A novel 2-cyanobenzothiazole-based (18)F prosthetic group for conjugation to 1,2-aminothiol-bearing targeting vectors

Org Biomol Chem. 2015 Mar 28;13(12):3667-76. doi: 10.1039/c4ob02637c.

Abstract

In a bid to find an efficient means to radiolabel biomolecules under mild conditions for PET imaging, a bifunctional (18)F prosthetic molecule has been developed. The compound, dubbed [(18)F]FPyPEGCBT, consists of a 2-substituted pyridine moiety for [(18)F]F(-) incorporation and a 2-cyanobenzothiazole moiety for coupling to terminal cysteine residues. The two functionalities are separated by a mini-PEG chain. [(18)F]FPyPEGCBT could be prepared from its corresponding 2-trimethylammonium triflate precursor (100 °C, 15 min, MeCN) in preparative yields of 11% ± 2 (decay corrected, n = 3) after HPLC purification. However, because the primary radiochemical impurity of the fluorination reaction will not interact with 1,2-aminothiol functionalities, the (18)F prosthetic could be prepared for bioconjugation reactions by way of partial purification on a molecularly imprinted polymer solid-phase extraction cartridge. [(18)F]FPyPEGCBT was used to (18)F-label a cyclo-(RGDfK) analogue which was modified with a terminal cysteine residue (TCEP·HCl, DIPEA, 30 min, 43 °C, DMF). Final decay-corrected yields of (18)F peptide were 7% ± 1 (n = 9) from end-of-bombardment. This novel integrin-imaging agent is currently being studied in murine models of cancer. We argue that [(18)F]FPyPEGCBT holds significant promise owing to its straightforward preparation, 'click'-like ease of use, and hydrophilic character. Indeed, the water-tolerant radio-bioconjugation protocol reported herein requires only one HPLC step for (18)F peptide purification and can be carried out remotely using a single automated synthesis unit over 124-132 min.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Benzothiazoles / chemical synthesis
  • Benzothiazoles / chemistry*
  • Chromatography, High Pressure Liquid
  • Chromatography, Thin Layer
  • Fluorine Radioisotopes
  • Nitriles / chemical synthesis
  • Nitriles / chemistry*
  • Peptides / chemical synthesis
  • Peptides / chemistry
  • Pyridines / chemistry
  • Radiopharmaceuticals
  • Reference Standards
  • Sulfhydryl Compounds / chemistry*

Substances

  • 2-cyanobenzothiazole
  • Benzothiazoles
  • Fluorine Radioisotopes
  • Nitriles
  • Peptides
  • Pyridines
  • Radiopharmaceuticals
  • Sulfhydryl Compounds
  • pyridine