Synthesis of conformationally restricted analogs of kainic acid. Is the conformation of the C4-substituent of kainoid important to its neuroexcitatory activity?

Conformationally restricted analogs of kainic acid, which have an azabicyclo[3.3.0]octane system, were synthesized through the intramolecular addition reaction of trimethylenemethane to the α,β-unsaturated ester. Every synthesized isomer showed very weak depolarizing activity. These results indicate that the plane of the isopropenyl group of kainic acid should be diagonal to the pyrrolidine ring to show potent activity.