Precipitation and separation of gadolinium complexes

Abstract

The present invention relates to a method for precipitating a gadolinium complex of formula (I) from a solution comprising said gadolinium complex by mixing a first solution comprising the complex with a second solution, and to a method for separating the precipitated gadolinium complex of formula (I) from a mixture comprising said precipitate; the gadolinium complexes of formula (I) can be used as contrast agents for magnetic resonance imaging (MRI). # imgabs0 #

Description

Technical Field

[0001] The present invention relates to the precipitation and separation of gadolinium complexes which are useful as contrast agents for magnetic resonance imaging (MRI). Background Art

[0002] Magnetic resonance imaging (MRI) is a well-known diagnostic imaging technique that is used in clinical diagnostics for an increasing number of indications. Gadolinium (Gd(III)) complexes are generally used as contrast agents in MRI.

[0003] WO 2017 / 098044 discloses dimeric Gd(III) complexes for use as contrast agents in MRI, such as dimeric Gd(III) complexes having the formula [μ-[1-[bis[2-(hydroxy-κO)-3-[4,7,10-tris[(carboxyl-κO)methyl]-1,4,7,10-tetraazacyclododecane-1-yl-κN 1 ,κN 4 ,κN 7 ,κN 10 ]propyl]amino]-1-deoxy-D-glucitol anion (6-)]]digadolinium complex (hereinafter referred to as compound 1)

[0004]

[0005] Compound 1 shows very good relaxivity, and in particular such relaxivity, which is due to and (a non-specific contrast agent currently used in diagnostic practice) exhibits a relaxivity more than 2-fold higher. Accordingly, Compound 1 is a promising contrast agent for in vivo MRI diagnostic imaging.

[0006] WO 2017 / 098044 also discloses the preparation of compound 1 and its isolation from the reaction mixture by spray drying.

[0007] Similarly, WO 2022 / 023240 discloses the preparation of compound 1 and its isolation from a reaction mixture by spray drying or lyophilization.

[0008] Spray drying and freeze drying effectively allow the isolation of compound 1, thereby providing a powder with good handling characteristics and maintaining its quality. However, some disadvantages are associated with these two methods, such as high energy consumption, the need for high-cost special equipment and the lack of purification (meaning that substantially all impurities present in the solution of the complex to be separated will also be present in the powder obtained by spray drying or by freeze drying). For these reasons, it is necessary to provide further techniques for isolating compound 1 (and similar complexes) from its reaction mixture that overcome the above-mentioned disadvantages. SUMMARY OF THE INVENTION

[0009] The present invention relates to a method for precipitating a complex of formula (I) from a solution thereof

[0010]

[0011] For example, for precipitating compound 1 from its solution

[0012]

[0013] As described in the claims.

[0014] The method allows selective precipitation of the complex by mixing two solutions, one of which contains the complex and the other contains ethanol used as an antisolvent. Accordingly, the inventive method provides precipitation of the complex, which has low energy consumption and does not require special dedicated equipment to implement. In addition, the precipitation obtained by the method is filterable, so that it can be easily separated and thus separated from its mixture. In addition, the precipitation method has high yield and purification capacity, because it allows selective precipitation of the complex from its solution; Accordingly, the inventive method provides a complex precipitation, which contains less impurities than the initial solution containing the complex. Additional, it has been surprisingly found that the inventive method does not substantially change the diastereoisomer ratio of the complex of formula (I) (especially when using compound 1). These and other advantages are described in more detail in the following section.

[0015] The invention also relates to a process for isolating the complex of formula (I) from a mixture thereof, as described in the claims. DETAILED DESCRIPTION OF THE INVENTION

[0017] The first aspect of the present invention is a method for precipitating a complex of formula (I) from a solution thereof

[0018]

[0019] Where R is C substituted with at least one hydroxyl (-OH) group 2 -C 6 -alkyl,

[0020] The method comprises the following steps:

[0021] a) providing a first solution comprising a complex of formula (I);

[0022] b) providing a second solution comprising ethanol; and

[0023] c) mixing the first solution of step a) with the second solution of step b) to precipitate the complex of formula (I).

[0024] As used herein, the term "C x -C y-alkyl", wherein x and y represent two integers, refers to a straight or branched hydrocarbon chain having a carbon number between x and y; for example, the term "C 2 -C 6 "-Alkyl" refers to a straight or branched hydrocarbon chain having 2 to 6 carbon atoms.

[0025] As mentioned above, the method of the present invention provides mixing of a first solution containing the complex of interest and a second solution acting as an antisolvent. Accordingly, the method of the present invention does not require specialized equipment and high energy consumption (or at least a lower degree of energy consumption compared to known spray drying and freeze drying methods) to implement.

[0026] In addition, using a second solution comprising ethanol provides a complex precipitation that is filterable and that can thereby be easily separated from its mixture. As shown in the experimental section below, it has been found that using an antisolvent comprising a solvent different from ethanol, such as methanol and isobutanol, the complex concerned does not precipitate or is not filterable.

