WO1992005807A1

WO1992005807A1 - Contrast medium comprising a paramagnetic cation associated with a schiff base

Info

Publication number: WO1992005807A1
Application number: PCT/EP1991/001893
Authority: WO
Inventors: Preet Paul Kaur Claire; Christopher John Jones; John Richard Thornbach; Kwok Wai Chiu
Original assignee: Medgenix Group S.A.
Priority date: 1990-10-05
Filing date: 1991-10-04
Publication date: 1992-04-16
Also published as: FR2667506A1; FR2667506B1

Abstract

A contrast medium for NMR imaging in the form of a complex between a chelating agent consisting of a Schiff base and a paramagnetic metal cation, a physiologically acceptable salt of this complex or a hydrate of this salt.

Description

CONTRAST AGENT COMPRISING A PARAMAGNETIC CATION ASSOCIATED WITH A SCHIFF BASE.

The invention relates to new contrast agents which can be used in diagnosis by magnetic resonance imaging (MRI).

Nuclear magnetic resonance is now widely used to obtain spatial images of human subjects for clinical diagnosis.

By this technique, an image of an organ or tissue is obtained in vivo by placing the subject in a strong external magnetic field and observing the effects of this field on the magnetic properties of protons, in particular the proton of water. , contained in, and in the vicinity of said organs or tissues.

Once the external energy source is removed, the excited state nuclei tend to return to a more stable energy state. The return of the nucleus to equilibrium is characterized by two relaxation times called T1 and T2. These two parameters depend on the physical and chemical environment of the organ or tissue water, and they describe the return to equilibrium of nuclear magnetism of the sample nuclei in directions parallel or perpendicular to the magnetic fields. applied. Thus, T1 represents a time constant which describes a mode of dissipation of energy, in particular the loss of energy towards the local molecular environment, that is to say the network. It is by studying the relaxation times of the protons of the molecules present, in particular of the water protons, that it is possible to produce, by relatively complex calculations, a visual image of the structure of the tissue concerned.

The image produced, however, often lacks definition and clarity, due to the similarity of signals from other tissues. To avoid this drawback, contrast agents are used. These are substances which have an effect on the NMR parameters (relaxation time T ₁ , T ₂ and relaxivity) of various chemical species present around them.

As contrast agents, we have already used products paramagnetics, which contain unpaired electrons which do not interact and are not coupled. These are, for example, ions in solution. Ainsl, the European patent publication EP 071 564 describes the use, for MRI diagnosis in humans, of Gd ³⁺ ions chelated with pentaacetic acid diethylene tπamine (DTPA). The chelate thus formed makes it possible to decrease the relaxation time T1 and thus to increase the contrast and the precision of the image. The Gd ³⁺ ion itself being toxic, it is necessary to chelate it for use in vivo. This compound has been used intravenously to demonstrate pathological alterations in the "blood brain barrier" (RC BRASCH et al American Journal of ROENTGENOLOGY, 142, page 625, 630 - 1984). However, this product is not suitable for other diagnostic uses. For example, in the liver, it is absorbed in the same way by normal cells and cancer cells and therefore we cannot distinguish healthy tissue from altered tissue.

The invention therefore aims to provide new contrast agents usable in MRI which have, compared to known agents, greater tissue specificity.

An object of the present invention is to provide a contrast agent of the paramagnetic chelate type soluble in aqueous solution which can be administered parenterally, for example by intravenous injection, so as to obtain a contrast effect in imaging by

NMR of a specific organ.

More specifically, an object of the present invention is to provide a contrast agent which, after administration at a low dose, leads to a specific increase in the relaxation of the proton of water in a particular organ without interfering with other organs and without causing side effects.

Another object is that the contrast agent has both high stability, low toxicity, that is to say is physiologically tolerable on the one hand, and that on the other hand it has the properties of relaxivity and d osmolarity satisfactory for good contrast imaging.

We have now found, surprisingly, that the compounds corresponding to the general formula of Schiff bases, allow the formation of paramagnetic metal ion chelates which exhibit increased tissue specificity when used as MRI contrast agents.

