Complex of gadolinium and a chelating ligand derived of a diastereoisomerically enriched PCTA and synthesis method

Abstract

The present invention relates to a complex of formula (II) constituted of at least 80% of a diastereoisomeric excess comprising a mixture of isomers II-RRR and II-SSS of formulae: ##STR00001## The present invention also relates to a process for preparing said complex of formula (II), and also to two synthetic intermediates.

Claims

1. A process for preparing the complex of formula (II) below: ##STR00024## having a diastereoisomeric excess of at least 80% of a mixture of isomers II-RRR and II-SSS of formulae: ##STR00025## comprising: a) complexing a hexaacid of formula (III) below: ##STR00026## with gadolinium to obtain the hexaacid gadolinium complex of formula (I) below: ##STR00027## b) isomerizing by heating the hexaacid gadolinium complex of formula (I) in an aqueous solution at a pH from 2 to 4 to obtain a diastereoisomerically enriched complex having a diastereoisomeric excess of at least 80% of a mixture of isomers I-RRR and I-SSS of the hexaacid gadolinium complex of formula (I), of formulae: ##STR00028## and c) reacting the diastereoisomerically enriched complex with 3-amino-1,2-propanediol to form the complex of formula (II).

2. The process of claim 1, wherein the hexaacid gadolinium complex of formula (I) is isomerized without being isolated or purified.

3. The process of claim 1, wherein the aqueous solution of step b) contains acetic acid.

4. The process of claim 3, wherein step b) is performed at a temperature of from 100° C. to 120° C. and from 12 hours to 48 hours.

5. The process of claim 1, wherein step b) comprises: b1) isomerizing by heating the hexaacid gadolinium complex of formula (I) in an aqueous solution at a pH of from 2 to 4 to obtain the diastereoisomerically enriched complex, and b2) isolating the diastereoisomerically enriched complex by crystallization.

6. The process of claim 5, wherein the crystallization is performed by seeding.

7. The process of claim 5, further comprising selectively decomplexing diastereoisomers of the complex of formula (I) other than the diastereoisomers I-RRR and I-SSS.

8. The process of claim 5, wherein step b) further comprises: b3) purifying by crystallization the isolated diastereoisomerically enriched complex obtained in step b2).

9. The process of claim 1, wherein the diastereoisomerically enriched complex obtained in step b) has a diastereoisomeric excess of at least 85%.

10. The process of claim 1, wherein the diastereoisomerically enriched complex obtained in step b) has a diastereoisomeric excess of at least 90%.

11. The process of claim 5, wherein the diastereoisomerically enriched complex obtained in step b) has a diastereoisomeric excess of at least 95%.

12. The process of claim 1, wherein step c) comprises: c1) reacting the diastereoisomerically enriched complex obtained in step b) with an alcohol of formula R.sub.1OH in the presence of an acid to form a triester of formula (VIII) below, ##STR00029## in which R.sub.1 represents a (C.sub.1-C.sub.6) alkyl group, and c2) aminolysing the triester of formula (VIII) with 3-amino-1,2-propanediol in the presence of an acid.

13. The process of claim 12, wherein the triester of formula (VIII) is not isolated between step c1) and step c2).

14. The process of claim 12, wherein R.sub.1 represents a methyl group.

15. The process of claim 12, wherein step c) comprises: c1) reacting the diastereoisomerically enriched complex obtained in step b) with methanol in the presence of an acid to form the methyl triester of formula (IV) below, and ##STR00030## c2) aminolysing the methyl triester of formula (IV) with 3-amino-1,2-propanediol in methanol in the presence of an acid, wherein the methanol is removed by vacuum distillation, until a temperature of greater than 55° C. is reached, the reaction medium being maintained at this temperature under vacuum for a time greater than 5 hours, before being cooled to room temperature and diluted with water.

16. The process of claim 15, wherein the hexaacid of formula (III) is obtained by alkylating the pyclene of formula (V): ##STR00031## with dibutyl 2-bromoglutarate, to obtain the butyl hexaester of formula (VI): ##STR00032## and hydrolyzing the butyl hexaester of formula (VI) to obtain the hexaacid of formula (III).

