1,2,3,4-Tetrahydro-1,4,5,8-tetraazaanthracene revisited: properties and structural evidence of aromaticity loss

• Arnault Heynderickx,
• Sébastien Nénon,
• Olivier Siri,
• Vladimir Lokshin and
• Vladimir Khodorkovsky

Beilstein J. Org. Chem. 2019, 15, 2059–2068, doi:10.3762/bjoc.15.203

• averaged distances from 1.363 to 1.367 Å (Table 1). The C1–C2 and C4–C5 distances vary between 1.447 and 1.421 Å, respectively, indicating poor conjugation through these bonds, as a result of a partial loss of the aromaticity of the central benzene ring. This feature is confirmed also by the deviation of

Synthesis and anion binding properties of phthalimide-containing corona[6]arenes

• Meng-Di Gu,
• Yao Lu and
• Mei-Xiang Wang

Beilstein J. Org. Chem. 2019, 15, 1976–1983, doi:10.3762/bjoc.15.193

• was evident that six bridging oxygen atoms formed roughly a plane. Interestingly, three tetrazine rings are procumbent on the plane while three phthalimide units were almost perpendicular to the plane. Judging from the bond lengths, all oxygen atoms in the linking positions tended to form conjugation

Norbornadiene-functionalized triazatriangulenium and trioxatriangulenium platforms

• Roland Löw,
• Talina Rusch,
• Tobias Moje,
• Fynn Röhricht,
• Olaf M. Magnussen and
• Rainer Herges

Beilstein J. Org. Chem. 2019, 15, 1815–1821, doi:10.3762/bjoc.15.175

• parameter controlling the cis–trans rate acceleration of azobenzenes and not the length of the spacer [1]. A full conjugation path from the azobenzene on top through the ethynyl spacer and the platform to a bulk gold surface shortens the half-life of the metastable cis-isomer from days to seconds even

• complete conjugation path across the double bond of norbornadiene to the metal. Additionally, it is known that electron-withdrawing groups in 2 or 3 position change the triplet energy hypersurface in such a way that a triplet excited quadricyclane 1b decays into the ground state of the norbornadiene 1a [9

• ], which is a precondition for an efficient QC→NBD isomerization via our postulated non-adiabatic singlet→triplet→singlet mechanism. Results and Discussion If our proposed spin change mechanism, mediated by the conducting electrons in bulk gold were correct, interruption of the conjugation path and

A golden opportunity: benzofuranone modifications of aurones and their influence on optical properties, toxicity, and potential as dyes

• Joza Schmitt and
• Scott T. Handy

Beilstein J. Org. Chem. 2019, 15, 1781–1785, doi:10.3762/bjoc.15.171

• shift of this lambda max by roughly 40 nm to around 338 nm, presumably due to their donating effect and conjugation with the carbonyl oxygen. Halogen substituents at the 6-position generally had little effect, with the exception of the most electron-withdrawing fluorine, which resulted in a slight blue

• expected due to the lack of direct conjugation with the carbonyl as well as the only modest electronic effects of alkyl, chlorine, and bromine. In general, the substituent effects are all fairly modest and result in fairly moderate changes in the extinction coefficient (although hydroxy substitution does

Synthesis, photophysical and electrochemical properties of pyridine, pyrazine and triazine-based (D–π–)₂A fluorescent dyes

• Keiichi Imato,
• Toshiaki Enoki,
• Koji Uenaka and
• Yousuke Ooyama

Beilstein J. Org. Chem. 2019, 15, 1712–1721, doi:10.3762/bjoc.15.167

• electron-donating and electron-accepting abilities of the D and A moieties and the expansion of π conjugation, respectively, can lead to a decrease in the energy gap between the HOMO and LUMO because the highest occupied molecular orbital (HOMO) is localized over the π-conjugated system containing the D

Diazocine-functionalized TATA platforms

• Roland Löw,
• Talina Rusch,
• Fynn Röhricht,
• Olaf Magnussen and
• Rainer Herges

Beilstein J. Org. Chem. 2019, 15, 1485–1490, doi:10.3762/bjoc.15.150

• to the trans-form, which slowly returns back to the stable cis-isomer. To investigate the thermal trans→cis isomerization as a function of the conjugation to the metal surface, we connected the acetylene spacer in meta (weak conjugation) and in para (strong conjugation) position. Both isomers form

