Trichloroacetic acid fueled practical amine purifications

• Aleena Thomas,
• Baptiste Gasch,
• Enzo Olivieri and
• Adrien Quintard

Beilstein J. Org. Chem. 2022, 18, 225–231, doi:10.3762/bjoc.18.26

• naphthalene or 2-methoxynaphthalene were chosen as representative model impurities given their potential π-stacking ability and solid state at room temperature. Consequently, they are more challenging to separate from the generated amine salts, demonstrating the power of the method. Aside from secondary

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

• formed Michael adduct (Scheme 1) [25]. The proposed catalytic cycle involved generation of the active complex through hydrogen bonding between catalyst and aniline followed by interaction with chalcone via π–π stacking of aromatic rings and hydrogen bonding leading to the Michael adduct. Likewise, Lee et

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

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

• surface area of the bicyclic nucleobases that enabled better π-stacking [97]. Despite the superior binding properties, the original report on K has not been followed up with more detailed studies and J remains the current gold standard for triple-helical recognition of G–C base pairs in PNA. However, more

• subtle modulation of the pKa and better π-stacking [99]. Several other research groups have further increased the pKa value by removing electronegative substituents from C arriving at derivatives of 2-aminopyridine (M, Figure 6) as more basic nucleobases that improve binding of triplex-forming

• ) 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

Recent advances in the application of isoindigo derivatives in materials chemistry

• Andrei V. Bogdanov and
• Vladimir F. Mironov

Beilstein J. Org. Chem. 2021, 17, 1533–1564, doi:10.3762/bjoc.17.111

• towards n-butanol. The lower limit of detection was 100 ppm with a response time of less than 10 s. The ability of polymeric isoindigo derivatives to strongly bind to carbon nanotubes due to π-stacking was used to create sensors for the determination of NO2 in the gaseous state (see polymer 61) and

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

• simultaneous removal of tert-butyldimethylsilyl and amidine protecting groups, respectively (Scheme 41 and Scheme 42) [26]. The incorporation of the double-headed nucleosides 159 and 163 into oligonucleotides resulted in the formation of thermally stable DNA:RNA duplexes due to an efficient π–π stacking

Design, synthesis and photophysical properties of novel star-shaped truxene-based heterocycles utilizing ring-closing metathesis, Clauson–Kaas, Van Leusen and Ullmann-type reactions as key tools

• Shakeel Alvi and
• Rashid Ali

Beilstein J. Org. Chem. 2021, 17, 1374–1384, doi:10.3762/bjoc.17.96

• be considered as a 1,3,5‐triphenylbenzene derivative enjoying with three methylene units clipped in such a manner that all the four benzene rings are in conjugation with coplanar arrangement, resulting strong π–π stacking in addition to the strong electron‐donating ability which in turns provide a

A comprehensive review of flow chemistry techniques tailored to the flavours and fragrances industries

• Guido Gambacorta,
• James S. Sharley and
• Ian R. Baxendale

Beilstein J. Org. Chem. 2021, 17, 1181–1312, doi:10.3762/bjoc.17.90

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

• preferentially to the basket-type quadruplex structure and thereby shift the equilibrium to this form. Furthermore, during all titrations of the derivatives 5a–e to 22AG no clear ICD band was detected, which is usually interpreted as an indication of terminal π stacking of the ligand to the quadruplex structure

Synthesis, structural characterization, and optical properties of benzo[f]naphtho[2,3-b]phosphoindoles

• Mio Matsumura,
• Takahiro Teramoto,
• Masato Kawakubo,
• Masatoshi Kawahata,
• Yuki Murata,
• Kentaro Yamaguchi,
• Masanobu Uchiyama and
• Shuji Yasuike

Beilstein J. Org. Chem. 2021, 17, 671–677, doi:10.3762/bjoc.17.56

• ]). The sum of the bond angles around the phosphorus atom is 295.99°, and hence the phosphorus atom is sp3-hybridized and has a trigonal pyramidal geometry. X-ray analysis revealed that the packing structure of 2 had π–π-stacking, with a distance of approximately 3.427 Å between two

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

• , Supporting Information File 2). Additionally, the complex 17 in a solid state is also stabilized with π–π stacking interactions between the 1,2-diazine moieties and the pyridin-2-yl substituents of the ligands (Figure S1b, Supporting Information File 2). The FTIR spectrum recorded for complex 17 confirmed

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

• interactions and secondary interactions such as π–π stacking [34][35][36][37][38][39][40]. The size and shape could be tuned through the free energy and the enthalpy/entropy interplay in the assembly process, which again are encoded in the molecular building block structure [31][37]. Supramolecular structures

