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

• [22]. Moreover, the E geometrical isomer in the –CH=N- double bond has a higher percentage when in dimethyl sulfoxide-d6 solution. On the other hand, the Z isomer can be stabilized in less polar solvents by an intramolecular hydrogen bond. In the present study, the spectral data were recorded in CDCl3

Recent advances in the asymmetric phosphoric acid-catalyzed synthesis of axially chiral compounds

• Alemayehu Gashaw Woldegiorgis and
• Xufeng Lin

Beilstein J. Org. Chem. 2021, 17, 2729–2764, doi:10.3762/bjoc.17.185

• forming a hydrogen bond with CPA 15. Moreover, the N–H group of ninhydrin-derived 3-indolylmethanols 52 was crucial in increasing the reactivity and enantioselectivity, but it is not important for ninhydrin-derived substrates to carry out the addition reaction. This suggests that this substrate could

• -naphthylamine and azodicarboxylate through a dual hydrogen bond activation mode and a π–π interaction strategy (Scheme 31) [2]. Diarylamines and related scaffolds are among the most common potentially atropisomeric chemotypes in medicinal chemistry. For example, the drugs binimetinib and bosutinib contain

• class 3 atropisomers under protic and aprotic conditions due to a strong intramolecular N–H–O hydrogen bond that locks one of the axes into a planar conformation and proposed that the quinoid-nitrogen axis exists in a planar exo conformation [97]. 4. Enantioselective synthesis of axially chiral allenes

N-Sulfinylpyrrolidine-containing ureas and thioureas as bifunctional organocatalysts

• Viera Poláčková,
• Dominika Krištofíková,
• Boglárka Némethová,
• Renata Górová,
• Mária Mečiarová and
• Radovan Šebesta

Beilstein J. Org. Chem. 2021, 17, 2629–2641, doi:10.3762/bjoc.17.176

• aldehydes and hydrogen-bond activation of nitroalkenes. Keywords: asymmetric organocatalysis; hydrogen bond; Michael addition; pyrrolidine; thiourea; urea; Introduction Asymmetric organocatalysis became one of the strategic ways for the efficient synthesis of chiral compounds [1]. Bifunctional catalysis

• has proven to be a successful concept in asymmetric organocatalysis [2][3][4][5][6][7][8]. An amine unit with a hydrogen-bond donating skeleton is highly efficient from among various possible combinations of catalytic moieties within an organocatalyst. This idea has been inspired by proline catalysis

• itself, in which the carboxylic function acts as an ancillary hydrogen-bond donor for the direction of one of the reagents [9]. Amines serve as basic units and nucleophilic components capable of carbonyl compounds activation via enamine or iminium ion formation [10][11]. In particular, pyrrolidine became

Adjusting the length of supramolecular polymer bottlebrushes by top-down approaches

• Tobias Klein,
• Franka V. Gruschwitz,
• Maren T. Kuchenbrod,
• Ivo Nischang,
• Stephanie Hoeppener and
• Johannes C. Brendel

Beilstein J. Org. Chem. 2021, 17, 2621–2628, doi:10.3762/bjoc.17.175

• established, commercial polymers in solution [17]. We recently reported the self-assembly of polyethylene oxide (PEO) polymers into cylindrical nanostructures, also called supramolecular polymer bottlebrushes (SPBs), based on the end group modification with hydrogen bond forming benzenetrisurea (BTU) and

Recent advances in organocatalytic asymmetric aza-Michael reactions of amines and amides

• Pratibha Sharma,
• Raakhi Gupta and
• Raj K. Bansal

Beilstein J. Org. Chem. 2021, 17, 2585–2610, doi:10.3762/bjoc.17.173

• asymmetric aza-MR. Thus, the review includes the examples wherein cinchona alkaloids, squaramides, chiral amines, phase-transfer catalysts and chiral bifunctional thioureas have been used, which activate the substrates through hydrogen bond formation. Most of these reactions are accompanied by high yields

Base-free enantioselective S_N2 alkylation of 2-oxindoles via bifunctional phase-transfer catalysis

• Mili Litvajova,
• Emiliano Sorrentino,
• Brendan Twamley and
• Stephen J. Connon

Beilstein J. Org. Chem. 2021, 17, 2287–2294, doi:10.3762/bjoc.17.146

• ester moieties at C-3 have been shown to participate in enantioselective phase-transfer-catalysed alkylations promoted by ad-hoc designed quaternary ammonium salts derived from quinine bearing hydrogen-bond donating substituents. For the first time in such phase-transfer-catalysed enolate alkylations

