Synthesis and pharmacological characterization of novel analogues of the nicotinic acetylcholine receptor agonist (+/-)-UB-165.
(+/-)-UB-165 (1) is a potent neuronal nicotinic acetylcholine receptor (nAChR) ligand, which displays functional selectivity between nAChR subtypes. Using UB-165 as a lead structure, two classes of racemic ligands were synthesized and assessed in binding assays for three major nAChR subtypes (alpha4beta2, alpha3beta4, and alpha7). The first class of compounds comprises the three pyridine isomers 4-6, corresponding to the 3-, 2-, and 4-substituted pyridine isomers, respectively. Deschloro UB-165 (4) displayed a 2-3-fold decrease in affinity at alpha4beta2 and alpha3beta4 nAChR subtypes, as compared with (+/-)-UB-165, while at the alpha7 subtype a 31-fold increase in affinity was observed. At each of the nAChR subtypes, high affinity binding was dependent on the presence of a 3-substituted pyridine, and the other isomers, 5 and 6, resulted in marked decreases in binding affinities. The second class of compounds is based on replacing the pyridyl unit of 1 with a diazine moiety, giving pyridazine (7), pyrimidine (8), and pyrazine (9), which retain the "3-pyridyl" substructure. Modest reductions in binding affinity were observed for all of the diazine ligands at all nAChR subtypes, with the exception of 7, which retained potency comparable to that of 4 in binding to alpha7 nAChR. In functional assays at the alpha3beta4 nAChR, all analogues 4-9 were less potent, as compared with 1, and the rank order of functional potencies correlated with that of binding potencies. Computational studies indicate that the 3-substituted pyridine 4 and 2-substituted pyridine 5, as well as the diazine analogues 7-9, all conform to a distance-based pharmacophore model recently proposed for the alpha4beta2 receptor. However, the nicotinic potencies of these ligands vary considerably and because 5 lacks appreciable nicotinic activity, it is clear that further refinements of this model are necessary in order to describe adequately the structural and electronic demands associated with this nAChR subtype. This rational series of compounds based on UB-165 presents a systematic approach to defining subtype specific pharmacophores.
Sharples
Christopher G V
CG
Department of Biology and Biochemistry, University of Bath, Bath BA2 7AY, UK.
Karig
Gunter
G
Simpson
Graham L
GL
Spencer
James A
JA
Wright
Emma
E
Millar
Neil S
NS
Wonnacott
Susan
S
Gallagher
Timothy
T
D000818:Animals; D001667:Binding, Competitive; D001921:Brain / Q000378:metabolism; D001952:Bridged-Ring Compounds / Q000138:chemical synthesis* / Q000737:chemistry / Q000378:metabolism; D002460:Cell Line; D008024:Ligands; D008968:Molecular Conformation; D009010:Monte Carlo Method; D009474:Neurons / Q000378:metabolism; D018722:Nicotinic Agonists / Q000138:chemical synthesis* / Q000737:chemistry / Q000378:metabolism; D011719:Pyrazines / Q000138:chemical synthesis / Q000737:chemistry / Q000378:metabolism; D011724:Pyridazines / Q000138:chemical synthesis / Q000737:chemistry / Q000378:metabolism; D011725:Pyridines / Q000138:chemical synthesis* / Q000737:chemistry / Q000378:metabolism; D011743:Pyrimidines / Q000138:chemical synthesis / Q000737:chemistry / Q000378:metabolism; D011869:Radioligand Assay; D051381:Rats; D011978:Receptors, Nicotinic / Q000187:drug effects / Q000378:metabolism; D013237:Stereoisomerism; D013329:Structure-Activity Relationship; D064569:alpha7 Nicotinic Acetylcholine Receptor
C407663:(2-chloro-5-pyridyl)-9-azabicyclo(4.2.1)non-2-ene; D001952:Bridged-Ring Compounds; C579165:Chrna7 protein, rat; D008024:Ligands; D018722:Nicotinic Agonists; D011719:Pyrazines; D011724:Pyridazines; D011725:Pyridines; D011743:Pyrimidines; D011978:Receptors, Nicotinic; D064569:alpha7 Nicotinic Acetylcholine Receptor; C403530:nicotinic receptor alpha3beta4; C403531:nicotinic receptor alpha4beta2; C030986:pyrimidine