Stability analysis of glutamic acid linked dimeric RGD peptides

Wednesday, October 10, 2012 — Poster Session II
Noon – 2:00 p.m	Natcher Conference Center, Building 45	NIBIB	CHEM-7

Authors

• L. Lang
• Y. Ma
• D. O. Kiesewetter
• X. Chen

Abstract

Glutamic acid (E) is commonly used as the linker to form dimeric peptides to enhance binding affinity and isothiocyanates are often used for peptide labeling by forming stable thioureas. Attachment of p-SCN-Bn-NOTA (1) to E[c(RGDyK)]2 (2) through a mini-PEG (P) and the product NOTA-PRGD2 (3) was stable at 100 °C in pH 4 buffer. When 1 was directly attached to α amine of E[c(RGDfK)]2 (4), the product NOTA-E[c(RGDfK)]2 (5) became unstable. We used LC-MS to identify the decomposition products of these dimeric peptides. The formation of RGD monomer was observed for 5 after 10 minutes of heating while 2 and 4 released monomer during 40 minutes of heating. In addition to the monomer, the other major product was the result of the loss of monomer and water molecule from the parent compound indicating internal cyclization. Based on LC-MS-MS analyses, the possible structures and mechanisms were proposed. The glutamic acid linked dimeric RDG peptides with a free α amine are labile due to the neighboring amine participation of the hydrolysis. The stability can be increased by converting free amine into an amide. The instability of thiourea formed from α amine may be caused by participation of thiol group derived from thiourea.

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