Discovery of 7-arylsulfonyl-1,2,3,4, 4a,9a-hexahydro-benzo[4,5]furo[2,3-c]pyridines: identification of a potent and selective 5-HT₆ receptor antagonist showing activity in rat social recognition test

Bioorg Med Chem Lett. 2012 Feb 1;22(3):1421-6. doi: 10.1016/j.bmcl.2011.12.026. Epub 2011 Dec 13.

Abstract

Serotoninergic neurotransmission has been implicated in modulation of learning and memory. It has been demonstrated that 5-hydroxytryptamine(6) (5-HT(6)) receptor antagonists show beneficial effect on cognition in several animal models. Based on a pharmacophore model reported in the literature, we have designed and successfully identified a 7-benzenesulfonyl-1,2,3,4-tetrahydro-benzo[4,5]furo[2,3-c]pyridine (3a) scaffold as a novel class of 5-HT(6) receptor antagonists. Despite good activity against 5-HT(6) receptor, 3a exhibited poor liver microsome stability in mouse, rat and dog. It was demonstrated that the saturation of the double bond of the tetrahydropyridine ring of 3a enhanced metabolic stability. However the resulting compound, 4a (7-phenylsulfonyl-1,2,3,4,4a,9a-hexahydro-benzo[4,5]furo[2,3-c] pyridine-HCl salt) exhibited ∼30-fold loss in potency along with introduction of two chiral centers. In our optimization process for this series, we found that substituents at the 2 or 3 positions on the distal aryl group are important for enhancing activity against 5-HT(6). Separation of enantiomers and subsequent optimization and SAR with bis substituted phenyl sulfone provided potent 5-HT(6) antagonists with improved PK profiles in rat. A potent, selective 5-HT(6)R antagonist (15k) was identified from this study which showed good oral bioavailability (F=39%) in rat with brain penetration (B/P=2.76) and in vivo activity in a rat social recognition test.

MeSH terms

  • Animals
  • Brain / drug effects*
  • Dogs
  • Heterocyclic Compounds, 3-Ring / chemistry*
  • Heterocyclic Compounds, 3-Ring / pharmacology*
  • Humans
  • Inhibitory Concentration 50
  • Mice
  • Microsomes, Liver / drug effects
  • Molecular Structure
  • Rats
  • Receptors, Serotonin
  • Serotonin Antagonists / chemistry*
  • Serotonin Antagonists / pharmacokinetics
  • Serotonin Antagonists / pharmacology*
  • Stereoisomerism
  • Sulfones / chemistry*
  • Sulfones / pharmacology*

Substances

  • Heterocyclic Compounds, 3-Ring
  • Receptors, Serotonin
  • Serotonin Antagonists
  • Sulfones
  • serotonin 6 receptor