide counterion in one step. 

Synthetic route used to yield new poly(vinyl-ester 1,2,3-triazolium)s

The ionic conductivity for the PIL reported is slightly lower than for other types of PIL. To tune this property, a variety of alkynes and azides are being tested in the ring forming step of the reaction, which will result in different substituents on the triazolium ring and on the spacer group between the polymer backbone and triazolium ring.  Changes in thermal properties in the the neutral precursor-to-PIL stage of the reaction were measured using broadband dielectric spectroscopy. Significant changes in solubility, and a 9⁰C rise in glass transition temperature to -16⁰C, were observed. 

The molecular variety introduced by this new synthetic approach offers large scope for fine tuning the electronic and mechanical material properties of these polyelectrolytes, further enabling their use in important technological applications. 

Read this Chemical Communication today – it’s free to access until 3rd April*: 

Poly(vinyl ester 1,2,3-triazolium)s: a new member of the poly(ionic liquid)s family
M. M. Obadia, G. Colliat-Dangus, A. Debuigne, A. Serghei, C. Detrembleurb and E. Drockenmuller
DOI: 10.1039/c4cc08847f 

*Access is free through a registered RSC account – click here to register

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Accessing Chiral Space with Visible Light

Researchers have made tremendous efforts to unlock stereoselective, catalytic organic transformations. In this recent ChemComm Feature Article, Professor Eric Meggers, one of the pioneers in the field of photoredox catalysis, provides a comprehensive review of the recent advances in asymmetric catalysis driven by visible light.

Asymmetric catalysis has been one of the most attractive yet challenging areas of organic chemistry for the synthesis of unique, biologically active natural products such as Taxol, Rapamycin, or Vinblastine that possess numerous stereocenters.

C4CC09268F gaRecently, visible light, a sustainable and affordable energy resource, gained substantial interest with its capability to selectively access chiral molecules from prochiral substrates without undesirable by-products. Transformations including aldehyde α-functionalization and [2+2] cycloadditions demonstrate the potential of visible light in the presence of a photosensitizer.

These photosensitizers are typically ruthenium or iridium complexes that can facilitate electron/energy transfer upon photoinduction. In most cases, a photoredox catalyst has to be coupled with a chiral co-catalyst to introduce stereocenters in the products.

Notable advances in the Meggers, Melchiorre, and MacMillan research groups have recently demonstrated that photoactivation can be achieved with a single chiral photosensitizer to provide products of high enantiomeric excess and good yield.

This inspirational review was just published in Chemical Communications as a Feature Article. I recommend reading “Asymmetric catalysis activated by visible light” (DOI: 10.1039/c4cc09268f) by Professor Eric Meggers to learn more about the recent advances with mechanistic details and his forecast for one of the rapidly-growing research topics in organic chemistry.

This article is free to access until 17th March.* Download it here:
Asymmetric catalysis activated by visible light
Eric Meggers �
Chem. Commun., 2015, Advance Article
DOI: 10.1039/C4CC09268F, Feature Article


Dr. Tezcan Guney is a guest web writer for Chemical Communications. Dr. Guney received his Ph.D. from the Department of Chemistry at Iowa State University with Prof. George Kraus, where he focused on the synthesis of biologically active polycyclic natural products and multifunctional imaging probes. Currently, he is a postdoctoral research scholar at the Memorial Sloan-Kettering Cancer Center in New York with Prof. Derek Tan, contributing to the efforts to access biologically active small molecules using the diversity-oriented synthetic approach.

*Access is free through a registered RSC account

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Capturing C60 in a Crystalline Copolymer Chain

Since its structural realisation in 1985, C60 has garnered much attention in the chemical world for not only its spherical shape, but also its stability, electronic properties and the ability to do chemistry on its surface.

One such avenue that has proven popular in recent times is the incorporation of C60 into one-, two- and three-dimensional arrays, either covalently or non-covalently, in attempts to control the distribution of the molecules in the solid- or solution-phase.  One problem that arises in the synthesis of these extended frameworks, however, is that there often a large amount of disorder and void space in the structure, so it can be difficult to ascertain with much degree of certainty how these C60 molecules are oriented. This uncertainty can consequentially result in the properties and behaviours of the new materials remaining unidentified.

