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

• and A succeeded as previously described in the literature; unit A (15) and C–D (16) were connected by Yamaguchi esterification to give 17 (Scheme 2) [45]. Then, Fmoc was cleaved from the N-terminus of unit C–D–A (17) using piperidine and the resulting crude amine was coupled to the corresponding

A survey of chiral hypervalent iodine reagents in asymmetric synthesis

• Soumen Ghosh,
• Suman Pradhan and
• Indranil Chatterjee

Beilstein J. Org. Chem. 2018, 14, 1244–1262, doi:10.3762/bjoc.14.107

• with excellent enantioselectivity (Scheme 2d). Another class of chiral I(V) reagents 6 was synthesized by Wirth et al. who synthesized the desired compounds through esterification between chiral alcohols and the I(I)-substituted aromatic acids followed by oxidation with dimethyldioxirane (Scheme 2e

Recyclable hypervalent-iodine-mediated solid-phase peptide synthesis and cyclic peptide synthesis

• Dan Liu,
• Ya-Li Guo,
• Jin Qu and
• Chi Zhang

Beilstein J. Org. Chem. 2018, 14, 1112–1119, doi:10.3762/bjoc.14.97

• mediated by hypervalent iodine(III) reagents in recent years. In 2012, for the first time, we reported that the hypervalent iodine(III) reagent iodosodilactone (Figure 1) can serve as a condensing reagent to promote esterification, macrolactonization, amidation and peptide coupling reactions in the

Preparation, structure, and reactivity of bicyclic benziodazole: a new hypervalent iodine heterocycle

• Akira Yoshimura,
• Michael T. Shea,
• Cody L. Makitalo,
• Melissa E. Jarvi,
• Gregory T. Rohde,
• Akio Saito,
• Mekhman S. Yusubov and
• Viktor V. Zhdankin

Beilstein J. Org. Chem. 2018, 14, 1016–1020, doi:10.3762/bjoc.14.87

• ; biheterocycles; hypervalent iodine; iodine; oxidatively assisted esterification; Introduction In recent years, the interest in heterocyclic organohypervalent iodine compounds has experienced an unprecedented growth [1][2][3][4][5][6]. A variety of new hypervalent iodine heterocycles have been prepared, and

• ), which is in agreement with the previously proposed mechanism of oxidatively assisted esterification or amidation [23][38]. Conclusion In summary, we have prepared the new bicyclic benziodazole 7a by the oxidation of 2-iodo-N,N’-diisopropylisophthalamide (6a) with m-CPBA. The solid structure of 7a was

• (1)–N(1) 2.177 (4) Å; N(1)–I(1)–C(1) 76.89 (18)°; N(2)–I(1)–C(1) 77.02 (18)°; N(1)–I(1)–N(2) 153.90 (15)°. Representative examples of benziodoxoles and benziodazoles. Preparation of bicyclic benziodazole 7a. Benziodadiazole 7a mediated oxidatively assisted esterification and amidation reactions

Polysubstituted ferrocenes as tunable redox mediators

• Sven D. Waniek,
• Jan Klett,
• Christoph Förster and
• Katja Heinze

Beilstein J. Org. Chem. 2018, 14, 1004–1015, doi:10.3762/bjoc.14.86

• application as redox mediator (Scheme 2) [55][56]. Ferrocenyl esters 1–4 are synthetically accessible via the acids of 1 [45][46], 2 [57], 3 and 4 [54] in a direct selective metalation of ferrocene [54][57][58][59][60], quenching with carbon dioxide, followed by esterification [45][46][47][48][54]. The 1,1

Volatiles from three genome sequenced fungi from the genus Aspergillus

• Jeroen S. Dickschat,
• Ersin Celik and
• Nelson L. Brock

Beilstein J. Org. Chem. 2018, 14, 900–910, doi:10.3762/bjoc.14.77

• an even number of carbons are much more widespread. Furthermore, esterification with S-adenosyl-l-methionine (SAM) by a methyltransferase is a very common process in nature, while ethyl esters are rarer and likely require a two-step pathway through reduction of acetyl-CoA to ethanol and its

• esterification by an acyl transferase. In Neurospora crassa acids of short chain alcohols are formed from alcohols and aldehydes via hemiacetals that are oxidised to the corresponding esters by an alcohol dehydrogenase [43]. The main compounds were ethyl pentanoate (35) and ethyl heptanoate (37), accompanied by

• small amounts of ethyl hexanoate (36), ethyl octanoate (38) and the unsaturated ester ethyl (Z)-hept-4-enoate (41) that was unambiguously identified by synthesis of a reference compound by esterification of (Z)-hept-4-enoic acid with ethanol. A compound with the retention index I = 1090 was reported

