Spectroscopic study of monosubstituted amides. II. Rotation isomers in amides substituted by aliphatic side-chain models

The influence of the substituents upon the Amide I and νNH frequencies has been analyzed for ten amides substituted by aliphatic side chains. By considering the aliphatic chain field effect, some data are obtained as to the conformation of the N? C_α bond. In two amides, the presence of an equilibrium between two conformers is shown and a semiquantitative estimation of the energies involved is obtained. The consequences for polypeptides conformation, especially for poly-L -valine, are discussed.     

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.     

Lipase-catalyzed transamidation of non-activated amides in organic solvent

A novel biocatalytic reaction of transamidation of non-activated amides with amines is reported. Among 45 different lipolytic and proteolytic enzymes tested, only the lipase from Candida antarcticawas able to catalyze this reaction. The reaction proceeded with up to ca. 80% conversion in anhydrous methyl tert-butyl ether and worked with both N-substituted and unsubstituted amides. The biocatalytic transamidation is an equilibrium process and, therefore, higher conversions to the desired amide were achieved by using increased concentrations of the amine nucleophile.     

Optical anisotropies of amides and peptides in dioxane

The molar Kerr constants _mK, molar refractions _mR, and dipole moments μ are reported for the N-methylacetamides CX₃CONHCH₃ (X = H, CH₃, F. CI, Br) and acetamides CX₃CONH₂ (X = H, F, Cl, Br). The components of the polarizability tensor α are deduced for N-methylacetamide and acetamide on the basis of the bond additivity approximation. This α is found to be considerably more anisotropic than was indicated in previous determinations by other methods. The data for N-methylacetamide were used to calculate _mK, μ, and γ² (anisotropy squared) of N-acetyl-N′-methylglycine amide and N-acetyl-N′-methyl-alanine amide as functions of the torsional angles (?,Ψ). The statistical mechanical averages of _mK, μ, and γ² were calculated from conformational energies obtained by the methods of Scheraga.     

Production of phenylpropanoid amides in recombinant Escherichia coli

Plant-specific phenylpropanoid amides were produced in a recombinant Escherichia coli that expressed 4-coumarate:coenzyme A ligase from Arabidopsis and serotonin N-hydroxycinnamoyltransferase from pepper plants. Upon exogenous treatment with several precursors, high concentrations of the following phenylpropanoid amides were produced abundantly in the culture medium in a few hours: 4-coumaroylserotonin (215 mg/l), 4-coumaroyloctopamine (208 mg/l), and 4-coumaroyltyramine (187 mg/l).     

Optical activity of simple cyclic amides in solution

The cyclic dipeptide, L -alanylglycyl anhydride, has been studied by optical rotatory dispersion; both L -alanylglycyl anhydride and the lactam, L -3-aminopyrrolidin-2-one, have been studied by circular dichroism. In hydroxylic solvents the circular dichroism spectra of 3-aminopyrrolidin-2-one can be attributed to an n–π* transition near 220 mμ and a π–π* transition near 190 mμ. In these solvents the optical activity of L -alanylglycyl anhydride can be explained as being due to contributions of n–π* transitions and a split π–π* transition. In acetonitrile, however, the circular dichroism spectrum of 3-aminopyrrolidin-2-one shows an additional apparent minimum near 200 mμ. The CD spectrum of the dipeptide is also quite distinctive in this solvent. The possible nature of the band at 200 mμ and the implications of these findings are discussed.     

Identification of fatty acid amides in human plasma

A family of five long-chain fatty acid carboxamides has been identified and semi-quantified in human plasma by GC-MS. One saturated and four unsaturated amides were found. Luteal phase plasma from 16 women was studied, and all five of the amides were found in ten of the subjects, but none in the other six. The structure of these endogenous amides was established by comparing their GC and MS characteristics with those of the synthetic amides prepared by ammonolysis of corresponding long-chain fatty acid acyl chlorides.     

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.     

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.     

Further amides from Echinacea purpurea

The aerial parts of Echinacea purpurea afforded, in addition to known compounds, five further highly unsaturated amides and a derivative of linolen