Now, researchers from the University of California, DavisMarilyn Olmstead and Alan Balch – have shown that coordination chemistry can be used to not only generate polymers that covalently link molecules of functionalised C60 in such a manner that can they can be studied crystallographically, but also that these polymers can be used to capture free C60 and C70.

Initially, polymers of C60 were synthesised through the mono-functionalisation of C60 with a piperazyl group, which, on account of its two tertiary amines, can coordinate in a linear fashion with transition metal ions, in this case rhodium(II) acetate. Upon the combination of these two components, a linear one-dimensional polymer was formed, in which it could be seen crystallographically that the C60 moieties were positioned on alternating sides of the polymer chain. These polymer chains were further found to extend into two dimensions through the interdigitation of neighbouring chains in a zipper-like fashion. C60-Rh(II) polymers can capture free C60

Perhaps more interestingly is that when these polymer chains were synthesised in the presence of either C60 or C70, free molecules of C60 or C70 were seen to occupy the void spaces between the C60 molecules of the polymer. Additionally, if a mixture of C60 and C70 was present in the polymer synthesis, it was observed that only C60 was captured by the polymer, most likely as a result of a better geometric match between the polymer and the spherical C60 in preference to the more elongated shape of C70.

This work elegantly demonstrates the generation of not only a self-assembling C60-containing polymer that can be characterised structurally in the solid state, but of one  that can entrap free molecules of C60 selectively over molecules of C70. Based on the properties of free C60 and transition metal complexes, the electronic and chromophoric properties of such a crystalline system could also be expected to offer some noteworthy results.

Read this HOT ChemComm article in full!

Zipping up fullerenes into polymers using rhodium(II) acetate dimer and N(CH2CH2)2NC60 as building blocks
Amineh Aghabali, Marilyn M. Olmstead and Alan L. Balch
Chem. Commun., 2014, Advance Article.
DOI: 10.1039/C4CC06995A

Biography

Anthea Blackburn is a guest web writer for Chemical Communications. Anthea is a graduate student hailing from New Zealand, studying at Northwestern University in the US under the tutelage of Prof. Fraser Stoddart (a Scot), where she is exploiting supramolecular chemistry to develop multidimensional systems and study the emergent properties that arise in these superstructures. When time and money allow, she is ambitiously attempting to visit all 50 US states before graduation.

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Inducing β-Peptide Structures from the Inside Out

The synthesis of tailor-made peptide chains represents a powerful tool for tuning the structure and properties of peptides, allowing for the development of  analogues for medical, technological and synthetic purposes.

For example, the β-peptide is a synthetic peptide, which, in contrast to its naturally-occurring α-peptide analogue, is bonded through the β-carbon rather than the α-carbon. As a result of this seemingly small structural change, alterations in the peptide’s secondary structure and thermodynamic stability are observed.

Adding fluoride groups to peptide chains represents another way to alter and stabilise the folding structure through the presence of stronger hydrogen bonds and the introduction of fluorophilicity. This approach is generally employed for the addition of fluoride groups at ‘remote positions,’ spaced two or more methylene units from the peptide backbone. However, this method has less of an effect on the conformation of the peptide itself, and instead primarily influences the tertiary and quaternary self-aggregation of peptide chains, as a result of the fluorophilic effect of the functionalised peptide chains.

Much less commonly studied is the effect of incorporating fluorine groups in ‘direct proximity’ to the peptide chain, that is, directly attached to the β-carbon, where it is proposed that the intramolecular hydrogen bonding will be directly affected, and consequently, so too will the secondary structure of the peptide chain.

Yasuhiro Ishida and co-workers from the RIKEN Center for Emergent Matter Science have  shown that this ‘direct’ fluorination of β-peptides can, in fact, affect the higher order structures of these peptide chains. Specifically, a hexameric β-peptide was designed, which consisted of cyclohexane-based β-amino acids in the 1-,3-,4- and 6-positions and L-alanine derivatives in the 2- and 5-positions, where the L-alanine methyl groups were either native or perfluorinated.

