The pseudopterosins and colombiasin A

This thesis is concerned with the total synthesis of natural products isolated from the Caribbean sea whip, Pseudopterogorgia elisabethae. The pseudopterosins are a family of such marine natural products exhibiting anti-inflammatory and analgesic properties. A total synthesis of pseudopterosin A-F aglycone is described. The route began with achiral starting materials and also leads to the synthesis of an unnatural pseudopterosin diastereoisomer. Key features include an arene alkylation with a g-methylene-g-butyrolactone and a subsequent hydrogenation-hydrogonolysis sequence, which proceed with excellent diastereoselectivity. Previous syntheses of the pseudopterosins, including synthetic approaches to the aglycone are reviewed in Chapter 1. Modifications to our approach are discussed, enabling the more rapid and efficient production of material. Studies towards pseudopterosin G-J aglycone are also described. We have developed a route to an unnatural diastereoisomer of colombiasin A, also isolated from Pseudopterogorgia elisabethae. Key features are an arene alkylation with a g-methylene-g-butyrolactone and an intramolecular Diels-Alder cycloaddition. A simple method to effect the conversion of 4-aryl-1-en-1-yl methyl ethers to the corresponding dihydronaphthalene is reported. Cyclisation is accomplished by warming a cyclohexane solution of the substrate with ethylene glycol and para-toluenesulfonic acid, and proceeds via the in situ formation of a 1,3-dioxolane. Studies towards elisabatin B are also described.