• the metal surface [11][18]. With increasing π-conjugation from the azobenzene into the platform, and thus coupling to the gold surface, the activation barrier drops to almost zero (≈8 kJ mol−1) and the frequency factors (log A) become negative [11]. Vanishing barriers and low frequency factors are

• the azo group, providing a full π-conjugation path of the N=N unit through the ethynyl spacer into the platform. Diazocine-TATA 2 is connected in meta-position and thus interrupting conjugation [24][25]. Both diazocine-TATAs are equipped with methoxy groups, which serve as “reporter units” indicating

Introduction of an isoxazoline unit to the β-position of porphyrin via regioselective 1,3-dipolar cycloaddition reaction

• Xiujun Liu,
• Xiang Ma and
• Yaqing Feng

Beilstein J. Org. Chem. 2019, 15, 1434–1440, doi:10.3762/bjoc.15.143

• Soret band and two weak Q bands. When compared to the spectrum of the precursor 2, a blue shift of ≈10 nm was observed in those of 3a or 3b, which may result from the loss of partial conjugation after the cycloaddition reaction between the nitrile oxides and C=C double bond. However, the substitution at

Formation of an unexpected 3,3-diphenyl-3H-indazole through a facile intramolecular [2 + 3] cycloaddition of the diazo intermediate

• Andrew T. King,
• Hugh G. Hiscocks,
• Lidia Matesic,
• Mohan Bhadbhade,
• Roger Bishop and
• Alison T. Ung

Beilstein J. Org. Chem. 2019, 15, 1347–1354, doi:10.3762/bjoc.15.134

• presented in Figure 3. The crystal and refinement data are given in Table 1. The 3H-indazole 8 (–N=N–CRR–) has a break in its conjugation at the sp3 carbon atom when it is compared to the 1H-indazole isomer –NH–N=CH– that is fully conjugated with the benzo group. Therefore, the 3H-indazole isomer is higher

Steroid diversification by multicomponent reactions

• Leslie Reguera,
• Cecilia I. Attorresi,
• Javier A. Ramírez and
• Daniel G. Rivera

Beilstein J. Org. Chem. 2019, 15, 1236–1256, doi:10.3762/bjoc.15.121

• as the conjugation of steroids to amino acids, peptides and carbohydrates. We demonstrate that steroids are available with almost all types of MCR reactive functionalities, e.g., carbonyl, carboxylic acid, alkyne, amine, isocyanide, boronic acid, etc., and that steroids are suitable starting

• supramolecular chemistry applications. Keywords: conjugation; heterocycles; macrocycles; multicomponent reactions; steroids; Review 1 Introduction The utilization of multicomponent reactions (MCRs) [1] for the derivatization of biomolecules has continuously grown over the last years. These diversity-oriented

• the steroidal nucleus, the assembly of nitrogen-heterocycles fused to the steroid-ring system, the steroid conjugation and macrocyclization, all relying on MCRs. 2 Modification of the steroidal nucleus and the side chain 2.1 Isocyanide-based MCRs 2.1.1 Steroids as carbonyl component: One of the first

Ugi reaction-derived prolyl peptide catalysts grafted on the renewable polymer polyfurfuryl alcohol for applications in heterogeneous enamine catalysis

• Alexander F. de la Torre,
• Gabriel S. Scatena,
• Oscar Valdés,
• Daniel G. Rivera and
• Márcio W. Paixão

Beilstein J. Org. Chem. 2019, 15, 1210–1216, doi:10.3762/bjoc.15.118

• ) – derived from a renewable resource like sugar cane biomass – for the incorporation of chiral pyrrolidine-based motifs capable to catalyze relevant asymmetric reactions. The incorporation of an organocatalyst into a polymer support requires either conjugation to the polymer or functionalization with a

Self-assembly behaviors of perylene- and naphthalene-crown macrocycle conjugates in aqueous medium

• Xin Shen,
• Bo Li,
• Tiezheng Pan,
• Jianfeng Wu,
• Yangxin Wang,
• Jie Shang,
• Yan Ge,
• Lin Jin and
• Zhenhui Qi

Beilstein J. Org. Chem. 2019, 15, 1203–1209, doi:10.3762/bjoc.15.117

• ]. However, we recently found that benzo-21-crown-7 (B21C7) displays impressive high water solubility in comparison with other macrocyclic hosts [55]. Moreover, the conjugation of B21C7s to the well-known supramolecular BTA core leads to the observation of special topological effects on ion selectivity in

A chemically contiguous hapten approach for a heroin–fentanyl vaccine

• Yoshihiro Natori,
• Candy S. Hwang,
• Lucy Lin,
• Lauren C. Smith,
• Bin Zhou and
• Kim D. Janda

