NO901138L - PROCEDURE FOR AA CHELAT BOND METAL IONS IN A SOLUTION SOLUTION THEREOF. - Google Patents

Description

Norbornane is a cyclic compound that is found in or can be derived from the remaining heavy hydrocarbons at the bottom of distillation towers in plants for the production of light hydrocarbons.

A number of derivatives of norbornane have been prepared, among them bis(methylamine). It is this compound which is phosphono-methylated which is the subject of the present invention.

It is well known that amines, such as ethylenediamine and diethylenetriamine can be reacted with formaldehyde and phosphoric acid so that methylenephosphonate derivatives of the amine are formed in which the methylenephosphonate group

replacing the amine hydrogens (U.S. 3,288,846) .

The use of methylenephosphonic acid-substituted alkylene polyamines

for the control of metal ions in less than stoichiometric amounts, was proposed in a patent (U.S. 2,609,390) issued in 1952. Later, a chelating, water-dispersible polymeric amine containing alkylene phosphonate derivatives was stated to

have "threshold" action in preparations to prevent calculus (see U.S. 3,331,773), this term is used to describe the use

of the agent in less than stoichiometric amounts. Diamine and polyamine methylenephosphonate derivatives are disclosed and claimed in U.S. Pat. 3,336,221 and 3,434,9 69. Some of the products disclosed in these two patents are available commercially, and are recommended as agents to prevent boiler scale when used in threshold amounts.

Other patents that discuss nitrogen-containing heterocyclic compounds that are useful as chelating agents and can be used in threshold amounts are U.S. Pat. 3,674,804; 3,720,498; 3,743,603; 3,859,211 and 3,954,761. Some of the compounds included therein are heterocyclic compounds having the formulas:

wherein R is hydrogen or alkyl and M is hydrogen, alkali metal, ammonium or a di- or triethanolamine radical; Certain phosphonic acid derivatives of the aliphatic acids can be prepared by reacting phosphoric acid with acid anhydrides or acid chlorides, e.g. the anhydrides or chlorides of acetic, propionic and valeric acids. The compounds produced have the formula wherein R is a lower alkyl radical having 1 to 5 carbon atoms. The procedure for the manufacture and use of these products is described in U.S. Pat. 3,214,454. The use of threshold amounts to prevent calcium precipitation is described and patented therein. It has now been discovered that new chelating agents and threshold agents to prevent precipitation of metal ions can be made from the bis(methylamine) derivatives of norbornane. This compound has the structure

This compound is also known by the more formal name 2(3), 5(6)-bis [aminomethyl] bicyclo(2,2,1)heptane. Its derivatives are those that have different substituents replacing the primary amine hydrogens.

A new type of compound is formed when norbornane bis(methylamine) reacts with certain compounds, e.g. formaldehyde and phosphoric acid will give methylenephosphonic acid derivatives. These new compounds have the structure

wherein the substituents A, B, X and Y are all independently selected from radicals consisting of hydrogen, hydroxyalkyl1 (wherein alkyl-

group contains 2-6 carbon atoms), methylene phosphonic acid, methylene, ethylene and propylene sulphonic acid, carboxylic acid radicals (which have 2-4 carbon atoms) and alkali and alkaline earth metals, ammonia and amine salts of some of phosphonic, sulphonic -or the carboxylic acid derivatives. At least one of the substituents must be different from hydrogen.

Methods for obtaining hydroxyalkyl, sulphonic acid or carboxylic acid derivatives of compounds of formula I are well known in the art.

The method of substituting a hydrogen in an amine with a hydroxyalkyl group by reaction with an epoxide, e.g. ethylene or propylene oxide, is shown in U.S. Pat. 3,398,198.

The sulfonic acid radicals can replace an amine hydrogen by reacting the amine with a mixture of sodium bisulfite and formaldehyde to obtain a methylene sulfonic acid group substituent on the nitrogen in the amine compound. This reaction is explained in "Preparation and Properties of Aminoethylenesulfonic Acids", J. Am. Chem. Soc. 77, 5512-15 (1955). Other alkylsulfonic acid derivatives can be prepared by reacting the amine with chloroalkylsulfonic acids.

The carboxylic acid group can replace an amine hydrogen by reacting the amine in aqueous solution with suitable nitriles such as glycolinitri1 and acrylonitrile in the presence of an excess of caustic soda (NaOH) and then transferring the salt form of the acid radical to the free carboxylic acid radical according to the well-known method.

When it comes to preparing amine salts from the acid radicals, the reaction is well known. In Richter's 3rd edition (1952) of his "Textbook of Organic Chemistry", page 246, it is stated "Amines of all types, like ammonia, are basic compounds and react readily with acids to form ionizable salts".

The present invention also applies to the use of bis-(aminomethyl 1) bicyclo [2 . 2. l] heptanes of formula I as complexing compounds for radionuclides when it comes to visualizing the skeletal system of animals.

