Formation of a pseudo-ß-hairpin motif utilizing the Ant-Pro reverse turn: consequences of stereochemical reordering.

Herein, we report a special case of pseudo-ß-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.

Structure elucidation of ß-cyclodextrin-xylazine complex by a combination of quantitative (1)H-(1)H ROESY and molecular dynamics studies.

The complexation of xylazine with ß-cyclodextrin was studied in aqueous medium. (1)H NMR titrations confirmed the formation of a 1:1 inclusion complex. A ROESY spectrum was recorded with long mixing time which contained TOCSY artifacts. It only confirmed the presence of xylazine aromatic ring in the ß-cyclodextrin cavity. No information regarding the mode of penetration, from the wide or narrow side, could be obtained. We calculated the peak intensity ratio from the inter-proton distances for the most stable conformations obtained by molecular dynamics studies in vacuum. The results show that highly accurate structural information can be deduced efficiently by the combined use of quantitative ROESY and molecular dynamics analysis. On the other hand, a ROESY spectrum with no spin diffusion can only compliment an averaged ensemble conformation obtained by molecular dynamics which is generally considered ambiguous.

A tetrazine templated method for the synthesis of ternary conjugates.

Conjugation is an important reaction that enables coupling of molecules. Many protocols exist for the synthesis of binary conjugates from two different molecules or for the polyvalent display of a single molecule. There aren't many methods for the synthesis of ternary conjugates. However, methods for ternary conjugation are important for understanding the interplay of interactions between three biomolecules (or any three molecules per se). A strategy for ternary bioconjugation using inverse electron demand Diels-Alder reaction with tetrazine is studied. Ternary conjugation was demonstrated by the reaction of a model glyco-peptide binary conjugate with a fluorescent tagged olefin.

Switching the H-bonding network of a foldamer by modulating the backbone chirality and constitutional ratio of amino acids.

This communication describes the folding propensity of a heterofoldamer motif featuring proline (Pro) and anthranilic acid (Ant) residues in a 1:2:1 (α:ß:α) constitutional ratio. Structural investigations unequivocally suggest that the hydrogen-bonding network of this foldamer motif can be switched between 9-membered and 6-membered by modulating the backbone chirality and constitutional ratio of the amino acid residues.

Sugar furanoid trans-vicinal diacid as a γ-turn inducer: synthesis and conformational study.

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.