Description

FIGURES

(1) FIG. 1: degradation under basic conditions of the groups of isomers iso1 to iso4 of the complex of formula (II), expressed as an area percentage of a given group of isomers over time.

EXAMPLES

(2) The examples given below are presented as non-limiting illustrations of the invention.

(3) Separation of the Groups of Isomers isoA, isoB, isoC and isoD of the Hexaacid Gadolinium Complex of Formula (I) by HPLC

(4) An HPLC machine constituted of a pumping system, an injector, a chromatography column, a UV spectrophotometric detector and a data processing and control station is used. The chromatography column used is a C18-250×4.6 mm-5 μm column (Symmetry® range from Waters).

(5) Mobile Phase: Route A: 100% acetonitrile and Route B: aqueous solution of H.sub.2SO.sub.4 (96%) at 0.1% v/v

(6) Preparation of the Test Solutions: Solution of the hexaacid gadolinium complex of formula (I) at 10 mg/mL in purified water

(7) Analytical Conditions:

(8) TABLE-US-00007 Column temperature 25° C. Sample temperature Room temperature (20-25° C.) Flow rate 1.0 ml/min Injection volume 20 μl UV detection 200 nm Analysis time 60 min

(9) Gradient:

(10) TABLE-US-00008 Time % Acn % H.sub.2SO.sub.4 0.1%  0  1 99 10  5 95 40 10 90 50 25 75 55  1 99 60  1 99 % Acn: % v/v of acetonitrile in the mobile phase % H.sub.2SO.sub.4 0.1%: % v/v of the solution of H.sub.2SO.sub.4 at 0.1% v/v in the mobile phase

(11) Four main peaks are obtained. Peak 4 of the HPLC plot, namely isoD, corresponds to a retention time of 35.7 minutes.

(12) Separation of the Groups of Isomers isoA, isoB, isoC and isoD of the Hexaacid Gadolinium Complex of Formula (I) by UHPLC

(13) A UHPLC machine constituted of a pumping system, an injector, a chromatography column, a UV detector and a data station is used. The chromatography column used is a UHPLC 150×2.1 mm-1.8 μm column (Waters Acquity UPLC HSS T3 column). It is a reverse-phase UPLC column containing spherical particles constituted of silica with trifunctional C18 (octadecyl) grafting, and the silanols of which have been treated with capping agents (end-capped). It is also characterized by a length of 150 mm, an inside diameter of 2.1 mm, a particle size of 1.8 μm, a porosity of 100 Å and a carbon content of 11%.

(14) Preferentially, the stationary phase used should be compatible with the aqueous mobile phases.

(15) Mobile Phase: Route A: 100% acetonitrile and Route B: aqueous solution of H.sub.2SO.sub.4 (96%) at 0.1% v/v

(16) Preparation of the Test Solutions: Solution of the hexaacid gadolinium complex of formula (I) at 0.8 mg/mL in purified water

(17) Analytical Conditions:

(18) TABLE-US-00009 Column temperature 35° C. Sample temperature Room temperature (20-25° C.) Flow rate 0.4 mL/min Injection volume 10 μl UV detection 200 nm Analysis time 32 min

(19) Gradient:

(20) TABLE-US-00010 Time % Acn % H.sub.2SO.sub.4 0.1%  0  1 99 14  8 92 20 11 89 25 25 75 27  1 99 32  1 99

(21) Four main peaks are obtained. Peak 4 of the UHPLC plot, namely isoD, corresponds to a retention time of 17.4 minutes.

(22) Separation of the Groups of Isomers Iso1, Iso2, Iso3 and Iso4 of the Complex of Formula (II) by UHPLC

(23) A UHPLC machine constituted of a pumping system, an injector, a chromatography column, a UV detector and a data station is used. The chromatography column used is a UHPLC 150×2.1 mm-1.6 μm column (Waters Cortecs® UPLC T3 column).

