Valorisation of plastic waste via metal-catalysed depolymerisation

• Francesca Liguori,
• Carmen Moreno-Marrodán and
• Pierluigi Barbaro

Beilstein J. Org. Chem. 2021, 17, 589–621, doi:10.3762/bjoc.17.53

• conditions, showing the best combination to be 196 °C, an EG/PET ratio of 2.45:1 (w/w) and a catalyst loading of 0.3 wt % (Table 2, entry 2) [129]. Under these conditions, an equilibrium yield of BHET around 65% was achieved within short reaction times (1 h), much faster than in the absence of catalysts or

Synthesis of (Z)-3-[amino(phenyl)methylidene]-1,3-dihydro-2H-indol-2-ones using an Eschenmoser coupling reaction

• Lukáš Marek,
• Lukáš Kolman,
• Jiří Váňa,
• Jan Svoboda and
• Jiří Hanusek

Beilstein J. Org. Chem. 2021, 17, 527–539, doi:10.3762/bjoc.17.47

• derivatives 9a–e. The substituent R4 strongly influences both the equilibrium between >C=N+HR4 and >C=NR4 as well as the nucleophilic attack of the internal C3 carbanion to give the thiirane intermediate in Scheme 2. While the EWG groups decrease the concentration of the α-thioiminium salt (that is much more

• the equilibrium concentration) of the intermediary α-thioiminium salt which is much more reactive towards an internal nucleophilic attack than the free thioimidate group. Although an electron-withdrawing substituent R4 also enhances the internal nucleophilic attack to both α-thioiminium and imine

Synthesis and physicochemical evaluation of fluorinated lipopeptide precursors of ligands for microbubble targeting

• Masayori Hagimori,
• Estefanía E. Mendoza-Ortega and
• Marie Pierre Krafft

Beilstein J. Org. Chem. 2021, 17, 511–518, doi:10.3762/bjoc.17.45

• interface, with equilibrium surface pressures reaching ≈7–10 mN m−1 versus less than 1 mN m−1 only for their hydrocarbon analog 4. The F-lipopeptides penetrate in the DPPC monolayers in both liquid expanded (LE) and liquid condensed (LC) phases without interfacial film destabilization. By contrast, 4

• , reflecting a progressive adsorption at the interface, then reached a plateau, and stabilized at the equilibrium surface pressure (πeq). The adsorption kinetics demonstrate that the F-lipopeptides formed stable monolayers at the interface. The πeq values increased with the degree of fluorination of the F

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

• ] and ribonuclease A [140] (Table 3). These results have been explained by considering the conformational bias of the residues (pucker, trans/cis equilibrium), an altered hydrophobicity and polarity and the local environment at the substitution sites. An elevated folding velocity, presumable due to

Identification of volatiles from six marine Celeribacter strains

• Anuj Kumar Chhalodia,
• Jan Rinkel,
• Dorota Konvalinkova,
• Jörn Petersen and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2021, 17, 420–430, doi:10.3762/bjoc.17.38

• from the roseobacter group is the production of the sulfur-containing antibiotic tropodithietic acid (TDA) in Phaeobacter piscinae DSM 103509T [28], a compound that is in equilibrium with its tautomer thiotropocin [29] that was first described from Pseudomonas sp. CB-104 [30]. Its biosynthesis depends

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

Synthesis of legonmycins A and B, C(7a)-hydroxylated bacterial pyrrolizidines

• Wilfred J. M. Lewis,
• David M. Shaw and
• Jeremy Robertson

Beilstein J. Org. Chem. 2021, 17, 334–342, doi:10.3762/bjoc.17.31

• and B, are related as 7a-epimers that interconvert in aqueous solution to form a pH-dependent equilibrium ratio of the two [9]; they are weakly antibacterial and were shown to prolong “the survival period of mice inoculated with leukaemia L-120 cells” [7][8]. Although the clazamycins are not

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

• -β2AR, changes in the NMR signals monitored within different helices of the protein revealed that agonist binding primarily shifted the equilibrium towards the G protein-specific active state of helix VI. In contrast, β-arrestin-biased ligands predominantly affected the conformation of specifically

• thermodynamic equilibrium binding constants (K) and kinetic rates of association (kon) and dissociation (koff) in protein–ligand binding events [37]. In order to achieve this, they analysed the binding of four different proline-rich peptides to a 5-FTrp-labelled Src homology 3 (SH3) recognition protein domain

