Site-specific labelling of native peptides and proteins: chemical and enzymatic strategies

• Antonio Angelastro,
• Jonathan Bargh,
• Subhajit Guria,
• Victor Laserna and
• Louis Luk

Beilstein J. Org. Chem. 2026, 22, 857–881, doi:10.3762/bjoc.22.67

• mutation of endoglycosidase S2 (EndoS2) catalytic Asp184 residue into Met (EndoS2 D184M), generating a variant capable of transferring a pre-assembled azido-glycan oxazoline donor substrate onto an antibody with high homogeneity [137]. However, while the elegance of this strategy is undeniable, synthesis

The trans-influence in gold chemistry from a catalytic perspective

• Manfred Bochmann

Beilstein J. Org. Chem. 2026, 22, 838–856, doi:10.3762/bjoc.22.66

• ) compounds the use of tridentate (pincer) and bidentate ligands has proved particularly successful. A number of pertinent structural types A–H and the symbolic representations used in this Perspective are shown in Scheme 2. The choice of the donor trans to the reactive ligands X is crucial; for example

• , while C^N^C and C^C^N ligand frameworks look like simple structural isomers, their reactivity and analysis of their bonding has shown that replacing the weak N(pyridine) donor by strongly donating anionic carbon leads to profound changes in gold orbital ordering, often with drastic consequences for

• biphenylyl dianion Chambrier et al. have demonstrated that apart from the donor strength the electron-withdrawing character and the π-acceptor capacity of the chelate ligand can play an important role [37]. This was found to be the reason why [(C^C)Au(diene)]+ complexes (diene = 1,5-cyclooctadiene (5) or

Total synthesis of the capsular polysaccharide repeating unit towards the development of a glycoconjugate vaccine against Klebsiella pneumoniae ST512

• Shuo Zhang,
• Ondřej Daněk and
• Peter H. Seeberger

Beilstein J. Org. Chem. 2026, 22, 821–827, doi:10.3762/bjoc.22.64

• furnished tetrasaccharide 15. Subsequently, donor 3 was coupled with compound 15 under NIS/TfOH promotion to yield pentasaccharide 16 in 89% yield. The stereoselective construction of the 1,2-cis linkage was directed by the bulky 4,6-O-silylidene protecting group of 3. Treatment with HF·pyridine

Synthesis and structural elucidation of a novel bis-spirooxindole from isatin and ethylenediamine

• Irene Moreno-Gutiérrez,
• Josefa L. López-Martínez,
• Sonia Berenguel-Gómez,
• Irene Torres-García,
• Duane Choquesillo-Lazarte,
• Manuel Muñoz-Dorado,
• Miriam Álvarez-Corral and
• Ignacio Rodríguez-García

Beilstein J. Org. Chem. 2026, 22, 813–820, doi:10.3762/bjoc.22.63

• NaBH4 or by the ethylenediamine acting as a hydride donor. In addition, if the formation of 28 by addition of the enol of 27 to the imine were reversible (and the reduction step irreversible), then the more stable, dipole-opposed C2-symmetric structure for 28 should be dominant, thus explaining the

Knoevenagel condensation of 4,5- and 1,8-diazafluorenes

• Darya S. Cheshkina,
• Christina S. Becker,
• Alina A. Sonina and
• Maxim S. Kazantsev

Beilstein J. Org. Chem. 2026, 22, 803–812, doi:10.3762/bjoc.22.62

• several electron-donor and electron-acceptor-substituted benzaldehydes (viz. 4-methoxybenzaldehyde, 4-bromobenzaldehyde, 3-nitrobenzaldehyde, and unsubstituted benzaldehyde) were first carried out under basic conditions, using t-BuONa in DMF or t-BuOH (Scheme 1 and Table 1). Both diazafluorenes 1 and 2

• ). Therefore, we changed the solvent in the reactions of 1,8-diazafluorene (2) to ethanol or toluene. As a result, condensation products of 2 with various donor- and acceptor-substituted benzaldehydes were obtained in moderate to good yields in both solvents (Table 1). Note, the yields were generally higher in

Halogenated azobenzene acrylates: from efficient solution photoswitching to stable solid-state photochromic materials

• Martina Vachtlová,
• Michaela Fecková,
• Vítězslav Zima,
• Jan Podlesný,
• Milan Klikar,
• Oldřich Pytela,
• Patrik Pařík,
• Jakub Opršal,
• Eliška Juhaňáková,
• Veronika Chrtová and
• Filip Bureš

