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Search for "methylation" in Full Text gives 254 result(s) in Beilstein Journal of Organic Chemistry. Showing first 200.

Come-back of phenanthridine and phenanthridinium derivatives in the 21st century

  • Lidija-Marija Tumir,
  • Marijana Radić Stojković and
  • Ivo Piantanida

Beilstein J. Org. Chem. 2014, 10, 2930–2954, doi:10.3762/bjoc.10.312

Graphical Abstract
  • intercalator able to differentiate between A–U(T) and G–C base pairs by sign of opposite fluorimetric response. An introduction of the permanent positive charge by methylation of the heterocyclic nitrogen changed the binding mode of the conjugates with shorter linkers from minor groove binding to intercalation
  • ), but this recognition was completely lost upon introduction of a permanent positive charge by methylation of phenanthridine-N5 13 [71]. Intriguingly, N5-methylated phenanthridine–adenine conjugate 13 exhibited preferred binding to peculiar protonated poly AH+ double stranded helix (Scheme 23) [71
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Published 10 Dec 2014

Synthesis of uniform cyclodextrin thioethers to transport hydrophobic drugs

  • Lisa F. Becker,
  • Dennis H. Schwarz and
  • Gerhard Wenz

Beilstein J. Org. Chem. 2014, 10, 2920–2927, doi:10.3762/bjoc.10.310

Graphical Abstract
  • full methylation of all secondary hydroxy groups of β-CD causes a significant drop of binding potential, while substitution at the primary site does not alter the binding potential or even increases it [20]. Especially substitution of all primary hydroxy groups by thioether groups gives rise to
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Published 09 Dec 2014

Total synthesis of the proposed structure of astakolactin

  • Takayuki Tonoi,
  • Keisuke Mameda,
  • Moe Fujishiro,
  • Yutaka Yoshinaga and
  • Isamu Shiina

Beilstein J. Org. Chem. 2014, 10, 2421–2427, doi:10.3762/bjoc.10.252

Graphical Abstract
  • constructed via an aldol reaction with ethyl acetate, followed by anti-selective methylation [32][33]. The trisubstituted alkene moiety of the prenyl chain of 3 could be stereoselectively constructed via a Johnson orthoester–Claisen rearrangement of 4 [34][35][36], which would be generated from compound 5
  • ethyl acetate to afford the adduct 19. Diastereoselective methylation of the ester enolate moiety of 19 with MeI afforded only the anti-product 20 [32][33], which was then subjected to the deprotection of the TBDPS group with HF·pyridine, followed by cleavage of the ethyl ester group in 21 to give the
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Published 17 Oct 2014

Photorelease of phosphates: Mild methods for protecting phosphate derivatives

  • Sanjeewa N. Senadheera,
  • Abraham L. Yousef and
  • Richard S. Givens

Beilstein J. Org. Chem. 2014, 10, 2038–2054, doi:10.3762/bjoc.10.212

Graphical Abstract
  • a photo-Favorskii rearrangement with quantum yields of 0.028 for 1,4-HNA DEP and 0.0076 for 1,4-MNA DEP. The lower quantum efficiency of 1,4-MNA in MeOH is fully in accord with a similar methylation of the hydroxy group of pHP DEP, emphasizing the role of the phenolic OH on the reaction and
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Published 29 Aug 2014

Supercritical carbon dioxide: a solvent like no other

  • Jocelyn Peach and
  • Julian Eastoe

Beilstein J. Org. Chem. 2014, 10, 1878–1895, doi:10.3762/bjoc.10.196

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  • through intelligent surfactant design and synthesis. Several structural aspects have thus far been identified as increasing CO2-philicity of hydrocarbon surfactants, including the degree of surfactant tail branching and methylation [49], where increased tail branching and methylation led to increased
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Published 14 Aug 2014

A complete series of 6-deoxy-monosubstituted tetraalkylammonium derivatives of α-, β-, and γ-cyclodextrin with 1, 2, and 3 permanent positive charges

