Complexes of iron or other metals with sulphonated derivatives of chitosan

Abstract: Complexes of iron or other metals with sulphonated derivatives of chitosan, having the following general formula (I): in which: R is H or a C₁- C₅ alkyl group, or an arylalkyl group; A is H or an alkaline metal or an alkaline earth metal; X is a pharmacologically acceptable anion; m is a whole number from 50 to 1000; n is zero or a whole number from 1 to 10; M is Fe II , Fe III , Mg, Ca or Bi

Description: Field of the invention This invention relates to water-soluble metal complexes with sulphonated derivatives of chitosan. When said complexes are of iron, they can be used in therapy for the treatment of sideropenia. Prior art Chitosan is a polysaccharide obtained by deacetylating chitin by treatment with strong bases. Chitin itself is a widely distributed natural polysaccharide consisting essentially of units of N-acetyl-D-glucosamine, which is extracted from crab shells. Chitosan is used industrially, for example in water treatment, in the preparation of photographic emulsions and in improving the dyeing of synthetic and natural fibres. In the pharmaceutical field chitosan is used in the preparation of cicatrizants. Also known are chitosan derivatives of type 6-0-sulphate having the formula: where n varies between 250 and 2300 or, as complexes with Fe++ in which coordination bounds are established between Fe++ and the amino- or hydroxy-groups present in 2, respectively 3 in chitosan. These derivatives, described in EP 194497, are useful in the treatment of sideropenia; however, the need was felt of derivatives having a higher iron content and a higher solubility, in order to obtain in the treatment of sideropenia a higher enteral iron absorption and therefore a higher antianaemic action. Furthermore, the need was felt of complexes with ions other than iron, useful in other therapeutic treatments. Summary of the Invention We have now found new compounds consisting of ferrous or ferric complexes or of complexes of other metals with sulphonated chitosan derivatives which allow to solve the prior art problems. Said complexes have the following general formula (I): in which: R is H or a C₁-C₅ alkyl group, or an arylalkyl group; A is H or an alkaline metal or an alkaline earth metal; X is a sulphate, nitrate, acetate or chloride anion; m is a whole number from 50 to 1000; n is zero or a whole number from 1 to 10; M is Fe II , Fe III , Mg, Ca or Bi. Said complexes are prepared by: a) hydrolyzing-activating commercial chitosan by treatment with an organic acid, possibly mixed with an alkaline nitrite, and later with alkaline hydroxyde; b) functionalizing by treatment in an organic solvent or in water or in a mixed organic-aqueous solvent with a chlorohydrin or epoxy compound carrying a sulphonated group at one end of its chain; c) treating with an Fe II and/or Fe III or Mg or Ca or Bi salt in aqueous solution and precipitating the complex by adding a water-soluble organic solvent; d) neutralizing the sulphonic group with an alkaline or alkaline-earth hydroxide or other strong base in aqueous and/or organic or mixed organic/aqueous solution and precipitating the neutralized complex by adding a water-soluble organic solvent if operating in an aqueous environment, or recovering the neutralized complex by filtration if operating in an organic solvent or mixed organic/aqueous solvent. The ferrous and ferric complexes according to the invention have a very high activity in the treatment of sideropenia. Detailed description of the invention The characteristics and advantages of the complexes of Fe II , Fe III , Mg, Ca or Bi with sulphonated derivatives of chitosan and of their preparation method according to the present invention will become apparent during the course of the following detailed description. The complexes according to the invention are prepared by a method which uses commercial chitosan as starting material. This product is not suitable for the direct preparation of soluble complexes according to the invention because of its too high molecular weight (> 1,000,000) and its low surface area, which limits its reactivity. To overcome this drawback, the commercial chitosan is subjected to hydrolyzing-activating pretreatment. This pretreatment is effected by adding to the chitosan an organic acid such as a 0.1 M solution of acetic acid or formic acid, heating under reflux for 20-30 hours and then precipitating the hydrolyzed product by adding 5 N NaOH. Alternatively 0.4-0.5 M commercial acetic acid and sodium nitrite can be added to the commercial chitosan and the mixture stirred at ambient temperature for 15-20 hours. The hydrolyzed