title: Conformationally constrained peptides and semipeptides derived from RGD as potent inhibitors of the platelet fibrinogen receptor and platelet aggregation.
abstract: Structure-activity studies have been pursued on cyclo-S,S-[Ac-Cys-(N alpha-Me)Arg-Gly-Asp-Pen]-NH2, 2 (SK&F 106760), a potent inhibitor of platelet aggregation, in an effort to improve potency and affinity for the GPIIb/IIIa receptor. Modifications on the N- and C-termini of 2 produced a series of peptides which indicate that the C-terminal carboxylate group may be a secondary receptor-binding element. Further modification by replacing the disulfide tether N alpha-acetylcysteine/penicillamineamide with the novel, inexpensive, achiral, constrained, and more lipophilic tether 2-mercaptobenzoyl/2-mercaptoaniline (Mba/Man) afforded the semipeptide cyclo-S,S-[Mba-(N alpha-Me)Arg-Gly-Asp-Man], 18 (SK&F 107260), which exhibited significant enhancement in both affinity and potency. To further investigate the effect of the phenyl ring at the C-terminus, peptides bearing the novel (2R,3S)- and (2R,3R)-beta-phenylcysteines were synthesized, which culminated in the cyclo-S,S-[Ac-Cys-(N alpha-Me)Arg-Gly-Asp-(2R,3S)-beta-phenylCys]-OH peptide, 22, which displayed substantial affinity and potency. We describe, herein, the development of both 18 and 22 and the additional structural modifications within the constrained cyclic disulfide ring to probe the stereochemical and steric requirements for receptor interaction.
authors.affiliation: Department of Medicinal Chemistry, SmithKline Beecham Pharmaceuticals Research and Development, King of Prussia, Pennsylvania 19406-0939.
authors.forename: F E
authors.initials: FE
authors.lastname: Ali
authors.forename: D B
authors.initials: DB
authors.lastname: Bennett
authors.forename: R R
authors.initials: RR
authors.lastname: Calvo
authors.forename: J D
authors.initials: JD
authors.lastname: Elliott
authors.forename: S M
authors.initials: SM
authors.lastname: Hwang
authors.forename: T W
authors.initials: TW
authors.lastname: Ku
authors.forename: M A
authors.initials: MA
authors.lastname: Lago
authors.forename: A J
authors.initials: AJ
authors.lastname: Nichols
authors.forename: T T
authors.initials: TT
authors.lastname: Romoff
authors.forename: D H
authors.initials: DH
authors.lastname: Shah
mesh_terms: D000595:Amino Acid Sequence; D001667:Binding, Competitive; D004220:Disulfides / Q000138:chemical synthesis* / Q000378:metabolism / Q000494:pharmacology*; D006801:Humans; D008969:Molecular Sequence Data; D010456:Peptides, Cyclic / Q000138:chemical synthesis* / Q000378:metabolism / Q000494:pharmacology*; D010975:Platelet Aggregation Inhibitors / Q000138:chemical synthesis* / Q000494:pharmacology; D010980:Platelet Membrane Glycoproteins / Q000037:antagonists & inhibitors*; D013329:Structure-Activity Relationship
chemical_list: D004220:Disulfides; D010456:Peptides, Cyclic; D010975:Platelet Aggregation Inhibitors; D010980:Platelet Membrane Glycoproteins; C071275:SK&F 106760; C086543:SK&F 107260