Computational tools for drawing, building and displaying carbohydrates: a visual guide

• Kanhaya Lal,
• Rafael Bermeo and
• Serge Perez

Beilstein J. Org. Chem. 2020, 16, 2448–2468, doi:10.3762/bjoc.16.199

• , Ser or Thr, then structure building is limited by to a set of “rules” (limiting building options to known carbohydrates). These rules may be deactivated with a switch button to draw freely. A list of 13 monosaccharides is deployed, and sequential clicking allows their addition to the existing

• structure and definition of the associated glycosidic bond (the relative sizes of the options available related to their real statistical value for that particular linkage). Upon building some specific motifs, if they are recognised, an option for repeating units appears. Other switch buttons allow the user

Hierarchically assembled helicates as reaction platform – from stoichiometric Diels–Alder reactions to enamine catalysis

• David Van Craen,
• Jenny Begall,
• Johannes Großkurth,
• Leonard Himmel,
• Oliver Linnenberg,
• Elisabeth Isaak and
• Markus Albrecht

Beilstein J. Org. Chem. 2020, 16, 2338–2345, doi:10.3762/bjoc.16.195

• compared to Li[Li3(5)6Ti2] [35][36]. Thus, the higher amount of undesired monomer in solution of Li[Li3(1)3(6)3Ti2] resulted in a partial switch-off of the stereoselectivity. Screening of the dienophile The variation of the dienophile was studied in chloroform using the helicate Li4[(1)3(4)3Ti2]. N

• systems possessing catalytic activity with improved solubility. Formation of hierarchically assembled lithium-bridged titanium(IV) helicates as well as the ligands used for the stereoselective Diels–Alder reaction. Previously reported on/off switch for “remote-controlled” [23][24][25][26][27][28][29][30

Azo-dimethylaminopyridine-functionalized Ni(II)-porphyrin as a photoswitchable nucleophilic catalyst

• Jannis Ludwig,
• Julian Helberg,
• Hendrik Zipse and
• Rainer Herges

Beilstein J. Org. Chem. 2020, 16, 2119–2126, doi:10.3762/bjoc.16.179

• + ion. Light of 435 nm (violet) isomerizes the ligand back to the trans configuration, which decoordinates for steric reasons. This so-called record player design has been used previously to switch the spin state of Ni2+ between singlet and triplet. We now use the coordination/decoordination process to

• switch the catalytic activity of the dimethylaminopyridine (DMAP) unit. DMAP is a known catalyst in the nitroaldol (Henry) reaction. Upon coordination to the Ni2+ ion, the basicity of the pyridine lone pair is attenuated and hence the catalytic activity is reduced. Decoordination restores the catalytic

• activity. The rate constants in the two switching states differ by a factor of 2.2, and the catalytic switching is reversible. Keywords: catalysis; Ni(II)-porphyrins; nucleophilic catalyst; photoswitch; record player molecules; spin switch; Introduction Photoswitchable catalysis has been realized

Design, synthesis and application of carbazole macrocycles in anion sensors

• Alo Rüütel,
• Ville Yrjänä,
• Sandip A. Kadam,
• Indrek Saar,
• Mihkel Ilisson,
• Astrid Darnell,
• Kristjan Haav,
• Tõiv Haljasorg,
• Lauri Toom,
• Johan Bobacka and
• Ivo Leito

Beilstein J. Org. Chem. 2020, 16, 1901–1914, doi:10.3762/bjoc.16.157

• possibility was investigated after the production of the first macrocycles bearing tert-butyl substituents, we decided to not switch substituents. The formation of macrocycles from 8 was achieved following two different synthetic strategies. For receptors MC003–MC010, amide bond formation was carried out

Pauson–Khand reaction of fluorinated compounds

• Jorge Escorihuela,
• Daniel M. Sedgwick,
• Alberto Llobat,
• Mercedes Medio-Simón,
• Pablo Barrio and
• Santos Fustero

Beilstein J. Org. Chem. 2020, 16, 1662–1682, doi:10.3762/bjoc.16.138

• the regiochemistry for terminal alkynes, affording the products substituted at the β-position. This regiochemistry switch might be regarded as the Holy Grail in Pauson–Khand chemistry. The synthetic potential of this methodology was demonstrated by the formal total synthesis of α-cuparenone [74][75

