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

• ], whereas tosylation is one of the few procedures compatible with red blood cells and animal labelling [51]. Alternatively, benzophenone 18, which can be incorporated in the form of an unnatural amino acid, can form a UV-induced diradical for protein modifications (Scheme 7b) [52][53][54][55]. Proteins

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

• hexafluorophosphate was used as supporting electrolyte. Pt, Pt wire, and Ag/AgCl were used as working, counter, and reference electrodes, respectively. The measurements were standardized by measuring the red/ox potential of ferrocene after each compound analysis. All potentials are reported vs Fc/Fc+ red/ox couple

• . LUMO energies were estimated using the onset red/ox potentials according to the equation: Elumo= −(Eredonset + 4.8) (eV) X-ray study. Neat compounds were crystallized by a slow vapor diffusion method from the CHCl3/hexane (4,5-DPDAF) and toluene/iPrOH (1,8-DPDAF) systems. The crystal growth time was

• crystallographic axes. The red line shows the (001) plane. The schematic packing motifs are shown in blue, whereas linking [ZnCl]+ moieties are illustrated by blue dots. Voids are shown as brown contact surfaces created using a probe radius of 1.2 Å. Knoevenagel reaction of 1 and 2 under basic conditions

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

• of the different halogen atoms, attaching a second halogen atom (e.g., mono/dichloro derivatives 1c and 1d in Figure 5) has more pronounced effect (red-shift). The shape of the obtained spectra is as expected for azobenzene derivatives with the E-isomers featuring a dominant band appearing at 270–400

• absorption maxima of the disubstituted Z-isomers are red-shifted by ≈5 nm. Considering very similar ϕZ values for all three investigated pairs, λZmax is influenced rather electronically via the second halogen atom. The UV–vis absorption spectra were further predicted via TD-DFT and using B3LYP and CAM-B3LYP

• functionals (Table 3 and Supporting Information File 1, Figures S65–88). Both methods afforded the spectra that are similar in shape but either red or blue-shifted compared to the experimental data. The range-separated CAM-B3LYP functional was used to better describe the excited states and charge-transfer

Design, synthesis, and biological evaluation of FXR/ASK1 dual-target modulators

• Xi Zhang,
• Jingyan Wang,
• Ziqiang Zhao,
• Caiyi Wang,
• Zenghui Ye,
• Wei-Yuan Ma,
• Jian-Xing Xu and
• Fengzhi Zhang

Beilstein J. Org. Chem. 2026, 22, 771–781, doi:10.3762/bjoc.22.59

• accumulation. The presence of lipid droplets was confirmed through direct visualization using Oil Red O staining (Figure 3A). The combined treatment with GW4064 and GS4997 exerted a stronger lipolytic effect than either positive control alone, and its activity was comparable to that of Z8. As anticipated, both

• , selonsertib, Z8, Z30, or the combination of GW4064 and selonsertib for 2 h prior to OA stimulation (600 μM). (A) Representative Oil Red O staining images (40×). (B) Quantification of staining intensity by ImageJ. Data are presented as mean ± SD (n = 3). Statistical significance was analyzed by one-way ANOVA

Anti-invasive and cytotoxic evaluation of a (+)-pinoresinol-based semisynthetic library against glioblastoma

• Chen Zhang,
• Kah Yean Lum,
• Jonathan M. White,
• Paul I. Forster,
• Nicholas Booth,
• Sunita A. Ramesh and
• Rohan A. Davis

Beilstein J. Org. Chem. 2026, 22, 691–704, doi:10.3762/bjoc.22.54

• converting resazurin to resorufin, i.e., blue to pink /red in color [40]. Changes in cell viability were detected using fluorescence (excitation at 530–560 and emission at 590 nm) or absorbance (detected at 570 and 600 nm) in a plate reader (FLUOstar Omega, BMG Labtech). In this study, cell viability was

Regioselective approach to 5-arylsulfonylisoxazoles and their antimicrobial activity

• Artem S. Sazonov,
• Dmitry A. Vasilenko,
• Denis V. Porfiriev,
• Yuri K. Grishin,
• Rimma A. Gazzaeva,
• Alisa P. Chernyshova,
• Maxim A. Kryakvin,
• Anna A. Baranova,
• Vera A. Alferova and
• Elena B. Averina