  • Martin Popr,
  • Simona Hybelbauerová and
  • Jindřich Jindřich

Beilstein J. Org. Chem. 2014, 10, 1390–1396, doi:10.3762/bjoc.10.142

Graphical Abstract
  • mono-Ts-CD with neat N,N,N’-trimethylethane-1,2-diamine or N,N,N’-trimethylpropane-1,3-diamine and subsequent methylation by CH3I in good yields. Finally, analogues bearing a moiety with three tetraalkylammonium sites were synthesized by reacting mono-Ts-CD with bis(3-aminopropyl)amine and subsequent
  • methylation. The majority of the presented reactions are very straightforward with a simple work-up, which avoids the need of chromatographic separation. Thus, these reactions are suitable for the multigram-scale production of monosubstituted cationic CDs. Keywords: cationic; cyclodextrins; monosubstitution
  • step, the installed triamine was quaternized by methylation with MeI. To achieve a full conversion, the use of a sterically hindered base was necessary. First, we attempted to methylate intermediate 27 containing a diethylenetriamine moiety. Different bases (K2CO3, 2,6-lutidine, 2,4,6-collidine and DBU
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Published 18 Jun 2014

Heronapyrrole D: A case of co-inspiration of natural product biosynthesis, total synthesis and biodiscovery

  • Jens Schmidt,
  • Zeinab Khalil,
  • Robert J. Capon and
  • Christian B. W. Stark

Beilstein J. Org. Chem. 2014, 10, 1228–1232, doi:10.3762/bjoc.10.121

Graphical Abstract
  • the farnesyl residue (for atom numbering see Scheme 1), followed by regio- and stereoselective nucleophilic addition of water (and methylation) would deliver heronapyrroles A and B. Similarly, regio- and stereoselective nucleophilic addition of water to a tris-epoxy farnesyl intermediate 4 could
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Published 26 May 2014

Phosphinate-containing heterocycles: A mini-review

  • Olivier Berger and
  • Jean-Luc Montchamp

Beilstein J. Org. Chem. 2014, 10, 732–740, doi:10.3762/bjoc.10.67

Graphical Abstract
  • refluxing THF to produce another phosphindole 8 in 48% yield (Scheme 4) [18]. A phosphindol-3-one 11 was prepared in 54% yield from butylphosphinate 9 by first methylation using DBU and iodomethane followed by a cross-coupling with ethyl 2-bromobenzoate (10) and then a Dieckmann-like condensation using
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Published 27 Mar 2014

Synthesis of complex intermediates for the study of a dehydratase from borrelidin biosynthesis

  • Frank Hahn,
  • Nadine Kandziora,
  • Steffen Friedrich and
  • Peter F. Leadlay

Beilstein J. Org. Chem. 2014, 10, 634–640, doi:10.3762/bjoc.10.55

Graphical Abstract
  • Dess–Martin oxidation, Pinnick oxidation and methylation. Methyl ester 12 was obtained in 10 steps with a good overall yield of 20%. Olefin cross metathesis of alkene 12 with crotonaldehyde in the presence of a second generation Grubbs catalyst required only a short filter column to isolate α,β
  • assay mixture, the latter will be transformed into their corresponding methyl esters by saponification and following methylation with trimethylsilyldiazomethane. The fully protected E-isomer 10a was obtained in 18% yield by a Horner–Wadsworth–Emmons reaction with phosphonate 25 or, alternatively, in 64
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Published 11 Mar 2014

Intermediates in monensin biosynthesis: A late step in biosynthesis of the polyether ionophore monensin is crucial for the integrity of cation binding

  • Wolfgang Hüttel,
  • Jonathan B. Spencer and
  • Peter F. Leadlay

Beilstein J. Org. Chem. 2014, 10, 361–368, doi:10.3762/bjoc.10.34

Graphical Abstract
  • steps in monensin biosynthesis, namely hydroxylation catalysed by the P450 monooxygenase MonD and O-methylation catalysed by the methyl-transferase MonE. The corresponding genes were deleted in-frame in a monensin-overproducing strain of Streptomyces cinnamonensis. The mutants produced the expected
  • MonE, are hydroxylation at C-26 and O-methylation of the hydroxy group at C-3. Although hydroxylation is shown as preceding methylation in Scheme 1, the preferred order of these events has not been established. The final catalysed step in biosynthesis is the release of mature monensins A and B from the
  • strain. These results lend support to the idea that the preferred order of events is hydroxylation at C-26 catalysed by MonD, followed by O-methylation at the hydroxy group borne at C-3 catalysed by MonE, as shown in Scheme 1. The amount of dehydroxymonensin A isolated from the MonE mutant was
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Published 10 Feb 2014

Synthesis of the B-seco limonoid core scaffold

  • Hanna Bruss,
  • Hannah Schuster,
  • Rémi Martinez,
  • Markus Kaiser,
  • Andrey P. Antonchick and
  • Herbert Waldmann

