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

• broad positive Cotton effect (CE) at 378 nm, negative ones at 314, 305, 272 nm and positive ones at 284, 279 and 224 nm (Figure 4a). The HPLC-ECD spectrum of the first-eluting enantiomer of 7b showed similar ECD pattern with somewhat different shape and intensities in the 290–240 nm range (Figure 4b

Synthesis of a sucrose dimer with enone tether; a study on its functionalization

• Zbigniew Pakulski,
• Norbert Gajda,
• Magdalena Jawiczuk,
• Jadwiga Frelek,
• Piotr Cmoch and
• Sławomir Jarosz

Beilstein J. Org. Chem. 2014, 10, 1246–1254, doi:10.3762/bjoc.10.124

• oxidized with osmium tetroxide to a diol. Absolute configurations of the allylic alcohol as well as the diol were determined by circular dichroism (CD) spectroscopy using the in situ dimolybdenum methodology. Keywords: CD-spectroscopy; Cotton effect; multivalent glycosystems; osmylation; stereoselective

• alcohol 6 (Scheme 3). The positive sign of the Cotton effect at around 307.0 nm recorded for the complex of the diol 14 with Mo2(OAc)4 unambiguously pointed at the 6R configuration (Figure 3). However, to exclude any errors we have also prepared 14 and epimeric alcohol 16; its synthesis is shown in Scheme

Molecular architecture with carbohydrate functionalized β-peptides adopting 3₁₄-helical conformation

• Nitin J. Pawar,
• Navdeep S. Sidhu,
• George M. Sheldrick,
• Dilip D. Dhavale and
• Ulf Diederichsen

Beilstein J. Org. Chem. 2014, 10, 948–955, doi:10.3762/bjoc.10.93

• providing a positive Cotton effect at 215 nm for right-handed β3-peptides with 314-helix conformation. The helical content correlates with the signal intensity and can be enhanced especially by ACHC incorporation at positions i and i+3; it is hardly sensitive to pH and ionic strength [59]. The CD spectra of

• the β-glycopeptides 1–8 were measured at pH 7 in triethylammonium acetate buffer at various temperatures (Figure 5). A strong positive Cotton effect at 215 nm for β-glycopeptides 2–6 indicates a right-handed 314-helix conformation [4][5][6]. Even at 80 °C the helical content drops only about 20–40

• % depending on the kind of sugar units incorporated. Oligomers 1–6 all have in common the (S)-configuration for the β3-sugar side chains; this is in agreement with the right-handed 314-helix and a positive Cotton effect. Nevertheless, β3-peptide 1 seems to provide a different structure and helical sense

Molecular assembly of amino acid interlinked, topologically symmetric, π-complementary donor–acceptor–donor triads

• M. B. Avinash,
• K. V. Sandeepa and
• T. Govindaraju

Beilstein J. Org. Chem. 2013, 9, 1565–1571, doi:10.3762/bjoc.9.178

• percentage of water in DMSO a bisignated cotton effect was observed in the range of 300–400 nm, besides the appearance of two new bands at ~420 nm and ~550 nm. The band at ~420 nm could be attributed to the aggregation band of NDI, while the band at ~550 nm is assigned to the charge-transfer complexation of

Stereogenic boron in 2-amino-1,1-diphenylethanol-based boronate–imine and amine complexes

• Sebastian Schlecht,
• Walter Frank and
• Manfred Braun

Beilstein J. Org. Chem. 2011, 7, 615–621, doi:10.3762/bjoc.7.72

• the imine complex 8. Previously, we have been able to assign the absolute configuration to the complex 4a, a regioisomer of 8, by comparison of the measured and calculated CD spectra [18]. The (R)-enantiomer of 4a is characterized by an intense, positive Cotton effect at high wavelength. As a similar

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

• temperature (S,R)-1b shows negative Cotton effect at λ = 245 nm of moderate intensity which decreases on increasing temperature from 20 to 50 °C. Further temperature increase of the gel sample resulted in the appearance of a new negative CD peak at λ = 234 nm corresponding to the shoulder band in the gelator

An enantiomerically pure siderophore type ligand for the diastereoselective 1 : 1 complexation of lanthanide(III) ions

• Markus Albrecht,
• Olga Osetska,
• Thomas Abel,
• Gebhard Haberhauer and
• Eva Ziegler

Beilstein J. Org. Chem. 2009, 5, No. 78, doi:10.3762/bjoc.5.78

• exhibits Λ2 conformation in solution, too. The positive Cotton effect at 295 nm as well as the negative Cotton effect at 280 nm are found in both spectra. These effects derive from an exciton coupling [38] of the 8-hydroxyquinoline chromophore and therefore they can be used for the unambiguous

• wavelengths exhibit a positive Cotton effect. As the calculated maximum of the UV spectrum (530 nm) shows a bathochromic shift relative to the measured UV spectrum (470 nm), the corresponding peak in the calculated CD spectrum (540 nm) is shifted to higher wavelengths relative to the experimentally measured