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Search for "stereoisomers" in Full Text gives 229 result(s) in Beilstein Journal of Organic Chemistry. Showing first 200.

Synthesis of carbohydrate-scaffolded thymine glycoconjugates to organize multivalency

  • Anna K. Ciuk and
  • Thisbe K. Lindhorst

Beilstein J. Org. Chem. 2015, 11, 668–674, doi:10.3762/bjoc.11.75

Graphical Abstract
  • products (cf. Supporting Information File 1). Both regioisomers can consist of four different stereoisomers, two cis and two trans isomers according to the relative steric orientation of the thymine methyl groups. It can be assumed that the irradiation of 7 in diluted solution favors the syn
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Published 07 May 2015

Novel stereocontrolled syntheses of tashiromine and epitashiromine

  • Loránd Kiss,
  • Enikő Forró and
  • Ferenc Fülöp

Beilstein J. Org. Chem. 2015, 11, 596–603, doi:10.3762/bjoc.11.66

Graphical Abstract
  • stereoisomers (determined on the basis of 1H NMR data) failed, but the mixture could be applied in the next ring-opening oxidation step, since it gave only one open-chain diformyl intermediate I2. Similarly to the cis isomer, this unstable dialdehyde intermediate was subjected without isolation to catalytic
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Published 30 Apr 2015

Enhancing the reactivity of 1,2-diphospholes in cycloaddition reactions

  • Almaz Zagidullin,
  • Vasili Miluykov,
  • Elena Oshchepkova,
  • Artem Tufatullin,
  • Olga Kataeva and
  • Oleg Sinyashin

Beilstein J. Org. Chem. 2015, 11, 169–173, doi:10.3762/bjoc.11.17

Graphical Abstract
  • would be assumed that similar [4 + 2] cycloadducts are formed according to the range of signals in the 31P NMR spectra. However, in this case, several stereoisomers are formed due to the high reactivity of the 1,2-diphospholes containing EWGs on the phosphorus atom. It should be noted that this is the
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Published 27 Jan 2015

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

Graphical Abstract
  • derivatives by means of PBr3, and subsequently reacted with appropriate amine providing desired pharmacologically valuable (R)- and (S)-stereoisomers of title drugs in an ee range of 84–98%, respectively. The modular amination procedure is based on a solvent-dependent stereodivergent transformation of the
  • profiles of its stereoisomers, obtaining both enantiomers in more than analytical quantities is particularly desirable. Moreover, the racemic mixture of this pharmaceutical is commercially available, however it is sold at high price, as its production by standard synthetic procedures is time-consuming and
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Published 18 Dec 2014

(2R,1'S,2'R)- and (2S,1'S,2'R)-3-[2-Mono(di,tri)fluoromethylcyclopropyl]alanines and their incorporation into hormaomycin analogues

  • Armin de Meijere,
  • Sergei I. Kozhushkov,
  • Dmitrii S. Yufit,
  • Christian Grosse,
  • Marcel Kaiser and
  • Vitaly A. Raev

Beilstein J. Org. Chem. 2014, 10, 2844–2857, doi:10.3762/bjoc.10.302

Graphical Abstract
  • with alkyl halides virtually yield single stereoisomers, in which the configuration of the newly formed stereogenic center at C-2 of the amino acid moiety is the same as that in the proline moiety of the chiral auxiliary in the starting material. In reactions of the enolate of this chiral glycine
  • triflates of threonine stereoisomers [47], the chiral auxiliary approach [48][49][50][51] and enantioselective hydrogenation over a chiral catalyst [52][53]. All these approaches ought to be applicable to prepare unsubstituted β-methylphenylalanine, but most if not all of them have severe drawbacks. Among
  • the chiral auxiliary approaches to β-branched arylalanines, including all four stereoisomers of β-methylphenylalanine, the one employing the "Evans amide" method with a 4-benzyl- or 4-phenyl-2-oxazolidinone moiety, has been used most frequently. Along this route, which requires eight procedural steps
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Published 03 Dec 2014

Preparation of neuroprotective condensed 1,4-benzoxazepines by regio- and diastereoselective domino Knoevenagel–[1,5]-hydride shift cyclization reaction

