An efficient and facile access to highly functionalized pyrrole derivatives

• Meng Gao,
• Wenting Zhao,
• Hongyi Zhao,
• Ziyun Lin,
• Dongfeng Zhang and
• Haihong Huang

Beilstein J. Org. Chem. 2018, 14, 884–890, doi:10.3762/bjoc.14.75

• with MeONa in MeOH or EtONa in EtOH at room temperature in moderate to good yields (40–66%, Scheme 3). It was noted that the ethyl ester in 12a was replaced by methyl ester through transesterification when 12a was treated with MeONa in MeOH to afford 13m. Therefore, this efficient protocol developed

Phosphodiester models for cleavage of nucleic acids

• Satu Mikkola,
• Tuomas Lönnberg and
• Harri Lönnberg

Beilstein J. Org. Chem. 2018, 14, 803–837, doi:10.3762/bjoc.14.68

• the next one are cleaved by a variety of enzymes [1]. The phosphodiester bonds of DNA are hydrolyzed, depending on the enzyme, either to a 3´- or 5´-phosphate, whereas the bonds in RNA, with few exceptions (above all RNase H-catalyzed cleavages) undergo transesterification to a 2´,3´-cyclic phosphate

• with phosphodiester models are aimed at providing firm mechanistic understanding of the hydrolysis and transesterification reactions of nucleic acids. Such information is indispensable for critical evaluation of mechanistic proposals of more complicated enzymatic processes and for the development of

• reactions of RNA phosphodiester linkages at physiological pH (pH 6–8) are pH-independent isomerization to 2´,5´-bonds (red line in Figure 6) and hydroxide-ion-catalyzed transesterification to a 2´,3´-cyclic phosphate by departure of the 5´-linked nucleoside, followed by subsequent hydrolysis to a mixture of

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

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

• released by a transesterification mechanism [35]. The 3'-start nucleoside is bound to one of the primary hydroxy groups of CPG-linked glycerol via an H-phosphonate linkage (Figure 5B). The removal of the TBDMS group from the remaining primary alcohol of glycerol induces the spontaneous cleavage of the H

• anchor (A) and by a transesterification mechanism (B). Release of the trinucleotide from the support under reductive conditions. Phosphitylation of trimers. Reaction conditions, in particular the choice of the phosphitylation reagent, are dependent on the nature of the protecting group at the

Synthesis of naturally-derived macromolecules through simplified electrochemically mediated ATRP

• Paweł Chmielarz,
• Tomasz Pacześniak,
• Katarzyna Rydel-Ciszek,
• Izabela Zaborniak,
• Paulina Biedka and
• Andrzej Sobkowiak

Beilstein J. Org. Chem. 2017, 13, 2466–2472, doi:10.3762/bjoc.13.243

• macroinitiator was received for the first time by the transesterification reaction of quercetin with 2-bromoisobutyryl bromide. In accordance with the “grafting from” strategy, a naturally-occurring star-like polymer with a polar 3,3',4',5,6-pentahydroxyflavone core and hydrophobic poly(tert-butyl acrylate

• -defined star-like polymers, consisting of a quercetin core and hydrophobic PtBA arms with narrow MWDs by ATRP under multiple-step potential electrolysis conditions. Results and Discussion A flavonoid-based macromolecule initiator with 5 Br atoms (QC-Br5) was synthesized by the transesterification reaction

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

• phosphonate involves trialkyl phosphite, the subsequent dealkylation of dialkyl phosphonate under mild conditions was of a great importance. The group of C. E. McKenna reported in 1977 the use of bromotrimethylsilane as a reagent that permitted an efficient transesterification of dialkyl phosphonate to bis

• was almost quantitative. Other studies indicated that this reaction can be also applied to diisopropyl phosphonate, or di-tert-butyl phosphonate leading to the conclusion that all dialkyl phosphonates can be dealkylated by the transesterification followed by a methanolysis or hydrolysis subsequent

Regiodivergent condensation of 5-alkoxycarbonyl-1H-pyrrol-2,3-diones with cyclic ketazinones en route to spirocyclic scaffolds

• Alexey Yu. Dubovtsev,
• Maksim V. Dmitriev,
• Аndrey N. Maslivets and
• Michael Rubin

Beilstein J. Org. Chem. 2017, 13, 2179–2185, doi:10.3762/bjoc.13.218

• involving Michael addition followed by intramolecular transesterification. Remarkably, the resulting bridged products 12 have reversed regiochemistry as compared to the earlier-described cycloadducts 5 (Scheme 1). It should also be pointed out that all of these products were formed as single 10-endo

