ABSTRACT
A series of 2'-substituted-3'-phenyl epibatidine analogues were synthesized and evaluated for inhibition of binding at nicotine acetylcholine receptors and for antinociceptive properties in mice. The introduction of a bulky phenyl group at the 3'-position exerted a profound influence on both receptor binding and antinociceptive effects. Substitution of different groups at the 2'-position distinguished between agonist and antagonist properties. These results demonstrate that structural requirements for receptor activities and recognition are distinctively different.
Subject(s)
Analgesics/chemical synthesis , Bridged Bicyclo Compounds, Heterocyclic/chemical synthesis , Nicotinic Antagonists/chemical synthesis , Pyridines/chemical synthesis , Receptors, Nicotinic/metabolism , Analgesics/chemistry , Analgesics/metabolism , Analgesics/pharmacology , Animals , Bridged Bicyclo Compounds, Heterocyclic/chemistry , Bridged Bicyclo Compounds, Heterocyclic/metabolism , Bridged Bicyclo Compounds, Heterocyclic/pharmacology , Cerebral Cortex , In Vitro Techniques , Male , Mice , Nicotinic Antagonists/chemistry , Nicotinic Antagonists/metabolism , Nicotinic Antagonists/pharmacology , Protein Subunits , Pyridines/chemistry , Pyridines/metabolism , Pyridines/pharmacology , Radioligand Assay , Rats , Stereoisomerism , Structure-Activity RelationshipABSTRACT
A convenient, high-yield synthesis of 7-tert-butoxycarbonyl-7-azabicyclo[2.2.1]hept-2-ene (5), which involved the addition of tributyltin hydride to 7-tert-butoxycarbonyl-2-p-toluenesulfonyl-7-azabicyclo[2.2.1]hept-2-ene (4) followed by elimination of the tributyltin and p-tolylsulfonyl groups using tetrabutylammonium fluoride was developed. The addition of 2-amino-5-iodopyridine to 5 under reductive Heck conditions provided 7-tert-butoxycarbonyl-2-exo-(2'-amino-5'-pyridinyl)-7-azabicyclo[2.2.1]heptane (6). Compound 6 was the key intermediate used to prepare epibatidine analogues where the 2'-chloro group on the pyridine ring was replaced with a fluorine (1b), bromine (1c), iodine (1d), hydroxy (1e), amino (1f), dimethylamino (1g), trifluoromethanesulfonate (1h), and hydrogen (1i) group. (+)- and (-)-Epibatidine and compounds 1b-d and 1i all possess similar binding affinities at the alpha(4)beta(2) nAChR receptors labeled by [(3)H]epibatidine. Compound 1f has affinity similar to nicotine, whereas compounds 1e, 1g, and 1h have much lower affinity. The binding affinity appears to be dependent upon the electronic nature of the substituent. However, other factors are also involved. None of the compounds possesses appreciable affinity for the alpha(7) nAChR labeled by [(125)I]iodo-MLA. With the exception of 1f and 1g, all the epibatidine analogues are full agonists (tail flick test) in producing antinociception after intrathecal injection in mice.
Subject(s)
Analgesics, Non-Narcotic/chemical synthesis , Analgesics, Non-Narcotic/pharmacology , Bridged Bicyclo Compounds, Heterocyclic/chemical synthesis , Bridged Bicyclo Compounds, Heterocyclic/pharmacology , Pyridines/chemical synthesis , Pyridines/pharmacology , Receptors, Nicotinic/metabolism , Animals , Binding, Competitive/drug effects , Cerebral Cortex/drug effects , Cerebral Cortex/metabolism , In Vitro Techniques , Male , Mice , Mice, Inbred ICR , Pain Measurement/drug effects , Radioligand Assay , Rats , Reaction Time/drug effects , Structure-Activity RelationshipABSTRACT
2164U90, [(3R,5R)-trans-3-butyl-3-ethyl-2,3,4,5-tetrahydro-5-phenyl-1,4- benzothiazepine 1,1-dioxide], was found to be a potent inhibitor of the ileal bile acid active transport system. In vitro, 2164U90 decreased uptake and active transport of taurocholic acid by rat everted ileal sacs with IC50s of 4.0 microM and 1.5 microM, respectively. In vivo, 2164U90 produced dose-dependent increases in 23,25-75Se-labeled homocholic acid taurine (SeHCAT) fecal excretion in rats and mice at doses of 3-30 mg/kg and 1-10 mg/kg, respectively. In rats, 30 mg/kg 2164U90 was equivalent to 500 mg/kg cholestyramine. Two days oral administration of 10 mg/kg 2164U90 to rats decreased the bile concentrations of total bile acids 42%, orally administered [3H]taurocholic acid ([3H]TC) 82%, and cholesterol 35%. Cholestyramine (500 mg/kg) had effects similar to 2164U90 on total bile acid and orally administered [3H]TC concentrations but had no effect on biliary cholesterol. The hypocholesterolemic activity of 2164U90 was determined in cholesterol-cholic acid-fed rats and cholesterol-cholic acid-coconut oil-fed mice. 2164U90 inhibited the dietary-induced increase in dextran sulfate-precipitable lipoprotein cholesterol (VLDL+LDL) at doses comparable to doses needed to increase the fecal excretion of bile acids. These data indicate that 2164U90 decreases bile acid absorption by inhibiting the ileal bile acid active transport system, resulting in hypocholesterolemic activity.
Subject(s)
Bile Acids and Salts/metabolism , Cholesterol/metabolism , Hypolipidemic Agents/pharmacology , Ileum/drug effects , Intestinal Absorption/drug effects , Thiazepines/pharmacology , Administration, Oral , Animals , Bile/metabolism , Biological Transport, Active/drug effects , Cholestyramine Resin/pharmacology , Feces/chemistry , Ileum/metabolism , Male , Mice , Rats , Rats, Sprague-Dawley , Taurocholic Acid/metabolismABSTRACT
Inhibition of the ileal bile acid active transport system, previously shown to be mechanism underlying the hypocholesterolemic activity of 2164U90 in rodents, was further characterized in isolated intestinal preparations from three species. 2164U90 inhibited sodium-dependent transport of taurocholic acid by Caco-2 cells and by monkey and human ileal brush border membrane vesicles in a concentration-dependent manner with IC50s of 7 microM, 5 microM, and 2 microM, respectively. In rat ileal brush border membrane vesicles, 2164U90 was a competitive inhibitor of sodium-dependent taurocholic acid uptake with an estimated Ki of 1.8 +/- 0.2 microM. In anesthetized rats, 5 microM 2164U90 placed in the isolated distal ileum with 3 mM [3H]taurocholic acid decreased ileal uptake, transport into the bile, and transport rate of taurocholic acid by 31-35%. Stereospecificity of inhibition by 2164U90 was demonstrated by the relative inactivity of three other possible stereoisomers in rat ileal sacs and brush border membrane vesicles. 2164U90 did not inhibit sodium-dependent glucose transport by monkey jejunal brush border membrane vesicles, indicating that 2164U90 may be specific for the bile acid transporter. These results suggest that 2164U90 is a potent, selective, stereospecific, competitive inhibitor of the sodium-dependent bile acid transporter in the ileal mucosal cell brush border membrane.
