A combinatorial approach to improving the performance of azoarene photoswitches

• Joaquin Calbo,
• Aditya R. Thawani,
• Rosina S. L. Gibson,
• Andrew J. P. White and
• Matthew J. Fuchter

Beilstein J. Org. Chem. 2019, 15, 2753–2764, doi:10.3762/bjoc.15.266

• . An emerging alternative approach to tune the properties of azoarene photoswitches is to replace one or both of the benzene rings with a heteroaromatic ring [15][16]. While several useful heteroaromatic azo scaffolds have been reported, we previously identified such photoswitches containing a pyrazole

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

• hydration reaction of alkynes serves as a green alternative to metal-catalyzed procedures. Previous work has shown that this method works well with terminal alkynes on keto-functionalized scaffolds, including 1,3-dicarbonyls and their heteroatom analogues. It was hypothesized that the reaction proceeds

• room temperature. Previous work by our group has shown that terminal alkynes on keto scaffolds undergo iodine-mediated hydration to form 1,4-diketo products 2 (Scheme 1) [15]. At that time, our studies revealed that a keto group must be present in the substrate, as the hydration requires neighboring

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

• -carboxylates bearing aryl moieties at the C-5 or C-4 position were appropriate starting substrates to construct TT scaffolds according to our strategy. Compounds 2a–k can be prepared either through direct palladium-catalyzed arylation of methyl 3-chlorothiophene-2-carboxylate [19] or through replacement of the

A toolbox of molecular photoswitches to modulate the CXCR3 chemokine receptor with light

• Xavier Gómez-Santacana,
• Sabrina M. de Munnik,
• Tamara A. M. Mocking,
• Niels J. Hauwert,
• Shanliang Sun,
• Prashanna Vijayachandran,
• Iwan J. P. de Esch,
• Henry F. Vischer,
• Maikel Wijtmans and
• Rob Leurs

Beilstein J. Org. Chem. 2019, 15, 2509–2523, doi:10.3762/bjoc.15.244

• . Results and Discussion Azologization design The chemokine receptor CXCR3 is endogenously activated by the chemotactic peptides CXCL11, CXCL10 and CXCL9. Synthetic small-molecule ligands can also bind to CXCR3 [25]. Multiple small-molecule CXCR3 antagonist scaffolds have been disclosed but small-molecule

Combining the Ugi-azide multicomponent reaction and rhodium(III)-catalyzed annulation for the synthesis of tetrazole-isoquinolone/pyridone hybrids

• Gerardo M. Ojeda,
• Prabhat Ranjan,
• Pavel Fedoseev,
• Lisandra Amable,
• Upendra K. Sharma,
• Daniel G. Rivera and
• Erik V. Van der Eycken

Beilstein J. Org. Chem. 2019, 15, 2447–2457, doi:10.3762/bjoc.15.237

• . Keywords: C–H activation; cyclization; isoquinolone; multicomponent reaction; tetrazole; Introduction Pyridones and isoquinolones are relevant heterocyclic scaffolds present in numerous bioactive compounds and natural products [1][2][3][4]. Similarly, molecules containing a tetrazole ring exhibit a wide

• , which has been considered of interest for medicinal chemistry applications [7][8]. In recent years, the preparation of hybrid heterocyclic scaffolds including the tetrazole ring (either fused or linked to other heterocycles) has rendered potent bioactive compounds [9][10][11][12][13], which confirms the

• reactions (MCRs) with the large synthetic scope of metal-catalyzed cyclization protocols [49][50][51][52][53][54]. In this sense, we envisioned that the application of modern Ru(II) or Rh(III)-catalyzed annulations on Ugi-azide-4CR-derived scaffolds could be a promising strategy to generate novel hybrid

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

• slides [46][47], steroids [48][49], calixpyrroles [50][51], calixarenes [52][53], and other scaffolds [54][55][56]. In particular, peptide based transmembrane anion transporters have attracted great interest. For example, Ghadiri [38], Ranganathan [39], and Granja [40] have independently reported

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

• generate a vast number of (poly)cyclic hydrocarbon scaffolds. Remarkably, this complex chemical reaction, comprising changes in bonding, hybridization as well as the introduction of specific stereochemistry, is performed in a single reaction cascade without consumption of a cofactor [11]. In this review we