Beilstein J. Org. Chem. 2014, 10, 194–208, doi:10.3762/bjoc.10.15

Graphical Abstract
  • (−)-quinic acid (16) according to the route reported by Arthurs et al. [40] with minor modifications. After Baylis–Hillman reaction and subsequent silylation of the resulting free primary hydroxy group, substrate-controlled α-methylation of the lithium enolate proceeded with full stereocontrol [41][42
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Published 16 Jan 2014

Recent applications of the divinylcyclopropane–cycloheptadiene rearrangement in organic synthesis

  • Sebastian Krüger and
  • Tanja Gaich

Beilstein J. Org. Chem. 2014, 10, 163–193, doi:10.3762/bjoc.10.14

Graphical Abstract
  • carbon dioxide [74][75] resulted in the formation of carboxylic acid 75. Birch reduction with concomitant methylation [76][77] followed by selective hydrogenation and reduction of the carboxylic acid resulted in the formation of alcohol 76. Installation of the remaining quarternary carbon center was
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Published 16 Jan 2014

Synthesis of novel derivatives of 5-hydroxymethylcytosine and 5-formylcytosine as tools for epigenetics

  • Anna Chentsova,
  • Era Kapourani and
  • Athanassios Giannis

Beilstein J. Org. Chem. 2014, 10, 7–11, doi:10.3762/bjoc.10.2

Graphical Abstract
  • -enzymes; Introduction Epigenetic modifications play a crucial role in cell differentiation and cell development [1]. They control gene expression through several mechanisms such as non-coding RNAs, histone modifications (acetylation, methylation, phosphorylation, etc.) [2], and DNA methylation [3][4][5
  • higher oxidation products such as 5-formylcytosine (5fC) and 5-carboxylcytosine (5caC) by the action of ten-eleven-translocation (TET) enzymes was discovered [9][10][11][12][13]. The TET proteins are identified as 2-oxoglutarate (2OG) and Fe(II)-dependent oxygenases [10][14]. Whereas the DNA methylation
  • , decarboxylation of the 5caC by an unknown decarboxylase excluding action of BER should also be considered [15][23]. This variety of demethylation pathways might indicate that different tissues utilize different demethylation pathways [1][24]. While DNA methylation is usually associated with gene repression [8][25
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Published 03 Jan 2014

[2H26]-1-epi-Cubenol, a completely deuterated natural product from Streptomyces griseus

  • Christian A. Citron and
  • Jeroen S. Dickschat

Beilstein J. Org. Chem. 2013, 9, 2841–2845, doi:10.3762/bjoc.9.319

Graphical Abstract
  • the homomonoterpene 1 proceeds by S-adenosylmethionine-dependent methylation of GPP followed by a cyclisation reaction [3][4][5]. For biosynthetic studies on secondary metabolites isotopically labelled precursors are frequently used. Historically, the usage of radiolabelled compounds was most
  • ], and A-factor biosynthesis may be significantly delayed on DMM. It is unknown whether the biosynthesis of 1 is also A-factor controlled in S. griseus, but an alternative explanation for its abolished production is that the biosynthesis of 1 requires additional chemistry, i.e., a methylation step [3][4
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Published 10 Dec 2013

Modulating NHC catalysis with fluorine

  • Yannick P. Rey and
  • Ryan Gilmour

Beilstein J. Org. Chem. 2013, 9, 2812–2820, doi:10.3762/bjoc.9.316

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  • yield (92%). A three step, one pot sequence consisting of methylation, treatment with phenylhydrazine and subsequent cyclisation furnished the triazolium salt 17 in 76% yield (3 steps). Finally, DAST-mediated TBDMS deprotection/deoxyfluorination completed the synthetic sequence to give 7 in 45% yield
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Published 06 Dec 2013

Halogenated volatiles from the fungus Geniculosporium and the actinomycete Streptomyces chartreusis

  • Tao Wang,
  • Patrick Rabe,
  • Christian A. Citron and
  • Jeroen S. Dickschat