This is why the subject of the invention is a contrast agent which can be used in MRI diagnosis consisting of a complex between a chelating agent and a metal cation, a physiologically acceptable salt of this complex or else a hydrate of this salt, having for formula :

[M (L)] ^{(n-2) +} [X-] _(n-2) .mH ₂ O (I) in which

- M denotes a paramagnetic metallic cation with divalent + n or trivalent charge,

- n = 2 or 3

- X is a physiologically acceptable monovalent anion.

- L is a cheatating agent of formula:

in which

- R ¹ to R ⁶ represent H, OH, a halogen, an optionally substituted alkyl, alkoxy, aryl, hydroxyalkyl, carboxyalkyl group,

Y represents NH, O, S, or

- p and m are integers ranging from 1 to 5

- A to F, A 'to F' and A "to F" represent H, OH, a halogen, an alkyl, alkoxy, hydroxyalkyl, carboxyl, carboxyalkyl, phosphonyl (PO ₃ H ₂ ), sulfonyl (SO ₃ H) group , nitro

(NO ₂ ), an alkyl group substituted by a phosphonyl or sulfonyl group,

- At least one of A to F, at least one of A 'to F' and at least one of A "to F" if appropriate, represent a hydroxyl, carboxyl, phosphonye or sulfonyie group or a alkyl substituted by these groups, groups whose hydrogen is replaced by the paramagnetic cation F "M ^{n +} ,

- Z designates N or C, when Z designates N then F, F 'and F "do not exist,

These complexes between the celating agent and the paramagnetic cation can be neutral or ionic depending on the charge of the cation.

When acid-labile hydrogen atoms of the substituent groups from A to F, A 'to F' and A "to F" are not replaced by the cation M ^{n +} , it is possible to increase the solubility of the complex to replace them with physiologically harmless cations from a mineral and / or organic base, especially an amino acid.

The presentation of the complex in salified form generally makes it possible to increase the solubility of the complex in the aqueous phase.

According to the present invention, the term “alkyl” or “alkoxy” is understood to mean radicals C ₁ to C ₇ preferably C ₁ to C ₃ and by aryl preferably phenyl.

Mention will in particular be made of the agents for which R ¹ to R ⁶ represent H, a halogen and a C ₁ -C ₃ alkyl.

The contrast agents of the invention are particularly effective when the paramagnetic metal is chosen from divalent or active ions of transition metals or paramagnetic lanthanides.

Mention may more particularly be made of the following ions: Co ²⁺ , Mn ²⁺ , Cu ²⁺ , Cr ³⁺ , Fe ²⁺ , Fe ³⁺ , Eu ²⁺ , Gd ³⁺ , Dy ³⁺ , Ho ³⁺ preferably Gd ³⁺

As a monovalent anion X, the halide ions, NO ₃ -, BPh ₄ - can be cited as an example,

The agents for which Y = O or NH and those for which p is an integer from 2 to 4 will also be mentioned more particularly.

Similarly, the agents for which A to F, A 'to F' and A "to F" represent H, OH or NO ₂ are more particularly cited, only one of A to F, A 'to F' and A "to F" representing an OH which are then in the form of hydroxylate.

In an embodiment A and A ', B and B', D and D ', E and E', F and F 'are identical two by two respectively.

In another embodiment (A, A 'and A "), (B, B' and B"), (D, D 'and D "), (E, E' and E"), as well as (F , F 'and F ") are identical three to three respectively.

Examples of suitable contrast agents according to the invention are cited the agents of formula: Gd (L ¹ ) X) with 1 = 1 to 5.

in which L ¹ has the formula:

L ² has the formula

)

L ³ has the formula:

L ⁴ has the formula:

or

L ⁵ has the formula:

Finally, the present invention also relates to a process for preparing the contrast agents according to the invention.

To prepare the compounds according to the invention, one proceeds firstly to the preparation of the Schiff bases which are then chelated with paramagnetic cations. The formation of the chelate is carried out very simply by reaction of a saline solution MXn, in particular of halide, of said metal cation in alcohol on a solution of the Schiff base in the same alcohol. The reaction process for preparing the Schiff base can be carried out in two stages, according to the following scheme under the conditions known to those skilled in the art:

then the complexation:

When Y =

the first stage of the preparation process can be carried out according to the following scheme:

Other advantages and characteristics of the invention will become apparent in the light of the examples which follow.

In all of the examples, the relaxation time T1 is measured using the Minispec Brϋcker, 20 MHz at 37 ° C.

