Synthesis of 4-(2-fluorophenyl)-7-methoxycoumarin: experimental and computational evidence for intramolecular and intermolecular C–F···H–C bonds

• Vuyisa Mzozoyana,
• Fanie R. van Heerden and
• Craig Grimmer

Beilstein J. Org. Chem. 2020, 16, 190–199, doi:10.3762/bjoc.16.22

• used for the synthesis of coumarins [42][43]. Methyl 2-fluorobenzoylacetate (3) was reacted with resorcinol (4) in the presence of H2SO4 at 35 °C, and 7-hydroxy-4-(2-fluorophenyl)coumarin (5) [39][44] was obtained as a light yellow solid. The last step of the synthesis was the methylation of the

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

• unit of indanocine (which is attached in ortho-position to the key south ring methoxy group) by a hydroxy function, giving HITub-1 (Figure 2). When HITub-1 later proved less bioactive than we had wished, we explored steric and polarity changes to this south ring hydroxy group by methylation (HITub-2

• ), methylation and shifting on the ring (HITub-3), or even its removal (HITub-4). We additionally controlled against our design logic of north ring substituent shortening (HITub-5). We also controlled for the SAR observation that CDIs should not tolerate a non-polar central north ring substituent (HITub-6), but

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

• , which were commercially available or prepared as described in our previous communication [7]. A final methylation of the tertiary amine 12a–e with MeI in DCM and subsequent precipitation with MTBE (methyl tert-butyl ether) gave 2a–e as orange powders with ≥99% trans-isomer in moderate to high yield

• performed following the strategies shown in Scheme 1 as disclosed for compounds 2a–e. Briefly, a reductive amination of 7 and 8b gave nitro compound 9b, which after reduction to 10b, coupling with nitroso compounds 11a–e to 13a–e and methylation gave iodide salts 3a–e with purities of trans-isomers ≥99% and

• was selectively reduced with DIBAL-H to benzyl alcohols 23f–h, which were oxidized with Dess–Martin periodinane to the corresponding benzaldehyde 26f–h. Reductive amination of 26f–h with 7 gave the tertiary amines 13f–h. Methylation with iodomethane and subsequent precipitation gave 3f–h as orange

Isolation and biosynthesis of an unsaturated fatty acid with unusual methylation pattern from a coral-associated bacterium Microbulbifer sp.

• Amit Raj Sharma,
• Enjuro Harunari,
• Tao Zhou,
• Agus Trianto and
• Yasuhiro Igarashi

Beilstein J. Org. Chem. 2019, 15, 2327–2332, doi:10.3762/bjoc.15.225

• analysis revealed that 1 is an unsaturated fatty acid in which a methyl group is located in an uncommon position as a natural product. Feeding experiments of 13C-labeled precursors clarified that ʟ-methionine-derived methylation takes place at the carbon which is derived from the carbonyl carbon of acetate

• . Compound 1 showed weak growth inhibition against Saccharomyces cerevisiae. Keywords: biosynthesis; fatty acid; marine bacteria; methylation; Microbulbifer; Introduction Marine microbial symbionts are currently recognized as a reservoir of new bioactive compounds [1]. The most well-studied host animal is

• biosynthetically unique: it has an uncommon methylation pattern in its carbon chain, derived from the C-methylation with ʟ-methionine at a carbon originated from a carbonyl carbon of acetate. In this paper, we report the isolation and structure determination of 1 and its biosynthetic origin proven by the feeding

Azologization and repurposing of a hetero-stilbene-based kinase inhibitor: towards the design of photoswitchable sirtuin inhibitors

• Christoph W. Grathwol,
• Nathalie Wössner,
• Sören Swyter,
• Adam C. Smith,
• Enrico Tapavicza,
• Robert K. Hofstetter,
• Anja Bodtke,
• Manfred Jung and
• Andreas Link

Beilstein J. Org. Chem. 2019, 15, 2170–2183, doi:10.3762/bjoc.15.214

• methylation was intended to be examined. For UV–vis spectroscopy 50 µM solutions in 5% DMSO (v/v) in enzyme assay buffer were used, as this reflects the enzyme assay conditions. However, for LC-HRMS and NMR analysis, a higher concentration of 10 mM in methanol was necessary to receive reliable chromatograms

