Photophysical, photostability, and ROS generation properties of new trifluoromethylated quinoline-phenol Schiff bases

• Inaiá O. Rocha,
• Yuri G. Kappenberg,
• Wilian C. Rosa,
• Clarissa P. Frizzo,
• Nilo Zanatta,
• Marcos A. P. Martins,
• Isadora Tisoco,
• Bernardo A. Iglesias and
• Helio G. Bonacorso

Beilstein J. Org. Chem. 2021, 17, 2799–2811, doi:10.3762/bjoc.17.191

• = Ph, R1 = 4-NO2) were analyzed, a significant difference was observed compared to the other compounds in the series 3. Thus, we can say that these characteristics exist because there is more stabilization of the excited state in a polar environment (DMSO and MeOH), adding to a possible push–pull

• ) and 3bc (R = Ph, R1 = 5-OMe) (Table 1). These values observed according to the solvent may be related to the stabilization of the excited state in each solution. Regarding the Stokes shifts (SS), higher values were observed for derivatives in a more polar solvent (DMSO and MeOH) than in CHCl3 (Table 1

• ) and also depending on the electronic properties of the substituents in the molecules. According to the characteristics and properties described herein, once again, we can attribute these differences to the stabilization of the excited states in more polar solvents combined with the properties of

The PIFA-initiated oxidative cyclization of 2-(3-butenyl)quinazolin-4(3H)-ones – an efficient approach to 1-(hydroxymethyl)-2,3-dihydropyrrolo[1,2-a]quinazolin-5(1H)-ones

• Alla I. Vaskevych,
• Nataliia O. Savinchuk,
• Ruslan I. Vaskevych,
• Eduard B. Rusanov,
• Oleksandr O. Grygorenko and
• Mykhailo V. Vovk

Beilstein J. Org. Chem. 2021, 17, 2787–2794, doi:10.3762/bjoc.17.189

• nitrogen atom to nitrenium intermediates occurred initially; further stabilization of these species resulted in the formation of hydroxylated lactams [44][45][46][47][48], azaspirocycles [49][50][51][52][53], or tricyclic nitrogen-containing heterocycles [44][53]. Our study commenced with the synthesis of

Synthetic strategies toward 1,3-oxathiolane nucleoside analogues

• Umesh P. Aher,
• Dhananjai Srivastava,
• Girij P. Singh and
• Jayashree B. S

Beilstein J. Org. Chem. 2021, 17, 2680–2715, doi:10.3762/bjoc.17.182

Synthesis of phenanthridines via a novel photochemically-mediated cyclization and application to the synthesis of triphaeridine

• Songeziwe Ntsimango,
• Kennedy J. Ngwira,
• Moira L. Bode and
• Charles B. de Koning

Beilstein J. Org. Chem. 2021, 17, 2340–2347, doi:10.3762/bjoc.17.152

• ) would allow for the stabilization of the radical by the methoxy substituent in the ortho position to the departing substituent. The methoxy substituent then presumably loses a hydrogen radical to form acetic acid and intermediate 17c. Further loss of formaldehyde would restore aromaticity and furnish

Halides as versatile anions in asymmetric anion-binding organocatalysis

• Lukas Schifferer,
• Martin Stinglhamer,
• Kirandeep Kaur and
• Olga García Macheño

Beilstein J. Org. Chem. 2021, 17, 2270–2286, doi:10.3762/bjoc.17.145

• enantioselective polycylization reaction of 51 (Scheme 11) [69]. Modification of the aromatic ring system on the chiral side of the thiourea catalyst proved to be crucial, as both the reactivity and the enantioselectivity were significantly influenced by the stabilization of the cationic substrate and not by

Chemical syntheses and salient features of azulene-containing homo- and copolymers

• Vijayendra S. Shetti

Beilstein J. Org. Chem. 2021, 17, 2164–2185, doi:10.3762/bjoc.17.139

• better stabilization of cation radicals, di-, and polycations by the unique dipolar nature of azulene, and in the case of iodine doping, it was attributed to the strengthened spin–spin interaction arising due to a high radical concentration. Recently, it was also established that the water-dispersible

• protonated 17 (1.32 eV) was also reduced compared to its neutral form (1.49 eV). These polymers, unlike 1,3-polyazulene 5, displayed reversible acid–base chemistry. With the help of absorption spectroscopy and EPR analysis, the authors could establish the fact that effective stabilization of 6 π-electron

• sensitivity could be attributed to the resonance stabilization of the positive charge on the five-membered ring of the azulene by the electron-donating groups at the 2-position. These polymers were quite robust as they underwent several cycles of electro-cycling before degradation. Azulene-fluorene copolymers

