Biochemistry of fluoroprolines: the prospect of making fluorine a bioelement

• Vladimir Kubyshkin,
• Rebecca Davis and
• Nediljko Budisa

Beilstein J. Org. Chem. 2021, 17, 439–460, doi:10.3762/bjoc.17.40

• carrying a molecule of GTP, the hydrolysis of which leads to a translocation event in which the empty tRNA leaves and peptidyl-tRNA moves to the P-site. The A-site remains empty, allowing the next ternary complexes to bind in response to the next codon in the mRNA sequence [84]. The translational

Mesoionic tetrazolium-5-aminides: Synthesis, molecular and crystal structures, UV–vis spectra, and DFT calculations

• Vladislav A. Budevich,
• Sergei V. Voitekhovich,
• Alexander V. Zuraev,
• Vadim E. Matulis,
• Vitaly E. Matulis,
• Alexander S. Lyakhov,
• Ludmila S. Ivashkevich and
• Oleg A. Ivashkevich

Beilstein J. Org. Chem. 2021, 17, 385–395, doi:10.3762/bjoc.17.34

• -containing alkylation reagents [27]. Very recently, this aminide was found to be a suitable ligand for manganese complexes [28] and used as the agent for the preparation of salts with high energy density [29]. Also, it is worth noting that today only a few examples of mesoionic tetrazole aminide X-ray

• data and structure refinement details for compounds 8a, 10, 11a, and 9. The lengths of the tetrazole ring and exocyclic C–N bonds (Å) in compounds 8a, 10, and 11a, and in the 1,3-di-tert-butyltetrazolium-5-aminide ligand in manganese complexes [29]. The bond lengths of the tetrazole ring and exocyclic

CF₃-substituted carbocations: underexploited intermediates with great potential in modern synthetic chemistry

• Anthony J. Fernandes,
• Armen Panossian,
• Bastien Michelet,
• Agnès Martin-Mingot,
• Frédéric R. Leroux and
• Sébastien Thibaudeau

Beilstein J. Org. Chem. 2021, 17, 343–378, doi:10.3762/bjoc.17.32

• a longer reaction time, allenes 127 undergo a subsequent intramolecular hydroarylation reaction leading to indenes 128. The authors suggested the formation of FeCl3–HFIP complexes being involved in a Lewis acid-assisted Brønsted acid catalysis. The CF3-substituted propargyl alcohol 129 was found to

¹⁹F NMR as a tool in chemical biology

• Diana Gimenez,
• Aoife Phelan,
• Cormac D. Murphy and
• Steven L. Cobb

Beilstein J. Org. Chem. 2021, 17, 293–318, doi:10.3762/bjoc.17.28

• excellent alternative parameters for the quantitative analysis of site-specific intramolecular distances, with a more particular significant value in the exploration of large proteins and macromolecular complexes where substrate spectral crowding and/or background incompatibility prevents the use of other

• distance restraints for ion channels and other protein complexes that would be difficult to be defined by using other analytical tools. DNA and RNA secondary and tertiary structure 19F NMR spectroscopy also represents a useful analytical approach to study the structure, function and molecular dynamics of

• -based G‐quadruplex complexes with different ligand molecules. This was exemplified by the Xu group who investigated the interaction of a RNA G‐quadruplex and the telomeric protein TRF2 [103] and the interaction of the DNA thrombin binding aptamer (TBA) G-quadruplex with thrombin [100]. Overall, these

Annulation of a 1,3-dithiole ring to a sterically hindered o-quinone core. Novel ditopic redox-active ligands

• Sergey V. Norkov,
• Anton V. Cherkasov,
• Andrey S. Shavyrin,
• Maxim V. Arsenyev,
• Viacheslav A. Kuropatov and
• Vladimir K. Cherkasov