[0027] In addition, the process of the invention provides a selective precipitation process for the complex with good yield. Since the precipitation process is selective for the complex, the process of the invention allows obtaining a filterable precipitate containing a lower amount of impurities than the amount present in the complex solution before precipitation. This advantage further characterizes the process of the invention compared to the prior art, since the known methods for isolating the complex in question, namely spray drying and freeze drying, provide a filterable precipitate containing all the impurities contained in the initial solution.

[0028] Additionally, it has been surprisingly found that the process of the present invention does not substantially change the diastereoisomer ratio of the complex of formula (I) (particularly when using compound 1). In particular, compound 1 has several stereocenters, whereby it exists in several diastereomers. These diastereomers may have mutually different chemical and physical properties, such as different solubility. Since the process of the present invention provides a process for the precipitation of complexes in a solvent-antisolvent mixture, it is possible to expect a change in the diastereoisomer ratio (i.e., a relative change in the amount of at least some diastereomers before and after precipitation), because some diastereomers may be easier or more difficult to dissolve than other diastereomers. However, as shown in the experimental section below, this expected change surprisingly does not occur, whereby the process of the present invention allows to maintain approximately the same diastereoisomer ratio.

[0029] According to an embodiment of the present invention, R is C substituted by at least one hydroxyl (-OH) group. 3 -C 6 -alkyl, preferably C substituted with at least one hydroxyl (-OH) group 4 -C 6 -alkyl, more preferably C substituted with at least one hydroxyl (-OH) group5 -C 6 -alkyl, and even more preferably C substituted with at least one hydroxyl (-OH) group 6 According to an even more preferred embodiment, R is C substituted with 5 hydroxyl (-OH) groups. 6 -alkyl, for example, thereby providing compound 1

[0030]

[0031] The first solution comprises a complex of formula (I) which is at least partially dissolved therein, and which may be substantially completely dissolved therein. The first solution is preferably an aqueous solution. The first solution can advantageously be a reaction mixture from which the complex of formula (I) is obtained, such as the reaction mixture of the coordination step 5) disclosed in WO 2022 / 023240, which may be after one or more purification steps. The first solution is advantageously miscible with the second solution (which actually acts as an antisolvent).

[0032] The second solution comprises ethanol, preferably in an amount of at least 90.0 vol%.According to a more preferred embodiment, the second solution is absolute ethanol, which is a solution comprising at least 99.0 vol% ethanol.

[0033] According to a preferred embodiment, the mixture prepared according to step c) also comprises at least one precipitant. The precipitant is selected from neutral salts of sodium and organic acids, preferably in an amount greater than 0.7 molar equivalents and less than 10.0 molar equivalents relative to the complex of formula (I). As shown in the experimental section below, the precipitant improves precipitation, allowing a precipitate with good handling characteristics to be obtained, especially when the precipitant is present in the amount disclosed above. According to a preferred embodiment, the precipitant is added to the first solution when the first solution is added to the second solution (or vice versa), so as to carry out the mixing step c), and then a mixture of the complex of formula (I), the antisolvent (ethanol) and the precipitant is obtained.

[0034] The term "neutral salt of sodium" as used herein refers to a compound as an ionic system in which the positively charged cation is sodium and the negatively charged anion is any inorganic anion, and wherein the neutral salt of sodium provides a substantially neutral solution (i.e., the solution has a pH of about 7) when dissolved in an aqueous medium. Suitable examples of neutral salts of sodium are sodium chloride, sodium bromide, sodium iodide, sodium fluoride, sodium nitrate and sodium sulfate; sodium chloride and sodium bromide are particularly preferred.

[0035] Preferably, the neutral salt of sodium is selected from sodium chloride, sodium bromide, sodium iodide, sodium fluoride, sodium nitrate and sodium sulfate; more preferably sodium chloride and sodium bromide. As shown in the experimental section below, these specific neutral salts of sodium, especially sodium chloride and sodium bromide, facilitate the precipitation of the complex and, in particular, allow to obtain a high precipitation yield and a filterable precipitate, which has very good handling characteristics and can be subsequently separated by conventional means. In addition, as shown in the experimental section below, in addition to providing a precipitate containing fewer impurities than the impurities present in the first solution, these specific neutral salts of sodium do not produce a monogadolinated complex. The term "monogadolinated complex" as used herein refers to a complex having the same structure as the dimeric complex of formula (I) but chelating only one (instead of two) gadolinium metal ions. The monogadolinated complex does not show the favorable relaxation quantitative properties of the complex of formula (I).

[0036] The term "organic acid" as used herein refers to a substituted or unsubstituted carboxylic acid having one or more -COOH groups; a suitable substitution is, for example, a hydroxyl (-OH) group. Suitable examples of organic acids are acetic acid, lactic acid, tartaric acid and citric acid; acetic acid and lactic acid are particularly preferred.

[0037] According to a preferred embodiment, the organic acid is C 1 -C 6 -(Hydroxy)alkyl-carboxylic acids, preferably C 2 -C 6 -(hydroxy)alkyl-carboxylic acids, such as acetic acid, lactic acid, tartaric acid and citric acid; more preferably, the organic acid is a C 1 -C 6 -(Hydroxy)alkyl-carboxylic acids. Similar to the neutral sodium salts disclosed above, these organic acids facilitate the precipitation of the complex and, in particular, allow obtaining high precipitation yields and filterable precipitates which have very good handling characteristics and can subsequently be isolated by conventional means.

