Synthesis of dibenzosuberenone-based novel polycyclic π-conjugated dihydropyridazines, pyridazines and pyrroles

• Ramazan Koçak and
• Arif Daştan

Beilstein J. Org. Chem. 2021, 17, 719–729, doi:10.3762/bjoc.17.61

• corresponding ketone 10bc. Eventually, pyrrole derivative 10bc, having a carbonyl group, was obtained by these reactions (Scheme 7). In order to increase the conjugation of dibenzosuberenone 1 for the photophysical aspect, the p-quinone methide derivative of dibenzosuberenone 11 was synthesized according to the

• fluorescent dyes 3a,b in detail. In the present study, the effects of functional groups with different conjugations on maximum absorbance (λmax, abs) and emission (λmax, ems), and wavelengths of dihydropyridazines 3c–f and 3k were investigated. Compounds 3c,d, with high conjugation, show the highest

• absorption and emission maxima values and compounds 3f and 3k, with low conjugation, show the lowest absorption and emission maxima values (Figure 3, Figure 4, and Figure 5). All these molecules (3c–f and 3k) have Stokes shifts greater than 100 nm. The fluorescence quantum yields of 3c–f and 3k were

[2 + 1] Cycloaddition reactions of fullerene C₆₀ based on diazo compounds

• Yuliya N. Biglova

Beilstein J. Org. Chem. 2021, 17, 630–670, doi:10.3762/bjoc.17.55

• ideal partner for drug lipophilization by conjugation [37]. Highly efficient fullerene conjugates with chemotherapeutic agents have been synthesized and patented; moreover, the biological activity profile is often preserved, but in some cases it can also change since a molecular structure with a

• synthesized (Scheme 10) [83]. As an alternative, a more efficient direct route for synthesizing fullerenylpeptides 23 [83] and 24 [88] by prolonged thermolysis of various diazoamides in the presence of C60 was developed (Scheme 11). For conjugation, some scientists successfully used mono- and

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

• Pauling electronegativity, the fluorine atoms, when directly linked to a carbenium ion, can be engaged in significant resonance electron donation (Scheme 2) [34]. While stabilizing the positively charged carbon center via lone pair conjugation, the electron density at the fluorine atom decreases, and this

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

• -phase peptide synthesis (SPPS) methods (15 and 16, Figure 1). A second well-established methodology for the 19F isotopic labelling of protein and peptides involves the post-translational chemical conjugation of an 19F probe to specific amino acids present within the protein, typically cysteine and

• receptor (β2AR) [29]. In this work conjugation of the CF3 group to an aromatic ring was shown to give rise to substantially improved 19F NMR chemical shift sensitivities over the more traditional thiol-specific trifluoromethyl tags (Figure 3b) [28]. In addition to chemical modification, novel methodologies

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

• disrotation at C2 and C3 during stereomutation in 1,1-difluorocyclopropanes [85]. An important feature in the fluorinated system was the stabilization of the intermediate 2,2-difluorotrimethylene radicals due to the conjugation of the radical centers with the σ*-orbital of C–F bond, which can be represented

Exploring the possibility of using fluorine-involved non-conjugated electron-withdrawing groups for thermally activated delayed fluorescence emitters by TD-DFT calculation

• Dongyang Chen and
• Eli Zysman-Colman

Beilstein J. Org. Chem. 2021, 17, 210–223, doi:10.3762/bjoc.17.21

• small group of structurally related N-heterocycles such as carbazole [5], dimethylacridine [13], phenoxazine [17], and phenothiazine [18]. Prior studies have shown that placing the donor groups ortho to the acceptor can lead to more limited conjugation between the two, resulting in emitters with

• , and 2CzBP of −1.70 eV, −1.63 eV, and −1.67 eV, respectively, are much deeper those of the fluorine-containing emitters in Figure 3, which is a reflection of the greater conjugation length present in compounds with an extended π-accepting framework. The corresponding ΔEg of 2CzBN (4.19 eV), 2CzTRZ

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

• positive charge of the allyl system by conjugation, affecting the following cyclization reaction. Meanwhile, the 2-substitued analogue VII does not present a conjugated system, and the total allyl charge cannot be stabilized, maintaining a positive value (+0.115). As a result, VII seems to be much more