Beilstein J. Org. Chem. 2021, 17, 273–282, doi:10.3762/bjoc.17.26

• coordination ability. The redox state of o-quinone (semiquinone or catechol) could be changed both as free species or when it is coordinated to a metal ion as a ligand. Thus, the redox isomerism phenomenon was reported for o-quinone complexes with both transition and non-transition metals [1][2][3]. The

• . o-Dioxolene redox-active species bearing additional functions are regarded as promising ligands for the synthesis of metallocomplexes exhibiting unusual magnetic, photovoltaic or luminescent properties. Thus, previously reported binuclear rare-earth metal complexes with redox-active triads such as o

• dithiocarboxylates [20][21][22][23]. There are some reports in the literature regarding their application as ligands for the preparation of complexes exhibiting non-linear optical activity as well as possessing extraordinary magnetic properties [24]. The simplest structures that were classified both as gem

The preparation and properties of 1,1-difluorocyclopropane derivatives

• Kymbat S. Adekenova,
• Peter B. Wyatt and
• Sergazy M. Adekenov

Beilstein J. Org. Chem. 2021, 17, 245–272, doi:10.3762/bjoc.17.25

• lengthening and weakening of the C2–C3 bond of the cyclopropane ring appeared to dictate the regioselectivity. Monofluoroalkenes 157 were formed from the reductive ring opening of gem-difluorocyclopropanes 156 with dimethylamine·borane and catalyzed by nickel(II) fluorido complexes (Scheme 67) [117]. 1

• -valent transition metals such as Pd(0) also have a valuable catalytic role, particularly because of their ability to participate in oxidative addition reactions and to form π-allyl complexes. In the absence of nucleophiles, homolysis of the distal C–C bond takes place under the effect of high temperature

Au(III) complexes with tetradentate-cyclam-based ligands

• Ann Christin Reiersølmoen,
• Thomas N. Solvi and
• Anne Fiksdahl

Beilstein J. Org. Chem. 2021, 17, 186–192, doi:10.3762/bjoc.17.18

• –59%) by a final optimized hydride reduction. Both the open tetraamine intermediates and the cyclam derivatives successfully coordinated with AuCl3 to give moderate to excellent yields (50–96%) of the corresponding novel tetra-coordinated N,N,N,N-Au(III) complexes with alternating five- and six

• -membered chelate rings. The testing of the catalytic ability of the cyclam-based N,N,N,N-Au(III) complexes demonstrated high catalytic activity of some complexes in selected test reactions (full conversion in 1–24 h, 62–97% product yields). Keywords: Au(III); carboalkoxylation; coordination studies

• catalytic active forms of gold, gold(I) has so far, received main attention, likely due to the higher stability, as demonstrated by the development of a high number of gold(I)-catalyzed transformations and ligated gold(I) complexes, along with improved mechanistic understanding [9][10][11][12][13][14][15

Insight into functionalized-macrocycles-guided supramolecular photocatalysis

• Minzan Zuo,
• Krishnasamy Velmurugan,
• Kaiya Wang,
• Xueqi Tian and
• Xiao-Yu Hu

Beilstein J. Org. Chem. 2021, 17, 139–155, doi:10.3762/bjoc.17.15

• complexes (1:1, 2:1, 1:2, and 2:2). For the 1:1, 2:1, and 1:2 host–guest complexes, the thermodynamic association (Ka) and dissociation constants (Kd) for the reactive guests and photoproducts are crucial for the fundamental understanding of supramolecular noncovalent interactions [12][13]. In addition

• cation, forming complexes. Crown ethers also contain a series of derivatives, such as aza-crowns, where the ether oxygen atoms are replaced by amino groups. A well-known tetrazacrown is cyclen. Due to the excellent host–guest properties of crown ethers, they play a very important role in the construction

• the outside possesses the polyhydroxy structure. This unique asymmetric barrel-shaped cavity allows them to combine with various guests. The driving forces for the formation of cyclodextrin-based supramolecular complexes are hydrophobic and van der Waals interactions between the cavity and the

Tuning the solid-state emission of liquid crystalline nitro-cyanostilbene by halogen bonding

