Georges Van Binst

Assignment of amino acids in peptides by correlation of α-hydrogen and carbonyl carbon-13 resonances

Abstract A 1H-13C 2D-correlated experiment has been used to obtain the connectivities between every a proton and the two 13C carbonyls belonging, respectively, to the same and the next amino acid. From such connectivities all proton spin systems may be assigned to individual amino acids. The technique is compared with other methods and the example of the tetrapeptide CH3CO-Thr-Phe-Thr-Ser-NH2 is discussed.

Saponins fromTridesmostemon claessenssi

Abstract Two new saponins have been isolated from Tridesmostemon claessenssi and their structures determined using a combination of 1 H and 13 C NMR, and californium plasma desorption mass spectrometry. They are 3- O -[β- d - glucopyranosyl-(1→6)-β- d -glucopyranosyl]-28- O -[α- l -rhamnopyranosyl(1→3)-β- d -Xylopyranosyl-(1→4)-(α- l -rhamnopyranosyl-(1→3))-α- l -rhamnopyranosyl-(1→2)-β- d -xylopyranosyll-16α-hydroxyprotobassic acid for which we propose the name of tridesmosaponin A and 3- O -[α- l -rhamnopyranosyl]-28- O -[(α- l -rhamnopyranosyl-(1→3))-(α- l - rhamnopyranosyl]-(1→4))-β- d -Xylopyranosyl-(1→4)-α- l -rhamnopyranosyl-(1→2)-β- d -xylopyranosyl]-16α-hydroxy- protobassic acid which we propose to name tridesmosaponin B. Their genin is the novel triterpene, 16α- hydroxyprotobassic acid. The ester chain of sugars is characterized by the unusual 1 C 4 conformation of its β- d -Xylose.

Identification and sequencing of sugars in an acetylated saponin of Blighia welwitschii by n.m.r. spectroscopy

Abstract High-resolution 2D 1 H-n.m.r. spectroscopy has been used to establish the structure of an acetylated pentasaccharide saponin from the fruit of Blighia welwitschii as acetylated 3β- O -[β- d -Xyl p -(1→3)-α- l -Ara p -(1→4)-β- d -Glc p -(1→3)-α- l -Rha p -(1→2)-α- l -Ara p ]hederagenin .

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.

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.

1H AND 31P NMR Spectroscopy of Agrocinopine

Abstract The 1H NMR data of agrocinopine in D2O solution as extracted from standard 2D NMR experiments, along with 1D 31P and 13C NMR experiments allow to support the trisaccharide structure originally proposed on basis of comparative 13C NMR measurements.

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.