Nanoreactors for green catalysis

• M. Teresa De Martino,
• Loai K. E. A. Abdelmohsen,
• Floris P. J. T. Rutjes and
• Jan C. M. van Hest

Beilstein J. Org. Chem. 2018, 14, 716–733, doi:10.3762/bjoc.14.61

• ) was encapsulated in the lumen of the polymersomes or in the Pickering emulsion water droplet. The esterification reaction of 1-hexanol and hexanoic acid was used to evaluate the catalytic performance of the CalB-loaded Pickering emulsions. Higher enzymatic activity was observed when CalB was

Latest development in the synthesis of ursodeoxycholic acid (UDCA): a critical review

• Fabio Tonin and
• Isabel W. C. E. Arends

Beilstein J. Org. Chem. 2018, 14, 470–483, doi:10.3762/bjoc.14.33

• oxidized in position C12 to the corresponding ketone, after which Wolff–Kishner reduction can be applied. This whole sequence comprises 5 steps [13]. After the protection of the carboxylic group by acid-catalyzed esterification (quantitative yield), the 3- and 7-OH groups are protected selectively with

• an infinitesimal change in the number of electrons [61]. The overall yield of the epimerization step is around 70% [12][15][62]. A further purification step is necessary for the preparation of free UDCA: it can be easily obtained with sequential esterification, extraction and hydrolysis (yield 91

5-Aminopyrazole as precursor in design and synthesis of fused pyrazoloazines

• Ranjana Aggarwal and
• Suresh Kumar

Beilstein J. Org. Chem. 2018, 14, 203–242, doi:10.3762/bjoc.14.15

• (5H)-one derivatives 204 by refluxing in 1 N sodium hydroxide. Pyrazolo[3,4-d]pyrimidinone 204 were further chlorinated by phosphorus oxychloride and subsequently converted to carboxylic esters 207 via cyanation followed by hydrolysis and esterification. Kaplan et al. [20] explored the synthesis of

Volatiles from the tropical ascomycete Daldinia clavata (Hypoxylaceae, Xylariales)

• Tao Wang,
• Kathrin I. Mohr,
• Marc Stadler and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2018, 14, 135–147, doi:10.3762/bjoc.14.9

• compound 9. This compound was synthesised by esterification of pent-4-en-2-ol (31) with acryloyl chloride (32) to 33, followed by ring-closing metathesis using the Hoveyda–Grubbs catalyst of the second generation (Scheme 8). The synthetic material proved to be identical to the volatile of D. clavata

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

• concept [32] (Scheme 4b) [34]. They first introduced alkene moieties to the chemically inert lignin structure by esterification of the hydroxy groups of lignin with 4-pentenoic acid. Subsequent radical thiol–ene reaction with aliphatic thiols, using [Ru(bpy]3Cl2 as photocatalyst and p-toluidine as redox

Aminosugar-based immunomodulator lipid A: synthetic approaches

• Alla Zamyatina

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

Recent progress in the racemic and enantioselective synthesis of monofluoroalkene-based dipeptide isosteres

• Myriam Drouin and
• Jean-François Paquin

Beilstein J. Org. Chem. 2017, 13, 2637–2658, doi:10.3762/bjoc.13.262

• )-monofluoroalkenes (Scheme 6) [32][33]. HWE olefination promoted by Mg(II) of (diethoxyphosphoryl)fluoroacetic acid (25) with triisopropylsilyl-protected 2-hydroxymethylcyclopentanone 26 was realized with excellent yield and stereoselectivity. Esterification of the resulting carboxylic acid 27 into the corresponding

Hydrolysis, polarity, and conformational impact of C-terminal partially fluorinated ethyl esters in peptide models

• Vladimir Kubyshkin and
• Nediljko Budisa

Beilstein J. Org. Chem. 2017, 13, 2442–2457, doi:10.3762/bjoc.13.241

• fluorination of peptide scaffolds. One of these methods involves esterification of the C-terminus of peptides using a diazomethane species. Here, we provide an investigation of the physicochemical consequences of peptide esterification with partially fluorinated ethyl groups. Derivatives of N-acetylproline are

• previously [50]. The reference methyl and ethyl esters 1 and 2 were prepared by stirring of 6 in acidic alcohol (methanol or ethanol, respectively) at room temperature overnight (Scheme 1A). We attempted to employ the same procedure for esterification of 6 in trifluoroethanol. However, this resulted in a

