WO2015091558A1 - Quinoline derivates as precursors of 18f-labelled radiotracers and radiolabelling method - Google Patents

Abstract

The present invention relates to the field of radiopharmaceuticals for in vivo imaging, in particular to precursors for the preparation of ¹⁸F-labelled tau imaging radiotracers. The invention provides alternative methods of preparation of such precursors, with fewer process steps. Also provided are protected quinoline intermediates useful in the synthesis, and methods of ¹⁸F-radiofluorination using precursors prepared via the method of the invention.

Description

QUINOLINE DERIVATES AS PRECURSORS OF 18F-LABELLED RADIOTRACERS AND RADIOLABELLING METHOD

Field of the Invention.

The present invention relates to the field of radiopharmaceuticals for in vivo imaging, in particular to precursors for the preparation of ¹⁸F-labelled tau imaging radiotracers. The invention provides alternative methods of preparation of such precursors, with fewer process steps. Also provided are protected quinoline intermediates useful in the synthesis, and methods of ¹⁸F-radiofluorination using precursors prepared via the method of the invention.

Background to the Invention.

Tau is a phosphoprotein having a physiological function of binding to tubulin to stabilise microtubules. The degree of tau phosphorylation determines the binding affinity to microtubles - tau hyperphosphorylation leads to weaker microtubule binding. There is growing evidence that tau malfunction is implicated in, or triggers neurodegeneration and dementia. There is therefore significant interest in the molecular imaging of tau in vivo.

EP 1574500 Al (BF Research Institute Inc.) discloses diagnostic probes for Tau proteins which comprise optionally radio labelled compounds of structure:

wherein:

Ri, R₂, and R₃ independently are H, Hal, OH, COOH, S0₃H, NH₂, N0₂, CO- NH-NH₂, Ci_4 alkyl or 0-Ci_₄ alkyl, wherein two Ri groups together, may form a benzene ring;

R4 and R₅ are independently H or Ci_₄ alkyl; and

m and n are independently integers of value 0 to 4. EP 2634177 Al (WO 2012/057312 Al) discloses Tau imaging radiotracers which are radio labelled compounds of Formula I):

(I)

wherein

A is

R is Hal, a -C(=0)-lower alkyl group (said alkyl group may be each independently substituted with one or more substituents selected from the group consisting of NR^aR^b, Hal, and OH), a lower alkyl group (said alkyl group may be each

independently substituted with one or more substituents selected from the group consisting of Hal and OH), an -O-lower alkyl group (said alkyl group may be each independently substituted with one or more substituents selected from the group consisting of Hal and OH), or

,R⁴

\

wherein

R⁴ and R⁵ are each independently H, a lower alkyl group, or a cycloalkyl group, or R⁴, R⁵, and the nitrogen atom to which they are attached are together form a 3- to 8-membered nitrogen-containing aliphatic ring (one or more carbon atoms constituting said nitrogen-containing aliphatic ring may be replaced by a N, S or O atom, and when the carbon atom is replaced by a N atom, said N atom may be substituted with a lower alkyl group), or

R⁴ and the nitrogen atom to which it is attached, together with the ring A, form an 8- to 16-membered nitrogen-containing fused bicyclic ring system (one or more carbon atoms constituting said nitrogen-containing fused bicyclic ring system may be replaced by a N, S or O atom, and when the carbon atom is replaced by a nitrogen atom, said nitrogen atom may be substituted with a lower alkyl group), and R⁵ is H, a lower alkyl group, or a cycloalkyl group,

where a solid line intersected with a broken line designates a linkage with another structural portion in the general formulae above,

R² or R³ is each independently Hal, OH, COOH, S0₃H, N0₂, SH, NR^aR^b, a lower alkyl group (said alkyl group may be each independently substituted with one or more substituents selected from the group consisting of Hal and OH), or an -O- lower alkyl group (said alkyl group may be each independently substituted with one or more substituents selected from the group consisting of Hal and OH),

the ring A is unsubstituted or substituted with R⁶ (wherein R⁶ is one or more substituents independently selected from the group consisting of Hal, OH, COOH, S0₃H, N0₂, SH, NR^aR^b, a lower alkyl group (said alkyl group may be each independently substituted with one or more substituents selected from the group consisting of Hal and OH), and an -O-lower alkyl group (said alkyl group may be each independently substituted with one or more substituents selected from the group consisting of Hal, OH, and an -O-lower alkyl group-O-lower alkyl group (said alkyl group may be each independently substituted with Hal))),