• conjugation. However, according to the energy profile, this observation does not have a reflection in the deprotonation step, which seems to be affected partially by the steric hindrance around the two hydrogen atoms, being clearly higher in Ha (a 2.2 kcal⋅mol−1 higher activation energy of TS10 than for TS8

• believe that the higher thermodynamic stability of XV (4.4 kcal⋅mol−1 lower than for XII), which is due to the conjugation of the nitrogen atom and the diene system, accounts for the preferential formation and the consequent formation of 15. It cannot be overlooked that the formation of the intermediates

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

• take place. The use of noncyclic analogues did not give the cycloaddition product. It is suggested that the restricted rotational freedom of 151 and the related enforced conjugation of the sulfur lone pair may block certain undesired cation reactions. Cycloaddition product 154 was subjected to the

UV resonance Raman spectroscopy of the supramolecular ligand guanidiniocarbonyl indole (GCI) with 244 nm laser excitation

• Tim Holtum,
• Vikas Kumar,
• Daniel Sebena,
• Jens Voskuhl and
• Sebastian Schlücker

Beilstein J. Org. Chem. 2020, 16, 2911–2919, doi:10.3762/bjoc.16.240

• the GCI chromophore. The red-shift in the spectral positions of the GCI peaks with respect to those of the GCP peaks is due to the extended conjugation induced by the indole ring of GCI. We chose 266 nm and 244 nm as laser excitation wavelengths for UVRR spectroscopy. The 266 nm excitation was chosen

Changed reactivity of secondary hydroxy groups in C8-modified adenosine – lessons learned from silylation

• Jennifer Frommer and
• Sabine Müller

Beilstein J. Org. Chem. 2020, 16, 2854–2861, doi:10.3762/bjoc.16.234

• conjugation of the desired moiety. A C8-alkynyl-modified adenosine derivative was synthesized, reviving an old synthetic pathway for iodination of purine nucleobases. Silylation of the C8-alkynyl-modified adenosine revealed unexpected selectivity of the two secondary sugar hydroxy groups, with the 3'-O-isomer

• for 5’- or 3’-terminal attachment of a desired functionality, nucleoside derivatives that, upon site-specific incorporation at a pre-determined position of RNA, can be used for post-synthetic conjugation, are required. A number of chemistries are available to specifically attach a molecular entity to

• is desired, in order to introduce two or even more functionalities in a specific manner. For example, in earlier work we have used amine-NHS coupling reactions in combination with CuAAC to prepare double labeled RNA molecules for FRET analysis [19]. The conjugation of, sometimes rather large

On the mass spectrometric fragmentations of the bacterial sesterterpenes sestermobaraenes A–C

• Anwei Hou and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2020, 16, 2807–2819, doi:10.3762/bjoc.16.231

• radical cation 1•+ is obtained from which the methyl group C23 can directly be lost by an α-cleavage leading to fragment a1+ (Scheme 1A). However, the radical centred at the bridgehead carbon C11 is orthogonal to, or in other words, not in conjugation with the radical cation at C12–13. Therefore, an

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

• assemblies of the peptides. The conjugation of Asp–Glu–Asp–Asp–Asp–Leu–Leu–Ile–Gly (DEDDDLLIG) sequences to the ε-amine of the lysine residue of a tetrapeptide Nap–ᴅ-Phe–ᴅ-Phe–ᴅ-Lys–ᴅ-Tyr (Nap-ffky) [9] produces the branched peptide 1, which forms micelles (Figure 1). When proteinase K catalyzed the

• allows the conjugation of the cleavable side chain, and tyrosine provides additional aromatic–aromatic interactions, as shown in a recent cryo-EM structure (PDB: 6X5I) [41]. Based on the above rationale, the DEDDDLLIG sequences attach to the ε-amine of the lysine residue of the tetrapeptide Nap-ffky to

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

• product by 1H NMR spectroscopy revealed a multitude of new signals in the alkenyl region. In contrast, the analog 2 lacks conjugation in the central portion of the molecule and was therefore expected to be more stable to UV light. Indeed, the exposure of 2 to sunlight in an identical manner to that

