Phosphodiester models for cleavage of nucleic acids

• Satu Mikkola,
• Tuomas Lönnberg and
• Harri Lönnberg

Beilstein J. Org. Chem. 2018, 14, 803–837, doi:10.3762/bjoc.14.68

• rate. High buffer concentration has to be used and this makes elimination of salt and co-solute effects difficult. Since histidine residues are known to play a central role in the catalytic center of RNase A [58], one of the most extensively studied protein nucleases, catalysis by imidazole/imidazolium

• interesting feature of the mechanism is that both the formation and breakdown of the phosphorane intermediate proceed through a minor ionic form in a pre-equilibrium mixture. The mole fraction of neutral phosphodiester, for example, is in imidazole buffers of the order of 10−6 (pKa of phosphodiester ≈ 1

• departure of the 5´-linked nucleoside by a factor of 107. The mechanistic proposal has partly been based on Breslow’s studies on hydrolysis of 4-tert-butylcatechol cyclic phosphate by regioisomers of β-cyclodextrins bearing two imidazole groups [60]. This reverse reaction of the cyclization of 4-tert

Enzyme-free genetic copying of DNA and RNA sequences

• Marilyne Sosson and
• Clemens Richert

Beilstein J. Org. Chem. 2018, 14, 603–617, doi:10.3762/bjoc.14.47

• neutral pH, i.e., conditions favoring longevity for this type of activated monomer, which requires protonation of the imidazole ring to be turned it into a good leaving group. Binding equilibria As mentioned above, primer extension involves the binding of the incoming nucleotide to the primer–template

Latest development in the synthesis of ursodeoxycholic acid (UDCA): a critical review

• Fabio Tonin and
• Isabel W. C. E. Arends

Beilstein J. Org. Chem. 2018, 14, 470–483, doi:10.3762/bjoc.14.33

• ] (yield 90%) and subsequently reduced with metallic sodium in presence of imidazole and 1-propanol (yield 80%) yielding the 7β-OH epimer (UDCA) as imidazole salt. Notably, the regiospecific oxidoreduction of the 7α-OH group is achieved using weak oxidants: this behavior can be explained by the peculiar

Recent advances on organic blue thermally activated delayed fluorescence (TADF) emitters for organic light-emitting diodes (OLEDs)

• Thanh-Tuân Bui,
• Fabrice Goubard,
• Malika Ibrahim-Ouali,
• Didier Gigmes and
• Frédéric Dumur

Beilstein J. Org. Chem. 2018, 14, 282–308, doi:10.3762/bjoc.14.18

• 5 hours for T13-based OLEDs. A comparison established with an iridium complex, i.e., tris[1-(2,4-diisopropyldibenzo[b,d]furan-3-yl)-2-phenyl-1H-imidazole]iridium(III) (Ir(dbi)3) evidenced the relevance of the TADF approach, as a device lifetime of only 18 hours was found while operating OLEDs in the

One-pot sequential synthesis of tetrasubstituted thiophenes via sulfur ylide-like intermediates

• Jun Ki Kim,
• Hwan Jung Lim,
• Kyung Chae Jeong and
• Seong Jun Park

Beilstein J. Org. Chem. 2018, 14, 243–252, doi:10.3762/bjoc.14.16

• -trifluoromethyloxadiazole substituent was not a viable substrate (Table 1, entry 10). Because of a similar result obtained with the N-methylimidazole substituted compound 7k, the difference between 7i and 7j could be explained by the imidazole-like structure of the 5-trifluoromethyloxadiazole moiety. The reduced inductive

• effect of the amine might be attributed to the resonance structures of imidazole (Table 1, entry 11) [72]. To determine the influence of substituents on the phenyl group, various arene(methyl)sulfanes 7l–p were tested (Table 1, entries 12–16,). Simple phenyl and electron-donating compounds 7l and 7m did

Photocatalytic formation of carbon–sulfur bonds

• Alexander Wimmer and
• Burkhard König

Beilstein J. Org. Chem. 2018, 14, 54–83, doi:10.3762/bjoc.14.4

• photoredox-generated thiocyanate radical can add to the heteroaromatic system, which subsequently rearomatizes via deprotonation. This method was suitable for substituted imidazoheterocycles, bearing electron-donating and withdrawing groups. Other imidazole derivatives were unreactive under the reported

