Analogues of Carbacholine: Synthesis and Relationship between Structure and Affinity for Muscarinic and Nicotinic Acetylcholine Receptors

Abstract

A series of acyclic and heterocyclic analogues of carbacholine (1) was synthesized using N-methylcarbacholine (MCC, 2), N,N-dimethylcarbacholine (DMCC, 3), and the corresponding tertiary amine (4) as leads. Whereas nicotinic acetylcholine receptor affinity was determined using [3H]nicotine as the radioactive ligand, [3H]oxotremorine-M ([3H]Oxo-M) and [3H]quinuclidinyl benzilate ([3H]QNB), in some cases supplemented with [3H]pirenzepine ([3H]PZ), were used as radioligands for muscarinic acetyicholine receptors on rat brain membranes. On the basis of receptor binding data, nicotinic/muscarinic (N/M) selectivity factors were determined, and muscarinic receptor efficacy (M agonist index) and M1 selectivity (M2/M1 index) estimated. In most cases, quaternized analogues showed higher affinity than the corresponding tertiary amines for muscarinic and, in particular, nicotinic receptor sites. Among the new compounds, N,N-diethylcarbacholine (9e) (IC50 = 0.046 microM), (S)-1-methyl-2-(N,N- dimethyl-aminocarbonyloxymethyl)pyrrolidine (17k) (IC50 = 0.068 microM), and the corresponding quaternized analogue, 18k (IC50 = 0.018 microM) showed the highest nicotinic receptor affinity. The tertiary amine, 17k showed much higher nicotinic receptor affinity than the acyclic analogue, 4 (IC50 = 5.7 microM), and the N/M selectivity factor determined for 17k (150) is an order of magnitude lower than that of nicotine (1400). THe N/M selectivity factors for MCC (2) and DMCC (3), previously reported to be highly selective nicotinic receptor ligands, were shown to be 6.5 and 60, respectively, the latter value being comparable with that of 18k (89).

Carbamoylcholine Homologs: Novel and Potent Agonists at Neuronal Nicotinic Acetylcholine Receptors

“…tent with (S)-nicotine (Beene et al, 2002). In analogy with the observations for ACh, the amino group of DMCC has to be quaternized to bind with high affinity to native nAChRs (compare DMCC and DMCAE in Table 1) (Søkilde et al, 1996). Although one has to be very cautious when comparing binding data on native neuronal nAChRs with functional data on a recombinant muscle-type nAChR, compound 7 seems to supplement ACh and (S)-nicotine with regard to the importance of the nature of the charge of the amino group.…”

“…Although one has to be very cautious when comparing binding data on native neuronal nAChRs with functional data on a recombinant muscle-type nAChR, compound 7 seems to supplement ACh and (S)-nicotine with regard to the importance of the nature of the charge of the amino group. Whereas the potency of nicotine was unaffected by the conversion from a tertiary to a quaternized amino group, and ACh and DMCC had to possess a quaternized amino group for optimal receptor interaction, the tertiary nature of the amine group of 7 seems to be crucial for effective binding to nAChRs (compare compounds 7 and 10 in Table 1) (Søkilde et al, 1996;Beene et al, 2002). This observation indicates that the protonated amino group of 7 must bind to the "aromatic pocket" of the nAChR in a mode different from those of both the quaternized amines ACh, MCC, and DMCC and from another protonated tertiary amine, (S)-nicotine.…”

“…Some years ago, we reported the synthesis of a series of conformationally restricted acyclic and heterocyclic analogs of MCC, DMCC, and the tertiary amine corresponding to DMCC, N,Ndimethylcarbamoyl-N,N-dimethylaminoethanol (DMCAE) ( Fig. 1) (Søkilde et al, 1996). However, none of these analogs displayed higher binding affinities for native nAChRs than MCC or DMCC.…”

“…Cells (2 ϫ 10 6 ) were split into a 15-cm tissue culture plate a day before transfection and transfected with 10 g ␣7/5-HT 3 -pCDNA3. (Søkilde et al, 1996). In the [ 3 H]Oxo-M binding assay, rat brains were homogenized in 100 volumes (w/v) of 10 mM sodium potassium phosphate buffer, pH 7.4, and diluted 1:10 with the same buffer.…”

Conformationally restrained carbamoylcholine homologues. Synthesis, pharmacology at neuronal nicotinic acetylcholine receptors and biostructural considerations

“…A C C E P T E D ACCEPTED MANUSCRIPT 6 The amino part of 1 has already been studied by means of chain elongation, resolution of the enantiomers, alpha methyl deletion or alkyl substitution [19], and incorporation into cyclic structures [23,24]. Herein, we present a systematic introduction of different cycles representing various degrees of constriction of the conformational space of 1.…”