Beilstein J. Org. Chem. 2013, 9, 2767–2777, doi:10.3762/bjoc.9.311

Graphical Abstract
  • diazonium salt followed by a Sandmeyer reaction resulted in 4b (61% over two steps). The isomer 4c was efficiently prepared by double methylation of 2-chlororesorcinol (8) with potassium carbonate and methyl iodide in acetone (88%), while 4f was obtained by chlorination of dimethoxybenzene 9 with
  • mixture of mono- and disubstitution products, but the target compounds 10f and 10g were obtained in better yields (29% and 17%). Derivative 10b was prepared from 3,5-dichlorocatechol (13) by methylation with potassium carbonate and methyl iodide in high yield (80%). Accordingly, methylation of 4,6
  • -dichlororesorcinol (14) provided 10h in 80% yield, and methylation of 2,3-dichlorohydroquinone (16), prepared from benzoquinone (15) by treatment with SO2Cl2 under acidic conditions, generated 10i (13% via two steps). Reduction of 2,6-dichlorobenzoquinone with ascorbic acid to the corresponding hydroquinone 18
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Published 03 Dec 2013

The total synthesis of D-chalcose and its C-3 epimer

  • Jun Sun,
  • Song Fan,
  • Zhan Wang,
  • Guoning Zhang,
  • Kai Bao and
  • Weige Zhang

Beilstein J. Org. Chem. 2013, 9, 2620–2624, doi:10.3762/bjoc.9.296

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  • for diacetate 14 was identical to the data reported for the natural product-derived D-chalcose diacetate [10]. A nearly identical synthetic procedure was used to transform 4′ into the C-3 epimer of chalcose (I′); this procedure began with a methylation to form 5′ (Scheme 7). The stereoselective
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Published 22 Nov 2013

The myxocoumarins A and B from Stigmatella aurantiaca strain MYX-030

  • Tobias A. M. Gulder,
  • Snežana Neff,
  • Traugott Schüz,
  • Tammo Winkler,
  • René Gees and
  • Bettina Böhlendorf

Beilstein J. Org. Chem. 2013, 9, 2579–2585, doi:10.3762/bjoc.9.293

Graphical Abstract
  • O-methylation, glycosylation, prenylation, oxygenation and subsequent cyclization or dimerization events [34]. Nitrogen-bearing congeners are rather scarce, with the bacterial aminocoumarins, such as the gyrase inhibitor novobiocin, being the most well-known examples [35]. Despite the larger number
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Published 20 Nov 2013

A protecting group-free synthesis of the Colorado potato beetle pheromone

  • Zhongtao Wu,
  • Manuel Jäger,
  • Jeffrey Buter and
  • Adriaan J. Minnaard

Beilstein J. Org. Chem. 2013, 9, 2374–2377, doi:10.3762/bjoc.9.273

Graphical Abstract
  • , oxidation and stereoselective methylation using organometallic reagents are the key steps, affording (S)-1 in high enantiomeric purity and in gram quantities. In all these approaches, however, protection of the primary hydroxy group of the 1,2,3-triol substructure is required for the selective oxidation of
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Published 06 Nov 2013

Towards stereochemical control: A short formal enantioselective total synthesis of pumiliotoxins 251D and 237A

  • Jie Zhang,
  • Hong-Kui Zhang and
  • Pei-Qiang Huang

Beilstein J. Org. Chem. 2013, 9, 2358–2366, doi:10.3762/bjoc.9.271

Graphical Abstract
  • ; ring closure; trans-methylation; Introduction Pumiliotoxins (PTXs, 1, Figure 1) such as pumiliotoxin 251D (2) are a subclass of indolizidine alkaloids isolated from the skin secretion of neotropical frogs. A total of 19 members have been isolated and partially characterized [1]. Pumiliotoxins are
  • minor diastereomer. Similar results have been reported by Nubbemeyer [27] and Li [8]. In view of the fruitless efforts of Nubbemeyer [27] and Li [8] in inversing the diastereoselectivity of the methylation reaction of keto-lactam 7, an alternative approach was envisaged. To develop a diastereoselective
  • approach to (8S,8aS)-5, it would be helpful to analyze the plausible stereochemical course of the methylation of keto-lactam 7. The observed unusual stereoselective cis-methylation implicates a preferential axial attack of the methylmagnesium iodide to the bicyclic keto-lactam 7 (Scheme 2). Although the
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Published 05 Nov 2013

An overview of the synthetic routes to the best selling drugs containing 6-membered heterocycles

  • Marcus Baumann and
  • Ian R. Baxendale

Beilstein J. Org. Chem. 2013, 9, 2265–2319, doi:10.3762/bjoc.9.265

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  • metabolism via oxidation or methylation pathways forming the corresponding pyridinium ions [9][10]. Although many of these metabolites are potentially highly toxic to humans they are conveniently and quickly excreted from the body via the kidneys. With a good understanding of the pharmacokinetics and
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Published 30 Oct 2013

