SYNTHETIC ROUTES TO 4-AMINO-3-CARBOXY-BETA-CARBOLINE DERIVATIVES - INCIDENTAL FORMATION OF NOVEL FURO[3,4-C]-BETA-CARBOLIN-2-ONES DISPLAYING HIGH AFFINITIES FOR THE BENZODIAZEPINE RECEPTOR

The synthesis of the first 4-amino-3-carboxy-beta-carboline derivative (35) is described. This synthesis is based on ozonolysis of the 4-vinyl-beta-carboline-3-carboxamide 17 to give the 4-aldehyde 20 and potassium permanganate oxidation of the latter to the 4-carboxylic acid 34 followed by a DPPA-promoted Curtius rearrangement. During the course of these transformations, a number of furo[3,4-c]-beta-carbolin-2-ones, differing in substituents at the C-10 position, were formed. While these beta-carboline lactones (15, 25, 26, 33) generally displayed good affinities for the central type benzodiazepine receptor in vitro (IC50's in the 10-50 nM range), one compound, 29, demonstrated an exceptionally high binding affinity (IC50 = 0.2 nM). Compound 29 was shown in electrophysiological and behavioral studies to act as a benzodiazepine receptor antagonist. The unusually high binding affinity of compound 29 corroborates the hypothesis that the benzodiazepine receptor preferentially recognizes the C-3 carbonyl function of 3-carboxy-beta-carbolines in an s-cis conformation (i.e., the carbonyl oxygen on the same side as the pyridinyl nitrogen).