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

• ). However, this requires knowledge of the chemical shifts and relaxation rates for both, the free and bound components in pure form, which are challenging to obtain for complexes with only moderate affinity. For example, the binding of a single GCP unit to the carboxylates of different N-acetylated amino

Palladium nanoparticles supported on chitin-based nanomaterials as heterogeneous catalysts for the Heck coupling reaction

• Tony Jin,
• Malickah Hicks,
• Davis Kurdyla,
• Sabahudin Hrapovic,
• Edmond Lam and
• Audrey Moores

Beilstein J. Org. Chem. 2020, 16, 2477–2483, doi:10.3762/bjoc.16.201

• ], environmental remediation [5], and catalysis [6]. With their high solubility and presence of functionalities such as hydroxy groups, sulfate half-esters, and carboxylates, CNCs are able to stabilize highly disperse metal nanoparticles (NPs), which can act as heterogeneous catalysts for a wide array of organic

• resistance to reduction was surprising and in contradiction to what we observed with deposition onto CNC of Pd in the presence of H2 [7], or Ag alone [20]. The striking difference between CNC on one hand and ChNC/ChsNC on the other is the presence of carboxylates on the latter. Carboxylates are expected to

Automated high-content imaging for cellular uptake, from the Schmuck cation to the latest cyclic oligochalcogenides

• Rémi Martinent,
• Javier López-Andarias,
• Dimitri Moreau,
• Yangyang Cheng,
• Naomi Sakai and
• Stefan Matile

Beilstein J. Org. Chem. 2020, 16, 2007–2016, doi:10.3762/bjoc.16.167

• as carboxylate (Figure 1, red part). Finally, the selectivity and specificity for different substrates can be achieved through the additional secondary interactions between the GCP side chain and the anionic substrates (Figure 1, green part). The binding of the Schmuck cation with carboxylates in

• aqueous solvents was evaluated by a series of experimental studies, such as NMR, UV, CD, and fluorescence titrations [23][25]. The Schmuck cation indeed showed a much higher affinity towards carboxylates, with dissociation constants of KD ≈ 1 mM (4: 620 µM; 5: 1.3 mM) compared to simple acylguanidinium

Design, synthesis and application of carbazole macrocycles in anion sensors

• Alo Rüütel,
• Ville Yrjänä,
• Sandip A. Kadam,
• Indrek Saar,
• Mihkel Ilisson,
• Astrid Darnell,
• Kristjan Haav,
• Tõiv Haljasorg,
• Lauri Toom,
• Johan Bobacka and
• Ivo Leito

Beilstein J. Org. Chem. 2020, 16, 1901–1914, doi:10.3762/bjoc.16.157

• silico ionophore design to functional sensor characterization. The biscarbazolylurea moiety was used to synthesize methylene-bridged macrocycles of different ring size aiming to fine tune selectivity towards different carboxylates. Cyclization was achieved with two separate strategies, using either amide

• synthesis to access up to –[CH2]10– macrocycles or acyl halides to access up to –[CH2]14– macrocycles. Seventy-five receptor–anion complexes were modelled and studied with COSMO-RS, in addition to all free host molecules. In order to predict initial selectivity towards carboxylates, 1H NMR relative

• sensor development, the results obtained in this work emphasize the importance of evaluating the binding behavior of receptors in real sensor membranes. Keywords: anion sensors; carboxylates; ionophores; macrocycles; sensor prototype; Introduction In 2013, Otto S. Wolfbeis asked the supramolecular

Polarity effects in 4-fluoro- and 4-(trifluoromethyl)prolines

• Vladimir Kubyshkin

Beilstein J. Org. Chem. 2020, 16, 1837–1852, doi:10.3762/bjoc.16.151

• isomerism were examined for diastereomeric 4-fluoroprolines, 4-(trifluoromethyl)prolines, and 1,1-difluoro-5-azaspiro[2.4]heptane-6-carboxylates. The preferred conformation on the proline ring originated from a preferential axial positioning for a single fluorine atom, and an equatorial positioning for a

Microwave-assisted efficient one-pot synthesis of N²-(tetrazol-5-yl)-6-aryl/heteroaryl-5,6-dihydro-1,3,5-triazine-2,4-diamines

• Moustafa Sherief Moustafa,
• Ramadan Ahmed Mekheimer,
• Saleh Mohammed Al-Mousawi,
• Mohamed Abd-Elmonem,
• Hesham El-Zorba,
• Afaf Mohamed Abdel Hameed,
• Tahany Mahmoud Mohamed and
• Kamal Usef Sadek