Beilstein J. Org. Chem. 2019, 15, 1020–1031, doi:10.3762/bjoc.15.100

• States has necessitated the development of new strategies to treat addiction. Monoclonal antibodies and antidrug vaccines provide a tool that both aids addiction management and reduces the potential for overdose. Dual drug vaccines formulated by successive conjugation or by mixture have certain drawbacks

• two individual vaccines together (admixture vaccine) [9][10]; or 2) successive conjugation steps of one hapten and then the second to a carrier protein [11][12]. To specifically address the escalating incidence of fentanyl-contamination in heroin, we investigated the efficacy of an admixture of

• carboxylic acids, allowing direct coupling of haptens to the carrier protein. Hapten conjugation reaction with carrier proteins BSA and KLH Test reactions on submilligram scale (0.1 mg hapten:0.1 mg BSA, 1 mg/mL protein) were performed with activated HF-1 and BSA, resulting in a moderate number of haptens

Synthesis of acylglycerol derivatives by mechanochemistry

• Karen J. Ardila-Fierro,
• Andrij Pich,
• Marc Spehr,
• José G. Hernández and
• Carsten Bolm

Beilstein J. Org. Chem. 2019, 15, 811–817, doi:10.3762/bjoc.15.78

• the mechanosynthesis of DAGs 5 was established, we turned our efforts towards the conjugation of DAG 5a with 7-hydroxycoumarin (9) (Scheme 5). Initially, removal of the TBDMS protecting group of 5a was attempted by milling. However, reacting DAG 5a with a mixture of BF3·CH3CN and silica gel followed

• through acyl migration of 6a under the basic milling conditions. Subsequently, the reaction mixture containing 8a and 8a’ was milled with 7-hydroxycoumarin (9) and triethylamine to achieve the conjugation of the DAGs 8 in 53% yield after two steps (Scheme 5c). A mixture of 10a and 10a’ (10a/10a’ 72:28

• ) was separated from the unreacted starting materials, and analyzed by UV–vis spectroscopy (Figure 3). Comparison of the UV–vis spectra of 6a and 10a/10a’ showed the successful conjugation of the DAG with the coumarin moiety [47]. Conclusion The implementation of ball milling techniques has provided the

Catalyst-free assembly of giant tris(heteroaryl)methanes: synthesis of novel pharmacophoric triads and model sterically crowded tris(heteroaryl/aryl)methyl cation salts

• Rodrigo Abonia,
• Luisa F. Gutiérrez,
• Braulio Insuasty,
• Jairo Quiroga,
• Kenneth K. Laali,
• Chunqing Zhao,
• Gabriela L. Borosky,
• Samantha M. Horwitz and
• Scott D. Bunge

Beilstein J. Org. Chem. 2019, 15, 642–654, doi:10.3762/bjoc.15.60

• despite significant steric crowding. Steric congestion restricts the conjugation of the carbocationic center with the aromatic/heteroaromatic substituents, as evidenced by the bond length shortenings from only 0.052 Å to 0.111 Å observed upon hydride abstraction. The optimized geometries confirm the

Design and synthesis of multivalent α-1,2-trimannose-linked bioerodible microparticles for applications in immune response studies of Leishmania major infection

• Chelsea L. Rintelmann,
• Tara Grinnage-Pulley,
• Kathleen Ross,
• Daniel E. K. Kabotso,
• Angela Toepp,
• Anne Cowell,
• Christine Petersen,
• Balaji Narasimhan and
• Nicola Pohl

Beilstein J. Org. Chem. 2019, 15, 623–632, doi:10.3762/bjoc.15.58

• recognition. To allow for both surface functionalization of this glycan to the bioerodible microparticles and conjugation of the fluorophore, two amine handles would be necessary (Figure 3). The design would also benefit from the development of a more efficient synthesis of the mannose oligomer sidechain

• used alkene fluorous tag [11][52][53]. The CbzF tag was also removed during global deprotection to readily provide an amine handle for conjugation to the dendrimeric core, avoiding further synthetic manipulations. Synthesis of glycodendrimer Attachment of the 5(6)-TAMRA fluorophore to the dendrimeric

• mechanisms of L. major immune suppression and evasion. The fluorescent-tagged pathogen-associated oligosaccharide probe was synthesized through orthogonal conjugation for ease of attachment to bioerodible microparticles. The PAMP carbohydrate 16 was further synthesized through iterative glycosylation and

