Planarized and structurally constrained B,N-phenylated dibenzoazaborine: diversity in electronic properties

This blog comes from Guest Writer A. Vamshi Krishna, a PhD student at the University of Hyderabad

Polycyclic aromatic hydrocarbons (PAHs) containing heteroatoms have recently been grabbing the attention of scientists as they exhibit intriguing photophysical properties and can be widely used as building blocks for π-conjugated materials due to the effect of heteroatoms on the electronic properties of the system.

PAHs are often employed in OLEDs. Over the last few years, these PAHs have been synthesized in several different ways. Kawashima et.al synthesized different acene-like π-extended dibenzoborines such as compound B which show fascinating photophysical properties. More recently, Hatakeyama et.al have reported the synthesis of various PAHs that contain multiple 1,4-azaborine rings, such as compound C, which show excellent thermally activated delayed fluorescence. By investigating these types of molecules in more detail, their electronic properties can be improved to make better OLEDs.

a) Representative examples of previously reported dibenzoazaborine-based pi-conjugated compounds and b) planarized B,N-phenylated dibenzoazaborine 1 together with reference compounds 2-4

a) Representative examples of previously reported dibenzoazaborine-based pi-conjugated compounds and b) planarized B,N-phenylated dibenzoazaborine 1 together with reference compounds 2-4

a) UV-vis absorption and b) fluorescence spectra of 1 (red), 2 (blue), 3 (green) and 4 (orange) in THF.

a) UV-vis absorption and b) fluorescence spectra of 1 (red), 2 (blue), 3 (green) and 4 (orange) in THF.

In their recent OBC publication, Professor Shigehiro Yamaguchi of the Institute of Transformative Bio- Molecules, Nagoya University et al. explored in detail the relation between the structure of materials and their electronic structures. They mainly focused on the correlation between the ring-fusion mode, where two cyclic rings fused in a planar manner, and the degree of structural constraint within the dibenzoazaborine skeleton. As constraining molecules into a planar fashion can extend π-conjugation and increase chemical stability, Shigehiro planarized the B-, N- phenyl groups in dibenzoazaborine to synthesize a new family of planarized triarylboranes with a carbazole substructure, confirming this structure by single-crystal X-ray diffraction analysis. They studied the photophysical properties of 1 and compared it with compunds 2-4. Compound 1 showed an intense absorption band at λabs= 402 nm unlike compounds 2-4 which showed λabs at 389 and 371, 400, 404 and 387 nm respectively. The fluorescence spectra of compound 1 showed an intense deep blue emission with a full width at half maximum (FWHM) of 27 nm which is due to its rigid structure. The optimized structure of 1 with respect to DFT calculations matched with the experimentally determined crystal structure. They report the time dependent DFT calculations which prove compound 1 to have the highest oscillator strength (f) amongst compounds 1-4, resulting in the largest molar absorption coefficient (ε). This clearly represents that it absorbs light strongly at the given wavelength. They also studied the electrochemical properties of 1-4 using cyclic voltammetry which resulted in one reversible reduction wave irrespective of the structural constraint showing that there are no electronic effects imposed on the structural constraint.

In conclusion, Shigehiro et al. succeeded in synthesizing structurally constrained, planarized dibenzoazaborines and investigating their photophysical and electronic effects.

Read their full article at https://rsc.li/2Xw8uoA.

Blog writer description: I am A. Vamshi Krishna, pursuing a PhD in organic chemistry with Prof. D. B. Ramachary at the University of Hyderabad. My research mainly focuses on asymmetric supramolecular-organocatalysis where we synthesise highly functionalized biologically active novel scaffolds with excellent selectivity and yields. I am passionate about scientific writing.

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Organic & Biomolecular Chemistry welcomes new Associate Editor Elizabeth Krenske

New OBC Associate Editor Elizabeth Krenske

We are delighted to welcome Dr Elizabeth Krenske to the OBC team as an Associate Editor. Elizabeth is an Associate Professor at the University of Queensland, Australia, where her research focuses on the computational study of organic reactions and modelling of drug molecules and interactions.

