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

• occurrence of the proton transfer as part of the rate limiting step may be evaluated by altering the acidity of the proton donor (or acceptor). Plotting of log k against the pKa of the proton donor (or acceptor) gives the Brönsted α (β for the acceptor) that refers to the extent of proton transfer in the

Cobalt-catalyzed directed C–H alkenylation of pivalophenone N–H imine with alkenyl phosphates

• Wengang Xu and
• Naohiko Yoshikai

Beilstein J. Org. Chem. 2018, 14, 709–715, doi:10.3762/bjoc.14.60

• , an increased acidity of the ortho position of the fluorine atom could have also contributed to the observed regioselectivity [31]. Curiously, the reaction of 2-naphthylimine resulted in the preferential alkenylation of the more hindered 1-position rather than the 3-position, with a regioselectivity

An alternative to hydrogenation processes. Electrocatalytic hydrogenation of benzophenone

• Cristina Mozo Mulero,
• Alfonso Sáez,
• Jesús Iniesta and
• Vicente Montiel

Beilstein J. Org. Chem. 2018, 14, 537–546, doi:10.3762/bjoc.14.40

• v/v) and 0.1 M H2SO4, or (ii) 0.5 M benzophenone in ethanol 96% /water (90:10 v/v) in the absence of the sulfuric acid electrolyte in order to explore the influence of the medium acidity upon the electrochemical hydrogenation. A peristaltic pump Ismatel Reglo DIG MS/CA 2–8 provided a catholyte flow

Aminomethylation/hydrogenolysis as an alternative to direct methylation of metalated isoquinolines – a novel total synthesis of the alkaloid 7-hydroxy-6-methoxy-1-methylisoquinoline

• Benedikt C. Melzer,
• Jan G. Felber and
• Franz Bracher

Beilstein J. Org. Chem. 2018, 14, 130–134, doi:10.3762/bjoc.14.8

• , due to its intrinsic C–H acidity, open opportunities for further functionalization. Since most isoquinoline alkaloids bear hydroxy and/or methoxy substituents at the positions 6 and 7, we regarded 7-hydroxy-6-methoxy-1-methylisoquinoline (1) as well as analogues containing a protected 7-hydroxy group

Halogen-containing thiazole orange analogues – new fluorogenic DNA stains

• Aleksey A. Vasilev,
• Meglena I. Kandinska,
• Stanimir S. Stoyanov,
• Stanislava B. Yordanova,
• David Sucunza,
• Juan J. Vaquero,
• Obis D. Castaño,
• Stanislav Baluschev and
• Silvia E. Angelova

Beilstein J. Org. Chem. 2017, 13, 2902–2914, doi:10.3762/bjoc.13.283

• for the success of the reaction because of the CH-acidity of the benzyl fragment, which otherwise leads to the possibility of side reactions if trimethylamine or other less hindered basic reagents are employed. Photophysical properties Absorption The longest wavelength absorption maxima of the studied

Position-dependent impact of hexafluoroleucine and trifluoroisoleucine on protease digestion

• Susanne Huhmann,
• Anne-Katrin Stegemann,
• Kristin Folmert,
• Damian Klemczak,
• Johann Moschner,
• Michelle Kube and
• Beate Koksch

Beilstein J. Org. Chem. 2017, 13, 2869–2882, doi:10.3762/bjoc.13.279

• strong, short C–F bonds and perturb the acidity and basicity of adjacent functional groups. Moreover, these changes may strongly influence hydrogen bonding and electrostatic interactions that are crucial for binding to receptors or, in context of protease stability, enzymes. Thus, when introduced in the

What contributes to an effective mannose recognition domain?