R^a and R^b are independently H or a lower alkyl group (said alkyl group may be each independently substituted with one or more substituents selected from the group consisting of Hal and OH),

m is an integer from 0 to 4, and

n is an integer from 0 to 4. EP 2634177 Al provides various syntheses of the claimed compounds. One such method is reaction of a com ound of formula (II) with a compound of formula (III):

wherein A, R¹, R² and m are as defined for formula (I) therein;

R⁷ is NH₂ or N0₂. EP 2634177 Al discloses the following 9-step synthesis of the ¹⁸F labelling precursors having alkoxy substituents at the 6-position functionalised with hydroxy and ¹⁸F groups:

where:

Boc = fert-butyloxycarbonyl; TBS = tert-butyldimethylsilyl THP = tetrahydropyran;

Ts = 4-toluenesulfonyl.

Okamura et al [J.Nucl.Med., 54(8), 1420-1427 (2013)] disclose that ¹⁸F- arylquino lines, in particular ¹⁸F-THK-5105 and ¹⁸F-THK-51 17 are novel imaging agents for imaging tau pathology in Alzheimer's disease. Okamura et al use the following precursors and radio fluorination method:

There is therefore still a need for alternative and/or improved methods of preparing the radio labelling precursors of the tau imaging agents of EP 2634177 Al and

Okamura et al.

The Present Invention.

The precursor synthesis method of the present invention provides a shorter synthesis than the prior art. In addition, the present method avoids: (i) the Mitsunobu coupling; (ii) the Suzuki cross coupling, of the prior art.

The present synthesis provides improved yields compared to the prior art. The present Friedlander synthesis is also believed to be easier to scale up due to improved robustness of the process.

The present method also provides a protected quinoline intermediate useful preparation of radio labelling precursors. Detailed Description of the Invention.

In a first aspect, the present invention provides a method of preparation of a radio labelling precursor of Formula (VI) which comprises alkylation of a quinoline of

Formula IV) with a disulfonate of Formula (V):

R¹ and R² independently comprise H or Ci_₄ alkyl, or R¹ and R² together with the N atom and optionally the phenyl ring to which they are attached comprise a 5- or 6- membered nitrogen-containing aliphatic or heteroaromatic ring, optionally incorporating one further heteroatom chosen from -O- , -S- , =N- and -NR^a-, where R^a is H or Ci_₄ alkyl;

R^3a and R^3b each independently comprise an R³ group;

R³ independently comprises Ci_₄ alkyl, Ci_₄ haloalkyl, C5-8 aryl or C_6-12 aralkyl;

Pg¹ is an alcohol protecting group.

The term "alkylation" has its' conventional meaning, and refers to an etherification reaction in which the quinoline hydroxy group of the quinoline (IV) is O-alkylated with an alkylating agent to give an ether.

By the term "radio labelling precursor" is meant a non-radioactive compound suitable for reaction with a supply of a radioisotope in a suitable solvent, to give the radiolabeled compound of interest in the minimum numbers of steps. Thus, the precursor is designed such that the chemical and radioactive yield is optimised, and the number of steps involving the handling of radioactivity is minimized. The precursor is particularly suitable for radiolabelling with ¹⁸F.

The term "disulfonate" refers to Compound (V) which has two sulfonate ester groups, i.e. groups which are sulfonic acid esters. These are the groups -OS0₂R^3a and

-OS0₂R^3b. R^3a and R^3b can be the same or different. Such sulfonate esters are important leaving groups in nucleophilic substitution, and the reactivity of the sulfonate ester towards nucleophilic substitution can be adjusted depending on the choice of R³. Thus, tresylates (R³ = -CH₂CFs) are -400 times less reactive than triflates (R³ = -CF3), but still -100 times more reactive than tosylates (R³ = -C₆H4- CH₃) [M.B.Smith and J. March, March 's Advanced Organic Chemistry, Fifth Edition, John Wiley & Sons Inc., (2001), pages 445-449].

The term 'haloalkyl' includes within its' scope such alkyl groups having a single halogen substituent, to fully halogenated alkyl groups, i.e. where all the hydrogen atoms have been replaced by a halogen atom. Fluorine is a preferred halogen substituent for the R³ group, so this includes mono fluoro alkyl groups (e.g. 2- fluoroethyl), perfluorinated groups (e.g. CF₃), and variants within (e.g. -CH₂CF₃). By the term "protecting group" is meant a removable group which inhibits or suppresses undesirable chemical reactions, and which is designed such that it can be both attached and removed to/from the functional group in question under mild enough conditions that do not modify or compromise the rest of the molecule. After deprotection the desired product is obtained. The use of protecting groups is described in Protective Groups in Organic Synthesis, 4^th Edition, Theodora W.

