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

• other recognition units render them promising building blocks for the construction of other high-order interlocked structures. Keywords: azide–alkyne cycloaddition; catenane; click chemistry; cucurbit[6]uril; mechanical bond; Introduction Catenanes are topologically non-trivial molecules possessing

• a preliminary study of a [6]catenane synthesis featuring the CB[6]-mediated azide–alkyne cycloaddition (CBAAC) using phenanthroline-based building blocks [24]. To further explore the applicability and generality of the CBAAC in the construction of mechanically interlocked molecules, we report here

• the efficient synthesis of a series of [3]catenanes from a combination of different azide and alkyne building blocks. These [3]catenanes were obtained in good yields (>85%) with straightforward purification procedures. The good compatibility of CBAAC with these various building blocks and the good

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

• anchoring i) of the photoreactive [Ru(TAP)2phen]2+ complex on the calix[4]arene small rim through a peptide-type coupling and ii) of the four c-[RGDfK] moieties on the opposite rim through a copper-catalyzed azide–alkyne cycloaddition (CuAAC) [66][67][68] (Figure 1). It was thus necessary to block the calix

• % yield. Diazotation followed by nucleophilic substitution with sodium azide gave the desired tetra-azido compound 4 in 56% overall yield from 3. It is noteworthy that the introduction of the azido groups on the calix[4]arene scaffold was clearly confirmed by the presence of an intense band at 2108 cm−1

• + CF3COO−]+ by comparison between the experimental and theoretical isotope distributions (see Supporting Information File 1). With RuII-calix[4]arene complex 7 in hands, we next moved to the introduction of the cellular targeting units on the large rim through copper-catalyzed azide–alkyne cycloaddition

Anomeric modification of carbohydrates using the Mitsunobu reaction

• Julia Hain,
• Patrick Rollin,
• Werner Klaffke and
• Thisbe K. Lindhorst

Beilstein J. Org. Chem. 2018, 14, 1619–1636, doi:10.3762/bjoc.14.138

• , in combination with the Ph3P-DEAD system, leaves the acid-labile protecting groups of 127 intact, other than when HF is used. Zbiral’s group on the other hand, developed the synthesis of glycosyl azides such as 128 in a Mitsunobu procedure with 127, using hydrazoic acid as the azide source (Scheme 27

Hypervalent organoiodine compounds: from reagents to valuable building blocks in synthesis

• Gwendal Grelier,
• Benjamin Darses and
• Philippe Dauban

Beilstein J. Org. Chem. 2018, 14, 1508–1528, doi:10.3762/bjoc.14.128

• triazolophenanthridines 56 that are obtained in a one-pot manner by combination of a cyclic diaryl-λ3-iodane with sodium azide and a terminal alkyne, in the presence of 10 mol % of CuI (Scheme 21) [61]. The expected triazolophenanthridines were generally isolated in good to excellent yields, but the presence of strong

• mechanism that first involves the formation of a 2’-iodobiphenyl-2-azide promoted by the copper complex. The latter then catalyzes an intermolecular [3 + 2] cycloaddition with the alkyne. Finally, the copper-triazole moiety inserts intramolecularly into the second Ar–I bond, allowing a ring closure after

• Jiang has very recently described a complementary method for the synthesis of carbazoles by combining cyclic diaryl-λ3-iodanes with sodium azide in the presence of copper(I) thiophene-2-carboxylate (CuTc) and triphenylphosphine. The reaction affords the expected of N–H free derivatives 63 in moderate to

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

• extend and possibly improve the supramolecular binding abilities of CyNSs, mixed cyclodextrin-calixarene co-polymers nanosponges (CyCaNSs) were recently synthesized by exploiting a classical “click-chemistry” approach, namely the CuAAC reaction (Cu-catalyzed azide–alkyne cycloaddition [28][29][30

• be largely tuned by varying the combination ratio between the two co-monomers. In fact, full reticulation is achieved even though the co-monomers are not reacted in equivalent amounts. Moreover, in the latter case reactive azide or alkyne functional groups in excess are present throughout the

• be tentatively attributed to methylene C atoms linked to unreacted azide groups and to the Csp atoms of unreacted alkyne groups. The latter finding provides further confirmation that the CuAAC reaction cannot run to completion under the conditions for the formation of the polymer network. In the

