Sustainable manganese catalysis for late-stage C–H functionalization of bioactive structural motifs

• Jongwoo Son

Beilstein J. Org. Chem. 2021, 17, 1733–1751, doi:10.3762/bjoc.17.122

• radioisotope for positron emission tomography (PET) in clinical and preclinical research is 18F. Radiopharmaceuticals should be prepared at the late stage of the entire synthetic protocol because of the short half-lives of radioisotopes [26][27][28][29]. In their study, the authors used an aqueous 18F-fluoride

Methodologies for the synthesis of quaternary carbon centers via hydroalkylation of unactivated olefins: twenty years of advances

• Thiago S. Silva and
• Fernando Coelho

Beilstein J. Org. Chem. 2021, 17, 1565–1590, doi:10.3762/bjoc.17.112

• reaction rate-determining step in a radical mechanism in which the alkane participates in both the initiation and propagation steps of the radical chain (Scheme 37C). Photoinduced electron transfer Under photoinduced electron transfer (PET) conditions, olefins generate cation radical species that are

• reported that when a polyene 99 or 100 containing an acidic hydrogen in its structure (e.g., a free hydroxy or enol) was subjected to a PET process, the radical cascade was accompanied by a hydrogen shift to give the formal hydroalkylated product 100 or 101 containing a quaternary carbon center (Scheme 38

• reaction was observed in its absence. The authors highlighted the role of the solvent hexafluoro-2-propanol (HFIP) in the stabilization of the radical cation induced by PET and its assistance in the hydrogen shift process. Miscellaneous Lewis acid catalysis in olefin hydroalkylation reactions The ability

Synthetic accesses to biguanide compounds

• Oleksandr Grytsai,
• Cyril Ronco and
• Rachid Benhida

Beilstein J. Org. Chem. 2021, 17, 1001–1040, doi:10.3762/bjoc.17.82

Synthesis of 10-O-aryl-substituted berberine derivatives by Chan–Evans–Lam coupling and investigation of their DNA-binding properties

• Peter Jonas Wickhorst,
• Mathilda Blachnik,
• Denisa Lagumdzija and
• Heiko Ihmels

Beilstein J. Org. Chem. 2021, 17, 991–1000, doi:10.3762/bjoc.17.81

• suppressed rotation about the Ar–O bond. Nevertheless, as the emission quantum yield of the derivatives 5a–e still remained low, even at high viscosity of the medium, there obviously exist additional relaxation pathways in the excited state, most likely a photo-induced electron transfer (PET) from the 10

Valorisation of plastic waste via metal-catalysed depolymerisation

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

Beilstein J. Org. Chem. 2021, 17, 589–621, doi:10.3762/bjoc.17.53

• (DEG), dipropylene glycol (DPG)) aminolysis (2-aminoethanol, 3-amino-1-propanol, ethylenediamine). Advantages of catalytic processes are obvious and can be witnessed in the hydrolysis and the glycolysis reactions of poly(ethylene terephthalate) (PET) [82][83]. Representative data are reported in

• graphical format in Figure 2 for the glycolysis reaction of PET, using titanium(IV) n-butoxide as the catalyst. Compared to the uncatalysed process, benefits include milder reaction conditions, higher selectivity and productivity and reduced generation of waste; in short, improved sustainability [84][85

• crystallinity, reduced chain mobility and hydrophobicity of polymers [114][115], which makes biodegradation often ineffective and time-consuming, particularly for polyolefins, such as polyethylene, polyvinyl chloride (PVC), polystyrene or PET [116][117]. Thus, abiotic pretreatments may be required, including UV

Formation of an exceptionally stable ketene during phototransformations of bicyclo[2.2.2]oct-5-en-2-ones having mixed chromophores

• Asitanga Ghosh

Beilstein J. Org. Chem. 2020, 16, 2297–2303, doi:10.3762/bjoc.16.190

• (characteristic of β,γ-enone moiety) and the type-B path (characteristic of an α,β-enone moiety). However, with the help of the photoinduced electron transfer (PET) reaction of 1a,c,d,g–h and photoreaction of the partially olefinated product of 1c,d,h, we have recognized that in a mixed α,β- and β,γ-enone system

Photosensitized direct C–H fluorination and trifluoromethylation in organic synthesis

• Shahboz Yakubov and
• Joshua P. Barham

Beilstein J. Org. Chem. 2020, 16, 2151–2192, doi:10.3762/bjoc.16.183

• isotopes for positron emission tomography (PET) due to their suitable half-life (t1/2 = 110 min) and low positron energy, which allows the production of high-resolution images [23]. Therefore, radiopharmaceuticals that contain fluorine substituents are in high demand. Fluorine enhances important properties

One-pot synthesis of isosorbide from cellulose or lignocellulosic biomass: a challenge?

