Synthesis and evaluation of in vitro bioactivity for vesicular acetylcholine transporter inhibitors containing two carbonyl groups

To identify selective high-affinity ligands for the vesicular acetylcholine transporter (VAChT), we have incorporated a carbonyl group into the structures of trozamicol and prezamicol scaffolds, and also converted the secondary amines of the piperidines of trozamicols and prezamicols into amides. Of 18 new racemic compounds, 4 compounds displayed high affinity for VAChT (K(i)=10-20 nM) and greater than 300-fold selectivity for VAChT over σ(1) and σ(2) receptors, namely (4-(4-fluorobenzoyl)-4'-hydroxy-[1,3'-bipiperidin]-1'-yl)(3-methylthiophen-2-yl)methanone oxalate (9g) (K(i-VAChT)=11.4 nM, VAChT/σ(1)=1063, VAChT/σ(2)=370), (1'-benzoyl-4'-hydroxy-[1,3'-bipiperidin]-4-yl)(4-methoxyphenyl)methanone oxalate (10c) (K(i-VAChT)=15.4 nM, VAChT/σ(1)=374, VAChT/σ(2)=315), (4'-hydroxy-1'-(thiophene-2-carbonyl)-[1,3'-bipiperidin]-4-yl)(4-methoxyphenyl)methanone oxalate (10e) (K(i-VAChT)=19.0 nM, VAChT/σ(1)=1787, VAChT/σ(2)=335), and (4'-hydroxy-1'-(3-methylthiophene-2-carbonyl)-[1,3'-bipiperidin]-4-yl)(4-methoxyphenyl)methanone oxalate (10g) (K(i-VAChT)=10.2 nM, VAChT/σ(1)=1500, VAChT/σ(2)=2030). These four compounds can be radiosynthesized with C-11 or F-18 to validate their possibilities of serving as PET probes for quantifying the levels of VAChT in vivo.