A total synthesis of natural (+)-duocarmycin SA (1) was achieved as shown in Chart 1, starting from L-malic acid (5) by using a Lewis acid-mediated indole formation reaction of a pyrrole precursor 14 to form the key compound 15.
Preparation of Alkyl-Substituted Indoles in the Benzene Portion. Part 15.1 Asymmetric Synthesis of (+)-Duocarmycin SA Using Novel Procedure for Preparation of Hydroxyindoles.
An asymmetric total synthesis of natural (+)-duocarmycin SA (1) starting from L-malic acid (7) was achieved as shown in Chart 5, establishing firmly the absoluteconfiguration of 1. In order to find suitable reaction conditions for the key step, i.e., the formation of an alkoxyindole derivative, model compounds 9 and 40 were synthesized and two acetalization conditions using i) 2-ethyl-2-methyl-1,3-dioxane