• Isaline Bonnin,
• Raphaël Mereau,
• Thierry Tassaing and
• Karine De Oliveira Vigier

Beilstein J. Org. Chem. 2020, 16, 1713–1721, doi:10.3762/bjoc.16.143

• -isosorbide) terephthalate, can replace polyethylene terephthalate (PET) [7]. In the production of polycarbonate and epoxy resins, the physicochemical properties of isosorbide allow the replacement of bisphenol A by this bio-based molecule [8][9]. At an industrial level, isosorbide is produced from the double

Pauson–Khand reaction of fluorinated compounds

• Jorge Escorihuela,
• Daniel M. Sedgwick,
• Alberto Llobat,
• Mercedes Medio-Simón,
• Pablo Barrio and
• Santos Fustero

Beilstein J. Org. Chem. 2020, 16, 1662–1682, doi:10.3762/bjoc.16.138

• use, fluorine-containing molecules have also found key applications in the field of medical diagnosis. Two of the most powerful imaging techniques used nowadays, positron-emission tomography (PET) and magnetic resonance imaging (MRI), are routinely carried out using fluorine-containing organic

Heterogeneous photocatalysis in flow chemical reactors

• Christopher G. Thomson,
• Ai-Lan Lee and
• Filipe Vilela

Beilstein J. Org. Chem. 2020, 16, 1495–1549, doi:10.3762/bjoc.16.125

[3 + 2] Cycloaddition with photogenerated azomethine ylides in β-cyclodextrin

• Margareta Sohora,
• Leo Mandić and
• Nikola Basarić

Beilstein J. Org. Chem. 2020, 16, 1296–1304, doi:10.3762/bjoc.16.110

• complex molecules and natural products [11] since the pioneering work of Kanaoka et al. [12]. Photochemical reactions of phthalimides include H-abstractions, cycloadditions and photoinduced electron transfer (PET)[13]. We became interested in the application of photochemical H-abstraction reactions

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

• central role in the rapid expansion of photocatalytic methods [12]. These catalysts typically absorb light in the blue region and promote different activation modes, including photoinduced electron transfer (PET) and energy transfer (EnT), which respectively lead to the formation of open-shell and

• organic dye-based consecutive photoinduced electron transfer (conPET) strategy for the reduction of various aryl halides in 2014 [81]. As depicted in Scheme 13 (box 1), the conPET mechanism involves a first PET (PET1), where the excited photocatalyst (PC*) is reduced by a sacrificial electron donor D

• a second PET (PET2). With this strategy, the authors could reduce a broad variety of aryl halides 13.1 using N,N-bis(2,6-diisopropylphenyl)perylene-3,4,9,10-bis(dicarboximide), (PDI, OD20) as a conPET photocatalyst for the generation of an aryl radical (box 2). The latter could be hydrogenated or

Fluorinated phenylalanines: synthesis and pharmaceutical applications

• Laila F. Awad and
• Mohammed Salah Ayoup

Beilstein J. Org. Chem. 2020, 16, 1022–1050, doi:10.3762/bjoc.16.91

• over the last few decades. ᴅ- or ʟ-fluorinated phenylalanines have had considerable industrial and pharmaceutical applications and they have been expanded also to play an important role as potential enzyme inhibitors as well as therapeutic agents and topography imaging of tumor ecosystems using PET

• pharmaceutical applications with a focus on published synthetic methods that introduce fluorine into the phenyl, the β-carbon or the α-carbon of ᴅ-or ʟ-phenylalanines. Keywords: α-fluorophenylalanine; β- and β,β-difluorophenylalanine; fluorinated phenylalanines; PET; pharmaceuticals application; Introduction

• -difluorophenylalanine derivatives 42a,b in quantitative yields [45] (Scheme 9). The radiolabeled 2-[18F]-fluoro-ʟ-phenylalanine 46 was synthesized as a promising radiopharmaceutical agent for molecular imaging by positron emission tomography (PET). The three-step synthesis of 46 started from [18F]-fluoride exchange in

Photophysics and photochemistry of NIR absorbers derived from cyanines: key to new technologies based on chemistry 4.0

• Bernd Strehmel,
• Christian Schmitz,
• Ceren Kütahya,
• Yulian Pang,
• Anke Drewitz and
• Heinz Mustroph

Beilstein J. Org. Chem. 2020, 16, 415–444, doi:10.3762/bjoc.16.40

• electron transfer and internal barriers Sensitized generation of reactive intermediates such as radicals and conjugate acid [5] also followed in the case of NIR sensitive materials a photoinduced electron transfer (PET). However, it did not work as smooth as disclosed for UV systems [83] because there was

