title: Novel 5-HT3 antagonists: indol-3-ylspiro(azabicycloalkane-3,5'(4'H)-oxazoles).
abstract: The synthesis and biochemical evaluation of a series of spirofused indole oxazoline 5-HT3 antagonists is described in which the oxazoline ring acts as a bioisosteric replacement for esters and amides. The effect of substitution about the indole ring has shown the steric limitations of the aromatic binding site. Incorporation of a variety of azabicyclic systems within the rigid spirofused framework has allowed the definition of a binding model which incorporates a number of known antagonists and agonists. In this model steric constraints limit substitution around the indole ring although there is some bulk tolerance at the 1- and 2-positions. The importance of constraining the basic nitrogen within an azabicyclic system is underlined by comparison with the monocyclic piperidine. The highest affinity was observed for those compounds in which the basic nitrogen occupies a bridgehead position, the most potent analogue in this group being the azabicyclic [3.3.1] system (pIC50 = 8.95), suggesting lipophilic interactions may play a role in increasing affinity. A suggested model for agonist binding is included in which the basic nitrogens are superimposed and the 5-hydroxyl group of 5-HT is superimposed on the H-bond-accepting atom of the heterocyclic linking group.
authors.affiliation: Department of Medicinal Chemistry, Merck Sharp and Dohme Research Laboratories, Harlow, Essex, U.K.
authors.forename: C J
authors.initials: CJ
authors.lastname: Swain
authors.forename: R
authors.initials: R
authors.lastname: Baker
authors.forename: C
authors.initials: C
authors.lastname: Kneen
authors.forename: R
authors.initials: R
authors.lastname: Herbert
authors.forename: J
authors.initials: J
authors.lastname: Moseley
authors.forename: J
authors.initials: J
authors.lastname: Saunders
authors.forename: E M
authors.initials: EM
authors.lastname: Seward
authors.forename: G I
authors.initials: GI
authors.lastname: Stevenson
authors.forename: M
authors.initials: M
authors.lastname: Beer
authors.forename: J
authors.initials: J
authors.lastname: Stanton
mesh_terms: D000818:Animals; D001665:Binding Sites / Q000187:drug effects; D001921:Brain / Q000187:drug effects / Q000378:metabolism; D001643:Bridged Bicyclo Compounds / Q000138:chemical synthesis* / Q000378:metabolism / Q000494:pharmacology; D007211:Indoles / Q000138:chemical synthesis* / Q000378:metabolism / Q000494:pharmacology; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D010080:Oxazoles / Q000138:chemical synthesis* / Q000378:metabolism / Q000494:pharmacology; D051381:Rats; D012702:Serotonin Antagonists / Q000138:chemical synthesis* / Q000378:metabolism / Q000494:pharmacology; D013237:Stereoisomerism; D013329:Structure-Activity Relationship; D014961:X-Ray Diffraction
chemical_list: D001643:Bridged Bicyclo Compounds; D007211:Indoles; D008024:Ligands; D010080:Oxazoles; D012702:Serotonin Antagonists