1,2,3-Triazolium macrocycles in supramolecular chemistry

• Mastaneh Safarnejad Shad,
• Pulikkal Veettil Santhini and
• Wim Dehaen

Beilstein J. Org. Chem. 2019, 15, 2142–2155, doi:10.3762/bjoc.15.211

• macroring. A second strategy is the macrocyclization of an acyclic precursor containing pre-functionalized triazole by other ring closure methods such as Grubbs metathesis [25] and amidation reactions. The macrocyclization is normally followed by N-alkylation (often methylation) leading to the synthesis of

• component catalytic system composed of 16c before methylation and TBAI as reference catalysts. Optimization studies of the reaction conditions showed that the addition of CHCl3 and lowering of the reaction temperature (to 10 °C) considerably increased the enantioselectivity (s value of 4.1). An evaluation

1,2,3,4-Tetrahydro-1,4,5,8-tetraazaanthracene revisited: properties and structural evidence of aromaticity loss

• Arnault Heynderickx,
• Sébastien Nénon,
• Olivier Siri,
• Vladimir Lokshin and
• Vladimir Khodorkovsky

Beilstein J. Org. Chem. 2019, 15, 2059–2068, doi:10.3762/bjoc.15.203

• (Figure 3). At the same time, the geometry optimized structure of 6a exhibits much greater torsion angles of 6.23 and 2.28 degrees. The X-ray structure analysis of 7a confirms that the methylation occurs at the N4 atom to form the respective cation (Figure 4). Examination of the bond distances revealed a

Attempted synthesis of a meta-metalated calix[4]arene

• Christopher D. Jurisch and
• Gareth E. Arnott

Beilstein J. Org. Chem. 2019, 15, 1996–2002, doi:10.3762/bjoc.15.195

• Ullmann-type coupling to give aryl azide 2, which readily reacted with phenylacetylene in a copper-catalyzed Huisgen 1,3-dipolar cycloaddition to give 1,2,3-triazole 3 (Scheme 1). The formation of the ruthenacycle was then achieved using Albrecht’s method involving regioselective methylation of triazole 3

• cycloaddition between monoazidocalix[4]arene 7 and phenylacetylene, affording monotriazolocalix[4]arene 11 in 87% yield (Scheme 4). Methylation of the triazole was also achieved using excess iodomethane in a rather protracted reaction, to yield the calix[4]arene triazolium iodide salt 12 in effectively

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

• form the A- and D-ring. The second one involves the reaction of the bicyclic intermediate 13 and 2-isopropyl-1,4-benzoquinone (14) to form the B- and C-ring. Finally, a regio- and stereoselective reduction, methylation and dehydration procedure and a selenylation, oxidation and elimination procedure

• triptolide (Figure 2, route I and Scheme 7) [74]. In this synthesis, commercially available 2-isopropylphenol (31) was used as starting material, protection of 31 with chloromethyl methyl ether (MOM), followed by ortho lithiation and methylation with iodomethane, provided intermediate 85, which was lithiated

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

• )-28. After reductive aziridine ring opening N-Boc-norephedrine ((1R,2S)-29) was formed. The synthesis of (−)-ephedrine ((1R,2S)-31) required prior methylation of the nitrogen atom and for this reason it was performed on the benzyl ether (2S,1'R,1''R)-32 (Scheme 10) [48]. Its reaction with methyl

• -step aziridine ring opening was performed on the silylated alcohol (2S,1'R,1''S)-58 and included N-methylation and reaction with the protected phenylmagnesium bromide to form (2S,3R)-59. The last step opened the way to synthesis of tyroscherin analogues [58]. The alcohol (2S,3R)-60 was obtained after

• sources and are known as precursors to tropane alkaloids [59]. Together with (−)-pseudohygroline (2S,2'R)-62 they were synthesized from a common intermediate (2S,1'R)-63 prepared from the aldehyde (2R,1'R)-6 by Wittig olefination [60] and a regioselective C=C bond reduction (Scheme 17) [61]. N-Methylation

Synthesis and conformational preferences of short analogues of antifreeze glycopeptides (AFGP)

• Małgorzata Urbańczyk,
• Michał Jewgiński,
• Joanna Krzciuk-Gula,
• Jerzy Góra,
• Rafał Latajka and
• Norbert Sewald