Beilstein J. Org. Chem. 2026, 22, 782–794, doi:10.3762/bjoc.22.60

• corresponding radical anion [27]. In contrast, possible reduction of an aliphatic ester substituent, such as our acrylate pendant, generally requires more negative potentials [28]. On the other hand, the first oxidation observed at ca. +1.47 V is most likely associated with the alkoxy donor fragment, in

• support the assignment of the first oxidation to the alkoxy donor moiety and the first reduction to the azobenzene acceptor fragment. If we consider the reduction of the azo bond as a one-electron process, a mutual comparison of the current maxima of the first oxidation and reduction provided an

Synthesis of heterocycles based on azomethine ylides from α-amino acids (or amines) and carbonyl compounds

• Ekaterina V. Berezhnaya,
• Alexander I. Ponyaev,
• Vitali M. Boitsov and
• Alexander V. Stepakov

Beilstein J. Org. Chem. 2026, 22, 705–741, doi:10.3762/bjoc.22.55

• method for the synthesis of polycyclic pyrrolidines 82–91, which in addition to their use in medicinal chemistry, serve as polydentate N-donor ligands. The authors described the trimethylaluminum-catalyzed (3 + 2)-cycloaddition of bis(2-pyridyl)imine 79 with a wide range of acyclic and cyclic olefins 36

Harnessing light energy with molecules

• Grace G. D. Han,
• Mogens Brøndsted Nielsen and
• Hermann A. Wegner

Beilstein J. Org. Chem. 2026, 22, 680–682, doi:10.3762/bjoc.22.52

• structure by a heteroatom (oxygen or nitrogen) in donor–acceptor, push–pull NBD derivatives are reported. In a computational study, Pawar and co-workers [7] further expanded the NBD structure by elongating the unsaturated bridge with different heteroatoms or functional groups. Azobenzenes, interconverting

• another publication, Leung and co-workers [11] describe how amphiphilic donor–acceptor Stenhouse adducts can be employed in supramolecular nanostructures controlled by visible light, which is of particular interest for the development of biomedical materials. Jones, Evans, and co-workers [12] studied X

• . Photoinduced charge separation is a key process in the development of systems for artificial photosynthesis, photovoltaics, and photocatalysis. Kobayashi and co-workers [19] studied in detail the excited-state dynamics of donor–acceptor dyads based on perylene and phenothiazine, in which triphenylamine units

Photoorganocatalytic trifluoromethylation of (het)arenes in green conditions

• Egor N. Boronin,
• Svetlana E. Kaurkina,
• Milena M. Svetlakova,
• Anton S. Bolshakov,
• Maxim V. Arsenyev,
• Vasilii F. Otvagin,
• Alexey Yu. Fedorov,
• Timothy Noël and
• Alexander V. Nyuchev

Beilstein J. Org. Chem. 2026, 22, 662–671, doi:10.3762/bjoc.22.50

• that CF3· behaves as an electrophilic radical [31][32], it was expected to react preferentially with electron-rich substrates compared to electron-neutral or electron-deficient ones. To probe this trend, trifluoromethylation was examined with substrates bearing donor substituents (methoxyarenes) and

• */PC·−) = 1.09 V) [33], together with the reduction potential of TFAA (Ered = −1.2 V) [34] and the oxidation potential of TMB (Ered = 1.43 V) [35], it can be concluded that in our reaction the photocatalyst acts primarily as an electron donor. Accordingly, for the pair of TFAA and TMB, reduction of

Synthesis and uranyl(VI) extraction performance of a calix[4]pyrrole–tetrahydroxamic acid receptor

• Sara Karnib,
• Rana Baydoun,
• Wissam Zaidan,
• Nancy AlHaddad,
• Omar El Samad,
• Bilal Nsouli,
• Francine Cazier-Dennin and
• Pierre-Edouard Danjou

Beilstein J. Org. Chem. 2026, 22, 486–494, doi:10.3762/bjoc.22.36

• aqueous solution, hexavalent uranium, the most dominant oxidation state, exists predominantly as the linear uranyl ion UO22+. In this ion, two oxo ligands occupy axial positions while the equatorial plane accommodates four to six donor atoms [74][75]. Complexes of UO22+ often adopt either a pseudoplanar

• pentacoordinate or hexacoordinate structure, as shown by X-ray crystallographic studies. Consequently, to bind UO22+ effectively, a ligand must present donor atoms positioned to match the uranyl equatorial coordination sites [76]. Hydroxamic acids act as bidentate ligands, with each functional unit offering two

