Synthesis of Anatoxin-a. A Constituent of Blue-Green Freshwater Algae.

Abstract
Anatoxin-a is a naturally occurring neurotoxin produced by the blue-green alga Anabaena flos-aquae and is a potent muscarinic and nicotinic receptor agonist. An improved synthetic pathway to racemic anatoxin-a is presented which opens possibilities for easy introduction of various side-chains for structure-activity relationship studies. Starting from 9-methyl-9-aza[4.2.1]nonan-2-one, the .alpha.,.beta.-enone structural element was introduced using Seebach''s carbonyl-"umpolung" method, followed by N-demethylation and dethioketalization to give pure anatoxin-a.