Models of necessity

• Timothy Clark and
• Martin G. Hicks

Beilstein J. Org. Chem. 2020, 16, 1649–1661, doi:10.3762/bjoc.16.137

• it is necessary to switch to the molecular-orbital picture to treat, for instance, the Woodward–Hoffmann rules [29]. Similarly, an extended version of the Lewis model exists alongside the molecular-orbital picture in inorganic chemistry. Is this not a solution to the problems described above

• ontologies [11] or personal paradigms [76] of chemists are assembled from available models and switch happily between them. Consider, for instance, the alternative Woodward–Hoffmann [29] and Dewar–Zimmerman [80][81] rules for electrocyclic reactions. They can be used interchangeably and both give correct

• chemist who uses predominantly the Lewis bonding picture or an inorganic chemist rooted in the VSEPR model switch quite happily to qualitative molecular-orbital arguments to explain electrocyclic reactions or the structure of ferrocene, even in teaching. In contrast, cheminformatics will need to adopt a

Development of fluorinated benzils and bisbenzils as room-temperature phosphorescent molecules

• Shigeyuki Yamada,
• Takuya Higashida,
• Yizhou Wang,
• Masato Morita,
• Takuya Hosokai,
• Kaveendra Maduwantha,
• Kaveenga Rasika Koswattage and
• Tsutomu Konno

Beilstein J. Org. Chem. 2020, 16, 1154–1162, doi:10.3762/bjoc.16.102

• deactivation process from the lowest singlet (S1) excited state to the ground (S0) state [9]. Interestingly, for such π-conjugated molecules, suitable structural modifications can switch the radiative S1→S0 process to another radiative deactivation process from the triplet (T1) excited state to S0 via an S1→T1

Recent advances in Cu-catalyzed C(sp³)–Si and C(sp³)–B bond formation

• Balaram S. Takale,
• Ruchita R. Thakore,
• Elham Etemadi-Davan and
• Bruce H. Lipshutz

Beilstein J. Org. Chem. 2020, 16, 691–737, doi:10.3762/bjoc.16.67

• excellent E:Z ratios within the resulting alkenes. This methodology could be applied to a wide variety of compounds, including those containing heterocycles (176–178). In a later study [67], they found that by changing ligands, a dramatic switch in the selectivity could be induced in silyl additions to

Potent hemithioindigo-based antimitotics photocontrol the microtubule cytoskeleton in cellulo

• Alexander Sailer,
• Franziska Ermer,
• Yvonne Kraus,
• Rebekkah Bingham,
• Ferdinand H. Lutter,
• Julia Ahlfeld and
• Oliver Thorn-Seshold

Beilstein J. Org. Chem. 2020, 16, 125–134, doi:10.3762/bjoc.16.14

• colchicine per se, aiming at compounds where one isomer would be almost biologically inactive such that light can be used to effect a photoisomerisation-based switch-on/switch-off of bioactivity. The end-to-end distance of the HTI scaffold is significantly longer than that in either the biaryl colchicine or

Reversible photoswitching of the DNA-binding properties of styrylquinolizinium derivatives through photochromic [2 + 2] cycloaddition and cycloreversion

• Sarah Kölsch,
• Heiko Ihmels,
• Jochen Mattay,
• Norbert Sewald and
• Brian O. Patrick

Beilstein J. Org. Chem. 2020, 16, 111–124, doi:10.3762/bjoc.16.13

• the intercalating monomers upon irradiation at 315 nm in the presence of DNA. As a result, it is possible to switch between these two ligands and likewise between two different binding modes by irradiation with different excitation wavelengths. Keywords: azoniahetarenes; DNA ligands

• intrinsic toxicity of the employed drugs [11][12][13]. As a result, there is an urgent need for DNA-targeting chemotherapeutic reagents that can be activated with an external stimulus only at the desired point of action. In this context, light offers several distinct advantages to switch on the activity of