  • László Tóth,
  • Yan Fu,
  • Hai Yan Zhang,
  • Attila Mándi,
  • Katalin E. Kövér,
  • Tünde-Zita Illyés,
  • Attila Kiss-Szikszai,
  • Balázs Balogh,
  • Tibor Kurtán,
  • Sándor Antus and
  • Péter Mátyus

Beilstein J. Org. Chem. 2014, 10, 2594–2602, doi:10.3762/bjoc.10.272

Graphical Abstract
  • ). TDDFT-ECD calculation was proved an efficient method to determine the absolute configuration of separated stereoisomers of bioactive synthetic [19] and natural derivatives [20][21] on the basis of their HPLC-ECD spectra. For the configurational assignment of the separated enantiomers, TDDFT-ECD
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Published 06 Nov 2014

Phosphinocyclodextrins as confining units for catalytic metal centres. Applications to carbon–carbon bond forming reactions

  • Matthieu Jouffroy,
  • Rafael Gramage-Doria,
  • David Sémeril,
  • Dominique Armspach,
  • Dominique Matt,
  • Werner Oberhauser and
  • Loïc Toupet

Beilstein J. Org. Chem. 2014, 10, 2388–2405, doi:10.3762/bjoc.10.249

Graphical Abstract
  • trans (strong CO IR band at 1985 cm−1 [55][56]) configured. Remarkably, the same ratio of stereoisomers was obtained when rhodium complex 13 (see Scheme 6) was treated with LiCl under CO (1 atm). When the reaction between HUGPHOS-2 and [RhCl(CO)2]2 was repeated, but applying a 1:1 instead of 1:0.5
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Published 15 Oct 2014

N–O Cleavage reactions of heterobicycloalkene-fused 2-isoxazolines

  • Jaipal R. Nagireddy,
  • Geoffrey K. Tranmer,
  • Emily Carlson and
  • William Tam

Beilstein J. Org. Chem. 2014, 10, 2200–2205, doi:10.3762/bjoc.10.227

Graphical Abstract
  • cleavage of carbobicycle-fused 2-isoxazolines converts both exo- and endo stereoisomers of 8 into the corresponding single isomer of cyclopentene 9 (Table 1) [20]. Since then, we have been interested in the outcomes of cleavage reactions of 2-isoxazolines fused to heterobicyclic compounds 10 or 11, which
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Published 16 Sep 2014

Building complex carbon skeletons with ethynyl[2.2]paracyclophanes

  • Ina Dix,
  • Lidija Bondarenko,
  • Peter G. Jones,
  • Thomas Oeser and
  • Henning Hopf

Beilstein J. Org. Chem. 2014, 10, 2013–2020, doi:10.3762/bjoc.10.209

Graphical Abstract
  • diastereomers are generated (as expected) by the oxidative dimerization of the mono ethynyl derivative [9], but assignment of the various spectra to specific stereoisomers remains an open question, and will only be possible after the resolution of the 4-ethynyl[2.2]paracyclophane, determination of its absolute
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Published 27 Aug 2014

Synthesis of rigid p-terphenyl-linked carbohydrate mimetics

  • Maja Kandziora and
  • Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2014, 10, 1749–1758, doi:10.3762/bjoc.10.182

Graphical Abstract
  • dioxolane C-2 (ratios close to 1:1). The preparation of syn-1,2-oxazine 4 was achieved in good yields ranging from 67–77% by stereocontrolled addition of lithiated (trimethylsilyl)ethoxyallene 9 to (Z)-nitrone 6 at −78 °C (Scheme 3). Although the formation of four stereoisomers is possible only two were
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Published 30 Jul 2014

Multicomponent reactions in nucleoside chemistry

  • Mariola Koszytkowska-Stawińska and
  • Włodzimierz Buchowicz

Beilstein J. Org. Chem. 2014, 10, 1706–1732, doi:10.3762/bjoc.10.179

Graphical Abstract
  • , the uridine example is shown) [114]. The coupling products 98 were obtained as (Z)-stereoisomers for studies related to the drug discovery against the hepatitis C virus. The methodology shown in Scheme 40 [114] was further elaborated on reactions of polyfunctional iodide 99 with four equivalents of
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Published 29 Jul 2014

cistrans Isomerization of silybins A and B

  • Michaela Novotná,
  • Radek Gažák,
  • David Biedermann,
  • Florent Di Meo,
  • Petr Marhol,
  • Marek Kuzma,
  • Lucie Bednárová,
  • Kateřina Fuksová,
  • Patrick Trouillas and
  • Vladimír Křen