Irrespective of the degree of perfluorination in the β-peptide, it was found that the chains were arranged in the same left-handed 14-helix structure, with the NH-amide of the second and fifth residues participating in stabilising intramolecular H-bonding interactions. Moreover, it was found that although the presence of fluoride groups did not noticeably alter the overall secondary structure of the β-peptide chains, the stability of these structures was dramatically enhanced, showing the significant effect that fluoride groups can have on the hydrogen-bond donating ability of NH-amides.

This new approach of modifying peptide chains offers an interesting method  for influencing the secondary, and higher order, structures of the compounds, as well as their kinetic and thermodynamic properties. The effect of these structural modifications offers the possibility of tuning the chemical and biological properties of these peptide chains for use in new types of antibiotics and synthetic systems.

Read this HOT ChemComm article in full!

Stabilization of β-peptide helices by direct attachment of trifluoromethyl groups to peptide backbones
Joonil Cho, Kyohei Sawaki, Shinya Hanashima, Yoshiki Yamaguchi, Motoo Shiro, Kazuhiko Saigo and Yasuhiro Ishida
Chem. Commun., 2014, 50, 9855–9858.

About the Writer

Anthea Blackburn is a guest web writer for Chemical Communications. Anthea is a graduate student hailing from New Zealand, studying at Northwestern University in the US under the tutelage of Prof. Fraser Stoddart (a Scot), where she is exploiting supramolecular chemistry to develop multidimensional systems and study the emergent properties that arise in these superstructures. When time and money allow, she is ambitiously attempting to visit all 50 US states before graduation.

 

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Congratulations to the Poster Prize winners at the Spring 2014 RSC Carbohydrate Group Meeting!

The Royal Society of Chemistry Carbohydrate Group held a successful meeting at the University of Bath from Wednesday 30 April–Thursday 1 May.

Three of our journals – ChemComm, Chemical Science and Organic & Biomolecular Chemistry – were delighted to sponsor a poster prize each and we would like to join in congratulating the winners. Jerry Turnbull, Chair of the RSC Carbohydrate Group, presented the prizes as follows:

ChemComm Poster Prize
‘Lactose as a ‘Trojan Horse’ for QD Cell Transport’
David Benito-Alifonso
University of Bristol

Chemical Science Poster Prize
The Biosynthesis of and Synthetic Approaches to Double C-glycosides’
Kevin Mahone
University of St. Andrews

Organic & Biomolecular Chemistry Poster Prize
‘L-glucose and D-idose from D-glucose’
Zilei Liu
Oxford University

Left to Right: David Benito-Alifonso; Kevin Mahoney; Zilei Liu; Jerry Turnbull

  For more details about the meeting, visit the RSC Carbohydrate 2014 website.

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Bath to host 2014 RSC Carbohydrate Meeting: 30 Apr-1 May

The University of Bath will host Spring 2014 Royal Society of Chemistry Carbohydrate Group Meeting from Wednesday 30 April – Thursday 1 May.

On Wednesday evening, the 2014 RSC Haworth Memorial Lecture will be delivered by David Crich, Schaap Professor of Organic Chemistry at Wayne State University, Detroit, USA.

The Meeting will also include the Inaugural Buchanan Award Lecture in honour of J Grant Buchanan, a former Visiting Professorial Fellow in the Department of Chemistry here at Bath, who died two years ago on 17 April 2012, at the age of 85. Grant was a great researcher and educator, and is remembered fondly for his infectious enthusiasm, collegiality and warm humanity.

 

The full programme of speakers for the Meeting is available online.

Local delegates are free to attend the lectures and are also encouraged to submit posters.

There will be a number of poster prizes awarded:

  • Chemical Science Poster Prize – Sponsored by the Royal Society of Chemistry Publishing
    Protein-Carbohydrate Interactions in Infectious Diseases (including certificate from Chemical Science)
  • Chem Comm Poster Prize – Sponsored by the Royal Society of Chemistry Publishing
    Boronic Acids in Saccharide Recognition (including certificate from Chem Comm)
  • OBC Poster Prize – Sponsored by Asynt
    DrySyn heating block starter kit (including certificate from OBC)

For further information about the Meeting, please contact the local Organising Committee – Tony James and Steve Bull or email: carbohydrate@bath.ac.uk

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Yong-Qiang Tu: ChemComm Editor’s Choice

Yong-Qiang TuMeet our Associate Editor in Organic Chemistry: Yong-Qiang Tu

Professor Yong-Qiang Tu (Lanzhou University, China) handles submissions to Chemical Communications (ChemComm) in organic chemistry.

