Precursors for radiofluorination

Abstract

A method for producing a radiofluorinated compound having an aromatic or heteroaromatic ring carrying [.sup.18F] fluorine as first substituent, a bonding unit, which can bind to a peptide or peptide mimetic, and a spacer group connected via bond A.sup.1 to the bonding unit and via bond A.sup.2 to the ring, wherein the bonding unit has second substituent(s) OH, CONH, and/or COOH. The steps include (a) providing a precursor having the ring carrying a substituent Y, bonding unit with the second substituent(s), and spacer group, wherein substituent Y is N.sup.+(R.sup.1R.sup.2R.sup.3), NO.sub.2, Cl, Br, F, or I, and R.sup.1, R.sup.2, and R.sup.3 are independently C.sub.1-C.sub.6 alkyl; and (b) reacting the precursor with a [.sup.18F] fluoride anion in the presence of an activation salt to the radiofluorinated compound, which has a cation N.sup.+(R.sup.4R.sup.5R.sup.6R.sup.7) with R.sup.4, R.sup.5, R.sup.6, and R.sup.7 being independently C.sub.1-C.sub.6 alkyl, wherein the substituent Y is replaced by [.sup.18F] fluoride.

Claims

1. A method for producing a radiofluorinated compound, which has an aromatic or heteroaromatic ring, which carries [.sup.18F] fluorine as a first substituent, a bonding unit, which can bind to a peptide and a spacer group, which connects the aromatic or heteroaromatic ring to the bonding unit, wherein the aromatic or heteroaromatic ring carries [.sup.18F] fluorine as the first substituent, wherein the bonding unit carries at least one second substituent selected from the group consisting of OH, CONH, and COOH, wherein the bonding unit is connected to the spacer group via a bond A.sup.1 and the spacer group is connected to the aromatic or heteroaromatic ring via a bond A.sup.2, wherein: the bonding unit is a bonding unit of general formula I: ##STR00027## wherein A.sup.l is the bond via which the bonding unit is connected to the spacer group, m and n are the same or different from each other and each are an integer of from 0 to 10; the spacer group is a spacer group of general formula II or general formula III: ##STR00028## wherein A.sup.1 is the bond via which the spacer group is connected to the bonding unit, A.sup.2 is the bond via which the spacer group is connected to the aromatic or heteroaromatic ring of the precursor or to the radiofluorinated compound, R.sup.9 is hydrogen or an unsubstituted or substituted C.sub.1-C.sub.6 alkyl group, and Z is an unsubstituted or mono- or poly-substituted hydrocarbon; and the method comprises the steps of: (a) providing a precursor, which has the aromatic or heteroaromatic ring, which carries a substituent Y, the bonding unit, which can bind to the peptide and which carries at least one second substituent selected from the group consisting of OH, CONH, and COOH, as well as the spacer group, wherein the aromatic or heteroaromatic ring, which carries a substituent Y, is of general formula VId ##STR00029## wherein X each is CR.sup.8 or N, with the provision that at most two of moieties X are N and the remaining of moieties X are CR.sup.8 and R.sup.8 each independently is the bond A.sup.2 to the spacer, hydrogen, or unsubstituted or substituted C.sub.1-C.sub.6 alkyl, with the provision that exactly one residue R.sup.8 is a bond A.sup.2 to the spacer group and the remaining ones of R.sup.8 are the same or different from each other and each represent hydrogen or unsubstituted or substituted C.sub.1-C.sub.6 alkyl; and substituent Y is selected from the group consisting of N.sup.+(R.sup.1R.sup.2R.sup.3), NO.sub.2, Cl, Br, F, or I, and R.sup.1, R.sup.2, and R.sup.3 are the same or different from each other and each are unsubstituted or substituted C.sub.1-C.sub.6 alkyl, wherein the precursor only differs from the radiofluorinated compound in that substituent Y is replaced by [.sup.18F]fluorine; and (b) reacting the precursor with a [.sup.18F] fluoride anion in the presence of an activation salt to the radiofluorinated compound in a one-stage synthesis, wherein substituent Y is replaced by [.sup.18F]fluoride and wherein the activation salt has a cation of general formula N.sup.+(R.sup.4R.sup.5R.sup.6R.sup.7), wherein R.sup.4, R.sup.5, R.sup.6, and R.sup.7 are the same or different from each other and each are unsubstituted or substituted C.sub.1-C.sub.6 alkyl.

2. The method according to claim 1, wherein R.sup.1, R.sup.2, and R.sup.3 each are methyl.

3. The method according to claim 1, wherein R.sup.4, R.sup.5, R.sup.6, and R.sup.7 each are n-butyl.

4. The method according to claim 1, wherein the activation salt has an anion selected from the group comprising hydrogen carbonate, hydrogen sulphate, oxalate, phosphate, and toluenesulphonate.

