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

• mixed with a chiral diol ligand forms complexes active in ECD in which a transfer of ligand chirality to the in situ-formed complex occurs in solution. Thus, stereochemistry of vic-diols can be easily assigned based on the helicity rule developed for this class of compounds. This rule correlates the

Synthesis of enantiomerically pure (2S,3S)-5,5,5-trifluoroisoleucine and (2R,3S)-5,5,5-trifluoro-allo-isoleucine

• Holger Erdbrink,
• Elisabeth K. Nyakatura,
• Susanne Huhmann,
• Ulla I. M. Gerling,
• Dieter Lentz,
• Beate Koksch and
• Constantin Czekelius

Beilstein J. Org. Chem. 2013, 9, 2009–2014, doi:10.3762/bjoc.9.236

• the K-4’-F3Ile spectrum demonstrates a complete loss of helicity in the corresponding peptide (Figure 2). The drastic decrease in helix propensity upon fluorination has been previously attributed to a possible burial of fluorocarbon side chains in the unfolded state of the model peptide [8]. The

• to a reduced α-helicity in comparison to its unbranched analogue ([ω]Leu= 1.06 [8]). This effect is amplified for K-4’-F3Ile which carries the voluminous CF3 group on its β-carbon atom. The close proximity of this sterically demanding group to the peptide backbone seems to prevent the formation of α

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

• excitonic cotton effects (Figure 3c–f). In DMSO, 2 (Figure 3c) and 3 (Figure 3e) exhibit a weak CD signal above 350 nm suggesting minimal excitonic coupling of NDI chromophores. However, CD studies for 2 (Figure 3d) and 3 (Figure 3f) in NMP show positive excitonic cotton effects indicating P-type helicity

Multivalent display of the antimicrobial peptides BP100 and BP143

• Imma Güell,
• Rafael Ferre,
• Kasper K. Sørensen,
• Esther Badosa,
• Iteng Ng-Choi,
• Emilio Montesinos,
• Eduard Bardají,
• Lidia Feliu,
• Knud J. Jensen and
• Marta Planas

Beilstein J. Org. Chem. 2012, 8, 2106–2117, doi:10.3762/bjoc.8.237

• mean residue ellipticity [θ] (deg cm2 dmol−1), calculated per mol of total amide groups present in the different peptides. The percentage helicity of the peptide was calculated as follows: α-helix (%) = , where [θ]222 is the experimentally observed absolute mean residue ellipticity at 222 nm. Values

Antifreeze glycopeptide diastereomers

• Lilly Nagel,
• Carsten Budke,
• Axel Dreyer,
• Thomas Koop and
• Norbert Sewald

Beilstein J. Org. Chem. 2012, 8, 1657–1667, doi:10.3762/bjoc.8.190

• recrystallization. The retro-inverso AFGP analogue 7 adopts a PPII helix with opposite helicity. The D-configured peptide backbone might, therefore, qualify for interaction with the achiral ice surface. However, the combination of a D-configured PPII helical peptide with the native D-GalNAc residues abolishes

• spectroscopy. According to these data, both peptides adopt polyproline II helical conformations, albeit with reduced propensity (5) or opposite helicity (7). The structure of the glycopeptides was correlated with their ability to inhibit ice growth in microphysical recrystallization assays. Both AFGP analogues

Design of a novel tryptophan-rich membrane-active antimicrobial peptide from the membrane-proximal region of the HIV glycoprotein, gp41

• Evan F. Haney,
• Leonard T. Nguyen,
• David J. Schibli and
• Hans J. Vogel

Beilstein J. Org. Chem. 2012, 8, 1172–1184, doi:10.3762/bjoc.8.130

• three amino acids: Lys, Leu and Trp [36]. Their results support the notion that the antimicrobial activity of a peptide is related to peptide amphipathicity and helicity as well as to the location of the Trp residues. However, their most potent peptide (LKWLLKWLL-NH2) also displayed significant

Control over molecular motion using the cis–trans photoisomerization of the azo group

• Estíbaliz Merino and
• María Ribagorda

Beilstein J. Org. Chem. 2012, 8, 1071–1090, doi:10.3762/bjoc.8.119

• and its α-helical conformation. The photoisomerization leads to the cis isomer, which disrupts this helicity inhibiting the association with DNA. The photoreversion to the trans isomer recovers again the final conformation of the α-helix of DNA. In 2011, the same group carried out the attachment of a

• process of azobenzene 26 [139]. The irradiation with light of the achiral trans isomer gives rise to the cis isomer with P helicity. A chiral clamp was synthesized, by anchoring a chiral cyclic imidazole peptide to both aromatic rings of azobenzene. The system is flexible enough to allow the isomerization

An easy α-glycosylation methodology for the synthesis and stereochemistry of mycoplasma α-glycolipid antigens

• Yoshihiro Nishida,
• Yuko Shingu,
• Yuan Mengfei,
• Kazuo Fukuda,
• Hirofumi Dohi,
• Sachie Matsuda and
• Kazuhiro Matsuda

Beilstein J. Org. Chem. 2012, 8, 629–639, doi:10.3762/bjoc.8.70

• 6–8). The isomer (Figure 4, entry 8) showed an overall conformational property similar to I-a and DPPC (Figure 5), although a small difference was observed in the conformer distribution at the sugar head moiety. However, it should be recognized here that the helical direction (helicity) of the gt