The first radionuclide widely used for bone scanning was Sr-85. Strontium-85 accumulates rapidly in bone tissue after intravenous administration, and visualization of the skeletal system is possible. However, Sr-85 has a long physical half-life (65 days) and a long biological half-life (-800 days), which limits the amounts that can be administered. Moreover, the high energy of the emitted gamma photons (514 kev) is difficult to collimate.

Fluorine-18 has also been used to visualize the skeletal system. It is a positron emitter with a half-life of 1.85 h. Although the F-18 has good physical properties for visualization, it has some serious drawbacks. Fluorine-18 is produced in a cyclotron, and is therefore expensive. Furthermore, the distribution is limited due to the short half-life.

Many organ scanning agents, including those for the skeletal system, have now been replaced with complexes of technetium-99m. This nuclide has ideal physical properties (T^=6t, gamma photon 141 kev) for visualization. Additionally, it is readily available due to Mo-99/Tc-99m generators. Thus, most of the visualization is now done using Tc-99m.

Technetium-99m can be obtained from generators in + 7 oxidation stages such as the pertechnetation (TcO^ ). To be able to form a complex, Tc must be at a lower oxidation state, e.g. +3, +4 or +5. Although other reducing agents can be used, Sn is most commonly used. Thus, Tc-99m complexes can be formed by reduction of TcO^ using Sn in the presence of a complexing compound. This is usually carried out in an aqueous saline solution suitable for intravenous injection.

Complexing compounds are sold commercially as "radiopharmaceutical kits". A "kit" consists of an evacuated ampoule containing the complexing compound, a reducing agent and possibly a buffer and stabilizing agents. To prepare the Tc-99m complexes, a few milliliters of sodium pertechnetate solution in saline is injected into the vial. An appropriate amount of the resulting solution is used for the visualization.

Subramanion et al (Radiology, Vol. 99, pages 192-196, 1971) reported the use of a complex of Tc-99m and an inorganic polyphosphate for skeletal visualization. Many others have reported inorganic polyphosphates as useful for this purpose

(see U.S. 3,852,414; 4,016,249 and 4,082,840). The use of pyro-phosphate (PYP) for skeletal visualization has also been shown (U.S. 3,851,044; 3,931,396 and 4,075,314). The Tc phosphates had quite

good success, but has been replaced by Tc-phosphonates.

Complexes of Tc-99m with phosphonic acid show greater bone uptake with faster blood clearance than Tc-99m/phosphate complexes. Phosphonic acids considered the best bone scan agents when complexed with Tc-99m include hydroxyethane diphosphonate (EHDP), methylene diphosphonate (MDP) and hydroxymethylene diphosphonate (see U.S. 3,983 . 227; 3,989 , 730 ; 4,032,625 and also J.Nucl.Med., 21, page 767, Radiology 136, page 209; J.Nucl.Med., 21, page 961; Radiology 136, page 747).

New stable complexing compounds for Tc-99m, which are derivatives of bicyclo [2 . 2. lj heptanebis (methylamines) have been found and are useful for visualizing the skeletal system in animals. These new complexing compounds are represented by formula I above. The complexes pass easily and efficiently through the kidneys and large amounts are taken up in the bone tissue. The ratio between absorption in the bone tissue and what is absorbed in soft tissue is large.

The new complexing compounds were found to form stable Tc-99m complexes when Sn 2 + was added to a salt-water solution containing complexing agents. The complex passes easily through the kidneys and a large amount is absorbed into the skeletal system and very little remains in the blood and soft tissue.

Therefore, as the absorption in bone tissue compared to that in the surrounding soft tissue is large, the visualization became sharp and clear. The ratio between the activity in bone tissue/soft tissue and bone tissue/blood comes out favorably in comparison with Tc bone tissue radiopharmaceuticals that are on the market.

The following examples illustrate the preparation and use of the new compounds produced according to the invention. Identification of the compounds is made with reference to formula I above.

Example 1

Distilled water (10 g) and H 2 PO 3 (9.9 g) were weighed into a 50 mL round bottom flask equipped with a water-cooled condenser, a thermometer, a stir bar, and an addition funnel. Concentrated HCl (11.8 g) was then added and 3.9 g of 2(3),5(6)-bis[aminomethyl]bicyclo-(2,2,1)heptane was slowly added with stirring. The solution was refluxed for approximately one hour and a 37 percent aqueous formaldehyde solution (8.51g) was added over a period of 2.5 hours. The solution was heated for another 3 hours with reflux. The compound formed was the fully phosphonomethylated norbornane derivative in which each of A, B, X and Y were methylenephosphonic acid groups, -CP^PO^H,,.

Example 2

The procedure in example 1 was followed by the addition of

3 molar equivalents of formaldehyde (24.3 g of a 37 percent solution) and phosphoric acid (25.1 g) to one molar equivalent of 2(3),5(6)-bis[aminomethyl]bicyclo(2,2,1)heptane (15.2g) . The resulting solution was neutralized with NaOH (aq) and one molar equivalent of glycolonitrile (14.7 g of a 38 percent solution) and NaOH (13.8 g of a 33.3 percent solution) was added. The compound formed was the sodium salt of the bicycloheptane derivative which had an average of three methylenephosphonic acid groups and one carboxymethyl group per molecule as A, B, X and Y substituents.