Greene and Peter G. M. Wuts, [Wiley Blackwell, (2006)]. The term "deprotection" has its conventional meaning in the field of chemistry and/or radiochemistry, i.e. the removal of a protecting group.

The alcohol protecting group (Pg¹) of the first aspect protects the secondary alcohol group of the compound of Formula (V). Suitable Pg¹ groups include ethers (alkyl, aryl, aralkyl, or silyl); esters or carbonates. When R¹ and R² together with the N atom and optionally the phenyl ring to which they are attached comprise a 5- or 6- membered nitrogen-containing aliphatic or heteroaromatic ring, that means that the 5- or 6- membered ring incorporating one or more of N, R¹ and R² may either be a substituent on the phenyl ring, or be fused with the phenyl ring bearing -NR'R². Examples of the former would be piperidine or morpholine rings singly bonded to the phenyl ring. A preferred example of a fused ring is when X¹ is:

Preferred aspects.

In the method of the first aspect, R¹ and R² are preferably chosen such that at least one, more preferably both of R¹ and R² is Ci_₄ alkyl, most preferably methyl.

In the method of the first aspect, R³ of the compound of Formula (VI) is preferably chosen from: -CH₃, -CF₃, -C₄F₉, -CH₂CF₃, -C₆H₄-CH₃, -C₆H₄-N0₂ or -C₆H₄-Br. R³ of

Formula (VI) is most preferably -CeH₄-CH₃

In Formula (V), preferably R^3A = R^3B, i.e. the disulfonate ester (V) is symmetrical.

In the method of the first aspect, X¹ is preferably:

Pg¹ is preferably a Pg^la group, wherein Pg^la comprises:

(i) -R^c;

(ifj -Ar¹ ;

(iii) -CF Ar¹),;

(n -QAr¹),;

(v) tetrahydropyranyl optionally substituted with one or more substituents chosen from Hal and OCH₃; (vi) -CH₂OR^b;

(vii) -SiR^d ₃;

(viii) -(C=0)R^d;

(ix) -(C=0)OR^e wherein R^e is H, R^d, Ci_₄ haloalkyl or vinyl; or

(x) -(C=0)NHR^d;

wherein:

each R^b is independently R^d or C_2-4 alkoxyalkyl optionally substituted with one or more Hal;

each R^c is independently Ci_₄ alkyl;

each R^d is independently R^c or Ar¹; and

Ar¹ is independently benzyl or phenyl optionally substituted with one or more substituents chosen from Hal, CH₃, OCH₃, N0₂ or -N(CH₃)₂.

Pg¹ is most preferably tetrahydropyranyl. In the method of the first aspect, the quinoline of Formula (IV) is preferably prepared by de rotection of a protected quinoline of Formula (III):

(III) (IV)

wherein:

Pg² is a phenol protecting group;

X¹ in Formula (III) is as defined for Formula (IV).

The term "protecting group" is as defined above. Suitable Pg² groups include ethers (alkyl, aryl, aralkyl, or silyl); esters or carbonates. Preferred Pg² groups are Pg^la groups as defined above.

The protected quinoline of Formula (III) is preferably prepared by reaction of a protected phenol of Formula (I) with a ketone of Formula (II):

Y¹ is -CHO, -CH₂OH or -CH=N-Ar².

Q is -NH₂ or -N0₂;

Ar² is independently benzyl or phenyl optionally substituted with one or more substituents chosen from Hal, CH₃ or OCH₃. Ar² is preferably -C₆H₄-CH₃; X¹ in Formula (II) is as defined for Formula (III), above. Pg² is preferably a Pg^2a group, where Pg^2a comprises:

(i) -R^c;

(ifj -Ar¹;

(iii) tetrahydropyranyl optionally substituted with one or more substituents chosen from Hal and OCH₃;

(iv) -CH₂OR^b;

(v) -SiR^d ₃;

(vi) -(C=0)R^d;

(vii) -(C=0)OR^e wherein R^e is H, R^d, Ci_₄ haloalkyl or vinyl; or

(viii) -(C=0)NHR^d;

wherein R^b, R^c, R^d, R^e and Ar¹ are as defined above.

Pg² is more preferably benzyl or ethoxymethyl (EOM).

When R^3a = R^3b, then Compound (V) is symmetrical, and such compounds can be obtained as follows: R^3a = R^3b = OTs and Pg¹ = THP [Nieto et al, Synthesis, (21), 3700-3704 (2011) and Adamsen et al, J.Lab.Comp.Radiopharm., 48, 923-927 (2005)]; R^3a = R^3b = OTs or OMs and Pg¹ = THP or Bz [Lim et al,

Appl.Radiat.Isotop., 44(8), 1085-1091 (1993)]; R^3a = R^3b = OTs and Pg¹ = Ac [Chan et al, Appl.Radiat.Isotop., 65, 682-686 (2007)].