[3 + 2]-Cycloaddition reaction of sydnones with alkynes

• Veronika Hladíková,
• Jiří Váňa and
• Jiří Hanusek

Beilstein J. Org. Chem. 2018, 14, 1317–1348, doi:10.3762/bjoc.14.113

• reaction conditions together with very high and reverse regioselectivity and efficiency (in most cases 85–99% yields) makes the CuSAC reaction a very good alternative to the well-established azide–alkyne click-reaction [117] useful not only in classical organic synthesis but also in bioconjugation

• , in deuteric solvent hydrolyzed to give 3-deutero pyrazole. However, Fokin et al. has recently [123] revealed that monomeric copper acetylide complexes are not reactive toward organic azides in analogous copper-catalyzed alkyne–azide cycloaddition (CuAAC) and the catalysis by an external Cu(I) salt is

• azide nitrogen N3 to π-bound copper of dinuclear copper complex with concerted addition of alkyne β-carbon to azide terminal nitrogen N1. An intermediate formed in which N3 is coordinated to both copper atoms undergoes fast ligand exchange between both copper atoms which makes them equivalent. Then the

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

• glycol spacer with a terminal azide results in a complete loss of activity. Docking studies of the novel cryptophycin analogues to β-tubulin provided a rationale for the observed cytotoxicities. Keywords: cryptophycin; cytotoxic agents; novel payloads; tubulin inhibitors; tumour targeting; Introduction

• ]. Based on this, we designed cryptophycin analogues modified in the unit B. Instead of the O-methyl group that is present in the natural cryptophycin, we attached a hydroxyethyl group or a triethylene glycol chain terminated with an alcohol or azide, respectively. These functional groups would allow the

• preparation of the two different spacers that were later connected to the phenol. Starting from triethylene glycol (3) or 2-allyloxyethanol (7) tosylations and nucleophilic displacements by azide or iodide substitution provided 6 and 9 in good yields. O-Alkylation of Boc-protected 3-chlorinated D-tyrosine 10

Atom-economical group-transfer reactions with hypervalent iodine compounds

• Andreas Boelke,
• Peter Finkbeiner and
• Boris J. Nachtsheim

Beilstein J. Org. Chem. 2018, 14, 1263–1280, doi:10.3762/bjoc.14.108

• arylations with moderate AE to highly atom efficient transformations using alkynyl and azide-substituted benziodoxolones. The given AE values are simplified and were calculated on the basis of the key substrates, whereas the required equivalents of all starting materials (iodane and usually its reaction

• , azidobenziodoxolones 36b (ABX), could be utilized for atom-economical reactions. Gillaizeau and co-workers developed an iron-catalysed oxyazidation of enamides 45 using ABX derivatives 36b (Scheme 24) [58]. The reaction proceeds with complete regio- and stereoselectivity introducing the azide group in C2 and the ester

• moiety in C3 position, affording the trans-isomer 46 exclusively. The reaction mechanism presumably follows a radical pathway, which begins with a single electron transfer (SET) from Fe(II) to 36b generating a Fe(III) species as well as benziodoxolonyl radical A or benzoyloxy radical A’ and an azide

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

• betulinic acid analogs were synthesized by using azide–alkyne click reaction and their anticancer activities against different cancer cell lines and normal human PBMC cell line were evaluated by MTT assay. Conjugate 42 was found to be extremely potent against HT-29 cell line with an IC50 value of 14.9 μM

Imide arylation with aryl(TMP)iodonium tosylates

• Souradeep Basu,
• Alexander H. Sandtorv and
• David R. Stuart

Beilstein J. Org. Chem. 2018, 14, 1034–1038, doi:10.3762/bjoc.14.90

• % yield from 1a (Scheme 3). We have previously described the coupling of aryl(TMP)iodonium tosylates with azide nucleophiles [14]. Azide is a notably stronger nucleophile than phthalimide and it is interesting to compare the reaction of these two nucleophiles with 1a under similar conditions (Table 2

• ). The Mayr nucleophilicity constant of azide [15] is 20.5 and high yield (95%) is observed in a reaction with 1a under relatively mild temperature (65 °C) and short reaction time (2 hours, Table 2, entry 1). The Mayr nucleophilicity constant for phthalimide is five-orders of magnitude lower (15.5) [3

Mechanochemistry of nucleosides, nucleotides and related materials

• Olga Eguaogie,
• Joseph S. Vyle,
• Patrick F. Conlon,
• Manuela A. Gîlea and
• Yipei Liang

