No abstract

Unique intramolecular rearrangement product ions have been observed in the product ion spectra of a number of peptides. Multiple stages of mass analysis (MS n ), molecular modeling, and chemical modifications of peptides have been used to provide insight into the mechanism of this rearrangement reaction. The rearrangement process begins with a four-residue immonium ion that transfers a proton from the immonium nitrogen to the primary amine on the N-terminus. The proton transfer leads to the rearrangement of the peptide, exposing an internal amino acid on the terminus of the new ion. The internal amino acid that becomes the terminus of the new ion is then readily lost. The reaction seems to benefit from an extended experimental time frame available for reaction. The reaction is most prominent in quadrupole ion trap and Fourier-transform ion cyclotron resonance experiments, is observed under some conditions in a triple quadrupole, but is not seen in a sector instrument. Without previous knowledge of this process, the peptide sequence as determined by MS/MS could be misidentified.

No abstract

Some of the peptide chains esterified to the hydroxymethyl-poly(styrene-co-divinylbenzene) resin are lost by acidolysis during solid-phase peptide synthesis. This loss has been minimized by using 4-(hydroxymethyl)phenylacetamidomethylpoly(styrene-co-divinylbenzene) as the solid support. The phenylacetamidomethyl (Pam) bridge between the peptide and the resin is sufficiently electron withdrawing that the peptidyl-OCH2-Pam-resin is 100 times more stable than the conventional peptidyl-OCH2-resin to cleavage of the ester bond by 50% trifluoroacetic acid in dichloromethane. Boc-Val-OCH2-Pam-resin, which was prepared by two routes, compared favorably with Boc-Val-OCH2-resin for synthesis of the model peptides leucylalanylglycylvaline and decalysylvaline. The greater acid stability of the Pam-resin is expected to result in much higher yields of large peptides prepared by solid-phase peptide synthesis.The solid support commonly used for solid-phase peptide synthesis,3 ie/T-butoxycarbonylaminoacyloxymethylpoly(styrene-co-divinylbenzene), is not completely stable under the acidic conditions required to remove the iert-butoxycarbonyl (Boc) group.4"7 Acidolysis of the benzyl ester link be-

No abstract