title: Stabilized analogs of thymopentin. 1. 4,5-Ketomethylene pseudopeptides.
abstract: The pentapeptide, thymopentin (Arg1-Lys2-Asp3-Val4-Tyr5) is known for its activity as an immunomodulating drug, but with limited half-life in plasma. In this first paper of a series of three studies, the synthesis of analogs stabilized at the peptide bond between the C-terminal amino acids via insertion of a ketomethylene moiety is described. N-Blocked pseudopeptides containing Val(k)Phe, Ala(k)Phe, and Val(k)Val units were prepared and attached to chloromethyl Merrifield resin via the carboxy terminal. Removal of the N-BOC group by trifluoroacetic acid was followed by sequential coupling with N-BOC dipeptides of aspartic acid to yield resin-bound N-BOC pseudotetrapeptides. Removal of N-BOC and coupling with N-BOC-r-N-tosylarginine followed by total cleavage of blocking groups and resin by HF afforded the target pseudopentapeptides. The analogs were found to compete favorably with thymopentin for binding to CEM cells, but binding was reduced by about 20-30% on average. All analogs showed significant enhancement of half-life versus thymopentin in mouse serum, but most showed only modest improvement in human serum. Insertion of proline or norleucine at position 2 in the chain caused a substantial increase in half-life (3-4-fold), while N-methylnorleucine conferred complete stability in the analogs.
authors.affiliation: Bio-Organic Chemistry Laboratory, SRI International, Menlo Park, California 94025, USA.
authors.forename: J I
authors.initials: JI
authors.lastname: DeGraw
authors.forename: R G
authors.initials: RG
authors.lastname: Almquist
authors.forename: C K
authors.initials: CK
authors.lastname: Hiebert
authors.forename: W T
authors.initials: WT
authors.lastname: Colwell
authors.forename: J
authors.initials: J
authors.lastname: Crase
authors.forename: T
authors.initials: T
authors.lastname: Hayano
authors.forename: A K
authors.initials: AK
authors.lastname: Judd
authors.forename: L
authors.initials: L
authors.lastname: Dousman
authors.forename: R L
authors.initials: RL
authors.lastname: Smith
authors.forename: W R
authors.initials: WR
authors.lastname: Waud
authors.forename: I
authors.initials: I
authors.lastname: Uchida
mesh_terms: D000276:Adjuvants, Immunologic / Q000097:blood / Q000737:chemistry* / Q000494:pharmacology; D000818:Animals; D002460:Cell Line; D006207:Half-Life; D006801:Humans; D007659:Ketones / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D051379:Mice; D009842:Oligopeptides / Q000737:chemistry*; D011869:Radioligand Assay; D016339:Spectrometry, Mass, Fast Atom Bombardment; D013329:Structure-Activity Relationship; D016305:Thymopentin / Q000031:analogs & derivatives* / Q000097:blood / Q000494:pharmacology
chemical_list: D000276:Adjuvants, Immunologic; D007659:Ketones; D009842:Oligopeptides; D016305:Thymopentin