Beilstein J. Org. Chem. 2019, 15, 1581–1591, doi:10.3762/bjoc.15.162

• with the aim of excluding pH-dependent charge effects and to simulate a protein environment. The introduction of a methyl amide function at the C-terminus of glycopeptides was carried out on solid phase. The N-methylation of the peptide terminus on solid support was an efficient four-step procedure

• . Moreover, performing this reaction on the resin has eliminated the need for product purification after each step. Modification of the resin was performed according to the protocol published by J. Chatterjee and co-workers [27]. This practical and straightforward strategy involved direct N-methylation of

Alkylation of lithiated dimethyl tartrate acetonide with unactivated alkyl halides and application to an asymmetric synthesis of the 2,8-dioxabicyclo[3.2.1]octane core of squalestatins/zaragozic acids

• Herman O. Sintim,
• Hamad H. Al Mamari,
• Hasanain A. A. Almohseni,
• Younes Fegheh-Hassanpour and
• David M. Hodgson

Beilstein J. Org. Chem. 2019, 15, 1194–1202, doi:10.3762/bjoc.15.116

• diethyl tartrate reacted with LiHMDS in the presence of LiCl and MeI, to give exclusively the corresponding trans-monomethylated tartrate in 72% yield [42]; this compares with methylation of acetonide tartrate 7 by Seebach, which was reported to give an inseparable mixture of monomethylated product (86:14

• rationalisation of stereoselectivity [17][18][19]. Tartrate alkylation with a non-activated alkyl iodide. Alkylated tartrate to diazoester sequence. TES protection approach to the squalestatin core. Tartrate acetonide methylation. Tartrate alkylation with various alkyl halides. Rationalisation of dialkylation

Phylogenomic analyses and distribution of terpene synthases among Streptomyces

• Lara Martín-Sánchez,
• Kumar Saurabh Singh,
• Mariana Avalos,
• Gilles P. van Wezel,
• Jeroen S. Dickschat and
• Paolina Garbeva

Beilstein J. Org. Chem. 2019, 15, 1181–1193, doi:10.3762/bjoc.15.115

• substrate 2-methyl-GPP to form 2-MIB (2) [25][26]. An S-adenosylmethionine (SAM) dependent methyl transferase is responsible for the methylation of GPP into 2-methyl-GPP (14, Scheme 2). Its isomerisation to 15 allows for a cyclisation via the cationic intermediates B and C to 2. Genes encoding for SAM

Electrophilic oligodeoxynucleotide synthesis using dM-Dmoc for amino protection

• Shahien Shahsavari,
• Dhananjani N. A. M. Eriyagama,
• Bhaskar Halami,
• Vagarshak Begoyan,
• Marina Tanasova,
• Jinsen Chen and
• Shiyue Fang

Beilstein J. Org. Chem. 2019, 15, 1116–1128, doi:10.3762/bjoc.15.108

• instability of the adduct under acidic conditions during ODN synthesis [7]. In recent years, applications of ODNs have extended to emerging areas such as nanotechnology [8][9], antisense drug development [10][11][12], DNA damage and repair [13][14], DNA methylation and demethylation [15][16][17][18], DNA

An efficient synthesis of the guaiane sesquiterpene (−)-isoguaiene by domino metathesis

• Yuzhou Wang,
• Ahmed F. Darweesh,
• Patrick Zimdars and
• Peter Metz

Beilstein J. Org. Chem. 2019, 15, 858–862, doi:10.3762/bjoc.15.83

• subjected to dibromoolefination with ylide 19 as described for the transformation of aldehyde 18. Use of the preformed ylide 19 led to reproducibly higher yields of 24 in comparison with the application of tetrabromomethane and triphenylphosphine [23]. One-pot alkyne formation and methylation [23] of 24 to

Azologization of serotonin 5-HT₃ receptor antagonists

• Karin Rustler,
• Galyna Maleeva,
• Piotr Bregestovski and
• Burkhard König

Beilstein J. Org. Chem. 2019, 15, 780–788, doi:10.3762/bjoc.15.74

• atmosphere afforded the quinoxaline azobenzene derivative 11 [68]. Subsequent methylation using methyl iodide [69] mainly resulted in the formation of the N-methylated non-photochromic product 12b but in low yields also the desired photochromic methoxy-substituted quinoxaline azobenzene derivative 12a

