Folate-labeled F-18

A compound of formula II: wherein: X1 to X5 are independently C or N, R1 and R2 are independently: H, Hal, -OR ', -NHR', C1-C12 alkoxy, C1- C12 alkanoyl, C1-C12alkyl, C2-C12alkenyl, C2-C12, (C1-C12) alkoxycarbonyl and (C1-C12) alkoxycarbonyl, in which R 'is H OC1-C6 alkyl, R3, R4 are independently each other: H, formyl, iminomethyl, nitroso, C1-C12, C1-C12, alcanoiloC1-C12 alkanoyl, C1-C12 halosubstituted R5 is H, C1-C12 alkyl, C1-C12 alkanoyl, C1-C12, C2-C12 alkenyl, C2-C12 alkynyl, (C1-C12) alkoxycarbonyl and (C1-C12) alkoxycarbonyl, R6, R7 are independently C1-C12 straight or branched chain alkyl, which is unsubstituted O- by the least one CN, Hal or NO2 or a group of formula III-Ar1-S2-18F -S1 III wherein S1 and S2 are independently a single bond or a spacer unit, such as C1-C12 chain linear or branched is unsubstituted or substituted by at least one CN, Hal or NO2 and the queuno or more of the CH2 groups not adjacent can be replaced independently by -O-, -CO-, -CO-O-, -OCO-, - -NR'-, -N> =, -NR'- CO-, -CO-NR'-, -NR'-CO-O-, -O-CO-NR'-, - NR'-CO-NR'- , -CH> = CH-, -C> = C-, -S-, -SO3R'-, -PR'-or aromatic ring of five or six members, which is unsubstituted or substituted by CN, Hal, NO2 , COR 'OCOOR', wherein R 'represents H or C1-C6 alkyl or a combination thereof yAr1 alkyl is a triazole or tetrazole, provided that one of R6 and R7 is a group of formula III, m is 0 or 1, p is 0, 1 or 2 and q has a value of 1 to 7.