• donor atoms, a carbonyl oxygen and a hydroxy oxygen, that can simultaneously coordinate to a uranyl ion [77]. In supramolecular systems, not all hydroxamic acid groups necessarily bind uranyl ions, as steric hindrance and site accessibility can limit coordination to a subset of available sites [78]. A

Structural reassignment of compound 968, an allosteric glutaminase inhibitor

• Lindsey A. Albertelli,
• Sainabou Jallow,
• Chun Li and
• Scott M. Ulrich

Beilstein J. Org. Chem. 2026, 22, 455–460, doi:10.3762/bjoc.22.33

• ]. Glutamine serves as a nitrogen donor for the biosynthesis of asparagine, amino sugars, and nucleotides. Glutamine is also hydrolyzed to glutamate by glutaminase (GLS) enzymes, which are often overexpressed in cancer cells. The resulting glutamate supports the biosynthesis of glutathione and can be

Synthesis and anti-cancer activity of naphthalimide–organylselanyl conjugates

• Rajkumar Ravi and
• Selvakumar Karuthapandi

Beilstein J. Org. Chem. 2026, 22, 416–435, doi:10.3762/bjoc.22.29

• interactions: van der Waals (Gly772), hydrogen bonding and carbon–hydrogen bonding (Met769), π–donor (Thr766), π–σ (Leu820), π–sulfur (Met742), amide–π (Phe771), alkyl (Leu694), and π–alkyl interactions (Val702, Ala719, Lys721, Leu764). In contrast, compound 8 formed eight interactions: van der Waals (Pro770

• six major interactions: hydrogen bonding (Met769), π–donor (Thr766), π–σ (Leu694, Val702, Leu820), π–lone pair (Phe771), alkyl (Leu694), and π–alkyl interactions (Ala719, Lys721). By comparison, compound 8 formed six interactions: hydrogen bonding (Met769), carbon–hydrogen bonding (Thr766), π–donor

Arene activation via π-bond localization: concepts and opportunities

• Paul Meiners,
• Julian J. Melder and
• Tobias Morack

Beilstein J. Org. Chem. 2026, 22, 257–273, doi:10.3762/bjoc.22.19

• substituent and the unbound portion of the aromatic ring (Scheme 1A). Thus, coordinating the metal to a benzene ring with a single π-donor substituent increases the interaction between the donor group and the uncoordinated diene moiety, further activating the uncoordinated ortho and para positions for

• unfolds in η2-naphthalene complexes, where transient formation of the less favored 2,3-η2-isomer imparts o-quinodimethane character (Figure 7) [52]. The third reactivity mode is purely activating in nature, with the metal acting as a π-donor that increases and localizes the electron density of the

Conformational analysis of difluoromethylornithine: factors influencing its gas-phase and bioactive conformations

• Matheus P. Freitas

Beilstein J. Org. Chem. 2026, 22, 237–243, doi:10.3762/bjoc.22.17

• -difluoroethane, the classical gauche effect is attributed to σCH → σ*CF hyperconjugation [8][9][10][19]. In DFMO, the σCH orbital of the difluoromethyl group acts as the primary donor, while the vicinal σ*CN orbital is the main acceptor. Additional antiperiplanar interactions within the (F₂H)C–C fragment, which

Configuration–packing synergy enabling integrated crystalline-state RTP and amorphous-state TADF

• Ruiyan Wang and
• Yunan Wu

Beilstein J. Org. Chem. 2026, 22, 224–236, doi:10.3762/bjoc.22.16

• Abstract A twisted D–π–A molecule, PI-Cz 1, was designed and synthesized using phthalimide as the acceptor, carbazole as the donor, and a phenylene bridge. Single-crystal X-ray diffraction revealed a markedly non-coplanar skeleton. Calculations based on the crystallographic geometry and frontier-orbital

• molecular design approaches for TADF include twisted donor–acceptor structures (for example, carbazole or phenoxazine as donors and triazine, nitrile, or carbonyl groups as acceptors) as well as B/N multiresonance frameworks [30][31][32]. These strategies have been successful in achieving efficient triplet

• intermolecular coupling to enhance SOC and suppress non-radiative decay channels, while TADF relies more on donor–acceptor decoupling and smaller ΔEST to lower the thermal activation barrier for RISC. Thus, a key challenge in the field is how to establish adjustable synergy between the molecular-scale

Base-promoted deacylation of 2-acetyl-2,5-dihydrothiophenes and their oxygen-mediated hydroxylation