Synthesis and characterization of S,N-heterotetracenes

• Astrid Vogt,
• Florian Henne,
• Christoph Wetzel,
• Elena Mena-Osteritz and
• Peter Bäuerle

Beilstein J. Org. Chem. 2020, 16, 2636–2644, doi:10.3762/bjoc.16.214

• species [29], whereas Sarkar et al. undertook quantum chemical investigations on the photovoltaic performance revealing an odd-even relation of the charge separation [30]. Furthermore, they calculated the single molecule transport behavior of various S,N-heteroacenes with different conjugation length

Synthesis of novel fluorinated building blocks via halofluorination and related reactions

• Attila Márió Remete,
• Tamás T. Novák,
• Melinda Nonn,
• Matti Haukka,
• Ferenc Fülöp and
• Loránd Kiss

Beilstein J. Org. Chem. 2020, 16, 2562–2575, doi:10.3762/bjoc.16.208

• (rac)-33 formed primarily (Scheme 22). A possible driving force of this reaction is the extended conjugation. Interestingly, the treatment of a mixture of (rac)-31 with H2O2/CF3COOH resulted in single allylic fluoride, (rac)-35 (Scheme 23). Unfortunately, the determination of the stereochemistry via

• fluorides via oxidation succeeded only in an acidic environment. Presumably, the presence of ester groups enabled the base-promoted E1cB elimination, driven by the extension of the conjugation. Further studies of other functionalized cyclic olefin substrates possessing varied architectural structures, and

Recent developments in enantioselective photocatalysis

• Callum Prentice,
• James Morrisson,
• Andrew D. Smith and
• Eli Zysman-Colman

Beilstein J. Org. Chem. 2020, 16, 2363–2441, doi:10.3762/bjoc.16.197

Formation of an exceptionally stable ketene during phototransformations of bicyclo[2.2.2]oct-5-en-2-ones having mixed chromophores

• Asitanga Ghosh

Beilstein J. Org. Chem. 2020, 16, 2297–2303, doi:10.3762/bjoc.16.190

• enones like D to minimize this route. Interestingly such rigid systems may either be considered as α,β- or β,γ-enone with δ-keto conjugation. However, in one of our previous works [16], we have established that the system should be considered as α,β-enone with δ-keto homoconjugation. Simple β,γ-enone

Styryl-based new organic chromophores bearing free amino and azomethine groups: synthesis, photophysical, NLO, and thermal properties

• Anka Utama Putra,
• Deniz Çakmaz,
• Nurgül Seferoğlu,
• Alberto Barsella and
• Zeynel Seferoğlu

Beilstein J. Org. Chem. 2020, 16, 2282–2296, doi:10.3762/bjoc.16.189

• electron-accepting group coupled with various donors connected via a π-conjugation bridge [31][32][33]. Such dyes offer good NLO characteristics when compared to Disperse Red 1 as well as remarkable thermal stabilities with dissociation temperatures up to 300 °C [31][32]. Schiff bases containing an

• corresponding Schiff base derivatives 8–12. However, the Schiff bases 8–12 had higher maximum absorption and emission wavelength values than the dyes 3–7 because of the extended conjugation system present in the Schiff bases. The observation of an intense red shift might be related to a significant contribution

• organic NLO chromophore is related to the presence of donor (D) and acceptor (A) groups linked through a π-conjugation path and is characterized by a large first-order hyperpolarizability value (β). However, a small energy gap between the HOMO and the LUMO (Egap) is an important indicator for high NLO

The B & B approach: Ball-milling conjugation of dextran with phenylboronic acid (PBA)-functionalized BODIPY

• Patrizia Andreozzi,
• Lorenza Tamberi,
• Elisamaria Tasca,
• Gina Elena Giacomazzo,
• Marta Martinez,
• Mirko Severi,
• Marco Marradi,
• Stefano Cicchi,
• Sergio Moya,
• Giacomo Biagiotti and
• Barbara Richichi