• an otherwise inactive substrate (prodrug) because light is noninvasive, traceless, and easy to apply, and it enables local and temporal control [14]. To this end, photochromic systems appear to be highly attractive as a basis for photocontrollable substrates because they allow to switch the

Photocontrolled DNA minor groove interactions of imidazole/pyrrole polyamides

• Sabrina Müller,
• Jannik Paulus,
• Jochen Mattay,
• Heiko Ihmels,
• Veronica I. Dodero and
• Norbert Sewald

Beilstein J. Org. Chem. 2020, 16, 60–70, doi:10.3762/bjoc.16.8

• (Py/Im) and TA (Hp/Py). However, N-methylhydroxypyrrole (Hp) is neither easy to synthesize nor sufficiently stable. In practice, therefore, Py/Py is used to address both AT and TA. Along this line, it is attractive to incorporate a molecular switch for the selective activation of an initially inactive

• switch in binding activity [29][30]. Importantly, it was demonstrated that the DNA binding was highly dependent on the linker length between the azobenzene and the distamycin moiety. Results and Discussion Here, we report on the design, synthesis, and characterization of photoswitchable minor groove

Light-controllable dithienylethene-modified cyclic peptides: photoswitching the in vivo toxicity in zebrafish embryos

• Sergii Afonin,
• Oleg Babii,
• Aline Reuter,
• Volker Middel,
• Masanari Takamiya,
• Uwe Strähle,
• Igor V. Komarov and
• Anne S. Ulrich

Beilstein J. Org. Chem. 2020, 16, 39–49, doi:10.3762/bjoc.16.6

• ) was recorded, and then in situ illumination (“photoactivation”) was applied to switch into the ring-open photoform and obtain the respective LD50(opened) values (see Figure 2 for the study design and the killing curves). Each time, 12–15 or 18–20 zebrafish embryos at 3 dpf were treated by applying the

Photoreversible stretching of a BAPTA chelator marshalling Ca²⁺-binding in aqueous media

• Aurélien Ducrot,
• Arnaud Tron,
• Robin Bofinger,
• Ingrid Sanz Beguer,
• Jean-Luc Pozzo and
• Nathan D. McClenaghan

Beilstein J. Org. Chem. 2019, 15, 2801–2811, doi:10.3762/bjoc.15.273

• ions and switch between complexes of different molecularity, albeit largely in organic solvents [32]. Azobenzene is generally considered relatively resistant to fatigue and has been employed to evoke changes in different biological systems, including ion channels based on changes of properties between

A combinatorial approach to improving the performance of azoarene photoswitches

• Joaquin Calbo,
• Aditya R. Thawani,
• Rosina S. L. Gibson,
• Andrew J. P. White and
• Matthew J. Fuchter

Beilstein J. Org. Chem. 2019, 15, 2753–2764, doi:10.3762/bjoc.15.266

• azoarenes have been ortho-substitution of the benzene ring(s) or replacement of one of the benzenes for a pyrazole (to give arylazopyrazole switches). Here we study the combination of such high-performance features within a single switch architecture. Through computational analysis and experimental

• demonstrate slow thermal Z–E relaxation and the potential to switch with red light, while the o-fluoro compounds reported by Hecht and co-workers [13][14] offer excellent two-way isomerization with visible light and the longest thermal half-life reported for an azobenzene molecule (≈700 days at 25 °C) to date

• that it is indeed possible to combinatorially integrate two high performing azo switch fragments to discover switches with very long thermal half-lives (i.e., months to years). We sought to further explain the trends observed through theoretical analysis of the minimum-energy geometries and noncovalent

A toolbox of molecular photoswitches to modulate the CXCR3 chemokine receptor with light

• Xavier Gómez-Santacana,
• Sabrina M. de Munnik,
• Tamara A. M. Mocking,
• Niels J. Hauwert,
• Shanliang Sun,
• Prashanna Vijayachandran,
• Iwan J. P. de Esch,
• Henry F. Vischer,
• Maikel Wijtmans and
• Rob Leurs