• Vladimir G. Ilkin,
• Margarita Likhacheva,
• Igor V. Trushkov,
• Tetyana V. Beryozkina,
• Vera S. Berseneva,
• Vladimir T. Abaev,
• Wim Dehaen and
• Vasiliy A. Bakulev

Beilstein J. Org. Chem. 2026, 22, 192–204, doi:10.3762/bjoc.22.13

• due to the stronger donor character of the pyrrolidine moiety due to its planar structure. The formation of the deacetylated products 2n,o (Scheme 2) may be attributed to increased steric hindrance, which makes proton transfer to B in Scheme 6 more difficult. The dimethyl-1-yl moiety likely exhibits a

• lower donor character compared to pyrrolidine, but higher than that of morpholine and piperidine. As a result, a mixture of products 2l and 2l′ is formed. Starting dihydrothiophenes 1 form more stable anions B in comparison with regioisomers 4 due to the delocalization of the negative charge over the

Asymmetric Mannich reaction of aromatic imines with malonates in the presence of multifunctional catalysts

• Kadri Kriis,
• Harry Martõnov,
• Annette Miller,
• Mia Peterson,
• Ivar Järving and
• Tõnis Kanger

Beilstein J. Org. Chem. 2026, 22, 151–157, doi:10.3762/bjoc.22.8

• product in a slightly less enantioselective way (71% ee). When comparing the halogen bond donor properties of tetrafluoroiodophenyl and iodophenyl moieties, the latter is weaker as it is less electron-withdrawing. However, there is a very small difference between reactivity and selectivity for catalysts E

Symmetrical D–π–A–π–D indanone dyes: a new design for nonlinear optics and cyanide detection

• Ergin Keleş,
• Alberto Barsella,
• Nurgül Seferoğlu,
• Zeynel Seferoğlu and
• Burcu Aydıner

Beilstein J. Org. Chem. 2026, 22, 131–142, doi:10.3762/bjoc.22.6

• 10.3762/bjoc.22.6 Abstract Three indan-2-one-based donor–π–acceptor–π–donor type dyes with symmetric donor groups were synthesized and characterized to study their nonlinear optical (NLO) properties and their potential use in the rapid and selective determination of cyanide. The designed structures

• feature symmetrical alkylaminophenyl donor groups and a strong electron-withdrawing dicyanovinylene as an acceptor connected through vinyl groups as a π-bridge. These strongly π-conjugated organic dyes can absorb in the NIR region, and they showed sensitivity towards the polarity of solvents with

• colorimetric and optical changes. Because of the strong donor–acceptor structure, second-order NLO properties were studied by measuring electric field-induced second harmonic (EFISH) values, which showed significant second-order NLO responses. The experimental results were explained using density functional

Highly electrophilic, gem- and spiro-activated trichloromethylnitrocyclopropanes: synthesis and structure

• Ilia A. Pilipenko,
• Mikhail V. Grigoriev,
• Olga Yu. Ozerova,
• Igor A. Litvinov,
• Darya V. Spiridonova,
• Aleksander V. Vasilyev and
• Sergey V. Makarenko

Beilstein J. Org. Chem. 2026, 22, 123–130, doi:10.3762/bjoc.22.5

• groups seems attractive for both theoretical chemistry and the synthesis of 2-aminocyclopropanecarboxylic acids, of which representatives have biologically active properties against kynurenine-3-monooxygenase [25] and GABA receptors [26]. Such aminocyclopropane derivatives can be classified as donor

Advances in Zr-mediated radical transformations and applications to total synthesis

• Hiroshige Ogawa and
• Hugh Nakamura

Beilstein J. Org. Chem. 2026, 22, 71–87, doi:10.3762/bjoc.22.3

• alkyl radicals 46. When γ-terpinene was employed as a hydrogen donor, the radicals were reduced to the corresponding alkanes 47. Alternatively, in the presence of olefins, radical addition proceeded smoothly to furnish functionalized products 48. This methodology proved broadly applicable to a wide

Sustainable electrochemical synthesis of aliphatic nitro-NNO-azoxy compounds employing ammonium dinitramide and their in vitro evaluation as potential nitric oxide donors and fungicides

• Alexander S. Budnikov,
• Nikita E. Leonov,
• Michael S. Klenov,
• Andrey A. Kulikov,
• Igor B. Krylov,
• Timofey A. Kudryashev,
• Aleksandr M. Churakov,
• Alexander O. Terent’ev and
• Vladimir A. Tartakovsky

