Spiro[[1]benzothiophen-4,4′-piperidines] – carba analogs of potent σ1 ligands
Abstract
Spiro[[1]benzothiophene-4,4′-piperidines] 5 are structurally related to aminoethyl substituted 1-benzothiophenes 4 and spirocyclic thienopyrans 3. The spirocyclic ring system 13 was established in a four step synthesis starting from 1-benzothiophen-4-one 7. The conjugate addition of an acetonitrile anion to the electron deficient double bond of 10 activated by two electron withdrawing groups and the hydrolysis of dinitrile 12 with H2O2/NaOH represent the key steps of the synthesis of the spirocyclic scaffold 13. LiAlH4 reduction of the spirocyclic imide 13 and subsequent reductive alkylation of the secondary amine 5a provided a set of spirocyclic σ ligands. Receptor binding studies revealed that exchange of the O-atom of the lead compound 3b (Ki = 0.31 nM) by a CH2 moiety (5b: Ki = 10.5 nM) decreased the σ1 affinity, whereas conformational restriction of the aminoethyl side chain of 4b (Ki = 49 nM) resulted in increased σ1 affinity. Conformational restriction as well as the ring O-atom is important for high σ1 affinity.