Selective ring-opening metathesis polymerization (ROMP) of cyclobutenes. Unsymmetrical ladderphane containing polycyclobutene and polynorbornene strands

• Yuan-Zhen Ke,
• Shou-Ling Huang,
• Guoqiao Lai and
• Tien-Yau Luh

Beilstein J. Org. Chem. 2019, 15, 44–51, doi:10.3762/bjoc.15.4

• ][8][9][10][11][12][13][14][15] or from biscyclobutene [16] linked with a range of different rigid linkers. When a flexible linker is used, bisnorbornene derivatives undergo cascade metathetical cyclopolymerization giving the corresponding polynorbornenes with hammock-like pendants [17][18

The design and synthesis of an antibacterial phenothiazine–siderophore conjugate

• Abed Tarapdar,
• James K. S. Norris,
• Oliver Sampson,
• Galina Mukamolova and
• James T. Hodgkinson

Beilstein J. Org. Chem. 2018, 14, 2646–2650, doi:10.3762/bjoc.14.242

• -cleavable linker. A polyethylene glycol (PEG) linker was selected as PEG linkers demonstrate enhanced water solubility in comparison to alkyl chain linkers. We then had to make a decision on the position of attachment for the PEG linker to compound 1. For siderophore conjugates, it is crucial that the

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

• . Naturally occurring amino acids, e.g., glycine, are often used in medicinal chemistry as linkers, structural components of scaffolds or even as precursors to useful building blocks. Wallentin and co-workers have described a method for the reductive decarboxylation of amino acids, using bis(4-chlorophenyl

• identical nature of the substituents on the product. This severely limits its potential applications, and the usefulness of this protocol is likely limited to the creation of linkers or pendant groups. Benzo-fused five-membered heterocycles also find widespread use in medicinal chemistry, with indoles

Coordination-driven self-assembly vs dynamic covalent chemistry: versatile methods for the synthesis of molecular metallarectangles

• Li-Li Ma,
• Jia-Qin Han,
• Wei-Guo Jia and
• Ying-Feng Han

Beilstein J. Org. Chem. 2018, 14, 2027–2034, doi:10.3762/bjoc.14.178

• and metallacages [6][7][8][9]. Following this approach, two self-assembled metallarectangles with different bridging linkers 3a,b were synthesized by utilizing the [Cp*2Rh2(μ-η2-η2-C2O4)Cl2] unit as molecular clips (Scheme 1, method A). Precursor complex 1, which bears two labile triflato ligands was

Chiral bisoxazoline ligands designed to stabilize bimetallic complexes

• Deepankar Das,
• Rudrajit Mal,
• Nisha Mittal,
• Zhengbo Zhu,
• Thomas J. Emge and
• Daniel Seidel

Beilstein J. Org. Chem. 2018, 14, 2002–2011, doi:10.3762/bjoc.14.175

• available. This led to the selection of naphthyridine, pyridazine, pyrazole, and phenol building blocks. We opted to connect these linkers to oxazolines via amide bonds. The reasoning for this was twofold. Firstly, this should provide ligands with significantly improved stabilities over for instance imine

• linkers. In addition, each amide moiety, upon deprotonation (a requirement for complex formation), would provide a formal negative charge on the ligand, thus resulting in increased complex stability while reducing the number of spectator anions associated with the two metals. Different combinations of

• contrast, a distorted square pyramidal binding mode is observed for Zn(2). Phenol-bridged bisoxazoline ligands. Ligands incorporating naphthyridine, pyridazine and pyrazole linkers discussed thus far bridge two metal atoms by attachment to two different nitrogen donor atoms. As a result, metal∙∙∙metal

A hemicryptophane with a triple-stranded helical structure

• Augustin Long,
• Olivier Perraud,
• Erwann Jeanneau,
• Christophe Aronica,
• Jean-Pierre Dutasta and
• Alexandre Martinez

Beilstein J. Org. Chem. 2018, 14, 1885–1889, doi:10.3762/bjoc.14.162

• / UCBL, Université Claude Bernard Lyon 1, 6 rue victor Grignard, 69622 Villeurbanne cedex, France 10.3762/bjoc.14.162 Abstract A hemicryptophane cage bearing amine and amide functions in its three linkers was synthesized in five steps. The X-ray molecular structure of the cage shows a triple-stranded