Beilstein J. Org. Chem. 2020, 16, 1706–1712, doi:10.3762/bjoc.16.142

• required temperature control and showed dependence on the amine nucleophile reactivity [27]. Another route involved the reaction of substituted biguanidines with acetic anhydrides, chlorides or carboxylates [11][28][29][30][31]. Liu et al. [32] reported a one-pot synthesis of N2,6-disubstituted-1,3,5

Photocatalyzed syntheses of phenanthrenes and their aza-analogues. A review

• Alessandra Del Tito,
• Havall Othman Abdulla,
• Davide Ravelli,
• Stefano Protti and
• Maurizio Fagnoni

Beilstein J. Org. Chem. 2020, 16, 1476–1488, doi:10.3762/bjoc.16.123

• exploited for the construction of phenanthridine 6-carboxylates (Scheme 12). Notably, the process occurred in water under metal-free conditions in the presence of rose bengal (5 mol %) and made use of molecular oxygen as the terminal oxidant. Thus, N-biarylglycine esters 12.1a–d promoted the reductive

• quenching of the excited photocatalyst, in turn triggering the formation of radicals 12.2·a–d. These smoothly underwent radical cyclization to give the corresponding methyl 5,6-dihydrophenanthridine-6-carboxylates and then the desired phenanthridine 6-carboxylates 12.3a–d in good yields. Noteworthy, the

• the synthesis of 6-(trifluoromethyl)phenanthridines 10.3a–e. Synthesis of phenanthridines via aryl–aryl-bond formation. Oxidative conversion of N-biarylglycine esters to phenanthridine-6-carboxylates. Photocatalytic synthesis of benzo[f]quinolines from 2-heteroaryl-substituted anilines and

Recent synthesis of thietanes

• Jiaxi Xu

Beilstein J. Org. Chem. 2020, 16, 1357–1410, doi:10.3762/bjoc.16.116

• ] (Scheme 54). They further investigated the photochemical [2 + 2] cycloadditions of alkyl and aryl 2-thioxo-3H-benzoxazole-3-carboxylates 302 and alkenes 215a,b, 251a, and 227, affording the corresponding spirobenzoxazole-thietane derivatives 303 [81][82][83][84] (Scheme 55). Upon the irradiation of

• chloromethylthiirane (epithiochlorohydrin, 398a), with hard and weak nucleophiles [105][106][107][108][109], including phenoxides [105], carboxylates and dicarboxylates [106][107], potassium cyanide, sodium azide, hydroxylamine, trifluoromethanesulfonamide, and pyridine [108]. However, the method could only applied to

Synthesis of 3-substituted isoxazolidin-4-ols using hydroboration–oxidation reactions of 4,5-unsubstituted 2,3-dihydroisoxazoles

• Lívia Dikošová,
• Júlia Laceková,
• Ondrej Záborský and
• Róbert Fischer

Beilstein J. Org. Chem. 2020, 16, 1313–1319, doi:10.3762/bjoc.16.112

• showed the applicability of the reductive cleavage of anomeric isoxazolidinyl carboxylates in the synthesis of the respective 5-unsubstituted 4-hydroxyisoxazolidines, this pioneering approach mainly suffered from a large number of synthetic steps starting from 2,3-dihydroisoxazoles, leading to the target

Ferrocenyl-substituted tetrahydrothiophenes via formal [3 + 2]-cycloaddition reactions of ferrocenyl thioketones with donor–acceptor cyclopropanes

• Grzegorz Mlostoń,
• Mateusz Kowalczyk,
• André U. Augustin,
• Peter G. Jones and
• Daniel B. Werz

Beilstein J. Org. Chem. 2020, 16, 1288–1295, doi:10.3762/bjoc.16.109

• the five-membered ring occurred regioselectively and the expected tetrahydrothiophene-3,3-carboxylates were the products. The studied reactions displayed an interesting stereoselectivity and, in the case of 2,5-diaryl-substituted products 9, both aryl groups were exclusively located at the opposite

Photocatalysis with organic dyes: facile access to reactive intermediates for synthesis

• Stephanie G. E. Amos,
• Marion Garreau,
• Luca Buzzetti and
• Jerome Waser

Beilstein J. Org. Chem. 2020, 16, 1163–1187, doi:10.3762/bjoc.16.103

• ), such as carboxylates or RAEs (Redox Active Esters), oxidative fragmentations, and reductive fragmentations of various redox-active groups (X) as well as hydrogen atom abstractions (Scheme 2). Decarboxylation Carboxylic acids are naturally abundant functionalities that provide an easy access to C(sp3

