Thionation of adatanserin hydrochloride (2) with Lawesson's reagent in toluene/triethylamine afforded novel compound, (3r,5r,7r)-N-(2-(4-(pyrimidin-2-yl)piperazin-1-yl)ethyl)adamantane-1-carbothioamide (thioadatanserin, 3) in 84-90% isolated yield. Thioadatanserin underwent a tandem double alkylation with methyl iodide and benzyl bromide in NaH/THF to produce novel dialkylated products 6 and 7 respectively. The single X-ray crystal structure of 7 was determined to be 1-(2-((E- ((3r,5r,7r)-adamantan-1-yl)benzylthio)methylene)amino)ethyl)-1-benzyl-4- (pyrimidin-2-yl)piperazin-1-ium bromide showing that the piperazine ring adopts a chair-like configuration that is not co-planar with the pyrimidine ring. Thioadatanserin emerged as a dual potent partial agonist with activity against 5-HTR1A (EC50 6.7 nM) and antagonist activity against 5-HTR2A (IC50 62.3 nM) and was selective over 5-HTR2C receptor (IC50 > 3333 nM) in the PathHunter® β-arrestin assays.
Keywords: 5-HTR(1A) partial agonist; 5-HTR(2A) antagonist; Adatanserin; Tandem alkylation; Thioadatanserin; Thionation; β-arrestin.
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