Yong-Qiang’s research interests centre on tandem rearrangement reactions and their application to the total syntheses of bioactive alkaloids, synthetic studies of biologically active natural products, and the construction of C-C and C-N bonds via C-H functionalisations. We invite you to submit your urgent research to his editorial office.

Read Yong-Qiang’s Editor’s Choice selection of ChemComm articles by clicking on the links below – all articles are FREE for a limited period!

ChemComm is the home of urgent high quality communications from across the chemical sciences. With a world-renowned reputation for quality and fast times to publication (average of 40 days), ChemComm is the ideal place to publish your research.


Yong-Qiang Tu’s Editor’s Choice:

Enantioselective total synthesis of (+)-brazilin, (−)-brazilein and (+)-brazilide A
Xuequan Wang, Hongbin Zhang, Xiaodong Yang, Jingfeng Zhao and Chengxue Pan  
DOI: 10.1039/C3CC42385A

Domino Rh-catalyzed hydroformylation–double cyclization of o-amino cinnamyl derivatives: applications to the formal total syntheses of physostigmine and physovenine
Wen-Hua Chiou, Chien-Lun Kao, Jui-Chi Tsai and Yun-Man Chang  
DOI: 10.1039/C3CC43257B

An organocatalytic asymmetric sequential allylic alkylation–cyclization of Morita–Baylis–Hillman carbonates and 3-hydroxyoxindoles
Qi-Lin Wang, Lin Peng, Fei-Ying Wang, Ming-Liang Zhang, Li-Na Jia, Fang Tian, Xiao-Ying Xu and Li-Xin Wang   
DOI: 10.1039/C3CC45139A

A modular total synthesis of (±)-trigonoliimine C
B. Narendraprasad Reddy and Chepuri V. Ramana  
DOI: 10.1039/C3CC45512B

Synthetic modification of salinomycin: selective O-acylation and biological evaluation
Björn Borgström, Xiaoli Huang, Martin Pošta, Cecilia Hegardt, Stina Oredsson and Daniel Strand  
DOI: 10.1039/C3CC45983G

Highly enantioselective synthesis of chiral 7-ring O- and N-heterocycles by a one-pot nitro-Michael–cyclization tandem reaction
Renate Rohlmann, Constantin-Gabriel Daniliuc and Olga García Mancheño  
DOI: 10.1039/C3CC47397J

A new versatile approach to synthesise enantioenriched 3-hydroxyoxindoles, 1,3-dihydroisobenzofuran and 3-isochromanone derivatives by a rhodium-catalyzed asymmetric arylation–cyclization sequence
Yi Li, Dong-Xing Zhu and Ming-Hua Xu  
DOI: 10.1039/C3CC47927G

Enantioselective total synthesis of virosaine A and bubbialidine
Hideki Miyatake-Ondozabal, Linda M. Bannwarta and Karl Gademann
DOI: 10.1039/C3CC38783F

A catalytic multicomponent coupling reaction for the enantioselective synthesis of spiroacetals  
Lara Cala, Abraham Mendoza, Francisco J. Fañanás and Félix Rodríguez  
DOI: 10.1039/C3CC00118K

An easy access to fluoroalkanes by deoxygenative hydrofluorination of carbonyl compounds via their tosylhydrazones
Arvind K. Yadav, Vishnu P. Srivastava and Lal Dhar S. Yadav
DOI: 10.1039/C3CC00122A


You might also be interested in these ChemComm Themed Collections:

Organocatalysis
Guest edited by Keiji Maruoka, Hisashi Yamamoto, Liu-Zhu Gong and Benjamin List

Nucleic acids: new life, new materials
Guest edited by Mike Gait, Makoto Komiyama, David Liu, Jason Micklefield, Ned Seeman and Oliver Seitz

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Intramolecular enolate arylation: formation of 4° amino-acid–derived hydantoins

The synthesis of quaternary amino acids is an important challenge facing researchers in bioorganic and medicinal chemistry. While there are a number of ways to transform tertiary amino acids into their quaternary counterparts, α-arylation of amino acids and their derivatives remains limited.

