Norarecoline hydrochloride

Synthesis and muscarinic activity of a series of tertiary and quaternary N-substituted guvacine esters structurally related to arecoline and arecaidine propargyl ester.[Pubmed: 2757669]

Arzneimittelforschung. 1989 May;39(5):539-44.

A series of tertiary and quaternary N-substituted guvacine (1,2,5,6-tetrahydro-3-carboxy-pyridine) methyl and propargyl esters have been synthesized and tested for muscarinic/antimuscarinic activity on rat ileum and electrically paced left atria.
METHODS AND RESULTS:
Arecoline and arecaidine propargyl ester (APE) as well as their corresponding N-demethyl derivatives, guvacoline (norarecoline, Norarecoline Hydrochloride) and guvacine propargyl ester, acted as full agonists at both atrial and ileal muscarinic receptors (range of pD2-values 6.09-8.07). However, in both preparations arecoline and APE were clearly more potent (up to 15-fold) than their N-demethyl analogues. Replacement of the N-methyl group in arecoline and APE by larger substituents (ethyl, n-propyl, n-butyl, benzyl, phenylethyl) as well as N-methylation resulted in a decrease or even a complete loss of agonistic activity. In both organs, the propargyl esters usually showed higher potency than the corresponding methyl ester analogues.
CONCLUSIONS:
N-Ethylguvacine propargyl ester and APE methiodide displayed pronounced agonistic activity in the atria (pD2 approximately 6.5; intrinsic activity = 0.79 and 0.67, respectively) but behaved as competitive antagonists in the ileum (pA2 = 6.06 and 5.62, respectively). Beside the lower sensitivity to muscarinic agonists of the rat ileum as compared to rat atria, the cardioselective stimulant action of both agents may also be due to their ability to recognize structural differences between atrial M2 alpha and ileal M2 beta muscarinic receptor subtypes.

Drug Des Discov. 1993;9(3-4):237-50.

Conformational aspects of the muscarinic receptor interactions of bicyclic isoxazole ester bioisosteres of arecoline.[Pubmed: 8400005]

METHODS AND RESULTS:
3-Methoxy-4,5,6,7-tetrahydroisoxazolo [4,5-c]pyridine (O-Me-THPO) and O,5-di-Me-THPO are conformationally restricted bioisosteres of the muscarinic agonists norarecoline(Norarecoline Hydrochloride ) and arecoline, respectively, showing partial agonist effects at muscarinic acetylcholine receptors. The 7-membered ring analogue of O-Me-THPO, 3-methoxy-5,6,7,8-tetrahydro-4H-isoxazolo[4,5-c]azepine (O-Me-THAO), shows higher affinity for muscarinic receptor sites than O-Me-THPO or O,5-di-Me-THPO. Similarly, O-Et-THAO binds much more tightly to muscarinic receptor sites than its 6-membered ring analogues, O-Et-THPO and O-Et-5-Me-THPO. Based on receptor binding data, O-Me-THPO and O-Me-THAO, and O-Et-THPO and O-Et-THAO, respectively, show similar degrees of partial agonism. They also show similar relative affinities for muscarinic M1 and M2 receptor sites. Using the semiempirical quantum mechanics programme, AM1, and the molecular mechanics programme, SYBYL, we have studied the conformational flexibility of the O-alkyl-THPO and O-alkyl-THAO ring systems.
CONCLUSIONS:
As expected, the 7-membered ring of the latter system was shown to be markedly more flexible than the piperidine rings of O-alkyl-THPO analogues. On the basis of this analysis, a common pharmacophore for these two classes of compounds was constructed.