• characterize and quantify the relative populations of monomeric, octameric, and higher oligomer species that populate the pathway from the native PrP state to fibril formation. The equilibrium constants between states were also analysed as a function of both temperature and pressure, allowing to determine the

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

• rearrangement of 1,1-difluoro-2-methylenecyclopropane (96) (Scheme 45) [92]. At 210 °C the rate of cleavage of the proximal bond was only 3.8 times faster than for the analogous hydrocarbon. It was also observed that the equilibrium lay significantly in favor of the rearranged product 97, which was by 1.9 kcal

Multiswitchable photoacid–hydroxyflavylium–polyelectrolyte nano-assemblies

• Alexander Zika and
• Franziska Gröhn

Beilstein J. Org. Chem. 2021, 17, 166–185, doi:10.3762/bjoc.17.17

• considers the interaction at multiple binding sites, which might be identical or non-identical. Thus, the model is generally applicable for any possible scenario with more than one ligand. In addition to the enthalpy, the titration curve contains direct information of the stoichiometries and equilibrium

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

• various photocatalytic reactions, there are still several issues to be addressed: 1) To develop supramolecular photocatalytic systems, it is critical to have a thorough understanding of the photochemical and photophysical aspects of the reactions, such as the kinetic equilibrium constants, the reaction

Supramolecular polymerization of sulfated dendritic peptide amphiphiles into multivalent L-selectin binders

• David Straßburger,
• Svenja Herziger,
• Katharina Huth,
• Moritz Urschbach,
• Rainer Haag and
• Pol Besenius

Beilstein J. Org. Chem. 2021, 17, 97–104, doi:10.3762/bjoc.17.10

• interactions [17][18]. By a careful design of the corresponding building blocks, extensive multilateral hydrogen bonds between the amino acid sequences of the oligopeptide backbone lead to secondary structures that direct the equilibrium to polymeric nano-scaled assemblies. A well-studied receptor making use

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

• tryptophan, the equilibrium between the monomer and the oligomer formation is shifted towards the latter [75][76]. Examples of PPIs within higher-order protein complexes PPIs are responsible for the assembly of large protein complexes, such as capsid proteins in viruses and protein containers. This section

All-carbon [3 + 2] cycloaddition in natural product synthesis

• Zhuo Wang and
• Junyang Liu

Beilstein J. Org. Chem. 2020, 16, 3015–3031, doi:10.3762/bjoc.16.251

•  3A). Trost and co-workers proposed that the catalytic mechanism involves an oxidative addition of palladium(0) into 62 affording the η3-Pd TMM complex A [37] (Scheme 3B). Methyl trimethylsilyl carbonate (64) is formed as side product, which is in equilibrium with carbon dioxide and methyl

• -workers proposed that the catalytic mechanism involves a reaction between phosphine catalyst A and allene 82 to give B and/or C (Scheme 5B). Catalytic [3 + 2] cycloaddition of B and/or C and alkene D gives the cyclic intermediates E and F in an equilibrium state through a 1,2-proton transfer. The loss of

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

• reversed back to the initial state (Figure 15b). Here, all translocations happen in an off-equilibrium system. Since the kinetic evolution of the lithium pulses was followed by color and luminescence changes of the lithium-sensitive probe 36, the system is suited for a multitude of new applications

• translocation, monitored by distinct emission colors. b) Working principle of the chemical fuel 50. Off-equilibrium lithium pulses generate c) SOS morse signals, and d) sawtooth signals. Adapted with permission from (Ghosh, A.; Paul, I.; Schmittel, M. J. Am. Chem. Soc. 2019, 141, 18954–18957 [61]). Copyright

Dirhamnolipid ester – formation of reverse wormlike micelles in a binary (primerless) system

• David Liese,
• Hans Henning Wenk,
• Xin Lu,
• Jochen Kleinen and
• Gebhard Haberhauer

Beilstein J. Org. Chem. 2020, 16, 2820–2830, doi:10.3762/bjoc.16.232

• G''min. The reciprocal of the frequency where G'' has a minimum approximately corresponds to the breaking/recombination time τb of the reverse micelles, which are self-organized systems that undergo constant scission and recombination processes in a dynamic equilibrium [36]. Therefore, τb is the

• increase in the number of micelles can be explained by the breakup of big branched micelles into plenty of small ones. At elevated temperatures, the micelles can dissolve into surfactant monomers (dynamic equilibrium), which then leads to a decrease in the number of micelles. The relaxation time (τR