Compound (IV) can be obtained by deprotection of the protected quinoline Compound (III) as described above.

The method of the first aspect is suitably carried out by treatment of the quinolone (IV) with the disulfonate (V) in the presence of a base, such as potassium carbonate in DMF with heat. Reducing the amount of dimerization is achieved by use of an excess of disulfonate (V). Further details are provided in the supporting Examples.

In a second aspect, the present invention provides a method of preparation of a radio labelling precursor of Formula (VI) which comprises:

(i) reaction of a protected phenol of Formula (I) with a ketone of Formula (II) to give a rotected quinoline of Formula (III):

(ii) deprotection of the protected quinoline of Formula (III) from step (i) to give a quinoline of Formula IV):

(Ml) (IV)

(iii) alkylation of the quinoline of Formula (IV) from step (ii) with a disulfonate of Formula (V) to give the radiolabelling precursor of Formula (VI):

(VI)

(IV) wherein: X¹, R^3a, R^3b, Pg¹ and Pg², plus Y¹ and Q together with preferred embodiments thereof are as described in the first aspect (above).

In a third aspect, the present invention provides a method of preparation of a quinoline of Formula (IV) which comprises deprotection of a protected quinoline of Formula III):

(I I I) (IV) wherein:

X¹ and Pg² together with preferred embodiments thereof are as described in the first aspect.

Suitable deprotection conditions for specific protecting groups Pg² are described in Protective Groups in Organic Synthesis, 4^th Edition, Theodora W. Greene and Peter G. M. Wuts, [Wiley Blackwell, (2006)]. The quinoline (IV) is suitably purified by flash chromatography.

In a fourth aspect, the present invention provides a method of preparation of a protected quinoline of Formula (III) which comprises reaction of a protected phenol of Formula I) with a ketone of Formula (II):

wherein:

Y¹, Q, X¹ and Pg² together with preferred embodiments thereof are as described in the first aspect (above). The method of the fourth aspect is based on the Friedlander quinoline synthesis, and typically carried out in aqueous or alcoholic solvent, optionally in the presence of a basic or acidic catalyst. Suitable reaction conditions are described by Shiri et al

[Friedlander Annulation in the Synthesis of Azaheterocyclic Compounds, Chapter 2 pages 139-227 in Adv. Heterocycl. Chem., Vol 102, Elsevier (2011)]. Compound (III) is suitably purified by recrystallisation or flash chromatography.

Illustrative compounds of Formula (I) can be obtained according to Scheme 1 :

Scheme 1.

The starting material is commercially available from Sigma- Aldrich. Further details are provided in the Examples. Compounds of Formula (II) are commercially available from Sigma- Aldrich.

In a fifth aspect, the present in ntion provides a protected quinoline of Formula (III):

wherein:

X¹ and Pg² together with preferred embodiments thereof are as described in the first aspect (above);

with the proviso that when X¹ = -C₆H₄-NR¹R² and R¹ = R² = H or Ci_₄ alkyl, then Pg² is not Ci_₄ alkyl. In Formula (III), Pg² is preferably a Pg^2a group as defined in the first aspect.

Protected quino lines of Formula (III) can be obtained as described in the fourth aspect (above).

In a sixth aspect, the present invention provides a method of preparation of an ¹⁸F- labelled radiotracer of Formula (VII), which comprises:

(a) carrying out the method of preparation of the first or second aspect to give a radio labelling precursor of Formula VI):

(VI)

(b) reaction of the precursor of Formula (VI) from step (a) with [¹⁸F] -fluoride in a suitable solvent, and removal of the Pg¹ protecting group, to give the ¹⁸F- labelled radiotracer of Formula VII):

(VII)

wherein X¹, R³ and Pg¹ together with preferred embodiments thereof are as described in the first aspect.

Step (b) of the method of the sixth aspect is preferably carried out using an automated synthesizer apparatus. More preferably, said automated synthesizer apparatus comprises a disposable cassette which comprises the precursor of Formula (VI).