Beilstein J. Org. Chem. 2025, 21, 2739–2754, doi:10.3762/bjoc.21.211

• applications, as both electrolyte and source of a =NNO2 group. The developed method is green, practical, and scalable due to constant current electrolysis in an undivided cell at high current densities. Synthesized products demonstrated pronounced NO-donor activity and fungicidal activity against

• . Subsequent nitration of the obtained diol 3f with a HNO3/Ac2O mixture afforded dinitrate 4f in 79% (74% over two stages, Scheme 3, reaction 2). Due to the presence of two nitrate groups, compound 4f may be of interest as a potential NO donor [92] and a precursor of new nitro-NNO-azoxy compounds via

• investigated an ability to release NO for the synthesized aliphatic nitro-NNO-azoxy compounds (Figure 4). Well-known NO-donor compounds 3-carbamoyl-4-(hydroxymethyl)furoxan (CAS-1609) [100][101] and nitroglycerin (NG) [102] were used as reference agents. The NO2− assumed to be formed as a result of NO

Chemoenzymatic synthesis of the cardenolide rhodexin A and its aglycone sarmentogenin

• Fuzhen Song,
• Mengmeng Zheng,
• Dongkai Wang,
• Xudong Qu and
• Qianghui Zhou

Beilstein J. Org. Chem. 2025, 21, 2637–2644, doi:10.3762/bjoc.21.204

• donor, through a late-stage glycosylation. The aglycon 2 can be derived from the Δ14 olefin intermediate 3 via Mukaiyama hydration and several functional group transformations. In turn, 3 would be generated from the key C14α-hydroxylated intermediate 4 via an elimination process. For the synthesis of 4

• hand, we first tried the synthesis of rhodexin A through direct glycosylation of 2 by the ʟ-rhamnose donor 2,3,4-tri-O-benzoyl-α-ʟ-rhamnopyranosyl trichloroacetimidate (14). However, the selective glycosylation at the C3-hydroxy group of 2 was a formidable challenge since competitive glycosylations of

Thiazolidinones: novel insights from microwave synthesis, computational studies, and potentially bioactive hybrids

• Luan A. Martinho,
• Victor H. J. G. Praciano,
• Guilherme D. R. Matos,
• Claudia C. Gatto and
• Carlos Kleber Z. Andrade

Beilstein J. Org. Chem. 2025, 21, 2618–2636, doi:10.3762/bjoc.21.203

• -bonded carbon atom. Given that 3n and 4n contain donor–acceptor (DA)-type groups separated by a π-bond, the study of their photophysical properties has become particularly interesting. This structural arrangement often facilitates an internal charge transfer (ICT) process, which is common for such

• , thus hindering an ICT process (see Supporting Information File 1, Scheme S2). The molecular structure of compounds 3n and 4n can be separated in three blocks: a donor region, a π bridge and an acceptor region (Figure 9) common to molecules with intramolecular charge transfer (ICT) states. M06-2X/def2

• -TZVPP single point calculations in CPCM water of compounds 3n and 4n in protonated, deprotonated, and neutral forms showed that there is a degree of charge transfer between a HOMO–LUMO excitation in their neutral and deprotonated forms [98]. Protonation of the nitrogen atom in the donor region shifts

Assembly strategy for thieno[3,2-b]thiophenes via a disulfide intermediate derived from 3-nitrothiophene-2,5-dicarboxylate

• Roman A. Irgashev

Beilstein J. Org. Chem. 2025, 21, 2489–2497, doi:10.3762/bjoc.21.191

• visible region, and improved morphological stability [4][5][6]. Recent reports have shown that the development of alkyl-supported TT-based semiconductors has led to high-performance, air-stable OFETs [7], while integration of TT frameworks into donor–acceptor architectures has enabled the development of

Ex-situ generation of gaseous nitriles in two-chamber glassware for facile haloacetimidate synthesis

• Nikolai B. Akselvoll,
• Jonas T. Larsen and
• Christian M. Pedersen

Beilstein J. Org. Chem. 2025, 21, 2465–2469, doi:10.3762/bjoc.21.188

• donor; haloacetimidates; haloacetonitrile; two-chamber reactor; Introduction Trifluoroacetonitrile is an electrophilic reagent that has seen a variety of uses, mostly for incorporating trifluoromethyl groups into organic compounds [1]. As an example it has been successfully utilized for the synthesis

• trifluoroacetonitrile [24]. Schmidt published the first synthesis of glycosyl trifluoroacetimidates and concluded that their glycosyl-donor properties were similar to the trichloroacetimidates, but more difficult to prepare and purify [24]. In contrast to these observations, Nakajima et al. reported the