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

• acidic removal of the Boc group (99%) gave norfloxacin as the hydrochloride salt (12) in an overall 35% yield from 8. Conclusion We have developed a novel and efficient synthetic route towards two privileged 4-quinolone-3-carboxylate scaffolds commonly used in medicinal chemistry. The highly attractive

An overview of the cycloaddition chemistry of fulvenes and emerging applications

• Ellen Swan,
• Kirsten Platts and
• Anton Blencowe

Beilstein J. Org. Chem. 2019, 15, 2113–2132, doi:10.3762/bjoc.15.209

• for the synthesis of complex polycyclic carbon scaffolds. As a result, fulvene cycloaddition chemistry has been employed extensively for the synthesis of natural products. More recently, fulvene cycloaddition chemistry has also found application to other areas including materials chemistry and dynamic

• fulvenes and complex polycyclic scaffolds. Keywords: cycloaddition; fulvene; polycyclic scaffolds; Introduction Fulvenes are an interesting organic class of cross-conjugated, cyclic molecules first discovered by Thiele in 1900, with the preparation of pentafulvenes by condensation of aldehydes and

• interest as a result of their unique reactivity resulting from their exocyclic double bond [9][29][30][31][32], and more recently, as intermediates in the synthesis of more complex polycyclic scaffolds via cycloaddition reactions. While this highlight article will focus primarily on the cycloaddition

Bipolenins K–N: New sesquiterpenoids from the fungal plant pathogen Bipolaris sorokiniana

• Chin-Soon Phan,
• Hang Li,
• Simon Kessler,
• Peter S. Solomon,
• Andrew M. Piggott and
• Yit-Heng Chooi

Beilstein J. Org. Chem. 2019, 15, 2020–2028, doi:10.3762/bjoc.15.198

• pathways in endothelial cells [25]. However, 12 showed no activity against wheat seedlings or wheat seed germination in this study. The sativene-type sesquiterpenoids contain a bicyclo[3.2.1]octane backbone and are related to seco-sativene and isosativene scaffolds [15] (Figure 5a). They were also proposed

• to be related to the bicyclo[4.2.1]nonane-containing longifolene and seco-longifolene sesquiterpenoids, as they were often co-isolated [3][4][6][15][26][27]. A closer examination of the biosynthetic relationship between sativene and longifolene scaffolds suggests that the two pathways branched early

• sesquiterpenoids isolated in this study. A) Different groups of sativene/longifolene-type sesquiterpenoid scaffolds; B) The branched pathways to sativene- and longifolene-type sesquiterpenoids. C) Detailed proposed pathways to the sativene-derived sesquiterpenoids from this study. 1H and 13C NMR data for

A review of the total syntheses of triptolide

• Xiang Zhang,
• Zaozao Xiao and
• Hongtao Xu

Beilstein J. Org. Chem. 2019, 15, 1984–1995, doi:10.3762/bjoc.15.194

• can ensure the optical purity of tripolide by utilizing the natural building block ʟ-dehydroabietic acid, and therefore could give a lot of inspiration for the future syntheses of triptolide and other related natural products from resource-abundant natural scaffolds. Alternatively, inspired by the use

Multicomponent reactions III

• Thomas J. J. Müller

Beilstein J. Org. Chem. 2019, 15, 1974–1975, doi:10.3762/bjoc.15.192

• of synthetic efficiency. Biologically and pharmaceutically relevant scaffolds are likewise tackled as chromophores, methodology development and conceptual design of macro(hetero)cycles go hand in hand with MCR-based heterocyclic chemistry. As in the previous thematic issues also this issue opens the

Reactions of 2-carbonyl- and 2-hydroxy(or methoxy)alkyl-substituted benzimidazoles with arenes in the superacid CF₃SO₃H. NMR and DFT studies of dicationic electrophilic species

• Dmitry S. Ryabukhin,
• Alexey N. Turdakov,
• Natalia S. Soldatova,
• Mikhail O. Kompanets,
• Alexander Yu. Ivanov,
• Irina A. Boyarskaya and
• Aleksander V. Vasilyev

Beilstein J. Org. Chem. 2019, 15, 1962–1973, doi:10.3762/bjoc.15.191

• –Crafts reaction; triflic acid; Introduction Imidazoles and benzimidazoles are important heterocyclic scaffolds in pharmaceuticals and agrochemicals [1][2][3][4][5][6][7][8][9][10]. They also have applications in the fields of dyes, chemo-sensing, and fluorescent materials [3]. (Benz)imidazoles are a

