Ernst Haslinger

The first structurally confirmed saponin from Solidago gigantea: structure elucidation by modern NMR techniques

Abstract A new bisdesmosidic triterpene saponin, containing ten carbohydrate residues has been isolated from Solidago gigantea var. serotina. The structure was determined mainly by NMR, using selective excitation by Gaus-shaped pulses in combination with multi-step relayed coherence transfer experiments.

The conformation of cyclo[l-pro-l-leu-l-val-(gly)thz-(gly)thz], a dolastatin 3 analog, in the crystalline and solution states

Abstract Cyclo[L-Pro-L-Leu-L-Val-(gly)Thz-(gly)Thz], (1), has been prepared in high yield using pentafluorophenol in the ring closure reaction. This dolastatin 3 analog has been subjected to crystal structure analysis (space-group P65, a = b = 34.897(9), c = 24.611(10)A, asymmetric unit contents:(C26H35N7O5S2)4·(C7H8)7·(CH30H)4, ϱcalc = 1.202gcm-3.) and solution (CDCl3 and DMSO-d6) studies using 1H- and 13C-NMR techniques. The molecule has been found to adopt a clearly preferred conformation both in the crystal and in solution. The conformation contains a cis (gly)Thz-Pro peptide bond and two intramolecular hydrogen bonds, one from Leu-NH to a thiazole endocyclic nitrogen atom and the other from a (gly)Thz-NH to the Leu-C=O. The results of this study not only demonstrate that the conformation of (1) is very similar in the crystal and solution, but also provide conclusive evidence that the conformation proposed by Bernier, et al 4. earlier is incorrect. The crystal packing demonstrates that (1) is a very hydrophobic cyclopeptide with a tendency to self associate. In the crystal (1) associates via systematic hydrogen bonding to form a network of interlocking hydrophobic tubes filled with toluene molecules. The solvent molecules migrate out of the crystals on exposure to air resulting in fragmentation.

Synthesis of 12-methoxyabietic acid methylester, a feeding deterrent of the larch sawflyPristiphora erichsonii (Hartig)

The diastereomeric methylesters of 12-methoxyabietic acid, an antifeedant for the larch sawflyPristiphora erichsonii (Hartig) have been synthesised from abietic acid methylester (2). The unknown configuration at C-12 of the natural product has been determined by comparing the spectral and analytical data of the synthesised compounds with data given in the literature for the natural product as being (S).Zusammenfassung12-Methoxyabietinsäuremethylester spielt eine Rolle als Repellent beim Freßverhalten der Larven vonPristiphora erichsonii (Hartig). Es wird die erstmalige Synthese (ausgehend) von Abietinsäuremethylester (2, in zwei Stufen) beschrieben. Beide Diastereomere wurden erhalten. Aufgrund von Vergleichen der spektroskopischen und analytischen Daten der Produkte mit den Literaturdaten des Naturproduktes konnte die Konfiguration an C-12 für den Naturstoff mit (S) festgelegt werden.

Synthetische Umwandlung des Abietinsäuregerüstes. Abbau der Carboxylfunktion

SummaryAluminiumoxide-induced rearrangement of the tosylate7 (derived from abietic acid methyl ester byLAH reduction and Tosylation), leads under migration of CH3-4 to a mixture of exocyclic and endocyclic olefines8 – 11. Photochemical isomerisation of these olefines yields the endocyclic isomer10 as single product.

Conformational behaviour ofZ-Pro-(thr)Ox-OMe in solution

The dipeptideZ-Pro-(thr)Ox-OMe was studied with respect to its conformation in solution using NMR spectroscopic methods. It is shown that two conformers exist at room temperature which are related to each other by acis-trans—isomerization of theZ-Pro—peptide bond. The free energy of activation of the process is estimated.ZusammenfassungDas DipeptidZ-Pro-(thr)Ox-OMe wurde mittels Kernresonanzspektroskopie im Hinblick auf seine Konformation in Lösung untersucht. Die erhaltenen Daten weisen auf das Vorliegen von zwei Konformeren bei Raumtemperatur hin, die durch einecis-trans-Isomerierung derZ-Pro-Peptidbindung ineinander übergehen. Die freie Aktivierungsenergie der Konformationsumwandlung konnte abgeschätzt werden.