C(8) Substituted 1-Azabicyclo[3.3.1]non-3-enes and C(8) Substituted 1-Azabicyclo[3.3.1]nonan-4-ones:  Novel Muscarinic Receptor Antagonists

Abstract

Expedient syntheses of C(8) substituted 1-azabicyclo[3.3.1]non-3-enes and C(8) substituted 1-azabicyclo[3.3.1]nonan-4-ones are reported to begin with 2,5-disubstituted pyridines. Catalytic reduction of the pyridine to the piperidine followed by treatment with ethyl acrylate and Dieckmann cyclization gave diastereomeric mixtures of C(8) substituted 3-ethoxycarbonyl-4-hydroxy-1-azabicyclo[3.3.1]non-3-enes, which were separable by chromatography. We found that the catalytic reduction (PtO2, H2) procedure provided the cis-substituted piperidine but that pyridine reduction was accompanied by competitive cleavage of the C(2) pyridyl substituent. Accordingly, an alternative route was devised that afforded a diastereomeric mixture of the cis- and trans-2,5-disubstituted piperidine. Treatment of the substituted pyridine with m-CPBA gave the pyridine N-oxide, which was reduced to the piperidine by sequential reduction with ammonium formate in the presence of Pd-C followed by NaBH3CN. Addition of ethyl acrylate completed the synthesis of the substituted piperidine. The overall four-step reaction gave higher yields (57%) than the two-step procedure (13%) with little cleavage of the C(2) pyridyl substituent. Acid decarboxylation of the bicyclo[3.3.1]non-3-enes provided the C(8) substituted 1-azabicyclo[3.3.1]nonan-4-ones. Structural studies revealed diagnostic 13C NMR signals that permit assignment of the orientation of the C(8) substituent. Pharmacological investigations documented that 3-ethoxycarbonyl-4-hydroxy-1-azabicyclo[3.3.1]non-3-enes efficiently bind to the human M1-M5 muscarinic receptors and function as antagonists. We observed that exo-8-benzyloxymethyl-3-ethoxycarbonyl-4-hydroxy-1-azabicyclo[3.3.1]non-3-ene (3) displayed the highest affinity, exhibiting Ki values at all five muscarinic receptors that were approximately 10-50 times lower than carbachol and approximately 30-230 times lower than arecoline. Receptor selectivity was observed for 3. Compound 3 contained two different pharmacophores found in many muscarinic receptor ligands, and preliminary findings indicated the importance of both structural elements for maximal activity. Compound 3 serves as a novel lead compound for further drug development.

Chemical Modification of the M1 Agonist VU0364572 Reveals Molecular Switches in Pharmacology and a Bitopic Binding Mode

“…Figure d shows a double reciprocal plot of equiactive concentrations in cells exposed to 1 μg of TET for 24 h and cells that were exposed to 25 ng test. A p K d value of CCh (5.08 ± 0.20; K d = 10.1 μM) was calculated from the fitted straight line (see Methods) and was found to be consistent with previously published results . Using this same approach, we performed full concentration response curve analysis of both VU0364572 and VU0357017 (Figure b and c).…”

“…In contrast to the calcium mobilization assay, the IP accumulation assay is not characterized by receptor reserve and orthosteric agonist potencies more closely reflect their affinities at M 1 . 14 Consistent with this, the orthosteric mAChR agonist carbachol (CCh) induced an increase in IP accumulation with an EC 50 value (EC 50 = 4.05 ± 0.492 μM) that is similar to its previously determined affinity at M 1 (12.5 ± 5.00 μM; see ref 24). VU0364572 induced a modest increase in IP accumulation with a maximal response that was approximately 30% of the response to CCh (Figure 6b).…”

“…14 Consistent with this, the orthosteric mAChR agonist carbachol (CCh) induced an increase in IP accumulation with an EC 50 value (EC 50 = 4.05 ± 0.492 μM) that is similar to its previously determined affinity at M 1 (12.5 ± 5.00 μM; see ref 24). VU0364572 induced a modest increase in IP accumulation with a maximal response that was approximately 30% of the response to CCh (Figure 6b).…”

“…A pK d value of CCh (5.08 ± 0.20; K d = 10.1 μM) was calculated from the fitted straight line (see Methods) and was found to be consistent with previously published results. 24 Using this same approach, we performed full concentration response curve analysis of both VU0364572 and VU0357017 (Figure 7b and c (Table 3). Furthermore, upon alternative analysis of these data using an operational model of receptor depletion, 27 we found that the operationally derived pK a values derived were in agreement with pK a values estimated from double reciprocal plots of the Furchgott analysis (see Figure 7e and f).…”

“…A pK d value of CCh (5.08 ± 0.20; K d = 10.1 μM) was calculated from the fitted straight line (see Methods) and was found to be consistent with previously published results. 24 Using this same approach, we performed full concentration response curve analysis of both VU0364572 and VU0357017 (Figure 7b and c). pK d values for VU0364572 (6.67 ± 0.29.; K d = 0.95 μM) and VU0357017 (5.66 ± 0.34; K d = 2.88 μM) were estimated from these analysis and were in agreement with the calculated K i values for each compound as assessed in measures of inhibition of [ 3 H]-NMS binding (Table 3).…”