Evolution of an Efficient and Scalable Nine-Step (Longest Linear Sequence) Synthesis of Zincophorin Methyl Ester.

Abstract

Because of both their synthetically challenging and stereochemically complex structures and their wide range of often clinically relevant biological activities, nonaromatic polyketide natural products have for decades attracted an enormous amount of attention from synthetic chemists and played an important role in the development of modern asymmetric synthesis. Often, such compounds are not available in quantity from natural sources, rendering analogue synthesis and drug development efforts extremely resource-intensive and time-consuming. In this arena, the quest for ever more step-economical and efficient methods and strategies, useful and important goals in their own right, takes on added importance, and the most useful syntheses will combine high levels of step-economy with efficiency and scalability. The nonaromatic polyketide natural product zincophorin methyl ester has attracted significant attention from synthetic chemists due primarily to the historically synthetically challenging C(8)-C(12) all-anti stereopentad. While great progress has been made in the development of new methodologies to more directly address this problem and as a result in the development of more highly step-economical syntheses, a synthesis that combines high levels of step economy with high levels of efficiency and scalability has remained elusive. To address this problem, we have devised a new synthesis of zincophorin methyl ester that proceeds in just nine steps in the longest linear sequence and proceeds in 10% overall yield. Additionally, the scalability and practicability of the route have been demonstrated by performing all of the steps on a meaningful scale. This synthesis thus represents by a significant margin the most step-economical, efficient, and practicable synthesis of this stereochemically complex natural product reported to date, and is well suited to facilitate the synthesis of analogues and medicinal chemistry development efforts in a time- and resource-efficient manner.