By the term "automated synthesizer" is meant an automated module based on the principle of unit operations as described by Satyamurthy et al [Clin.Positr.Imag., 2(5), 233-253 (1999)]. The term 'unit operations' means that complex processes are reduced to a series of simple operations or reactions, which can be applied to a range of materials. Such automated synthesizers are preferred for the method of the present invention especially when a radiopharmaceutical composition is desired. They are commercially available from a range of suppliers [Satyamurthy et al, above], including: GE Healthcare; CTI Inc; Ion Beam Applications S.A. (Chemin du

Cyclotron 3, B-1348 Louvain-La-Neuve, Belgium); Raytest (Germany) and Bioscan (USA).

Commercial automated synthesizers also provide suitable containers for the liquid radioactive waste generated as a result of the radiopharmaceutical preparation.

Automated synthesizers are not typically provided with radiation shielding, since they are designed to be employed in a suitably configured radioactive work cell. The radioactive work cell provides suitable radiation shielding to protect the operator from potential radiation dose, as well as ventilation to remove chemical and/or radioactive vapours. The automated synthesizer preferably comprises a cassette. By the term "cassette" is meant a unit piece of apparatus designed such that the whole unit fits removably and interchangeably onto an automated synthesizer apparatus (as defined above), in such a way that mechanical movement of moving parts of the synthesizer controls the operation of the cassette from outside the cassette, i.e.

externally. Suitable cassettes comprise a linear array of valves, each linked to a port where reagents or vials can be attached, by either needle puncture of an inverted septum-sealed vial, or by gas-tight, marrying joints. Each valve has a male-female joint which interfaces with a corresponding moving arm of the automated synthesizer. External rotation of the arm thus controls the opening or closing of the valve when the cassette is attached to the automated synthesizer. Additional moving parts of the automated synthesizer are designed to clip onto syringe plunger tips, and thus raise or depress syringe barrels.

The cassette is versatile, typically having several positions where reagents can be attached, and several suitable for attachment of syringe vials of reagents or chromatography cartridges (e.g. solid phase extraction or SPE). The cassette always comprises a reaction vessel. Such reaction vessels are preferably 1 to 10 cm³, most preferably 2 to 5 cm³ in volume and are configured such that 3 or more ports of the cassette are connected thereto, to permit transfer of reagents or solvents from various ports on the cassette. Preferably the cassette has 15 to 40 valves in a linear array, most preferably 20 to 30, with 25 being especially preferred. The valves of the cassette are preferably each identical, and most preferably are 3-way valves. The cassettes are designed to be suitable for radiopharmaceutical manufacture and are therefore manufactured from materials which are of pharmaceutical grade and ideally also are resistant to radio lysis.

Preferred automated synthesizers of the present invention comprise a disposable or single use cassette which comprises all the reagents, reaction vessels and apparatus necessary to carry out the preparation of a given batch of radio fluorinated

radiopharmaceutical. The cassette means that the automated synthesizer has the flexibility to be capable of making a variety of different radiopharmaceuticals with minimal risk of cross-contamination, by simply changing the cassette. The cassette approach also has the advantages of: simplified set-up hence reduced risk of operator error; improved GMP (Good Manufacturing Practice) compliance; multi-tracer capability; rapid change between production runs; pre-run automated diagnostic checking of the cassette and reagents; automated barcode cross-check of chemical reagents vs the synthesis to be carried out; reagent traceability; single-use and hence no risk of cross-contamination, tamper and abuse resistance. The invention is illustrated by the non-limiting Examples detailed below. Example 1 provides the synthesis of a protected phenol within the scope of Formula (I). Example 2 provides the synthesis of Compound 1 (a quinoline within the scope of Formula IV). Example 3 provides the syntheses of Compounds 2 to 5. Examples 4 to 6 provide the syntheses of Compounds 6 to 8, which are non-radioactive ¹⁹F analogues of the ¹⁸F compounds of Formula (VII).

Compounds of the Invention.

Compound 9 _o.THP

H

Compound 10

H

Abbreviations.

Ac: Acetyl

Acm: Acetamidomethyl

ACN: Acetonitrile

AcOH: Acetic acid.

Boc: tert-Butyloxycarbonyl

tBu: tertiary-butyl

DCM: Dichloromethane

DIPEA: N,N-Diisopropylethyl amine

DMF: Dimethylformamide

DMSO: Dimethylsulfoxide

HPLC: High performance liquid chromatography;

MW: molecular weight;

Ms: mesylate i.e. sulfonate ester of methanesulfonic acid.

RP-HPLC: reverse-phase high performance liquid chromatography;

tBu: tert-butyl;

TFA: Trifluoroacetic acid;

THF: Tetrahydrofuran;

Trt: Trityl;

Tf: triflate i.e. sulfonate ester of trifluoromethanesulfonic acid.

Ts: tosylate i.e. sulfonate ester of para-tolunesulfonic acid.