Beilstein J. Org. Chem. 2020, 16, 2272–2281, doi:10.3762/bjoc.16.188

• , Poland 10.3762/bjoc.16.188 Abstract Mechanochemistry is an emerging and reliable alternative to conventional solution (batch) synthesis of complex molecules under green and solvent-free conditions. In this regard, we report here on the conjugation of a dextran polysaccharide with a fluorescent probe, a

• the mechanochemical approach (the B & B, ball milling for boronic acid conjugation) as bioconjugation strategy for the labeling of biocompatible carbohydrates. Fluorescent labeling is of key importance to follow up the fate of molecules and (nano)materials inside cells and in the human body. In this

• properties of BODIPY and the biocompatibility of dextran. The BODIPY dextran nanoparticles were characterized regarding their size, morphology, polarity, and toxicity in vitro. We demonstrate the feasibility of mechanochemistry for boronic ester formation [23] to a glycan polymer as a route of conjugation

Tools for generating and analyzing glycan microarray data

• Akul Y. Mehta,
• Jamie Heimburg-Molinaro and
• Richard D. Cummings

Beilstein J. Org. Chem. 2020, 16, 2260–2271, doi:10.3762/bjoc.16.187

• response [13][22][23]. An overview of a typical glycan microarray experiment is provided in Figure 1. The protocol involves the chemical covalent conjugation or noncovalent attachment of glycans (usually 20 up to ≈700 glycans) in multiple replicates and often at varying concentrations to a slide surface

Synthetic approaches to bowl-shaped π-conjugated sumanene and its congeners

• Shakeel Alvi and
• Rashid Ali

Beilstein J. Org. Chem. 2020, 16, 2212–2259, doi:10.3762/bjoc.16.186

• mono-substituted sumanene derivatives 49b–d in a stereoselective manner as can be inspected from Scheme 10 [41][42]. In another event, Amaya, Ito, Katoh and Hirao reported a vital building block 53 to extend the π-conjugation bidirectionally through regioselective functionalization (Scheme 11) [43]. To

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

• effect of the electron poor porphyrin should be weak. There are eight bonds between the porphyrin β-position and the pyridine ring including one meta-phenyl connection attenuating the through-bond conjugation. A closer look at the kinetic data in Table 1 (sample I, II, and VII) might give an explanation

Synthesis of 3(2)-phosphonylated thiazolo[3,2-a]oxopyrimidines

• Ksenia I. Kaskevich,
• Anastasia A. Babushkina,
• Vladislav V. Gurzhiy,
• Dmitrij M. Egorov,
• Nataly I. Svintsitskaya and
• Albina V. Dogadina

Beilstein J. Org. Chem. 2020, 16, 1947–1954, doi:10.3762/bjoc.16.161

• -trifluoromethyl-2-thiouracil (1e) enhances the acidity of the N3H hydrogen by direct conjugation to the carbonyl moiety. As a result, 2-thiouracil 1e acts as an ambident nucleophile. Thus, the attack of the carbon atom attached to the chlorine by the N3 nitrogen atom is accompanied by the elimination of hydrogen

Et₃N/DMSO-supported one-pot synthesis of highly fluorescent β-carboline-linked benzothiophenones via sulfur insertion and estimation of the photophysical properties

• Dharmender Singh,
• Vipin Kumar and
• Virender Singh

Beilstein J. Org. Chem. 2020, 16, 1740–1753, doi:10.3762/bjoc.16.146

• substituents at C1 (R4), compound 4eA with aromatic substituent exhibited better fluorescence due to extended conjugation. The effect of R2 substituent in these derivatives (4bA, 4dA, 4fA and 4gA) was also investigated and it was found that N-alkylation improved the photophysical properties along with higher

Synthesis of Streptococcus pneumoniae serotype 9V oligosaccharide antigens

• Sharavathi G. Parameswarappa,
• Claney L. Pereira and
• Peter H. Seeberger

Beilstein J. Org. Chem. 2020, 16, 1693–1699, doi:10.3762/bjoc.16.140

• acetate loss during isolation, purification, or protein conjugation leads to structurally altered CPS. Vaccines based on synthetic carbohydrate antigens [11][12][13][14][15] such as the first commercially available semisynthetic glycoconjugate vaccine Quimi Hib® against H. influenzae [16] and Shigella