• ). At the lipid tail position, the gt-conformer with clockwise helicity is predominant over the anticlockwise gg-conformer. The observed conformation was very close to what we have seen in DPPC (Figure 5). Although these results were based on the solution state in a solvent mixture of CHCl3 and CH3OH

• conformational property similar to the natural isomer I-a and DPPC. However, it should be mentioned here that the chiral helicity of gt-conformers in I-b is reversed (anticlockwise) from the clockwise helicity of DPPC and GGPL-I. The difference in chirality seems critical in biological recognition events and

The interplay of configuration and conformation in helical perylenequinones: Insights from chirality induction in liquid crystals and calculations

• Elisa Frezza,
• Silvia Pieraccini,
• Stefania Mazzini,
• Alberta Ferrarini and
• Gian Piero Spada

Beilstein J. Org. Chem. 2012, 8, 155–163, doi:10.3762/bjoc.8.16

• essentially determined by the axial chirality (helicity) of the core of the perylenequinones. Keywords: chirality; conformational analysis; DFT calculations; helical twisting power; nematic liquid crystals; Introduction The phenomenon of chiral induction in nematic mesophases has been known for a long time

• ) [27], shown in Figure 1. They have the same stereochemical features: Two bulky methoxy groups or a strained seven-membered ring in positions 6 and 7, two side chains in positions 1 and 12 and a nonplanar helical shape. The helicity generates axial chirality, which, when associated with the presence of

• is that which is expected for helicoidal disc-like dopants, as binaphthyl derivatives [20] and helicene-like molecules [22][24], i.e., left-handed for the M and right-handed for the P molecular helicity. In view of the similar molecular shape of 1 and 2, the difference between the absolute values of

Synthesis of enantiomerically enriched (R)-¹³C-labelled 2-aminoisobutyric acid (Aib) by conformational memory in the alkylation of a derivative of L-alanine

• Stephen P. Fletcher,
• Jordi Solà,
• Dean Holt,
• Robert A. Brown and
• Jonathan Clayden

Beilstein J. Org. Chem. 2011, 7, 1304–1309, doi:10.3762/bjoc.7.152

• alanine by this method [36], and recently Soai showed that Seebach’s methods can be used to make selectively deuterated Aib [54]. In a previous paper [55], we reported the synthesis and use of a 13CH3-labelled Aib probe made by Kouklovsky’s method [36], to gather evidence of helicity switching in Aib

• , protected Aib (R)-6* for use in the synthesis, on gram scale, of spectroscopic probes for helicity [56]. Experimental (S)-2,2-Dimethyl-4-methyl-3-(1-naphthoyl)-oxazolidin-5-one (3): By a modification of the method of Branca [36][57], sodium hydride (575 mg of a 60% dispersion in mineral oil, 12.4 mmol) was

Towards racemizable chiral organogelators

• Jian Bin Lin,
• Debarshi Dasgupta,
• Seda Cantekin and
• Albertus P. H. J. Schenning

Beilstein J. Org. Chem. 2010, 6, 960–965, doi:10.3762/bjoc.6.107

• and coworkers have observed that the separate enantiomers assemble into fibers with opposite helicity while the racemic mixture yield nanoscale, spherical structures [15]. In order to create chiral response materials based on such systems, it would be interesting to develop organogelators that can be

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

• investigated by spectrophotometric methods. Only in the case of La3+ and Eu3+ were well defined 1 : 1 complexes formed. On the basis of CD spectroscopy and DFT calculations the configuration at the metal centre of the La3+ complex was determined to show Λ helicity. The coordination compounds [(1a)Ln] presented

• determination of the helicity. Even the Cotton effects at around 350 nm are of the same sign in both spectra. However, the calculations overestimate the intensity of this excitation; this overestimation can also be found in the calculated UV spectrum. Moreover, in both spectra the excitations at higher

• ) ions, while smaller cations lead to an unspecific complex formation (probably oligomerization or polymerization). On the basis of ab initio calculations and CD spectroscopy we could show that the formed complex (1a)La exhibits exclusively Λ helicity. We were able to isolate the corresponding lanthanum

Chiral amplification in a cyanobiphenyl nematic liquid crystal doped with helicene-like derivatives

• Alberta Ferrarini,
• Silvia Pieraccini,
• Stefano Masiero and
• Gian Piero Spada

Beilstein J. Org. Chem. 2009, 5, No. 50, doi:10.3762/bjoc.5.50

• , allows us to extend our knowledge of the molecular origin of the chirality amplification in liquid crystals and to confirm the simple relationship “molecular P-helicity” → “cholesteric P-handedness” for helical-shaped helicene-like derivatives. Keywords: chirality; cholesteric; helical twisting power

• , which, despite the clear structural helicity and the similar orientational behavior, exhibit no trivial relationship between molecular stereochemical descriptor (aR or aS) and cholesteric handedness (P or M) [50]. Changes in the molecular geometry, arising from the presence of substituents or

• conformational equilibria, can have a dramatic effect on the twisting ability of a dopant [2]. Moreover, in the case of dopants with low twisting power, cholesterics of opposite handedness may be induced in different LC solvents [8]. However, for solutes with clearly defined helicity and alignment axes, a weak