• helical arrangement of the linkers stabilized by intramolecular hydrogen bonds between amide and amine groups. The chirality of the cyclotriveratrylene unit controls the propeller arrangement of the three aromatic rings in the opposite part of the cage. 1H NMR studies suggest that this structure is

• part). They display recognition properties toward neurotransmitters and carbohydrates, and can act as molecular switches and supramolecular catalysts [11]. Their C3 symmetry makes them promising candidates to build molecular cages displaying a triple helical arrangement of the linkers. Furthermore, we

Efficient catenane synthesis by cucurbit[6]uril-mediated azide–alkyne cycloaddition

• Antony Wing Hung Ng,
• Chi-Chung Yee,
• Kai Wang and
• Ho Yu Au-Yeung

Beilstein J. Org. Chem. 2018, 14, 1846–1853, doi:10.3762/bjoc.14.158

• linkers between the terminal azide and alkyne groups, so that any other possible preorganization effects, except that of the ammonium binding to CB[6] could be eliminated to study the efficiency of CBAAC in the catenane formation. In our first trial, a 1:1:2 mixture of DN-N3, DN-CC and CB[6] in 0.2 M HCl

Synthesis and photophysical studies of a multivalent photoreactive Ru^II-calix[4]arene complex bearing RGD-containing cyclopentapeptides

• Sofia Kajouj,
• Lionel Marcelis,
• Alice Mattiuzzi,
• Adrien Grassin,
• Damien Dufour,
• Pierre Van Antwerpen,
• Didier Boturyn,
• Eric Defrancq,
• Mathieu Surin,
• Julien De Winter,
• Pascal Gerbaux,
• Ivan Jabin and
• Cécile Moucheron

Beilstein J. Org. Chem. 2018, 14, 1758–1768, doi:10.3762/bjoc.14.150

• carbon atoms of RGDfK units exceed 30 Å. Along the MD simulations, we noticed that the Ru complex remained far from the cyclic pentapeptides. This is due to the fact that the linkers of each arm are smaller than the size of the calixarene platform, preventing contacts between the Ru complex and the RGDfK

• and the cyclic pentapeptides. This large variation in the distance is due to the flexibility of the linkers between the calixarene platform and the RGDfK units, together with the many possibilities of H-bonding between: (i) oxygen atoms at C=O in the linker and the hydrogen atoms of (N–H) of arginine

Design, synthesis and structure of novel G-2 melamine-based dendrimers incorporating 4-(n-octyloxy)aniline as a peripheral unit

• Cristina Morar,
• Pedro Lameiras,
• Attila Bende,
• Gabriel Katona,
• Emese Gál and
• Mircea Darabantu

Beilstein J. Org. Chem. 2018, 14, 1704–1722, doi:10.3762/bjoc.14.145

• central building blocks (A–C) already contain a standard m-trivalent core (benzene-1,3,5-triyl or s-triazin-2,4,6-triyl) connected to 1,4-disubstituted six-membered (hetero)cycle linkers. These linkers were chosen based on their intimate nature: flexible (piperazin-1-yl)methyl (in A), rigid 1,4-phenylene

• installation of the piperazine linkers on 2a (Table 1, entry 3) and on D-Cl (Table 1, entry 5) was ensured by the use of a 300% molar excess of this inexpensive reagent. We note the long-reaction time and large temperature domains (Table 1) required in order to obtain the quantitative results shown in Scheme 2

• realised by covalent and/or (carboxyl/amino) ionic trimerisations, to recommend two G-1 N-substituted melamine dendrons with piperzine-1,4-diyl (linkers) and 4-(n-octyloxyphenyl)amino (peripheral units), D-Cl and D-N

  NH, as promising scaffolds for future dendritic elaborations. Tandem DFT-(VT) NMR

Hyper-reticulated calixarene polymers: a new example of entirely synthetic nanosponge materials

• Alberto Spinella,
• Marco Russo,
• Antonella Di Vincenzo,
• Delia Chillura Martino and
• Paolo Lo Meo