Beilstein J. Org. Chem. 2014, 10, 1047–1063, doi:10.3762/bjoc.10.105

Graphical Abstract
  • ; 10,11-cis-silybin; isomerization; silibinin; silybin; silymarin; Introduction The flavonolignan silybin (alternative name silibinin), occurring in the fruits of Silybum marianum (milk thistle), consists of two stereoisomers – silybin A (1a) and B (1b) – in a ca. 1:1 ratio (Figure 1). Their absolute
  • (or 10 from 1b) on silica gel was not feasible, analogous to the preparative separation of silybin stereoisomers 1a and 1b (Figure 1), which was a challenge for several decades. It was accomplished as the separation of the respective silybin glycosides for the first time [13][14], later by HPLC [3
  • -glucopyranoside 6''-gallate, Figure 6) was subjected to both, basic and acidic hydrolysis during its structure elucidation. However, under these conditions four stereoisomers of the original aglycon (2R,3R)-taxifolin were formed. Base-catalyzed isomerization of another taxifolin glycoside, (2R,3R)-2,3
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Published 08 May 2014

Structure elucidation of female-specific volatiles released by the parasitoid wasp Trichogramma turkestanica (Hymenoptera: Trichogrammatidae)

  • Armin Tröger,
  • Teris A. van Beek,
  • Martinus E. Huigens,
  • Isabel M. M. S. Silva,
  • Maarten A. Posthumus and
  • Wittko Francke

Beilstein J. Org. Chem. 2014, 10, 767–773, doi:10.3762/bjoc.10.72

Graphical Abstract
  • an initial approach we aimed at the synthesis of a library of stereoisomers of A (Figure 2). The commercially available racemic anti-dimethyl 2,4-dimethylglutarate (1) was reduced to the corresponding racemate of 2,4-dimethylpentan-1,5-diol (2) [13], which was further transformed to the monosilyl
  • position 2 underwent ca. 6% epimerization to yield 7 as a mixture of 4 stereoisomers. The synthesis of 2,6,8,12-tetramethyltrideca-2,4-diene (8) was completed by Wittig reaction using (3-methylbut-2-en-1-yl)triphenylphosphonium bromide [15]. As expected, the obtained mixture of all possible stereoisomers
  • with malonate and another methylmalonate (including deoxygenation steps) seemed to be plausible [16]. These biogenetic considerations excluded methyl groups at positions 9 and 11. To prepare a mixture of all stereoisomers of 14, we again used 2 as the starting material (Figure 2). Monobenzylation to 9
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Published 02 Apr 2014

Group-assisted purification (GAP) chemistry for the synthesis of Velcade via asymmetric borylation of N-phosphinylimines

  • Jian-bo Xie,
  • Jian Luo,
  • Timothy R. Winn,
  • David B. Cordes and
  • Guigen Li

Beilstein J. Org. Chem. 2014, 10, 746–751, doi:10.3762/bjoc.10.69

Graphical Abstract
  • by avoiding traditional purification methods such as chromatography or recrystallization. The pure products, often pure stereoisomers, can be easily obtained by washing the crude products with common solvents or co-solvents [22][23][24][25]. Our GAP concept was attributed to the study of a series of
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Published 31 Mar 2014

Synthesis of fluorescent (benzyloxycarbonylamino)(aryl)methylphosphonates

  • Michał Górny vel Górniak,
  • Anna Czernicka,
  • Piotr Młynarz,
  • Waldemar Balcerzak and
  • Paweł Kafarski

Beilstein J. Org. Chem. 2014, 10, 741–745, doi:10.3762/bjoc.10.68

Graphical Abstract
  • chromatography, a significant enrichment in one of the diastereomers had been observed. For example, compound 7b obtained as a 55:45 molar mixture of stereoisomers after purification by means of chromatography was obtained as 85:15 molar mixture. The approach to obtain mixed esters bearing two aromatic moieties
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Published 28 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
  • preferentially accepts the 2D,3D-configured precursor, if all four potential stereoisomers of 3-hydroxy-2-methyl-SNAc-pentanoate model substrates are presented [7]. A commonly accepted model suggests that DHs from PKS I systems catalyze the removal of water by syn-dehydration and that a 2D,3D-configured
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Published 11 Mar 2014

