Architecture and synthesis of P,N-heterocyclic phosphine ligands

• Wisdom A. Munzeiwa,
• Bernard Omondi and
• Vincent O. Nyamori

Beilstein J. Org. Chem. 2020, 16, 362–383, doi:10.3762/bjoc.16.35

• to obtain cyclopropyl intermediate 45. The latter was converted into compound 46 by reaction with lithium diphenylphosphide in dry THF. Finally, the desired ligand 47 was obtained after quenching the intermediate compound 46 with a saturated solution of ammonium chloride. Ligand 47 was investigated

• magnesium-containing triazoles 66 which, upon quenching with ammonium chloride, afforded the triazoles 67. Lithiation followed by coupling with the appropriate chlorophosphines resulted in the desired 1,5-disubstitued triazolylphosphine ligands 68. The procedure could be performed in one pot by directly

• quenching the metalated triazole 66 with chlorophosphine. However, a separation of the triazole before phosphorylation makes purification of the final ligand easier [74]. The direct ortho-metalation of pyridyltriazole 69 and subsequent reaction with chlorophosphines gave the isomeric ligands 71 and 72 in

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

• conditions (λexcitation = 540 nm at room temperature). Thus, the quenching observed in an EB–DNA solution upon addition of the compounds 11 and 12 may reveal their competition to EB for the DNA-intercalation sites as monitored by fluorescence emission spectroscopy with λexcitation = 540 nm. A significant

• quenching of the EB–DNA fluorescence (up to 68.5% of the initial fluorescence for compound 12 (Figure 4) was found in the presence of the compounds. The as-observed quenching (which is in good agreement (R = 0.99) with the linear Stern–Volmer equation [72]) may be attributed to the competition of compounds

• (up to the value of r = 0.35) [11]. EB-displacement studies The ability of compounds 11 and 12 to displace EB from its DNA–EB conjugate was investigated by fluorescence emission spectroscopy. The Stern–Volmer constant (KSV, in M−1) was used to evaluate the quenching efficiency for each compound

Recent developments in photoredox-catalyzed remote ortho and para C–H bond functionalizations

• Rafia Siddiqui and
• Rashid Ali

Beilstein J. Org. Chem. 2020, 16, 248–280, doi:10.3762/bjoc.16.26

• hand, S1 can also transition to the spin-forbidden T1 through intersystem crossing (ISC), which then decays by (longer) radiative processes to S0 (phosphorescence. Figure 3) [41][42][43]. The triplet excited state is oxygen-sensitive as O2 carries out quenching in solution, thereby leading to the

• ]. In photoredox catalysis, visible light gets absorbed by the photocatalyst (PC), which transitions into a photoexcited state (*PC) that can undergo either energy transfer or redox pathways. As can be seen in Figure 4, the redox pathway consists of reductive and oxidative quenching pathways

• hydroxylation of arenes (Scheme 18) [157]. They realized that the photoredox catalyst 8 possesses a great oxidizing ability (Ered vs SCE = 2.72 V) at ambient conditions. The mechanism of the reaction was studied by fluorescence quenching and transient absorption spectroscopy. They observed that the one-electron

The reaction of arylmethyl isocyanides and arylmethylamines with xanthate esters: a facile and unexpected synthesis of carbamothioates

• Narasimhamurthy Rajeev,
• Toreshettahally R. Swaroop,
• Ahmad I. Alrawashdeh,
• Shofiur Rahman,
• Abdullah Alodhayb,
• Seegehalli M. Anil,
• Kuppalli R. Kiran,
• Chandra,
• Paris E. Georghiou,
• Kanchugarakoppal S. Rangappa and
• Maralinganadoddi P. Sadashiva

Beilstein J. Org. Chem. 2020, 16, 159–167, doi:10.3762/bjoc.16.18

• thiomethyl group via transition state TS3 forms the third intermediate Int3, consisting of a carbene and a thiolate anion. The steps leading to the observed product carbamothioate 4a occur from the final quenching hydrolysis of Int3, which occurs via several energetically favorable steps (e.g., A–C), as has

