Studies on Zwitter-ionization of Drugs. III. Synthesis and Pharmacological Activities of N-Alkylcarboxylic Acid Derivatives of 1, 2, 3, 4, 10, 14b-Hexahydrodibenzo [c, f]-pyrazino [1, 2-α] azepine and 2, 3, 4, 9-Tetrahydro-1H-dibenzo [3, 4 : 6, 7] cyclohepta [1, 2-c] pyridine

The N-alkylcarboxylic acids of 1,2,3,4,10,14b-hexahydrodibenzo[c,f]pyrazino[1,2-alpha]az epi ne (6a) and 2,3,4,9-tetrahydro-1H-dibenzo[3,4: 6,7]cyclohepta[1,2- c]pyridine (6b) were synthesized and examined for pharmacological activities in vitro: an inhibitory effect on the monoamine [noradrenaline (NA) and 5-hydroxytryptamine (5-HT)] uptake into the rat crude synaptosome, an inhibitory effect on the 5-HT- and NA-induced contraction in the isolated rabbit aorta and on the histamine- and acetylcholine-induced contraction in the isolated guinea-pig ileum, and binding affinity for alpha 2-adrenoceptor and D2-receptor. The in vitro tests indicated that zwitter-ionization was capable of maintaining antihistaminic activity while greatly reducing other pharmacological activities such as effects on central nervous system. 3-[2,3,4,9-Tetrahydro-1H-dibenzo[3,4: 6,7]cyclohepta[1,2- c]pyridin-2-yl]propionic acid (6b-2), selected as a candidate antiallergic agent having equally potent activities in rats and guinea-pigs, exhibited strong inhibitory effects on 48 h homologous passive cutaneous anaphylaxis (PCA) in rats (ED50 = 0.012 mg/kg, p.o.) and on histamine-induced bronchoconstriction in anesthetized guinea-pigs (ED50 = 0.0088 mg/kg, p.o.).