One-pot three-component synthesis and photophysical characteristics of novel triene merocyanines

  • Christian Muschelknautz,
  • Robin Visse,
  • Jan Nordmann and
  • Thomas J. J. Müller

Beilstein J. Org. Chem. 2014, 10, 599–612, doi:10.3762/bjoc.10.51

Graphical Abstract
  • flexible and fixed acceptor moieties. DFT-computed energy differences of the stereoisomers of 2Z,4Z-8a and 2Z,4E-8a. DFT-computed energy differences of the stereoisomers of 10a and 10h. DFT-computed (B3LYP functional, 6-31G* basis set) HOMO (left) and LUMO (right) of merocyanine 8a. Absorption and emission
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Published 05 Mar 2014

Self-assembly of metallosupramolecular rhombi from chiral concave 9,9’-spirobifluorene-derived bis(pyridine) ligands

  • Rainer Hovorka,
  • Sophie Hytteballe,
  • Torsten Piehler,
  • Georg Meyer-Eppler,
  • Filip Topić,
  • Kari Rissanen,
  • Marianne Engeser and
  • Arne Lützen

Beilstein J. Org. Chem. 2014, 10, 432–441, doi:10.3762/bjoc.10.40

Graphical Abstract
  • -protected [(dppp)Pd]2+ and [(dppp)Pt]2+ ions. The self-assembly process of the racemic ligand preferably occurs in a narcissistic self-recognising manner. Hence, a mixture of all three possible stereoisomers [(dppp)2M2{(R)-L}2](OTf)4, [(dppp)2M2{(S)-L}2](OTf)4, and [(dppp)2M2{(R)-L}{(S)-L}](OTf)4 was
  • (Figure 2a,b). In principle, three stereoisomers of the dinuclear metallosupramolecular rhombi can form from racemic ligands upon coordination to [(dppp)Pd(OTf)2] or [(dppp)Pt(OTf)2] – a racemic mixture of two enantiomeric homochiral assemblies and an achiral heterochiral complex. These are expected to
  • heterochiral one in both cases – the palladium and the platinum complexes and independent of the solvents we used. This corresponds to an amplification of the homochiral stereoisomers via self-recognition by a factor of approximately three. Although these NMR spectra already provide a very good proof for the
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Published 18 Feb 2014

Concise, stereodivergent and highly stereoselective synthesis of cis- and trans-2-substituted 3-hydroxypiperidines – development of a phosphite-driven cyclodehydration

  • Peter H. Huy,
  • Julia C. Westphal and
  • Ari M. P. Koskinen

Beilstein J. Org. Chem. 2014, 10, 369–383, doi:10.3762/bjoc.10.35

Graphical Abstract
  • Abstract A concise (5 to 6 steps), stereodivergent, highly diastereoselective (dr up to >19:1 for both stereoisomers) and scalable synthesis (up to 14 g) of cis- and trans-2-substituted 3-piperidinols, a core motif in numerous bioactive compounds, is presented. This sequence allowed an efficient synthesis
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Published 11 Feb 2014

Studies on the interaction of isocyanides with imines: reaction scope and mechanistic variations

  • Ouldouz Ghashghaei,
  • Consiglia Annamaria Manna,
  • Esther Vicente-García,
  • Marc Revés and
  • Rodolfo Lavilla

Beilstein J. Org. Chem. 2014, 10, 12–17, doi:10.3762/bjoc.10.3

Graphical Abstract
  • involves a sequential double isocyanide incorporation into the C=N bond. The final step is a nucleophilic 4-exo-dig cyclization, and the anti addition modes likely lead to less stable stereoisomers which spontaneously isomerize to the observed compounds. Furthermore, we have determined the scope of the
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Published 06 Jan 2014

Plakilactones G and H from a marine sponge. Stereochemical determination of highly flexible systems by quantitative NMR-derived interproton distances combined with quantum mechanical calculations of 13C chemical shifts

  • Simone Di Micco,
  • Angela Zampella,
  • Maria Valeria D’Auria,
  • Carmen Festa,
  • Simona De Marino,
  • Raffaele Riccio,
  • Craig P. Butts and
  • Giuseppe Bifulco