• hydrogen bond-donating functionality – while keeping the N-3,5-di-tert-butylbenzyl unit unchanged – were then introduced. Removing the two electron-withdrawing -CF3 groups from the ureaphenyl moiety resulted in diminished enantioselectivity (Table 1, entry 5), whereas increasing the steric demand in this

• region of the catalyst led to racemic products (Table 1, entries 6 and 7). Employing a different hydrogen bond-donating motif such as the squaramide (catalyst 8, Table 1, entry 8) resulted in a substantial drop of the enantiocontrol as well as in the reduction of the reaction rate [29][31] – probably due

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

• developed in the past decades, all based on polarized hydrogen bond motifs. While commonly based on N–H bonds [15][16][17][18], also polarized O–H [19][20] and even C–H [21][22] bond-based systems have been realized. As a consequence of the importance and increasing attention of this field, there are

• the concepts and implementation of natural principles of anion recognition by small molecule catalysts. Review Hydrogen bonding to neutral substrates or anion binding? In the early stages of anion-binding-catalysis development, some reactions might have potentially been mistaken to be hydrogen-bond

• catalyzed [15][23]. While both catalyses are closely related by making use of hydrogen-bond interactions as the directing noncovalent force, they can be distinguished by the type of substrate that is bound to and activated by the catalyst (Figure 2a). In H-bond catalysis, neutral substrates such as carbonyl

(Phenylamino)pyrimidine-1,2,3-triazole derivatives as analogs of imatinib: searching for novel compounds against chronic myeloid leukemia

• Luiz Claudio Ferreira Pimentel,
• Lucas Villas Boas Hoelz,
• Henayle Fernandes Canzian,
• Frederico Silva Castelo Branco,
• Andressa Paula de Oliveira,
• Vinicius Rangel Campos,
• Floriano Paes Silva Júnior,
• Rafael Ferreira Dantas,
• Jackson Antônio Lamounier Camargos Resende,
• Anna Claudia Cunha,
• Nubia Boechat and
• Mônica Macedo Bastos

Beilstein J. Org. Chem. 2021, 17, 2260–2269, doi:10.3762/bjoc.17.144

• against K562 cells and more toxic to WSS-1 than IMT (used as a positive control), with a low SI (Table 1). According to Xie and co-workers, the high selectivity of IMT is related to an important hydrogen bond between the Glu305 residue and its amide group, which is probably absent when the synthesized

• compounds 2c and 2d, which presented almost equivalent interaction energy values. In addition, the hydrogen bond between the amino group of IMT with the Thr334 residue [32][38] (Figure 4a) was not observed for compounds 2c, 2d, and 2g, which suggests a lower binding energy of the synthesized compounds when

• compared to IMT (Table 2). The lacking of that interaction prevents the pyridine ring from mimicking the ATP adenine in the hinge region [39]. As previously mentioned, the absence of the hydrogen-bond interaction between the Glu305 residue and the amide group of 2c, 2d, and 2g (Figure 4b–d) also

Constrained thermoresponsive polymers – new insights into fundamentals and applications

• Patricia Flemming,
• Alexander S. Münch,
• Andreas Fery and
• Petra Uhlmann

Beilstein J. Org. Chem. 2021, 17, 2123–2163, doi:10.3762/bjoc.17.138

Progress and challenges in the synthesis of sequence controlled polysaccharides

• Giulio Fittolani,
• Theodore Tyrikos-Ergas,
• Denisa Vargová,
• Manishkumar A. Chaube and
• Martina Delbianco

Beilstein J. Org. Chem. 2021, 17, 1981–2025, doi:10.3762/bjoc.17.129

• , fluorine, and carboxymethyl groups, prevented the formation of insoluble aggregates by disrupting hydrogen-bond networks. Dramatic differences in the conformation (e.g., radius of gyration and glycosidic bond conformation) and aggregation behaviour (i.e., crystallinity and solubility) were observed for

• -mediated aglycon delivery (BMAD) with the use of a diboron catalyst allowed for regio-, as well as stereoselective glycosylation to achieve an α(1-3)-pentaglucoside [175]. Regioselective 1,2-cis-glycosylation could also be achieved by boron-catalyzed coupling via a SNi-type mechanism [176]. Hydrogen bond