Cationic oligonucleotide derivatives and conjugates: A favorable approach for enhanced DNA and RNA targeting oligonucleotides

• Mathias B. Danielsen and
• Jesper Wengel

Beilstein J. Org. Chem. 2021, 17, 1828–1848, doi:10.3762/bjoc.17.125

• effects. The best stabilization was obtained for the 2-(aminoethyl)guanidine monomer 45 and tris(2-aminoethyl)amine (monomer 44) variants [80]. Another chemical group utilized for the 2’-modification is 2’-O-carbamoyl [85][86][87]. However, it has proven difficult to stabilize the duplex formed between

• been synthesized [84]. When incorporated centrally in a 2’-OMe-RNA ON, a significant stabilization relative to that of 2′-O-carbamoyluridine was observed against the RNA target. However, relative to the control ON carrying pure 2’-OMe RNA modified ONs, monomer 46 had an affinity-lowering effect [84]. A

• giving the best stabilization (up to 5.7 °C for four incorporations in an 18-mer ON relative to the control), whereas all gave similar and/or decreased thermal stability against RNA relative to the natural control ON [97]. It is noteworthy to mention that all monomers allowed the design of ASOs that were

Sustainable manganese catalysis for late-stage C–H functionalization of bioactive structural motifs

• Jongwoo Son

Beilstein J. Org. Chem. 2021, 17, 1733–1751, doi:10.3762/bjoc.17.122

• anticonvulsant drug used to treat epilepsy and anxiety disorders [39], and an analogue of pregabalin was transformed to azidated derivative 11a. It is noteworthy that positional selectivity was observed for the α-position of the carbamate functional group due to the stabilization of the carbon radical by the

Chemical approaches to discover the full potential of peptide nucleic acids in biomedical applications

• Nikita Brodyagin,
• Martins Katkevics,
• Venubabu Kotikam,
• Christopher A. Ryan and
• Eriks Rozners

Beilstein J. Org. Chem. 2021, 17, 1641–1688, doi:10.3762/bjoc.17.116

• , most likely because of enhanced stacking of the bicyclic π-system [104][105]. However, beyond the original studies, 7-Cl-bT has not been further explored for either duplex or triplex stabilization. Similar to L, substitution of thymine with 2-thiouracil (s2U) or 5-halouracils (e.g., BrU, Figure 6

• ) strengthens the Hoogsteen recognition of A. The stabilization provided by these nucleobases is most likely due to improved π-stacking, which may be sensitive to sequence context that needs to be further studied [106][107]. MacKay and co-workers designed an extended nucleobase based on isoorotic acid (Io4

Methodologies for the synthesis of quaternary carbon centers via hydroalkylation of unactivated olefins: twenty years of advances

• Thiago S. Silva and
• Fernando Coelho

Beilstein J. Org. Chem. 2021, 17, 1565–1590, doi:10.3762/bjoc.17.112

• reaction was observed in its absence. The authors highlighted the role of the solvent hexafluoro-2-propanol (HFIP) in the stabilization of the radical cation induced by PET and its assistance in the hydrogen shift process. Miscellaneous Lewis acid catalysis in olefin hydroalkylation reactions The ability

Double-headed nucleosides: Synthesis and applications

• Vineet Verma,
• Jyotirmoy Maity,
• Vipin K. Maikhuri,
• Ritika Sharma,
• Himal K. Ganguly and
• Ashok K. Prasad

Beilstein J. Org. Chem. 2021, 17, 1392–1439, doi:10.3762/bjoc.17.98

• followed by their duplex formation studies against complimentary oligonucleotide strands had described a very selective zipper-interaction [35], whereas a relative stabilization was observed due to stacking of these additional nucleobases across the minor groove [31]. The biological activity of the acyclic

• duplexes. The introduction of two double-headed nucleosides in two complementary DNA sequences forming a DNA-zipper motif showed a stabilization of the duplex and increased base–base stacking interactions. Nielsen and co-workers [30][31][65] synthesized double-headed nucleosides 5′-(S)-C-(thymine-1-yl

• the second nucleobase thymine through Mitsunobu reaction followed by deprotection steps in the presence of TBAF and methanolic ammonia (Scheme 28) [30][65]. The nucleoside monomer 118 was phosphitylated and then incorporated into oligodeoxynucleotides but stabilization in the secondary structures due

Synthesis of 10-O-aryl-substituted berberine derivatives by Chan–Evans–Lam coupling and investigation of their DNA-binding properties

• Peter Jonas Wickhorst,
• Mathilda Blachnik,
• Denisa Lagumdzija and
• Heiko Ihmels