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

• enthalpy of the ligand binding (ΔHb) is hardly accessible. Hence, we explain the very low ΔTm values for G4-DNA a2 in the presence of the ligands 4a–e with a very low affinity of these ligands at the melting temperature, which may be caused by the delicate, temperature-dependent equilibrium of the

• . Additional information about the complex formation between the ligands and the quadruplex DNA forms 22AG and a2 was provided by CD spectroscopy. The changes of the CD spectrum of 22AG upon the addition of derivatives 4a–e clearly indicate a shift of the equilibrium between the different quadruplex forms of

• the characteristic CD pattern with a strong positive band at 295 nm and a weak negative one at 260 nm [60]. These observations show that all ligands stabilize preferentially the basket-type quadruplex structure of 22AG. In the case of the G4-DNA a2 the addition of the ligands shifts the equilibrium

Activation of pentafluoropropane isomers at a nanoscopic aluminum chlorofluoride: hydrodefluorination versus dehydrofluorination

• Maëva-Charlotte Kervarec,
• Thomas Braun,
• Mike Ahrens and
• Erhard Kemnitz

Beilstein J. Org. Chem. 2020, 16, 2623–2635, doi:10.3762/bjoc.16.213

• dehydrofluorination product 2,3,3,3-tetrafluoropropene (HFO-1234yf, 1) and the isomerization product 1,1,1,2,2-pentafluoropropane (HFC-245cb, 10b) in a 1:2 ratio (Scheme 2, top) with almost full conversion. The group of Kemnitz previously showed that 1 and 10b can be in an equilibrium when HF is present in the

• equilibrium between 5 and 6, that depends on the amount of HF or HSiEt3 present in the reaction mixture. Additionally, it is conceivable that 14 can further react to form 5 via allylic hydrodefluorination [16]. Therefore, the reactivity of 14 was tested in the presence of ACF and silane in C6D12 or C6D6

Anion exchange resins in phosphate form as versatile carriers for the reactions catalyzed by nucleoside phosphorylases

• Julia N. Artsemyeva,
• Ekaterina A. Remeeva,
• Tatiana N. Buravskaya,
• Irina D. Konstantinova,
• Roman S. Esipov,
• Anatoly I. Miroshnikov,
• Natalia M. Litvinko and
• Igor A. Mikhailopulo

Beilstein J. Org. Chem. 2020, 16, 2607–2622, doi:10.3762/bjoc.16.212

• letter to the editor Kalckar reported for the first time that specific inosine nucleosidase from rat liver catalyzes the reversible reaction “inosine + phosphate ⇌ hypoxanthine + ribose-1-phosphate”: the equilibrium of this reaction in water at pH 6.5 is displaced to the nucleoside synthesis. Moreover

• , he made the very interesting observation that the reaction of hypoxanthine and ribose-1-phosphate reached equilibrium after 20 min at a 70% concentration of inosine and “The synthesis of inosine would probably proceed further if all traces of inorganic phosphate were removed, since with equimolar

• -phosphate buffer, pH 7.4; 45 °C) [41]. It was shown that the N7-isomer formed predominantly at the beginning of the reaction and the ratio of N7- and N9-isomers displaced gradually to the latter getting equilibrium at ca. 1:4.8 ratio after 24 h. Results and Discussion The analysis of the experimental works

Particle size effect in the mechanically assisted synthesis of β-cyclodextrin mesitylene sulfonate

• Stéphane Menuel,
• Sébastien Saitzek,
• Eric Monflier and
• Frédéric Hapiot

Beilstein J. Org. Chem. 2020, 16, 2598–2606, doi:10.3762/bjoc.16.211

• occur over longer times, suggesting that shear, friction, and collision effects did not anymore affect the β-CD particle size and morphology over time. In fact, crystal breaking reduced the particle size up to some critical threshold, as a result of the equilibrium between comminution and aggregation

• . While the deprotonation/protonation equilibrium preferentially takes place at the 2- and 6-positions of the β-CD [29], the alkoxide located on the primary face at the 6-position is more inclined to react with the bulky mesitylenesulfonate group than the alkoxide on the secondary face at the 2-position

Thermodynamic and electrochemical study of tailor-made crown ethers for redox-switchable (pseudo)rotaxanes

• Henrik Hupatz,
• Marius Gaedke,
• Hendrik V. Schröder,
• Julia Beerhues,
• Arto Valkonen,
• Fabian Klautzsch,
• Sebastian Müller,
• Felix Witte,
• Kari Rissanen,
• Biprajit Sarkar and
• Christoph A. Schalley