Example 1: Synthesis of 5-(Benzyloxy)-2-nitrobenzaldehyde,

5-Hydroxy-2-nitrobenzaldehyde (Sigma- Aldrich; 5 g, 29.9 mmol) and potassium carbonate (4.96 g, 35.9 mmol) were suspended in DMF (25 mL, 323 mmol) under argon. Benzyl bromide (3.91 mL, 32.9 mmol) was added and the mixture was stirred overnight. The temperature was raised to 60 °C for two hours and after cooling, the mixture was filtered and diluted with ethyl acetate (100 mL). The organic phase was washed with water (3 x 200 mL) and dried. 6.8 g of the title compound was obtained. 1H NMR, 400 MHz (CDCls, 25 °C): 10.51 ppm (s, 1H), 8.17 ppm (d, 1H, J=9.1 Hz), 7.47-7.36 ppm (m, 6H), 7.22 ppm (dd, 1H, J=9.1, 2.8 Hz), 5.23 ppm (s, 2H).

Example 2: Synthesis of 4-(6-(Benzyloxy)auinolin-2-yl)-N-methylaniline

(Compound 1).

5-(Benzyloxy)-2-nitrobenzaldehyde (Example 1; 1.931 g, 7.50 mmol), ethanol (26.3 mL, 450 mmol), iron (1.677 g, 30.0 mmol) and hydrochloric acid (3.75 mL, 0.375 mmol) were charged in a thick walled glass tube with a magnetic stir bar and capped. The tube was heated to 100 °C in an oil bath with 1200 rpm stirring. After lh the tube was cooled and opened and l-(4-(methylamino)phenyl)ethanone (Sigma- Aldrich; 1.120 g, 7.51 mmol) and potassium hydroxide (0.505 g, 9.01 mmol) were added. Then the tube was capped and heated at 100 °C overnight. The following day, the reaction mixture was taken up in DCM (500 mL) and water (500 mL). The aqueous phase was washed once with DCM and the combined organic phases were dried and evaporated to dryness. The crude material was recrystallised from ethyl acetate to yield 2.2 g of the title compound as light yellow flakes.

lH NMR, 400 MHz (CDCI₃, 25 °C): 8.25-8.0 ppm (m, 4H), 7.78 ppm (d, 1H, J=7.9 Hz), 7.54- 7.34 ppm (m, 6H), 7.16 ppm (d, 1H, J=2.7Hz), 6.77-6.71 ppm (m, 2H), 5.21 ppm (s, 2H), 2.93 ppm, (s, 3H), 1.62 ppm (bs, lH).

Example 3: Synthesis of 2-(4-(Methylamino)phenyl)quinolin-6-ol (Compound 2) and Compounds 3 to 5. Compound 1 (Example 2; 1021 mg, 3 mmol) was dissolved in dichloromethane (12 mL, 187 mmol). Boron tribromide (6.00 mL, 6.00 mmol) was added at ambient temp in 6 portions every 10 minutes and the reaction mixture was sonicated after each addition. The reaction was quenched with carefully added methanol (3 mL) and poured into water (100 ml) and pH was adjusted to 8 with NaOH (6M) with good stirring. The formed precipitate was collected and dried. 620 mg of the title compound was obtained.

lH NMR, 400 MHz (DMSO D₆, 25 °C): 9.80 ppm (s, 1H), 8.08 ppm (d, 1H, J=8.8 Hz), 7.99 ppm (d, 2H, J=8.8 Hz), 7.85 ppm (d, 1H, J=8.8 Hz), 7:80 ppm (d, 1H, 8.8 Hz), 7.25 ppm (dd, 1H, J=9.1, 2.7 Hz), 7.09 ppm (d, 1H, 2.7 Hz), 5.99 ppm (bs, 1H), 2.75 ppm (d, 3H, J=4.7 Hz).

The following compounds were obtained in a similar fashion:

2-(pyridin-3-yl)quinolin-6-ol (Compound 3) HPLC/MS (TOF ES+ , m/e): 223.2 [M⁺].

2-(pyridin-2-yl)quinolin-6-ol (Compound 4) HPLC/MS (TOF ES+ , m/e): 223.2

[M+].

2-(quinoxalin-6-yl)quinolin-6-ol (Compound 5) HPLC/MS (TOF ES+ , m/e): 274.3 [M⁺].

(2S)-3-((2-(6-(methylamino)pyridin-3-yl)quinolin-6-yl)oxy)-2-((tetrahydro-2H-pyran- 2-yl)oxy)propyl 4-methylbenzenesulfonate (Compound 9) HPLC/MS (TOF ES+ , m/e): 564.2 [M+].