• ]. Keeping this in mind we decided to test the reactivity of ketazinones 17 that were obtained via condensation of cyclohexanediones 8 with hydrazone of acetophenone. We anticipated the formation of spirolactones 20 in this process, resulting from intramolecular transesterification involving the enol moiety

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

• ) technique for the synthesis of dialkyl carbonates [90]. Using potassium carbonate, alkyl halide and 2 equiv of phase-transfer catalyst 18-crown-6 yielded dialkyl carbonate in 74%. However, in absence of 18-crown-6 the yield was only 2% at 17 h (Scheme 20). Transesterification is a synthetic approach mostly

• being used for making higher homologous esters from the simpler ones. Ranu and co-workers developed simple method for transesterification under mechanomilling [91]. The mixture of ester and alcohols were adsorbed on the surface of basic alumina and followed by milling of the materials for 2–3 h led to

• dialkyl carbonates [90]. Mechanochemical transesterification reaction using basic Al2O3 [91]. Mechanochemical carbamate synthesis [92]. Mechanochemical bromination reaction using NaBr and oxone [96]. Mechanochemical aryl halogenation reactions using NaX and oxone [97]. Mechanochemical halogenation

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

Synthesis of oligonucleotides on a soluble support

• Harri Lönnberg

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

• commercially available building blocks turned out to be too hydrophobic to allow precipitation of the support-bound oligonucleotides from MeOH. The 1-methoxy-1-methylethyl group could be removed quantitatively as a dimethyl acetal of acetone upon acid-catalyzed transesterification in MeOH. The 3'-terminal

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

• crystallization step. A solution for these issues is provided, suggesting that the poor-reproducibility of croton oil-based anti-inflammatory assays are the result of poor quality and/or inconsistent composition of croton oil. Keywords: croton oil; diterpenoids; natural products; phorbol; transesterification

• of phorbol from the transesterification reaction mixture, a viscous oil for the presence of glycerol, that requires extended periods (four weeks according to ref. [6]). Furthermore, the unstable ethanol solvate has to be transformed into a more stable hydrate by recrystallization from hot water, a

• , problematic for the multigram isolation of phorbol due to the extensive handling of the toxic croton oil and the ultra-toxic mixture of phorbol diesters obtained in the acidic transesterification step. Furthermore, the tritylation of the crude mixture of phorbol diesters suffered from interference from

First total synthesis of kipukasin A

• Chuang Li,
• Haixin Ding,
• Zhizhong Ruan,
• Yirong Zhou and
• Qiang Xiao

Beilstein J. Org. Chem. 2017, 13, 855–862, doi:10.3762/bjoc.13.86

• ’-transesterification is inevitable to occur in nucleosides [19][20][21]. The synthetic route would be lengthy and cumbersome. Therefore, a practical total synthesis is in high demand to facilitate the preparation of other kipukasins and their analogues. The retrosynthetic analysis is shown in Figure 2 (path b

• . Various spectral analyses (NMR, HPLC) showed no evidence that 2,3-O-transesterification occurred during the esterification reaction. After cleavage of the acetonide group with acetic acid/acetic anhydride/H2SO4, the key glycosylation donor 16 was obtained in 74% yield as a mixture of isomers (α/β = 1:8

Cyclodextrins tethered with oligolactides – green synthesis and structural assessment

• Cristian Peptu,
• Mihaela Balan-Porcarasu,
• Alena Šišková,
• Ľudovít Škultéty and
• Jaroslav Mosnáček

Beilstein J. Org. Chem. 2017, 13, 779–792, doi:10.3762/bjoc.13.77

• oligomers with odd number of monomer units could be observed as well. These oligomer species with odd number of lactates resulted from intramolecular and/or intermolecular transesterification reactions and are in lower amount, when compared with the oligomers containing even number of monomers. This

• signifies that the predominance of transesterification is rather low in the employed reaction conditions. The presented spectrum was measured directly from the HPLC collected fraction with rather low concentration of products, thus resulting in a poor spectrum quality. The f7 fraction (Figure 1 – LC–ELSD

• number of lactate monomer units. These species could be formed as a result of transesterification reactions (intra- or intermolecular), which may occur in the melt reaction system. The presence of PLA homopolymers was also observed, their corresponding m/z being calculated by the following equation: m/z

Synthesis of structurally diverse 3,4-dihydropyrimidin-2(1H)-ones via sequential Biginelli and Passerini reactions

