Extension of the “ring switch” approach to glutamate antagonists to δ-lactam urethanes

The versatile “ring switching” approach to antagonists of glutamate receptors has been extended to the use of δ-lactam urethanes. Three different types of δ-lactam urethane aldehydes 17, 26 and 59 have been used successfully in this approach. Altering diastereoisomeric ratios in the synthesis by use of a hindered proton source has allowed homochiral products with two chiral centres to be obtained. Although the δ-lactam urethane system did not prove to be as versatile as the corresponding pyroglutamate or β-lactam urethanes, a variety of homologues of glutamate antagonists have been prepared.