Beilstein J. Org. Chem. 2020, 16, 2576–2588, doi:10.3762/bjoc.16.209

• anticipated sigmoidal shape of a 1:1 bonded complex (see Figure S5a in Supporting Information File 1). The curve shape suggests a more complex chemical equilibrium that involves more than one chemical process generating heat, taking place in the titration experiment. One process is likely a proton transfer

• ). These results suggest that both ammonium axles form a similar type of equilibrium with NDIC7, where the protonation of the tertiary amine and the complexation in a nonthreaded complex might contribute. When using BArF24− as the counterion for A1, the binding energies increase by 6–8 kJ/mol, which

• . Both compounds exhibit two reversible reduction processes. The lariat ether NDIC7 is not suitable for rotaxane synthesis as it forms a complex equilibrium involving the deprotonation of the secondary ammonium axle and does not form 1:1 pseudorotaxanes. Additionally, the pseudorotaxane is hampered by

Comparative ligand structural analytics illustrated on variably glycosylated MUC1 antigen–antibody binding

• Christopher B. Barnett,
• Tharindu Senapathi and
• Kevin J. Naidoo

Beilstein J. Org. Chem. 2020, 16, 2540–2550, doi:10.3762/bjoc.16.206

• analysis were carried out. These analyses were used to rapidly assess key features of the system, interrogate the dynamic structure of the ligand, and determine the role of glycosylation on the conformational equilibrium. The glycopeptide conformations in solution change relative to the peptide; thus a

• -structure relative to the random coil and the effects of the glycosylation were hypothesized to relate to the conformational properties of the peptides in solution (as opposed to their equilibrium structures in solution) [25]. A comprehensive structural study of the O-glycosylation-induced changes in a

• equilibrium of the peptide backbone near the glycosylated residue for a 15-residue mucin peptide. The APDTRP fragment resembled an S-shaped bend and a clustering of low-energy conformations revealed structural similarities between glycosylated and nonglycosylated peptides [23]. The work by Movahedin et al

NMR Spectroscopy of supramolecular chemistry on protein surfaces

• Peter Bayer,
• Anja Matena and
• Christine Beuck

Beilstein J. Org. Chem. 2020, 16, 2505–2522, doi:10.3762/bjoc.16.203

• a direct measure of the fraction bound and can be used directly to determine the dissociation constant (KD), provided sufficient saturation can be reached [83]. Line broadening occurs due to chemical exchange, that is the interconversion of at least two species in an equilibrium, e.g., the free and

• , a 15N weighting factor of WN = 0.154 was determined [97]. In the case of a two-state equilibrium, signals always shift in a straight line and produce a hyperbolic binding curve [83]. If the signal trajectory is curved, more than one binding site contributes to the chemical shift perturbation. In

• relative intensities of the binary complex in the absence of a stabilizing ligand indicate kinetics of the binding equilibrium in the fast-to-intermediate time regime, resulting in line broadening. In the presence of a stabilizing ligand, a ternary complex consisting of 14-3-3, the peptide and the ligand

Dawn of a new era in industrial photochemistry: the scale-up of micro- and mesostructured photoreactors

• Emine Kayahan,
• Mathias Jacobs,
• Leen Braeken,
• Leen C.J. Thomassen,
• Simon Kuhn,
• Tom van Gerven and
• M. Enis Leblebici

Beilstein J. Org. Chem. 2020, 16, 2484–2504, doi:10.3762/bjoc.16.202

• of the photocatalytic oxidation of thiophenol to phenyl disulfide using a Taylor flow in a microreactor that consists of a capillary tube. By varying the flow rate of the gas and liquid phase and comparing the oxygen concentration in the liquid phase with the equilibrium concentration without a

Conformational preferences of fluorine-containing agrochemicals and their implications for lipophilicity prediction

• Daniela Rodrigues Silva,
• Joyce K. Daré and
• Matheus P. Freitas

Beilstein J. Org. Chem. 2020, 16, 2469–2476, doi:10.3762/bjoc.16.200

• conformational equilibrium of penoxsulam (I, Figure 1). This compound has a 1,2–disubstituted ethane motif that could adopt three main staggered conformations, namely Igg, Iag and Iga (g = gauche and a = anti; see Figure 1), thus we have explored the intramolecular interactions governing its conformational