5. The method according to claim 1, wherein the activation salt is tetra-n-butyl-ammonium hydrogen carbonate.

6. The method according to claim 1, wherein Z is a group of formula VII: ##STR00030##

7. The method according to claim 1, wherein the precursor is a compound of formula IVa: ##STR00031##

8. The method according to claim 6, wherein the precursor is a compound of formula Va: ##STR00032##

Description

EXAMPLE 1

(1) Synthesis of a Precursor of Formula IVb

(2) ##STR00025##

(3) Synthesis of the starting compound VI is as described in literature (Ravert et al., J. Label Compd. Radiopharm 2016, 59, 439-50; Bouvet et al., EJNMMMI Research, 2016, 6: 40). In a mixture of 23.5 ml of trifluoroacetic acid, 0.62 ml of triisopropylsilane, and 0.62 ml of water 2.48 g of the starting compound XX were dissolved and stirred for 3 h at room temperature. Subsequently, the reaction mixture was dropwise added to 241 ml of MTB ether under cooling with an ice bath and vigorously stirring. The precipitated white solid was sucked off by a frit and washed two times with 100 ml of MTB ether. 1.82 g (84%) of the precursor of formula IVb (=5-((S)-5-carboxy-5-(3-((S)-1,3-dicarboxy-propyl)ureido)pentyl-carbamoyl)-N,N,N-trimethylpyridine-2-aminium-2,2,2-trifluoro-acetate) were separated as a white solid.

EXAMPLE 2

(4) Synthesis of a Precursor of Formula Vb

(5) ##STR00026##

(6) The synthesis of the starting compound VIII is as described in literature (Cardinale et al., J. Nucl. Med. 2016, accepted for publication; WO 2015/062370 A1). 0.2 mmol of the starting compound VIII were shaken in 3.5 ml of dimethylformamide for 30 min. Thereafter, 109 mg of N,N,N-trimethyl-5-((2,3,5,6-tetrafluorophenoxy)-carbonyl)pyridine-2-aminiumchloride (Olberg et al., J. Med. Chem. 2010, 53, 1732-1740) and 0.042 ml of triethylamine were added. The reaction mixture was shaken for 2 h, before the resin was filtered and washed three times with DMF and three times with dichloromethane. For cleavage and deprotection, the resin was shaken with a mixture of 4 ml of trifluoroacetic acid, 0.11 ml of triisopropylsilane, and 0.11 ml of water for 90 min. Subsequently, the mixture was filtered, and the filtrate was added dropwise to 40 ml of MTB ether. The mixture was centrifuged, the supernatant solution was pipetted off, and the residue was washed three times with MTB ether. Purification was by HPLC. 172 mg (72%) of the precursor of formula Vb (=5-((S)-4-carboxy-1-((S)-4-carboxy-1-(4-((S)-1-((S)-5-carboxy-5-(3-((S)-1,3-dicarboxy-propyl)-ureido)pentylamino)-3-(naphthalene-2-yl)-1-oxopropane-2-ylcarbamoyl)-benzylamino)-1-oxobutane-2-ylamino)-1-oxobutane-2-ylcarbamoyl)-N,N,N-trimethylpyridine-2-aminium-2,2,2-trifluoroacetate) were separated as a white solid.

EXAMPLE 3

(7) Reaction of a Precursor of Formula IVb in the Presence of Tetra-n-Butyl-Ammonium-Hydrogen Carbonate to [.sup.18F]-DCFPyL

(8) A reaction mixture of 7.5 mg of a precursor of formula IVb in 1 ml of DMF, 1 ml of 0.075M tetra-n-butyl-ammonium hydrogen carbonate (TBA-HCO.sub.3) and [.sup.18F] fluoride anions was reacted at a pH value of about 8.5 for 14 min at 75 C. 47.9% of [.sup.18F]-DCFPyL were obtained. Additionally, radioactive by-compounds could be detected. The proportion of [.sup.18F] fluoride was 28.6%.

EXAMPLE 4

(9) Reaction of a Precursor of Formula IVb in the Presence of Tetra-n-Butyl-Ammonium Toluene Sulphonate to [.sup.18F]-DCFPyL

(10) A reaction mixture of 7.5 mg of a precursor of formula IVb in 1 ml of DMF, 750p of 0.075M tetra-n-butyl-ammonium toluene sulphonate (TBA toluene sulphonate), and [.sup.18F] fluoride anions was reacted at a pH value of about 5.0 for 14 min at 75 C. 37.4% of [.sup.18F]-DCFPyL and 30.9% of [.sup.18F] fluoride were detected. Additionally, radioactive by-compounds were detected the proportion of which was approx. 30%.