• subsequent dilute aqueous/DMF quenching conditions, we were unable to detect the hydrolysis products by HRMS. Furthermore, using the same reaction conditions, which were employed to the S-methyl dithiocarbonates 1a–f, but using S-ethyl or S-benzyl dithiocarbonates, none of the corresponding expected reaction

• products were obtained. As well, reductive quenching with aqueous NaCNBH3 failed to trap Int3 and only afforded the same reaction products. Conclusion There are several reports, which have discussed interesting reactions or reactivity of isocyanides. Among these are those which showed that the isocyanide

Potent hemithioindigo-based antimitotics photocontrol the microtubule cytoskeleton in cellulo

• Alexander Sailer,
• Franziska Ermer,
• Yvonne Kraus,
• Rebekkah Bingham,
• Ferdinand H. Lutter,
• Julia Ahlfeld and
• Oliver Thorn-Seshold

Beilstein J. Org. Chem. 2020, 16, 125–134, doi:10.3762/bjoc.16.14

• , lithium diisopropylamide (LDA)-mediated cyclisation of 2-(methylthio)benzamides, which were obtained by directed ortho-metalation of the respective benzamides followed by quenching with dimethyl disulfide [27] (Supporting Information File 1, Scheme S1). In general, we found the LDA-mediated cyclisation

Automated glycan assembly of arabinomannan oligosaccharides from Mycobacterium tuberculosis

• Alonso Pardo-Vargas,
• Priya Bharate,
• Martina Delbianco and
• Peter H. Seeberger

Beilstein J. Org. Chem. 2019, 15, 2936–2940, doi:10.3762/bjoc.15.288

• linker as solid support [25]. A typical AGA cycle consisted of three modules. The acidic wash module prepared the resin for glycosylation by quenching any remaining base from a previous cycle. In the glycosylation module, the thioglycoside donor was coupled to the resin upon activation with NIS and TfOH

A green, economical synthesis of β-ketonitriles and trifunctionalized building blocks from esters and lactones

• Daniel P. Pienaar,
• Kamogelo R. Butsi,
• Amanda L. Rousseau and
• Dean Brady

Beilstein J. Org. Chem. 2019, 15, 2930–2935, doi:10.3762/bjoc.15.287

• also investigated this option for the first time in the synthesis of β-ketonitriles from esters, as described later (see Table 1). Finally, it is probable that the presence of protic IPA suppresses enolization as the reaction progresses, by quenching KOt-Bu generated enolates and similarly, reactive

Preparation of anthracene-based tetraperimidine hexafluorophosphate and selective recognition of chromium(III) ions

• Qing-Xiang Liu,
• Feng Yang,
• Zhi-Xiang Zhao,
• Shao-Cong Yu and
• Yue Ding

Beilstein J. Org. Chem. 2019, 15, 2847–2855, doi:10.3762/bjoc.15.278

• paramagnetic nature of chromium(III) can cause fluorescence quenching of the fluorophore via the enhancement of spin–orbit coupling [30][31][32][33][34][35]. So far, only a few successful examples of fluorescence enhancement sensors for Cr3+ have been reported [36][37][38][39][40]. Thus, developing new and

Design, synthesis and investigation of water-soluble hemi-indigo photoswitches for bioapplications

• Daria V. Berdnikova

Beilstein J. Org. Chem. 2019, 15, 2822–2829, doi:10.3762/bjoc.15.275

• extent depends on the particular sequence of RNA. Photoswitching of the RNA-bound hemi-indigo Z-2 to the E-form results in emission quenching. The ON–OFF fluorescence switching of Z-2–RNA complexes can be performed reversibly by repeated irradiation with blue (470 nm) and amber (590 nm) light. Conclusion

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

• electron-transfer reaction, while ion binding blocks this quenching pathway restoring emission. Thus, ion liberation from 1 and transfer to 3 would result in a fluorescence off–on switching of the latter. To perform the ion-transfer experiment, the fluorescent dye is loaded with one equivalent of Ca2