• often no reaction between a cationic sensitizer and an electron acceptor; i.e. an iodonium salt [5]. However, the use of stronger emitting LEDs resulted sometimes in successful PET [67]. Particularly, light sources with low emission intensity arose these issues. This supports the idea that the system

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

• the use in multimodal (PET/OI) medical imaging of mitochondria in cancerous cells. Results: A dihalogenated fluorinatable pyridinyl rhodamine could be successfully synthesized with the high yield of 85% by application of a halogen dance (HD) rearrangement. The near-infrared dye shows a quantum yield

• optical properties for medical and bioimaging. As a compound with intrinsic mitochondria targeting ability, the radiolabelled analogue can be applied in multimodal (PET/OI) imaging of mitochondria for diagnostic and therapeutic use in, e.g., cancer patients. Keywords: halogen-dance reaction

• of the ester group in 2’-position, an isopropyl ester derivative; another one might be the effects of the fluorine atoms and the ester group on the HOMO energy level of the benzene moiety. Since our group is interested in PET-active near-infrared (NIR) dyes for bimodal medical imaging (PET/optical

Metal-free mechanochemical oxidations in Ertalyte^® jars

• Andrea Porcheddu,
• Francesco Delogu,
• Lidia De Luca,
• Claudia Fattuoni and
• Evelina Colacino

Beilstein J. Org. Chem. 2019, 15, 1786–1794, doi:10.3762/bjoc.15.172

• significantly by switching to an Ertalyte® jar (86%) [68] which could be further enhanced (93%) by slightly increasing the amount of the oxidant agent (1.5 equiv). Ertalyte® jars (Figure S1b, in Supporting Information File 1) are composed of polyethylene terephthalate (PET-P) and characterized by wear- and

Complexation of a guanidinium-modified calixarene with diverse dyes and investigation of the corresponding photophysical response

• Yu-Ying Wang,
• Yong Kong,
• Zhe Zheng,
• Wen-Chao Geng,
• Zi-Yi Zhao,
• Hongwei Sun and
• Dong-Sheng Guo

Beilstein J. Org. Chem. 2019, 15, 1394–1406, doi:10.3762/bjoc.15.139

• as well-demonstrated fluorescence quenchers acting through a photoinduced electron transfer (PET) mechanism [8][28][29], we hypothesize an electron transfer-induced quenching in the GC5A–Fl complex as underlying mechanism. The binding stoichiometry between GC5A and Fl was determined to be 1:1

• a PET pathway. The fluorescence lifetime of AlPcS4 remains unaltered after addition of GC5A, indicating the absence of dynamic quenching of the residual uncomplexed AlPcS4 and therefore confirming the formation of a statically quenched complex. UV–vis titration further verified the formation of a

• ground-state complex, with drastic changes in both, band shapes and intensities. The calculated rate constant of PET is faster than that of fluorescence and intersystem crossing, which makes it a more favorable deactivation pathway of the first excited singlet state leading to both fluorescence quenching

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

• body. Synthons are becoming more prevalent in imaging modalities like positron emission tomography (PET) as there is a greater need to further investigate lesions, and disease tissues on the molecular level. However, issues with the stability of sulfonyl fluorides have been reported in the literature

Synthesis of nonracemic hydroxyglutamic acids

• Dorota G. Piotrowska,
• Iwona E. Głowacka,
• Andrzej E. Wróblewski and
• Liwia Lubowiecka

Beilstein J. Org. Chem. 2019, 15, 236–255, doi:10.3762/bjoc.15.22

• a few steps into (2S,5'S)-tricholomic acid [47]. The absolute configuration of (R)-(−)-carnitine was established by enzymatic decarboxylation of (2S,3R)-3-hydroxyglutamic acid followed by exhaustive methylation [121]. Fluoroglutamic acids are of special interest for PET imaging [122] and among other

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

• -overexpressing breast cancers in a patients pilot study (n = 5) by using a PET tracer based on the hY1R-specific NPY analogue [F7,P34]-pNPY [35]. This study demonstrated that it is not to be expected that NPY-based diagnostic or therapeutic PDCs will pass the blood-brain barrier and therefore could induce

Thermophilic phosphoribosyltransferases Thermus thermophilus HB27 in nucleotide synthesis

• Ilja V. Fateev,
• Ekaterina V. Sinitsina,
• Aiguzel U. Bikanasova,
• Maria A. Kostromina,
• Elena S. Tuzova,
• Larisa V. Esipova,
• Tatiana I. Muravyova,
• Alexei L. Kayushin,
• Irina D. Konstantinova and
• Roman S. Esipov