• Andreas C. Boukis,
• Baptiste Monney and
• Michael A. R. Meier

Beilstein J. Org. Chem. 2017, 13, 54–62, doi:10.3762/bjoc.13.7

• performed first, in order to avoid undesired transesterification reactions (of the Passerini product) due to the acidic conditions of the Biginelli reaction [33]. A general challenge, which has to be faced in this context, is the choice of solvent and the selection of bifunctional components (which can

Electron-transfer-initiated benzoin- and Stetter-like reactions in packed-bed reactors for process intensification

• Anna Zaghi,
• Daniele Ragno,
• Graziano Di Carmine,
• Carmela De Risi,
• Olga Bortolini,
• Pier Paolo Giovannini,
• Giancarlo Fantin and
• Alessandro Massi

Beilstein J. Org. Chem. 2016, 12, 2719–2730, doi:10.3762/bjoc.12.268

• homogeneous conditions and their subsequent utilization in transesterification and amidation processes by the reaction telescoping approach [12]. Similarly, the group of Brown reported on the oxidative esterification and amidation of aldehydes in undivided microfluidic electrolysis cells mediated by

• reaction setup [22][23][24]. An integrated flow system for the synthesis of biodiesel employing an uninterrupted sequence of two fixed-bed reactors packed with a supported acid for esterification of free fatty acids and with an immobilized imidazolidene catalyst for transesterification has been recently

Synthesis of medronic acid monoesters and their purification by high-performance countercurrent chromatography or by hydroxyapatite

• Elina Puljula,
• Jouko Vepsäläinen and
• Petri A. Turhanen

Beilstein J. Org. Chem. 2016, 12, 2145–2149, doi:10.3762/bjoc.12.204

• ] and medronic acid [30] can also be used as the starting material for the synthesis of mixed tetraesters. If the starting point is a tetraester of medronic acid, several routes can be taken, for example transesterification [31]. In addition, after dealkylation, the corresponding triester can be

Ionic liquids as transesterification catalysts: applications for the synthesis of linear and cyclic organic carbonates

• Maurizio Selva,
• Alvise Perosa,
• Sandro Guidi and
• Lisa Cattelan

Beilstein J. Org. Chem. 2016, 12, 1911–1924, doi:10.3762/bjoc.12.181

• Maurizio Selva Alvise Perosa Sandro Guidi Lisa Cattelan Dipartimento di Scienze Molecolari e Nanosistemi, Università Ca’ Foscari Venezia, Via Torino, 155 – Venezia Mestre, Italy 10.3762/bjoc.12.181 Abstract The use of ionic liquids (ILs) as organocatalysts is reviewed for transesterification

• reactions, specifically for the conversion of nontoxic compounds such as dialkyl carbonates to both linear mono-transesterification products or alkylene carbonates. An introductory survey compares pros and cons of classic catalysts based on both acidic and basic systems, to ionic liquids. Then, innovative

• green syntheses of task-specific ILs and their representative applications are introduced to detail the efficiency and highly selective outcome of ILs-catalyzed transesterification reactions. A mechanistic hypothesis is discussed by the concept of cooperative catalysis based on the dual (electrophilic

(Thio)urea-mediated synthesis of functionalized six-membered rings with multiple chiral centers

• Giorgos Koutoulogenis,
• Nikolaos Kaplaneris and
• Christoforos G. Kokotos

Beilstein J. Org. Chem. 2016, 12, 462–495, doi:10.3762/bjoc.12.48

• transformation is initiated by a Michael addition of 158 to alkylidene azlactone 159, followed by a Mannich reaction and finally transesterification. The same year, Yuan and co-workers reported the double Michael reaction between 160 and alkylidene azlactone 161 to produce the spiro-fused cyclohexanone/5

Diastereoselective synthesis of new O-alkylated and C-branched inositols and their corresponding fluoro analogues

• Charlotte Collet,
• Françoise Chrétien,
• Yves Chapleur and
• Sandrine Lamandé-Langle

Beilstein J. Org. Chem. 2016, 12, 353–361, doi:10.3762/bjoc.12.39

• several methods of acetylation were carried out on myo-14, which was used as model. The best results for the acetylation of the tertiary alcohol in good yield was obtained with the transesterification method using isopropenyl acetate as acylating agent and p-toluenesulfonic acid as catalyst at 80 °C for 2

Stereoselective synthesis of hernandulcin, peroxylippidulcine A, lippidulcines A, B and C and taste evaluation