After starting out her career in chemistry as an undergraduate at the University of Queensland, Elizabeth undertook a PhD in the field of synthetic main-group chemistry at The Australian National University’s Research School of Chemistry, under the supervision of Professor S. Bruce Wild. She spent a further two years carrying out postdoctoral research at the Australian National University, before receiving a Fulbright Scholarship and commencing postdoctoral studies at UCLA with Ken Houk. Elizabeth returned to Australia in 2009 as an Australian Research Council (ARC) Australian Postdoctoral Fellow at the University of Melbourne, and moved to The University of Queensland in 2012 as an ARC Future Fellow. She is currently an Associate Professor and Strategic Research Fellow in the University of Queensland School of Chemistry and Molecular Biosciences. To find out more about Elizabeth and her research, visit her webpage or browse some of her recent publications below.

 

Elizabeth’s recent publications:

 

The fate of copper catalysts in atom transfer radical chemistry

Polym. Chem., 2019, 10, 1460-1470

 

Asymmetric synthesis of multiple quaternary stereocentre-containing cyclopentyls by oxazolidinone-promoted Nazarov cyclizations

Chem. Sci., 2018, 9, 4644-4649

 

Synthesis of spirocyclic orthoesters by ‘anomalous’ rhodium(II)-catalysed intramolecular C–H insertions

Org. Biomol. Chem., 2018, 16, 256-261

 

Claisen rearrangements of benzyl vinyl ethers: theoretical investigation of mechanism, substituent effects, and regioselectivity

Org. Biomol. Chem., 2017, 15, 7887-7893

 

An unprecedented stereoselective base-induced trimerization of an α-bromovinylsulfone

Org. Biomol. Chem., 2017, 15, 5529-5534

 

Submit your research to Elizabeth now!
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OBC Highlight: A new atom and mass efficient synthetic route for tamoxifen

This blog was written by A. Vamshi Krishna, a PhD student in Organic chemistry with Prof. D. B. Ramachary at University of Hyderabad.

Nowadays, chemists are increasingly interested in revealing simpler methodologies for the synthesis of various drugs with high selectivity and purity. Transition metal catalysis has opened a wide window for the synthesis of different natural products and drugs with greater ease.

Z-Tamoxifen is one such drug, which is used in the treatment of breast cancer. Although there are many well-established synthetic procedures for the synthesis of Z-tamoxifen by various research groups such as T. Stiidemann et.al. and P. L. Coe et.al. etc., there are disadvantages to current methods, such as the use of multiple synthetic steps and generation of stoichiometric amounts of waste. Thus, there is a need to overcome these drawbacks.

In their recent OBC publication, Prof. Ben L. Feringa et.al. of Stratingh Institute for Chemistry, University of Groningen, Nijenborgh develop a fantastic two step protocol for the synthesis of Z-tamoxifen from commercially available starting materials. Usually, the transmetallation of anions formed by carbolithiation of (diphenyl)acetylenes with magnesium, boron, zinc or aluminium results in an active cross coupling partner, but with low atom efficiency. Here, Feringa et.al., for the first time proposed the direct cross coupling of the formed organolithium reagent with aryl halides in the presence of an active palladium nanoparticle based catalyst, cutting down the number of synthetic steps required to two, with excellent selectivities and yields. They report the thorough screening of reaction conditions such as solvent, temperature, catalyst loading etc. and explain the effect of various reaction parameters. The 0.67 atom economy and 22% RME achieved in the study is twice as good as the previously reported best protocol, and the scientists found that THF gave the desired product without encouraging any side reactions. Another advantage of this reaction is that the formed side product (lithium halide) can be easily removed.