Asymmetric organocatalyzed synthesis of coumarin derivatives

• Natália M. Moreira,
• Lorena S. R. Martelli and
• Arlene G. Corrêa

Beilstein J. Org. Chem. 2021, 17, 1952–1980, doi:10.3762/bjoc.17.128

• discussed above, the organocatalysts may also proceed by noncovalent activation, in which a hydrogen bond or an ion pair is formed. A broad variety of mono- and bifunctional chiral hydrogen-bonding organocatalysts has been developed, in special using cinchona alkaloid derivatives [52]. In this sense, Lin

• presence of a carbonyl group in the coumarin, since it makes a hydrogen bond with the organocatalyst and when it is replaced by other electron-withdrawing groups, the hydrogen bond formation is blocked, consequently there is no product formation (Scheme 19). Lin et al. described an organocatalyzed Mannich

• half-thioesters 67 to coumarins 66 using a sulphonamide organocatalyst 69 was reported by Nakamura et al. [55]. The hydrogen bond between the secondary amine and the coumarin carboxyl provides a nucleophilic addition on the Re face, and therefore resulting in products 68 with R absolute configuration

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

• similar to A-type DNA and RNA, and allows the O1P oxygen from each DNA phosphate to form a hydrogen bond to the amide proton of each residue of the PNA backbone of the Hoogsteen strand [41]. More recent structural work by Rozners and co-workers confirmed that the PNA–dsRNA triplex had similar structural

• cationic RNA binding compounds, perhaps, because the protonation event is coupled with the Hoogsteen hydrogen bond formation. As a result, the partially protonated M strengthens the triple helix without compromising the sequence specificity of recognition [28][30][31]. As discussed above, guanidine groups

• recognition of pyrimidines in hypothetical X•T–A or X•C–G triplets is complicated by two problems: 1) pyrimidines present only one hydrogen bond acceptor (C=O in T or U) or donor (-NH2 in C) in the major groove, and 2) the six-membered pyrimidine ring extends further out in the major groove than the five

Breaking paracyclophane: the unexpected formation of non-symmetric disubstituted nitro[2.2]metaparacyclophanes

• Suraj Patel,
• Tyson N. Dais,
• Paul G. Plieger and
• Gareth J. Rowlands

Beilstein J. Org. Chem. 2021, 17, 1518–1526, doi:10.3762/bjoc.17.109

• [2.2]paracyclophane (4) to the side-products was in the range of 4:1:1 (Scheme 1). One, 5, was clearly an isomer of a hydroxynitro[2.2]paracyclophane with characteristic 1H NMR signal at 10.79 ppm for an internal hydrogen bond, and a signal at 7.53 ppm for C–H ortho to the nitro group. But the upfield

Synthesis of multiply fluorinated N-acetyl-D-glucosamine and D-galactosamine analogs via the corresponding deoxyfluorinated glucosazide and galactosazide phenyl thioglycosides

• Vojtěch Hamala,
• Lucie Červenková Šťastná,
• Martin Kurfiřt,
• Petra Cuřínová,
• Martin Dračínský and
• Jindřich Karban

Beilstein J. Org. Chem. 2021, 17, 1086–1095, doi:10.3762/bjoc.17.85

• desolvation penalty associated with binding of hydrophilic natural carbohydrates [8], and (2) create additional contacts with the binding cavity via electrostatic and dipolar interactions with C–F bonds [9][10], new intermolecular hydrogen bonds [11], or rearrangement of hydrogen bond-mediating water

Nitroalkene reduction in deep eutectic solvents promoted by BH₃NH₃

• Chiara Faverio,
• Monica Fiorenza Boselli,
• Patricia Camarero Gonzalez,
• Alessandra Puglisi and
• Maurizio Benaglia

Beilstein J. Org. Chem. 2021, 17, 1041–1047, doi:10.3762/bjoc.17.83

• two or three naturally occurring components, able to engage in reciprocal hydrogen bond interactions to form an eutectic mixture with a melting point lower than that of either of the individual components. DESs feature several favorable properties: they do not need any purification and the

Synthetic accesses to biguanide compounds

• Oleksandr Grytsai,
• Cyril Ronco and
• Rachid Benhida

Beilstein J. Org. Chem. 2021, 17, 1001–1040, doi:10.3762/bjoc.17.82

• of the π-electron density along the molecule, together with an intramolecular hydrogen bond (Figure 1, 1c). Despite the plurality of evidence showing this representation as inappropriate [1], structure 1a remains commonly used in the scientific literature. In this review, biguanides will be