Beilstein J. Org. Chem. 2021, 17, 991–1000, doi:10.3762/bjoc.17.81

• as CD and LD spectroscopy. Fluorimetric DNA melting analysis with different types of quadruplex DNA revealed a moderate stabilization of the telomeric quadruplex-forming oligonucleotide sequence G3(TTAG3)3. The derivatives showed a moderate affinity towards quadruplex DNA (Kb = 5–9 × 105 M−1) and ct

• forms, the effect of thermally induced unfolding of dye-labeled, quadruplex-forming oligonucleotides in the presence of the ligands was studied. In general, the binding of the ligand to the G4-DNA leads to a stabilization and thus to an increasing melting temperature of the DNA (Table 2). This effect of

• quadruplex structures. Although the ∆Tm values do not necessarily correlate directly with the binding affinity [23], as they only refer to the stabilization at elevated temperatures, the data show that these ligands do not bind extremely strong to G4-DNA. Nevertheless, as these screening experiments revealed

Metal-free glycosylation with glycosyl fluorides in liquid SO₂

• Krista Gulbe,
• Jevgeņija Lugiņina,
• Edijs Jansons,
• Artis Kinens and
• Māris Turks

Beilstein J. Org. Chem. 2021, 17, 964–976, doi:10.3762/bjoc.17.78

• halosulfites may dissociate. Thus, we proposed that a plausible formation of the fluorosulfite species and stabilization of the oxocarbenium ion intermediate could facilitate the glycosylation with glycosyl fluorides as glycosyl donors in liquid SO2 without the need of external promoter. Results and Discussion

• stabilization of the oxocarbenium ion intermediate in a form of a dioxolenium ion by the remote protecting group in C3 or C6 position could be the reason for such a good α-selectivity in liquid SO2 [75]. Within this study, several experiments were also carried out to test the reactivity of peracylated manno

Prins cyclization-mediated stereoselective synthesis of tetrahydropyrans and dihydropyrans: an inspection of twenty years

• Asha Budakoti,
• Pradip Kumar Mondal,
• Prachi Verma and
• Jagadish Khamrai

Beilstein J. Org. Chem. 2021, 17, 932–963, doi:10.3762/bjoc.17.77

• and co-workers explained the formation of all-cis-2,4,6-trisubstituted THPs with the help of density functional theory (DFT) and stated that in the presence of an external nucleophile, the stabilization of the carbocation intermediate is favored through hyperconjugation [28]. The vacant p-orbital of

Beyond ribose and phosphate: Selected nucleic acid modifications for structure–function investigations and therapeutic applications

• Christopher Liczner,
• Kieran Duke,
• Gabrielle Juneau,
• Martin Egli and
• Christopher J. Wilds

Beilstein J. Org. Chem. 2021, 17, 908–931, doi:10.3762/bjoc.17.76

• increased thermal stability when binding to either DNA or RNA complements with Tm increases of +1 to +8 and +2 to +10 °C, respectively [127][128][130][131][132][133][134]. The higher stabilization of RNA can be attributed to the preorganization of LNA nucleosides towards formation of A-form duplexes [128

• revealed that thermal stabilization may be attributed to nonconventional hydrogen bonds in the backbone [195][196][197]. Gene silencing by RNAi has also been explored with siRNA containing FANA residues [198]. These studies have shown that FANA is accommodated in the sense strand and 5'-end and 3'-termini

• modified with 4'-fluoro modifications have more labile glycosidic linkages under similar conditions [203][204]. Rosenberg attributed this contrast to the electronegativity differences between the groups and the effect this would have on the stabilization of the resulting oxocarbenium ion [202]. Oligomers

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

• ]. It is noteworthy that most of the phospholipid-stabilized MBs investigated in research and preclinical development are stabilized by a fluorocarbon (FC) gas [11][31][34]. FCs are known to contribute to MB stabilization through an osmotic effect [31]. In addition, FCs were also found to act as co

The synthesis of chiral β-naphthyl-β-sulfanyl ketones via enantioselective sulfa-Michael reaction in the presence of a bifunctional cinchona/sulfonamide organocatalyst

• Deniz Tözendemir and
• Cihangir Tanyeli

Beilstein J. Org. Chem. 2021, 17, 494–503, doi:10.3762/bjoc.17.43

• ). The solvent effects on the SMA of the chalcone derivatives and naphthalene-1-thiol are summarized in Figure 2. This behavior might be related to the better stabilization of the transition state of the substrates containing electron-withdrawing substituents or halogen atoms with THF, or vice versa. In

