Dependency of the regio- and stereoselectivity of intramolecular, ring-closing glycosylations upon the ring size

• Patrick Claude,
• Christian Lehmann and
• Thomas Ziegler

Beilstein J. Org. Chem. 2011, 7, 1609–1619, doi:10.3762/bjoc.7.189

• , justifying a more profound conformational analysis of this product (Figure 6). Conformational molecular dynamics runs (MD) were performed on both anomers of the two regioisomers of 8d to simulate the behavior of the molecule during more than 5000 ps of molecular motion. Thereby, it was found that for the

NMR studies of anion-induced conformational changes in diindolylureas and diindolylthioureas

• Damjan Makuc,
• Jennifer R. Hiscock,
• Mark E. Light,
• Philip A. Gale and
• Janez Plavec

Beilstein J. Org. Chem. 2011, 7, 1205–1214, doi:10.3762/bjoc.7.140

• between H1 and H7α (4.2–5.3%) were considerably stronger with respect to NOE between H7α and H6 (0–2.8%) upon addition of dihydrogen phosphate to 1. The observed NOE enhancements for 1·H2PO4− complex suggest a preference for the syn–syn conformer in DMSO-d6. Conformational analysis of 1 and its anion

• H1 and H7α NMR resonances prevented conformational analysis of 2 upon addition of other anions used in the study. The conformational preferences of 2 were evaluated by quantum mechanical calculations at the B3LYP/6-311+G(d,p) level of theory. The freely optimized anti–anti conformer of 2 exhibited

• detailed conformational analysis of the anion–receptor complexes for 3 and 4. Experimental NMR experiments 1H, 13C and 15N NMR spectra were acquired on a Varian Unity Inova 300 MHz NMR spectrometer. All data were recorded in DMSO-d6 at 298 K. Chemical shifts were referenced to the residual solvent signal

Oxalyl retro-peptide gelators. Synthesis, gelation properties and stereochemical effects

• Janja Makarević,
• Milan Jokić,
• Leo Frkanec,
• Vesna Čaplar,
• Nataša Šijaković Vujičić and
• Mladen Žinić

Beilstein J. Org. Chem. 2010, 6, 945–959, doi:10.3762/bjoc.6.106

• conformations of (S,R)-1b and (S,S)-1b are distinctly different with all i-Bu groups cis-oriented in (S,R)-1b, while the i-Bu groups in α- and β-Leu of (S,S)-1b have the trans-arrangement with respect to the plane containing the amide and oxalamide groups (Figure 10a). Conformational analysis reveals why such

(Pseudo)amide-linked oligosaccharide mimetics: molecular recognition and supramolecular properties

• José L. Jiménez Blanco,
• Fernando Ortega-Caballero,
• Carmen Ortiz Mellet and
• José M. García Fernández

Beilstein J. Org. Chem. 2010, 6, No. 20, doi:10.3762/bjoc.6.20

• ] that were found to form rigid secondary structures predetermined by the linkage position as evidenced from CD and NMR measurements. Moreover, conformational analysis by molecular modelling calculation on the β(1→2)-linked decamer 9 supported a helical arrangement, stabilised by a intramolecular

• and co-workers undertook the synthesis of carbopeptoids based on the oxetane template (Figure 7) [46][47][48]. Conformational analysis was carried out for two oxetane β-SAA hexamers with the 6-deoxy-L-altro and D-arabino configurations by means of detailed NMR and IR studies in combination with

• acid. Following the same objective, Xie’s group prepared orthogonally protected cyclic homo-oligomers with two to four SAA units that can be selectively or fully deprotected to afford macrocycles that can undergo further functionalisation (Figure 11) [55]. Conformational analysis by molecular modelling

[3.3]Dithia-bridged cyclophanes featuring a thienothiophene ring: synthesis, structures and conformational analysis

• Sabir H. Mashraqui,
• Yogesh Sanghvikar,
• Shailesh Ghadhigaonkar,
• Sukeerthi Kumar,
• Auke Meetsma and
• Elise Trân Huu Dâu

Beilstein J. Org. Chem. 2009, 5, No. 74, doi:10.3762/bjoc.5.74

• case of 11, also by single crystal X-ray crystallography. Conformational analysis by variable temperature NMR suggests that cyclophanes 7, 9 and 11 exhibit conformationally rigid bridges and rings at least up to 130 °C. Energy minimization of 11 revealed anti-11 to be the most stable conformation

• conformational analysis of thienothiophenophanes 7, 9 and 11 The 1H NMR (300 MHz) spectrum of dithia-cyclophane 7 revealed two AB spin systems (4H each) in the range of δ 3.21–4.30 due to the geminal couplings of the bridged –CH2- protons. A singlet centered at δ 2.31 accounted for the C3/C4 methyl groups. The

• former slightly displaced from the center of the latter. In order to evaluate the energy minimized conformations for 11, we performed the conformational analysis by random search Monte Carlo method [33] and optimized by PRCG Conjugated Gradient molecular mechanics minimization using the Macromodel

Ring strain and total syntheses of modified macrocycles of the isoplagiochin type

• Andreas Speicher,
• Timo Backes,
• Kerstin Hesidens and
• Jürgen Kolz

Beilstein J. Org. Chem. 2009, 5, No. 71, doi:10.3762/bjoc.5.71

• conformational analysis and MD investigations clearly confirmed the biaryl axis A to be configurationally stable at room temperature due to the second (more flexible) biaryl axis B, an (even more flexible) helical stilbene unit C and their combination with the ring-strain of the entire molecule. By experimental

Mitomycins syntheses: a recent update

• Jean-Christophe Andrez

Beilstein J. Org. Chem. 2009, 5, No. 33, doi:10.3762/bjoc.5.33

A stable enol from a 6-substituted benzanthrone and its unexpected behaviour under acidic conditions

• Marc Debeaux,
• Kai Brandhorst,
• Peter G. Jones,
• Henning Hopf,
• Jörg Grunenberg,
• Wolfgang Kowalsky and
• Hans-Hermann Johannes

Beilstein J. Org. Chem. 2009, 5, No. 31, doi:10.3762/bjoc.5.31

• the relevant molecules 4, 7 and 9–18 were obtained by first applying an extended conformational analysis using the OPLS2005 force field [12] together with a Monte Carlo torsional sampling as implemented in the Macromodel 9.5 program [13]. Each lowest energy conformation of 4, 7 and 9–18, respectively

A convenient allylsilane- N-acyliminium route toward indolizidine and quinolizidine alkaloids

• Roland Remuson

Beilstein J. Org. Chem. 2007, 3, No. 32, doi:10.1186/1860-5397-3-32

• synthesis of the four racemic diastereomers of this indolizidine and a conformational analysis of these diastereomers has been discussed. [36][37] Its identification as (5R,7S,9R)-5,7dimethylindolizidine has been firmly established. [38] We describe here the first asymmetric synthesis of this alkaloid; [39

A superior P-H phosphonite: Asymmetric allylic substitutions with fenchol- based palladium catalysts

• Bernd Goldfuss,
• Thomas Löschmann,
• Tina Kop-Weiershausen,
• Jörg Neudörfl and
• Frank Rominger

Beilstein J. Org. Chem. 2006, 2, No. 7, doi:10.1186/1860-5397-2-7

• the NH3 model nucleophile corresponds to the experimental R-alkylation product. The two most stable ONIOM(B3LYP/SDD(+ECP) (Pd) /6-31G* (C, H, O, N, P) : UFF) optimized transition structures with BIFOP-H, due to systematic conformational analysis (60° rotations at P-Pd). ZPE (unscaled) corrected total