• difficult to be directly activated by the excited state photocatalyst. For these reasons, the photocatalyzed decarboxylation often proceeds on the corresponding carboxylates, which are easier to be oxidized. This photoinduced SET, followed by the loss of CO2 as the sole byproduct, gives access to the

• use of the strong oxidant Mes-Acr-Ph+ (OD3, E(PC+*/PC) ≈ 2 V) as organic photocatalyst leads to the oxidation/decarboxylation of the in situ-generated carboxylates (Eox ≈ 1.3 V). An organic disulfide cocatalyst, (PhS)2, activated by the reduced photocatalyst, was found to act as a co-base (PhS−) and a

Synthesis of organic liquid crystals containing selectively fluorinated cyclopropanes

• Zeguo Fang,
• Nawaf Al-Maharik,
• Peer Kirsch,
• Matthias Bremer,
• Alexandra M. Z. Slawin and
• David O’Hagan

Beilstein J. Org. Chem. 2020, 16, 674–680, doi:10.3762/bjoc.16.65

• enantiomerically pure fluorinated diphenylcyclopropane carboxylates as potential chiral dopants to induce a cholesteric phase, but this was not extended to the exploration of positive or negative dielectrics. Recently, we reported the efficient synthesis of α,β,β-trifluorocyclopropanes 7 (Figure 2) through

Visible-light-induced addition of carboxymethanide to styrene from monochloroacetic acid

• Kaj M. van Vliet,
• Nicole S. van Leeuwen,
• Albert M. Brouwer and
• Bas de Bruin

Beilstein J. Org. Chem. 2020, 16, 398–408, doi:10.3762/bjoc.16.38

• . Single-electron oxidation can produce carbon-centered radicals from substrates such as amines [17], alkenes [18], and carboxylates [19], or by hydrogen-atom transfer to an oxidatively formed thiolate radical [20]. Single-electron reduction produces carbon-centered radicals from, for example, aryl

Room-temperature Pd/Ag direct arylation enabled by a radical pathway

• Amy L. Mayhugh and
• Christine K. Luscombe

Beilstein J. Org. Chem. 2020, 16, 384–390, doi:10.3762/bjoc.16.36

• reported for decarboxylative coupling between indole and 2-nitrobenzoic acids at 110 °C [18]. Under such conditions, silver carboxylates decompose to produce carbonyl and phenyl radicals, which could explain the origin of nitrobenzene incorporation [19][20]. When the radical trapping agent BHT was added to

p-Pyridinyl oxime carbamates: synthesis, DNA binding, DNA photocleaving activity and theoretical photodegradation studies

• Panagiotis S. Gritzapis,
• Panayiotis C. Varras,
• Nikolaos-Panagiotis Andreou,
• Katerina R. Katsani,
• Konstantinos Dafnopoulos,
• George Psomas,
• Zisis V. Peitsinis,
• Alexandros E. Koumbis and
• Konstantina C. Fylaktakidou

Beilstein J. Org. Chem. 2020, 16, 337–350, doi:10.3762/bjoc.16.33

• experimental values are shown in Table 1. DNA binding studies Our previous DNA-binding studies with a series of amidoxime, ethanone oxime and aldoxime carboxylates as well as sulfonates of high, moderate or poor DNA photocleaving ability showed no substantial differences on the DNA affinities among the three

• according to previously reported methods [9]. General structures of oxime derivatives with possible DNA photocleavage ability. Left: Oxime carboxylates: O-acyl amidoximes (I), O-acyl ketoximes (II), O-acyl aldoximes (III). Centre: Oxime sulfonates: O-sulfonyl amidoximes (IV), O-sulfonyl ketoximes (V). Right

Ultrasonic-assisted unusual four-component synthesis of 7-azolylamino-4,5,6,7-tetrahydroazolo[1,5-a]pyrimidines

• Yana I. Sakhno,
• Maryna V. Murlykina,
• Oleksandr I. Zbruyev,
• Anton V. Kozyryev,
• Svetlana V. Shishkina,
• Dmytro Sysoiev,
• Vladimir I. Musatov,
• Sergey M. Desenko and
• Valentyn A. Chebanov