Hence, Prof. Ben L. Feringa laid a new efficient pathway for the synthesis of biologically important Z-tamoxifen through his works.

Read their full article now.

 

About the Blog Writer: A. Vamshi Krishna is currently pursuing a PhD  in Organic chemistry with Prof. D. B. Ramachary at University of Hyderabad. His research mainly focuses on asymmetric supramolecular catalysis and organocatalysis, where he synthesises highly functionalized biologically active novel scaffolds with excellent selectivities and yields. He is passionate about scientific writing.

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Outstanding Reviewers for Organic & Biomolecular Chemistry in 2018

We would like to highlight the Outstanding Reviewers for Organic & Biomolecular Chemistry in 2018, as selected by the editorial team, for their significant contribution to the journal. The reviewers have been chosen based on the number, timeliness and quality of the reports completed over the last 12 months.

We would like to say a big thank you to those individuals listed here as well as to all of the reviewers that have supported the journal. Each Outstanding Reviewer will receive a certificate to give recognition for their significant contribution.

Professor Jonathan Clayden, University of Bristol (http://orcid.org/0000-0001-5080-9535)
Dr Yumin Dai, Takeda Pharmaceuticals (http://orcid.org/0000-0002-9228-3671)
Professor Lourdes Gude, Universidad de Alcalá (http://orcid.org/0000-0002-0220-3755)
Dr Koji Hirano, Osaka University (http://orcid.org/0000-0001-9752-1985)
Dr Maxim Kuznetsov, “Instituto Superior Tecnico Centro de Quimica Estrutural” (http://orcid.org/0000-0001-5729-6189)
Dr Rafal Loska, Institute of Organic Chemistry of the Polish Academy of Sciences (http://orcid.org/0000-0002-0823-4675)
Professor Sripada Ramasastry, Indian Institute of Science Education and Research Mohali (http://orcid.org/0000-0001-5814-9092)
Dr Rui Shang, University of Tokyo
Professor Colin Suckling, University of Strathclyde (http://orcid.org/0000-0003-4515-5498)
Professor Dean Tantillo, University of California, Davis
Professor Mark Taylor, University of Toronto (http://orcid.org/0000-0003-3424-4380)
Dr Akhilesh Verma, University of Delhi (http://orcid.org/0000-0001-7626-5003)
Professor Mario Waser, Johannes Kepler University Linz (http://orcid.org/0000-0002-8421-8642)
Professor Robert Young, GSK (http://orcid.org/0000-0002-7763-0575)
Professor Jian Zhou, East China Normal University

We would also like to thank the Organic & Biomolecular Chemistry board and the organic and chemical biology communities for their continued support of the journal, as authors, reviewers and readers.

If you would like to become a reviewer for our journal, just email us at obc@rsc.org with details of your research interests and an up-to-date CV or résumé. You can find more details in our author and reviewer resource centre

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Editor’s Choice: Santanu’s recommended articles

Professor Santanu Mukherjee (Indian Institute of Science, Bangalore), recently joined the Organic & Biomolecular Chemistry team as an Associate Editor. Santanu works in the field of asymmetric catalysis, with a focus on the discovery of new enantioselective transformations. His research group investigates hydrogen bonding, Lewis base and bifunctional catalysis, and more recently, he has focused on iridium-catalyzed asymmetric allylic substitution reactions.

 

To find out more about Santanu, take a look at our recent blog welcoming him to the team.