• Subrata Nath,
• Alexander Kappelt,
• Matthias Spengler,
• Bibhisan Roy,
• Jens Voskuhl and
• Michael Giese

Beilstein J. Org. Chem. 2021, 17, 124–131, doi:10.3762/bjoc.17.13

• groups employed halogen bonding for the formation of liquid crystalline materials [8][9]. For instance, Palacio et al. used (E)-1-(4-(octyloxy)phenyl)-2-(2,3,5,6-tetrafluoro-4-iodophenyl)diazene as a photo-switchable halogen bond donor and investigated the light-induced phase transition of the complexes

• and S15). In our initial set of assemblies, we combined F4St with NO2-Cn with varying alkoxy-chain lengths (n = 8, 9, 10 and 11). The halogen-bonded assemblies exhibited mesogenic behaviour starting with an alkoxy chain length of n = 8. POM investigations revealed nematic mesophases for all complexes

• -induced emission properties were combined with alkoxystilbazoles to form hydrogen-bonded mesogens. Since NO2-Cn is known to be fluorescent, we were curious how the formation of the halogen-bonded complexes affects the AIE behaviour of NO2-Cn. Therefore, we studied the photophysical properties of 1:1

Direct synthesis of anomeric tetrazolyl iminosugars from sugar-derived lactams

• Michał M. Więcław and
• Bartłomiej Furman

Beilstein J. Org. Chem. 2021, 17, 115–123, doi:10.3762/bjoc.17.12

• Charette et al. In their procedure the combination of triflic anhydride and pyridine [6] (or its 2-fluoro derivative [7]) was used as an activating agent to transform amides into reactive iminium complexes. Another stoichiometric approach was presented by Georg et al. by utilization of zirconocene chloride

• formamides [11] and reduction of isothiocyanates to thioformamides [12] by its means. There have also been some catalytic protocols developed for the reduction of amides to imines. The most notable examples incorporate iridium complexes and silanes [13][14]. Cheng and Brookhart showed that the chlorobis

Molecular basis for protein–protein interactions

• Brandon Charles Seychell and
• Tobias Beck

Beilstein J. Org. Chem. 2021, 17, 1–10, doi:10.3762/bjoc.17.1

• design. Protein–protein interactions and their discovery are thus an interesting avenue for understanding how protein complexes, which make up the majority of proteins, work. Keywords: characterisation methods; heterooligomeric complex; homooligomeric complex; molecular interactions; protein–protein

• functionality and the corresponding pathways. Important roles of PPIs include hormone reception [2], protease inhibition [3], antibody–antigen complexes [4], gene regulation [5], and large biomolecular assemblies [6]. PPI identification and prediction are important for targeting anticancer strategies [7

• –protein complex formation. Finally, we will give a brief account of some examples for higher-order protein complexes and the PPIs involved. Review Characterisation methods for PPIs Particular PPIs can be relatively difficult to study since in vivo, any particular protein is present amongst a plethora of

Silver-catalyzed synthesis of β-fluorovinylphosphonates by phosphonofluorination of aromatic alkynes

• Yajing Zhang,
• Qingshan Tian,
• Guozhu Zhang and
• Dayong Zhang

Beilstein J. Org. Chem. 2020, 16, 3086–3092, doi:10.3762/bjoc.16.258

• -fluorovinylphosphonates under mild conditions. First, we examined the catalytic activity of various transition metal catalysts, including Au, Ag, Cu, Rh, and Pd complexes (Supporting Information File 1). Among these metal salts, silver salts, especially AgOAc, were the most effective catalysts for generating the desired

Amine–borane complex-initiated SF₅Cl radical addition on alkenes and alkynes

• Audrey Gilbert,
• Pauline Langowski,
• Marine Delgado,
• Laurent Chabaud,
• Mathieu Pucheault and
• Jean-François Paquin