Selectivity in multiple multicomponent reactions: types and synthetic applications

• Ouldouz Ghashghaei,
• Francesca Seghetti and
• Rodolfo Lavilla

Beilstein J. Org. Chem. 2019, 15, 521–534, doi:10.3762/bjoc.15.46

• access to a variety of structural types. On the contrary, when di(poly)functionalized substrates display conjugation between the reactive FGs, selectivity may arise. When the initial MCR adduct is less reactive than the starting material, a sequential procedure may lead to the following transformation

Convergent synthesis of the pentasaccharide repeating unit of the biofilms produced by Klebsiella pneumoniae

• Arin Gucchait,
• Angana Ghosh and
• Anup Kumar Misra

Beilstein J. Org. Chem. 2019, 15, 431–436, doi:10.3762/bjoc.15.37

• contrast to the natural version. The synthesized molecules can be linked with appropriate functionalities for their conjugation with a protein for the preparation of glycoconjugates. Recently, Cescutti et al. [11] reported the structure of a pentasaccharide composed of D-glucose, D-mannose and D-glucuronic

• pentasaccharide may provide ready availability of an amino functionality to expedite the conjugation of the pentasaccharide with an appropriate protein without affecting the sugar rings in the molecule [12][13]. Results and Discussion The target pentasaccharide as its 2-aminoethyl glycoside 1 was synthesized

Syntheses and chemical properties of β-nicotinamide riboside and its analogues and derivatives

• Mikhail V. Makarov and
• Marie E. Migaud

Beilstein J. Org. Chem. 2019, 15, 401–430, doi:10.3762/bjoc.15.36

Sigmatropic rearrangements of cyclopropenylcarbinol derivatives. Access to diversely substituted alkylidenecyclopropanes

• Guillaume Ernouf,
• Jean-Louis Brayer,
• Christophe Meyer and
• Janine Cossy

Beilstein J. Org. Chem. 2019, 15, 333–350, doi:10.3762/bjoc.15.29

• substituent at C1. Whereas conjugation with the phenyl group (R = Ph) provides the driving force for the base-promoted isomerization of 1-benzyl-3,3-difluorocyclopropene (A’, R = Ph) into the corresponding benzylidene(gem-difluoro-cyclopropane) (B’) [18], methylene(gem-difluorocyclopropane) (B’’, R = H) is

• rearrangement of 10a occurred was attributed to the relief of ring strain but also to the favorable conjugation of the olefin with the two phenyl groups (R1 = R’1 = Ph). Alkylidenecyclopropane 11a could also be obtained in similar yields (92% or 87%, respectively) by heating acetate 10a in dichloromethane at

Synthesis of a tubugi-1-toxin conjugate by a modulizable disulfide linker system with a neuropeptide Y analogue showing selectivity for hY1R-overexpressing tumor cells

• Rainer Kufka,
• Robert Rennert,
• Goran N. Kaluđerović,
• Lutz Weber,
• Wolfgang Richter and
• Ludger A. Wessjohann

Beilstein J. Org. Chem. 2019, 15, 96–105, doi:10.3762/bjoc.15.11

• Pharmaceuticals GmbH, Leberstr. 20, A-1110 Vienna, Austria 10.3762/bjoc.15.11 Abstract Tubugi-1 is a small cytotoxic peptide with picomolar cytotoxicity. To improve its cancer cell targeting, it was conjugated using a universal, modular disulfide derivative. This allowed conjugation to a neuropeptide-Y (NPY

• strongly hampered in its cytotoxic activity, and the peptide moiety ensures the target-specific toxin delivery toward the diseased cells, while omitting (most) healthy cells. To assess the impact of the chemical modifications due to the linker-assisted peptide–toxin conjugation and toxin liberation on the

• the target cells much lower toxicity than the cytotoxic compound tubugi-1 alone, thus opening a feasible therapeutic window for the class of tubugi toxins. In that context, a loss of tubugi-1 activity is expectable due to its chemical modification caused by the linker-based conjugation, and after

A simple and effective preparation of quercetin pentamethyl ether from quercetin

• Jin Tatsuzaki,
• Tomohiko Ohwada,
• Yuko Otani,
• Reiko Inagi and
• Tsutomu Ishikawa

Beilstein J. Org. Chem. 2018, 14, 3112–3121, doi:10.3762/bjoc.14.291

• by deprotonation of a single OH group of quercetin (2) were calculated. The deprotonation is an endothermic process in this calculation model. The most stable anion was derived from the OH group at 7 position (7-anion 2A), which is stabilized by the conjugation with the carbonyl group at 4 position