Beilstein J. Org. Chem. 2019, 15, 2509–2523, doi:10.3762/bjoc.15.244

• the para-position of the central ring. A variety of efficacy differences between the trans and cis forms emerges from these compounds. Tool compounds VUF15888 (4d) and VUF16620 (6e) represent more subtle efficacy switches, while VUF16216 (6f) displays the largest efficacy switch, from antagonism to

• , exemplified by partial agonist 1c and equal full agonists 1d and 1e (VUF11418, Figure 2A). A tentative explanation for this efficacy switch includes a variation of the dihedral angle of the biaryl moiety, an increase of the electron density in the biaryl unit and/or a postulated halogen bond of the halogen

Experimental and computational electrochemistry of quinazolinespirohexadienone molecular switches – differential electrochromic vs photochromic behavior

• Eric W. Webb,
• Jonathan P. Moerdyk,
• Kyndra B. Sluiter,
• Benjamin J. Pollock,
• Amy L. Speelman,
• Eugene J. Lynch,
• William F. Polik and
• Jason G. Gillmore

Beilstein J. Org. Chem. 2019, 15, 2473–2485, doi:10.3762/bjoc.15.240

• anion rather than a photoexcited state. The reduction of the molecular switch necessary for electrochromism is in a sense catalytic: the rearranged product is reoxidized to a neutral LW isomer, which reverts thermally to SW upon standing, just as it does when the LW is generated photochemically. The

Ultrafast processes triggered by one- and two-photon excitation of a photochromic and luminescent hydrazone

• Alessandro Iagatti,
• Baihao Shao,
• Alberto Credi,
• Barbara Ventura,
• Ivan Aprahamian and
• Mariangela Di Donato

Beilstein J. Org. Chem. 2019, 15, 2438–2446, doi:10.3762/bjoc.15.236

• absorption cross-section of the molecule. Keywords: hydrazone; molecular switch; pump-probe spectroscopy; time-resolved fluorescence; Introduction Molecular switches are systems that are able to rapidly respond to an external stimulus, which can be of chemical or physical nature, through a variation of

Effect of ring size on photoisomerization properties of stiff stilbene macrocycles

• Sandra Olsson,
• Óscar Benito Pérez,
• Magnus Blom and
• Adolf Gogoll

Beilstein J. Org. Chem. 2019, 15, 2408–2418, doi:10.3762/bjoc.15.233

• the resulting macrocycle. Keywords: DFT; molecular mechanics; photostability; photo-switch; ring-strain; stiff stilbene; Introduction The stiff stilbene (SS) molecule has drawn a lot of interest due to its photodynamic properties [1]. Stiff stilbenes typically undergo light triggered isomerization

Reversible switching of arylazopyrazole within a metal–organic cage

• Anton I. Hanopolskyi,
• Soumen De,
• Michał J. Białek,
• Yael Diskin-Posner,
• Liat Avram,
• Moran Feller and
• Rafal Klajn

Beilstein J. Org. Chem. 2019, 15, 2398–2407, doi:10.3762/bjoc.15.232

• photochromism in the spiropyran switch [18]. Other recent studies of photochromic systems within macrocyclic and supramolecular hosts [19] include dihydroazulene switches [20] and red-shifted azobenzenes [21][22] inside cucurbiturils and cyclodextrins. The behavior of light-responsive compounds can also be

Aggregation-induced emission effect on turn-off fluorescent switching of a photochromic diarylethene

• Luna Kono,
• Yuma Nakagawa,
• Ayako Fujimoto,
• Ryo Nishimura,
• Yohei Hattori,
• Toshiki Mutai,
• Nobuhiro Yasuda,
• Kenichi Koizumi,
• Satoshi Yokojima,
• Shinichiro Nakamura and
• Kingo Uchida

Beilstein J. Org. Chem. 2019, 15, 2204–2212, doi:10.3762/bjoc.15.217

• turn-off type fluorescent switch (Figure 6c and Figure 7e) [29][30]. The emission from the aggregates quenched much faster than the solution (Figure 6c) (Supporting Information File 2, Movie 1). This is due to a “giant amplification of fluorescence photoswitching” ascribed by a very efficient

Norbornadiene-functionalized triazatriangulenium and trioxatriangulenium platforms