Iodine-mediated hydration of alkynes on keto-functionalized scaffolds: mechanistic insight and the regiospecific hydration of internal alkynes

• Zachary Lee,
• Brandon R. Jones,
• Nyochembeng Nkengbeza,
• Michael Phillips,
• Kayla Valentine,
• Alexis Stewart,
• Brandon Sellers,
• Nicholas Shuber and
• Karelle S. Aiken

Beilstein J. Org. Chem. 2019, 15, 2747–2752, doi:10.3762/bjoc.15.265

• 8 were observed after 21 h, where new signals emerged and the substrate’s resonances disappeared. However, signals for 10 were also observed, suggesting that as soon as the intermediate 9 was formed, it was converted to the final hydration product 10. Quenching of this reaction mixture cleanly

• the signals observed in Figure 1b and Figure 1c confirmed that the I2- and ICl-mediated hydrations occurred via the same intermediate. Furthermore, quenching of the ICl-facilitated reaction also resulted in the formation of compound 10. Importantly, the existence of the α-iodo intermediate 9 holds

Emission solvatochromic, solid-state and aggregation-induced emissive α-pyrones and emission-tuneable 1H-pyridines by Michael addition–cyclocondensation sequences

• Natascha Breuer,
• Irina Gruber,
• Christoph Janiak and
• Thomas J. J. Müller

Beilstein J. Org. Chem. 2019, 15, 2684–2703, doi:10.3762/bjoc.15.262

• molecular aggregation in the solid state causes fluorescence quenching [16]. In recent years, we have coined diversity-oriented syntheses of functional chromophores by multicomponent strategies [17][18], opening accesses to substance libraries for systematic studies of structure–property relationships on

A photochemical determination of luminescence efficiency of upconverting nanoparticles

• Baptiste Amouroux,
• Clément Roux,
• Jean-Claude Micheau,
• Fabienne Gauffre and
• Christophe Coudret

Beilstein J. Org. Chem. 2019, 15, 2671–2677, doi:10.3762/bjoc.15.260

• intense as the emitted energy increases, (iii) the intensities of the emission lines but not their wavelength vary with the UCNP size, as the surface quenching becomes the most efficient deactivation path for small nanoparticles. Therefore, the assessment of the upconversion quantum yields (UCQY) is a hot

Arylisoquinoline-derived organoboron dyes with a triaryl skeleton show dual fluorescence

• Vânia F. Pais,
• Tristan Neumann,
• Ignacio Vayá,
• M. Consuelo Jiménez,
• Abel Ros and
• Uwe Pischel

Beilstein J. Org. Chem. 2019, 15, 2612–2622, doi:10.3762/bjoc.15.254

• of 0.2–0.4, reaching in some cases values as high as 0.5–0.6. Laser-flash photolysis provided evidence for the existence of excited triplet states. The dyes form fluoroboronate complexes with fluoride anions, leading to the observation of the quenching of the long-wavelength emission band and

• these dyes such as intramolecular charge-transfer processes and tunable red-shifted emission bands. Generally, the so far investigated borylated arylisoquinoline dyes show principally fluorescence quenching (on-off switching) on the formation of the corresponding fluoroboronate complexes [37]. Herein

• for dye 17). These transients showed lifetimes in the microsecond range (τT = 4.2 μs (16) and 4.4 μs (17)), were efficiently quenched by oxygen (bimolecular quenching constant kq ca. 1.1–1.2 × 109 M−1s−1), and led to the energy-transfer triplet-sensitization of β-carotene (observation of the triplet

Safe and highly efficient adaptation of potentially explosive azide chemistry involved in the synthesis of Tamiflu using continuous-flow technology

• Cloudius R. Sagandira and
• Paul Watts

Beilstein J. Org. Chem. 2019, 15, 2577–2589, doi:10.3762/bjoc.15.251

• vial at room temperature. Azide 5 selectivity was reduced with time in the vial. Therefore, the development of a suitable quenching procedure may be helpful. The TBAA procedure seems to be a promising NaN3 procedure replacement when considering the aforementioned anhydrous telescoping due to its

