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.
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.
Kim
Myoung Goo
MG
Division of Medicinal Chemistry and Natural Products, School of Pharmacy, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7360, USA.
Bodor
Erik T
ET
Wang
Chen
C
Harden
T Kendall
TK
Kohn
Harold
H
D000818:Animals; D001667:Binding, Competitive; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology; D002460:Cell Line; D018360:Crystallography, X-Ray; D006801:Humans; D007295:Inositol Phosphates / Q000096:biosynthesis; D009682:Magnetic Resonance Spectroscopy; D008566:Membranes; D018727:Muscarinic Antagonists / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology; D011869:Radioligand Assay; D013237:Stereoisomerism; D013329:Structure-Activity Relationship
C474828:8-benzyloxymethyl-3-ethoxycarbonyl-4-hydroxy-1-azabicyclo(3.3.1)non-3-ene; D019086:Bridged Bicyclo Compounds, Heterocyclic; D007295:Inositol Phosphates; D018727:Muscarinic Antagonists