(24) Mobile Phase: Route A: 100% acetonitrile and Route B: aqueous solution of H.sub.2SO.sub.4 (96%) at 0.0005% v/v

(25) Preparation of the Test Solutions: Solution of the complex of formula (II) at 2 mg/mL in purified water

(26) Analytical Conditions:

(27) TABLE-US-00011 Column temperature 40° C. Sample temperature Room temperature (20-25° C.) Flow rate 0.3 mL/min Injection volume 1 μl UV detection 200 nm Analysis time 20 min

(28) Gradient:

(29) TABLE-US-00012 Time % Acn % H.sub.2SO.sub.4 0.0005%  0  1 99  3  5 95 12 10 90 15 25 75 16  1 99 20  1 99

(30) Four main peaks are obtained. Peak 4 of the UHPLC plot, namely iso4, corresponds to a retention time of 6.3 minutes.

(31) Relaxivity Measurements

(32) The relaxation times T.sub.1 and T.sub.2 were determined via standard procedures on a Minispec® mq20 machine (Bruker) at 20 MHz (0.47 T), at 60 MHz (1.41 T) and 37° C. The longitudinal relaxation time T.sub.1 is measured using an inversion recovery sequence and the transverse relaxation time T.sub.2 is measured via the CPMG (Carr-Purcell-Meiboom-Gill) technique.

(33) The relaxation rates R.sub.1 (=1/T.sub.1) and R.sub.2 (=1/T.sub.2) were calculated for different concentrations of total metal (ranging from 0.5×10.sup.−3 to 5×10.sup.−3 mol/L) in aqueous solution at 37° C. The correlation between R.sub.1 or R.sub.2 as a function of the concentration is linear, and the slope represents the relaxivity r.sub.1 (R.sub.1/C) or r.sub.2 (R.sub.2/C) expressed in (1/second)×(1/mMol/L), i.e. (mM.sup.−1.Math.s.sup.−1).

(34) Measurement of the Kinetic Inertia of the Groups of Isomers of the Complex of Formula (II) in Acidic Medium

(35) The dissociation of the gadolinium complexes present in the four unresolved peaks of isomers iso1 to iso4 (C=8×10.sup.−6 M) is studied at 37° C., pH 1.2 in a hydrochloric acid solution under pseudo-first order kinetic conditions without control of the ionic strength by monitoring the release of gadolinium into the solution. The amount of free gadolinium was determined by spectrometry at 654 nm after adding a solution of Arsenazo III (C=5.3×10.sup.−4 M).

(36) The half-life times (T.sub.1/2) that were determined for each of the groups of isomers are collated in the table below:

(37) TABLE-US-00013 Groups of isomers T.sub.1/2 (pH 1.2-37° C.) Iso1 18 hours Iso2 6 hours Iso3 8 days Iso4 27 days
Study of Depredation Under Basic Conditions of the Groups of Isomers of the Complex of Formula (II)

(38) The complex of formula (II) will be referred to as AP in the rest of this example.

(39) The kinetics of degradation of the unresolved peaks of isomers iso1 to iso4, referred to by the generic term isoX, are evaluated by measuring the HPLC purity and by monitoring the area of each unresolved peak of isomers over time. The magnitudes measured are thus: P.sub.HPLC (time), and

(40) $\begin{array}{cc}\frac{{\mathrm{Area}}_{\mathrm{IsoX}}\left(t\right)}{{\mathrm{Area}}_{\mathrm{IsoX}}\left(t_0\right)}& \left[\mathrm{Math}1\right]\end{array}$

(41) The degradation conditions chosen are the following: [AP]=1 mM in 0.1 N sodium hydroxide. Under these dilution conditions, the impact of the degradation of AP on the experimental medium is low. The degradation products do not modify the pH of the medium, this parameter being critical in the study of the degradation kinetics. This is confirmed experimentally by measuring the initial pH and the pH at the end of degradation (72 hours, 37° C.):

(42) TABLE-US-00014 Solution of AP pH of 0.1N NaOH (T.sub.0) 12.9 pH (after 72 hours at 37° C.) 12.8

(43) The method for preparing the solutions is described below: weigh out about 0.05 g of each product qs 10 mL of mQ water, to obtain a solution A such that [AP].sub.A=5 mM, dilution: 2 mL of solution A qs 10 mL NaOH (0.1 N), to obtain a solution B such that [AP].sub.B=1 mM and [NaOH]=0.08 M, aliquot of the solutions in HPLC flasks, and incubation of the HPLC flasks containing the solutions of AP in NaOH at the study temperature (37° C.).