product is again precipitated with 5 N NaOH. This pretreatment results in chitosan having a molecular weight comprised between 15.000 and 300.000 and a morphology which make it much more reactive than the starting substance and suitable for preparing complexes with a high solubility. The chitosan formed in this manner is functionalized by treatment with a chlorohydrin or epoxy compound comprising from two to twelve carbon atoms and carrying a sulphonated group at one end of the hydrocarbon chain as indicated by the structures (II) and (III): where n is zero or a whole number from 1 to 10, and M is H or an alkaline or alkaline-earth metal. This treatment is conducted in an organic solvent or in water or in a mixed organic/aqueous solvent. Organic solvents which can be used include ethylene glycol, methanol and higher linear or branched homologous alcohols up to 7 carbon atoms, either alone or in mixture with each other. Aprotic dipolar solvents can also be used, such as N,N-dimethylformamide, N,N-dimetylacetamide and dimethylsulphoxide. The molar ratio of chitosan to be chlorohydrin or epoxy compound can vary from 1:0.5 to 1:6 depending on the degree of substitution and solubility required. The treatment is conducted at a temperature of between 60°C and 120°C for a time of between 6 and 16 hours. In this manner a compound is obtained of general formula (IV): which is a new compound, usable for the subsequent reactions and possibly for other uses. An alkyl or arylalkyl group is introduced into the secondary amino group of (IV) by conventional N-alkylation methods. Preparation of the metal complex The compound (IV), possibly alkylated in the aforesaid manner, is dissolved in water in such a quantity as to obtain a concentration of between 8% and 13% w/v. An Fe II , Fe III , Mg, Ca or Bi salt is added to this solution in a quantity such as to obtain a compound (IV) monomer unit to metal ion molar ratio of between 1:1 and 1:1.5 and operating at acid pH such as to keep said salt in solution. Said salt is a sulphate, nitrate, acetate or chloride. The mixture is kept at a temperature of between 10°C and 25°C, under stirring, for 15-20 hours and the reaction product is recovered by precipitation by adding a volume of organic solvent equal to 8 times the volume of the reaction mixture. Suitable solvents are acetone, methanol, isopropanol or other water-miscible solvents. The solid product obtained is filtered off, washed with ethyl ether and dried under vacuum. In this manner the metal ion complex of formula (V) is obtained: The compound (V) is suspended in water or in a suitable organic or aqueous/organic system in a quantity of between 8% and 13% w/v and added at ambient temperature to the stoichiometric quantity of alkaline or alkaline-earth hydroxide or another strong base to neutralize the sulphonic group. The pH must exceed 7.5. The final compound (I) is precipitated from the obtained solution by adding an organic solvent in a quantity of 8 times the solution volume. The solvent used can be acetone, methanol, isopropanol or another water-miscible solvent. If the system is organic the compound (I) is recovered by filtration. The compound (I) is washed with ethyl ether and dried under vacuum. The compound (I) has high water solubility and high stability in aqueous solution. If (I) is the Fe II or Fe III complex it can be used in solution form in therapy to compensate for iron deficiency. The release of iron into the intestinal tract occurs gradually, the polymer part not being absorbed and not giving rise to any side effect. The following examples of the preparation of complexes according to the invention and the pharmacological tests are given for non-limiting illustrative purposes only. EXAMPLE 1 20.0 g of commercial chitosan with an 80% degree of deacetylation, equivalent to 0.12 moles, are hydrolyzed by treatment with 1.0 litres of 0.1 N HCOOH under reflux for 24 h. The hydrolysis product is precipitated with 5 N NaOH and then washed with isopropanol until a water content of 15% is determined by the Karl Fischer method. 18.0 g of hydrolyzed product are obtained having a molecular weight of 100.000 46.3 grams of sodium 3-chloro-2-hydroxypropyl sulphonate (0.24 moles) are dissolved in 40.0 ml of water, after which 8.5 g (0.212 moles) of solid NaOH are added. The mixture is stirred for 6 h after which 130 ml of isopropanol and the 18.0 g of chitosan from the previous stage are added. The mixture is heated under reflux for 8 h after which it is filtered while hot. The solid obtained is washed 3 times with a methanol/water (10/3) mixture, using 150 ml each time, and once with 100 ml of methanol. 