A method of preparing a formula or a pharmaceutically acceptable salt thereof, the method comprising contacting a compound of the formula: or a pharmaceutically acceptable salt thereof with a fluoride or radiofluoride source, wherein L is a linker comprising a moiety of the formula -NH-CH 2 CH 2 -(OCH 2 CH 2 -) y -C -or a group of the formula wherein y is 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12; m is 1, 2, 3, or 4; each n is independently 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12; R 1 is phenyl or pyridyl; wherein the phenyl or pyridyl is substituted with an - or [ 18 F]-fluoro group and optionally substituted with a second group selected from halogen, cyano, and nitro; each R 2 is independently hydrogen or C 1 -C 6 alkyl; R 3 is phenyl or pyridyl; wherein the phenyl or pyridyl is substituted with a leaving group and optionally substituted with a second group selected from halogen, cyano, and nitro; and each R is independently hydrogen or a protecting group selected from the group consisting of alkyl, alkenyl, haloalkyl, benzyl, triphenylmethyl (trityl), diphenylmethyl, o-nitrobenzyl, 2,4,6-trimethylbenzyl, p-bromobenzyl, p-nitrobenzyl, p-methoxybenzyl, 2,6-dimethoxybenzyl, 4-(methylsulfinyl)benzyl, 4-sulfobenzyl, 4-azidomethoxybenzyl, and piperonyl, preferably selected from the group consisting of methyl, ethyl, propyl, isopropyl, tert -butyl, allyl, trifluoromethyl, trifluoroethyl, benzyl, triphenylmethyl (trityl), diphenylmethyl, o-nitrobenzyl, 2,4,6-trimethylbenzyl, p-bromobenzyl, p-nitrobenzyl, p-methoxybenzyl, 2,6-dimethoxybenzyl, 4-(methylsulfinyl)benzyl, 4-sulfobenzyl, 4-azidomethoxy-benzyl, and piperonyl; provided that when L is a group of the formula m·(n+2) is greater than or equal to 3 and less than or equal to 21. L is a linker comprising a moiety of the formula -NH-CH 2 CH 2 -(OCH 2 CH 2 -) y -C -or a group of the formula wherein y is 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12; m is 1, 2, 3, or 4; each n is independently 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12; y is 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12; m is 1, 2, 3, or 4; each n is independently 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12; R 1 is phenyl or pyridyl; wherein the phenyl or pyridyl is substituted with an - or [ 18 F]-fluoro group and optionally substituted with a second group selected from halogen, cyano, and nitro; each R 2 is independently hydrogen or C 1 -C 6 alkyl; R 3 is phenyl or pyridyl; wherein the phenyl or pyridyl is substituted with a leaving group and optionally substituted with a second group selected from halogen, cyano, and nitro; and each R is independently hydrogen or a protecting group selected from the group consisting of alkyl, alkenyl, haloalkyl, benzyl, triphenylmethyl (trityl), diphenylmethyl, o-nitrobenzyl, 2,4,6-trimethylbenzyl, p-bromobenzyl, p-nitrobenzyl, p-methoxybenzyl, 2,6-dimethoxybenzyl, 4-(methylsulfinyl)benzyl, 4-sulfobenzyl, 4-azidomethoxybenzyl, and piperonyl, preferably selected from the group consisting of methyl, ethyl, propyl, isopropyl, tert -butyl, allyl, trifluoromethyl, trifluoroethyl, benzyl, triphenylmethyl (trityl), diphenylmethyl, o-nitrobenzyl, 2,4,6-trimethylbenzyl, p-bromobenzyl, p-nitrobenzyl, p-methoxybenzyl, 2,6-dimethoxybenzyl, 4-(methylsulfinyl)benzyl, 4-sulfobenzyl, 4-azidomethoxy-benzyl, and piperonyl; provided that when L is a group of the formula m·(n+2) is greater than or equal to 3 and less than or equal to 21.