(S)-l-fluoro-3-((2-(6-(methylamino)pyridin-3-yl)quinolin-6-yl)oxy)propan-2-ol (Compound 10) HPLC/MS (TOF ES+ , m/e): 328.1 [M+].

Example 4: Synthesis of l-Fluoro-3-ff2-fpyridin-3-yl)quinolin-6-yl)oxy)propan-2- ol (Compound 6).

Compound 3 (Example 3; 135 mg, 0.607 mmol) was dissolved in DMF (0.706 mL, 9.1 1 mmol) in a thick walled vial and epifluorohydrin (0.059 mL, 0.911 mmol) and potassium carbonate (168 mg, 1.215 mmol) were added. The vial was capped and heated to 90 °C overnight. The following day the mixture was evaporated to dryness and redissolved in 25 mL water/acetonitrile 90/10. The material was purified by preparative HPLC in one injection. Relevant fractions were collected and evaporated to dryness to furnish 90 mg of the title compound.

HPLC/MS (TOF ES+ , m/e): 299.3 [M+]. Example 5: Synthesis of l-Fluoro-3-(|2-(auinoxalin-6-yl)quinolin-6- yl)oxy)propan-2-ol (Compound 7) plus Compound 8.

Compound 5 (Example 3; 820 mg, 3 mmol) was dissolved in DMF (4 mL, 51.7 mmol) in a thick walled vial and epifluorohydrin (0.333 mL, 5.17 mmol) and potassium carbonate (952 mg, 6.89 mmol) was added. The vial was capped and heated to 90 °C with stirring overnight. The following day the mixture was evaporated to dryness and redissolved in 60 mL water/acetonitrile 90/10. The material was purified by preparative HPLC in two injections. Relevant fractions were collected and evaporated to dryness. 300 mg of the obtained material was dissolved in water (30 mL) and left overnight. The following day the resulting red precipitate was isolated and dried to yield 100 mg of the title compound as dark red crystalline product.

lH NMR, 400 MHz (CDC1₃, 25 °C): 9.03 ppm (d, IH, J=l,7 Hz), 8.99 ppm (d, IH, J=1.7 Hz), 8.90 ppm (d, IH, J=1.9 Hz), 8.81 ppm (dd, IH, J=8.8, 2.0 Hz), 8.46 ppm (d, IH, J=8.7 Hz), 8.4 ppm (d, IH, J=8.7 Hz), 8.26 ppm (d, IH, J=8.9 Hz), 8.11-8.06 ppm (m, IH), 7.53-7.49 ppm (m, 2H), 4.67-4.56 ppm (m, IH), 4.56-4.45 ppm (m, IH), 4.23-4.09 ppm (m, 3H). l-Fluoro-3-((2-(pyridin-2-yl)quinolin-6-yl)oxy)propan-2-ol (Compound 8) was obtained in a similar fashion: HPLC/MS (TOF ES+ , m/e): 299.3 [M+].

Claims

CLAIMS.

1. A method of preparation of a radio labelling precursor of Formula (VI) which comprises alkylation of a quinoline of Formula (IV) with a disulfonate of Formula (V :

R¹ and R² independently comprise H or Ci_₄ alkyl, or R¹ and R² together with the N atom and optionally the phenyl ring to which they are attached comprise a 5- or 6- membered nitrogen-containing aliphatic or hetero aromatic ring, optionally incorporating one further heteroatom chosen from -O- , -S- , =N- and -NR^a-, where R^a is H or Ci_₄ alkyl;

R^3a and R^3b each independently comprise an R³ group;

R³ independently comprises Ci_₄ alkyl, Ci_₄ haloalkyl, C5-8 aryl or C_6-12 aralkyl;

Pg¹ is an alcohol protecting group.

2. The method of claim 1 , where X¹ is:

3. The method of claim 1 or claim 2, where R³ is chosen from: -CH₃, -CF₃, -C4F9, -CH2CF3, -C₆H₄-CH₃, -C₆H₄-N0₂ or -C₆H₄-Br.

4. The method of any one of claims 1 to 3, where Pg¹ is a Pg^la group, wherein Pg^la comprises:

(i) -R^c;

(ifj -Ar¹ ;

(iii) -CH(Ar¹)₂;

(v) tetrahydropyranyl optionally substituted with one or more substituents chosen from Hal and OCH₃;

(vi) -CH₂OR^b;

(vii) -SiR^d ₃;

(viii) -(C=0)R^d;

(ix) -(C=0)OR^e wherein R^e is H, R^d, Ci_₄ haloalkyl or vinyl; or

(x) -(C=0)NHR^d;

wherein:

each R^b is independently R^d or C₂_₄ alkoxyalkyl optionally substituted with one or more Hal;

each R^c is independently Ci_₄ alkyl;

each R^d is independently R^c or Ar¹; and

Ar¹ is independently benzyl or phenyl optionally substituted with one or more substituents chosen from Hal, CH₃, OCH₃, N0₂ or -N(CH₃)₂.