Synthesis of novel sulfide-based cyclic peptidomimetic analogues to solonamides

• José Brango-Vanegas,
• Luan A. Martinho,
• Lucinda J. Bessa,
• Andreanne G. Vasconcelos,
• Alexandra Plácido,
• Alex L. Pereira,
• José R. S. A. Leite and
• Angelo H. L. Machado

Beilstein J. Org. Chem. 2019, 15, 2544–2551, doi:10.3762/bjoc.15.247

• reported for solonamides. Keywords: antivirulence drug; bacteria; macrocyclization; pathoblocker; quorum quenching; Introduction The cyclodepsipeptides called solonamides A and B are natural molecules extracted from the marine bacterium Photobacterium halotolerans [1][2] (Figure 1). They are able to

In search of visible-light photoresponsive peptide nucleic acids (PNAs) for reversible control of DNA hybridization

• Lei Zhang,
• Greta Linden and
• Olalla Vázquez

Beilstein J. Org. Chem. 2019, 15, 2500–2508, doi:10.3762/bjoc.15.243

• effect of the scrambled PNA 19 is the opposite, i.e., signal decrease. We determined a slightly lower fluorescence value than in the case of BHQ-ssDNA; this can be probably attributed to the quenching ability of both PNA probes [52]. Along these lines, the quenching ability of oF4Azo-containing PNA was

Ultrafast processes triggered by one- and two-photon excitation of a photochromic and luminescent hydrazone

• Alessandro Iagatti,
• Baihao Shao,
• Alberto Credi,
• Barbara Ventura,
• Ivan Aprahamian and
• Mariangela Di Donato

Beilstein J. Org. Chem. 2019, 15, 2438–2446, doi:10.3762/bjoc.15.236

• be responsible for the fluorescence quenching in the Z-form. A comparison of the kinetic traces recorded on the maximum of the excited state absorption band in the three analyzed solvents (Figure 6) demonstrates that the excited state decay time decreases on going from acetonitrile to toluene, and

Sugar-derived oxazolone pseudotetrapeptide as γ-turn inducer and anion-selective transporter

• Sachin S. Burade,
• Sushil V. Pawar,
• Tanmoy Saha,
• Navanath Kumbhar,
• Amol S. Kotmale,
• Manzoor Ahmad,
• Pinaki Talukdar and
• Dilip D. Dhavale

Beilstein J. Org. Chem. 2019, 15, 2419–2427, doi:10.3762/bjoc.15.234

• the rate of quenching in fluorescence at λem = 535 nm (λex = 455 nm) was monitored using transporter 2a by creating a Cl– gradient across the lipid membrane by applying NaCl in the extravesicular buffer (Figure S14 in Supporting Information File 1). The compound 2a showed a significant decrease in the

Targeted photoswitchable imaging of intracellular glutathione by a photochromic glycosheet sensor

• Xianzhi Chai,
• Hai-Hao Han,
• Yi Zang,
• Jia Li,
• Xiao-Peng He,
• Junji Zhang and
• He Tian

Beilstein J. Org. Chem. 2019, 15, 2380–2389, doi:10.3762/bjoc.15.230

• broad and strong absorption makes the 2D MnO2 nanosheets a potential energy acceptor for the fluorophores which are stacked on the nanosheets plane, leading to the fluorescence quenching through FRET mechanism [32][34]. The transmission electron microscopy (TEM) image of the prepared product revealed

• effective FRET between the attached Glyco-DTE and 2D MnO2, which again suggested the close stacking of Glyco-DTE to the nanosheet surface. Aggregation-caused quenching might be another reason for the fluorescence quenching because of the close distance between fluorescence molecules when absorbed on the

• ” sensor towards GSH, which is illustrated as fluorescence turn-on and sequential on-off cycles. Besides, the quenching of the reporter fluorescence by MnO2 contributes to a significantly lowered background signal, which makes it an excellent material for intracellular precision imaging. Cell-targeted

