Tandem mass spectrometry for the structural determination of backbone-modified peptides

AbstractA variety of backbone-modified peptides were desorbed by fast atom bombardment and collisionally activated. These peptide modifications involve the replacement of a normal [CONH] peptide linkage with such groups as thiomethylene ether (CH2S), thioamide (CSNH), methyleneamine (CH2NH), and thiomethylene sulfoxide (CH2SO) moieties. Modified linear peptides decompose to give fragmentations characteristic of the modifications as well as typical peptide bond fragments. The presence of a replacement group in cyclic peptides can induce new fragmentations. The presence of other functional groups, such as exocyclic N-terminal residue, however, can dominate the observed fragmentations. Upon collisional activation, unmodified linear peptides fragment to give N-terminal ions as the most abundant daughter ions. In comparison, ψ[CH2NH] and ψ[CH2S] modified linear peptides decompose to give prominent C-terminal sequence ions. The ψ[CH2SO] modified linear peptides, however, fragment in both N- and C-terminal ions of high relative abudance. Depending on the modification, daughter ions or internal fragment ions are observed that are characteristic of the amide bond replacement. Useful structural information can therefore be obtained

Synthesis and characterization of cyclic pseudopeptide libraries containing thiomethylene and thiomethylene-sulfoxide amide bond surrogates

We describe the first examples of a series of cyclic pseudopeptide libraries that have been prepared in a systematic approach in order to facilitate both synthesis and subsequent deconvolution attempts. Our synthetic strategy involved the attachment of a trifunctional amino acid (Asp, Asn or Glu) to a polystyrene resin via its side chain, and stepwise chain elongation using either protected amino acids or a pseudodipeptide building block. Head to tail cyclic peptides were formed by removal of the temporary N- and C-terminal protecting groups followed by ring closure by amide formation. Cyclization of the hexa, hepta, and octapseudopeptides on the resin avoided dimer formation, as monitored by mass spectrometry. We utilized a ‘psi-scan’ approach in which a second fixed position was serially addressed by stepping a dipeptide surrogate, Proψ[CH 2 S]Gly around the rings to generate a group of cyclic pseudopeptide sub-libraries. Oxidation of ψ[CH 2 S] to ψ[CH 2 SO] helped validate the synthesis and also provides a strategy for forming a new set of pseudopeptide libraries (previously described as ‘libraries from libraries’). Our results suggest that libraries of cyclic pseudopeptides are an efficient method of preparing and assaying these synthetically more challenging entities as potential drug leads.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43245/1/11030_2004_Article_169023.pd

I. Aromatic Chlorocarbons: Their Chemistry And Conformations. Ii. Thiazole-containing Ferrocene Condensation Polymers.

PhDOrganic chemistryUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/187275/2/7229213.pd

Synthesis and biological activity of a cyclic pseudohexapeptide analog of somatostatin

A cyclic pseudohexapeptide analog of somatostatin, cyclo(Pro[CH 2S]Phe-D- Trp-Lys-Thr-Phe) was synthesized by solid phase methods and diphenylphosphoryl azide ring closure. The resulting crystalline compound possessed 23% of the growth hormone inhibitory activity of the parent tetradecapeptide and approximately 6% of the activity of the all-amide cyclic hexapeptide analog inspite of the absence of one of the two postulated intramolecular hydrogen bonds

Biological Activities of Thionated Thyrotropin-Releasing Hormone Analogs

No abstract available