Example 3

An amount (15.2 g, 0.1 mol) of 1(2),4(5)-bis[aminomethyl]bicyclo(2,2,1)heptane was placed in a stainless steel beaker and 50 ml of distilled water was added, followed by the addition of 37 ml of 50 percent NaOH. This solution was heated to about 70° with stirring and carboxymethylation was carried out by dropwise addition of 8.9 g of 38 percent glycolonitrile while heating was continued, over a period of one hour. After about 15 minutes of the addition, the temperature was at reflux and NH was released. Distilled water was periodically added to replace the evaporated water. After the addition of glycolonitrile was complete, the solution was heated for another hour with stirring and purging with N 2 . The compound formed was the tetracarboxymethyl derivative where A, B, X and Y were

CH2-COONA.

The usefulness of the compounds prepared according to the invention was determined by performing boiler scale inhibition tests according to the National Association of Corrosion Engineers<1>(NACA) test method TM-0 3-74. The calcium carbonate scale inhibition results are shown in Table I and compared with a commercially available scale inhibitor, aminotri-(methylenephosphonic acid). Inhibition of the calcium sulfate boiler was also investigated and the results are shown in Table II.

The utility of the compounds prepared according to the present invention in acting as chelating agents was demonstrated by titrating the compounds with standard copper solution in the presence of chromazurol-S indicator. The compound in example 1 was titrated and found to complex approximately 1.5 mol of copper per moles of ligand. This compound can act either as a threshold compound or a chelating compound.

It should be clear that the compounds prepared according to the invention can have several different groups such as A, B, X and Y substituents on the same molecule, but that when mixed derivatives are prepared it is not possible to direct or predict which amine hydrogens will be substituted. The product probably contains a mixture of isomeric compounds.

While all compounds will chelate metal ions, only those containing at least one methylenephosphonic acid group or its salt will produce a threshold effect.

Example 4

One hundred µl of the solution prepared in Example 1 was placed in a vial and one ml of 0.9 percent saline solution (aq) was added. The pH of the solution was adjusted to 3.5 using dilute NaOH and HCl and 0.1 ml of a freshly eluted TcO₂ solution was added. This was followed by the addition of 100 µl of saturated tin (II) tartrate solution. Leaching of paper chromatography strips with saline and acetone showed less than 5 percent activity as TcO 3 or reduced uncomplexed Tc.

The above Tc complex (50 µl, -1mCi) was injected into the needle vein of rats. Scintillation scanning of the anesthetized rats bee taken at several time points after the injection. The bone tissue scan was of high quality, which entails the use of this as a tool for human patients.

Example 5

The Tc complexes prepared in Example 4 (50 µl, -1mCi) were injected into the tail vein of mice. The mice were killed at various times after the injection, the organs and tissues were removed, and the radiation was measured with a Nal counter. The activity was found primarily in the bone tissue and the bladder, while no other organs showed any great affinity for the complex. 120 Minutes after the injection, the bone tissue, muscles and liver had respectively 5.1<0.01 and 0.24 percent dose/g of the activity.

Example 6

The Tc complex of Example 4 (50 µl, -1mCi) was injected into the tail vein of a number of rats. The animals were killed after 2 hours and the radiation from several tissues was measured quantitatively using a Nal scintillation counter. Table III below shows the results compared to Tc-MDP (methylene diphosphonate), the commercial Tc bone tissue agent, measured in an identical manner.

Example 7

The complex from Example 4 was injected into the ear vein of a number of rabbits. The rabbits were killed within 3 hours of the injection. The radiation in several tissues was measured quantitatively by counting using a Nal scintillation counter. Table IV below shows the results compared to those of a commercial Tc bone tissue agent, MDP.

Scintillation scanning of the above rabbits, 2 hours after the injections with the complex of Example 4, compared favorably with those using commercial Tc-MDP kits.

Claims (4)

1. Process for chelating metal ions in an aqueous solution thereof, characterized in that at least one stoichiometric amount, based on the metal ions present, of a phosphonic acid derivative with the structural formula is added to the solution: wherein the substituents A, B, X and Y are each independently hydrogen or a methylenephosphonic acid radical, and alkali or alkaline earth metal, ammonium and amine salts of any of the phosphonic acid derivatives, and wherein at least one of the substituents is a methylenephosphonic acid radical. 2. Process according to claim 1, characterized in that each of A, B, X and Y in formula I are methylenephosphonic acid radicals. 3. Method according to claim 1, characterized in that two of A, B, X and Y in formula I are methylenephosphonic acid radicals and the remaining two are hydrogen radicals. 4. Method according to one of claims 2-3, characterized in that the compound of formula I is in the form of an alkali metal or alkaline earth metal salt.