Beilstein J. Org. Chem. 2013, 9, 2940–2949, doi:10.3762/bjoc.9.331

Graphical Abstract
  • ). Over 200 conformers were found for each of the stereoisomers for 2a–h (see Experimental), and their geometries were optimized at the DFT theoretical level by using the MPW1PW91 functional and 6-31G(d) [26] basis set (Gaussian 09 Software Package [27]). From the DFT-optimized geometries interproton
  • -calculated interproton distances for 2a,b,e,f differed by more than 0.03 Å (≈ 1%) from each other. The data reported in Table 3 clearly show that the diastereoisomer 2b represents the best fit with the experimentally derived distances (MAE 4.1% and standard deviation (STD) 5.0%). The stereoisomers 2a, 2e and
  • 2f poorly agree with the NOE-derived distances. The maximum error shown by the calculated distances for 2b is 9.4%, whereas the other stereoisomers have at least three calculated distances with an associated error higher than 10%. The largest errors (>10%) are relative to protons around the
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Published 30 Dec 2013

Synthesis and determination of the absolute configuration of (−)-(5R,6Z)-dendrolasin-5-acetate from the nudibranch Hypselodoris jacksoni

  • I. Wayan Mudianta,
  • Victoria L. Challinor,
  • Anne E. Winters,
  • Karen L. Cheney,
  • James J. De Voss and
  • Mary J. Garson

Beilstein J. Org. Chem. 2013, 9, 2925–2933, doi:10.3762/bjoc.9.329

Graphical Abstract
  • individual stereoisomers (see below). The 3:1 ratio of E/Z-isomers was confirmed via analytical HPLC. In principle, the rearrangement of 6 could afford either [1,2]-rearranged products (e.g. 7a/b or 8) or [2,3]-rearranged products such as 9 or 10 depending on which site adjacent to the ether oxygen is
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Published 23 Dec 2013

Novel supramolecular affinity materials based on (−)-isosteviol as molecular templates

  • Christina Lohoelter,
  • Malte Brutschy,
  • Daniel Lubczyk and
  • Siegfried R. Waldvogel

Beilstein J. Org. Chem. 2013, 9, 2821–2833, doi:10.3762/bjoc.9.317

Graphical Abstract
  • ) provides an open side to access the concave regime. As anticipated, two stereoisomers are formed in this condensation reaction of 5b with 4. After separation via column chromatography, these products were identified as the all-syn- and anti,anti,syn-isomers of the desired product 8, which were obtained in
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Published 09 Dec 2013

Multigramme synthesis and asymmetric dihydroxylation of a 4-fluorobut-2E-enoate

  • James A. B. Laurenson,
  • John A. Parkinson,
  • Jonathan M. Percy,
  • Giuseppe Rinaudo and
  • Ricard Roig

Beilstein J. Org. Chem. 2013, 9, 2660–2668, doi:10.3762/bjoc.9.301

Graphical Abstract
  • enantiomers 29a and 29b was excellent, with over 6 minutes separating the stereoisomers in the chromatograms. Due to the robust nature of the dibenzoylation chemistry and the excellent chromatograms produced, the derivatisation/chiral HPLC assay was used routinely. However, direct measurement of the ee's of
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Published 26 Nov 2013

Stereodivergent synthesis of jaspine B and its isomers using a carbohydrate-derived alkoxyallene as C3-building block

  • Volker M. Schmiedel,
  • Stefano Stefani and
  • Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2013, 9, 2564–2569, doi:10.3762/bjoc.9.291

Graphical Abstract
  • Volker M. Schmiedel Stefano Stefani Hans-Ulrich Reissig Institut für Chemie und Biochemie, Freie Universität Berlin, Takustr. 3, D-14195 Berlin, Germany 10.3762/bjoc.9.291 Abstract Herein we present the synthesis of the anhydrophytosphingosine jaspine B and three of its stereoisomers using a
  • therefore leads to a stereodivergent approach to the natural product and its enantiomer. The gold-catalyzed 5-endo-cyclization affords the corresponding dihydrofurans, which after separation, azidation of the enol ether moiety and two subsequent reduction steps give the natural product and its stereoisomers
  • synthesis of stereoisomers of the natural product [4][12][16][17][19][26][27][28] because these compounds also showed comparable biological activities [4][5]. During our current studies on the synthesis of highly functionalized heterocycles utilizing alkoxyallenes as versatile C3-building blocks we chose
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Published 19 Nov 2013
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