Synthesis of the polyketide section of seragamide A and related cyclodepsipeptides via Negishi cross coupling

• Jan Hendrik Lang and
• Thomas Lindel

Beilstein J. Org. Chem. 2019, 15, 577–583, doi:10.3762/bjoc.15.53

• [39] proved to be superior to the more commonly employed n-BuLi/MeI reagent combination that led to the formation of a series of side products. We also attempted a Bestmann–Ohira reaction with in situ formation of the diazo phosphonate [40] that gave a slightly inferior yield after methylation of the

• . Boc protection yielded N-Boc-D-3-iodotyrosine (21), which underwent three-fold methylation to N-methyl-O-methyliodotyrosine methyl ester 22 (82% yield, er 4:1, CHIRALPAK® IA, hexane/iPrOH 9:1). Partial racemization of 21 could not be suppressed since a slight excess of base was always necessary

• , whereas the use of exactly stoichiometric amounts resulted in incomplete N-methylation. Treating the Boc-protected methyl ester of iodotyrosine 21 with a larger excess of base and methyl iodide (10 equiv each) led to the formation of the α-quaternary amino acid 23 (Scheme 4). An alternative route to the N

Synthesis and biological investigation of (+)-3-hydroxymethylartemisinin

• Toni Smeilus,
• Farnoush Mousavizadeh,
• Johannes Krieger,
• Xingzhao Tu,
• Marcel Kaiser and
• Athanassios Giannis

Beilstein J. Org. Chem. 2019, 15, 567–570, doi:10.3762/bjoc.15.51

• 24% and 16% yield, respectively. Protection of the free hydroxy group of 16 as a silyl ether and methylation of the obtained lactone in α-position (LDA/MeI/HMPA) afforded derivative 17. After removal of the TES protecting group (+)-3-hydroxymethyl-9-epi-artemisinin (18, Scheme 3) was obtained

Synthesis and SAR of the antistaphylococcal natural product nematophin from Xenorhabdus nematophila

• Frank Wesche,
• Hélène Adihou,
• Thomas A. Wichelhaus and
• Helge B. Bode

Beilstein J. Org. Chem. 2019, 15, 535–541, doi:10.3762/bjoc.15.47

• phthalimides 16 and 23 [29]. These intermediary compounds 16 and 23 also allowed an N-methylation of the azaindole moiety with sodium hydride (NaH) and methyl iodide (MeI) to yield 17 and 24. By ethanolic hydrazinolysis and microwave irradiation the phthalimides (16, 17, 23, and 24) were deprotected yielding

Synthesis and selected transformations of 2-unsubstituted 1-(adamantyloxy)imidazole 3-oxides: straightforward access to non-symmetric 1,3-dialkoxyimidazolium salts

• Grzegorz Mlostoń,
• Małgorzata Celeda,
• Katarzyna Urbaniak,
• Marcin Jasiński,
• Vladyslav Bakhonsky,
• Peter R. Schreiner and
• Heinz Heimgartner

Beilstein J. Org. Chem. 2019, 15, 497–505, doi:10.3762/bjoc.15.43

• approach to these products comprises the alkylation (in most cases methylation) of 1-hydroxyimidazole N-oxides. However, the products of the monomethylation could not be obtained, but symmetric N,N-disubstituted imidazolium salts resulting from double O-alkylation were isolated [18]. On the other hand

• reported earlier for their synthesis comprises the two-fold alkylation (methylation with Me2SO4 or benzylation using benzyl bromide) of some 1-hydroxyimidazole 3-oxides leading to symmetric 1,3-dialkoxyimidazolium salts [18]. In a recent publication, however, sequential alkylation of 1-hydroxyimidazole 3

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

• give dimethyl ester 98 (Scheme 25). Silver oxide-promoted methylation introduces a MeO-C4 unit. Regioselective aziridine ring opening in 99 was then carried out in the known way with benzyl alcohol or methanol to produce substituted dimethyl L-glutamates 100 and 101. To ensure clean deprotection in the

• 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 and biological activity of methylated derivatives of the Pseudomonas metabolites HHQ, HQNO and PQS