Aminosugar-based immunomodulator lipid A: synthetic approaches

• Alla Zamyatina

Beilstein J. Org. Chem. 2018, 14, 25–53, doi:10.3762/bjoc.14.3

Reactivity of bromoselenophenes in palladium-catalyzed direct arylations

• Aymen Skhiri,
• Ridha Ben Salem,
• Jean-François Soulé and
• Henri Doucet

Beilstein J. Org. Chem. 2017, 13, 2862–2868, doi:10.3762/bjoc.13.278

• allowed the coupling of several heteroaromatics such as thiazole, pyrrole, furan or imidazole derivatives with aryl bromides [36]. 2-Bromoselenophene, which was easily prepared by reaction of selenophene with N-bromosuccinimide [37], and 2-ethyl-4-methylthiazole were employed as model substrates for our

Nucleophilic dearomatization of 4-aza-6-nitrobenzofuroxan by CH acids in the synthesis of pharmacology-oriented compounds

• Alexey M. Starosotnikov,
• Dmitry V. Shkaev,
• Maxim A. Bastrakov,
• Ivan V. Fedyanin,
• Svyatoslav A. Shevelev and
• Igor L. Dalinger

Beilstein J. Org. Chem. 2017, 13, 2854–2861, doi:10.3762/bjoc.13.277

• to proceed depending on the structure of the substrate and the nucleophile. The first, Beirut reaction [1][2][3][4][5][6][7][8][9][10], allowing to transform the furoxan ring to pyrazine or imidazole N-oxides as well as N-hydroxyimidazole occurs under the action of α-unsubstituted aldehydes, ketones

Synthetic mRNA capping

• Fabian Muttach,
• Nils Muthmann and
• Andrea Rentmeister

Beilstein J. Org. Chem. 2017, 13, 2819–2832, doi:10.3762/bjoc.13.274

• , comprising phenylthio [56], 5-chloro-8-quinolyl [57], morpholidate [48] and imidazolide moieties [58][59]. Imidazole activation in DMF with ZnCl2 was first reported by Sekine et al. [60] and is the most often used method for the formation of triphosphates. P-Imidazoles are known to react with numerous

• hydrolytically less stable than other purine nucleosides. Under basic conditions which are commonly used for RNA deprotection and cleavage from the solid support, opening of the imidazole ring of the 7-methylguanine would occur [111]. Thus, for synthesis of the cap structure on the solid support, standard

• trypanosomatid cap4 structure, characterized by 2′-O-methylation of the first four nucleotides and additional methylation at the first adenosine and the fourth uridine, was reported in 2004 by the group of Darzynkiewicz. The preparation was achieved by reacting an imidazole activated m7GDP with the 5

CF₃SO₂X (X = Na, Cl) as reagents for trifluoromethylation, trifluoromethylsulfenyl-, -sulfinyl- and -sulfonylation. Part 1: Use of CF₃SO₂Na

• Hélène Guyon,
• Hélène Chachignon and
• Dominique Cahard

Beilstein J. Org. Chem. 2017, 13, 2764–2799, doi:10.3762/bjoc.13.272

A novel synthetic approach to hydroimidazo[1,5-b]pyridazines by the recyclization of itaconimides and HPLC–HRMS monitoring of the reaction pathway

• Dmitry Yu. Vandyshev,
• Khidmet S. Shikhaliev,
• Andrey Yu. Potapov,
• Michael Yu. Krysin,
• Fedor I. Zubkov and
• Lyudmila V. Sapronova

Beilstein J. Org. Chem. 2017, 13, 2561–2568, doi:10.3762/bjoc.13.252

• -addition by the activated C=C double bond and subsequent intramolecular recyclization of the intermediate with the amino group involved. Keywords: cascade reaction; diaminoimidazoles; HPLC–HRESIMS; imidazo[1,5-b]pyridazines; itaconimides; Introduction Among the numerous bicyclic fused imidazole

• ], antitumor agents [9], and are stimulators of guanylate cyclase [10], whereas imidazo[1,5-c]pyrimidines demonstrate anti-infectious effects in the treatment of brucellosis [11], etc. However, the chemistry, medicinal chemistry and pharmacology of imidazo[1,5-b]pyridazines, with the imidazole ring connected

• to search for new reagents for the synthesis of their imidazo[1,5-b]-annelated analogues. There are two general approaches to the construction of an imidazo[1,5-b]pyridazine scaffold: the annulation of the imidazole ring to the b-bond of the pyridazine (route A, Scheme 1) and the heterocyclization of

¹⁵N-Labelling and structure determination of adamantylated azolo-azines in solution