All chemical reagents, unless otherwise indicated, are commonly available commercially and used as such without a subsequent purification step.

The infrared spectra are recorded on a PE 297 device. The NMR spectra are recorded on a Jeol 6 x 270 device (270 MHz) and the mass spectra are recorded on a Kratos MS80 device using Fab spectrometry. argon. EXAMPLE 1 Preparation of the compound [Gd (L ¹ )] CI

Compound L has the following formula:

It is prepared according to the method described in the publication C.J. Jones et al., J. Chem. Soc. Dalton Trans, 1 989, 1405.

To a colorless solution of GdCl, (0.17 g; 0.64 mmol) in 50 ml of ethanol, a solution of L ¹ (0.23 g; 0.65 mmol) in 30 ml of ethanol is added and an immediate deposit of a bright yellow microcrystalline solid is observed. After stirring the mixture for two hours at 20 ° C, the yellow solid is filtered, washed with ethanol and ether, and dried in vacuo. A yield of 68.6% is observed (0.24 g of product recovered). The product obtained has the following characteristics corresponding to the formula C ₂₀ H ₂₂ N ₇ O ₄ CIGd:

- calculated: C, 43.91; H, 4.02; N, 5, 12%

- found: C, 45.7; H, 5.0; N, 6.5%.

Mass spectrum M / Z = 512.

IR ν (C = N) = 1650 cm ^-1 .

EXAMPLE 2 Preparation of the product [Gd (L ² )] CI, H ₂ O.

The product L ² has the following formula:

To prepare it, a solution of tetraethylenepentamine (0.5 g; 0.32 ml; 2.64 mmol) in 10 ml of ethanol is added dropwise to a solution of salicylaldehyde (0.63 g; 0.56 ml ; 5.20 mmol). The reaction mixture is stirred for 24 hours at 20 ° C., then the solution is filtered and the volatiles are removed in vacuo to give an orange-yellow oil.

It is found by NMR that the yellow oil obtained is suitable as regards its purity, for the subsequent synthesis of the metal complex.

The analysis for C _{2 2} H _{3 1} N ₅ O ₂ + 0.5H ₂ O gives the following results:

- calculated: C, 65.02; H, 7.90; N, 17.24%.

- found: C, 64.9; H, 7.2,; N, 16.4

IR: ν (C = N) = 1625 cm ^{- 1} .

1 h vmr (DCI ₃ ):

The final chelate compound is prepared by adding dropwise a solution of L ² (1.05 g; 266 mmol) in 30 ml of ethanol to a solution of

Gd Cl ₃ (0.7 g; 266 mmol). The immediate deposition of a pale yellow solid microcrystalline is observed. The reaction mixture is then heated to

60 ° C for two hours, then after cooling, the pale yellow solid is filtered and washed with an ethanol / ether mixture.

After recrystallization from the ethanol / ether mixture, colorless crystals are obtained (yield: 56%, ie 0.9 g of product). Analysis of the product C ₂₂ H ₃₁ N ₅ O ₃ GdCl gives the following results:

- calculated: C, 43.6; H, 5.2; N, 11.6%.

- found: C, 44.2; H, 5.3; N, 12.0%.

Mass spectrum: M / Z = 553

IR: (C = N) = 1620 cm ^-1

EXAMPLE 3 Preparation of [Gd (L ³ )] Cl. 3H ₂ O.

The heand L ³ has the following formula:

To a solution of NH ₂ C ₂ H ₄ OC ₂ H ₄ OC ₂ H ₄ NH ₂ (0.309 g; 2.08 mmol, in ethanol (25 ml) a solution of 2-hydroxy 5-neto benzyl aldehyde (0 , 65 g; 3.36 mmol) in ethanol (50 ml) under a nitrogen atmosphere The reaction mixture is added at 20 ° C. for 16 hours. An orange solid is filtered and washed with ethanol and l ether then dried under vacuum at 60 ° C. The yield is 64.5% (0.9 g), melting point: 144-155 ° C. Microanalysis for C ₂₀ H ₂₂ N ₂ O ₈ ;

Found C: 53.6; H: 4.95; N: 12.6%

Calculated C: 53.8; H: 4.93; N: 12.6%

IR: ν (C = N) = 1658 cm ^-1 .