Beilstein J. Org. Chem. 2018, 14, 1498–1507, doi:10.3762/bjoc.14.127

• , V.le delle Scienze ed. 17, 90128 Palermo, Italy 10.3762/bjoc.14.127 Abstract New calixarene-based nanosponges (CaNSs), i.e., hyper-reticulated polymers constituted by calixarene monomer units joined by means of bis(1,2,3-trialzolyl)alkyl linkers, were synthesized, characterized and subjected to

• was assessed by means of FTIR and 13C{1H} CP-MAS solid-state NMR techniques, whereas morphological characterization was provided by SEM microghaphy. The materials were proved to possess pH-dependent sequestration abilities, due to the presence of the weakly basic triazole linkers. Sequestration

• . For instance, increased porosity of the CyNS obtained has been recently claimed by the use of a rigid terephthalonitrile unit as the linker [13]. On the other hand, it has been recently shown that polyamine linkers give rise to pH-sensitive materials with tunable adsorption abilities [12]. In order to

Novel unit B cryptophycin analogues as payloads for targeted therapy

• Eduard Figueras,
• Adina Borbély,
• Mohamed Ismail,
• Marcel Frese and
• Norbert Sewald

Beilstein J. Org. Chem. 2018, 14, 1281–1286, doi:10.3762/bjoc.14.109

• to investigate whether the high biological activity of the parent compound is retained and thus, construction of ADCs and PDCs would be feasible. This preparation could be done using traceless cleavable linkers that are sensitive to the distinct physiology of the tumour with enhanced level and

An overview of recent advances in duplex DNA recognition by small molecules

• Sayantan Bhaduri,
• Nihar Ranjan and
• Dev P. Arya

Beilstein J. Org. Chem. 2018, 14, 1051–1086, doi:10.3762/bjoc.14.93

• and 10 with longer linkers exhibit relatively higher cytotoxicity in comparison to both distamycin and uramustine. The distamycin fragment directs binding to the A·T-rich sequences in the minor groove, and higher flexibility due to the longer linker allows optimal positioning of the mustard for DNA

• , including quinolyl and benzoyl derivatives, and alkenes as linkers in order to investigate their antimicrobial properties [58][59]. One of these structural analogs, MGB-BP-3 (Figure 4), containing a stilbene like fragment as head group and two N-methylpyrroles attached to an aminoethylmorpholine as tail

• –indole amide minor groove binders connected through alkyl or ethoxyethyl linkers were developed by Tecilla et al. [111]. The authors confirmed that these conjugates with tach units, either free or Zn(II)-complexed forms, bind strongly to the minor groove through electrostatic interactions with the

On the design principles of peptide–drug conjugates for targeted drug delivery to the malignant tumor site

• Eirinaios I. Vrettos,
• Gábor Mező and
• Andreas G. Tzakos

Beilstein J. Org. Chem. 2018, 14, 930–954, doi:10.3762/bjoc.14.80

• as prodrugs, due to the covalent coupling of a peptide to a drug via specific linkers. The main building blocks of a simple PDC include a cytotoxic agent (drug), a tumor-homing peptide (navigating/targeting moiety) and a linker between them (Figure 2B). This class of prodrugs is continuously gaining

• not to perturb the binding affinity of the peptide to its receptor and the drug efficacy. An inappropriate linker may impede the release of the drug from the PDC and therefore diminish its overall therapeutic potency. Linkers utilized in PDCs exist in different categories and vary on their length

• , stability, release mechanism, functional groups, hydrophilicity/hydrophobicity etc. This linker can be designed to bear an enzyme-hydrolyzable unit (EHU) like a carboxylic ester or an amide bond, cleaved by esterases and amidases, respectively. The most commonly utilized linkers that bear a carboxylic ester

Mannich base-connected syntheses mediated by ortho-quinone methides

• Petra Barta,
• Ferenc Fülöp and
• István Szatmári

Beilstein J. Org. Chem. 2018, 14, 560–575, doi:10.3762/bjoc.14.43

• ). Rokita et al. focused on generating o-QMs and used them as cross-linking and DNA alkylating agents. Starting from Mannich base 56 and transforming it by a number of synthetic steps, they were managed to elaborate a process that provides easy access to o-QM precursors containing a broad array of linkers

