Novel triazolopeptides: chirospecific synthesis and conformational studies of proline derived analogs

Replacing the backbone amide function by a heterocyclic bioisostere, [3+2] azide-alkyne cycloaddition has been applied for the construction of biologically relevant peptidomimetics. Starting from aminoalkynoates, triazole formation was accomplished by addition of hydrazoic acid. NMR studies displayed that the newly developed 4,5-triazolopeptides, which incorporate a biomimetic triazole NH-function as polar constraint element, showed a substantially higher tendency to form a cis-prolyl-geometry than a comparable native peptide sequence.     

Substitution effect on the regioselective halogen/metal exchange of 3-substituted 1,2,5-tribromobenzenes

Regioselective halogen/metal exchange reactions using isopropylmagnesium chloride were studied on 3-substituted 1,2,5-tribromoarenes. Seven examples are given.     

A New Supramolecular Assembly Formed by Melamine and Sulfuric Acid

Polymeric melaminium sulfate [(LH₂)₂(SO₄)₂]_n has been synthesized by reaction of melamine L with sulfuric acid in aqueous solution. The compound was characterized by elemental analysis, ¹H NMR, ESI MS and a single crystal X‐ray diffraction analysis. The architecture of the assembly formed is based on hydrogen bonded dimers of diprotonated melaminium cations (LH₂)²⁺ which are linked by a hydrogen bonded network with sulfate ions forming 2D sheets. A 3D polymeric structure results from the presence of mutual hydrogen bonds between sulfate ions and melaminium cations in different sheets. Significant π‐π stacking is also present between the aromatic cations in this supramolecular arrangement.     

Planning a purely translational motion for a convex object in two-dimensional space using generalized Voronoi diagrams

AnO(n logn) algorithm for planning a purely translational motion for a simple convex object amidst polygonal barriers in two-dimensional space is given. The algorithm is based on a new generalization of Voronoi diagrams (similar to that proposed by Chew and Drysdale [1] and by Fortune [2]), and adapts and uses a recent technique of Yap for the efficient construction of these diagrams.Work on this paper by the second author has been supported in part by a grant from the U.S.-Israeli Binational Science Foundation.