Isosteric replacement of amide by ester function. Synthesis and benzodiazepine receptor affinity of indol-3-ylglyoxylyl ester derivatives.

A number of benzyl and phenylethyl esters of indol-3-ylglyoxylic acid were synthesized and tested for their ability to displace [3H]Ro 15-1788 binding from bovine brain membranes. In these new compounds the oxygen atom of the ester function replaced the amide NH group of a class of previously described indolylglyoxylylamides, since it is reported in literature that in the beta-carboline series an ester function is more favourable to the activity than an amide group. However, none of the compounds showed an affinity at the Benzodiazepine receptor higher than that of the corresponding amides, demonstrating that the presence of the amide NH group is favourable to the interaction of ligands with the receptor site.