Macrocyclic peptides are an important class of bioactive substances. When inserting an aromatic foldamer segment in a macrocyclic peptide, the strong folding propensity of the former may influence the conformation...
Hybrid sequences comprising a peptide with several Cys residues and an aromatic foldamer helix with several chloroacetamide functions at its surface were synthesized. Such products may in principle form numerous macromulticyclic thioether products by intramolecularly combining all Cys residues and all chloroacetamide functions. However, we show that the reactive sites on the structurally defined helix can be placed at such locations that the peptide selectively stitches itself to form a series of different macrocycles within mostly one preferred product. Reactions were monitored by HPLC and products with two, three or four macrocycles were identified using LC-MS and NMR. The series of selective macrocyclizations define a sort of reaction trail where reaction sites otherwise identical are involved successively because of their precise positioning in space. The trails can be predicted to a large extent based on structural considerations and the assumption that smaller macrocycles form faster.
Es wurden hybride Sequenzen synthetisiert, die Peptide mit einer Reihe von Cystein-Resten und aromatische Foldamer-Helices mit mehreren Chloracetamid-Funktionen an ihrer Oberfläche umfassen. Solche Produkte können im Prinzip zahlreiche makromultizyklische Thioetherbrücken bilden, indem sie alle Cys-Reste und alle Chloracetamidfunktionen intramolekular verbinden. Wir zeigen indes, dass die reaktiven Stellen auf der strukturell definierten Helix an solchen Positionen platziert werden können, so dass das Peptid selektiv reagiert, um eine Reihe unterschiedlicher Makrozyklen innerhalb meist eines bevorzugten Produkts zu bilden. Die Reaktionen wurden mittels HPLC überprüft und die Produkte mit zwei, drei oder vier Makrozyklen wurden mittels LC-MS und NMR identifiziert. Die Reihe selektiver Makrozyklisierungen definiert eine Art Reaktionspfad, bei dem ansonsten identische Reaktionsstellen aufgrund ihrer genauen Positionierung im Raum nacheinander beteiligt sind. Die Reaktionspfade lassen sich weitgehend auf der Grundlage struktureller Überlegungen und der Annahme, dass sich kleinere Makrozyklen schneller bilden, vorhersagen.
A helical aromatic foldamer was identified that undergoes tRNA acylation by a flexizyme and ribosomal peptide initiation with yields sufficiently high to perform an mRNA display selection of macrocyclic foldamer-peptide hybrids. A hybrid macrocyle binder to the C-lobe of the E6AP HECT domain was selected that showed highly converged peptide residues. A crystal structure and molecular dynamics simulations revealed that both the peptide and foldamer are helical in an intriguing reciprocal stapling fashion. The strong residue convergence could be rationalized based on their involvement in specific interactions. The foldamer stabilizes the peptide helix through stapling and through contacts with key residues. It appears to also contribute to protein binding by direct protein interactions. The results altogether highlight possible benefits in inserting an aromatic foldamer into a peptide macrocycle for the purpose of protein recognition.
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