2-(4-Methylsulfonylphenyl)pyrimidines as Prospective Radioligands for Imaging Cyclooxygenase-2 with PET—Synthesis, Triage, and Radiolabeling

• Published in: Molecules (Basel, Switzerland) Vol. 23; no. 11; p. 2850
• Main Authors: Cortes-Salva, Michelle Y., Shrestha, Stal, Singh, Prachi, Morse, Cheryl L., Jenko, Kimberly J., Montero Santamaria, Jose A., Zoghbi, Sami S., Innis, Robert B., Pike, Victor W.
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 02.11.2018; MDPI
• Subjects: Alzheimer's disease; Carbon; carbon-11; COX-2; Drug development; Enzymes; Fluorine; fluorine-18; Inflammation; Labeling; Ligands; Nonsteroidal anti-inflammatory drugs; radioligand; radioligand; carbon-11; fluorine-18; COX-2
• ISSN: 1420-3049; 1420-3049
• DOI: 10.3390/molecules23112850

Cyclooxygenase 2 (COX-2) is an inducible enzyme responsible for the conversion of arachidonic acid into the prostaglandins, PGG2 and PGH2. Expression of this enzyme increases in inflammation. Therefore, the development of probes for imaging COX-2 with positron emission tomography (PET) has gained interest because they could be useful for the study of inflammation in vivo, and for aiding anti-inflammatory drug development targeting COX-2. Nonetheless, effective PET radioligands are still lacking. We synthesized eleven COX-2 inhibitors based on a 2(4-methylsulfonylphenyl)pyrimidine core from which we selected three as prospective PET radioligands based on desirable factors, such as high inhibitory potency for COX-2, very low inhibitory potency for COX-1, moderate lipophilicity, and amenability to labeling with a positron-emitter. These inhibitors, namely 6-methoxy-2-(4-(methylsulfonyl)phenyl-N-(thiophen-2ylmethyl)pyrimidin-4-amine (17), the 6-fluoromethyl analogue (20), and the 6-(2-fluoroethoxy) analogue (27), were labeled in useful yields and with high molar activities by treating the 6-hydroxy analogue (26) with [11C]iodomethane, [18F]2-fluorobromoethane, and [d2-18F]fluorobromomethane, respectively. [11C]17, [18F]20, and [d2-18F]27 were readily purified with HPLC and formulated for intravenous injection. These methods allow these radioligands to be produced for comparative evaluation as PET radioligands for measuring COX-2 in healthy rhesus monkey and for assessing their abilities to detect inflammation.