Concise Total Synthesis of Neopterosin A and C by a Pd-catalyzed Tandem Reaction

Dedication

This paper is dedicated to Professor Minoru Isobe for his great contribution to the chemistry of sugar acetylene.

Abstract

Neopterosins A and C are novel, naturally occurring indole C-mannosides isolated from a marine sponge Neopetrosia chaliniformis, in which the mannose conformation is inverted due to the steric hindrance of the indole moiety. Herein, we describe the eight-step total synthesis of these natural products from tri-O-acetyl-d-glucal, involving two palladium-catalyzed reactions: a Sonogashira coupling of α-ethynyl-mannose with o-iodo-N-tosyl-anilide, and a tandem reaction in the presence of carbon monoxide to construct both the indole and lactone frameworks.

Keywords

Sugar acetylene - Mannosyl-indole - Sonogashira coupling - ¹C₄ conformation - Pd-catalyzed tandem reaction

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