32.5 g of a white solid are obtained which on microanalysis is shown to have an S content of 8.0% and a sodium content of 5.7%. The 32.5 g of functionalized product (0.11 moles) are dissolved in 320 ml of water and 60.7 g (0.22 moles) of FeSO₄.7H₂O are added. After 16 hours at 25°C the product is precipitated by adding acetone in a quantity of 2600 ml, filtered off, washed with ethyl ether and dried. 36 g of product are obtained having an Fe II content of 15.0%. This solid is suspended in 360 ml of water and 4.4 g (0.11 moles) of solid NaOH are then added to mixture. The obtained product is recovered by precipitation by adding acetone in the manner of the previous step. 37.0 g of water-soluble product are obtained, a 5% w/v solution of which has a pH of about 8.0 and which has an Fe II content of 12%. EXAMPLE 2 30.0 g of 2[N(sodium 2-hydroxypropyl sulphonate)] poly-D-glucosamine (0.10 moles), prepared as in Example 1, are suspended in 300 ml of methanol and 90 ml of water. 40.4 g of Fe(NO₃)₃.9H₂O (0.1 moles) are added to this suspension under stirring. Stirring is continued for 16 hours at a temperature of 25°C. The solid is then filtered off and washed 3 times with 100 ml of methanol until uncomplexed Fe III is eliminated. 38.0 g of a yellow solid product are obtained containing 12.5% of Fe III . It is then treated with NaOH as specified in Example 1. In this manner 42.0 g of product are obtained with an Fe III content of 10.5% EXAMPLE 3 30.0 g of 2-[N-(sodium 2-hydroxypropyl sulphonate)] poly-D-glucosamine (0.10 moles) are suspended in 300 ml of isopropanol. 20.5 ml of a 40% w/v solution of formic aldehyde (0.2730 moles) and 17.0 g of 98% formic acid (0.364 moles) are then added to this suspension in the stated order. It is heated under reflux until CO₂ evolvement ceases. The suspension is then filtered and the solid washed with a little isopropanol. In this manner 30.5 g of water-soluble product are obtained. The solid obtained is dissolved in 305 ml of distilled water. 49.3 g of FeSO₄.7H₂O (0.18 moles) are added to this solution, which is then left stirring at 25°C for 16 hours. 31.5 g of product are obtained containing 13.5% of Fe II . This quantity is suspended in 315.0 ml of distilled water containing 3.5 g of NaOH (0.088 moles) and the suspension left stirring for 1 hour at 25°C. The solid product is recovered in the manner of Example 1. 33.0 g of water-soluble product are obtained, a 5% w/v solution of which has a pH of about 8.3 and which has an Fe II content of 11.0% EXAMPLE 4 173.9 grams of sodium 3-chloro-2-hydroxy-butyl-sulphonate (0.885 moles) are suspended under stirring in 150 ml of deionized water. 31.8 g (0.800 moles) of solid sodium hydroxide are then added. The mixture is left stirring at 25°C for 1 hour. 30.0 g (0.177 moles) of chitosan having molecular weight of 100.000 hydrolyzed and activated as described in Example 1 and 450 ml of butanol are then added and the mixture heated under reflux for 8 hours. The cooled suspension is then acidified to pH 3.0 with 1.5 N HCl and finally filtered. The solid is washed with methanol/water as described in Example 1. 57.5 g of a water-soluble white solid are obtained with a sodium content < 0.2% and an S content of 7.0%. This solid is dissolved in 600 ml of deionized water. 44.5 g (0.160 moles) of FeSO₄.7H₂O are added to this solution, which is then left stirring at 25°C for 16 hours. 70.0 g of product are obtained with an Fe II content of 12%. The solid is resuspended in 700 ml of deionized water containing 18.0 g of potassium hydroxide (0.32 moles) and the suspension kept stirring for 1 hour at 25°C. By precipitating in the manner described in Example 1, 65.0 g of water-soluble product are obtained, a 5% w/v solution of which has a pH of 8.4 and which has an Fe II content of 11% and a potassium content of 8.6%. Pharmacological Tests Using the product obtained in Example 1 of the present invention and product A of EP 194497, tests were made on the human absorption of iron and on treatment of sideropenic anaemia in rats. The tests on human iron absorption were made following the method described by Brise H. & Hallenberg L. (Acta Med. Scand. Suppl. 