Complexation of chiral amines by resorcin[4]arene sulfonic acids in polar media – circular dichroism and diffusion studies of chirality transfer and solvent dependence

• Bartosz Setner and
• Agnieszka Szumna

Beilstein J. Org. Chem. 2019, 15, 1913–1924, doi:10.3762/bjoc.15.187

• a hydrophobic effect, while the other one has a more directional character, or application of multidentate interaction sites [3]. Macrocyclic compounds with persistent hydrophobic cavities constitute a fundamental class of scaffolds for the construction of supramolecular host–guest complexes in

Identification of optimal fluorescent probes for G-quadruplex nucleic acids through systematic exploration of mono- and distyryl dye libraries

• Xiao Xie,
• Michela Zuffo,
• Marie-Paule Teulade-Fichou and
• Anton Granzhan

Beilstein J. Org. Chem. 2019, 15, 1872–1889, doi:10.3762/bjoc.15.183

• reviews on this subject [34][35][36][37][38][39]. Moreover, novel probes continue to be regularly reported. However, in most cases, the discovery of novel probes is based on serendipitous findings or limited variations of already established fluorogenic scaffolds. This provokes a flood of “one-molecule

• and these high Stokes shifts contributes to make the selected styryl dyes excellent tools for optical imaging. Discussion Despite the wealth of scaffolds already reported for the fluorimetric detection of G4 structures, the published studies usually lack a systematic investigation of the factors

• fluorescence enhancement with any of the analytes). Can it be considered as a general rule? Considering the significant structural diversity of our library and the related works [41][49], this is highly probable, with regard to mono- and distyryl scaffolds. This implies that styryl-based fluorescent probes

Synthesis of a [6]rotaxane with singly threaded γ-cyclodextrins as a single stereoisomer

• Jason Yin Hei Man and
• Ho Yu Au-Yeung

Beilstein J. Org. Chem. 2019, 15, 1829–1837, doi:10.3762/bjoc.15.177

• relatively large cavity size that could accommodate up to two aromatic guests to form 1:2 host–guest complexes, in contrast to the usual formation of 1:1 complex by α-CD and β-CD [10][11]. In addition to host–guest chemistry, the favourable binding of CDs to common organic scaffolds has also made CDs popular

Vicinal difunctionalization of alkenes by four-component radical cascade reaction of xanthogenates, alkenes, CO, and sulfonyl oxime ethers

• Shuhei Sumino,
• Takahide Fukuyama,
• Mika Sasano,
• Ilhyong Ryu,
• Antoine Jacquet,
• Frédéric Robert and
• Yannick Landais

Beilstein J. Org. Chem. 2019, 15, 1822–1828, doi:10.3762/bjoc.15.176

• xanthate 1c, 2b and 3a gave the corresponding keto oxime 5l in 39% yield. The functionalized α-keto oximes obtained herein should be useful scaffolds for further functionalization. Indeed, the α-keto oximes were reported to be used for the synthesis of a variety of synthetic intermediates, including

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

• diversified compounds. In this review we wish to focus attention on applications of 5–8 in syntheses of biologically important compounds having a 2-amino-1,3-disubstituted propane unit implanted into their structures because vicinal amino alcohol and 2-aminopropane-1,3-diol scaffolds are present in many

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

• heterocycles have blossomed in the last many years. These heterocyclic scaffolds occupy a pivotal role in the realm of both natural products and synthetic organic chemistry. Their importance as precursors to many biologically active compounds has created a tremendous amount of focused attention on developing

• methods to functionalize these systems [1][2]. In one such context, imidazopyridines are one of the fascinating classes of fused N-heterocyclic scaffolds of versatile concern. Their chemistry has drawn substantial attention in last few years owing to their involvement in various medicinal applications viz

Synthesis of ([1,2,4]triazolo[4,3-a]pyridin-3-ylmethyl)phosphonates and their benzo derivatives via 5-exo-dig cyclization

• Aleksandr S. Krylov,
• Artem A. Petrosian,
• Julia L. Piterskaya,
• Nataly I. Svintsitskaya and
• Albina V. Dogadina