EXAMPLE 5

(11) Reaction of a Precursor of Formula IVb in the Presence of Tetra-n-Butyl-Ammonium Phosphate to [.sup.18F]-DCFPyL

(12) A reaction mixture of 2.5 mg of a precursor of formula IVb in 1.5 ml of DMF, 750 l of 0.075M tetra-n-butyl-ammonium phosphate (TBA phosphate) and [.sup.18F] fluoride anions was reacted at a pH value of about 4.7 for 10 min at 85 C. Under these conditions, the precursor was almost quantitatively converted to [.sup.18F]-DCFPyL (97.0%). The by-compounds could be reduced to less than 2%, residual [.sup.18F] fluoride could only be detected in traces.

EXAMPLE 6

(13) Reaction of a Precursor of Formula IVb in the Presence of Tetra-n-Butyl-Ammonium Hydrogen Sulphate to [.sup.18F]-DCFPyL

(14) A reaction mixture of 7.5 mg of a precursor of formula IVb in 1 ml of DMF, 750 l of 0.075M tetra-n-butyl-ammonium hydrogen sulphate (TBA hydrogen sulphate) and [.sup.18F] fluoride anions was reacted at a pH value of about 1.7 for 14 min at 75 C. 15.6% of [.sup.18F]-DCFPyL were obtained, whereas the proportion of [.sup.18F] fluoride was 73.4%. Thus, labeling with [.sup.18F]fluoride anions was relatively poor.

(15) Examples 3 to 6 show that the reaction of precursors of formula IVb with [.sup.18F] fluoride anions in the presence of TBA as an activation salt in a one-stage method results in relatively high yields of the radiofluorinated compound [.sup.18F]-DCFPyL. Example 5 shows that in the slightly acidic pH range with TBA phosphate only traces of the by-compounds are generated and an extremely high labeling yield can be achieved.

EXAMPLE 7

(16) Reaction of a Precursor of Formula Vb in the Presence of Tetra-n-Butyl-Ammonium Hydrogen Carbonate to [.sup.18F]-PSMA-1007

(17) A reaction mixture of 10 mg of a precursor of formula Vb in a mixture of 1 ml of acetonitrile and 600 l of DMF, 750 l of 0.075M TBA hydrogen carbonate, and [.sup.18F] fluoride anions was incubated at a pH value of approx. 7 for 10 min at 120 C. In addition to 37.9% of free [.sup.18F]fluoride, 59.3% of [.sup.18F]F-PSMA-1007 were detected. A radioactive by-product could be detected in traces.

EXAMPLE 8

(18) Reaction of a Precursor of Formula Vb in the Presence of Tetra-n-Butyl-Ammonium Hydrogen Carbonate to [.sup.18F]-PSMA-1007

(19) A reaction mixture of 2.5 mg of a precursor of formula Vb in 1.5 ml of DMF, 750 l of 0.075M TBA hydrogen carbonate, and [.sup.18F] fluoride anions was incubated at a pH value of approx. 7 for 10 min at 85 C. In addition to 8.2% of free [.sup.18F] fluoride, 90.7% of [.sup.18F]-PSMA-1007 were detected. A radioactive by-product could be detected in traces.

EXAMPLE 9

(20) Reaction of a Precursor of Formula Vb in the Presence of Tetra-n-Butyl-Ammonium Phosphate to [.sup.18F]-PSMA-1007

(21) A reaction mixture of 2.5 mg of a precursor of formula Vb in 1.5 ml of DMF, 750 l of 0.075M TBA phosphate, and [.sup.18F] fluoride anions was incubated at a pH value of approx. 4.7 for 10 min at 85 C. The desired product [.sup.18F]-PSMA-1007 was quantitatively formed (99.6%). Free [.sup.18F] fluoride could only be detected in traces.

(22) Examples 7 to 9 show that the reaction of precursors of formula Vb with [.sup.18F] fluoride anions in the presence of TBA as an activation salt in a one-stage method results in relatively high yields of the radiofluorinated compound [.sup.18F]-PSMA-1007. Example 9 shows that in the slightly acidic pH range with TBA phosphate a quantitative labeling yield can be achieved.

EXAMPLE 10

(23) Fully Automated Reaction of a Precursor of Formula Vb in the Presence of Tetra-n-Butyl-Ammonium Hydrogen Carbonate to [.sup.18F]-PSMA-1007 by Means of a Synthesis Module GE TRACERlab MX.sub.FDG

(24) With solvent-resistant stopcocks a cassette for the synthesis of [.sup.18F]-PSMA-1007 was established in analogy to a FDG synthesis cassette on a GE TRACERlab MX.sub.FDG and a synthesis sequence was developed. In detail, the synthesis proceeds in accordance with the following steps: concentrating the [.sup.18F] fluoride on a QMA cartridge, elution with 0.750 ml of TBA hydrogen carbonate, and subsequently drying at 95 C. for 15 min, radioactive labeling with 3 mg of a precursor of formula Vb in 2 ml of DMF for 14 min at 85 C., SPE purification and reformulation. [.sup.18F]-PSMA-1007 could be obtained in radiochemical yields >40%. The radiochemical purity was >95%.