Beilstein J. Org. Chem. 2026, 22, 592–602, doi:10.3762/bjoc.22.45

• the expression of the katushka2S gene. When scanning, the signal from the RFP protein was displayed in green pseudocolor, and from Katushka2S in red. Most of the studied compounds demonstrated low antibacterial activity against the reporter strains, however, 3-nitrosulfonylisoxazoles 3h, 3g and

• red pseudocolor, respectively. Inhibition of Klenow fragment of E. coli DNA polymerase I. A) The principal scheme of the Klenow fragment test. If DNA polymerase I is inhibited by antibiotic doxorubicin, the synthesis of the full-length product will be compromised, and a complete product will not be

Kinetic resolution of racemic planar-chiral vinylcymantrenes by molybdenum-catalyzed asymmetric metathesis dimerization

• Haruna Imazu,
• Hitoshi Izu,
• Yasuhiro Ohki and
• Masamichi Ogasawara

Beilstein J. Org. Chem. 2026, 22, 568–574, doi:10.3762/bjoc.22.42

• ) presence of a substituent (Br or Me) at the position adjacent to the vinyl group in the clockwise direction, (2) absence of a substituent other than hydrogen at the position adjacent to the vinyl group in the counterclockwise direction (CH or P). The substituent adjacent to the vinyl group (marked in red

Molecular tweezer–peptide conjugates disrupt the protein–protein interaction between survivin and histone H3 essential in mitosis

• Catherine Gsell,
• Philipp Rebmann,
• Karina Opara,
• Christine Beuck,
• Peter Bayer,
• David Bier,
• Ingrid R. Vetter and
• Thomas Schrader

Beilstein J. Org. Chem. 2026, 22, 557–567, doi:10.3762/bjoc.22.41

• the peptide tweezer 1 on either K-121 or K-129 (bottom). The positive residues of the H3 peptide are bound to the negatively charged area (red) whereas the phosphorylated threonine contacts a positively charged area, as known from the existing crystal structures. The tweezer moiety can associate with

• complex. A) Lewis structure of the truncated tweezer peptide monophosphate 2b. B) Close-up of the binding motif formed by 2b (tweezer: green, butynyl ester: red) on the survivin surface encapsulating Lys-121 after MD simulation (Desmond, 100 ns, 300 K, 0.15 mM NaCl) using explicit water solvent. A

• red, tweezer green. A) Lewis structures of the new slightly extended binding peptide 3b and the respective click conjugates with butynyl tweezer, mono- and diphosphate 2c and 2d. B) Lewis structures of the new binding peptide 3c and the resulting mono- and diphosphate tweezer conjugates 2e and 2f

Get a better glimpse on sequential photoreactions of trisnorbornadienes with ¹⁹F NMR spectroscopy

• Julian Felix Maria Hebborn,
• Ben Eric Merten,
• Thomas Paululat and
• Heiko Ihmels

Beilstein J. Org. Chem. 2026, 22, 527–534, doi:10.3762/bjoc.22.38

• variation often leads to a red-shifted absorption, the half-lives of the corresponding quadricyclanes are often decreased at the same time. In particular, the addition of an acetylene unit between the linking aromatic part and the norbornadiene often leads to short half-lives [29][30][31]. As arene-linked

• the photoreaction of 1f; blue: 1f; purple: 2f2,1; pink: 2f1,2; red: 2f0,3. Photochromic reaction of norbornadiene (1a) and quadricyclane (2a) and selected physicochemical properties; λonset = low-energy zero onset of absorption of 1a; t1/2 = half-life of 2a; ΔH = reaction enthalpy of the

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

• using thin-layer chromatography, with the appearance of the characteristic red spot upon treatment with FeCl3 confirming the presence of the hydroxamic acid functionality. Moreover, the formation of the tetra-hydroxamic acid product was confirmed by 1H NMR spectroscopy in deuterated DMSO, as evidenced

• leaching into water was confirmed by depositing a drop of the aqueous supernatant on a TLC plate, which showed no formation of the characteristic red iron-hydroxamate complex upon treatment with FeCl3. These physicochemical properties precluded standard liquid–liquid extraction but were suitable for a

Synthesis of a HDAC inhibitor–nanogold probe for cryo-EM visualization in class I HDAC co-repressor complexes