Mass spec. : M / Z = 447.

1H rmn (CDCl ₃ ):

The complex [Gd (L ³ )] Cl. 3H ₂ ) is prepared as follows

To a solution of L ³ H ₂ (0.20 g; 0.45 mmol) in ethanol (50 ml), add the solution of GdCl ₃ (0.103 g; 0.39 mmol) in ethanol (30 ml). The reaction mixture is brought to reflux for 2 hours under a nitrogen atmosphere. A pale yellow solid is filtered and washed with ethanol and retrier; the product is then dried under vacuum at 60 ° C.

Yield: 0.18 g, 64%;

Microanalysis for C ₂₀ H ₂₆ N ₄ O ₁₁ CIGd:

Found: C: 34.5; H: 4.16; N: 8.0%

Calculated: C: 34.8; H: 3.8; N: 8.2%

IR: ν (C = N) = 1660 cm ^-1 .

Mass spec. : M / Z = 602.

EXAMPLE 4: preparation of [Gd (L ⁴ )] Cl, H ₂ O.

The ligand L ⁴ H ₂ has the following formula:

To a solution of 2-hydroxy 5-nιtro benzylaldehyde (0.5 g. 2.99 mmol) in ethanol (50 ml), tetraethylene pentaamine (0.26 ml, 1.49 mmol) is added. The reaction mixture is stirred at 20 ° C for 24 hours under a nitrogen atmosphere. The volatile materials are removed under vacuum to give a yellow oil. After washing with ether, a pale yellow solid is isolated. Yield: 0.59 g, 82%; Melting point: 1 49 - 1 51 ° C. Microanalysis for C ₂₂ H ₂₉ N ₇ O ₆ ;

Found C: 53.2; H: 6.7; N: 20.7%

Calculated C: 53.8; H: 5.99; N: 20.1%

IR: ν (C = N) = 1650 cm- ¹ .

Mass spec. : M / Z = 488. 1H rmn (CDC l ₃ ):

The complex [Gd (L ⁴ )] C l, H ₂ O is prepared as follows: To a suspension of L ⁴ (0.1 1 g; 0.23 mmol) in ethanol (40 mi), the solution of GdC l ₃ (0.054 g; 0.21 mmol) in ethanol (30 ml) with stirring under a nitrogen atmosphere. The reaction mixture is brought to reflux for 5 hours. The solution is filtered. The filtrate is concentrated under vacuum to 10 ml to give a pale yellow microcrystalline solid. Yield: 71 mg, 51%;

Microanalysis for C ₂₇ H _{3 1} N ₇ O ₇ ClGd;

Found: C: 37.34; H: 4.27; N: 14.0%

Calculated: C: 37.84; H: 4.18; N: 14.04%

IR: ν (C = N) = 1640 cm ^{- 1} .

Mass spec. : M / Z = 643.

EXAMPLE 5 Preparation of [Gd (L ⁵ )] C l, 2H ₂ O.

The ligand L ⁵ H ₂ has the following formula

To a solution of 2-hydroxy 5-nιtro benzylaldehyde (0.5 g,

2.99 mmol) in ethanol (40 ml), triethylene tetraamine is added

(0.22 ml, 1.5 mmol). The reaction mixture is stirred at 20 ° C for 24 hours under a nitrogen atmosphere. The pale yellow microcrystalline solid is formed, filtered and washed with ethanol and ether and dried under vacuum at 60 ° C.

Yield: 0.57 g, 85%; Melting point: 210 ° C.

Microanalysis for C ₂₇ H ₂₇ N ₇ O ₉ ;

Found: C: 54.25; H: 4.84; N: 16.89%

Calculated: C: 54.64; H: 4.55; N: 16.53%

IR: (C = N) = 1650 cm ^{- 1}

Mass spec. : M / Z = 594

¹ Hrmn (CDC I ₃ ):

The complex [Gd (L ⁵ )] Cl, 2H ₂ O is prepared as sult:

To a suspension of L ⁵ H ₂ (0.1 g; 0.24 mmol) in ethanol (50 ml), the solution of GdCl ₃ (0.63 mg; 0.24 mmol) in ethanol is added (30 ml) with stirring under a nitrogen atmosphere. The reaction mixture is brought to reflux for 12 hours, after cooling, the solution is filtered, the filtrate is concentrated under vacuum to 5 ml to give a pale yellow microcrystalline material which is then filtered and washed with ether. Yield: 0.11 g, 71%;

Microanalysis for C ₂₀ H ₂₆ N ₆ O ₈ ClGd;

Found: C: 35.32; H: 4.26; N: 12.97%

Calculated: C / 35.79; H: 4.18; N: 12.52%

IR: ν (C = N) = 1640 cm ^-1 .

