Archive for the ‘Organic’ Category

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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Mind the gap – Enhancing intercalation of luminescent aggregates

Particular molecules, which are not luminescent in solution, can luminesce intensely upon molecular aggregation; this is known as aggregation-induced emission (AIE). AIE luminogens are used widely as efficient electroluminescent materials, sensitive chemosensors, and as bioprobes. The main cause of the AIE effect is the restriction of intramolecular rotation. Therefore it can be promoted by introducing the molecules into inorganic materials with a rigid skeleton such as α-zirconium phosphate layers.

Jihong Yu and colleagues from Jilin University in China have published a method describing the intercalation of a quaternary tetraphenylethene (TPEN) cation, an AIE chromophore, into α-zirconium phosphate. At first glance, this does not seem to be too difficult a task– after all, the TPEN has two permanent positive charges on either end suitable to interact with the negatively charged phosphate layers. But, in this case, size does matter. The chromophore is almost three times larger than the distance between phosphate layers, more than a tight fit!

Stretching the layers of α-zirconium phosphate by preintercalation of butylamine before introduction of the chromophore

To overcome this problem, Yu and colleagues carried out a preintercalation step with butylamine before performing a cation exchange step to place the TPEN chromophore within the phosphate layers. Ultimately, they stretched the layer before putting the final molecule inside, just like you would stretch a pair of shoes in an effort to make them fit before placing your sensitive feet inside.

The intercalated product was found to be highly emissive in the blue region of the electromagnetic spectrum and was readily internalized by cells. The system also showed good biocompatibility, suggesting that it would make an excellent base for fluorescent labels in future biomedical imaging applications.

To read the details, check out the HOT Chem Comm article in full:

AIE cation functionalized layered zirconium phosphate nanoplatelets: ion-exchange intercalation and cell imaging

Dongdong Li, Chuanlong Miao, Xiaodan Wang, Xianghui Yu, Jihong Yu and Ruren Xu
Chem. Commun., 2013, 49, Accepted Manuscript
DOI: 10.1039/C3CC45041D

Iain Larmour is a guest web writer for ChemComm.  He has researched a wide variety of topics during his years in the lab including nanostructured surfaces for water repellency and developing nanoparticle systems for bioanalysis by surface enhanced optical spectroscopies.  He currently works in science management with a focus on responses to climate change.  In his spare time he enjoys reading, photography and art.

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A new, functionally tolerant route to organo-aluminium reagents

Paul Knochel and colleagues at the Ludwig Maximilians University in Munich have reported a new general synthesis of aryl and heteroaryl aluminium reagents.  The route described allows a larger range of functional groups to be incorporated, compared with the more usual approach of inserting Al into aryl halide bonds directly.  The synthetic methodology uses di-isobutyl aluminium chloride and n-BuLi at -78C in an exchange reaction with a functionalised aryl or heteroaryl halide.

General scheme for preparation and derivitisation of aryl aluminium reagents

The synthesis of a group of derivatives is described, via the reaction of the aluminium reagents with a variety of electrophiles.  Typical cross coupling reactions using palladium catalysis, as well as copper-catalysed Michael additions, allylation and acylations are reported, involving a rich variety of incorporated functional groups. Importantly, further derivitisation of the organo-aluminium reagents includes no further transmetalation steps.

Of note are the reactivities of electron-rich furan and thiophene bromides functionalised with ester groups, which also could remain intact during the reaction with di-isobutylaluminium chloride and butyl-lithium at -78C, yielding the desired reagents that were further derivatised, as in other examples.

N-heterocycles such as 3-bromo-quinoline also received attention, yielding the aluminium reagent in 73% yield, and smoothly converting in a palladium catalysed cross coupling reaction with 4-iodobenzonitrile.  Full NMR data for the products of the reactions described is given in the supplementary information.

In general, this Communication describes a considerable step forward in the field of organo-aluminium reagents for organic synthesis, and no doubt will be of interest to synthetic chemists in many fields.

Read this HOT ChemComm article today!

Generation of Functionalised Aryl and Heteroaryl Aluminium Reagents by Halogen/Lithium Exchange
Thomas Klatt, Klaus Groll and Paul Knochel
Chem. Commun., 2013,49, 6953-6955
DOI: 10.1039/C3CC43356K, Communication

Kevin Murnaghan is a guest web-writer for Chemical Communications. He is currently a Research Chemist in the Adhesive Technologies Business Sector of Henkel AG & Co. KGaA, based in Düsseldorf, Germany. His research interests focus primarily on enabling chemistries and technologies for next generation adhesives and surface treatments. Any views expressed here are his personal ones and not those of Henkel AG & Co. KGaA.

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Synthesis of non-toxic HSP90 inhibitors via Suzuki–Miyaura reaction

HSP90 (Heat Shock Protein 90) is a chaperone protein which is involved in the disease pathways of many cancers, and such neurodegenerative illnesses as Alzheimer’s and Parkinson’s disease.  The inhibition of HSP90 has gained a great deal of attention since its discovery, and offers the potential to treat many serious illnesses.  Much interest has focused on geldanamycin—a benzoquinone ansamycin which is highly effective in the inhibition of HSP90.  Unfortunately, geldanamycin suffers from high liver toxicity in addition to poor stability and solubility which greatly limits its therapeutic utility.

Christopher Moody at the University of Nottingham has devoted much research toward the targeting and inhibition of HSP90.  His group recently discovered that the 19-position plays a key role in geldanamycin’s toxicity, and that substitution at that position can render the compound non-toxic, through the suppression of conjugate addition reactions which are thought to be responsible for its hepatotoxicity.

While Moody previously utilized the Stille reaction for substitution at this position, the transformation was limited in cases, not scalable, and its industrial application was hampered by undesirable, toxic reagents and waste products.  In this Communication, Moody and Kitson overcome these problems by employing the Suzuki–Miyaura reaction to install functionality at the 19-position.  Using a modification of the Suzuki–Miyaura reaction previously described by Eli Lilly researchers, Moody was able to obtain functionalised geldanamycins in yields which compare well with or exceed those obtained by the Stille protocol.

Beginning with readily accessible 19-iodogeldanamycin (1), the cross-coupling reaction allows a range of substituents to be installed easily, using an array of widely available boronic acids and esters. Aryl-, vinyl- and allyl-groups could be installed with excellent yields, while the use of alkyl boronic acids and esters afforded moderate results. The electronic supplementary information contains full details of the reaction optimisation.

This method allows non-toxic 19-substituted-geldanamycins to be prepared efficiently and without the disadvantages associated with the previous Stille route.  Not only will this benefit the synthesis of geldanamycins within the pharmaceutical industry, but it should also encourage further clinical research of these important compounds.

For more, check out the ChemComm article in full:

An improved route to 19-substituted geldanamycins as novel Hsp90 inhibitors – potential therapeutics in cancer and neurodegeneration
Russell R. A. Kitson and Christopher J. Moody
Chem. Commun., 2013, Advance Article
DOI: 10.1039/C3CC43457E

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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