title: Total synthesis, structural, and biological evaluation of stylissatin A and related analogs.
abstract: The natural product cyclic peptide stylissatin A (1a) was reported to inhibit nitric oxide production in LPS-stimulated murine macrophage RAW 264.7 cells. In the current study, solid-phase total synthesis of stylissatin A was performed by using a safety-catch linker and yielded the peptide with a trans-Phe(7) -Pro(6) linkage, whereas the natural product is the cis rotamer at this position as evidenced by a marked difference in NMR chemical shifts. In order to preclude the possibility of 1b being an epimer of the natural product, we repeated the synthesis using d-allo-Ile in place of l-Ile and a different site for macrocyclization. The resulting product (d-allo-Ile(2) )-stylissatin A (1c) was also found to have the trans-Phe(7) -Pro(6) peptide conformations like rotamer 1b. Applying the second route to the synthesis of stylissatin A itself, we obtained stylissatin A natural rotamer 1a accompanied by rotamer 1b as the major product. Rotamers 1a, 1b, and the epimer 1c were separable by HPLC, and 1a was found to match the natural product in structure and biological activity. Six related analogs 2-7 of stylissatin A were synthesized on Wang resin and characterized by spectral analysis. The natural product (1a), the rotamer (1b), and (d-allo-Ile(2) )-stylissatin A (1c) exhibited significant inhibition of NO(.) . Further investigations were focused on 1b, which also inhibited proliferation of T-cells and inflammatory cytokine IL-2 production. The analogs 2-7 weakly inhibited NO(.) production, but strongly inhibited IL-2 cytokine production compared with synthetic peptide 1b. All analogs inhibited the proliferation of T-cells, with analog 7 having the strongest effect. In the analogs, the Pro(6) residue was replaced by Glu/Ala, and the SAR indicates that the nature of this residue plays a role in the biological function of these peptides. Copyright © 2016 European Peptide Society and John Wiley & Sons, Ltd.
authors.affiliation: H. E. J. Research Institute of Chemistry, International Center for Chemical and Biological Sciences, University of Karachi, Karachi, 75270, Pakistan.
authors.forename: Farzana
authors.initials: F
authors.lastname: Shaheen
authors.affiliation: Dr. Panjwani Center for Molecular Medicine and Drug Research, International Center for Chemical and Biological Sciences, University of Karachi, Karachi, 75270, Pakistan.
authors.forename: Almas
authors.initials: A
authors.lastname: Jabeen
authors.affiliation: H. E. J. Research Institute of Chemistry, International Center for Chemical and Biological Sciences, University of Karachi, Karachi, 75270, Pakistan.
authors.forename: Samreen
authors.initials: S
authors.lastname: Ashraf
authors.affiliation: H. E. J. Research Institute of Chemistry, International Center for Chemical and Biological Sciences, University of Karachi, Karachi, 75270, Pakistan.
authors.forename: Muhammad
authors.initials: M
authors.lastname: Nadeem-Ul-Haque
authors.affiliation: H. E. J. Research Institute of Chemistry, International Center for Chemical and Biological Sciences, University of Karachi, Karachi, 75270, Pakistan.
authors.forename: Zafar Ali
authors.initials: ZA
authors.lastname: Shah
authors.affiliation: H. E. J. Research Institute of Chemistry, International Center for Chemical and Biological Sciences, University of Karachi, Karachi, 75270, Pakistan.
authors.forename: Muhammad Asad
authors.initials: MA
authors.lastname: Ziaee
authors.affiliation: Dr. Panjwani Center for Molecular Medicine and Drug Research, International Center for Chemical and Biological Sciences, University of Karachi, Karachi, 75270, Pakistan.
authors.forename: Nida
authors.initials: N
authors.lastname: Dastagir
authors.affiliation: School of Pharmacy, University of East Anglia, Norwich Research Park, Norwich, NR4 7TJ, UK.
authors.forename: A
authors.initials: A
authors.lastname: Ganesan
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D049109:Cell Proliferation / Q000187:drug effects*; D003500:Cyclization; D006801:Humans; D007376:Interleukin-2 / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D007532:Isoleucine / Q000737:chemistry; D019169:Jurkat Cells; D008264:Macrophages / Q000166:cytology / Q000187:drug effects / Q000276:immunology; D051379:Mice; D009569:Nitric Oxide / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D010456:Peptides, Cyclic / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology; D010649:Phenylalanine / Q000737:chemistry*; D011137:Polystyrenes / Q000737:chemistry; D011392:Proline / Q000737:chemistry*; D011487:Protein Conformation; D060327:Solid-Phase Synthesis Techniques / Q000379:methods*; D013237:Stereoisomerism; D013329:Structure-Activity Relationship
chemical_list: D007376:Interleukin-2; D010456:Peptides, Cyclic; D011137:Polystyrenes; C514402:Wang resin; C000614899:stylissatin A; D007532:Isoleucine; D009569:Nitric Oxide; D010649:Phenylalanine; D011392:Proline
keywords: cyclic peptides; inflammation; interleukin 2; nitric oxide; proline rotamers; reactive oxygen species; solid-phase peptide synthesis