• aminonaphthols and cyclic amines. Brønsted acid-catalysed reaction between aza-o-QMs and 2- or 3-substituted indoles. Formation of 3-(α,α-diarylmethyl)indoles 52 in different synthetic pathways. Alkylation of o-QMs with N-, O- or S-nucleophiles. Formation of DNA linkers and o-QM mediated polymers. Comparison of

Carbohydrate inhibitors of cholera toxin

• Vajinder Kumar and
• W. Bruce Turnbull

Beilstein J. Org. Chem. 2018, 14, 484–498, doi:10.3762/bjoc.14.34

• synthesis, so they designed second generation inhibitors by changing the synthetically challenging α-Neu5Ac with alpha-hydroxy acids 2 [33][34]. Using a combinatorial approach, a library of non-hydrolyzable, non O-glycosidic third generation inhibitors were synthesised using appropriate linkers. The CTB

• chelating mechanism. Hughes and co-workers synthesised and evaluated bivalent 1,2,3 triazole-linked galactopyranosides 14 and 15 as shown in Figure 7 [48]. They used a piperazine core as central divalent core on to which the galactose units were attached via flexible linkers. They found that these compounds

• Bundle and co-workers were also working on analogous designs for shiga-like toxin [59]). They synthesised the inhibitors on a pentacyclene core on which galactose and m-nitrophenyl-α-D-galactopyranoside were attached by long flexible linkers (Figure 10) [60][61]. They found million-fold increases in

Stimuli-responsive oligonucleotides in prodrug-based approaches for gene silencing

• Françoise Debart,
• Christelle Dupouy and
• Jean-Jacques Vasseur

Beilstein J. Org. Chem. 2018, 14, 436–469, doi:10.3762/bjoc.14.32

Synthesis and biological evaluation of RGD and isoDGR peptidomimetic-α-amanitin conjugates for tumor-targeting

• Lizeth Bodero,
• Paula López Rivas,
• Barbara Korsak,
• Torsten Hechler,
• Andreas Pahl,
• Christoph Müller,
• Daniela Arosio,
• Luca Pignataro,
• Cesare Gennari and
• Umberto Piarulli

Beilstein J. Org. Chem. 2018, 14, 407–415, doi:10.3762/bjoc.14.29

• synthesized by joining integrin ligands to α-amanitin via various linkers and spacers. The conjugates were evaluated for their ability to inhibit biotinylated vitronectin binding to the purified αVβ3 receptor, retaining good binding affinity, in the same nanomolar range as the free ligands. The

• and co-workers conjugated α-amanitin to pHLIP (pH low insertion peptide) via linkers of different hydrophobicities [7]. The results indicated that pHLIP could deliver α-amanitin into cells and induce cell death in 48 h by a pH-mediated direct translocation across the membrane and cleavage of the

• conjugates, the integrin ligands are bound to α-amanitin via a 6’-ether with two different linkers: an “uncleavable” six carbon aliphatic chain (Figure 3, compounds 7 and 8) and a lysosomally cleavable Val-Ala linker bound to a self-immolative spacer (Figure 3, compounds 9, 10 and 11). Integrin receptor

Preparation of trinucleotide phosphoramidites as synthons for the synthesis of gene libraries

• Ruth Suchsland,
• Bettina Appel and
• Sabine Müller

Beilstein J. Org. Chem. 2018, 14, 397–406, doi:10.3762/bjoc.14.28

• . Instead, linkers that allow a release of the trimers by a non-nucleophilic and/or non-basic treatment are required. In terms of trimer synthesis only one report in the literature describes such a strategy: The start nucleoside was loaded onto controlled pore glass (CPG) via an oxalyl anchor (Figure 5A

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

• distribution of the LUMO over the central pyrimidine acceptor core and the adjacent phenylene linkers small ΔEST were determined (0.16 and 0.15 eV for T29 and T30, respectively), indicative of reduced electronic correlations between frontier orbitals and accounting for their high performance. Indeed, EQEs of

Fluorogenic PNA probes

• Tirayut Vilaivan

Beilstein J. Org. Chem. 2018, 14, 253–281, doi:10.3762/bjoc.14.17

• , as well as the types of linkers, need to be fine-tuned in order to obtain optimal results. In this respect, the ability to site-specifically label anywhere in the PNA molecule using a pre-formed dye-labeled monomer or a functionalized monomer that allows post-synthetic labeling is important [84

