β-Carboline-3-carboxylic Acid (9H-Pyrido[3,4-b]indole-3-carboxylic Acid) and Related Compounds

The synthesis of β-carboline-3-carboxylic acid and its esters (4) by oxidation of the corresponding 1,2,3,4-tetrahydro derivatives (2) or of the 3,4-dihydro derivatives (3) has been studied. A novel synthesis of the esters (3) [and hence of (4)] has been achieved in high yield by cyclization and elimination from the enamine (5). The relative inhibition of binding of a benzodiazepine to rat brain membranes by the esters (2)-(4) has been determined.