Beilstein J. Org. Chem. 2020, 16, 281–289, doi:10.3762/bjoc.16.27

• -aryl-4,5,6,7-tetrahydropyrazolo[1,5-a]pyrimidine-7-carboxylates (substituents = H, CH3) 4d–o were isolated in 45–80% yields (Scheme 4, Table 1). The same products were isolated while carrying out this reaction in acetic acid at room temperature with intensive stirring instead of ultrasonic irradiation

Bacterial terpene biosynthesis: challenges and opportunities for pathway engineering

• Eric J. N. Helfrich,
• Geng-Min Lin,
• Christopher A. Voigt and
• Jon Clardy

Beilstein J. Org. Chem. 2019, 15, 2889–2906, doi:10.3762/bjoc.15.283

• further oxidation to carbonyls or carboxylates. Other reactions, such as epoxidation, ether bond formation, and structural rearrangement have also been reported (Figure 7). CYP114 in gibberellin (5) biosynthesis, for example, catalyzes the unique oxidation/six-membered to five-membered ring contraction of

Photoreversible stretching of a BAPTA chelator marshalling Ca²⁺-binding in aqueous media

• Aurélien Ducrot,
• Arnaud Tron,
• Robin Bofinger,
• Ingrid Sanz Beguer,
• Jean-Luc Pozzo and
• Nathan D. McClenaghan

Beilstein J. Org. Chem. 2019, 15, 2801–2811, doi:10.3762/bjoc.15.273

• over Mg2+ ions, and relative insensitivity to pH in biological media due to the relatively low pKa of the electron-poor aniline nitrogens [1]. BAPTA-type molecules complex Ca2+ in an octacoordinated fashion, involving the two aniline functions, the two central ether oxygens and the four carboxylates

Synthesis of aryl-substituted thieno[3,2-b]thiophene derivatives and their use for N,S-heterotetracene construction

• Nadezhda S. Demina,
• Nikita A. Kazin,
• Nikolay A. Rasputin,
• Roman A. Irgashev and
• Gennady L. Rusinov

Beilstein J. Org. Chem. 2019, 15, 2678–2683, doi:10.3762/bjoc.15.261

• . N. Yeltsin, Mira St., 19, Ekaterinburg, 620002, Russia 10.3762/bjoc.15.261 Abstract Fiesselmann thiophene synthesis was applied for the convenient construction of thieno[3,2-b]thiophene derivatives. Thus, new 5- or 6-aryl-3-hydroxythieno[3,2-b]thiophene-2-carboxylates were obtained by condensation

• of 5- or 4-aryl-3-chlorothiophene-2-carboxylates, respectively, with methyl thioglycolate in the presence of potassium tert-butoxide. The saponification of the resulting esters, with decarboxylation of the intermediating acids, gave the corresponding thieno[3,2-b]thiophen-3(2H)-ones. The latter

• synthesis [16], viz., the interaction of ethyl thioglycolate with ethyl 3-chlorobenzo[b]thiophene-2-carboxylates, to form a benzo[b]thieno[2,3-d]thiophene scaffold [17][18], we have decided to apply a similar approach to the synthesis of aryl-substituted TT derivatives. Thus, 3-chloro- or 3-bromothiophene-2

Mono- and bithiophene-substituted diarylethene photoswitches with emissive open or closed forms

• A. Lennart Schleper,
• Mariano L. Bossi,
• Vladimir N. Belov and
• Stefan W. Hell

Beilstein J. Org. Chem. 2019, 15, 2344–2354, doi:10.3762/bjoc.15.227

• , substitution of fluorine and/or the addition of nucleophiles to the electron-poor double bond take place. Therefore, tert-butyl protection is required for carboxylates present in diarylethenes with “oxidized” benzothiophene units and perfluorocyclopentene rings. Photoswitches containing the free carboxylic

Cyclopropanation–ring expansion of 3-chloroindoles with α-halodiazoacetates: novel synthesis of 4-quinolone-3-carboxylic acid and norfloxacin

• Sara Peeters,
• Linn Neerbye Berntsen,
• Pål Rongved and
• Tore Bonge-Hansen

Beilstein J. Org. Chem. 2019, 15, 2156–2160, doi:10.3762/bjoc.15.212

• retrosynthetic approach towards quinolone-3-carboxylates, as outlined in Scheme 2. Cyclopropanation–ring expansion of 3-chloroindole derivatives with X-EDA would give ethyl 4-chloro-quinoline-3-carboxylates, which would subsequently undergo alcoholysis to give 4-quinolone-3-carboxylates. Results and Discussion