• Sergey L. Deev,
• Alexander S. Paramonov,
• Tatyana S. Shestakova,
• Igor A. Khalymbadzha,
• Oleg N. Chupakhin,
• Julia O. Subbotina,
• Oleg S. Eltsov,
• Pavel A. Slepukhin,
• Vladimir L. Rusinov,
• Alexander S. Arseniev and
• Zakhar O. Shenkarev

Beilstein J. Org. Chem. 2017, 13, 2535–2548, doi:10.3762/bjoc.13.250

• against influenza A virus compared with the currently used antiviral drug rimantadine (1-(1-adamantyl)ethanamine) [3]. More recently, Roberge et al. described new inhibitors of the influenza A virus M2 proton channel. Among the studied compounds, adamantyl imidazole 3 showed good activity [4]. An azolo

Exploring mechanochemistry to turn organic bio-relevant molecules into metal-organic frameworks: a short review

• Vânia André,
• Sílvia Quaresma,
• João Luís Ferreira da Silva and
• M. Teresa Duarte

Beilstein J. Org. Chem. 2017, 13, 2416–2427, doi:10.3762/bjoc.13.239

• framework and have simultaneously the characteristics of MOFs and zeolites, making them very promising for biomedical applications [90][91]. In their work, Beldon et al. explored the synthesis of new ZIFs using imidazole (HIm), 2-methylimidazole (HMeIm) and 2-ethylimidazole (HEtIm) as ligands. Initially

• , they used LAG with ZnO and the previous imidazole ligands in the presence of DMF as a space-filling liquid. However, this method only partially succeeded: with HIm the quantitative formation of ZIF-4 was obtained after 60 min, whereas with HMeIm only partial formation of ZIF-8 was achieved and with

The effect of milling frequency on a mechanochemical organic reaction monitored by in situ Raman spectroscopy

• Patrick A. Julien,
• Ivani Malvestiti and
• Tomislav Friščić

Beilstein J. Org. Chem. 2017, 13, 2160–2168, doi:10.3762/bjoc.13.216

• mechanochemical synthesis of a MOF from ZnO and imidazole in the presence of a small amount of N,N-dimethylformamide [41]. This study revealed reaction kinetics consistent with a 2nd order reaction rate law, rationalized through a “pseudo-fluid” reaction model in which the rate-determining factor is the frequency

An efficient synthesis of a C₁₂-higher sugar aminoalditol

• Łukasz Szyszka,
• Anna Osuch-Kwiatkowska,
• Mykhaylo A. Potopnyk and
• Sławomir Jarosz

Beilstein J. Org. Chem. 2017, 13, 2146–2152, doi:10.3762/bjoc.13.213

• , 6.72; N, 0.88. To a stirred solution of 8 (0.35 g, 0.21 mmol) in DMF (20 mL) containing imidazole (1.5 mg), sodium hydride (60% dispersion in mineral oil, 80.6 mg, 2.1 mmol) was added, and the mixture was stirred at 20 °C for 30 min. Benzyl bromide (0.2 mL, 1.68 mmol) was added dropwise and the mixture

NHC-catalyzed cleavage of vicinal diketones and triketones followed by insertion of enones and ynones

• Ken Takaki,
• Makoto Hino,
• Akira Ohno,
• Kimihiro Komeyama,
• Hiroto Yoshida and
• Hiroshi Fukuoka

Beilstein J. Org. Chem. 2017, 13, 1816–1822, doi:10.3762/bjoc.13.176

• regeneration of C and its reaction with 6a took place predominantly. It seems surprising that compound 12 could be quantitatively generated from C and HClO4 regardless of equimolar amounts of DIPEA, while analogous intermediates derived from imidazole NHC were protonated by the acid alone [23]. Conclusion We

Chiral phase-transfer catalysis in the asymmetric α-heterofunctionalization of prochiral nucleophiles

• Johannes Schörgenhumer,
• Maximilian Tiffner and
• Mario Waser

Beilstein J. Org. Chem. 2017, 13, 1753–1769, doi:10.3762/bjoc.13.170

• facilitates the asymmetric intramolecular cycloetherification of starting materials 27 (Scheme 13). One of the important observations in this impressive report was the necessity of the imidazole moiety to achieve high selectivities [125]. In a subsequent study, the same group also expanded this concept to 6

An efficient Pd–NHC catalyst system in situ generated from Na₂PdCl₄ and PEG-functionalized imidazolium salts for Mizoroki–Heck reactions in water

• Nan Sun,
• Meng Chen,
• Liqun Jin,
• Wei Zhao,
• Baoxiang Hu,
• Zhenlu Shen and
• Xinquan Hu