• Roland Löw,
• Talina Rusch,
• Tobias Moje,
• Fynn Röhricht,
• Olaf M. Magnussen and
• Rainer Herges

Beilstein J. Org. Chem. 2019, 15, 1815–1821, doi:10.3762/bjoc.15.175

• are possible to account for the presence of these two species: Either they correspond to a mixture of adsorbed NBD-TATA 1a and QC-TATAs 1b or to coadsorption of 1a and the pure octyl-TATA 6. The first case may be possible, because the molecules are able to switch to the 1b state at a wavelength of 385

Design, synthesis and biological evaluation of immunostimulating mannosylated desmuramyl peptides

• Rosana Ribić,
• Ranko Stojković,
• Lidija Milković,
• Mariastefania Antica,
• Marko Cigler and
• Srđanka Tomić

Beilstein J. Org. Chem. 2019, 15, 1805–1814, doi:10.3762/bjoc.15.174

• affect the Th1/Th2 switch of the immune response [52]. The presented results demonstrate the great immunostimulating potential of glycolyl-modified desmuramyl peptides. Peptidoglycan fragments with mycobacterial structural features, such as synthesized compounds 20–22, could efficiently link innate and

An azobenzene container showing a definite folding – synthesis and structural investigation

• Abdulselam Adam,
• Saber Mehrparvar and
• Gebhard Haberhauer

Beilstein J. Org. Chem. 2019, 15, 1534–1544, doi:10.3762/bjoc.15.156

• the high dispersion energy in the compact cis,cis-isomer. Keywords: azobenzene; macrocycles; molecular switch; Introduction In supramolecular chemistry rigid scaffolds are required to arrange different recognition units in predefined distances and spatial orientation to each other [1]. One example

• coefficient of the compound. To examine this, DOSY spectra of the container 10 after synthesis and after irradiation with light of the wavelength λ = 365 nm were recorded (Figure 8). Please note, that a change in the geometry of a switch need not result in a change of the size of the diffusion coefficient

Diazocine-functionalized TATA platforms

• Roland Löw,
• Talina Rusch,
• Fynn Röhricht,
• Olaf Magnussen and
• Rainer Herges

Beilstein J. Org. Chem. 2019, 15, 1485–1490, doi:10.3762/bjoc.15.150

• gold. To investigate this mechanism further and to examine scope and limitation of the “spin-switch catalysis” we now prepared analogous diazocine systems. Diazocines, in contrast to azobenzenes, are stable in the cis-configuration. Upon irradiation with light of 405 nm the cis-configuration isomerizes

• ordered monolayers on Au(111) surfaces. Keywords: cis–trans isomerization; diazocine; molecular switch; photochrome; self-assembled monolayers; TATA platform; Introduction Catalysts increase chemical reaction rates by lowering the activation energies and thus create more favorable reaction pathways [1

Complexation of a guanidinium-modified calixarene with diverse dyes and investigation of the corresponding photophysical response

• Yu-Ying Wang,
• Yong Kong,
• Zhe Zheng,
• Wen-Chao Geng,
• Zi-Yi Zhao,
• Hongwei Sun and
• Dong-Sheng Guo

Beilstein J. Org. Chem. 2019, 15, 1394–1406, doi:10.3762/bjoc.15.139

• accompanied by a drastic quenching of fluorescence, which is a proper feature to be applied in IDA, product-selective STA and BDA, resulting in a desired switch-on sensing (Scheme 1) or activatable phototheranostics. With respect to the sensing application, the reporter pairs can be used in very dilute

• naphthalenesulfonic acids generally shows large binding affinities and a prominent fluorescence enhancement. Differing from the complexation-induced quenching of ACQ dyes, the fluorescence enhancement of ICT dyes upon complexation with GC5A would benefit for substrate-selective STA, realizing the desired switch-on

• typical difference from ICT dyes [56]. The extraordinary fluorescence enhancement of P-TPE upon complexation with GC5A (Ibound/Ifree = 42) would be beneficial for substrate-selective STA, realizing the desired switch-on sensing (Scheme 1). The complexation between calixarenes and AIEgens also offers the