Beilstein J. Org. Chem. 2020, 16, 3069–3077, doi:10.3762/bjoc.16.256

• freshly prepared [37]. It is therefore of interest to address this challenge in order to widen the scope of this transformation. Compared to trialkylboranes, amine–borane complexes have shown to be more stable [38]. Indeed, they are usually air-stable, and their preparation from NaBH4, H2SO4 and amines

• involves traditional mild acidic work-up without degradation. They are therefore much easier to handle on a laboratory scale and can be stored on the shelf for months without noticeable alteration of their properties and purity [39]. Amine–borane complexes have been extensively used in the literature as

• recently, it has been shown that some of these common amine–borane complexes can also be used as radical initiators for atom transfer radical addition of alkyl halides to alkenes [48]. They were also used in the free-radical polymerization of alkene-containing monomers such as methyl methacrylate or

Pentannulation of N-heterocycles by a tandem gold-catalyzed [3,3]-rearrangement/Nazarov reaction of propargyl ester derivatives: a computational study on the crucial role of the nitrogen atom

• Giovanna Zanella,
• Martina Petrović,
• Dina Scarpi,
• Ernesto G. Occhiato and
• Enrique Gómez-Bengoa

Beilstein J. Org. Chem. 2020, 16, 3059–3068, doi:10.3762/bjoc.16.255

• of the accuracy of the computational method we have used for the comparison of the isomeric complexes I and V. Our previous experience in this area taught us that seven-membered azepane-derived enynyl acetates react faster than the corresponding piperidine analogues 1, prompting us to prepare enynyl

Chiral anion recognition using calix[4]arene-based ureido receptors in a 1,3-alternate conformation

• Tereza Horáčková,
• Jan Budka,
• Vaclav Eigner,
• Wen-Sheng Chung,
• Petra Cuřínová and
• Pavel Lhoták

Beilstein J. Org. Chem. 2020, 16, 2999–3007, doi:10.3762/bjoc.16.249

• isotherms obtained from the complexation-induced chemical shift (CIS) values of urea NH protons or aromatic CH signals (Figure 5) [50][51][52]. The nonlinear curve-fitting of the experimental data was performed using the freely available software Bindfit [53]. The stoichiometry of the complexes was

Secondary metabolites of Bacillus subtilis impact the assembly of soil-derived semisynthetic bacterial communities

• Heiko T. Kiesewalter,
• Carlos N. Lozano-Andrade,
• Mikael L. Strube and
• Ákos T. Kovács

Beilstein J. Org. Chem. 2020, 16, 2983–2998, doi:10.3762/bjoc.16.248

• Bacillus spp. produce various SMs [33][34]. The most prominent and bioactive SMs are nonribosomal peptides (NRPs), of which isoforms belong to the families of surfactins, fengycins, or iturins [35][36] (Figure 1). They are biosynthesised by large enzyme complexes, nonribosomal peptide synthetases (NRPSs

Regioselective synthesis of heterocyclic N-sulfonyl amidines from heteroaromatic thioamides and sulfonyl azides

• Vladimir Ilkin,
• Vera Berseneva,
• Tetyana Beryozkina,
• Tatiana Glukhareva,
• Lidia Dianova,
• Wim Dehaen,
• Eugenia Seliverstova and
• Vasiliy Bakulev

Beilstein J. Org. Chem. 2020, 16, 2937–2947, doi:10.3762/bjoc.16.243

• synthesis of complexes of bis(sulfonyl amidines) 3aj–an with metals is in progress. 1H and 13C NMR spectra including 2D HMBC and HSQC experiments of compounds 3a–an, as well as high-resolution mass spectra are consistent with the proposed structures. Carbon signals of the amidine groups of compounds 3

Using multiple self-sorting for switching functions in discrete multicomponent systems