• Christoph P. Sager,
• Deniz Eriş,
• Martin Smieško,
• Rachel Hevey and
• Beat Ernst

Beilstein J. Org. Chem. 2017, 13, 2584–2595, doi:10.3762/bjoc.13.255

• to gain enthalpy, and thereby increase affinity. UPEC perfects this approach with the calcium-devoid binding site of FimHLD (I). A possible explanation for the lack of a calcium ion in the FimH binding site may relate to the slight acidity of urine (pH 5.5–7.0), with a calcium clearance of 20–300 mg

Hydrolysis, polarity, and conformational impact of C-terminal partially fluorinated ethyl esters in peptide models

• Vladimir Kubyshkin and
• Nediljko Budisa

Beilstein J. Org. Chem. 2017, 13, 2442–2457, doi:10.3762/bjoc.13.241

• limited the substrate scope. Nonetheless, due to the high acidity of the C-terminal carboxylic group [50], a number of C-terminally modified peptides were readily prepared by this method with full conversion. The availability of the C-terminal 2,2-difluoroethanol-esterified peptides also enables the

Asymmetric synthesis of propargylamines as amino acid surrogates in peptidomimetics

• Matthias Wünsch,
• David Schröder,
• Tanja Fröhr,
• Lisa Teichmann,
• Sebastian Hedwig,
• Nils Janson,
• Clara Belu,
• Jasmin Simon,
• Shari Heidemeyer,
• Philipp Holtkamp,
• Jens Rudlof,
• Lennard Klemme,
• Alessa Hinzmann,
• Beate Neumann,
• Hans-Georg Stammler and
• Norbert Sewald

Beilstein J. Org. Chem. 2017, 13, 2428–2441, doi:10.3762/bjoc.13.240

• % [21]. Synthesis of propargylamines containing electron-withdrawing substituents Aromatic and carbonyl substituents in the Cβ-position of propargylamines (occurring in analogoues of the amino acids phenylalanine, tyrosine, histidine, tryptophan, aspartic acid and asparagine) increase the acidity of the

• adjacent protons considerably. In the precursor sulfinylimines 5 of the target propargylamines the acidity of the protons of the methylene moiety is further increased by the electron-withdrawing effect of the adjacent sulfinyl imino moiety. Thus, the nucleophilic addition of (trimethylsilyl)ethynyllithium

• additionally increase the acidity of the α-proton. Nevertheless, glycine derivatives with electron-withdrawing substituents like formylglycine [58][59], phenylglycine [60][61] and fluorinated alanine [62][63][64] have attracted great attention as peptidomimetics, drugs or in the bioorthogonal functionalization

Electron-deficient pyridinium salts/thiourea cooperative catalyzed O-glycosylation via activation of O-glycosyl trichloroacetimidate donors

• Mukta Shaw,
• Yogesh Kumar,
• Rima Thakur and
• Amit Kumar

Beilstein J. Org. Chem. 2017, 13, 2385–2395, doi:10.3762/bjoc.13.236

• trichloroacetimidate donors using a synergistic catalytic system of electron-deficient pyridinium salts/aryl thiourea derivatives at room temperature is demonstrated. The acidity of the adduct formed by the 1,2-addition of alcohol to the electron-deficient pyridinium salt is increased in the presence of an aryl

• presence of Schreiner′s thiourea in the reaction medium enhances the acidity of the ammonium salt due to doubling their dual hydrogen bonding ability with the carboxylate and the alkoxy group of the ammonium salt. A thiourea derivative also enhances the nucleophilicity of the glycosyl acceptor by imparting

• to lower acidity of the ammonium salt formed by 1,2-addition of the acceptor to the pyridinium salt. The conjugate base formed after the release of a proton from the ammonium salt may be quite stable to impart a negative charge to the acceptor oxygen. The acidity of the ammonium salt may be enhanced

Synthesis and application of trifluoroethoxy-substituted phthalocyanines and subphthalocyanines

• Satoru Mori and
• Norio Shibata

Beilstein J. Org. Chem. 2017, 13, 2273–2296, doi:10.3762/bjoc.13.224

• sensors [51]. Due to the strong electronegativity of fluorine, the acidity of these pyrrole rings is increased in TFEO-H2Pc. For this reason, it is susceptible to deprotonation, whereas protonation hardly occurs. Trifluoroethoxy-substituted nickel phthalocyanine (TFEO-NiPc) and trifluoroethoxy-substituted