Now, in this HOT ChemComm article, Professor Jonathan Clayden and co-workers at the University of Manchester have revealed an elegant intramolecular arylation of tertiary amino acid derivates, which exploits the use of a urea linkage to connect the amino acid derivative—a nitrile or acid—and the aryl “electrophile”. During the course of the reaction, this N-aryl substituent migrates to the α-carbon of the amino acid moiety. This is followed by a cyclisation, leading to a heterocyclic hydantoin derivative. The reaction is mediated by strong base, and is thought to proceed via the metallated enolate.

Interestingly, the researchers found that the migration of the aryl ring was not influenced by its electronic properties, and that the transition-metal–free reaction could be applied successfully to a range of natural and unnatural tertiary amino acid substrates. If the tertiary amino acid nitrogen is protected with a PMB (p-methoxybenzyl) group, the resulting hydantoin product can subsequently be hydrolysed, affording the acyclic quaternary amino acid.

The reaction was monitored by in situ infrared spectroscopy (ReactIR) to identify the reaction intermediates and cast light on the mechanism of the arylation. Further details of the ReactIR analysis can be found in the electronic supplementary information. Ultimately, Clayden and his group hope to further develop this useful methodology to allow the enantioselective arylation of amino acids.

For more, check out this HOT ChemComm article in full:

Rachel C. Atkinson, Daniel J. Leonard, Julien Maury, Daniele Castagnolo, Nicole Volz and Jonathan Clayden
Chem. Commun., 2013, 49, 9734–9736
DOI: 10.1039/C3CC46193A

Ruth E. Gilligan is a guest web-writer for ChemComm.  She has recently completed her PhD in the group of Prof. Matthew J. Gaunt at the University of Cambridge, focusing on the development and application of C–H functionalisation methodology.

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The big bang theory (made safe) — Impact insensitive dinitromethanide salts

The improvement of high energy density materials (HEDM) is an ongoing challenge. These materials are widely used in propellants, explosives, and pyrotechnics, and researchers face the difficult task of optimising their explosive potential while ensuring their safety and ease of handling. Nitro-substituted methanide compounds are an important class of HEDM, but often suffer from thermal instability and impact sensitivity. This HOT ChemComm article addresses this challenge by highlighting the preparation and analysis of impact insensitive dinitromethanide salts.

Jean’ne Shreeve at the University of Idaho, working with Ling He at Sichuan University and co-workers at the US Naval Research Laboratory, proposed that by combining an oxygen-rich polynitromethanide anion (either a nitroform anion TNM, or a dinitromethanide anion DNM) with nitrogen-rich cations such as guanidinium, triazolium and tetrazolium anions, the resulting salt would exhibit high energetic properties as well as improved stability.

Using a range of guanidinium, triazolium and tetrazolium halides, the researchers prepared nine DNM salts and analysed their physicochemical properties. All of the salts displayed good thermal and detonation properties while being significantly less sensitive to impact than common explosives such as 2,4,6-trinitrotoluene (TNT) and cyclotrimethylenetrinitramine (RDX).

Molecular structure and Packing diagram of DNM salt 3

Guanidinium–DNM salt 3, decomposing at 187 °C, displayed the best thermal stability among all other known DNM salts. X-ray crystallography revealed that this increased stability is due to its strongly hydrogen-bonded structure. Each guanidinium cation forms six hydrogen bonds with the NO2 groups of four surrounding anions, creating a planar, layered packing structure.

Insights such as these will allow researchers to design HEDM with better thermal stability and less impact sensitivity, controlling their energetic potential yet ensuring greater safety and utility.

For more, check out the ChemComm article in full:
Impact insensitive dinitromethanide salts
Ling He, Guo-Hong Tao, Damon A. Parrish, and Jean’ne M. Shreeve
Chem. Commun., 2013, Accepted Manuscript
DOI: 10.1039/C3CC46518G

Ruth E. Gilligan is a guest web-writer for ChemComm.  She has recently completed her PhD in the group of Prof. Matthew J. Gaunt at the University of Cambridge, focusing on the development and application of C–H functionalisation methodology.

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