Synthesis and spectroscopic properties of β-meso directly linked porphyrin–corrole hybrid compounds

• Baris Temelli and
• Hilal Kalkan

Beilstein J. Org. Chem. 2018, 14, 187–193, doi:10.3762/bjoc.14.13

• applications [21][22][23]. In order to achieve rapid energy and electron transfer between macrocycles, the short distance between subunits keeps an important place. Therefore, two important factors affect the physical and electronic properties of porphyrin–corrole conjugates: (i) type of linkers and (ii

• ) position of substitution (meso or β). So far, corrole macrocyles have been integrated into porphyrin conjugates via anthracene, biphenylene, xanthene, dibenzofuran [16][17][18][19][20], amide [21] and triazole [22][23] linkers. Despite the large number of studies on the synthesis of porphyrin–corrole

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

• further biomedical/pharmaceutical applications [71], such as cancer therapy [81][82][83]. MOFs combine coordination and supramolecular chemistry. Coordination chemistry is present in the coordination of organic molecules (linkers) to metal ions or clusters (coordination centers), while supramolecular

• chemistry relies on the formation of intermolecular interactions between linker molecules. This combination results in 1D, 2D or 3D porous frameworks. The pore size can be adjusted by varying the size of the linkers, a modification that can be associated to the change in functional groups in the organic

• environmental reasons. These issues also led to the quest for biodegradable MOFs, the first being prepared in 2010 by Miller et al. [77]. Another family of MOFs, ZIFs (zeolitic imidazolate frameworks), that involves organic imidazoles as linkers, has been explored for medicinal purposes as a result of the

Structure–property relationships and third-order nonlinearities in diketopyrrolopyrrole based D–π–A–π–D molecules

• Jan Podlesný,
• Lenka Dokládalová,
• Oldřich Pytela,
• Adam Urbanec,
• Milan Klikar,
• Numan Almonasy,
• Tomáš Mikysek,
• Jaroslav Jedryka,
• Iwan V. Kityk and
• Filip Bureš

Beilstein J. Org. Chem. 2017, 13, 2374–2384, doi:10.3762/bjoc.13.235

• to the first absorption bands. The positions of the emission maxima copy trends seen in the absorption spectra. Increasing the donating ability of the attached peripheral R1-substituents results in a slight bathochromic shift, whereas extension of the π-system by acetylene linkers has an opposite

• in modular way prepared by Suzuki–Miyaura, Migita–Stille, and Sonogashira cross-coupling reactions. The chromophores differ in the π-system extension as well as in the peripheral substitution. The thermal stability of 1–5 is mostly affected by the presence of acetylene linkers, 1,4-phenylene and 2,5

• -thienylene linkers, and ferrocene termini. From the electrochemical data we can conclude that variation of the peripheral donors influences mostly the HOMO, which dictates the HOMO–LUMO gap. Absorption spectra showed two bands localized around 600 nm, which position weakly depend on the peripheral

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

• diacetylene linkers, via a butadiyne and via an aryldiacetylene moiety (Figure 2). Such binuclear phthalocyanines that are connected via a rigid acetylene linker synthesized by Glaser or Sonogashira reactions have attracted attention due to their interesting effects resulting from further expansion of

Intramolecular glycosylation

• Xiao G. Jia and
• Alexei V. Demchenko

Beilstein J. Org. Chem. 2017, 13, 2028–2048, doi:10.3762/bjoc.13.201

• , equal amounts of α- and β-anomers were obtained. Also, when a glucosyl acceptor was employed, mainly the 1,2-cis-linked product was obtained. Valverde et al. also investigated succinoyl tethers [54], but their studies were mainly focusing on phthaloyl and non-symmetrical linkers described below. Among

• other flexible linkers investigated are carbonate [57], as well as oxalic [57], malonic [53][57][58], and glutaric [59] dicarboxylic acids. However, like in the case of succinoyl linkers, higher flexibility led to more relaxed stereoselectivity. Further variations upon this method involved the

• freedom and also to form smaller ring sizes [81]. Templated oligosaccharide synthesis Recently, Demchenko and co-workers introduced templated oligosaccharide synthesis, wherein bisphenol A (BPA) was used as the template and succinoyl, glutaryl or phthaloyl linkers were used to tether glycosyl donors and