(44) For each point, an aliquot is taken and analysed by HPLC without dilution of the sample (ammonium acetate method).

(45) The results obtained are given in FIG. 1.

(46) Preparation of the Butyl Hexaester of Formula (VI)

(47) 184 kg (570 mol) of dibutyl 2-bromoglutarate and 89 kg (644 mol) of potassium carbonate are mixed in a reactor and heated to 55-60° C. An aqueous solution of 29.4 kg (143 mol) of pyclene in 24 kg of water is added to the preceding preparation. The reaction mixture is maintained at 55-60° C. and then refluxed for about 10 hours. After reaction, the medium is cooled, diluted with 155 kg of toluene and then washed with 300 litres of water. The butyl hexaester is extracted into the aqueous phase with 175 kg (1340 mol) of phosphoric acid (75%). It is then washed three times with 150 kg of toluene. The butyl hexaester is re-extracted into a toluene phase by dilution with 145 kg of toluene and 165 kg of water, followed by basification with 30% sodium hydroxide (m/m) to reach a pH of 5-5.5. The lower aqueous phase is removed. The butyl hexaester is obtained by concentrating to dryness under vacuum at 60° C., in a yield of about 85%.

(48) Preparation of the Hexaacid of Formula (III)

(49) 113 kg (121 mol) of butyl hexaester are placed in a reactor along with 8 kg of ethanol. The medium is brought to 55±5° C. and 161 kg (1207.5 mol) of 30% sodium hydroxide (m/m) are then added over 3 hours. The reaction mixture is maintained at this temperature for about 20 hours. The butanol is then removed by decantation of the reaction medium. The hexaacid of formula (III) obtained in sodium salt form is diluted with water to obtain an aqueous solution of about 10% (m/m). This solution is treated on an acidic cationic resin. The hexaacid of formula (III) in aqueous solution is obtained in a yield of about 90% and a purity of 95%.

(50) Preparation of the Hexaacid Gadolinium Complex of Formula (I)

(51) Experimental Protocol

(52) Complexation and Isomerization

(53) Without Acetic Acid

(54) 418 kg (117 kg of pure hexaacid of formula (III)/196 mol) of an aqueous solution of hexaacid of formula (III) at 28% by weight are placed in a reactor. The pH of the solution is adjusted to 2.7 by adding hydrochloric acid, and 37 kg (103.2 mol) of gadolinium oxide are then added. The reaction medium is heated at 100-102° C. for 48 hours to achieve the expected isomeric distribution of the hexaacid of formula (III).

(55) With Acetic Acid

(56) Gadolinium oxide (0.525 molar eq.) is suspended in a solution of hexaacid of formula (III) at 28.1% by mass.

(57) 99-100% acetic acid (50% by mass/pure hexaacid of formula (III)) is poured into the medium at room temperature.

(58) The medium is heated to reflux followed by distillation up to 113° C. by mass by refilling the medium with acetic acid gradually as the water is removed. Once the temperature of 113° C. is reached, a sufficient amount of acetic acid to arrive at the starting volume is added.

(59) The medium is maintained at 113° C. overnight.

(60) Crystallization, Recrystallization

(61) Crystallization

(62) The hexaacid gadolinium complex of formula (I) in solution is cooled to 40° C., the primer is added and the agents are left in contact for at least 2 hours. The product is then isolated by filtration at 40° C. and washed with osmosed water.

(63) Recrystallization

(64) 180 kg of the hexaacid gadolinium complex of formula (I) obtained previously (solids content of about 72%) are suspended in 390 kg of water. The medium is heated to 100° C. to dissolve the product, and then cooled to 80° C. to be primed by adding a small amount of primer. After cooling to room temperature, the hexaacid gadolinium complex of formula (I) is isolated by filtration and drying.

(65) Selective Decomplexation

(66) The dry product is placed in the reactor with osmosed water at 20° C. The mass of water added is equal to twice the theoretical mass of hexaacid gadolinium complex of formula (I). 30.5% sodium hydroxide (m/m) (6.5 eq.) is poured into the medium at 20° C. At the end of the addition of NaOH, the medium is left in contact at 50° C. for 16 hours. The medium is cooled to 25° C. and the product is filtered off on a bed of Clarcel.