• Wiktoria A. Pytel,
• John W. R. Schwabe and
• James T. Hodgkinson

Beilstein J. Org. Chem. 2026, 22, 480–485, doi:10.3762/bjoc.22.35

• . Error bars represent ± S.E.M. (n = 3). For full assay conditions see Supporting Information File 1. Final round of 2D classification of the cross-linked CoREST complex in the presence of Au–(CI-994) (87,649 particles). Red arrows indicate the position of the Au–(CI-994) probe localized with the CoREST

Synthesis and stereochemical analysis of dynamic planar chiral oxa[7]orthocyclophene

• Yukiho Hashimoto,
• Yuuya Kawasaki,
• Kazunobu Igawa and
• Katsuhiko Tomooka

Beilstein J. Org. Chem. 2026, 22, 436–442, doi:10.3762/bjoc.22.30

• alkyne 6. Subsequent preparation of the lithium acetylide using n-BuLi, followed by treatment with formaldehyde, afforded propargyl alcohol 3a in 70% yield over three steps. The reaction of 3a with Red-Al generated a vinyl aluminum species, which was then treated with iodine to provide the iodinated Z

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

• concentration of 2 × 10−5 M, as shown in Supporting Information File 1, Figure S21. Both compounds have slightly similar absorption bands. Compound 7 shows an absorption maximum at 395 nm as a broad band peak. In comparison to compound 7, compound 8 displays a slight bathochromic (red) shift, with absorption

• analysis provides vital insights into the electronic characteristics of atoms within a molecule [61]. In the MEP maps, the colour distribution follows the order blue, green, and red, representing increasing electrostatic potential. The blue regions correspond to more electropositive areas, while the red

Cone p-aminocalix[4]arenes enriched with ‘clickable’ alkyne or azide functionalities

• Ilia Korniltsev,
• Vasily Bazhenov,
• Alexander Gorbunov,
• Dmitry Cheshkov,
• Stanislav Bezzubov,
• Vladimir Kovalev and
• Ivan Vatsouro

Beilstein J. Org. Chem. 2026, 22, 399–415, doi:10.3762/bjoc.22.28

• ]arenes by joining propargyl/2-azidoethyl and p-amino groups on a common platform. Parts of 1H,13C HMBC spectra of calixarenes 12 (a) and 13 (b) recorded in CDCl3 solutions at 600 MHz. Red lines show the key correlations between signals from the calixarene narrow-rim substituents and aromatic units

Electrosynthetic access to unsymmetrical oxaza[8]helicenes with high chiral stability and strong circularly polarized luminescence (CPL)

• Tin Zar Aye,
• Rubal Sharma,
• Muthu Karuppasamy,
• Daiya Suzuki,
• Haruka Nakajima,
• Yoshitane Imai,
• Mitsuhiro Arisawa,
• Mohamed S. H. Salem and
• Shinobu Takizawa

Beilstein J. Org. Chem. 2026, 22, 372–382, doi:10.3762/bjoc.22.25

• ]helicenes 5a and 5b in chloroform (1 × 10−5 M) were recorded and compared with those of the corresponding oxaza[7]helicenes 6a and 6b (Figure 4A and 4B). As expected, extension of the helical π-systems in 5 leads to enhanced conjugation relative to 6, manifested in red-shifted absorption and emission bands

• and second fractions of the chiral HPLC analysis were assigned as the (P)- and (M)-enantiomers, respectively, for all 5a,b and 6a,b. As expected, the increase in helical length (n) from 7 to 8, 5a and 5b exhibited more red-shifted maximum |gabs| values at around 350 nm, whereas 6a and 6b showed values

• dashed lines for (P)-configuration of 5a (black), 5b (blue), 6a (green), and 6b (red). Recent examples of hetero[8]helicenes: (A) symmetric hetero[8]helicenes; (B) unsymmetrical hetero[8]helicenes; (C) short-step electrosynthetic access to new unsymmetrical oxaza[8]helicenes. Short-step synthesis of

Spirobarbiturates with a pyrrolizidine moiety: synthesis, structure and biological evaluation

• Arthur A. Puzyrkov,
• Andrew S. Drachuk,
• Ekaterina A. Popova,
• Alexander V. Stepakov and
• Vitali M. Boitsov

Beilstein J. Org. Chem. 2026, 22, 274–288, doi:10.3762/bjoc.22.20

• CrystalExplorer 21.5 [55]. On the Hirshfeld surface, color coding indicates the nature of intermolecular interactions: red highlights contacts shorter than the van der Waals radius, white represents distances equal to the van der Waals radius, and blue denotes contacts longer that the van der Waals radius. Figure

