Exploring a Ring-Closing Metathesis Approach to the Archazolid Macrocycle

Modular Total Synthesis of iso-Archazolids and Archazologs

Full details on the design, development, and successful implementation of suitable synthetic strategies directed toward the total synthesis of iso-archazolids and archazologs are reported. Both a biomimetic and a multistep total synthesis of iso-archazolid B, the most potent and least abundant archazolid, are described. The bioinspired conversion from archazolid B was realized by a high-yielding 1,8-Diazabicyclo[5.4.0]undec-7-ene catalyzed one-step double-bond shift. A highly stereoselective total synthesis was accomplished in 25 steps, involving a sequence of highly stereoselective aldol reactions, an efficient aldol condensation to forge two elaborate fragments, and a challenging ring-closing metathesis macrocyclization with an unusual Stewart-Grubbs catalyst. These strategies proved to be generally useful and could be successfully implemented for the preparation of three novel iso-archazolids as well as five novel archazologs, lacking the thiazole side chain. A wide variety of further archazolids and archazologs may now be targeted for exploration of the promising anticancer potential of these polyketide macrolides.

Design, Synthesis and Biological Evaluation of Highly Potent Simplified Archazolids

The archazolids are potent antiproliferative compounds that have recently emerged as a novel class of promising anticancer agents. Their complex macrolide structures and scarce natural supply make the development of more readily available analogues highly important. Herein, we report the design, synthesis and biological evaluation of four simplified and partially saturated archazolid derivatives. We also reveal important structure-activity relationship data as well as insights into the pharmacophore of these complex polyketides.

Total syntheses of the archazolids: an emerging class of novel anticancer drugs

V-ATPase has recently emerged as a promising novel anticancer target based on extensive in vitro and in vivo studies with the archazolids, complex polyketide macrolides which present the most potent V-ATPase inhibitors known to date, rendering these macrolides important lead structures for the development of novel anticancer agents. The limited natural supply of these metabolites from their myxobacterial source renders total synthesis of vital importance for the further preclinical development. This review describes in detail the various tactics and strategies employed so far in archazolid syntheses that culminated in three total syntheses and discusses the future synthetic challenges that have to be addressed.

Synthesis of a C1-C23 fragment of the archazolids and evidence for V-ATPase but not COX inhibitory activity

A convergent synthesis of a C1-C23 fragment of the archazolids has been completed based on a high yielding Stille coupling to costruct the substituted Z,Z,E-conjugated triene. After removal of the protecting groups, the resulting tetrol exhibited evidence for inhibition of the vacuolar-type ATPase (V-ATPase) but not cyclooxygenase (COX) inhibitory activity.

Synthesis of the C1-C17 fragment of the archazolids by complex cis-homodimer cross metathesis

A synthesis of the C1-C17 fragment of the archazolids is described featuring a complex cross-metathesis coupling reaction between a cis-homodimer (prepared by silyl-tethered ring-closing metathesis) and the Z,Z-terminal triene containing "eastern domain" of the archazolid natural products. This cross-metathesis was only successful when using the cis- as opposed to the monomer or trans-homodimer, with the cis-dimer added batchwise to minimize cis/trans-isomerization. The product was obtained in an optimized 78% yield using the Hoveyda-Grubbs catalyst at 50 °C in toluene.