Solution-Phase Parallel Synthesis of a Pharmacophore Library of HUN-7293 Analogues:  A General Chemical Mutagenesis Approach To Defining Structure−Function Properties of Naturally Occurring Cyclic (Depsi)peptides

Abstract

HUN-7293 (1), a naturally occurring cyclic heptadepsipeptide, is a potent inhibitor of cell adhesion molecule expression (VCAM-1, ICAM-1, E-selectin), the overexpression of which is characteristic of chronic inflammatory diseases. Representative of a general approach to defining structure-function relationships of such cyclic (depsi)peptides, the parallel synthesis and evaluation of a complete library of key HUN-7293 analogues are detailed enlisting solution-phase techniques and simple acid-base liquid-liquid extractions for isolation and purification of intermediates and final products. Significant to the design of the studies and unique to solution-phase techniques, the library was assembled superimposing a divergent synthetic strategy onto a convergent total synthesis. An alanine scan and N-methyl deletion of each residue of the cyclic heptadepsipeptide identified key sites responsible for or contributing to the biological properties. The simultaneous preparation of a complete set of individual residue analogues further simplifying the structure allowed an assessment of each structural feature of 1, providing a detailed account of the structure-function relationships in a single study. Within this pharmacophore library prepared by systematic chemical mutagenesis of the natural product structure, simplified analogues possessing comparable potency and, in some instances, improved selectivity were identified. One potent member of this library proved to be an additional natural product in its own right, which we have come to refer to as HUN-7293B (8), being isolated from the microbial strain F/94-499709.

Solution‐Phase Combinatorial Libraries: Modulating Cellular Signaling by Targeting Protein–Protein or Protein–DNA Interactions

“…[74] The subsequent implementation of this approach in the convergent parallel synthesis of a library of key analogues of HUN-7293 was used to define in detail the structure-function relationships of the natural product (Scheme 15). [75,76] A solution-phase approach to the simultaneous preparation of the library was utilized enlisting simple acid-base liquid-liquid extractions for isolation and purification of the synthetic intermediates and final products (Scheme 16). Notably, this approach provided each intermediate and final product sufficiently pure for subsequent use even in the multistep synthesis of HUN-7293 and its structurally challenging analogues.…”

“…[76] As discussed in Section 6.1, a solid-phase synthesis of the library would require a parallel linear synthesis of each analogue, whereas the implementation of a solution-phase convergent synthesis allowed the single synthesis of the key tri-and tetrapeptide subunits of the natural product (3 and 4) and their respective combination with diversified tetra-and tripeptides containing single-point changes in the HUN-7293 structure (Scheme 2). Thus, the advantages commonly associated with a convergent synthesis were combined with those of a divergent synthesis to provide a family of closely related structures.…”

Kombinatorische Flüssigphasensynthese von Bibliotheken: auf der Suche nach Modulatoren für Protein‐Protein‐ und Protein‐DNA‐Wechselwirkungen in der zellulären Signaltransduktion

“…[76] Bei einer Festphasenstrategie wäre die parallele lineare Synthese jedes Analogons erforderlich -bei einer konvergenten Synthese in flüssiger Phase genügt die einmalige Synthese der entscheidenden Tri-und Tetrapeptideinheiten des Naturstoffs (3 und 4) und ihre Kombination mit diversifizierten Tetra-bzw. Tripeptiden mit einzelnen Unterschieden zur HUN-7293-Struktur (Schema 2).…”

“…[74] Die konvergente Parallelsynthese einer Bibliothek von HUN-7293-Schlüsselanaloga ermöglichte die detaillierte Aufklärung der Struktur-Wirkungs-Beziehung dieses Naturstoffs (Schema 15). [75,76] Die Mutagenese durch Austausch von Aminosäuren gegen Alanin ("Alanin-Scan") ist aufschlussreich, um Epitope in Proteinen festzulegen. [416] Indem man jede einzelne Aminosäure-Seitenkette durch eine Methylgruppe ersetzt, ohne die Konformation des Peptidrückgrats zu verändern, kann man die Bedeutung der einzelnen Seitenketten erkennen.…”

Targeting HER3 by interfering with its Sec61-mediated cotranslational insertion into the endoplasmic reticulum

“…Lapatinib was purified from commercial Tykerb tablets by organic extraction as previously described 2 . CT8 was synthesized using modifications of published protocols 9,32 . Bortezomib was obtained from Selleckchem.com.…”