•  4 shows front and back views of the Hirshfeld surfaces (dnorm) for compounds 4b and 4c. The Hirshfeld surface for compound 4b with dnorm map plotted (ranging from −0.8499 (red) to 1.4229 (blue) a.u.) is presented in Figure 5. Analysis of the HS revealed the presence of several intermolecular

• one of the water hydrogens interacts with a carbonyl group of the barbiturate ring (C=O···H–O = 2.867 Å). The HS for compound 4c with dnorm map plotted (ranging from −0.6673 (red) to 1.4313 (blue) a.u.), is shown in Figure 6. The dnorm map highlights key intermolecular interactions (marked in red

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

• )/CBS level of theory. Color labels: H = white, C = grey, N = blue, O = red, F = electric blue. (S)-DFMO bound within the active site of human arginase I obtained from the Protein Data Bank (3GN0) (https://doi.org/10.2210/pdb3gn0/pdb, [21]). Dotted lines represent hydrogen-bonding interactions with

• amino acid residues and water molecules, while the ligand is delineated by a contour line to distinguish it from the binding cavity. Lowest-energy type-I, type-II, and type-III conformers of the zwitterionic form of (S)-DFMO. Color labels: H = blue, C = pink, N = orange, O = red, F = yellow. DFT

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

• essentially unchanged, whereas its fluorescence emission undergoes a monotonic red shift with increasing solvent polarity (or polarizability), accompanied by an enlarged Stokes shift – a typical solvatochromic behavior. The weak solvent dependence of the absorption spectra indicates that the difference in

• the ground state, lowering the excited-state energy and thus the photon energy, which manifests macroscopically as a red-shifted emission. In polar media, the oriented polar solvent shell stabilizes the CT state more effectively than the ground or locally excited (LE) state, further decreasing the

• a result of RTP, as the sub-second lifetime and the pronounced thermal quenching behavior are characteristic features of RTP. Additionally, the red shift observed in the delayed emission spectrum compared to the steady-state emission is consistent with the behavior of lower-energy emissions that are

Improved synthesis and physicochemical characterization of the selective serotonin 2A receptor agonist 25CN-NBOH

• Adrian G. Rossebø,
• Hannah G. Kolberg,
• Anders E. Tønder,
• Louise Kjaerulff,
• Poul Erik Hansen,
• Karla A. Frydenvang,
• Jesper Østergaard and
• Jesper L. Kristensen

Beilstein J. Org. Chem. 2026, 22, 175–184, doi:10.3762/bjoc.22.11

• recrystallized from ethanol (Figure 3, purple), a similar pattern is observed, indicating a high degree of crystallinity. Furthermore, samples of 1·HCl prepared either by rapid precipitation in organic solvents, as described in the Experimental section (red), or material isolated from a saturated solution of 1

• , oxygen atoms red, and chloride ion green. b) The crystal packing reveals alternating layers, a polar layer with hydrogen bonds (black dashed lines), and a hydrophobic layer with π–π-stacking (grey dashed lines). SCXRD and XRPD spectra of different preparations of 1·HCl. Blue: SCXRD spectrum of 1·HCl. Red

• , green, and purple: XRPD spectra of 1·HCl after recrystallization (red), directly as synthesized (green), and of a slurry obtained by stirring excess solid in ultrapure water for 3 days (purple). TGA and DSC thermograms of 1·HCl. Calculated pH-dependent species distribution curves for 25CN-NBOH (1). a

A new synthesis of Tyrian purple (6,6’-dibromoindigo) and its corresponding sulfonate salts

• Holly Helmers,
• Mark Horton,
• Julie Concepcion,
• Jeffrey Bjorklund and
• Nicholas C. Boaz

Beilstein J. Org. Chem. 2026, 22, 167–174, doi:10.3762/bjoc.22.10

• red shift by 16 and 15 nm with a moderate increase in molar absorptivity, respectively, for compounds 9 and 10 [29]. This means that to the human eye, di- and trisulfonated derivatives of 1 appear blue, not purple. A smaller shift in λmax is observed when indigo is sulfonated, allowing for its blue

Design and synthesis of an axially chiral platinum(II) complex and its CPL properties in PMMA matrix