• Amit Ghosh and
• Michael Schmittel

Beilstein J. Org. Chem. 2020, 16, 2831–2853, doi:10.3762/bjoc.16.233

• ), cucurbit[7]uril (3), and the two chalcones 1 and 2 in aqueous solution [48]. When the hosts 3 and 4 were mixed with the trans-chalcones 1 and 2 as guests in a 1:1:1:1 ratio, instantly a statistical mixture formed displaying all four possible host–guest complexes. After the exposure to an acid, the ensuing

• rearrangement after the protonation of 1 and 2 furnished exclusively the two complexes [(1•H+)(3)] and [(2•H+)(4)] (Figure 3). The reduced affinity of the cucurbit[7]uril toward the protonated diethylamino-substituted guest in combination with the concomitant increased binding for the dimethylammonium

• . Interestingly, the fullerene C60 was not taken up as a guest by the tetramer (6)4 in chlorinated solvents. For a more defined self-sorting, the authors switched the solvent from CDCl3 to [d8]-toluene. Now, a 2-fold completive self-sorting delivered the homoleptic inclusion complexes [(5)4(C60)] and [(6)4(C60

Synthesis and investigation of quadruplex-DNA-binding, 9-O-substituted berberine derivatives

• Jonas Becher,
• Daria V. Berdnikova,
• Heiko Ihmels and
• Christopher Stremmel

Beilstein J. Org. Chem. 2020, 16, 2795–2806, doi:10.3762/bjoc.16.230

• examined with photometric and fluorimetric titrations, thermal DNA denaturation analysis, and CD spectroscopy. The results from the spectrometric titrations indicated the formation of 2:1 or 1:1 complexes (ligand:G4-DNA) with log Kb values of 10–11 (2:1) and 5–6 (1:1), which are typical for berberine

• determine the binding constants, Kb, of 4a–e with G4-DNA 22AG and a2 (cf. Supporting Information File 1). As a general trend, the experimental data could be adequately fitted to a binding stoichiometry ligand/G4-DNA of 2:1 or 1:1. Except for compound 4a, all ligands formed 2:1 complexes with 22AG and a2

• . The complexes of ligands 4b–e with 22AG have essentially the same log Kb values at 10.7–10.8 (Kb in M−2), whereas the log Kb values of ligands 4a–e with a2 increase slightly in the 2:1 complexes from 10.3 to 11.1 with increasing chain length n (Table 1). At the same time, 1:1 complexes were found for

Ring-closing metathesis of prochiral oxaenediynes to racemic 4-alkenyl-2-alkynyl-3,6-dihydro-2H-pyrans

• Viola Kolaříková,
• Markéta Rybáčková,
• Martin Svoboda and
• Jaroslav Kvíčala

Beilstein J. Org. Chem. 2020, 16, 2757–2768, doi:10.3762/bjoc.16.226

• metathesis or enantioselective RCEYM reactions catalyzed by ruthenium complexes are known (Scheme 3). The only RCEYM of a system containing two triple and one double bonds has been described by Gouverneur et al., who synthesized a series of dihydrooxaphosphinines by the diastereoselective metathesis of

• conditions) [22][23][37] are the major factors influencing the success of the RCEYM. As precatalysts, we chose the Grubbs 1st and 2nd generation (G-I and G-II), as well as the more stable Hoveyda–Grubbs 2nd generation (HG-II) complexes (Figure 2). Room temperature (25 °C) was chosen as it is common for this

• ). The search for the saddle points (starting complexes of both unsaturated compounds 12b and 13, transition states 15A–D and the corresponding Diels–Alder products 14A–D (Figure 4)) showed that the reaction is strongly exergonic and irreversible with an activation free Gibbs energy in the range between

Selective recognition of ATP by multivalent nano-assemblies of bisimidazolium amphiphiles through “turn-on” fluorescence response

• Rakesh Biswas,
• Surya Ghosh,
• Shubhra Kanti Bhaumik and
• Supratim Banerjee

Beilstein J. Org. Chem. 2020, 16, 2728–2738, doi:10.3762/bjoc.16.223

• involved in a number of essential biological functions including active transport and cell division [28][29]. For ATP detection, metal complexes using metal ions such as Zn(II), Cu(II) and lanthanide ions have been frequently employed [30][31][32][33][34][35]. A variety of other systems such as aptamers