• Detailed experimental procedures and analytical data for the compounds are available in Supporting Information File 1. General procedure for the synthesis of ethyl 4-chloroquinoline-3-carboxylates from X-EDA and 3-chloroindoles X-EDA was synthesized according to a literature procedure [35]. This gave X-EDA

• -chloroquinoline-3-carboxylates to ethyl 4(1H)-oxoquinolone-3-carboxylates [33] To the desired ethyl 4-chloro-quinoline-3-carboxylate derivative (1–2 mmol) was added 5 mL dry ethanol. This solution was refluxed for 24 h or monitored by TLC analysis. The reaction mixture was cooled after the starting material was

N-(1-Phenylethyl)aziridine-2-carboxylate esters in the synthesis of biologically relevant compounds

• Iwona E. Głowacka,
• Aleksandra Trocha,
• Andrzej E. Wróblewski and
• Dorota G. Piotrowska

Beilstein J. Org. Chem. 2019, 15, 1722–1757, doi:10.3762/bjoc.15.168

• racemization, alternative three-carbon chirons would be of great value in enantioselective syntheses of natural compounds and/or drugs. This review article summarizes applications of N-(1-phenylethyl)aziridine-2-carboxylates, -carbaldehydes and -methanols in syntheses of approved drugs and potential

• catalytic hydrogenation but metal-ammonia reduction (Birch reaction) and organic acid in anisole (vide infra) can be efficiently applied. We begin with a short presentation of syntheses of aziridine-2-carboxylates, the corresponding aldehydes and 2-methanols. Review Syntheses of starting materials Synthesis

• of N-(1-phenylethyl)aziridine-2-carboxylates 5 In general, enantiomerically pure starting materials used in asymmetric syntheses are prepared from natural products. This does not hold for N-(1-phenylethyl)aziridine-2-carboxylates 5 since after synthesis in the Gabriel–Cromwell reaction between 3,3

Recent advances on the transition-metal-catalyzed synthesis of imidazopyridines: an updated coverage

• Gagandeep Kour Reen,
• Ashok Kumar and
• Pratibha Sharma

Beilstein J. Org. Chem. 2019, 15, 1612–1704, doi:10.3762/bjoc.15.165

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

• carbon–carbon triple bond attached to a nitrogen atom that gives them both nucleophilic and electrophilic properties. This dual reactivity is similar to that shown by isocyanides, as they may react with iminium ions and carboxylates as isocyanides do. However, in comparison with the typical Ugi-4CR where

Novel (2-amino-4-arylimidazolyl)propanoic acids and pyrrolo[1,2-c]imidazoles via the domino reactions of 2-amino-4-arylimidazoles with carbonyl and methylene active compounds

• Victoria V. Lipson,
• Tetiana L. Pavlovska,
• Nataliya V. Svetlichnaya,
• Anna A. Poryvai,
• Nikolay Yu. Gorobets,
• Erik V. Van der Eycken,
• Irina S. Konovalova,
• Svetlana V. Shiskina,
• Alexander V. Borisov,
• Vladimir I. Musatov and
• Alexander V. Mazepa

Beilstein J. Org. Chem. 2019, 15, 1032–1045, doi:10.3762/bjoc.15.101

• -arylpropanoic acids. The interaction of 2-amino-4-arylimidazoles with aromatic aldehydes or isatins and acyclic methylene active compounds has led to the formation of pyrrolo[1,2-c]imidazole-6-carbonitriles, pyrrolo[1,2-с]imidazole-6-carboxylates and spiro[indoline-3,7'-pyrrolo[1,2-c]imidazoles], which can be

• ]imidazole-6-carboxylates. A mixture of the corresponding 2-amino-4-arylimidazole 1 (1.0 mmol), aromatic aldehyde 2 (2.0 mmol) and ethyl 2-cyanoacetate 15 (1.0 mmol) in 2 mL of 2-propanol was refluxed during 20–30 min. After cooling, the yellow solid products 16 were filtered off and crystallized from iPrOH

• : С, 69.43; H, 5.07; N, 22.64. General procedure for the synthesis of 3',5'-diamino-1-alkyl-2-oxo-1'-arylspiro[indoline-3,7'-pyrrolo[1,2-c]imidazole]-6'-carboxylates: The mixture of corresponding 2-amino-4-arylimidazoles 1 (1.0 mmol), isatin 18 (1.0 mmol) and ethyl 2-cyanoacetate 15 (1.0 mmol) in 2 mL