3,4,6-Tri-O-acetyl-2-deoxy-2-[ super(18)F]fluoroglucopyranosyl Phenylthiosulfonate: A Thiol-Reactive Agent for the Chemoselective super(18)F-Glycosylation of Peptides

• Published in: Bioconjugate chemistry 2007-01, Vol.18 (1), p.254-262
• Main Authors: Prante, O, Einsiedel, J, Haubner, R, Gmeiner, P, Wester, H-J, Kuwert, T, Maschauer, S
• Format: Article
• Language: English
• ISSN: 1043-1802
• DOI: 10.1021/bc060340v

3,4,5-Tri-O-acetyl-2-[ super(18)F]fluoro-2-deoxy-D-glucopyranosyl 1-phenylthiosulfonate (Ac sub(3)-[ super(18)F]FGlc-PTS) was developed as a thiol-reactive labeling reagent for the site-specific super(18)F-glycosylation of peptides. Taking advantage of highly accessible 1,3,4,6-tetra-O-acetyl-2-deoxy-2-[ super(18)F]fluoroglucopyranose, a three-step radiochemical pathway was investigated and optimized, providing Ac sub(3)-[ super(18)F]FGlc-PTS in a radiochemical yield of about 33% in 90 min (decay-corrected and based on starting [ super(18)F]fluoride). Ac sub(3)-[ super(18)F] FGlc-PTS was reacted with the model pentapeptide CAKAY, confirming chemoselectivity and excellent conjugation yields of >90% under mild reaction conditions. The optimized method was adopted to the super(18)F-glycosylation of the alpha sub(v) beta sub(3)-affine peptide c (RGDfC), achieving high conjugation yields (95%, decay-corrected). The alpha sub(v) beta sub(3) binding affinity of the glycosylated c(RGDfC) remained uninfluenced as determined by competition binding studies versus super(125)I-echistatin using both isolated alpha sub(v) beta sub(3) and human umbilical vein endothelial cells (K sub(i) = 68 plus or minus 10 nM ( alpha sub(v) beta sub(3)) versus K sub(i) = 77 plus or minus 4 nM (HUVEC)). The whole radiosynthetic procedure, including the preparation of the super(18)F-glycosylating reagent Ac sub(3)-[ super(18)F]FGlc-PTS, peptide ligation, and final HPLC purification, provided a decay-uncorrected radiochemical yield of 13% after a total synthesis time of 130 min. Ac sub(3)-[ super(18)F]FGlc-PTS represents a hovel super(18)F-labeling reagent for the mild chemoselective super(18)F-glycosylation of peptides indicating its potential for the design and development of F-labeled bioactive S-glycopeptides suitable to study their pharmacokinetics in vivo by positron emission tomography (PET).