Phosphonic acid: preparation and applications

• Charlotte M. Sevrain,
• Mathieu Berchel,
• Hélène Couthon and
• Paul-Alain Jaffrès

Beilstein J. Org. Chem. 2017, 13, 2186–2213, doi:10.3762/bjoc.13.219

• first pKa ranging from 1.1 to 2.3 and the second acidity which features a pKa ranging from 5.3 to 7.2 [11]. The values strongly depend on the electronic properties induced by the substituent R. It must be noted that due to the high polarity of the phosphonic acid function, the purification of phosphonic

• phosphonic acid from phosphonates without the need of intense purification in the final step. Indeed, the purification is limited to remove the solvent and volatile reagents that are frequently used in excess (see section 3). Due to the acidity of phosphonic acid this function is deprotonated in water and

• analogue) [11]. Meanwhile, the phosphonic acid derivatives are more acidic when compared to their carboxylic acid equivalents (1.9 to 2.9 units of pKa below for the first acidity of phosphonic acid derivatives) [11]. This property was used to design Brönsted acid catalysts that were used for the

New bio-nanocomposites based on iron oxides and polysaccharides applied to oxidation and alkylation reactions

• Daily Rodríguez-Padrón,
• Alina M. Balu,
• Antonio A. Romero and
• Rafael Luque

Beilstein J. Org. Chem. 2017, 13, 1982–1993, doi:10.3762/bjoc.13.194

• can be deduced from the intense and well-defined bands observed at 1449 and 1600 cm−1, which can be attributed to Lewis acid centers (Figure 4A). Additionally, in the spectrum of Fe2O3-PS4-MNP, having bands at 1440 and 1618 cm−1, indicates the peculiar Lewis acidity of this material (Figure 4B

• ). Furthermore, in both materials, a band of lesser intensity can be seen around 1490 cm−1, which is due to the presence of both Brønsted and Lewis centers. These materials maintained a remarkable acidity, even at high temperatures (200 and 300 °C) with visible acid centers distinguishable from noise. This

• behavior has a high value for acid-catalyzed processes such as alkylation. Furthermore, the Fe2O3-PS4 sample does not show appreciable acidity [43]. Pyridine (PY) and 2,6-dimethylpyridine (DMPY) titration The acidic properties of these materials have also been determined by the chromatographic method of

Base-promoted isomerization of CF₃-containing allylic alcohols to the corresponding saturated ketones under metal-free conditions

• Yoko Hamada,
• Tomoko Kawasaki-Takasuka and
• Takashi Yamazaki

Beilstein J. Org. Chem. 2017, 13, 1507–1512, doi:10.3762/bjoc.13.149

• this interesting and efficient protocol, computation was performed [7] for obtaining the rough indication of the acidity of both protons Ha and Hb in 1F. Moreover, the corresponding allylic alcohols 2F as well as their non-fluorinated counterparts 1H and 2H were also employed for comparison whose

• present instance to afford the desired compound 7a in 67% isolated yield (Table 2, entry 2). The result that the stronger tertiary amine DBU worked more effectively than Et3N was a clear support of our computation at least from a qualitative point of view which estimated the lower acidity of the allylic

Towards open-ended evolution in self-replicating molecular systems

• Herman Duim and
• Sijbren Otto

Beilstein J. Org. Chem. 2017, 13, 1189–1203, doi:10.3762/bjoc.13.118

• -state. Instead, the environment may be continuously changing. Consider for instance changes in temperature, acidity, light intensity and humidity to which a system will inevitably be subjected. A replicator that is very well adapted to a certain environment, might not persist at a later time when the

• interact with the evolutionary process. Can environmental conditions like acidity or temperature, for instance, be an incentive towards the development of novel functionalities in the replicators? And how is the notion of death introduced in an experiment in which the researcher does not actively intervene