Beilstein J. Org. Chem. 2018, 14, 955–970, doi:10.3762/bjoc.14.81

• (Scheme 5) [42]. In the absence of light, azobenzene derivatives were isolated as the pure E-isomers. In their original report, Sharpless and co-workers described the use of copper turnings to promote a regioselective azide–alkyne [3 + 2]-cycloaddition ("click") reaction over 24 hours [43]. High-speed

• and carboxylic acid Boc protection using an improvised attritor-type mill. Nucleobase Boc protection via transient silylation using an improvised attritor-type mill. Chemoselective N-acylation of an aminonucleoside using LAG in a MBM. Azide–alkyne cycloaddition reactions performed in a copper vessel

A stereoselective and flexible synthesis to access both enantiomers of N-acetylgalactosamine and peracetylated N-acetylidosamine

• Bettina Riedl and
• Walther Schmid

Beilstein J. Org. Chem. 2018, 14, 856–860, doi:10.3762/bjoc.14.71

• -catalyzed, stereo- and regioselective epoxide opening and subsequent nucleophilic substitution of an azide functionality. This approach enables the synthesis of the naturally D- and unnaturally L-configured GalNAc, as well as both enantiomers of the largely unknown N-acetylidosamine (IdoNAc). Keywords

• -diethyl tartrate (L-DET) directing the reaction towards the D-galacto-configured epoxythreitol 5a. Alternatively, epoxidation of 4b with D-DET was used to access L-galacto-configured epoxythreitol 5b. A procedure by Miyashita et al. [19] for nucleophilic substitution of epoxides by an azide functionality

• was applied for the presented approach. Therefore, 5a and 5b had to be converted first to the unsaturated esters 6a and 6b (Scheme 2) [20][21]. These compounds were reacted with trimethylsilyl azide (TMSN3) under Pd0 catalysis. With this protocol, the azide was introduced under double inversion of the

An uracil-linked hydroxyflavone probe for the recognition of ATP

• Márton Bojtár,
• Péter Zoltán Janzsó-Berend,
• Dávid Mester,
• Dóra Hessz,
• Mihály Kállay,
• Miklós Kubinyi and
• István Bitter

Beilstein J. Org. Chem. 2018, 14, 747–755, doi:10.3762/bjoc.14.63

• -Azidomethyluracil (4) [59]: The azido compound was synthesized as previously described. To a solution of 5-chloromethyluracil [63] (1.00 g, 6.23 mmol) in dimethylformamide (24 mL), sodium azide (0.81 g, 12.5 mmol, 2 equiv) was added. The mixture was stirred at ambient temperature for 1 h, then poured to 50 mL of

• as follows. Propargyl derivative 3 (200 mg, 0.596 mmol) and azide compound 4 (100 mg, 0.596 mmol, 1 equiv) was dissolved in tetrahydrofuran (25 mL), and TBTA [64] (32 mg, 0.1 equiv) and [Cu(MeCN)4]BF4 (14 mg, 0.075 equiv) were added. The reaction mixture was stirred for 24 h, and the product

AuBr₃-catalyzed azidation of per-O-acetylated and per-O-benzoylated sugars

• Jayashree Rajput,
• Srinivas Hotha and
• Madhuri Vangala

Beilstein J. Org. Chem. 2018, 14, 682–687, doi:10.3762/bjoc.14.56

• ], glycoconjugates [30][31][32], N-glycosyl heterocycles [33][34], N-glycosyl triazole [35][36], etc. Glycosyl azides can be accessed from the corresponding glycosyl halides [37][38][39][40] by nucleophilic displacement with NaN3 or using trimethylsilyl azide in the presence of a phase transfer catalyst [41][42][43

• ][44][45]. More commonly, glycosyl azides are synthesized from per-O-acetylated sugars using trimethylsilyl azide in the presence of a variety of Lewis acids such as SnCl4 [46], TiCl4 [47][48], BF3·OEt2 [49], TMSOTf [50][51], etc. However, at higher concentration Lewis acids can potentially lead to

• slow anomerization [52]. In 2011, Chen’s group reported that 5 mol % FeCl3 can catalyze the reaction of trimethylsilyl azide with per-O-acetylated β-monosaccharides to afford glycosyl azides in 3–7 h, whereas per-O-acetylated β-di- and trisaccharides required 22–28 h for complete conversion [53

Sequential Ugi reaction/base-induced ring closing/IAAC protocol toward triazolobenzodiazepine-fused diketopiperazines and hydantoins

• Robby Vroemans,
• Fante Bamba,
• Jonas Winters,
• Joice Thomas,
• Jeroen Jacobs,
• Luc Van Meervelt,
• Jubi John and
• Wim Dehaen