5. The method of any one of claims 1 to 4, where the quinoline of Formula (IV) is pre ared by deprotection of a protected quinoline of Formula (III):

(I II) (IV)

wherein:

Pg² is a phenol protecting group;

X¹ in Formula (III) is as defined for Formula (IV) in claim 1 or claim 2.

6. The method of claim 5, where the protected quinoline of Formula (III) is prepared by reaction of a protected phenol of Formula (I) with a ketone of Formula (II :

wherein:

Y¹ is -CHO, -CH₂OH or -CH=N-Ar².

Q is -NH₂ or -N0₂;

Ar² is independently benzyl or phenyl optionally substituted with one or more substituents chosen from Hal, CH₃ or OCH₃;

X¹ in Formula (II) is as defined for Formula (III) in claim 5.

7. The method of claim 5 or 6, wherein Pg² is a Pg^2a group, and Pg^2a comprises:

(i) -R^c;

(ifj -Ar¹;

(iii) tetrahydropyranyl optionally substituted with one or more substituents chosen from Hal and OCH₃;

(iv) -CH₂OR^b;

(v) -SiR^d ₃;

(vi) -(C=0)R^d;

(vii) -(C=0)OR^e wherein R^e is H, R^d, Ci_₄ haloalkyl or vinyl; or

(viii) -(C=0)NHR^d;

wherein R^b, R^c, R^d, R^e and Ar¹ are as defined in claim 4.

8. A method of preparation of a radio labelling precursor of Formula (VI) which comprises:

(i) reaction of a protected phenol of Formula (I) with a ketone of Formula (II) to give a protected quinoline of Formula (III):

(I) (I N)

(I I)

(ii) deprotection of the protected quinoline of Formula (III) from step (i) to give a quinoline of Formula (IV):

(III) (IV) (iii) alkylation of the quinoline of Formula (IV) from step (ii) with a disulfonate of Formula (V) to give the radiolabelling precursor of Formula (VI):

(VI)

(IV)

wherein:

R^3a and R^3b are as defined in claim 1 or 3;

X¹ is as defined in claim 1 or claim 2;

Pg¹ is as defined in claim 1 or claim 4;

Pg² is as defined in claim 5 or claim 7;

Y¹ and O are as defined in claim 6.

9. A method of preparation of a quinoline of Formula (IV) which comprises deprotection of a protected quinoline of Formula (III):

(Ill) (IV) wherein:

X¹ is as defined in claim 1 or claim 2, and Pg² is as defined in claim 5 or claim 7.

10. A method of preparation of a protected quinoline of Formula (III) which com rises reaction of a protected phenol of Formula (I) with a ketone of Formula (II):

wherein:

Y¹ and O are as defined in claim 6:

X¹ is as defined in claim 1 or claim 2; and

Pg² is as defined in claim 5 or claim 7.

1 1. A protected quino line of Formula (III) :

(III)

wherein:

X¹ is as defined in claim 1 or claim 2; and

Pg² is as defined in claim 5 or claim 7;

with the proviso that when X¹ = -C₆H₄-NR¹R² and R¹ = R² = H or Ci_₄ alkyl, then Pg² is not Ci_₄ alkyl.

12. The protected quinoline of claim 1 1 , where Pg² is a Pg^2a group as defined in claim 7.

13. A method of preparation of an ¹⁸F-labelled radiotracer of Formula (VII), which comprises:

(a) carrying out the method of preparation of any one of claims 1 to 8 to give a precursor of Formula (VI):

(VI)

(b) reaction of the precursor of Formula (VI) from step (a) with [¹⁸F] -fluoride in a suitable solvent, and removal of the Pg¹ protecting group, to give the ¹⁸F- labelled radiotracer of Formula VII):

(VII)

wherein:

X¹ is as defined in claim 1 or claim 2;

R³ is as defined in claim 1 or claim 3; and

Pg¹ is as defined in claim 1 or claim 4.

14. The method of claim 13, where step (b) is carried out using an automated synthesizer apparatus.

15. The method of claim 14, where the automated synthesizer apparatus comprises a disposable cassette which comprises the precursor of Formula (VI).