(67) Content of Diastereoisomeric Excess Comprising a Mixture of Diastereoisomers I-RRR and I-SSS

(68) The ratio in which the various isomers of the complex of formula (I) are present in the mixture of diastereoisomers depends on the conditions under which the complexation and isomerization steps are performed, as is seen in Table 3 below.

(69) TABLE-US-00015 TABLE 3 content of the mixture I-RRR and I-SSS as a function of the complexation/isomerization conditions Diastereoisomeric Content of excess comprising hexaacid of a mixture pH Temperature formula (III) Time I-RRR and I-SSS 5.7  80° C. 40%  3 hours   19% 3.5  90° C. 50% 10 hours   49% 3.0 101° C. 40% 10 hours   68% 2.7 101° C. 28% 48 hours 98.04%

(70) The additional steps of recrystallization and selective decomplexation make it possible to increase the diastereoisomeric excess of the mixture I-RRR and I-SSS (see Table 4).

(71) TABLE-US-00016 TABLE 4 content of diastereoisomeric excess comprising a mixture I-RRR and I-SSS after crystallization/recrystallization/selective decomplexation After the first After After selective crystallization recrystallization decomplexation Diastereoisomeric 98.04% 99.12% 99.75% excess comprising a mixture I-RRR and I-SSS

(72) Preparation of the Complex of Formula (II)

(73) 90 kg (119 mol) of the hexaacid complex of formula (I) and 650 kg of methanol are placed in a reactor. The mixture is cooled to about 0° C. and 111 kg (252 mol) of a methanolic solution of hydrochloric acid (8.25% of HCl in methanol) are then poured in while maintaining the temperature at 0° C. The reaction medium is brought to room temperature and stirring is then continued for 16 hours. After cooling to 0-5° C., 120 kg (1319 mol) of 3-amino-1,2-propanediol are added. The reaction medium is then heated while distilling off the methanol under vacuum until a temperature of 60-65° C. is reached. The concentrate is maintained for 16 hours at this temperature under vacuum. At the end of contact, the medium is diluted with 607 kg of water while cooling to room temperature. The solution of the crude complex of formula (II) is neutralized with 20% hydrochloric acid (m/m). 978.6 kg of solution are thus obtained, with a concentration of 10.3%, representing 101 kg of material. The yield obtained is 86.5%.

(74) Tests of Conversion of Isomers Starting with the Complexes of Formula (II)

(75) The isomers of the complex of formula (II) were synthesized from the groups of isomers isoA, isoB, isoC and isoD of the hexaacid complex of formula (I) isolated by preparative HPLC. The four groups of isomers were isolated and then amidated with R and S 3-amino-1,2-propanediol (APD). Eight isomers were thus obtained:

(76) isoA+APD(R) and isoA+APD(S),

(77) isoB+APD(R) and isoB+APD(S),

(78) isoC+APD(R) and isoC+APD(S), and

(79) isoD+APD(R) and isoD+APD(S).

(80) Each of these isomers was placed under conditions allowing isomerization of the hexaacid gadolinium complex of formula (I).

(81) Thus, an HCl solution at pH 3 is prepared by diluting 1 mL of 1N HCl in 1 litre of water. The isomers are added at a concentration of 1 mM to the HCl solution at pH 3. 10 mg of powder are dissolved in 10 mL of this solution. The eight solutions obtained are heated to 100° C. and then analysed at T.sub.0 and at T.sub.0+23 hours by HPLC.

(82) The purity percentages measured by HPLC are given in the table below.

(83) TABLE-US-00017 isoA + isoB + isoC + isoD + APD(S) APD(S) APD(S) APD(S) T.sub.0 95.4% 92.3% 91% 98.6% T.sub.0 + 23 h   86%   83% 84%   92%

(84) The loss of purity is due to the chemical degradation (hydrolysis of the amide functions) of the product due to the conditions imposed by the isomerization reaction.

(85) Since the conditions allowing the isomerization of the various compounds lead to substantial chemical degradation of the products via hydrolysis of the amide functions, the isomerization cannot be performed in a clean and selective manner directly on the complex of formula (II) obtained according to the process described in EP 1 931 673.