Abstract
Three methods are described for labeling methanesulfonyl (mesyl) chloride with no‐carrier‐added (NCA) carbon‐11 (t~1/2~=20.4 min; β^+^=99.8%) to provide a new labeling agent of potential value in radiopharmaceutical development for positron emission tomography (PET). Each method uses NCA [^11^C]iodomethane, which is readily prepared from cyclotron‐produced [^11^C]carbon dioxide or [^11^C]methane by known procedures. The first method (route 1) consisted of converting [^11^C]iodomethane into [^11^C]methyllithium and then treatment with sulfuryl chloride. NCA [^11^C]mesyl chloride was obtained in 78% decay‐corrected radiochemical yield (RCY) from [^11^C]iodomethane at 30 min from the end of radionuclide production (ERP). However, co‐production of n‐butanesulfonyl chloride limited the extent of reaction of this labeling agent with 1,2,3,4‐tetrahydroisoquinoline (THIQ). Two new syntheses were devised, based on converting [^11^C]iodomethane into [^11^C]methanethiol by passage over heated sodium hydrogen sulfide for subsequent treatment with either chlorinated water (route 2) or over heated manganese(IV) oxide and then calcium hypochlorite (route 3). These procedures gave NCA [^11^C]mesyl chloride in 77% (route 2) and 28% (route 3) RCYs from [^11^C]iodomethane at about 20 min from ERP. Crude [^11^C]mesyl chloride, produced by route 2 or 3, reacted rapidly with THIQ to give the corresponding NCA [^11^C]methanesulfonamide in 49 or 74% RCY, respectively. Phenol was also converted rapidly with [^11^C]mesyl chloride into the corresponding [^11^C]mesylate (>90% RCY). Copyright © 2003 John Wiley & Sons, Ltd.