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

• modification is accommodated in an A'-form duplex [75]. Interestingly, an unconventional C–H···O hydrogen bond was observed between the amide’s carbonyl oxygen and the nearby uracil C6–H6. The thermal stability of this modified duplex was, however, quite similar to native RNA. Typically, there is a decrease of

• suggested the addition of a polarizable group in the longer 2'-O-alkyl chains that could hydrogen bond with nucleobases in the minor groove of the duplex would be well tolerated [114]. This supported the hypothesis that the 2'-O-[2-(methoxy)ethyl] (MOE) modification (Figure 5B) wouldn’t lead to significant

Synthetic reactions driven by electron-donor–acceptor (EDA) complexes

• Zhonglie Yang,
• Yutong Liu,
• Kun Cao,
• Xiaobin Zhang,
• Hezhong Jiang and
• Jiahong Li

Beilstein J. Org. Chem. 2021, 17, 771–799, doi:10.3762/bjoc.17.67

• spectroscopy shows that phosphono radicals could proceed throughout the reaction. A halogen bond (XB) is a noncovalent interaction formed between a halogen atom and a neutral or negatively charged Lewis base. It is a kind of weak intermolecular interaction analogous to a hydrogen bond and basically can be

Amino- and polyaminophthalazin-1(2H)-ones: synthesis, coordination properties, and biological activity

• Zbigniew Malinowski,
• Emilia Fornal,
• Agata Sumara,
• Renata Kontek,
• Karol Bukowski,
• Beata Pasternak,
• Dariusz Sroczyński,
• Joachim Kusz,
• Magdalena Małecka and
• Monika Nowak

Beilstein J. Org. Chem. 2021, 17, 558–568, doi:10.3762/bjoc.17.50

• angles equal to 27.61 and 28.71°, respectively, and moreover, the methyl groups of the methoxy substituents are directed opposite and towards to the pyridin-2-yl substituents, respectively. The crystal structure of complex 17 is stabilized with a 3D intermolecular hydrogen bond network (Figure S1a

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

• rapidly equilibrating (Z)/(E)-isomers [2], the derivatives containing a secondary nitrogen slightly prefer [2][9][48] the (Z)-configuration due to an intramolecular hydrogen bond. A substitution of hydrogen at the methylidene carbon by an aryl group and a secondary nitrogen, enabling an intramolecular

• hydrogen bond, results in the geometry of a double bond that is locked in a (Z)-configuration [12]. The same (Z)-configuration was observed by us for the primary 3-[amino(aryl)methylidene]oxindoles [33]. The usual method used for the configuration assignment of 3-amino(aryl)methylidene derivatives involves

• solid state by X-ray diffraction. The important role of the intramolecular hydrogen bond fixing the (Z)-configuration has also been observed in the crystal structures of other 3-aminomethylidene derivatives containing a primary or secondary nitrogen [14][49][50][51][52]. The (Z)-configuration of the

1,2,3-Triazoles as leaving groups: S_NAr reactions of 2,6-bistriazolylpurines with O- and C-nucleophiles

• Dace Cīrule,
• Irina Novosjolova,
• Ērika Bizdēna and
• Māris Turks

Beilstein J. Org. Chem. 2021, 17, 410–419, doi:10.3762/bjoc.17.37

• hydrogen bond. This is supported by a smaller deviation of the C(2’’) chemical shift value (61.7 ppm) in comparison to the theoretical shifts for a Csp2 centre. Similar structural analogues are known in the literature [54][83][84][85] but their structural analysis was incomplete. As the aforementioned

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

• of a hydrogen bond between the exocyclic N5 atom and the solvent is taken into account (model structure in Figure 4b). For the methanol and water solutions, the agreement between the calculated and experimental spectra is observed only when the protonation of the N5 atom is taken into account (model

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

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

• resemblance of the pumpkin of the Cucurbitaceae family. The oxygen atoms are located along the edges of the band, which can identify positively charged guests through ion–dipole and hydrogen bond interactions. The internal cavity exhibits a strong hydrophobicity. Depending on the size and shape of the guest

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

• -complementary [14] binding units (BU, blue) and a connecting linker unit (LU, green) to connect the BUs. In this case, the BUs are ureidopyrimidone units, which dimerize due to a fourfold hydrogen bond, thus allowing for strong supramolecular interactions [15]. Due to the flexibility of the LUs, the BUs can