• Daiki Tauchi,
• Sota Ogura,
• Misa Sakura,
• Kazunori Tsubaki and
• Masashi Hasegawa

Beilstein J. Org. Chem. 2026, 22, 143–150, doi:10.3762/bjoc.22.7

• -derived pendant group, which exhibited aggregation-enhanced red phosphorescence and CPL properties in the solid states [20], while Yam and co-workers also reported pincer-type platinum(II) complexes containing chiral amine moieties, and investigated their aggregation behavior and chiroptical properties

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

• can be shifted in the deep red/NIR region by changing the donor group with increased conjugated systems [19][20][21][22]. Gupta et al. studied optical properties of D–π–A system-based indan-2-one derivatives, and symmetric derivatives showed a significant bathochromic shift (≈300 nm) compared to

• more polarized than the ground states, as shown by the positive observed μβ values. Moreover, both the ground and excited states were polarized in the same direction for all studied compounds. The standard reference is Disperse Red 1 (μβ = 450 × 10−48 esu) [33]. Comparing the µβ values of Disperse Red

• 1 with the measured values of 2a–c shows that the molecules exhibited a higher NLO response than Disperse Red 1, except for 2c. The dipole moment (μ), polarizability (α), first-order hyperpolarizability (β), and its components, which were calculated at the B3LYP/6-31+G(d,p) level of theory in CHCl3

One-pot synthesis of ethylmaltol from maltol

• Immanuel Plangger,
• Marcel Jenny,
• Gregor Plangger and
• Thomas Magauer

Beilstein J. Org. Chem. 2025, 21, 2755–2760, doi:10.3762/bjoc.21.212

• Immanuel Plangger Marcel Jenny Gregor Plangger Thomas Magauer Department of Organic Chemistry and Center for Molecular Biosciences, University of Innsbruck, Innrain 80−82, 6020 Innsbruck, Austria Red Bull Central Laboratory, Betriebsgebiet Hängender Stein 1, 6713 Ludesch, Austria Red Bull Service

• Laboratory of Red Bull Service GmbH and was found to meet the quality parameters of commercial ethylmaltol (1), posing no concerns from a food safety perspective (see Supporting Information File 1). Conclusion In conclusion, we have developed a new synthetic approach to the flavor enhancer ethylmaltol (1

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

• 0.01 M solutions of 1-nitro-1-nitroso compounds 1a, 1f, 1c, and 1i in MeCN, these substances do not undergo noticeable oxidation up to +2.4 V. On the other hand, 1-chloro-1-nitrosocyclohexane (S3, green curve) and 1-nitrosocyclohexyl acetate (S4, red curve) are oxidized at +1.82 V and +1.77 V

• our study [87], ADN exhibits two irreversible oxidation peaks (red curve) at +1.8 V and +2.1 V, which are higher than or comparable to those of S2–S4 (Figure 2). Upon the addition of ADN to a solution of 1a (Figure 2, green curve), a single oxidation peak was observed at +1.89 V. Finally, the reaction

• ]/CPCM(MeCN) level of theory (in the case of >15 conformers, 15 most stable according to GFN2-xTB were analyzed). CV-curves of 0.01 M solutions of a) 1a (blue), b) 1f (azure), c) 1c (pink), d) 1i (yellow), e) S4 (red), f) S3 (green), g) S2 (brown), and h) S1 (orange) in 0.1 M n-Bu4NBF4 solution in MeCN

Recent advancements in the synthesis of Veratrum alkaloids

• Morwenna Mögel,
• David Berger and
• Philipp Heretsch

Beilstein J. Org. Chem. 2025, 21, 2657–2693, doi:10.3762/bjoc.21.206

• of green for strategic connections, yellow for neutral, e.g., functional group interconversion and isomerization, orange for non-strategic reactions, and red for protecting group (PG) manipulations (Scheme 3). Protecting group manipulations refer to any protection or deprotection of a functional

• and as a semisynthesis, poses some non-strategic redox transformations (orange) and protecting manipulations (red) especially in the beginning and in the endgame of the synthesis. Nevertheless, several transformations are desirable green transformations, although it is noticeably more difficult to

• the semisynthesis of Liu/Qin [26] 15 years later. The only non-green transformations displayed at the start were a protecting group installation (red) and a condensation (yellow), which was needed for the C–H activation (light green). All other transformations connect either C–C or C–heteroatom bonds