Synthesis and structure-affinity relationships of novel N-(1-ethyl-4-methylhexahydro-1,4-diazepin-6-yl)pyridine-3-carboxamides with potent serotonin 5-HT3 and dopamine D2 receptor antagonistic activity.
A structurally original series of N-(1-ethyl-4-methylhexahydro-1,4-diazepin-6-yl)pyridine-3-carboxamides derived from the corresponding benzamide 5 were prepared and evaluated for their binding affinity for the dopamine D(2) and serotonin 5-HT(3) receptors using rat striatum and rat cortical membrane, respectively. Many of the synthesized pyridine-3-carboxamides exhibited nanomolar binding affinity for the serotonin 5-HT(3) receptor along with moderate to high binding affinity for the dopamine D(2) receptor. Introduction of the more lipophilic bromine atom and methylamino group at the 5- and 6-positions of the pyridine ring, respectively, enhanced the affinity for the dopamine D(2) receptor while keeping a potent serotonin 5-HT(3) receptor binding affinity. As a result of structure-affinity relationships, the 5-bromo-2-methoxy-6-methylaminopyridine-3-carboxamide 53 was selected as the most promising product showing a high binding affinity for both receptors. Compound 53 affinity for the dopamine D(2) and serotonin 5-HT(3) receptors was much more potent than that of metoclopramide (dopamine D(2) receptor; 23.3 nM vs 444 nM, serotonin 5-HT(3) receptor; 0.97 nM vs 228 nM). Optical resolution of the racemate 53 brought about a dramatic change in the pharmacological profile with (R)-53 exhibiting a strong affinity for both the dopamine D(2) and serotonin 5-HT(3) receptors, while the corresponding (S)-53 had a potent serotonin 5-HT(3) receptor binding affinity and a moderate dopamine D(2) receptor binding affinity. X-ray crystallographic study of (R)-53 revealed the existence of two energically stable conformers just like two mirror images. This may account for (R)-53 high affinity for both the dopamine D(2) and serotonin 5-HT(3) receptors. Pharmacologically, (R)-53 [AS-8112] showed a potent antagonistic activity for both the dopamine D(2) and serotonin 5-HT(3) receptors in vivo tests and dose-dependently inhibited both the incidence and frequency of emetic episodes induced by cisplatin (ferrets) and morphine (dogs) with ID(50) values of 27.1 microg/kg, po and 136 microg/kg, po, respectively. On the basis of this pharmacological profile, (R)-53 is now under further investigation as a potential broad antiemetic agent.
Hirokawa
Yoshimi
Y
Medicinal Chemistry Group, Chemistry Research Laboratories, Dainippon Pharmaceutical Co. Ltd., Enoki 33-94, Suita, Osaka 564-0053, Japan. yoshi-hirokawa@dianippon-pharm.co.jp
Fujiwara
Iwao
I
Suzuki
Kenji
K
Harada
Hiroshi
H
Yoshikawa
Takashi
T
Yoshida
Naoyuki
N
Kato
Shiro
S
D000818:Animals; D000932:Antiemetics / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology; D001381:Azepines / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology; D001921:Brain / Q000378:metabolism; D018360:Crystallography, X-Ray; D004285:Dogs; D018492:Dopamine Antagonists / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology; D005289:Ferrets; D066298:In Vitro Techniques; D008958:Models, Molecular; D011725:Pyridines / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology; D051381:Rats; D017448:Receptors, Dopamine D2 / Q000187:drug effects* / Q000378:metabolism; D011985:Receptors, Serotonin / Q000187:drug effects* / Q000378:metabolism; D044406:Receptors, Serotonin, 5-HT3; D012702:Serotonin Antagonists / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology; D013237:Stereoisomerism; D013329:Structure-Activity Relationship
C431510:5-bromo-N-(1-ethyl-4-methylhexahydro-1H-1,4-diazepin-6-yl)-2-methoxy-6-methylamino-3-pyridinecarboxamide 2-fumarate; D000932:Antiemetics; D001381:Azepines; D018492:Dopamine Antagonists; D011725:Pyridines; D017448:Receptors, Dopamine D2; D011985:Receptors, Serotonin; D044406:Receptors, Serotonin, 5-HT3; D012702:Serotonin Antagonists