18F-labelled folates

A method of direct radiolabeling of the glutamate moiety of a folate compound with 18F comprising:

• reacting a compound of formulae VII or VIIa with 18F,
• wherein
• X1 to X5 are N,
• X6, X7 are independently of each other O or NH,
• R1, R2 are independently of each other H, Hal, —OR′, —NHR′, C1-C12 alkyl, C1-C12 alkoxy, C1-C12 alkanoyl, C2-C12 alkenyl, C2-C12 alkynyl, (C1-C12 alkoxy)carbonyl, or (C1-C12 alkylamino)carbonyl,
• R′ is H or C1-C6 alkyl,
• R3, R4 are independently of each other H, formyl, iminomethyl, nitroso, C1-C12 alkyl, C1-C12 alkoxy, C1-C12 alkanoyl, or halosubstituted C1-C12 alkanoyl,
• R5 is H, CN, Hal, NO2, C1-C12 alkyl, C1-C12 alkoxy, C1-C12 alkanoyl, C2-C12 alkenyl, C2-C12 alkynyl, (C1-C12 alkoxy)carbonyl, or (C1-C12 alkylamino)carbonyl,
• R6, R7 are independently of each other H or straight chain or branched C1-C12 alkyl, which is unsubstituted or substituted by at least one CN, Hal, or NO2,
• S2 is straight chain or branched C1-C6 alkyl, which is unsubstituted or substituted by at least one CN, Hal, or NO2,
• m is 1,
• p is 0, 1 or 2,
• q has a value of 1 to 7,
• Z is a leaving group, and
• wherein 18F is activated by phase transfer catalyst in combination with potassium carbonate or oxalate,
• to obtain a 18F-labeled compound of formulae VI or VIa,