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

• supramolecular hosts to recognize guests through hydrophobicity, π–π stacking, cation–π interactions, ion–dipole interactions, etc. [31][32]. Due to the cavity-shape limitation of calixarenes, most calixarene-based photocatalytic systems are mainly based on the fabrication of hybrid materials for energy transfer

Naphthalonitriles featuring efficient emission in solution and in the solid state

• Sidharth Thulaseedharan Nair Sailaja,
• Iván Maisuls,
• Jutta Kösters,
• Alexander Hepp,
• Andreas Faust,
• Jens Voskuhl and
• Cristian A. Strassert

Beilstein J. Org. Chem. 2020, 16, 2960–2970, doi:10.3762/bjoc.16.246

• to the fact that preventing π–π stacking in the solid state with bulky substituents and simultaneously restricting the degree of rotovibrational freedom in solution appears contradictory. Firstly, bright molecules in solution require substantial structural rigidity to limit submolecular vibrational

• increasing water fractions from 0% to 30%, but only a weak ACQ effect upon further increase of water fraction, as compared to H. This is probably due to the steric effects suppressing intermolecular stacking in the aggregates: in the case of H, π–π stacking is favored upon increasing the water fraction

• ) Intermolecular CH…π interactions for compound Me. B) Weak intermolecular π–π stacking interactions. C) Packing of compound Me along the a-axis. Color code: black = carbon, grey = hydrogen and blue = nitrogen. The unit cell is shown in Supporting Information File 1, Figure S32. Normalized absorption spectra 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

• undemanding building blocks. The plethora of self-sorting systems depends on either the geometric fit of their global shapes and/or matching of their local interactions. Various noncovalent interactions, such as H‐bonding [8][9], metal–ligand coordination [10][11][12][13], electrostatic interactions [14], π

• ‐stacking [15][16], dipole–dipole interactions [17] or hydrophobic interactions [18], have proven their significance as key players [19] in the creation of self-sorted supramolecular assemblies, such as 1D, 2D [20], and 3D architectures [21], polymers [22], gels [23], and most recently, of stand-alone

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

• terminated with an N-benzylamide functionality to establish the attractive hydrogen bonding and π stacking with the thymidine residues in the loops in G4-DNA, so that this ligand binds with very high selectivity to the particular quadruplex-forming oligonucleotide J19 [49]. Overall, the above-mentioned

• -established for berberines [33][34][35][36][37][38][39][40][41][42]. Based on these general similarities between the derivatives 4a–e and the established quadruplex-binding berberine derivatives it is deduced that the berberine unit in 4a–e binds like the latter ones to the G4-DNA by terminal π-stacking

• contributed significantly to the binding affinity depending on their spacing from the π-stacking unit. In the case of 4a–e, however, the position of the triazole and adenine unit relative to the berberine does not appear to be highly relevant for the overall binding affinity. It may be concluded that the

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

• with a typical π-stacking distance of 3.58 Å and a tilt angle of 5.8°. The free electron pair of the tertiary amine points towards the inside of the crown ether. In contrast, single crystals of NDIC8 (Figure 2c), obtained by slow evaporation of a concentrated dimethylformamide (DMF) solution, exhibit a

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

• best binding (KD = 0.6 mM) due to π-stacking between the phenyl side chain of the amino acid and the acylguanidinium unit of the GCP. Ac-Lys exhibits the least interaction (KD = 3 mM) due to electrostatic repulsion of the positively charged Lys side chain with the also positively charged GCP unit. For

Synthesis, docking study and biological evaluation of ᴅ-fructofuranosyl and ᴅ-tagatofuranosyl sulfones as potential inhibitors of the mycobacterial galactan synthesis targeting the galactofuranosyltransferase GlfT2

• Marek Baráth,
• Jana Jakubčinová,
• Zuzana Konyariková,
• Stanislav Kozmon,
• Katarína Mikušová and
• Maroš Bella

Beilstein J. Org. Chem. 2020, 16, 1853–1862, doi:10.3762/bjoc.16.152

• hydroxy group and the phenyl ring created a cation–π stacking interaction with the arginine R171 side chain (Figure 2). The observed theoretical binding energy in kcal/mol represented by the docking scores and the predicted binding affinities for the UDP-Galf, fructofuranose, and tagatofuranose compounds

Heterogeneous photocatalysis in flow chemical reactors

• Christopher G. Thomson,
• Ai-Lan Lee and
• Filipe Vilela

Beilstein J. Org. Chem. 2020, 16, 1495–1549, doi:10.3762/bjoc.16.125

• (PDI) aggregates have become a popular choice of heterogeneous photocatalyst. As PDI is a large, planar, polyaromatic hydrocarbon molecule, it spontaneously forms ordered 1D supramolecular assemblies through efficient π–π stacking and side chain interactions [192]. Despite the PDI units having only non