• . Although the yield increased, it remained low (20%). The poor yields in the aqueous medium are explained by the high reactivity of the diazomethane species, which favors nonspecific reactions in water [52]. Very recently, more specific diazomethane reagents for water-tolerant esterification have also been

Phosphonic acid: preparation and applications

• Charlotte M. Sevrain,
• Mathieu Berchel,
• Hélène Couthon and
• Paul-Alain Jaffrès

Beilstein J. Org. Chem. 2017, 13, 2186–2213, doi:10.3762/bjoc.13.219

• hydroxymethylenebisphosphonic acid 45 [167]. The trans-esterification of phosphonate with bromotrimethylsilane to produce silylated phosphonate requires at least two equivalents of BrSiMe3 per phosphonate function. Usually an excess is engaged in the reaction to guarantee a full conversion of dialkyl phosphonate into the

Mechanochemical synthesis of small organic molecules

• Tapas Kumar Achar,
• Anima Bose and
• Prasenjit Mal

Beilstein J. Org. Chem. 2017, 13, 1907–1931, doi:10.3762/bjoc.13.186

• NaHCO3 (base); 2) esterification of N-protected amino acid using different dialkyl dicarbonate or alkyl chloroformate in the presence of DMAP as catalyst and followed by acidic workup. For N-terminal protection, different precursors like Fmoc-Cl, benzoyl chloride and Boc2O were used successfully to get

Selective enzymatic esterification of lignin model compounds in the ball mill

• Ulla Weißbach,
• Saumya Dabral,
• Laure Konnert,
• Carsten Bolm and
• José G. Hernández

Beilstein J. Org. Chem. 2017, 13, 1788–1795, doi:10.3762/bjoc.13.173

• Ulla Weissbach Saumya Dabral Laure Konnert Carsten Bolm Jose G. Hernandez Institute of Organic Chemistry, RWTH Aachen University, Landoltweg 1, D-52074 Aachen, Germany 10.3762/bjoc.13.173 Abstract A lipase-catalyzed esterification of lignin model compounds in the ball mill was developed combining

• biocatalyst for these transformations. Noteworthy, various acyl donors of different chain lengths were tolerated under the mechanochemical conditions. Keywords: ball milling; enzymes; esterification; lignin derivatization; mechanochemistry; Introduction Mechanochemical reactions, particularly those carried

• lipophilicity, for instance through sulfation [18], silylation or esterification [19] of the aliphatic hydroxy and phenolic groups found in lignin. Chemical esterification of lignin [19][20][21] or its model compounds [22], using acetic anhydride in organic solvents such as DCM or pyridine have previously been

The chemistry and biology of mycolactones

• Matthias Gehringer and
• Karl-Heinz Altmann

Beilstein J. Org. Chem. 2017, 13, 1596–1660, doi:10.3762/bjoc.13.159

• of the mycolactone core Currently, all mycolactone partial and total syntheses share the (projected) final esterification of the C5-hydroxy group of the appropriately protected extended mycolactone core with the respective polyunsaturated fatty acid under Yamaguchi conditions (Figure 7). Two

A new member of the fusaricidin family – structure elucidation and synthesis of fusaricidin E

• Marcel Reimann,
• Louis P. Sandjo,
• Luis Antelo,
• Eckhard Thines,
• Isabella Siepe and
• Till Opatz

Beilstein J. Org. Chem. 2017, 13, 1430–1438, doi:10.3762/bjoc.13.140

• the esterification with DIC/DMAP [12] as the double acylation product 18 could be detected (Scheme 3). Further investigations suggested DMAP to be responsible for the cleavage of the ΨMe,Me'Pro and after reduction of the amount of DMAP to 5 mol %, nearly no doubly acylated product was found. Besides

• contrast to literature reports [12], it was found that cleavage from the resin with “reagent K” [12][21] was inferior to a TFA/TIS/H2O mixture (95:2.5:2.5). Due to the instability of ΨMe,Me'Pro during esterification and cyclization, the isolated yield of 19 was only 6% (Scheme 4). To improve this, O-tert

• -butyl-protected D-allo-Thr was employed instead. For the O-tert-butyl-protected D-allo-Thr, clean and complete conversion was observed during both esterification and deprotection. This time, cyclization was performed with PyAOP and NMM in NMP to provide 19 in an isolated yield of 37% (Scheme 5

A speedy route to sterically encumbered, benzene-fused derivatives of privileged, naturally occurring hexahydropyrrolo[1,2-b]isoquinoline