• Marco G. Rigamonti and
• Francesco G. Gatti

Beilstein J. Org. Chem. 2015, 11, 2117–2124, doi:10.3762/bjoc.11.228

• ) stereogenic center by means of a Mitsunobu reaction, followed by transesterification of the ester to give 4 (Scheme 1). (S)-Isopulegone was prepared by Jones oxidation of (−)-isopulegol following a reported procedure [14]; but on a large scale we have observed that a partial loss of the optical purity of the

Dicarboxylic esters: Useful tools for the biocatalyzed synthesis of hybrid compounds and polymers

• Ivan Bassanini,
• Karl Hult and
• Sergio Riva

Beilstein J. Org. Chem. 2015, 11, 1583–1595, doi:10.3762/bjoc.11.174

• transesterification reactions, ‘activated’ esters are usually employed in order to make the reactions irreversible thanks to the release of alcohols that are poor nucleophiles (halogenated derivatives of ethanol, vinyl or isopropenyl alcohol) [13][14][15]. This has been also the case with several reports on the use

First chemoenzymatic stereodivergent synthesis of both enantiomers of promethazine and ethopropazine

• Paweł Borowiecki,
• Daniel Paprocki and
• Maciej Dranka

Beilstein J. Org. Chem. 2014, 10, 3038–3055, doi:10.3762/bjoc.10.322

• Lipozyme TL IM were established as optimal biocatalysts for the enantioselective transesterification when suspended in 30 equiv of vinyl acetate as the acyl donor, methyl tert-butyl ether (MTBE) as co-solvent, and carried out at 25 °C, with agitation speed of the magnetic stirrer arranged at 500 rpm, and

• most promising catalyst only on the basis of single random results obtained from the analysis of the reaction mixtures. By virtue of the importance of enzyme selection, and to find the most suitable catalyst for the transesterification of racemic alcohol (±)-3 as well as to provide better insight into

• -activated esters (i.e., ethyl acetate, methyl acetate), and anhydrides (i.e., acetic acid anhydride, succinic acid anhydride) are most commonly used. Unfortunately, there are several drawbacks of incorporating the above-mentioned reagents into transesterification processes, i.e., trifluoroethyl esters are

A green approach to the synthesis of novel phytosphingolipidyl β-cyclodextrin designed to interact with membranes

• Yong Miao,
• Florence Djedaïni-Pilard and
• Véronique Bonnet

Beilstein J. Org. Chem. 2014, 10, 2654–2657, doi:10.3762/bjoc.10.278

• with a promising yield. Keywords: fatty ester; green chemistry; lipase; mono-substituted amphiphilic cyclodextrins; peptide Coupling; solvent-free medium; transesterification; Introduction Cyclodextrins (CDs) are sustainable compounds which are particularly interesting in the frame of pharmaceutical

• transesterification with the corresponding fatty ester, which may lead to bicatenar amphiphilic CDs. At the same time, the two remaining secondary alcohols might increase the solubility of the modified CD compounds. The aim of this work is to synthesize new bicatenar CDs using green methods described for the first

• enzymatic transesterification, sphingolipid myelin analogues bearing CD as polar heads were synthesized to interact with ceramids of brain membranes. Results and Discussion Insertion of the spacer A procedure for the preparation of compound 1 has already been described in previous articles [8]. The reaction

Regio- and stereoselective synthesis of new diaminocyclopentanols

• Evgeni A. Larin,
• Valeri S. Kochubei and
• Yuri M. Atroshchenko

Beilstein J. Org. Chem. 2014, 10, 2513–2520, doi:10.3762/bjoc.10.262

• [29]. The treatment of the corresponding acetates 4 with mesyl chloride and subsequent transesterification of mesylated substrates 5 resulted in the formation of 6a,b. Epoxides 3 and 6 were identified by 1H NMR data [28]. Morpholine (7a), 2-methyl-1H-imidazole (7b), N-acetylpiperazine (7c) and 9H

Synthesis and immunological evaluation of protein conjugates of Neisseria meningitidis X capsular polysaccharide fragments

• Laura Morelli,
• Damiano Cancogni,
• Marta Tontini,
• Alberto Nilo,
• Sara Filippini,
• Paolo Costantino,
• Maria Rosaria Romano,
• Francesco Berti,
• Roberto Adamo and
• Luigi Lay

Beilstein J. Org. Chem. 2014, 10, 2367–2376, doi:10.3762/bjoc.10.247

• of the hemiacetal under these reaction conditions. Compound 9 was subjected to Zemplén transesterification with NaOMe in methanol to afford alcohol 10, and the hydrogenolytic removal of the remaining protective groups furnished the spacer-linked monomer 1 in excellent yield (Scheme 2). Chemical