[0038] The term "(hydroxy)alkyl-carboxylic acid" as used herein refers to a straight or branched hydrocarbon chain in which at least one hydrogen is replaced by a carboxyl (-COOH) group and optionally substituted by one or more hydroxyl (-OH) groups. x -C y -(hydroxy)alkyl-carboxylic acid", wherein x and y represent two integers, refers to a (hydroxy)alkyl-carboxylic acid as defined above having a number of carbons between x and y; for example, the term "C 1 -C 6 "-(Hydroxy)alkyl-carboxylic acid" refers to a (hydroxy)alkyl-carboxylic acid as defined above having 2 to 6 carbon atoms.

[0039] Preferably, the amount of precipitant is 0.8 to 9.0 molar equivalents, more preferably 0.9 to 5.0 molar equivalents, even more preferably 0.9 to 3.0 molar equivalents, and most preferably 1.0 to 2.0 molar equivalents, such as 1.0 to 1.5 molar equivalents, relative to the complex of formula (I).

[0040] According to a preferred embodiment, the concentration of the complex in the first solution is 20 to 70% w / w, preferably 30 to 60% w / w, and more preferably 40 to 60% w / w.

[0041] Step c) provides a first solution and a second solution and preferably a mixture of a precipitant, as defined above in any of its embodiments. Mixing step c) allows precipitation of the complex of formula (I) in the mixture of the first and second solutions because the second solution acts as an antisolvent. This step can be easily performed and advantageously does not require high energy consumption or special equipment. Mixing step c) can be performed as follows: the first solution of step a) is added to the second solution of step b), or the second solution of step b) is added to the first solution of step a), as shown in the experimental section below; optionally, a precipitant is also added according to any embodiment discussed above. The precipitant can alternatively be present in the first solution and / or in the second solution, preferably in the first solution, thereby allowing the first solution to be added to the second solution (or vice versa) to precipitate the complex of formula (I). The addition can be performed dropwise for a period of preferably 15 minutes to 6 hours, more preferably 30 minutes to 4 hours and even more preferably 1 to 3 hours.

[0042] According to a preferred embodiment, the mixing of step c) is carried out such that the amount by weight of ethanol is 1 to 20 times, preferably 2 to 15 times, more preferably 3 to 10 times, and even more preferably 4 to 8 times the weight of the complex of formula (I).

[0043] The second aspect of the present invention is a method for separating a complex of formula (I) from a mixture

[0044]

[0045] Where R is C substituted with at least one hydroxyl (-OH) group 2 -C 6 -alkyl, preferably C substituted with at least one hydroxyl (-OH) group 3 -C 6 -alkyl, more preferably C substituted with at least one hydroxyl (-OH) group 4 -C 6 -alkyl, even more preferably C substituted by at least one hydroxyl (-OH) group 5 -C 6 -alkyl, and most preferably substituted with at least one hydroxyl (-OH) group. 6-alkyl,

[0046] The steps include:

[0047] (i) performing a method for precipitating a complex of formula (I) (e.g. according to any one of its embodiments) to obtain a precipitate of the complex in a mixture; and

[0048] (ii) filtering the complex precipitate from the mixture.

[0049] According to a preferred embodiment of the separation method, R is C substituted with 5 hydroxyl (-OH) groups. 6 -alkyl, thereby providing, for example, a method for separating compound 1 from a mixture

[0050]

[0051] The separation method of the present invention provides the implementation of the precipitation method of the present invention (step (i)), whereby the separation method has all the advantages of the precipitation method of the present invention. The separation method also provides filtering out the complex precipitate (step (ii)); this can be achieved because the precipitate obtained by step (i) is filterable. The precipitate obtained has suitable to very good handling characteristics and contains low amounts of impurities due to the precipitation method carried out in step (i).

[0052] Step (ii) can be carried out according to conventional means, such as using a filter, such as a sintered glass funnel. After filtering out the precipitate, it can be washed once or more, such as twice, with a second solution, such as with fresh absolute ethanol. The second solution is preferably at a temperature below 20° C., such as about 5° C. to 10° C. during washing. The washed precipitate can finally be dried by conventional means (such as in a static furnace, possibly under vacuum).

[0053] According to a preferred embodiment of the separation method of the present invention, before step (ii) and preferably after step (i), the temperature of the mixture is 20°C or higher, and the temperature is then reduced to a temperature of 0°C to 10°C, preferably 5°C, the reduction of temperature also being carried out before step (ii). Preferably, the temperature is gradually reduced for a period of 6 to 48 hours, more preferably 12 to 36 hours and even more preferably 22.5 hours. The gradual reduction of the temperature allows to improve the filterability of the precipitate. According to a particularly preferred embodiment the filterability can be further improved, wherein the gradual reduction is carried out according to the following temperature ramp:

[0054] (ia) maintaining the mixture containing the complex precipitate at 20° C. or higher for 15 minutes to 1 hour, preferably 30 minutes; and then

[0055] (ib) cooling the mixture to 0°C to 10°C, preferably to 5°C, for 3 to 12 hours, preferably 6 hours; and finally

[0056] (ic) maintaining the mixture at 0°C to 10°C, preferably at 5°C, for 8 to 32 hours, preferably 16 hours.