• Olga Bakulina,
• Alexander Ivanov,
• Vitalii Suslonov,
• Dmitry Dar’in and
• Mikhail Krasavin

Beilstein J. Org. Chem. 2017, 13, 1413–1424, doi:10.3762/bjoc.13.138

• 9), isolation of pure diastereomeric CCR adducts was achieved by total esterification of the carboxylic acid product mixture and chromatographic separation of the respective methyl esters (the 0.8:1 anti/syn-10e mixture stereoconverged to anti-10e' on esterification, vide infra). The trans

• formed as a 0.8:1 mixture of anti/syn diastereomers (Table 1). However, it was promptly noted that this mixture converges to thermodynamically more stable anti-10e (the isomerization occurs on heating to 80 °C or, more slowly, even at room temperature). Esterification of anti/syn-10e in the presence of

Synthesis of oligonucleotides on a soluble support

• Harri Lönnberg

Beilstein J. Org. Chem. 2017, 13, 1368–1387, doi:10.3762/bjoc.13.134

• order by esterification of phosphoric acid with the 3´-OH of one and the 5´-OH of the other nucleoside. Usually, the 3´-OH is first esterified with an appropriate derivative of phosphoric acid and the resulting building block is then reacted with the 5´-OH (Figure 1). Either a linear or a convergent

• of the phosphoramidite for coupling, the fully protected hexamer was obtained in 67% yield. Ammonolysis and ion-exchange chromatographic purification then gave hexamer d(5´-ATGCTT-3´) in isolated 39% yield. Esterification of a 5´-O-DMTr-3´-O-succinylthymidine with 3-(2-hydroxyethyl)-1-methyl-1H

An improved preparation of phorbol from croton oil

• Alberto Pagani,
• Simone Gaeta,
• Andrei I. Savchenko,
• Craig M. Williams and
• Giovanni Appendino

Beilstein J. Org. Chem. 2017, 13, 1361–1367, doi:10.3762/bjoc.13.133

• activity. While efficient chemoselective esterification protocols have been developed for phorbol, its isolation from croton oil is technically complicated, and involves extensive manipulation of very toxic materials like the oil or its native diterpenoid fraction. Results: The preparation of a crude non

• group. Partition between methanol and hexane afforded a crude mixture of phorbol diesters, that was next tritylated. After deacylation by basic treatment and chromatography, 20-tritylphorbol (1c) was obtained, as a hydrate, in sufficient purity to be used as starting material for the esterification [18

Strategies toward protecting group-free glycosylation through selective activation of the anomeric center

• A. Michael Downey and
• Michal Hocek

Beilstein J. Org. Chem. 2017, 13, 1239–1279, doi:10.3762/bjoc.13.123

• ]. 5.1.2 Esterification of benzoic acids with glycosyl donors: Again in 2015 Kawabata and co-workers applied the Mitsunobu reaction to an unprotected and unactivated donor in the first step of the total synthesis of two ellagitannins. Using a moderate excess

Total syntheses of the archazolids: an emerging class of novel anticancer drugs

• Stephan Scheeff and
• Dirk Menche

Beilstein J. Org. Chem. 2017, 13, 1085–1098, doi:10.3762/bjoc.13.108

• could successfully couple the three main fragments 39, 40 and 6 by first a Stille reaction, followed by a Kita esterification. Notably, this esterification was critical to avoid unfavorable isomerizations. For closing of the macrolide core they planned a challenging Hoye relay ring closing metathesis

• . Completion of the total synthesis Final assembly of the fragments as shown in Scheme 11 began with an unusual [Ru]-catalyzed Kita esterification due to the instability of fragment 40 towards basic esterification approaches [84]. The following Stille coupling with stannane 39 was then accomplished by CuTC co

• useful for new approaches to the 24-membered macrolide core. For the completion of the synthesis of 3 the side chain would have to be introduced, followed by an oxidation to the acid and a ring closing esterification. Concise synthesis of the thiazole fragment In an earlier synthesis the O’Neil group had

Conformational study of L-methionine and L-cysteine derivatives through quantum chemical calculations and ³J_HH coupling constant analyses

• Weslley G. D. P. Silva,
• Carolyne B. Braga and
• Roberto Rittner

Beilstein J. Org. Chem. 2017, 13, 925–937, doi:10.3762/bjoc.13.94

• compounds [31]. Compounds 3 and 4 were obtained by the esterification of the corresponding N-acetyl-L-amino acids (Sigma-Aldrich), following a known procedure [23][32]. The detailed syntheses are described in Supporting Information File 1. Spectroscopic measurements 1H NMR spectra for 1, 3 and 4 were