Complexation Behavior of Pinene–Bipyridine Ligands towards Lanthanides: The Influence of the Carboxylic Arm

The complexation behavior of two novel, chiral pinene–bipyridine-type ligands ((–)-HL1 and (–)-HL2) containing a carboxylic arm towards lanthanide Ln(III) (Ln = La, Eu, Lu) ions was investigated through spectroscopic methods. The association constants of the mononuclear complexes determined from the UV-Vis titrations indicated that the ligand (–)-HL1 possessing a shorter carboxylic arm formed more stable complexes compared with (–)-HL2, whose carboxylic arm had one more methylene unit. This is due to the formation of more stable seven-member metal chelate rings in the first case as compared with the eight-member metal chelate rings in the second. IR and fluorescence spectroscopy provided additional information about the structure of these complexes.

Radical Formation in Sugar-Derived Acetals under Solvent-Free Conditions

The degradation of acetal derivatives of the diethylester of galactarate (GalX) was investigated by electron paramagnetic resonance (EPR) spectroscopy in the context of solvent-free, high-temperature reactions like polycondensations. It was demonstrated that less substituted cyclic acetals are prone to undergo radical degradation at higher temperatures as a result of hydrogen abstraction. The EPR observations were supported by the synthesis of GalX based polyamides via ester-amide exchange-type polycondensations in solvent-free conditions at high temperatures in the presence and in the absence of radical inhibitors. The radical degradation can be offset by the addition of a radical inhibitor. The radical is probably formed on the methylene unit between the oxygen atoms and subsequently undergoes a rearrangement.

Receptor selectivity from minimal backbone modification of a polypeptide agonist

Human parathyroid hormone (PTH) and N-terminal fragments thereof activate two receptors, hPTHR1 and hPTHR2, which share ∼51% sequence similarity. A peptide comprising the first 34 residues of PTH is fully active at both receptors and is used to treat osteoporosis. We have used this system to explore the hypothesis that backbone modification of a promiscuous peptidic agonist can provide novel receptor-selective agonists. We tested this hypothesis by preparing a set of variants of PTH(1–34)-NH2 that contained a single β-amino-acid residue replacement at each of the first eight positions. These homologs, each containing one additional backbone methylene unit relative to PTH(1–34)-NH2 itself, displayed a wide range of potencies in cell-based assays for PTHR1 or PTHR2 activation. The β-scan series allowed us to identify two homologs, each containing two α→β replacements, that were highly selective, one for PTHR1 and the other for PTHR2. These findings suggest that backbone modification of peptides may provide a general strategy for achieving activation selectivity among polypeptide-modulated receptors, and that success requires consideration of both β2- and β3-residues, which differ in terms of side-chain location.

The synthesis and structural characterization of twin liquid crystalline perylenebisimides

A smectic to nematic LC phase switch is achieved by changing one methylene unit in the central spacer segment.

adj-Dicarbachlorin, the first free base carbaporphyrinoid system with an internal methylene unit

Base-catalyzed condensation of dicyclopentadienylmethane with a dipyrrylmethane dialdehyde gave a dicarbachlorin with an internal CH2 group.

Conformational steering in dicarboxy acids: the native structure of succinic acid

The torsional freedom of the carbon backbone and hydroxyl groups induces numerous plausible conformers. Rotational spectroscopy supported by quantum chemical methods evidences that the “folding of methylene unit” is favoured.

Crystal structure of 1-(piperidin-1-yl)butane-1,3-dione

In the title compound, C9H15NO2, the piperidine ring exhibits a chair conformation. The butanedione subunit exhibits a conformation with the ketone C atom in an eclipsed position with respect to the amide carbonyl group. In the crystal, a two-dimensional layered arrangement is formed by hydrogen bonds of the C—H...O type between the methyl group and the exocyclic methylene unit as donor sites and the amide carbonyl O atom as the acceptor of a bifurcated hydrogen bond. These layers are oriented parallel to theabplane.