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This communication describes the influence of β-aminobenzenesulfonic acid ((S)Ant) on the conformational preferences of hetero foldamers. The designed (Aib-(S)Ant-Aib)n and (Aib-(S)Ant-Pro)n oligomers display a well-defined folded conformation featuring intramolecular mixed hydrogen bonding (7/11) and intra-residual (6/5) H-bonding interactions, respectively.

Herein, we report a special case of pseudo-β-hairpin formation by tetrapetide sequences featuring a two-membered Ant-Pro dipeptide motif (Ant = anthranilic acid and Pro = proline) at the loop region. These folded structures uniquely feature the presence of C9- and C17-H-bonding patterns at reverse turn and interstrand regions, respectively. Their hairpin nucleation and folding propensities have been expounded using solution and solid state studies of distinct stereochemically altered sequences.

Although known for their inferiority as hydrogen-bonding acceptors when compared to amides, esters are often found at the C-terminus of peptides and synthetic oligomers (foldamers), presumably due to the synthetic readiness with which they are obtained using protected peptide coupling, deploying amino acid esters at the C-terminus. When the H-bonding interactions deviate from regularity at the termini, peptide chains tend to "fray apart". However, the individual contributions of C-terminal esters in causing peptide chain end-fraying goes often unnoticed, particularly due to diverse competing effects emanating from large peptide chains. Herein, we describe a striking case of a comparison of the individual contributions of C-terminal ester vs. amide carbonyl as a H-bonding acceptor in the folding of a peptide. A simple two-residue peptide fold has been used as a testing case to demonstrate that amide carbonyl is far superior to ester carbonyl in promoting peptide folding, alienating end-fraying. This finding would have a bearing on the fundamental understanding of the individual contributions of stabilizing/destabilizing non-covalent interactions in peptide folding.

Dimedone derivatives (L1-L4) with methyl substitution at the ortho, para and meta positions were synthesized and their anti-radical, photoreactive and photostability activities were evaluated. All compounds are characterized by spectroscopic techniques and by single crystal X ray diffraction. UV exposure experiments on pBR322 showed inhibition of plasmid DNA fragmentation by UV radiation in a dose dependent manner. Radical scavenging assays and ESR spectra indicate that these compounds possess antiradical activities and do not photodegrade to form other side products as confirmed by chromatographic analysis. They are non-cytotoxic towards human keratinocyte HaCaT cell line indicates their potentiality in sunscreens., (© Georg Thieme Verlag KG Stuttgart · New York.)

A simple method for the synthesis of a sugar furanoid trans vicinal diacid and its incorporation into the N-terminal tetrapeptide sequence (H-Phe-Trp-Lys-Thr-OH) to get glycopeptide has been described. 2D NMR and MD simulation studies of clearly show that the sugar diacid adopts a γ-turn conformation towards the N-terminus.

Strikingly dissimilar hydrogen-bonding patterns have been observed for two sets of closely similar hetero foldamers containing carboxamide and sulfonamides at regular intervals. Although both foldamers maintain conformational ordering, the hydrogen-bonding pattern and backbone helical handedness differ diametrically.

Orthanilic acid (2-aminobenzenesulfonic acid, (S)Ant), an aromatic β-amino acid, has been shown to be highly useful in inducing a folded conformation in peptides. When incorporated into peptide sequences (Xaa-(S)Ant-Yaa), this rigid aromatic β-amino acid strongly imparts a reverse-turn conformation to the peptide backbone, featuring robust 11-membered-ring hydrogen-bonding.

In the title compound, C(21)H(18)N(2)OS(2), a strong intramolecular N-H...O hydrogen bond [N...O = 2.642 (3) Å] between the amide N atom and the benzoyl O atom forms an almost planar six-membered ring in the central part of the molecule. In the crystal, molecules are packed through weak N-H...S interactions. Intra- and intermolecular hydrogen bonds and van der Waals interactions are the stabilizing forces for the crystal structure.

Two folded peptides featuring carboxamide and sulfonamide at the core of the peptide fold have been shown to possess almost similar conformational features, despite the well-known fact that carboxamides and sulfonamides have strikingly different hydrogen-bonding and geometrical preferences.

This communication describes a set of hybrid foldamers that do not feature inter-residual, but intra-residual backbone hydrogen-bonding, yet adopt a preferentially folded conformation displaying right-handed helical architecture. Conformational ordering is apparently due to the combined conformational restrictions imposed by the conformationally restricted individual amino acid residues with which the oligomers are made of.