Structure of 1,5-benzodiazepinones in the solid state and in solution: Effect of the fluorination in the six-membered ring

  • Marta Pérez-Torralba,
  • Rosa M. Claramunt,
  • M. Ángeles García,
  • Concepción López,
  • M. Carmen Torralba,
  • M. Rosario Torres,
  • Ibon Alkorta and
  • José Elguero

Beilstein J. Org. Chem. 2013, 9, 2156–2167, doi:10.3762/bjoc.9.253

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  • to compound 1 indicate a greater deformation in the seven-membered ring owing to the presence of the N-methyl substituent. The N-methylation prevents the dimerization by hydrogen bonding leading to a very different packing. Therefore, the most significant intermolecular interaction is the F–F contact
  • ) > b (18 kJ mol−1 in average), the other tautomers having considerably higher energies. Always tautomer b is destabilized by N-methylation (in average, 8.4 kJ mol−1) probably due to a steric effect; the conjugated tautomer b tends to be planar and this is indeed the case for 1H-derivatives 1b, 3b and
  • -2-one) [27]. When using calculated values it is possible to analyze the main effects on the barriers that in the present case are three: i) N-methylation; ii) 6,7,8,9-tetrafluorination; iii) the substituent at position 4 (CH3 or C6H5). This last effect is negligible, the other two interact, then a
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Published 21 Oct 2013

Non-cross-linked polystyrene-supported 2-imidazolidinone chiral auxiliary: synthesis and application in asymmetric alkylation reactions

  • Quynh Pham Bao Nguyen and
  • Taek Hyeon Kim

Beilstein J. Org. Chem. 2013, 9, 2113–2119, doi:10.3762/bjoc.9.248

Graphical Abstract
  • polystyrene (NCPS)-supported 2-phenylimino-2-oxazolidine, which facilitated the synthesis of several chiral amides in excellent stereoselectivity (>96% ee). However, the sterically undemanding methylation has not been investigated [20]. Recently, we introduced 2-imidazolidinone [26][27], a versatile auxiliary
  • investigated. As shown in Table 3, benzyl bromide, allyl iodide and methyl iodide reacted very well to give the alkylated products 7 in moderate to good yields and excellent de values of >99% (Supporting Information File 1). Especially, the diastereocontrol of asymmetric methylation in this case was better
  • diastereoselectivity (>99% de) without using any special strategy. To the best of our knowledge, no studies have reported successful diastereocontrol by using other polymer-supported chiral auxiliaries in asymmetric alkylation reactions, especially in the methylation case [13][14][15][16][17][18][19][20][21][22][23
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Published 15 Oct 2013

The chemistry of isoindole natural products

  • Klaus Speck and
  • Thomas Magauer

Beilstein J. Org. Chem. 2013, 9, 2048–2078, doi:10.3762/bjoc.9.243

Graphical Abstract
  • after methylation, 26 is obtained [27]. As already mentioned before, indolocarbazoles are characterized by their excellent biological activities and unusual architecture and hence drawing an enormous interest from the synthetic organic chemistry community. This led to several syntheses of the natural
  • –Spengler reaction of dopamine (99) with 4-hydroxyphenylacetaldehyde (100), both derived from L-tyrosine (98) (Scheme 11). After oxidation and O-methylation, which is carried out by S-adenosylmethionine (SAM), (S)-reticuline (101) is obtained. Oxidation of the N-methyl group to the iminium ion and
  • cyclization gives the tetracyclic carbon skeleton, which upon further methylation and oxidation furnishes berberine (92) [80]. Prechilenine (102), itself isolated as its O-methyl ether is formed via oxidation [78]. A base-catalyzed semipinacol-type rearrangement yields 93 [76]. Chilenine (93) can be further
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Published 10 Oct 2013

A practical synthesis of long-chain iso-fatty acids (iso-C12–C19) and related natural products

  • Mark B. Richardson and
  • Spencer J. Williams

Beilstein J. Org. Chem. 2013, 9, 1807–1812, doi:10.3762/bjoc.9.210

Graphical Abstract
  • determined. Conversion of iso-C17 acid 6 to the N-acyloxazolidinone 28 was achieved using pivalyl chloride/LiCl [62] and (S)-4-benzyloxazolidinone. Diastereoselective methylation [63] of the chelated Z-enolate, derived from deprotonation of 28, using NaHMDS, followed by addition of iodomethane, yielded 29 as
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Published 04 Sep 2013
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