 

Santanu has picked out a selection of his personal favourite recent OBC articles which you can read now for free*

 

Santanu’s Recommended OBC Articles:

 

Catalyst-controlled positional-selectivity in C–H functionalizations

Virendra Kumar Tiwari and Manmohan Kapur

 

 

 

An enantioselective synthesis of α-alkylated pyrroles via cooperative isothiourea/palladium catalysis

W. Rush Scaggs, Toya D. Scaggs and Thomas N. Snaddon

 

Organocatalytic asymmetric synthesis of highly substituted pyrrolidines bearing a stereogenic quaternary centre at the 3-position

Soumendranath Mukhopadhyay and Subhas Chandra Pan

 

Total synthesis of incargranine A

Patrick D. Brown and Andrew L. Lawrence

 

 

 

 

Studies toward the synthesis of strevertenes A and G: stereoselective construction of C1–C19 segments of the molecules

Tapan Kumar Kuilya, Subhendu Das, Dhiman Saha and Rajib Kumar Goswami

 

Formal [4 + 2] benzannulation of 2-alkenyl indoles with aldehydes: a route to structurally diverse carbazoles and bis-carbazoles

Ankush Banerjee, Avishek Guin, Shuvendu Saha, Anushree Mondal and Modhu Sudan Maji

 

Vinylogous acyl triflates as an entry point to α,β-disubstituted cyclic enones via Suzuki–Miyaura cross-coupling

Daria E. Kim, Yingchuan Zhu and Timothy R. Newhouse

 

 

 

 

*Access is free until 28/02/2019 through a registered RSC account.

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OBC warmly welcomes Professor Anthony Davis as our new Editorial Board Chair

We are delighted to announce the appointment of Prof. Anthony Davis as the new Organic & Biomolecular Chemistry Editorial Board Chair. Tony returns to the Board after serving for many years as an Editorial Board member and we are very pleased to welcome him to his new role as Chair.

 

Tony is a Professor of Supramolecular Chemistry at the University of Bristol, with research focusing on anion recognition and transport, carbohydrate recognition, and crystal engineering. He started his chemistry career at Oxford University, obtaining both his undergraduate degree and D.Phil (in the group of Dr Gordon Whitham), followed by two years of postdoctoral work under the supervision of Prof. Jack Baldwin. He joined the group of Prof. Albert Eschenmoser in 1981, working as a Royal Society European Exchange Fellow, before becoming a Lecturer in Organic Chemistry at Trinity College, Dublin, in 1982. In September 2000, he moved to his current institution, and you can find out more about his current group on the research group webpage.

 

Tony is also a co-founder of Ziylo, a biotechnology company focusing on the development of new treatments for diabetes patients, which was recently sold to Novo Nordisk. A second company spun out of Ziylo, Carbometrics, continues to work on carbohydrate sensing.

 

Prof. Davis is the recipient of numerous awards including the Tilden Medal and the RSC Award for Physical Organic Chemistry. He has published hundreds of articles, and you can see a selection of his great work below.

 

Upon becoming Chair, Tony commented, “OBC is a cornerstone of organic chemical publishing, and I’m delighted to take on this responsibility.”

 

Read some of Tony’s latest publications:

Maltodextrin recognition by a macrocyclic synthetic lectin

Chem. Commun., 2018, 54, 8649-8652

 

Anion transport by ortho-phenylene bis-ureas across cell and vesicle membranes

Org. Biomol. Chem., 2018, 16, 1083-1087

(Included in the 2018 OBC HOT article collection)

 

Enantioselective carbohydrate recognition by synthetic lectins in water

Chem. Sci., 2017, 8, 4056-4061

 

Synthesis and evaluation of a desymmetrised synthetic lectin: an approach to carbohydrate receptors with improved versatility

Org. Biomol. Chem., 2016, 14, 1930-1933

(Included in the 2016 OBC HOT article collection)

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Harnessing biosynthetic pathways to efficiently derivatize biologically active natural products

Nature is unrivaled in its ability to produce structurally complex molecules with high biological potency. Natural products have been used medicinally for centuries and have provided a profitable source of potential drug leads. Developing efficient strategies for their total synthesis, as well as the production of analogues, has always been challenging.

In a recent OBC publication, Professor Shuangjun Lin of Shanghai Jiao Tong University has identified a key enzyme in the biosynthesis of the natural product, Streptonigrin, a highly fictionalized aminoquinone isolated from the bacterium Streptomyces flocculus.

