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Relationships Between Structure and Alpha-Adrenergic Receptor Affinity of Clonidine and Some Related Cyclic Amidines

Relationships Between Structure and Alpha-Adrenergic Receptor Affinity of Clonidine and Some Related Cyclic Amidines

A P De Jong, W Soudijn

Eur J Pharmacol. 1981 Jan 16;69(2):175-88.

PMID: 6258944

Abstract:

The inhibition of specific [3H]clonidine binding to alpha-adrenergic receptors in rat brain has been studied for 43 compounds structurally related to clonidine. Oxymetazoline was found to be the most potent compound in displacing [3H]clonidine from its binding sites. 2-Methylimidazoline, 1,2,3,5-tetrahydroimidazo[2,1-b]quinazoline and heterocyclic N-methyl-substituted compounds showed no affinity at all for [3H]clonidine receptor sites. There was a good correlation between hypotensive activity and alpha 2-adrenergic receptor affinity to some 2-(phenylamino)imidazolidines. Parallelisms between Ki's and pharmacological activities were also observed for other compounds. Apparent structural requirements for alpha 2-receptor affinity were the presence of an aromatic moiety and a N-hydrogen in the heterocyclic ring. Ortho substitution in the phenyl ring was necessary for high affinity. Compounds with an oxazolidine ring had approximately similar affinities for the [3H]clonidine binding sites compared with the corresponding imidazolines (except for the 2,6-dichlorophenyl-substituted compound) whereas the pyrrolidine derivatives showed a 10-fold weaker affinity. [3H]Clonidine sites showed a homogeneous character. KD values from saturation and displacement experiments were in good agreement with one another (2.6 and 2.7 nM, respectively) and with values in the literature.

Chemicals Related in the Paper:

Catalog Number	Product Name	Structure	CAS Number	Price
AP1391053501	Oxymetazoline Related Compound A		1391053-50-1	Price
CS31041177	Clonidine Related Compound B			Price

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