Beilstein J. Org. Chem. 2019, 15, 1563–1568, doi:10.3762/bjoc.15.159

• -Hydrazinylpyridines (a) and pyridinylhydrazones (b), as well as their acylated derivatives (c), are versatile scaffolds for the preparation of triazolopyridines (Scheme 1). The known methods for the [1,2,4]triazolopyridine ring formation use various condensation agents such as HCOOH, orthoesters, Lawesson’s reagent

An azobenzene container showing a definite folding – synthesis and structural investigation

• Abdulselam Adam,
• Saber Mehrparvar and
• Gebhard Haberhauer

Beilstein J. Org. Chem. 2019, 15, 1534–1544, doi:10.3762/bjoc.15.156

• the high dispersion energy in the compact cis,cis-isomer. Keywords: azobenzene; macrocycles; molecular switch; Introduction In supramolecular chemistry rigid scaffolds are required to arrange different recognition units in predefined distances and spatial orientation to each other [1]. One example

• ][22]. Beside the usage of the side chains of the amino acids and the azole rings for molecular recognition, the functional groups of the scaffolds of these cyclopeptides have also been applied as receptors for Y-shaped anions [23] and as ligands for copper(II) complexes [24][25]. Of special interest

Host–guest interactions between p-sulfonatocalix[4]arene and p-sulfonatothiacalix[4]arene and group IA, IIA and f-block metal cations: a DFT/SMD study

• Valya K. Nikolova,
• Cristina V. Kirkova,
• Silvia E. Angelova and
• Todor M. Dudev

Beilstein J. Org. Chem. 2019, 15, 1321–1330, doi:10.3762/bjoc.15.131

• are not as good as those of other common macrocycles. Two positions (phenolic OH groups and p-positions) in the calixarenes’ structure can be easily modified by subsequent reactions [4]. As a result, calixarenes have a great potential as simple scaffolds to build molecular receptors and multivalent

Doebner-type pyrazolopyridine carboxylic acids in an Ugi four-component reaction

• Maryna V. Murlykina,
• Oleksandr V. Kolomiets,
• Maryna M. Kornet,
• Yana I. Sakhno,
• Sergey M. Desenko,
• Victoriya V. Dyakonenko,
• Svetlana V. Shishkina,
• Oleksandr A. Brazhko,
• Vladimir I. Musatov,
• Alexander V. Tsygankov,
• Erik V. Van der Eycken and
• Valentyn A. Chebanov

Beilstein J. Org. Chem. 2019, 15, 1281–1288, doi:10.3762/bjoc.15.126

• synergetic application of several diversity-oriented synthesis (DOS) instruments allows an effective decoration of the privileged scaffolds for creating collections of unique, highly potent bioactive compounds [4][5]. The pyrazolopyridine scaffold can be regarded as a privileged motif as it exhibits various

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

• two different steroidal scaffolds [65], but it failed for the ligation of larger peptides to steroids due to the poor solubility of the former ones. In this sense, Rivera’s group introduced a solid-phase multicomponent procedure enabling the conjugation of steroids and lipids to peptides longer than

• scaffolds containing the rigid steroid skeleton. In this regard, Wessjohann can be considered as the pioneer of the synthesis of steroidal macrocycles using MCRs [12][13] including remarkable examples of huge macrocycles formed by the condensation of up to twelve components. Whereas the reports up to 2008

Towards the preparation of synthetic outer membrane vesicle models with micromolar affinity to wheat germ agglutinin using a dialkyl thioglycoside

• Dimitri Fayolle,
• Nathalie Berthet,
• Bastien Doumeche,
• Olivier Renaudet,
• Peter Strazewski and
• Michele Fiore

Beilstein J. Org. Chem. 2019, 15, 937–946, doi:10.3762/bjoc.15.90

• addition to its high efficiency and selectivity, the TEC reaction does not require any metal, a key feature for the preparation of potential vaccines. Results and Discussion Preparation of alkyl glycosides from unprotected sugars and lipophilic scaffolds Thioglycolipids are not native in OMV [1], but

• compounds similar to other efficient multivalent glycoconjugates obtained by TEC of sugar thiols with different multivalent scaffolds such as octasilsesquioxanes [35], cyclopeptides [36][37] and polymers [38]. Both compounds 5 and 8 showed low IC50 values (a tenth to some hundreds of micromolars) where the