Synthesis and biological activity of cyclolinopeptide A analogues modified with γ-bis(homo-phenylalanine).

Cyclolinopeptide A (CLA), an immunosuppressive nonapeptide derived from linen seeds, was modified with S or R-γ-bis(homo-phenylalanine) in positions 3 or 4, or both 3 and 4. These modifications changed the flexibility of new analogues and distribution of intramolecular hydrogen bonds. Analogues 11 c(Pro-Pro-Phe-S-γ-hhPhe-Leu-Ile-Ile-Leu-Val), 13 c(Pro-Pro-S-γ-hhPhe-R-γ-hhPhe-Leu-Ile-Ile-Leu-Val) and 15 c(Pro-Pro-R-γ-hhPhe-Phe-Leu-Ile-Ile-Leu-Val) existed as a mixture of stable cis/trans isomers of Pro-Pro peptide bond.

Synthesis and biological activity of cyclolinopeptide A analogues modified with γ(3)-bis(homophenylalanine).

Cyclolinopeptide A, naturally occurring immunomodulatory nonapeptide, was modified with S or R-γ(3)-bis(homophenylalanine) in positions 3 or 4, or both 3 and 4. The replacement of one or both Phe residues by γ(3)-hhPhe led to decrease of their conformational flexibility in the analogues in comparison to CLA. All cyclic peptides, except 11, exist as isomers with the cis Pro-Pro peptide bond.

Phosphate additives determination in meat products by 31-phosphorus nuclear magnetic resonance using new internal reference standard: hexamethylphosphoroamide.

New (31)P NMR internal reference standard - hexamethylphosphoroamide (HMPA) was applied for determination of added polyphosphates and their ionic forms in raw pork meat and meat products. Phosphate species were determined after extraction with a boric acid buffer (pH=9) and EDTA solution, using internal standard (HMPA) procedure. Hexamethylphosophoroamide was also used as the NMR reference standard.

Solid state NMR spectroscopy as a precise tool for assigning the tautomeric form and proton position in the intramolecular bridges of o-hydroxy Schiff bases.

Two analogous Schiff bases, (S,E)-2-((1-hydroxy-3-methyl-1,1-diphenylbutan-2-ylimino)methyl)phenol (1) and (S,Z)-2-hydroxy-6-((1-hydroxy-3-methyl-1,1-diphenylbutan-2-ylamino)methylene)cyclohexa-2,4-dienone (2), exist in the solid state as phenol-imine and keto-amine tautomers, respectively. Their crystal structures were solved using the X-ray diffraction method. Sample 1 forms orthorhombic crystals of space group P2(1)2(1)2(1), while 2 forms monoclinic crystals of space group P2(1).