Beilstein J. Org. Chem. 2017, 13, 1735–1744, doi:10.3762/bjoc.13.168

• salt L1, bearing a pyridine-2-methyl substituent at the N3 atom of the imidazole ring, showed the best catalytic activity. Under the optimal conditions, a wide range of substituted alkenes were achieved in good to excellent yields from various aryl bromides and alkenes with the catalyst TON of up to

• reaction sequence as depicted in Scheme 1. Firstly, the commercially available MeO-PEG1900-OH was reacted with MsCl using pyridine as base in CH2Cl2 to form MeO-PEG1900-OMs, which was then treated with sodium imidazole in THF to form the imidazole-functionalized PEG (MeO-PEG1900-Im). The resulted MeO

• –L3 from commercially available MeO-PEG1900-OH, imidazole, and various arylmethyl bromides (2-bromomethylpyridine for L1, benzyl bromide for L2 and 1-bromomethylnaphthalene for L3). It was shown that these imidazolium salts L1–L3 could be utilized as water soluble NHC ligand precursors in combination

Block copolymers from ionic liquids for the preparation of thin carbonaceous shells

• Sadaf Hanif,
• Bernd Oschmann,
• Dmitri Spetter,
• Muhammad Nawaz Tahir,
• Wolfgang Tremel and
• Rudolf Zentel

Beilstein J. Org. Chem. 2017, 13, 1693–1701, doi:10.3762/bjoc.13.163

• . In a first step the PIL block is synthesized using 1-vinyl-3-cyanomethylimidazolium bromide (1) as an IL monomer, which was prepared following a literature procedure [16]. During this process the nitrogen atom in the imidazole ring in position 3 is quaternized. Monomer 1 was polymerized with 2

The chemistry and biology of mycolactones

• Matthias Gehringer and
• Karl-Heinz Altmann

Beilstein J. Org. Chem. 2017, 13, 1596–1660, doi:10.3762/bjoc.13.159

Direct catalytic arylation of heteroarenes with meso-bromophenyl-substituted porphyrins

• Alexei N. Kiselev,
• Olga K. Grigorova,
• Alexei D. Averin,
• Sergei A. Syrbu,
• Oskar I. Koifman and
• Irina P. Beletskaya

Beilstein J. Org. Chem. 2017, 13, 1524–1532, doi:10.3762/bjoc.13.152

• date certain tetrapyrrole derivatives of such type were described in the literature, for example, porphyrins with imidazole and benzimidazole substitutents at meso-positions [6][7], meso-pyridinyl and meso-quinolinyl-substituted porphyrins [8], an imidazolyl group was attached to the meso-position also

Synthesis of the heterocyclic core of the D-series GE2270

• Christophe Berini,
• Thibaut Martin,
• Pierrik Lassalas,
• Francis Marsais,
• Christine Baudequin and
• Christophe Hoarau

Beilstein J. Org. Chem. 2017, 13, 1407–1412, doi:10.3762/bjoc.13.137

• of chiral thioamide 16. Reaction conditions: a) SnCl2∙2H2O, dioxane/H2O (1:3), 0 °C to rt, 5 h, then NaHCO3, benzyl chloroformate, rt, 18 h, 96%. b) TBDMSCl, imidazole, DMF, rt, 16 h, 99%. c) LiOH∙H2O, DME/H2O (1:1), 0 °C to rt, 72 h, then HCl, 96%. d) DCC, HOSu, THF, rt, 16 h, then Lawesson’s

Strategies toward protecting group-free glycosylation through selective activation of the anomeric center

• A. Michael Downey and
• Michal Hocek

Beilstein J. Org. Chem. 2017, 13, 1239–1279, doi:10.3762/bjoc.13.123

• modern protecting-group-free synthesis (Scheme 29) [89]. The Hindsgaul group reacted imidazole and DMC to form an activated species termed 2-imidazolyl-1,3-dimethylimidazolinium chloride (ImIm) which reacted with UMP within one hour to form an activated phosphoester. Then, over 18 h at 37 °C, Gal-1-P can

Synthesis of D-manno-heptulose via a cascade aldol/hemiketalization reaction

• Yan Chen,
• Xiaoman Wang,
• Junchang Wang and
• You Yang

Beilstein J. Org. Chem. 2017, 13, 795–799, doi:10.3762/bjoc.13.79

• was subjected to benzoyl chloride and DMAP in dichloromethane at room temperature or tert-butyldimethylsilyl chloride and imidazole in DMF at room temperature, no reaction occurred probably because of the steric hindrance between the 2-OH group and the surrounding functional groups. To overcome the