• Sven Thierbach,
• Max Wienhold,
• Susanne Fetzner and
• Ulrich Hennecke

Beilstein J. Org. Chem. 2019, 15, 187–193, doi:10.3762/bjoc.15.18

• are associated with quorum sensing and virulence of the human pathogen Pseudomonas aeruginosa, have been prepared. While the synthesis by direct methylation was successful for 3-unsubstituted 2-heptyl-4(1H)-quinolones, methylated derivatives of the Pseudomonas quinolone signal (PQS) were synthesized

• from 3-iodinated quinolones by methylation and iodine–metal exchange/oxidation. The two N- and O-methylated derivatives of the PQS showed strong quorum sensing activity comparable to that of PQS itself. Staphylococcus aureus, another pathogenic bacterium often co-occurring with P. aeruginosa especially

• in the lung of cystic fibrosis patients, was inhibited in planktonic growth and cellular respiration by the 4-O-methylated derivatives of HQNO and HHQ, respectively. Keywords: antibiotic acitivity; methylation; Pseudomonas aeruginosa; quinolones; quorum sensing; Introduction 2-Alkyl-4(1H

A simple and effective preparation of quercetin pentamethyl ether from quercetin

• Jin Tatsuzaki,
• Tomohiko Ohwada,
• Yuko Otani,
• Reiko Inagi and
• Tsutomu Ishikawa

Beilstein J. Org. Chem. 2018, 14, 3112–3121, doi:10.3762/bjoc.14.291

• University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0013, Japan 10.3762/bjoc.14.291 Abstract Among the five hydroxy (OH) groups of quercetin (3,5,7,3',4'-pentahydroxyflavone), the OH group at 5 position is the most resistant to methylation due to its strong intramolecular hydrogen bonding with the

• carbonyl group at 4 position. Thus, it is generally difficult to synthesize the pentamethyl ether efficiently by conventional methylation. Here, we describe a simple and effective per-O-methylation of quercetin with dimethyl sulfate in potassium (or sodium) hydroxide/dimethyl sulfoxide at room temperature

• for about 2 hours, affording quercetin pentamethyl ether (QPE) quantitatively as a single product. When methyl iodide was used in place of dimethyl sulfate, the C-methylation product 6-methylquercetin pentamethyl ether was also formed. A computational study provided a rationale for the experimental

Volatiles from the hypoxylaceous fungi Hypoxylon griseobrunneum and Hypoxylon macrocarpum

• Jan Rinkel,
• Alexander Babczyk,
• Tao Wang,
• Marc Stadler and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2018, 14, 2974–2990, doi:10.3762/bjoc.14.277

• other two isomers 2,3,4-trimethylanisole (24d) and 2,4,5-trimethylanisole (24) were obtained by ortho-methylation of 3,4-dimethylphenol (28) via a known procedure [33], followed by HPLC purification of the products 2,4,5-trimethylphenol (29a) and 2,3,4-trimethylphenol (29b) and subsequent O-methylation

• (methyl-2H3)methionine. While the methylation pattern of the alternative structure 24c is difficult to understand via a polyketide biosynthesis mechanism, the formation of the assigned structure of 24 by a polyketide synthase (PKS) can be easily rationalised (Scheme 2). The acetate starter unit, bound to

• the acyl carrier protein (ACP) of an iterative fungal PKS, can be elongated with malonyl-SCoA (mal-SCoA) followed by C-methylation with S-adenosyl-L-methionine (SAM). Two more rounds of elongation with mal-SCoA, the first extension with C-methylation and action of a ketoreductase (KR), result in a

Synthesis of unnatural α-amino esters using ethyl nitroacetate and condensation or cycloaddition reactions

• Glwadys Gagnot,
• Vincent Hervin,
• Eloi P. Coutant,
• Sarah Desmons,
• Racha Baatallah,
• Victor Monnot and
• Yves L. Janin

Beilstein J. Org. Chem. 2018, 14, 2846–2852, doi:10.3762/bjoc.14.263

• -amino esters, we tried their preparation via a C-methylation of α-nitroester 6a in DMF using sodium hydride and methyl iodide. Upon purification, this gave 46% of the nitro compound 9 with 94% purity (as assessed by 1H NMR). Despite this modest yield, the ensuing reduction using zinc and hydrochloric