Mass spec. : M / Z = 600.

EXAMPLE 6: Results

The relaxation time T ₁ and the relaxivity R were measured for the two complexes of Examples 1 and 2.

The relaxation time T ₁ was determined on Minispec Brϋcker at 20 MHz at 37 ° C. The relaxivity of the compounds according to the invention was measured on the 20 MHz minispec. The results are shown in Table 1 above. The measurements were made in water.

These complexes injected into the rat at a dose of 0.1 mmol / kg, gives a percentage of increase in contrast in the for about 30%, 20 minutes after the injection, even as for Magnevist ^R (Gd (DTPA) the increase 20 minutes after the injection is zero.

Claims

1. Contrast agent for NMR imaging consisting of the complex between a chelating agent and a metal cation, a physiologically acceptable salt of this complex or else a hydrate of this salt, having the formula:

[M (L)] ( ^{n-2) +} [X-] _(n-2) .mH ₂ O (I) in which

- M denotes a paramagnetic metallic charge cation

+ n divalent or tri are worth.

- n = 2 or 3

- X is a physiologically acceptable monovalent anion,

- L is a chelating agent of formula:

in which

- R ¹ to R ⁶ represent H, OH, a halogen, an optionally substituted alkyl, alkoxy, alkyl, hydroxyalkyl, carboxyalkyl group,

- Y represents NH, O, S,

or

- p and m are integers ranging from 1 to 5

- A to F, A 'to F' and A "to F" represent H, OH, a halogen, an alkyl, alkoxy, hydroxyalkyl, carboxyl, carboxyaikyl, phosphonyl (PO ₃ H ₂ ), sulfonyl (SO ₃ H) group , nitro

(NO), an alkyl group substituted by a phosphonyl or sulfonyl group,

- At least one of A to F, at least one of A 'to F' and at least one of A "to F", where appropriate, represent a hydroxyl, carboxyl, phosphonyl or sulfonyl group or an alkyl substituted by these groups, groups whose hydrogen is replaced by the paramagnetic cation M ^{n +} ,

- Z denotes N or C, when Z denotes N then F, F 'and F "do not exist.

2. Contrast agent according to claim 1 characterized in that M represents a divalent or trivalent cation of transition metal or lanthanides in particular Co ²⁺ , Mn ²⁺ , Cu ²⁺ , Eu ²⁺ , Cr ³⁺ , Fe ^{3 +} , Gd ³⁺ , D3 ²⁺ , Ho ³⁺ preferably G3 ²⁺ .

3. Contrast agent according to one of claims 1 or 2 characterized in that Y = O or NH.

4. Contrast agent according to one of claims 1 to 3 characterized in that A to F, A 'to F' and A "to F" represent H, OH or NO _2, at least one of A to F , A 'to F' and A "to F", where appropriate, being a hydroxylate.

5. Contrast agent according to one of claims 1 to 4 characterized in that p is an integer from 2 to 4.

6. Contrast agent according to one of claims 1 to 5 characterized in that R to R represent H, a halogen, a C ₁ to C ₃ alkyl optionally substituted by a halogen.

7. Contrast agent according to one of claims 1 to 6 characterized in that X is a halide, NO ₃ -, BPh ₄ -.

8. Contrast agent according to one of claims 1 to 7 characterized in that the metal cation is Gd ^{3 +} .

9. Contrast agent according to one of claims 1 to 8 characterized in that it corresponds to the formula Gd (L ¹ ) X, in which L ¹ represents:

L ¹ of formula:

L ² of formula:

L ³ of formula

L ⁴ of formula:

or

L ⁵ of formula

10. Process for the preparation of a contrast agent according to one of claims 1 to 9, characterized in that in an alcoholic medium, a solution of a salt of the metal cation M ^{n +} , in particular a halide salt, is reacted with a basic Schiff solution of formula (II):