• reduced from that of the neural species (2B: −43.8°). In particular, 4'-anion 2B and 5-anion 2B are affected by conjugation between the chromenone moiety and the phenyl group (biaryl dihedral angle: −29.6° in 4'-anion 2B; −29.6° in 5-anion 2B). Change of proton affinity during the methylation reaction

1,8-Bis(dimethylamino)naphthyl-2-ketimines: Inside vs outside protonation

• A. S. Antonov,
• A. F. Pozharskii,
• P. M. Tolstoy,
• A. Filarowski and
• O. V. Khoroshilova

Beilstein J. Org. Chem. 2018, 14, 2940–2948, doi:10.3762/bjoc.14.273

• internitrogen space, even if other centres of basicity are present in the molecule. The only exceptions are compounds 2 and 3 which are protonated to aza- and carbonyl groups, respectively (Scheme 2) [6]. This unusual protonation site originates from the conjugation between the C=N (C=O) and the NMe2 groups

• substituent that is more basic than the peri-dimethylaminonaphthalene core. Such an imine basicity boost can originate from the fact that upon protonation, NMe2 groups lose conjugation with the ring whereas the C=N moiety does not. As a result, the imino nitrogen saves the electron density supply from both

Olefin metathesis catalysts embedded in β-barrel proteins: creating artificial metalloproteins for olefin metathesis

• Daniel F. Sauer,
• Johannes Schiffels,
• Takashi Hayashi,
• Ulrich Schwaneberg and
• Jun Okuda

Beilstein J. Org. Chem. 2018, 14, 2861–2871, doi:10.3762/bjoc.14.265

• investigated, including methylene (Ru-4), ethylene (Ru-5) to a propylene (Ru-6) spacers [56]. Thereby, it was aimed to locate the active center properly within the protein cavity. The challenge in the conjugation of the GH-type catalyst into narrow protein cavities is to overcome the space demand of the bulky

• NHC ligand. The conjugation was performed via maleimide-thiol “click” reaction under slightly basic (pH 7.5) conditions. Within the small cavity of NB4, only the GH-type catalyst Ru-6 with the longest spacer was able to undergo conjugation; however, the conjugational yield was very low (25%). Within

• the bigger cavity of NB11, all three catalysts Ru-4/5/6 were able to undergo conjugation, and gradually increasing conjugation yields by elongation of the spacer was observed (from 29% for Ru-4 up to 89% for Ru-6; Scheme 5) [56]. These artificial metalloproteins were purified and characterized by

Oxidative and reductive cyclization in stiff dithienylethenes

• Michael Kleinwächter,
• Ellen Teichmann,
• Lutz Grubert,
• Martin Herder and
• Stefan Hecht

Beilstein J. Org. Chem. 2018, 14, 2812–2821, doi:10.3762/bjoc.14.259

• approximation reflecting the HOMO–LUMO gap. The sole exception to this trend is the only derivative with an H-substituted double bond ethene-Me, which exhibit the expected behavior of a less facile oxidation of the Z-isomer due to its somewhat twisted π-system leading to less pronounced π-conjugation and

• -conjugation between both hemispheres. Similar to the model compound sDTE66-Me, all available sDTE66 derivatives as well as both Z-configured sDTE77 derivatives undergo electrocyclization upon oxidation. This also holds true for all cyclopentene-bridged DTE derivatives. However, in butene-Me the formation of

• the Z-isomers of sDTEs are able to undergo oxidative cyclization. In contrast, in the dianionic state formal cross-conjugation between the thiophene moieties and the central double bond persists and no rotation takes place. Thus, only the dianion of the Z-isomer undergoes cyclization while the

Synthesis and biological evaluation of 1,2-disubstituted 4-quinolone analogues of Pseudonocardia sp. natural products

• Stephen M. Geddis,
• Teodora Coroama,
• Suzanne Forrest,
• James T. Hodgkinson,
• Martin Welch and
• David R. Spring

Beilstein J. Org. Chem. 2018, 14, 2680–2688, doi:10.3762/bjoc.14.245

• allyl-substituted substrates 13ab and 13bb underwent an isomerisation under the reaction conditions, with the double bond moving into conjugation with the amine to give inseparable mixtures of enamine-type products 14ab and 14bb. Given the likely hydrolytic instability of synthetic precursors possessing