In this article, full details regarding our total synthesis of avrainvillamide and the stephacidins are presented. After an introduction and summary of prior synthetic studies in this family of structurally complex anticancer natural products, the evolution of a final synthetic approach is described. Thus, a thorough description of three separate model studies is provided for construction of the characteristic bicyclo[2.2.2]diazaoctane ring system common to these alkaloids. The first and second approaches sought to build the core using formal Diels-Alder and vinyl radical pathways, respectively. Although these strategies failed in their primary objective, they fostered the development of a new and mechanistically intriguing method for the synthesis of indolic enamides such as those found in numerous bioactive natural products. The scope and generality of this simple method for the direct dehydrogenation of tryptophan derivatives is described. Finally, details of a third and successful route to the core of these alkaloids are described which features oxidative C-C bond formation. Specifically, the first heterocoupling of two different types of carbonyl species (ester and amide) is accomplished in good yield, on a preparative scale, and with complete stereocontrol. The information gained in these model studies enabled an enantioselective total synthesis of stephacidin A. The absolute configuration of these alkaloids was firmly established in collaboration with Professor William Fenical. A full account of our successful efforts to convert stephacidin A into stephacidin B via avrainvillamide is presented. Finally, the first analogues of these natural products have been prepared and evaluated for anticancer activity.
Enantioselective total syntheses of the naturally occurring forms of the highly oxidized indole alkaloids avrainvillamide (CJ‐17,665) and stephacidin B (see formula) are reported, facilitated by a remarkable oxidation of stephacidin A. A streamlined route to stephacidin A is also reported along with the absolute configuration determination of this family of natural products.
Die enantioselektiven Totalsynthesen der natürlich vorkommenden hoch oxidierten Indol‐Alkaloide Avrainvillamid (CJ‐17,665) und Stephacidin B (siehe Formel) werden durch eine bemerkenswerte Oxidation von Stephacidin A erleichtert. Eine verbesserte Route zu Stephacidin A wird ebenso beschrieben wie die Bestimmung der Absolutkonfiguration dieser Naturstoff‐Familie.
Ein attraktiver Weg zum heptacyclischen Indolalkaloid Stephacidin A (1) umfasst eine einfache Methode für die Synthese substituierter Tryptophane im Gramm ‐Maßstab, eine bemerkenswerte Methode für die Indolanellierung und die erste Enolatkupplung zwischen einem Amid und einem Ester. Diese Synthese stellt die relative Konfiguration des Naturstoffs sicher und weist einen möglichen Weg zu einigen seiner Analoga.
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