• stacking interactions with the nucleobases which contributes to the stability of the complexes. In many cases, these stacking interactions provide binding selectivity among the nucleotides [53][54][55][56]. Most of the aforementioned receptors were predominantly “molecular” in nature with the binding of

Enzyme-instructed morphological transition of the supramolecular assemblies of branched peptides

• Dongsik Yang,
• Hongjian He and
• Bing Xu

Beilstein J. Org. Chem. 2020, 16, 2709–2718, doi:10.3762/bjoc.16.221

• noncovalent synthesis [41][42] in a cellular environment. Results and Discussion Molecular design We designed the branched peptides including the DEXXXLLI sequences [43] for this study. The DEXXXLLI (X is any amino acid) sequences are sorting signals of adaptor protein (AP) complexes, which play a critical

A heterobimetallic tetrahedron from a linear platinum(II)-bis(acetylide) metalloligand

• Matthias Hardy,
• Marianne Engeser and
• Arne Lützen

Beilstein J. Org. Chem. 2020, 16, 2701–2708, doi:10.3762/bjoc.16.220

• diastereomers. The new complexes were characterized by NMR and UV–vis spectroscopy and ESI mass spectrometry. Using GFN2-xTB we generated energy-minimized models of the diastereomers of this cage that further corroborated the results from analytical findings. Keywords: cage compounds; heterobimetallic

• complexes; pyridylimine ligands; self-assembly; supramolecular chemistry; Introduction The understanding of the general design principles for the self-assembly of metallosupramolecular aggregates [1][2][3][4][5] allowed to access more and more complex and large assemblies over the past decades like

• platinum(II) ions to be especially suitable to prepare a linear metalloligand due to their highly predictable square-planar coordination environment that can easily be employed to access tetravalent planar or divalent V-shaped cis- or linear trans-configurated complexes [43][44][45]. In this context

Optical detection of di- and triphosphate anions with mixed monolayer-protected gold nanoparticles containing zinc(II)–dipicolylamine complexes

• Lena Reinke,
• Julia Bartl,
• Marcus Koch and
• Stefan Kubik

Beilstein J. Org. Chem. 2020, 16, 2687–2700, doi:10.3762/bjoc.16.219

• /bjoc.16.219 Abstract Gold nanoparticles covered with a mixture of ligands of which one type contains solubilizing triethylene glycol residues and the other peripheral zinc(II)–dipicolylamine (DPA) complexes allowed the optical detection of hydrogenphosphate, diphosphate, and triphosphate anions in

• )–dipicolylamine complexes beyond 25% had a negative impact on the limit of detection and the optical response. Transmission electron microscopy provided evidence that the changes of the nanoparticle properties observed in the presence of the phosphates were due to a nanoparticle crosslinking, consistent with the

• preferred binding mode of zinc(II)–dipicolylamine complexes with phosphate anions which involves binding of the anion between two metal centers. This work thus provided information on how the behavior of mixed monolayer-protected gold nanoparticles is affected by multivalent interactions, at the same time

Vicinal difluorination as a C=C surrogate: an analog of piperine with enhanced solubility, photostability, and acetylcholinesterase inhibitory activity

• Yuvixza Lizarme-Salas,
• Alexandra Daryl Ariawan,
• Ranjala Ratnayake,
• Hendrik Luesch,
• Angela Finch and
• Luke Hunter

Beilstein J. Org. Chem. 2020, 16, 2663–2670, doi:10.3762/bjoc.16.216

• geometry of 2 might be favoured in AChE but not in BACE-1. These possibilities all remain speculative in the absence of high-resolution structural data of the enzyme–ligand complexes. Conclusion A threo-difluorinated piperine analog (2) was successfully synthesised through a stepwise route. The