Synthesis of 5-hydroxy-2,3,4,5-tetrahydro-[1H]-2-benzazepin-4-ones: selective antagonists of muscarinic (M3) receptors

Abstract

Two approaches to tetrahydro-[1H]-2-benzazepin-4-ones of interest as potentially selective, muscarinic (M₃) receptor antagonists have been developed. Base promoted addition of 2-(tert-butoxycarbonylamino)methyl-1,3-dithiane 5 with 2-(tert-butyldimethylsiloxymethyl)benzyl chloride 14 gave the corresponding 2,2-dialkylated 1,3-dithiane 15 which was taken through to the dithiane derivative 19 of the parent 2,3,4,5-tetrahydro-[1H]-2-benzazepin-4-one by desilylation, oxidation and cyclisation via a reductive amination. After conversion into the N-tert-butyloxycarbonyl, N-toluene p-sulfonyl and N-benzyl derivatives 20–22, hydrolysis of the dithiane gave the N-protected tetrahydro-[1H]-2-benzazepin-4-ones 23–25. However, preliminary attempts to convert these into 5-cycloalkyl-5-hydroxy derivatives were not successful. In the second approach, ring-closing metathesis was used to prepare 2,3-dihydro-[1H]-2-benzazepines which were hydroxylated and oxidized to give the required 5-hydroxy-2,3,4,5-tetrahydro-[1H]-2-benzazepin-4-ones. Following preliminary studies, ring-closing metathesis of the dienyl N-(2-nitrophenyl)sulfonamide 48 gave the dihydrobenzazepine 50 which was converted into the 2-butyl-5-cyclobutyl-5-hydroxytetrahydrobenzazepin-4-one 55 by hydroxylation and N-deprotection followed by N-alkylation via reductive amination, and oxidation. This chemistry was then used to prepare the 2-[(N-arylmethyl)aminoalkyl analogues 69, 72, 76 and 78. N-Acylation followed by amide reduction using the borane–tetrahydrofuran complex was also used to achieve N-alkylation of dihydrobenzazepines and this approach was used to prepare the 5-cyclopentyl-5-hydroxy-2,3,4,5-tetrahydro-[1H]-2-benzazepin-4-one 103 and the 5-cyclobutyl-8-fluoro-5-hydroxy-2,3,4,5-tetrahydro-[1H]-2-benzazepin-4-one 126. The structures of 2-tert-butyloxycarbonyl-4,4-propylenedithio-2,3,4,5-tetrahydro-[1H]-2-benzazepine 20 and (4RS,5SR)-2-butyl-5-cyclobutyl-4,5-dihydroxy-2,3,4,5-tetrahydro-[1H]-2-benzazepine 53 were confirmed by X-ray diffraction. The racemic 5-cycloalkyl-5-hydroxy-2,3,4,5-tetrahydro-[1H]-2-benzazepin-4-ones were screened for muscarinic receptor antagonism. For M₃ receptors from guinea pig ileum, these compounds had log₁₀K_B values of up to 7.2 with selectivities over M₂ receptors from guinea pig left atria of approximately 40.