Beilstein J. Org. Chem. 2018, 14, 626–633, doi:10.3762/bjoc.14.49

• together all necessary functionalities for further transformations. The Ugi adducts were then subjected to a base-induced ring closing and an intramolecular azide–alkyne cycloaddition reaction in succession to obtain highly fused benzodiazepine frameworks. Keywords: benzodiazepine; 2,5-diketopiperazine

• ; hydantoin; intramolecular azide–alkyne cycloaddition; Ugi reaction; Introduction The versatile bioactivities of multiring-fused heterocyclic scaffolds continue to attract significant attention in developing new methods for their synthesis. A plethora of functionalized fused heterocycles can be easily

• multicomponent reactions with intramolecular azide–alkyne cycloaddition (IAAC) for the generation of triazole-fused heterocycles [12][13][14][15][16][17][18][19][20][21][22][23]. In this report we disclose our results on the development of a sequential synthetic approach involving Ugi 4-component reaction (4-CR

Continuous multistep synthesis of 2-(azidomethyl)oxazoles

• Thaís A. Rossa,
• Nícolas S. Suveges,
• Marcus M. Sá,
• David Cantillo and
• C. Oliver Kappe

Beilstein J. Org. Chem. 2018, 14, 506–514, doi:10.3762/bjoc.14.36

• from vinyl azides through an azirine intermediate (Scheme 3). The process starts with the generation of the azirine from the vinyl azide by thermolysis. Formation of azirines from vinyl azides by photolysis and thermolysis in continuous flow has been previously described [38][39]. The azirine

• fully continuous process are described in detail. Results and Discussion Thermolysis of the vinyl azide and oxazole formation. Batch optimization The reaction conditions for the thermolysis of the vinyl azide and the subsequent ring expansion of the intermediate azirine to form the oxazole ring were

• initially optimized in batch. For these experiments, vinyl azide 1a was used as a model substrate. The small-scale batch thermolyses were carried out using sealed 1.5 mL vials heated in an aluminum platform. A 0.5 M solution of substrate 1a was prepared using acetone as the solvent. The experiments were

Synthetic and semi-synthetic approaches to unprotected N-glycan oxazolines

• Antony J. Fairbanks

Beilstein J. Org. Chem. 2018, 14, 416–429, doi:10.3762/bjoc.14.30

• the GlcNAc acceptor has an azide or sulfonamide at position 2, rather than acetamide or N-phthalamide. Scheme 5 shows an example of the synthesis of a modified core N-glycan tetrasaccharide oxazoline from the several reported by Wang [77] using this approach. In this case following formation of the

• the incorporation of tags into the glycan structure, which allows further modifications to be made later. In this case, following conversion of the azide at position 2 of the glucosamine unit into an acetamide, azide was introduced at position 6 of the two terminal mannose residues. Protecting group

• interconversions, and peracetylation were followed by conversion to the oxazoline, using TMSBr, BF3·Et2O and collidine, and finally deacetylation. It was found that the incorporated azide was tolerated by the ENGase enzyme (Endo A), and so a modified glycoprotein (RNase) was made by enzymatic attachment of this

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

• disulfide linker in the cytoplasm. In another example, Perrin and co-workers conjugated the N-propargylasparagine of an amanitin analog to a cycloRGD integrin ligand (cyclo[RGDfK]) using a copper-catalyzed azide–alkyne cycloaddition [8]. The conjugates were tested in the U87 glioblastoma cell line, but only

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

• -azidomethylbenzoyl)-protected nucelosides, followed by removal of the 5'-O-DMTr group and extension of the dimer to the trimer by coupling of another N-acyl-3'-O-(o-chlorophenylphosphate)nucleoside. The final removal of the 2-azidomethylbenzoyl group occurred by reduction of the azide with triphenylphosphine in

Fluorogenic PNA probes

• Tirayut Vilaivan

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

• high background. The masking of fluorophores by a more stable group, such as azides, is more attractive. Unfortunately, the phosphine probe generally required for the unmasking of the azide probe is susceptible to rapid aerobic oxidation. Accordingly, new developments in this area are still required

• . One promising example is the release of fluorophores by a phosphine-free photocatalyzed reduction of a self-immolative azide-based linker [105]. Single-labeled PNA probes with additional interacting partners PNA-based strand displacement probes Strand displacement probes consist of a fluorescence