 

Streptonigrin has a long history and has attracted considerable attention from both the synthetic and biochemical communities due to its challenging molecular framework and potent antimicrobial and broad-spectrum anticancer activities. In the 1970’s, Streptonigrin reached phase-II clinical trials, though ultimately failed due to high levels of toxicity and side effects. Nevertheless, interest in its medicinal properties still remains, and many studies detailing its chemical and biosynthesis have been reported, with the hopes of enabling the production of Streptonigrin-based analogues, which would mitigate the natural product’s cytotoxicity while harnessing is broad biological capabilities.

Prof. Lin reports that previous genetic and biochemical studies successfully identified a key β-carboline (3) intermediate in the biosynthetic pathway of Streptonigrin. The β-carboline moiety is a common structural feature within a large group of natural and synthetic indole alkaloids however, the enzymes catalyzing their formation have not been well characterized or reported. Lin and coworkers have identified a protein, StnK2, which they propose catalyzes a Pictet-Spengler reaction responsible for β-carboline formation from (2S,3S)-β-methyl tryptophan and erythrose (Figure).

The study focussed on the biochemical characterization of StnK2 as a Pictet-Spenglerase, analyzing in detail its stereoselectivity and substrate specificity. StnK2 exhibited exclusive aldehyde specificity, though was flexible towards various tryptophan analogues. Additionally, StnK2 demonstrated high stereoselectivity, only recognizing S-enantiomers and producing the (R)-C-1 of the β-carboline scaffold.

This study has not only contributed to our knowledge of Pictet-Spenglerase enzymes, but has established a new means through which Streptonigrin analogues can be efficiently generated and their medicinal properties explored.

To find out more see:

StnK2 catalysing a Pictet–Spengler reaction involved in the biosynthesis of the antitumor reagent streptonigrin
Xiaozheng Wang, Dekun Kong, Tingting Huang, Zixin Deng and Shuangjun Lin
DOI:10.1039/C8OB02710B

For more papers from the OBC Biosynthesis Themed Collection


Victoria Corless completed her Ph.D. in organic chemistry with Prof. Andrei Yudin at the University of Toronto. Her research centered on the synthesis of kinetically amphoteric building blocks with particular emphasis on creating novel biologically active molecules. She is passionate science and communicating new discoveries to enhance science literacy.

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Introducing Professor Santanu Mukherjee, OBC Associate Editor

OBC is delighted to welcome our new Associate Editor, Professor Santanu Mukherjee, to the Editorial Board.

Santanu started his career in chemistry at R. K. Mission Residential College, Narendrapur, India, obtaining his BSc in 2000. He went on to study for his MSc in chemistry at IIT, Kanpur, 2002, before joining Professor Albrecht Berkessel at Universität zu Köln for his doctoral studies. After completing these in 2006, he worked as a postdoctoral fellow with Professor Benjamin List at Max-Planck Institut für Kohlenforschung in Mülheim an der Ruhr until 2008 and with Professor E. J. Corey at Harvard University from 2008-2010. In 2010, Santanu returned to India to join the Department of Organic Chemistry at Indian Institute of Science, Bangalore as an Assistant Professor and was promoted to Associate Professor in 2015.

His research interests focus on asymmetric catalysis, with a particular emphasis on the discovery of new enantioselective transformations, and recently, on iridium-catalyzed asymmetric allylic substitution reactions. To find out more about his research interests, you can visit the group webpage.