Current understanding and biotechnological application of the bacterial diterpene synthase CotB2

• Ronja Driller,
• Daniel Garbe,
• Norbert Mehlmer,
• Monika Fuchs,
• Keren Raz,
• Dan Thomas Major,
• Thomas Brück and
• Bernhard Loll

Beilstein J. Org. Chem. 2019, 15, 2355–2368, doi:10.3762/bjoc.15.228

• carbocation (3) and finally the quenching of the carbocation by a base or water [16][17]. TPSs can be divided into two distinct classes, which are distinguished by their substrate activation mechanism. Whereas ionization of an isoprenoid diphosphate is caused by hydrolysis of the pyrophosphate by a trinuclear

Synthesis of a dihalogenated pyridinyl silicon rhodamine for mitochondrial imaging by a halogen dance rearrangement

• Jessica Matthias,
• Thines Kanagasundaram,
• Klaus Kopka and
• Carsten S. Kramer

Beilstein J. Org. Chem. 2019, 15, 2333–2343, doi:10.3762/bjoc.15.226

• negative value of the HOMO energy level and/or the oxidation potential [15], but it is also influenced by other factors. Nonradiative quenching (e.g., bond rotation) can effectively contribute to depopulation of the fluorophore’s excited state [28], yielding a lower quantum yield. However, the rational

Functionalization of 4-bromobenzo[c][2,7]naphthyridine via regioselective direct ring metalation. A novel approach to analogues of pyridoacridine alkaloids

• Benedikt C. Melzer,
• Alois Plodek and
• Franz Bracher

Beilstein J. Org. Chem. 2019, 15, 2304–2310, doi:10.3762/bjoc.15.222

• metalation at C-5 with TMPMgCl∙LiCl at −40 °C. Quenching with various electrophiles gives a broad range of 5-substituted products, which are building blocks for the synthesis of heterocyclic natural products and analogues thereof. In combination with a Parham-type cyclization a novel approach to pyrido[4,3,2

• 5-subsituted products (Scheme 1). Quenching of metalated 9d with aldehydes 11a–d while warming to room temperature led to the formation of the expected racemic secondary alcohols 12a–d in moderate to good yields (50–66%, Scheme 1). Any attempts to improve the yields failed. The use of 2.2

• equivalents of base, longer reaction times, higher or lower temperatures did not increase the yields. In order to explore additional metalations at other positions than C-5 or imaginable halogen dance reactions [24] during the metalation process, we performed a D2O quenching experiment after the metalation

Fluorescent phosphorus dendrimers excited by two photons: synthesis, two-photon absorption properties and biological uses

• Anne-Marie Caminade,
• Artem Zibarov,
• Eduardo Cueto Diaz,
• Aurélien Hameau,
• Maxime Klausen,
• Kathleen Moineau-Chane Ching,
• Jean-Pierre Majoral,
• Jean-Baptiste Verlhac,
• Olivier Mongin and
• Mireille Blanchard-Desce

Beilstein J. Org. Chem. 2019, 15, 2287–2303, doi:10.3762/bjoc.15.221

• quenching is prevented thanks to the design of the fluorophore [42]. It should be noted that the largest dendrimers, in particular generation 4, display very large two-photon absorption cross-sections (σ2 up to 55,900 GM), which are comparable to those measured for the best quantum dots [43]. Thus these

• the previous examples of dendrimers bearing as terminal functions compounds having TPA properties is soluble in water, and thus they cannot be used for biological purposes. Furthermore, many fluorophores are sensitive to the presence of water, which induces in many cases a quenching of the

Recent advances in transition-metal-catalyzed incorporation of fluorine-containing groups

• Xiaowei Li,
• Xiaolin Shi,
• Xiangqian Li and
• Dayong Shi

Beilstein J. Org. Chem. 2019, 15, 2213–2270, doi:10.3762/bjoc.15.218