[0057] Experimental Section

[0058] Materials and methods

[0059] The reactants and / or solvents used in the examples below which were not specifically synthesized are known and readily available. If they are not commercially available per se, they can be prepared according to methods known from the literature.

[0060] The water content (KF) in the following examples has been determined by Karl Fischer titration using a titrator Compact V10S (Mettler Toledo) and the reactants HYDRANAL TM and anhydrous MeOH as solvent.

[0061] The NaCl content in the following examples has been determined by silver titration using analytical grade AgNO 3 .

[0062] The following HPLC procedure has been used to determine the diastereomeric distribution, the amount of the monogadolinated complexes, and the major impurities Gd-DOTA and Gd-DO3A:

[0063] - Column: Xselect HSS T3 150x3 mm 3.5μm

[0064] -Mobile phase: A=KH 2 PO 4 +K 2 HPO 4 40mM+EDTA 0.02mM; B=Phase A / ACN 60 / 40

[0065] t(min) A B Flow rate (ml / min) 0 100 0 0,35 4 100 0 0,35 20 85 15 0,35 25 85 15 0,35 30 0 100 0,35 40 0 100 0,35 43 100 0 0,35 50 100 0 0,35

[0066] -Injection volume: 10um

[0067] - Temperature: 40℃

[0068] - Detector: DAD 210 nm + FLD λex = 275 nm - λem = 314 nm.

[0069] The following HPLC procedure has been used to determine the free Gd 3+ Amount of ions:

[0070] - Column: YMC-PACK ODS-AQ, 250 x 4.6 mm, 5 μm

[0071] - Mobile phase: A = CH3COONH4 1,5 g / L, EDTA (0,55 g / L); B = MeOH

[0072] t(min) A B Flow rate (ml / min) 0 100 0 1 5 100 0 1 10 50 50 1 15 50 50 1 16 100 0 1 25 100 0 1

[0073] -Injection volume: 20um

[0074] - Temperature: 40℃

[0075] -Detector: FLD detector: λex=275nm-λem=314nm.

[0076] Example 1 (Comparative) - Precipitation of Compound 1 (Using Comparative Antisolvent)

[0077] Several solutions of Compound 1 (1.0 g, 0.77 mmol) with concentrations ranging from 40 to 60% w / w were prepared (first solution). The following comparative antisolvents were prepared and mixed with the first solution:

[0078] - tert-amyl alcohol;

[0079] -anisole;

[0080] - isobutanol;

[0081] - methanol; and

[0082] -Isopropyl alcohol.

[0083] After mixing, a non-filterable sticky solid or oil was obtained. Accordingly, none of the above antisolvents allowed obtaining a filterable Compound 1 solid that could be subsequently isolated.

[0084] Example 2 - Precipitation of Compound 1 (Using the Second Solution)

[0085] Several solutions of Compound 1 (1.0 g, 0.77 mmol) having a concentration of 40 to 60% w / w were prepared (first solutions). Several second solutions containing ethanol were prepared and mixed with the first solution.

[0086] A solid precipitate was obtained for all tests. The precipitate formed had satisfactory but not very good handling and transferability characteristics.

[0087] Example 3 - Precipitation of Compound 1 (Using a Second Solution and a Neutral Salt of Sodium) and Isolation of the Precipitate

[0088] NaCl (11.16 g, 0.19 mol, 1.46 mol eq) was added to a 50% w / w aqueous solution (first solution) containing compound 1 (166.05 g, 0.13 mol) at 30°C. The first solution was kept under stirring until completely dissolved. EtOH (996.31 g, 6 w / w Cpd1 - second solution). During the addition, a white suspension was observed in the reactor.

[0089] At the end of loading, set the following temperature change:

[0090] 1. Keep at 20℃ for 30 minutes;

[0091] 2. Cool to 5°C within 6 hours; and

[0092] 3. Keep at 5°C for 16 hours.

[0093] After the temperature shift, the mixture was filtered on a sintered glass funnel (porosity 4) and the filtered precipitate was washed with fresh absolute ethanol (166.05 g) pre-cooled at 5°C.

[0094] The solid obtained was finally dried at 40° C. in a static oven under vacuum (<20 mbar).

[0095] The physical characterization of the Compound 1 precipitate is shown in Table 1.

[0096]

[0097] Table 1

[0098] Table 1 shows high precipitation yields, even greater than 90%.

