Stereoselective synthesis of N-galactofuranosyl amides

α- or β-Galactofuranosyl (Galf) amides can be synthesized with high stereoselectivity by traceless Staudinger ligation starting from unprotected β-galactofuranosyl azide or tetra-O-acetyl-β-galactofuranosyl azide, respectively. The resulting Galf amides are hitherto unknown molecules, with interesting potential as inhibitors of mycobacterial growth.     

New amides from the roots of Anisodus tanguticus

Two new amides (1 and 2) and four known analogues (3–6) were isolated from the roots of Anisodus tanguticus (Maxim.) Pascher. Their structures were determined by extensive spectroscopic analyses. The absolute configuration of compound 1 was determined by comparison of the calculated optical rotation (OR) value with the experimental OR value. All known amides were isolated from the genus Anisodus for the first time, of which compounds 3, 5, and 6 were first reported from the family Solanaceae. Furthermore, the chemotaxonomic significance of these secondary metabolites is discussed.     

Aliphatic acid amides of the fruits of Zanthoxylum piperitum

Six aliphatic acid amides (1-6) were isolated from the pericarp of Zanthoxylum piperitum fruits. MS and NMR spectroscopic investigation revealed that these compounds have a ketone and/or hydroxyl group(s) in the unsaturated aliphatic acid moiety of the structure of the amides. Combinations 3-4 and 5-6 are stereoisomers in terms of the relative configurations of their two asymmetric carbons.     

On the interaction of lithium salts with model amides

Results of a study of the interaction of alkali metal salts on model aliphatic amides are reported. Lithium salts appear to interact more strongly with amides than those of other alkali metals. Spectroscopic investigations suggest that Li⁺ ion binds to the amide group at the carbonyl oxygen, causing a change in the spectroscopic properties and the geometry of the amide. Such binding of ions to amide groups may be of importance when one studies the spectral and conformational changes of polypeptides and proteins in high salt media.     

Kerr constants of amides and peptides

Molar Kerr contants _mK have been determined for N-methylacetamide, N-ethyl-acatamide, N-methylpropionamide, N-acetylglycine-N′-methylamide, N-acetyl-L -ala-nine-N′-methylamide, and N-acetyl-L -leucine-N′-methylamide from electric birefringence measurements on dilute solutions in dioxane. The resultes are compared with configurational averatges 〈_mK〉 calculated on the basis of conformational energies. Values of_mK calculated for various fixed confromations on the peptides vary over a wide range depending on the choice of conformation; hece, the configurational averages 〈_mK〉 are sensitive to smalll changes in the conformational enerey. Kerr constants are calculated for random coiled oligoglycine and oligoalanine peptides as functions of chain length. The Kerr constant is an especially acute index of the average conformation.     

Sequential processing reactions in the formation of hormone amides

The substrate specificity of an enzyme with amidating activity, present in porcine pituitary, was investigated by examining its ability to convert the synthetic peptides D-Tyr-Val-Gly and D-Tyr-Val-Gly-Lys-Arg to the dipeptide amide D-Tyr-Val-CONH2. The purified enzyme catalysed the amidation reaction with the tripeptide but did not accept the pentapeptide as a substrate. With the mixture of enzymes present in a membrane fraction from porcine pituitary or the enzymes in a secretory granule fraction, both the tripeptide and pentapeptide substrates gave rise to D-Tyr-Val amide; the formation of dipeptide amide from the pentapeptide, however, involved a latency period after which amidation occurred at a similar rate with the two substrates. Evidence was obtained that arginine and lysine were released from the C terminus of the pentapeptide before amidation took place since the rate of formation of dipeptide amide was reduced at pH values that were compatible with amidation but unfavourable to the action of carboxypeptidase H. In addition formation of the dipeptide amide from the pentapeptide was blocked by guanidinoethylmercaptosuccinic acid and glycylarginine, which are inhibitors of carboxypeptidase enzymes. The experiments demonstrate that removal of basic residues from the C terminus of a peptide and amidation at C-terminal glycine are reactions that take place consecutively. These prohormone-processing reactions, which are intrinsic to the formation of hormone amides, did not synergise.     

Solid-phase preparation of amides using N-acylbenzotriazoles

Wang resin linked amines were efficiently converted into amides using acylbenzotriazoles. Cleavage of resins gave the desired amides 7Aa-Gf in 30-99% yields with good to excellent purities.     

Spilanthol-related amides from Acmella ciliata

From the flower heads of Acmella ciliata amides closely related to spilanthol were isolated. They possess isobutylamine, 2-phenylethylamine and 2-methylbutylamine parts. In the acidic part deca-2E,6Z,8E-trienoic acid, known from spilanthol, and its 2,3-dihydro derivative were found. Two compounds bear ester groups, a novelty for unsaturated amides. The structures were elucidated by means of high field ¹H NMR and high resolution mass spectrometry.