Transition-metal-free one-pot synthesis of alkynyl selenides from terminal alkynes under aerobic and sustainable conditions

• Adrián A. Heredia and
• Alicia B. Peñéñory

Beilstein J. Org. Chem. 2017, 13, 910–918, doi:10.3762/bjoc.13.92

• environment and moderate acidity of the methylene protons in benzyl selenocyanate (7h) or dibenzyl diselenide (8h) may afford intermediates prone to decomposition, directly affecting formation of 5h. Furthermore, the electronic and steric effects offered by different substituents on the aryl moieties attached

• yield of product 5j to 52%. This is ascribed to a lower acidity of the acetylenic proton in 6c in relation to the unsubstituted alkyne 6a (Table 4, entry 3). For phenylethynyl derivatives substituted in para or ortho position by halides, the yields of the corresponding products 5k and 5l were 64% and 61

• detected (Table 4, entry 6). This result indicates that although the acidity of acetylenic proton in 6f is higher than that for the unsubstituted one 6a, the resulting anion is highly stabilized by this group, thus reducing its nucleophilic character and being unreactive against di(n-octyl) diselenide (8a

Metal-free hydroarylation of the side chain carbon–carbon double bond of 5-(2-arylethenyl)-3-aryl-1,2,4-oxadiazoles in triflic acid

• Anna S. Zalivatskaya,
• Dmitry S. Ryabukhin,
• Marina V. Tarasenko,
• Alexander Yu. Ivanov,
• Irina A. Boyarskaya,
• Elena V. Grinenko,
• Ludmila V. Osetrova,
• Eugeniy R. Kofanov and
• Aleksander V. Vasilyev

Beilstein J. Org. Chem. 2017, 13, 883–894, doi:10.3762/bjoc.13.89

• room temperature (see Table 2, entries 16 and 28). Presumably, at higher temperatures the second protonation takes place at the C=C double bond giving rise to reactive dications D. The acidity of H2SO4, which is lower than that of FSO3H and TfOH, is not sufficient to promote this reaction. Thus, the

• temperature (Table 2, entries 13, 16, 27, 28, and 30). Increasing the acidity of the reaction medium promotes the protonation of deactivated oxadiazoles. Thus, compound 1b in the system TfOH-SbF5 (20 mol %) reacted with benzene within 0.5 h at room temperature (Table 2, entry 9), but in less acidic neat TfOH

New approach toward the synthesis of deuterated pyrazolo[1,5-a]pyridines and 1,2,4-triazolo[1,5-a]pyridines

• Aleksey Yu. Vorob’ev,
• Vyacheslav I. Supranovich,
• Gennady I. Borodkin and
• Vyacheslav G. Shubin

Beilstein J. Org. Chem. 2017, 13, 800–805, doi:10.3762/bjoc.13.80

• -methoxy-N-aminopyridinium cation possesses significantly lower acidity for both N–H and C–H hydrogens possibly due to the electron-donating effect of the methoxy group. These quantum chemical data together with Zoltewicz’s work [27] suggest 7-deuterium-labeled pyrazolo[1,5-a]pyridines could be obtained

• a 93% DD for the methyl group after two runs in D2O. The 4-methoxy derivative 1c slowly underwent an H/D exchange at the 2-position of the pyridinium ring probably by reason of a lower acidity due to the electron-donating effect of the methoxy group. Thus, 5-methoxypyrazolopyridine 6 was obtained in

Continuous-flow processes for the catalytic partial hydrogenation reaction of alkynes

• Carmen Moreno-Marrodan,
• Francesca Liguori and
• Pierluigi Barbaro

Beilstein J. Org. Chem. 2017, 13, 734–754, doi:10.3762/bjoc.13.73

• support material, e.g., acid/base properties [184][185], morphology, grain size [186], porosity [187], strong metal–support interactions, swelling propensity [188]). In propyne hydrogenation, for instance, catalyst resistance was shown to decrease with increasing acidity of the support [189]. In order to