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

• thermodynamic stabilization of proteins [29][30][31]. The regulation of the proline content in proteins is an evolutionary strategy for environmental adaptation in extremophilic organisms. Proline is of a higher abundance in the proteomes of thermophilic organisms (organisms living at a high temperature) and of

• modifications of proline residues are sparse. The most common among them is hydroxylation at position 4 by molecular oxygen, which is mediated by prolyl-4-hydroxylase [34]. This process has a remarkable relevance in the stabilization of collagen in higher organisms [35]. The experimental expression of the

• the conformations. However, R-Flp stabilizes the C4-exo-pucker, while S-Flp stabilizes the C4-endo system [51]. It is believed that Dfp has no conformational preference akin to proline [52]. The stabilization of the puckers is one of the most prominent features of fluoroprolines that justifies their

Synthesis of trifluoromethyl ketones by nucleophilic trifluoromethylation of esters under a fluoroform/KHMDS/triglyme system

• Yamato Fujihira,
• Yumeng Liang,
• Makoto Ono,
• Kazuki Hirano,
• Takumi Kagawa and
• Norio Shibata

Beilstein J. Org. Chem. 2021, 17, 431–438, doi:10.3762/bjoc.17.39

• success of our DMF-free systems lies in the generation of sterically demanding cationic species, [P4-t-Bu]H+ or glyme capsulized K+, resulting in the stabilization of CF3− from HCF3 by ion separation. The sterically demanding [P4-t-Bu]H+ or encapsulation of K+ by glymes effectively inhibits the contact of

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

• very small π-electron density calculated in the 2pC orbital of CF3CH2+ (0.04 electrons) led the authors to conclude that “there is no hyperconjugative stabilization by the CF3 group”. The presence of this attractive interaction should, however, not be discarded. Indeed, the quantitative PMO analysis at

• spectroscopic evidence for the complete ionization of several α-(trifluoromethyl) alcohol precursors 9a–c in a superacidic FSO3H–SbF5–SO2 medium. They also brought experimental 19F NMR variation values up to Δδ = +24.8 ppm (Scheme 3). This suggests a partial stabilization of the cationic center by

• partial stabilization of the cationic center by the phenyl groups. Similarly, Laali et al. observed significant 19F NMR downfield chemical shifts upon the formation of α-(trifluoromethyl)pyrenylcarbenium- and α-(trifluoromethyl)anthracenylcarbenium ions 12a–d from the corresponding carbinols 11a–d (Scheme

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

• opening was attributed to the stabilization of the developing cationic center by the +M effect of the fluorine atoms. The formation of the 2,2-difluorohomoallyl cation or 3,3-difluorocyclobutyl cation did not occur as a result of the strong destabilization by the −I effect of the fluorine atoms [96]. On

• . Such selectivity is caused by the possibility of the resonance stabilization of the biradical that is formed. If other reagents are absent, the biradical can rearrange and recombine, leading to isomerization of the starting material as was observed in the case of 1,1-difluoro-2,3-dialkylcyclopropanes

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

• to the greatest stabilization of the HOMO level at −5.89 eV. 2CzTRZ, and 2CzBP possess destabilized HOMO levels of −5.69 and −5.60 eV, respectively. The LUMOs of 2CzBN, 2CzTRZ and 2CzBP are each located on the bridging benzene ring and the electron-acceptor groups. The LUMO levels for 2CzBN, 2CzTRZ

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

• immediate color change into dark red/brown took place after addition of complex 6b-Au(III), indicating a low stabilization of the coordinated diphenyl ligand and a fast release of Au. The de-coordination resulted in full conversion within 15 min in both reactions (Table 1, entries 3 and 6), compared to 24

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

• BODIPY and the zinc porphyrin. The excited zinc porphyrin further transferred the electron to the fullerene, yielding a charge-separated state, with a long lifetime of 23 µs, indicating the charge stabilization of the supramolecular assembly. Thus, an artificial photocatalytic system that can mimic the

Supramolecular polymers with reversed viscosity/temperature profile for application in motor oils

• Jan-Erik Ostwaldt,
• Christoph Hirschhäuser,
• Stefan K. Maier,
• Carsten Schmuck and
• Jochen Niemeyer

Beilstein J. Org. Chem. 2021, 17, 105–114, doi:10.3762/bjoc.17.11

• precoordinating effect to favor the cyclic form at lower temperatures. Thus, the alkylene-bridged monomer A shows no effect in terms of viscosity improvement. In contrast, the gem-dimethyl unit in monomer B leads to sufficient stabilization of the cyclic form at lower temperatures. This allows a ring–chain