[0099] Table 2 shows that in solution before precipitation and in the solid precipitate after precipitation:

[0100] - major impurities, which can generally be present in a solution of compound 1 after synthesis (e.g. as disclosed in WO 2022 / 023240), namely Gd-DOTA and Gd-DO3A (Gd-DOTA is gadoteric acid; Gd-DO3A is the complex 2-[4,7-di(carboxylic acid methyl)-1,4,7-triaza-10-amidoanion heterocyclododecane-1-yl]acetate; gadolinium(3+)),

[0101] - Minor impurities, which are free Gd 3+ ions (free Gd) and monogadolinium complexes (mono-Gd); and

[0102] - the diastereomeric ratios of the three possible enantiomeric pairs of compound 1 (referred to as D1, D2 and D3) (in the case where D-glucosamine is used for the synthesis of compound 1, as disclosed, for example, in WO 2022 / 023240),

[0103] It is expressed as area percentage detected by HPLC, fluorescence detector (% area, FLD), or as ppm / compound 1 (for free Gd and mono-Gd).

[0104]

[0105] Table 2

[0106] Table 2 clearly shows the purification characteristics of the process of the present invention, as both the main impurities Gd-DOTA and Gd-DO3A were found to be reduced after precipitation.

[0107] Furthermore, it can be observed that the diastereoisomer ratio is approximately the same before and after precipitation.

[0108] Finally, Table 2 shows that the minor impurities (minor means that they are present in smaller amounts compared to the major impurities reported above) free Gd 3+ The amount of ions (free Gd) remained essentially unchanged before and after precipitation; similarly, the amount of monogadolinium complex (mono-Gd) remained below the quantitative level (nq, which is 400 ppm). This means that the process of the present invention does not cause decomplexation of compound 1 when sodium chloride is used.

[0109] Example 4 - Precipitation of Compound 1 (Using a Second Solution and a Neutral Salt of Sodium) and Isolation of the Precipitate

[0110] NaCl (5.89 g, 0.10 mol, 1.28 mol eq) was added to a 50% w / w aqueous solution of compound 1 (100.35 g, 0.078 mol) at 30°C (first solution). The mixture was kept under stirring until completely dissolved. EtOH (416.4 g, 4.2 w / w Cpd.1 - second solution). During the addition, a white suspension was observed in the reactor.

[0111] At the end of loading, set the following temperature change:

[0112] 1. Keep at 20℃ for 30 minutes;

[0113] 2. Cool to 5°C within 6 hours;

[0114] 3. Keep at 5°C for 16 hours.

[0115] After the temperature shift, the mixture was filtered on a sintered glass funnel (porosity 4) and the filtered precipitate was washed with fresh absolute ethanol (100.4 g) precooled at 5°C.

[0116] The resulting solid was dried at 40° C. in a static oven under vacuum (<20 mbar).

[0117] The physical characterization of the precipitate is shown in Table 3.

[0118]

[0119] Table 3

[0120] Table 4 shows the major impurities and diastereoisomer ratios expressed as % area FLD (or ppm / compound 1 where indicated) before and after precipitation.

[0121]

[0122] Table 4

[0123] In view of the data presented in Tables 3 and 4, the same conclusions discussed above for Example 3 can be drawn for Example 4.

[0124] Example 5 - Precipitation of Compound 1 (Using a Second Solution and a Neutral Salt of Sodium) and Isolation of the Precipitate

[0125] NaCl (2.22 g, 0.038 mol, 1.52 mol eq) was added to a 30% w / w aqueous solution of compound 1(I) (31.9 g, 0.025 mol) at 30°C, and the mixture was kept under stirring until completely dissolved (first solution). EtOH (221.8 g, 7 w / w Cpd.1 - second solution). During the addition, a white suspension was observed in the reactor.

[0126] At the end of loading, set the following temperature change:

[0127] 1. Keep at 20℃ for 30 minutes;

[0128] 2. Cool to 5°C within 6 hours;

[0129] 3. Keep at 5°C for 16 hours.

[0130] After the temperature shift, the mixture was filtered on a sintered glass funnel (porosity 4) and the filtered precipitate was washed with fresh absolute ethanol (49.3 g) pre-cooled at 4°C.

[0131] The resulting solid was dried at 40° C. in a static oven under vacuum (<20 mbar).

[0132] The physical characterization of the Compound 1 precipitate is shown in Table 5, while Table 6 shows the major impurities and diastereoisomer ratios expressed as % area FLD (or ppm / Compound 1, where indicated) before and after precipitation.

[0133]

[0134] Table 5

[0135]

[0136] Table 6

[0137] Similar to Tables 1 and 2, Tables 5 and 6 clearly show the good purification yield of the method of the present invention, as well as the preservation of the purification capacity and diastereoisomer ratio. In addition, it is also possible to understand from this experiment that free Gd 3+ The amount of ions (free Gd) remained essentially unchanged before and after precipitation, and the amount of monogadolinated complex (mono-Gd) remained below quantitative levels.

[0138] Example 6 - Precipitation of Compound 1 (Using a Second Solution and a Neutral Salt of Sodium) and Isolation of the Precipitate

[0139] NaCl (5.21 g, 0.09 mol, 1.5 mol eq) was added to an aqueous solution of compound 1 (77.49 g, 0.06 mol), and the thick suspension was kept under stirring until the salt was completely dissolved (first solution).