Santanu is a recipient of numerous recognitions and awards, and has published a large number of papers in high quality journals. Below are just a few examples of these publications:

 

Iridium-catalyzed enantioselective direct vinylogous allylic alkylation of coumarins

Chem. Sci., 2018, 9, 5767-5772,  Edge Article

“On water” catalytic enantioselective sulfenylation of deconjugated butyrolactams

Org. Biomol. Chem., 2017, 15, 6921-6925,  Paper

Nitro-enabled catalytic enantioselective formal umpolung alkenylation of β-ketoesters

Chem. Sci., 2017, 8, 6686-6690,  Edge Article

Catalytic enantioselective cascade Michael/cyclization reaction of 3-isothiocyanato oxindoles with exocyclic α,β-unsaturated ketones en route to 3,2′-pyrrolidinyl bispirooxindoles

Org. Biomol. Chem., 2016, 14, 10175-10179,  Communication

 

Submit a manuscript for Santanu to handle today

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Bristol Synthesis Meeting 2019

Organic & Biomolecular Chemistry are proud to sponsor the 2019 Bristol Synthesis Meeting, to be held in the Victoria Rooms, University of Bristol, 9th April 2019.

The meeting boasts a fantastic line up of speakers including OBC Advisory Board members Helma Wennemers (ETH Zurich) and Ilan Marek (Technion, Israel Institute of Technology).

Registration is now open, so for the full list of speakers and to register, see the Bristol Synthesis Meeting webpage.

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Novel application of fluorescent peptide displacement for small molecule screens against RNA targets

Recent advances in our understanding of RNA have expanded its role beyond just a carrier of genetic information. Modern views of RNA encompass a diverse range of molecules, which play a central role in modulating a number of important biological processes, including the progression of various cancers and nontumorigenic diseases.

In her recent OBC publication, Professor Amanda Hargrove of Duke University has created a general, high throughput screening technique for the identification of small molecule inhibitors of different RNA proteins using a fluorescence indicator displacement (FID) assay.

Small molecule RNA inhibitors offer advantages such as enhanced absorption, distribution, and oral bioavailability over commonly employed oligonucleotides used in antisense technologies. Fluorescence-based assays are widely used techniques used to screen small molecule libraries, however, the incorporation of fluorescent tags can lead to alterations in the RNA’s native structure and often pose synthetic challenges. FID, on the other hand, is a ‘tagless’ approach in which the indicator displays different fluorescent properties in the presence or absence of an oligonucleotide.

The Hargrove group implemented the Tat FID assay in order to simultaneously screen a library of small molecules against multiple RNA targets. This provides an efficient means of measuring binding affinity as well as evaluating specificity. The Tat FID assay requires a Tat peptide construct labeled with a Förster Resonance Enhancement Transfer (FRET) pair—a 5-carboxyfluorescein (FAM) at the N-terminus and 5-carboxytetramethylrhodamine (TAMRA) at the C-terminus (see figure). When the peptide is bound to RNA, the distance between fluorophores allows for excitation of FAM and emission detection from TAMRA. Displacement of the Tat peptide results in quenching of the fluorescent signal, which can be used to quantify binding affinity.

A library of 30 small molecules (including known RNA binding small molecules) was screened against four select RNA structures. The assay was successful in identifying hits for all four RNA molecules and identified indiscriminate and differential binding of individual small molecules. Binding results correlated with known literature results and statistical analysis was used to clarify the relationship between small molecule structures/RNA based on their binding affinity and selectivity.

As with any fluorescence-based assay, the Tat FID assay possesses inherent limitations. However, it has been shown to be a powerful high throughput technique as a result of its ease of operation, low concentration requirement for both ligand and target, and its ability to rapidly assess small molecule/RNA binding interactions.

To find out more see:

Fluorescent peptide displacement as a general assay for screening small molecule libraries against RNA
Neeraj N. Patwardhan, 
DOI:10.1039/C8OB02467G


Victoria Corless has recently completed her Ph.D. in organic chemistry with Prof. Andrei Yudin at the University of Toronto. Her research is centered on the synthesis of kinetically amphoteric building blocks which offer a versatile platform for the development of chemoselective transformations with particular emphasis on creating novel biologically active molecules. She is passionate about communicating new discoveries to enhance science literacy.

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