Patricia Verheyden

1H NMR study of the interaction of N,N′,N″-triacetyl chitotriose with Ac-AMP2, a sugar binding antimicrobial protein isolated from Amaranthus caudatus

The interaction between Ac‐AMP2, a lectin‐like small protein with antimicrobial and antifungal activity isolated from Amaranthus caudatus, and N,N′,N″‐triacetyl chitotriose was studied using 1H NMR spectroscopy. Changes in chemical shift and line width upon increasing concentration of N,N′,N″‐triacetyl chitotriose to Ac‐AMP2 solutions at pH 6.9 and 2.4 were used to determine the interaction site and the association constant K a. The most pronounced shifts occur mainly in the C‐terminal half of the sequence. They involve the aromatic residues Phe18, Tyr20 and Tyr27 together with their surrounding residues, as well as the N‐terminal Val‐Gly‐Glu segment. Several NOEs between Ac‐AMP2 and the N,N′,N″‐triacetyl chitotriose resonances are reported.

New amino acids derived from L-pyroglutamic acid: Synthesis of Trans-4-benzyl-cis-5-phenyl-L-proline, L-α-(2-benzyl-3-phenylpropyl)-glycine and L-α-(3-phenylpropyl)-glycine

Abstract A convenient synthesis of three new amino acids, L-α-(3-phenylpropyl)-glycine, L-α-(2-benzyl-3-phenylpropyl)-glycine and its conformationally constrained analog, trans-4-benzyl-cis-5-phenyl-L-proline is reported. All compounds were prepared in good diastereomeric or enantiomeric purity from L-pyroglutamic acid. Trans-4-benzyl-cis-5-phenyl-L-proline was prepared by benzylation of Boc-L-Pyr-OBn, ring opening with phenyllithium and subsequent cyclisation. Hydrogenolysis under mild conditions then furnished L-α-(2-benzyl-3-phenylpropyl)-glycine. In a similar way, L-α-(3-phenylpropyl)-glycine was prepared from cis-5-phenyl-L-proline by catalytic hydrogenolysis.

Equilibrium of the Cis-Trans Isomerisation of the Peptide Bond with N-alkyl Amino Acids Measured by 2D NMR

The conformational cis-trans equilibrium around the peptide bond in model tripeptides has been determined by 2D NMR methods (HOHAHA, ROESY). The study was limited to three different N-substituted amino acids in position 2, namely Pro (proline), Tic (1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid), and N-MePhe (N-methylphenylalanine). In all cases the amino acid in position 1 was tyrosine and in position 3, phenylalanine. The results of our studies show that the cis-trans ratio depends mostly on the configuration of the amino acids forming the peptide bond undergoing the cis-trans isomerisation. The amino acid following the sequence (in position 3) does not have much influence on the cis-trans isomerisation, indicating that there is no interaction of the side chains between these amino acids. The model peptides with the L-Tyr-L-AA-(L- or D-)Phe (where AA is N-substituted amino acid) chiralities give 80–100% more of the cis form in comparison to the corresponding peptides with the D-Tyr-L-AA-(L-or D-)Phe chiralities. These results indicate that the incorporation of N-substituted amino acids in small peptides with the same chirality as the precedent amino acid involved in the peptide bond undergoing the cis/trans isomerisation moves the equilibrium to a significant amount of the cis form.

Side reactions in the preparation of 1,2,3,4-tetrahydro-β-carboline-3-carboxylic acid

During a study on the preparation of the conformationally restricted analogue of tryptophan into 1,2,3,4-tetrahydro-β-carboline-3-carboxylic acid1 by a Pictet-Spengler condensation with formaldehyde, two site products were detected:N-hydroxymethyl-1,2,3,4-tetrahydro-β-carboline-3-carboxylic acid2 and a dimer3 of two 1,2,3,4-tetrahydro-β-carboline-3-carboxylic acid units linked by a methylene group. Their structures were determined by HPLC-MS and 2D NMR spectroscopy. By changing the isolation procedure, theN-hydroxymethyl compound was removed. Treatment of the mixture with TFA in water converted the dimer into 1,2,3,4-tetrahydro-β-carboline-3-carboxylic acid1.

Conformational study of three endothelin antagonists with 1H NMR at low temperature and molecular dynamics

The conformations of three endothelin antagonists, a cyclic pentapeptide, a linear tripeptide and a linear hexapeptide, are compared by 1H NMR and molecular dynamics. The three analogues have a Leu and a dTrp side chain which are oriented parallel, and an acidic group next to the dTrp residue.

The γ-methyl-E-olefin as isosteric replacement of the peptide bond

Abstract Different olefination methods on Boc-phenylalanine methyl ketone for the synthesis of γ-methyl-E-olefin Phe-Gly isosteres are investigated. The Horner phosphonate reagent gave the highest yield of E-isomer. The conformational behaviour of four tetrapeptides containing the E-olefin isostere with and without a vinyl methyl group is studied by 1 H NMR. No evidence for turn structures is found.

α-Bn-o-AMPA as a cis peptide bond mimic in somatostatin analogues

In a previous communication we reported the racemic synthesis of the cis peptide bond mimic α-benzyl-o-aminomethylphenylacetic acid and its incorporation in the cyclic somatostatin analoguesc[α(R andS)Bn-o-AMPA-Phe7-d-Trp8-Lys9-Thr10]. Since the epimeric peptides exhibit different binding affinities, we completed the structure-activity study with an asymmetric synthesis. A model for the solution conformation ofc[α(R andS)Bn-o-AMPA-Phe7-d-Trp8-Lys9-Thr10] is proposed on the basis of a 2D NMR study in CD3OH and restrained molecular dynamics.