[0140] In a reactor equipped with mechanical stirring (pre-filled with absolute ethanol (464.94 g, 6.0 w / w Cpd.1 -second solution) and kept at 20°C), the first solution was added dropwise (addition time = 2÷3 hours) while keeping the stirring rate at >350 rpm. During the addition, the formation of a white precipitate was observed.

[0141] At the end of loading, set the following temperature change:

[0142] 1. Keep at 20℃ for 30 minutes;

[0143] 2. Cool to 5°C within 6 hours;

[0144] 3. Keep at 5°C for 16 hours.

[0145] After the temperature change, the mixture was filtered on a sintered glass funnel (porosity 4) and the filtered precipitate was washed with fresh absolute ethanol (77.49 g) precooled at 5° C. The solid obtained was dried at 40° C. in a static oven under vacuum (<20 mbar).

[0146] At the end point, a white powder with a moisture content of about 9.15% w / w was obtained, with a wet / dry ratio of about 1.9%. The precipitation yield was 83.6%.

[0147] Table 7 shows the major impurities and diastereoisomer ratios expressed as % area FLD (or ppm / Compound 1 where indicated) before and after precipitation.

[0148]

[0149] Table 7

[0150] Table 7 shows the purification ability of the method of the present invention and the preservation of the diastereoisomer ratio. Table 7 also shows that the method of the present invention has a purification ability even with respect to the monogadolinated complex, the amount of which is above the quantitative level before precipitation, and which is reduced after precipitation, in the case of using a neutral salt of sodium.

[0151] Example 7 (Comparative) - Precipitation of Compound 1 (Using a Second Solution and a Low Amount of Neutral Sodium Salt)

[0152] NaCl (3.16 g, 0.054 mol, 0.7 mol eq) was added to a 50% w / w aqueous solution of compound 1 (99.80 g, 0.077 mol) and the mixture was kept under stirring until completely dissolved (first solution). EtOH (399.21 g, 4.0 w / w) was loaded dropwise over 2 hours. During the addition, the mixture became a non-stirrable sticky solid.

[0153] This comparative example shows that, in the presence of a precipitating agent, it may be necessary to add it in a specific amount to obtain a precipitate that can be further processed to isolate compound 1.

[0154] Example 8 - Precipitation of Compound 1 (Using a Second Solution and an Organic Acid) and Isolation of the Precipitate

[0155] Acetic acid (2.31 g, 0.04 mol, 1 mol eq) was added to an aqueous solution of Compound 1 (50% w / w, 46.75 g, 0.04 mol), and the resulting mixture was kept under stirring until completely homogenized (first solution). The pH of the solution was about 4.69.

[0156] The first solution was added dropwise (addition time = 1 ÷ 3 hours) to a reactor equipped with mechanical stirring (pre-loaded with absolute ethanol (280.51 g, 6.0 w / w Cpd.1 -second solution) and kept at 20°C) while maintaining the stirring rate at >350 rpm. During the addition, a white precipitate was observed to form.

[0157] At the end of loading, set the following temperature change:

[0158] 1. Keep at 20℃ for 30 minutes;

[0159] 2. Cool to 5°C within 6 hours;

[0160] 3. Keep at 5°C for 16 hours.

[0161] After the temperature shift, the mixture was filtered on a sintered glass funnel (porosity 4) and the filtered precipitate was washed with fresh absolute ethanol (1 w / w vs complex) precooled at 5° C. The solid obtained was dried at 40° C. in a static oven under vacuum (<20 mbar).

[0162] At the end point, a white powder was obtained with a wet / dry ratio of about 2.7%. The precipitation yield was 84.0%.

[0163] Table 8 shows the major impurities and diastereoisomer ratios expressed as % area FLD (or ppm / Cpd.1 where indicated) before and after precipitation.

[0164]

[0165] Table 8

[0166] Table 8 shows the purification capability and diastereoisomer ratio preservation of the process of the present invention. It can be further observed from Table 9 that the amount of monogadolinated complex (mono-Gd) increased from non-quantifiable (nq) to 800 ppm when an organic acid was used as a precipitant. This can be explained by the pH of the solution containing compound 1 after the addition of acetic acid; the acidic pH may promote partial decomplexation of the complex, thereby generating the monogadolinated complex.

[0167] Example 9 - Precipitation of Compound 1 (Using a Second Solution and an Organic Acid (Lactic Acid)) and Isolation of the Precipitate

[0168] A 50% w / w aqueous solution of lactic acid (1.24 g, 0.01 mol, 1 mol eq) was added to an aqueous solution of Compound 1 (51% w / w, 17.80 g, 0.01 mol) and the resulting mixture was kept under stirring until completely homogenized (first solution). The pH of the solution was about 3.35.

[0169] In a reactor equipped with mechanical stirring (pre-loaded with absolute ethanol (106.79 g, 6.0 w / w Cpd.1 -second solution) and kept at 20°C) the first solution was added dropwise (addition time = 1.5 hours). During the addition, the formation of a precipitate was observed.