• -bonding interactions, the narrow π–π stacking provides a sufficient π orbital overlap to produce semiconductor-type electronic band structures and an efficient interplanar charge transport similar to g-C3N4 [192]. Duan and co-workers reported the synthesis of a zinc PDI assembly as a heterogeneous

• , first reported in 1834 by Liebig, which he named “melon” [119]. The material consists of two-dimensional sheets of hexatopic, hexagonal sp2-hybridised carbon and nitrogen atoms, linked by bridging tertiary amines (Figure 9) [120]. The material is crystalline as sheets are held together by strong π

Highly selective Diels–Alder and Heck arylation reactions in a divergent synthesis of isoindolo- and pyrrolo-fused polycyclic indoles from 2-formylpyrrole

• Carlos H. Escalante,
• Eder I. Martínez-Mora,
• Carlos Espinoza-Hicks,
• Alejandro A. Camacho-Dávila,
• Fernando R. Ramos-Morales,
• Francisco Delgado and
• Joaquín Tamariz

Beilstein J. Org. Chem. 2020, 16, 1320–1334, doi:10.3762/bjoc.16.113

• 8b/7c and 8c/7c (Figure 4a,b and Supporting Information File 1, Appendix 6). All the observable π···π interactions were parallel-displaced (offset) π-stacking, and the distance values were within the range of the known values, whether determined from X-ray structures or calculated values (3.2–4.0 Å

Towards triptycene functionalization and triptycene-linked porphyrin arrays

• Gemma M. Locke,
• Keith J. Flanagan and
• Mathias O. Senge

Beilstein J. Org. Chem. 2020, 16, 763–777, doi:10.3762/bjoc.16.70

• [C11 to C16, centroid···centroid distance of 3.755(3) Å and shift distance of 1.593(5) Å] involved in a head-to-head slip plane π-stacking interaction with another triptycene molecule either side, while the third face ring iii of the triptycene exhibits C23–H23B···π interactions between the isopropyl

• molecule. In this structure, it should be noted that there is a high degree of π-stacking between the porphyrin macrocycle. This is highlighted in Figure 4; however, there is a clear preference for the homo-metallic selective interactions between the porphyrin rings. As such, in the crystal packing the Ni

• Supporting Information File 1). While this feature is an interesting take on the selective homo interactions, the explanation of this motif formation is potentially more mundane in this case. Considering that during the crystallization process, the spontaneous formation of the homo or hetero π-stacking of

Direct borylation of terrylene and quaterrylene

• Haruka Kano,
• Keiji Uehara,
• Kyohei Matsuo,
• Hironobu Hayashi,
• Hiroko Yamada and
• Naoki Aratani

Beilstein J. Org. Chem. 2020, 16, 621–627, doi:10.3762/bjoc.16.58

• their intrinsic physical properties as a function of molecular length (Figure 1e) [19][20], while the low solubility of tert-butylpentarylene indicates that even such bulky group had reached its limit to interrupt π-stacking. The synthesis of higher oligorylenes would require more robust solubilizing

Synthesis of triphenylene-fused phosphole oxides via C–H functionalizations

• Md. Shafiqur Rahman and
• Naohiko Yoshikai

Beilstein J. Org. Chem. 2020, 16, 524–529, doi:10.3762/bjoc.16.48

• packing of 8a did not involve columnar π–π stacking of the PAH moiety (Figure S1, Supporting Information File 1). This is likely due to the fact that such π-stacking is inhibited by the steric bulk of the phosphole substituents (i.e., the butyl groups, the phenyl group, and the oxygen atom). Upon the

Synthesis and circularly polarized luminescence properties of BINOL-derived bisbenzofuro[2,3-b:3’,2’-e]pyridines (BBZFPys)

• Ryo Takishima,
• Yuji Nishii,
• Tomoaki Hinoue,
• Yoshitane Imai and
• Masahiro Miura

Beilstein J. Org. Chem. 2020, 16, 325–336, doi:10.3762/bjoc.16.32

• . The crystal of 4b is classified into a space group P4322 (tetragonal) with a biaryl torsion angle of 74.4° (Figure 4b). A considerable intermolecular π–π stacking interaction was observed in between its polyaromatic fragments whose distance is approximately 3.44 Å. The polycyclic subunits overlap each

• other, being line-symmetrically aligned (Figure 5a). Meanwhile, the isomer 4c has two independent molecules in the unit cell, and the torsion angles are 67.1° and 106.8°, respectively (Figure 4d and 4f). As displayed in Figure 4b, the aromatic fragments are point-symmetrically overlapped with the π–π

• stacking distance of around 3.45 Å. It is noteworthy that both 4b and 4c pile up while minimizing the steric repulsion between the tert-butyl groups which occupy “staggered” orientations in their crystal structures (Figure 5c and 5d). Unfortunately, the crystal structure of 4a was not determined after