Beilstein J. Org. Chem. 2018, 14, 3098–3105, doi:10.3762/bjoc.14.289

• thermophilic transferases in nucleotide synthesis. A scheme of purine nucleotide synthesis using TthAPRT and TthHPRT is shown in Figure 2. Results and Discussion Genes TT_RS08985 and TT_RS06315 from T. thermophilus HB27, coding TthHPRT and TthAPRT, were cloned into expression plasmid vectors pET 23a+ and pET

• ΔEcoRI-B int::(lacI::PlacUV5::T7 gene1) i21 Δnin5. Plasmid vector: pET 23a+, pET 23d+ (Merck Millipore, USA, MA). Enzymes: NdeI, XhoI, NcoI, T4 DNA-ligase (Thermo Scientific, USA, MA), Encyclo-polymerase (Eurogen, Russia). The protein concentration was determined by the Bradford method [17], using BSA as

• . thermophilus HB27 strain by a polymerase chain reaction (PCR) using synthetic primers. The genes were cloned into the expression vectors pET-23a+ and pET-23d+ respectively. The E. coli strains BL21(DE3)/pER- TthAPRT and C3030/pER- TthHPRT produced the target enzymes mainly in soluble form (culturing conditions

Organometallic vs organic photoredox catalysts for photocuring reactions in the visible region

• Aude-Héloise Bonardi,
• Frédéric Dumur,
• Guillaume Noirbent,
• Jacques Lalevée and
• Didier Gigmes

Beilstein J. Org. Chem. 2018, 14, 3025–3046, doi:10.3762/bjoc.14.282

• and redox reactions are possible. This process is called photoinduced electron transfer (PET). In this context, photoredox catalysis was developed. Light is used to excite the photoredox catalyst which allows electron transfer processes with additives. Both oxidation and reduction reactions can be

Novel solid-phase strategy for the synthesis of ligand-targeted fluorescent-labelled chelating peptide conjugates as a theranostic tool for cancer

• Sagnik Sengupta,
• Mena Asha Krishnan,
• Premansh Dudhe,
• Ramesh B. Reddy,
• Bishnubasu Giri,
• Sudeshna Chattopadhyay and
• Venkatesh Chelvam

Beilstein J. Org. Chem. 2018, 14, 2665–2679, doi:10.3762/bjoc.14.244

• tracking molecule to understand the destination of delivered cargos or biologics. For bioimaging of cancer and inflammatory diseases through specific biomarkers [2], several methods including single positron emission computed tomography (SPECT), positron emission tomography (PET) and magnetic resonance

Applications of organocatalysed visible-light photoredox reactions for medicinal chemistry

• Michael K. Bogdos,
• Emmanuel Pinard and
• John A. Murphy

Beilstein J. Org. Chem. 2018, 14, 2035–2064, doi:10.3762/bjoc.14.179

• excited state (S1) or a triplet excited state (T1), by absorption of a photon with energy hν, which then undergoes photoinduced electron transfer (PET). Following this, the photocatalyst is reduced or oxidised accordingly, such that it returns to its ground state and native oxidation state (Figure 1 and

• molecules have some UV absorbance, but little or no absorbance in the visible part of the spectrum, hence excitation of other reactants is unlikely. Visible light photons are high enough in energy to produce excited states of sufficient reactivity to undergo PET. Once a molecule is electronically excited

• likely to be involved in PET. A molecule with a low Φf will be unlikely to be found in the S1 state, as this state will be highly susceptible to other decay pathways in the timescale of PET. For a molecule to undergo PET when in the T1 state, the intersystem crossing quantum yield (ΦISC) must be

Rational design of boron-dipyrromethene (BODIPY) reporter dyes for cucurbit[7]uril

• Mohammad A. Alnajjar,
• Jürgen Bartelmeß,
• Robert Hein,
• Pichandi Ashokkumar,
• Mohamed Nilam,
• Werner M. Nau,
• Knut Rurack and
• Andreas Hennig

Beilstein J. Org. Chem. 2018, 14, 1961–1971, doi:10.3762/bjoc.14.171

• motifs for CB7. The unprotonated dyes show low fluorescence due to photoinduced electron transfer (PET), whereas the protonated dyes are highly fluorescent. Encapsulation of the binding motif inside CB7 positions the aniline nitrogen at the carbonyl rim of CB7, which affects the pKa value, and leads to a

• quenching by photoinduced electron transfer (PET), whereas the protonated form was brightly fluorescent [31]. We report herein the synthesis and photophysical characterization of BODIPY derivatives with an aniline substituent in the meso-position to which different anchor groups have been attached, and we

• accordance with the anticipated PET mechanism [31][45]. Further, the change in free energy, ∆G, associated with PET was calculated using the Rehm–Weller equation [46]. Therefore, we used a reduction potential of −1.55 V for the 1,3,7,9-tetramethyl-BODIPY core acceptor of 1, 2, and 5 [47] and of −1.81 V for