[0170] At the end of loading, set the following temperature change:

[0171] 1. Keep at 20℃ for 30 minutes;

[0172] 2. Cool to 5°C within 6 hours;

[0173] 3. Keep at 5°C for 16 hours.

[0174] After the temperature change, the mixture was filtered on a sintered glass funnel (porosity 4). The solid obtained was dried at 40° C. in a static oven under vacuum (<20 mbar).

[0175] At the end point, a white powder was obtained with a wet / dry ratio of about 1.7%. The precipitation yield was 90.3%.

[0176] Table 9 shows the major impurities and diastereoisomer ratios expressed as % area FLD (or ppm / Cpd.1 where indicated) before and after precipitation.

[0177]

[0178] Table 9

[0179] Table 9 shows the purification capacity and maintenance of the diastereoisomer ratio of the process of the present invention. Furthermore, it can be observed from Table 9 that the amount of monogadolinated complex (mono-Gd) increases from 298 ppm to 3570 ppm in the case of using an organic acid as a precipitant. This can be explained by the pH of the solution containing compound 1 after the addition of lactic acid, which causes partial decomplexation of compound 1. Such decomplexation appears to occur in higher amounts compared to Example 8, since lactic acid (used in this example) has a lower pKa compared to acetic acid (used in Example 8), thereby promoting even more decomplexation.

[0180] Example 10 (Comparative) - Precipitation of Compound 1 (Using the Second Solution and Carboxylate Salt)

[0181] Potassium monobasic tartrate (4.78 g, 0.01 mol, 1 mol eq) was added to a 48% w / w aqueous solution of compound 1 (16.45 g, 0.01 mol) at 20°C, and the mixture was kept under stirring until completely dissolved. EtOH (98.68 g, 6.0 w / w Cpd.1 ). During the addition, the mixture became an unstirrable sticky solid.

[0182] This comparative example shows that in order to obtain a precipitate that can be further processed to isolate Compound 1, the type of precipitant is critical.

[0183] Example 11 (Comparative) - Precipitation of Compound 1 (Using the Second Solution and High Amounts of Organic Acid)

[0184] Acetic acid (2.88 g, 0.05 mol, 10 mol eq) was added to a 52% w / w aqueous solution of compound 1 (6.20 g, 0.005 mol) at 20°C, and the mixture was kept under stirring until complete dissolution. EtOH (49.58 g, 8 w / w Cpd.1 ). During the addition, the mixture became an unstirrable sticky solid.

[0185] Similar to Comparative Example 7, this Comparative Example shows that in the presence of a precipitating agent, it may be necessary to add it in a specific amount to obtain a precipitate that can be further processed to isolate the complex of formula (I).

[0186] Example 12 - Precipitation of Compound 1 (Using a Second Solution and a Neutral Salt of Sodium (NaBr)) and Isolation of the Precipitate

[0187] NaBr (3.97 g, 0.039 mol, 1 mol eq) was added to a 58% w / w aqueous solution of compound 1 (49.90 g, 0.039 mol) (first solution) at 30°C, and the mixture was kept under stirring. EtOH (199.60 g, 4 w / w Cpd.1 - second solution).

[0188] At the end of loading, set the following temperature change:

[0189] 1. Keep at 20℃ for 30 minutes;

[0190] 2. Cool to 5°C within 6 hours;

[0191] 3. Keep at 5°C for 16 hours.

[0192] After the temperature change, the mixture was filtered on a sintered glass funnel (porosity 4) and the filtered precipitate was washed with fresh absolute ethanol (99.80 g) precooled at 5° C. The solid obtained was dried at 40° C. in a static oven under vacuum (<20 mbar).

[0193] The physical characterization of the precipitated Compound 1 is shown in Table 9, while Table 10 shows the major impurities and diastereoisomer ratios expressed as % area FLD (or ppm / Cpd.1, where indicated) before and after precipitation.

[0194]

[0195] Table 9

[0196]

[0197] Table 10

[0198] Similar to Tables 1 and 2, Tables 9 and 10 clearly show the good purification yield of the method of the present invention, as well as the preservation of the purification capacity and diastereoisomer ratio. In addition, it is also possible to understand from this experiment that free Gd 3+ Both the ion (free Gd) and the monogadolinated complex (mono-Gd) remain essentially unchanged before and after precipitation.

[0199] Example 13 (Comparative) - Precipitation of Compound 1 (Using the Second Solution and a Neutral Salt of Potassium)

[0200] KCl (2.88 g, 0.039 mol, 1 mol eq) was added to a 58% w / w aqueous solution of compound 1 (49.90 g, 0.039 mol) at 30°C, and the mixture was kept under stirring until completely dissolved. EtOH (199.60 g, 4 w / w Cpd.1 ). During the addition, the mixture became an unstirrable sticky solid.

[0201] Similar to Comparative Example 10, this Comparative Example shows that the type of precipitant is critical in order to obtain a precipitate that can be further processed to isolate the complex of formula (I).

[0202] Summary of Examples 1 to 13

[0203] Table 11 summarizes the experiments of Examples 1 to 13 and their results, highlighting for each example whether a filterable solid was obtained, the precipitation yield (where feasible and established), and the percent purification of the two impurities Gd-DOTA and Gd-DO3A (% purif. DOTA and % purif. DO3A, respectively, where feasible and established).