Substitution of fluorine in M[C₆F₅BF₃] with organolithium compounds: distinctions between O- and N-nucleophiles

• Anton Yu. Shabalin,
• Nicolay Yu. Adonin and
• Vadim V. Bardin

Beilstein J. Org. Chem. 2017, 13, 703–713, doi:10.3762/bjoc.13.69

• ion pair (solution of Li[C6F5B(OMe)3] in CH2Cl2), such migration of −OMe and its subsequent elimination is hindered [42]. In the case of pentafluorophenyltrifluoroborates the similar conversion does not occur even with Li[C6F5BF3] in DME (contact ion pairs) due to the higher Lewis acidity of C6F5BF2

Unpredictable cycloisomerization of 1,11-dien-6-ynes by a common cobalt catalyst

• Abdusalom A. Suleymanov,
• Dmitry V. Vasilyev,
• Valentin V. Novikov,
• Yulia V. Nelyubina and
• Dmitry S. Perekalin

Beilstein J. Org. Chem. 2017, 13, 639–643, doi:10.3762/bjoc.13.62

• structure to that of 1a,b. We can speculate that COOEt groups of 1l formed a chelate complex with ZnI2 and therefore strongly diminished its Lewis acidity, which is necessary for catalyst activation. All the compounds obtained were characterized by 1H and 13C NMR spectroscopy as well as high-resolution mass

Transition-metal-catalyzed synthesis of phenols and aryl thiols

• Yajun Liu,
• Shasha Liu and
• Yan Xiao

Beilstein J. Org. Chem. 2017, 13, 589–611, doi:10.3762/bjoc.13.58

• chemical properties, such as acidity and nucleophilicity, and thus to some extent, the synthetic methods could be developed analogously to each other. In this context, it is valuable to compare their existing synthetic methods for better understanding, so as to inspire organic chemists to invent new

Structure–efficiency relationships of cyclodextrin scavengers in the hydrolytic degradation of organophosphorus compounds

• Sophie Letort,
• Michaël Bosco,
• Benedetta Cornelio,
• Frédérique Brégier,
• Sébastien Daulon,
• Géraldine Gouhier and
• François Estour

Beilstein J. Org. Chem. 2017, 13, 417–427, doi:10.3762/bjoc.13.45

• consisted first in the selective introduction of the imidazole substituent in position 2 in unit B of 6 by making use of the higher acidity of this hydroxy group compared to the OH groups in positions 3 and 6. As expected, the substitution reaction with the benzyl-like reactant 7 led to a higher yield than

(Z)-Selective Takai olefination of salicylaldehydes

• Stephen M. Geddis,
• Caroline E. Hagerman,
• Warren R. J. D. Galloway,
• Hannah F. Sore,
• Jonathan M. Goodman and
• David R. Spring

Beilstein J. Org. Chem. 2017, 13, 323–328, doi:10.3762/bjoc.13.35

• acetylated (14) and the relevant proton is therefore absent. This implies that increased acidity is not the primary factor at play. Instead, based on the higher (Z)-selectivity observed whenever the electron-withdrawing group was closer to the aldehyde moiety (Table 2), we propose that it is withdrawal of

Spectral and DFT studies of anion bound organic receptors: Time dependent studies and logic gate applications

• Srikala Pangannaya,
• Neethu Padinchare Purayil,
• Shweta Dabhi,
• Venu Mankad,
• Prafulla K. Jha,
• Satyam Shinde and
• Darshak R. Trivedi

Beilstein J. Org. Chem. 2017, 13, 222–238, doi:10.3762/bjoc.13.25

• receptors for anions have been developed based on various modes of interactions such as hydrogen bond and electrostatic interactions which rely on directionality and distance-dependent nature, respectively. Hydrogen bond formation is further tuned by the acidity of protons by virtue of the presence of