Photocatalytic formation of carbon–sulfur bonds

• Alexander Wimmer and
• Burkhard König

Beilstein J. Org. Chem. 2018, 14, 54–83, doi:10.3762/bjoc.14.4

• -methacryloylbenzamides is similar and includes alkyl substituents on the nitrogen atom and electron-rich and poor aromatic moieties. Mao and Zhou applied vinyl azides for the radical cross-coupling with sodium sulfinate salts (Scheme 56) [95]. They observed that the azide moiety decomposes during the reaction (loss of

Aminosugar-based immunomodulator lipid A: synthetic approaches

• Alla Zamyatina

Beilstein J. Org. Chem. 2018, 14, 25–53, doi:10.3762/bjoc.14.3

• starting from azide 1 by first protecting the 3-OH group with an allyloxycarbonyl (Alloc) protecting group followed by regioselective reductive opening of the 4,6-O-benzylidene acetal using NaCNBH3 and HCl in diethyl ether, and successive phosphitylation of the liberated 4’-OH functionality with N,N

• deprotected by treatment with tetrabutylammonium fluoride buffered with acetic acid, and the resulting lactol was converted to the imidate donor 11 which was coupled to the orthogonally protected acceptor, an azide 12, using triflic acid as promotor (Scheme 2). Subsequent hydrolytic cleavage of the

• azide 12 with the imidate donor 43 furnished fully orthogonally protected βGlcN(1→6)GlcN 44. Next, the 2’-N-Fmoc group in 44 was removed by treatment with DBU and the first unusual branched acyloxyacyl residue was installed. For the preparation of (R)-3-hydroxy-13-methyltetradecanoic and (R)-3

Recent applications of click chemistry for the functionalization of gold nanoparticles and their conversion to glyco-gold nanoparticles

• Vivek Poonthiyil,
• Thisbe K. Lindhorst,
• Vladimir B. Golovko and
• Antony J. Fairbanks

Beilstein J. Org. Chem. 2018, 14, 11–24, doi:10.3762/bjoc.14.2

• glycoscience. In this review we present recent advances made in the use of one type of click chemistry, namely the azide–alkyne Huisgen cycloaddition, for the functionalization of gold nanoparticles and their conversion to glyco-gold nanoparticles. Keywords: azide–alkyne Huisgen cycloaddition; carbohydrates

• functionalized carbohydrates (Figure 1c). Various types of reaction, such as reductive amination [32], oxime formation [33], amidation [34], and perfluorophenyl azide (PFPA) photocoupling [35][36], have been used to functionalize the surface of AuNPs with carbohydrates. The detailed information regarding the

• synthesis and application of GAuNPs can be found in the reviews by Penadés and co-workers [9][26] and also in a recent review by Compostella et al. [10]. In this regard, azide–alkyne click chemistry is an attractive approach that could be used to synthesize GAuNPs. The functionalization of AuNPs using the

Nucleophilic dearomatization of 4-aza-6-nitrobenzofuroxan by CH acids in the synthesis of pharmacology-oriented compounds

• Alexey M. Starosotnikov,
• Dmitry V. Shkaev,
• Maxim A. Bastrakov,
• Ivan V. Fedyanin,
• Svyatoslav A. Shevelev and
• Igor L. Dalinger

Beilstein J. Org. Chem. 2017, 13, 2854–2861, doi:10.3762/bjoc.13.277

• Discussion The only method for the synthesis of 1 described so far deals with the reaction of commercially available 2-chloro-3,5-dinitropyridine (4) with NaN3 followed by thermolysis of the intermediate azide [25][26]. We developed an alternative safe and efficient method for the synthesis of 1 starting

Synthetic mRNA capping

• Fabian Muttach,
• Nils Muthmann and
• Andrea Rentmeister

Beilstein J. Org. Chem. 2017, 13, 2819–2832, doi:10.3762/bjoc.13.274

• tetrazoles. Even photo-crosslinking moieties were enzymatically transferred to the N7-position of the mRNA cap from suitable AdoMet analogues. Notably, quantitative modification at the N7-position was achieved [96]. Diazirine and aryl–azide photo-crosslinker moieties were functional showing cross-linking to

• ) followed by treatment with aqueous ammonia (rt, 3 h). Click chemistry for the preparation of capped RNA and cap analogues. (A) Preparation of capped RNA via a copper-catalyzed azide–alkyne cycloaddition (CuAAC) of an azido-modified cap analogue with a 5'-alkyne bearing RNA [120]. (B) An alkyne-modified