[0204]

[0205] Table 11

Claims

1. A method for precipitating a complex of formula (I) from a solution thereof wherein R is a C2-C6-alkyl radical substituted by at least one hydroxyl (-OH) group, The method comprises the following steps: a) providing a first solution comprising a complex of formula (I); b) providing a second solution comprising ethanol; and c) mixing the first solution of step a) with the second solution of step b) to precipitate the complex of formula (I).

2. The process according to claim 1, wherein R is a C3-C6-alkyl radical substituted by at least one hydroxyl (-OH) group.

3. The process according to claim 2, wherein R is a C4-C6-alkyl radical substituted by at least one hydroxyl (-OH) group.

4. The process according to claim 3, wherein R is a C5-C6-alkyl radical substituted by at least one hydroxyl (-OH) group.

5. The process according to claim 4, wherein R is a C6-alkyl group substituted by at least one hydroxyl (-OH) group.

6. The method according to claim 5, wherein the complex is compound 1 7. The method according to any one of claims 1 to 6, wherein the mixture prepared according to step c) further comprises at least one precipitant selected from sodium and neutral salts of organic acids, the amount of the precipitant being greater than 0.7 molar equivalents and less than 10.0 molar equivalents relative to the complex of formula (I).

8. The method according to claim 7, wherein the amount of the precipitant is 0.8 to 9.0 molar equivalents relative to the complex of formula (I).

9. The method according to claim 8, wherein the amount of the precipitant is 0.9 to 5.0 molar equivalents relative to the complex of formula (I).

10. The method according to claim 9, wherein the amount of the precipitant is 0.9 to 3.0 molar equivalents relative to the complex of formula (I).

11. The method according to claim 10, wherein the amount of the precipitant is 1.0 to 2.0 molar equivalents relative to the complex of formula (I).

12. A process according to any one of claims 7 to 11, wherein the neutral salt of sodium is selected from the group consisting of sodium chloride, sodium bromide, sodium iodide, sodium fluoride, sodium nitrate and sodium sulfate.

13. The process according to claim 12, wherein the neutral salt of sodium is selected from sodium chloride and sodium bromide.

14. The process according to any one of claims 7 to 13, wherein the organic acid is a C1-C6-(hydroxy)alkyl-carboxylic acid.

15. The process according to claim 14, wherein the organic acid is a C2-C6-(hydroxy)alkyl-carboxylic acid.

16. The method according to claim 14 or 15, wherein the organic acid is selected from acetic acid, lactic acid, tartaric acid and citric acid.

17. The method according to claim 16, wherein the organic acid is selected from acetic acid and lactic acid.

18. A method according to any one of claims 1 to 17, wherein the concentration of the complex in the first solution is 20% to 70% w / w.

19. A method according to claim 18, wherein the concentration of the complex in the first solution is 30% to 60% w / w.

20. The process according to any one of claims 1 to 19, wherein the mixing in step c) is carried out so that the amount by weight of ethanol is 1 to 20 times the amount by weight of the complex of formula (I).

21. The process according to claim 20, wherein the mixing in step c) is carried out so that the amount by weight of ethanol is 2 to 15 times the amount by weight of the complex of formula (I).

22. The process according to claim 21, wherein the mixing in step c) is carried out so that the amount by weight of ethanol is 3 to 10 times the amount by weight of the complex of formula (I).

23. The process according to claim 22, wherein the mixing in step c) is carried out so that the amount by weight of ethanol is 4 to 8 times the amount by weight of the complex of formula (I).

24. A method for separating a complex of formula (I) from a mixture wherein R is a C2-C6-alkyl radical substituted by at least one hydroxyl (-OH) group, The method for separation comprises the following steps: (i) carrying out a process according to any one of claims 1 to 23 to obtain a precipitation of the complex in the mixture; and (ii) filtering the complex precipitate from the mixture.

25. The process according to claim 24, wherein R is a C3-C6-alkyl radical substituted by at least one hydroxyl (-OH) group.

26. The process according to claim 25, wherein R is a C4-C6-alkyl radical substituted by at least one hydroxyl (-OH) group.

27. The process according to claim 26, wherein R is a C5-C6-alkyl radical substituted by at least one hydroxyl (-OH) group.

28. The method according to claim 27, wherein R is a C6-alkyl group substituted with at least one hydroxyl (-OH) group.

29. The method according to claim 28, wherein the complex is compound 1 30. A process according to any one of claims 24 to 29, wherein prior to step (ii), the temperature of the mixture is reduced to 0°C to 10°C.

31. The method according to claim 30, wherein prior to step (i), the temperature of the mixture is reduced to 5°C.

32. A method according to any one of claims 24 to 31 , wherein the temperature is gradually reduced over a period of 6 to 48 hours.

33. A method according to claim 32, wherein the temperature is gradually reduced over a period of 12 to 36 hours.

34. A method according to claim 33, wherein the temperature is gradually reduced over a period of 22.5 hours.

Images