376,171; 7-22, 1962) operating as described in EP 194497. Using the product of Example 1 of the present invention in all cases an increase of between 20 and 30% in the iron absorption was obtained, with respect to the absorption obtained with product A of the mentioned EP. The tests on the treatment of sideropenic anaemia were performed by administration of the product of Example 1 of the present invention and product A of EP 194.497 to rats in which sideropenic anaemia had been induced by keeping them on a iron deficient diet and bleeding them. 40 male Wistar rats (Charles River Italia, Calco, Como) weighing 40-50 g were employed just after weaning. A group of 10 animals (normal controls) were kept in standard diet conditions with pellets of rat feed (TR-M, GLP-Nossan, Correzzana, Milan) and faucet water. All other animals were fed with a Altromin-Rieper iron deficient diet (purified diet DP/1038) and distilled water, to induce sideropenic anaemia, for 5 weeks and then bled by intercardiac injection at the end of the 3rd and 4th treatment weeks. At the end of the 5th week the degree of anaemia was evaluated on a blood sample extracted from each of these animals by cardiac punctura. The animals were then divided in the following homogeneous treatment groups: Anaemia controls Product of Example 1 (2 mg Fe/kg) Product A of EP 194497 (2 mg Fe/kg) The compounds under examination were administered daily per os, by means of a metal gastric probe, for the 3 ensuing weeks. All the animals, including the normal controls group, were killed at the end of 3 weeks of treatment by bleeding in ether anesthesia and on the blood collected the following tests were made: Erythrocytes (microcellular counter) hematocrit (centrifugation in Wintrobe capillary) hemoglobin (Boeringer-Biochemia colorimetric method) sideremia (Boeringer-Biochemia colorimetric method) The obtained results are reported in Table 1. From the table one can see that the product of Example 1 of the present invention produces a considerably higher hematological improvement with respect to the one obtained with Product A of EP 194497.

Claims: Claims for the following Contracting States : AT, BE, CH, DE, DK, FR, GB, IT, LI, LU, NL, SE Complexes of iron or other metals with sulphonated derivatives of chitosan, having the following general formula (I): in which: R is H or a C₁-C₅ alkyl group, or an arylalkyl group; A is H or an alkaline metal or an alkaline earth metal; X is a sulphate, nitrate, acetate or chloride anion; m is a whole number from 50 to 1000; n is zero or a whole number from 1 to 10; M is Fe II , Fe III , Mg, Ca or Bi Functionalized chitosan of general formula (IV): in which: m is a whole number from 50 to 1000; R is H or a C₁-C₅ alkyl group, or an arylalkyl group; n is zero or a whole number from 1 to 10; A is H or an alkaline metal or an alkaline earth metal A method for preparing complexes of iron or other metals with sulphonated derivatives of chitosan, having the following general formula (I): in which: R is H or a C₁-C₅ alkyl group, or an arylalkyl group; A is H or an alkaline metal or an alkaline earth metal; X is a sulphate, nitrate, acetate or chloride anion; m is a whole number from 50 to 1000; n is zero or a whole number from 1 to 10; M is Fe II , Fe III Mg, Ca or Bi; characterised by the following steps: a) hydrolyzing-activating commercial chitosan by treatment with an organic acid, possibly mixed with an alkaline nitrite, and later with alkaline hydroxyde; b) functionalizing by treatment in an organic solvent or in water or in a mixed organic-aqueous solvent with a chlorohydrin or epoxy compound having the general structure (II) or (III): where n is between 0 and 10, and carrying at one end of the chain a sulphonated group where M is hydrogen or an alkaline or alkaline-earth metal; c) treating with an Fe II , Fe III , Mg, Ca or Bi salt in aqueous solution and precipitating the complex by adding a water-soluble organic solvent; d) neutralizing the sulphonic group with an alkaline or alkaline-earth hydroxide or other strong base in aqueous and/or organic or mixed organic/aqueous solution and recovering the neutralized complex by adding a water-soluble organic solvent if operating in water, or by filtration in the remaining cases. A method as claimed in claim 3, characterised in that said hydrolysis-activation is conducted by treating commercial chitosan firstly with 0.1 M acetic or formic acid and then with 5N NaOH. A method as claimed in claim 4, characterised in that said treatment with acetic or formic acid is conducted under reflux for 24 hours. A method as claimed in claim 3, characterised in that said hydrolysis-activation is conducted by treating commercial chitosan firstly with 0.4-0.5 M acetic acid and sodium nitrite and then with 5N NaOH. A method as claimed in claim 6, characterised in that said treatment is conducted at ambient temperature. A method as claimed in claim 3, characterised in that said functionalization is conducted in an aqueous medium or in an organic solvent or in a mixed organic/aqueous solvent. A method as claimed in claim 8, characterised in that said organic solvent is ethylene glycol, methanol or higher homologous alcohols up to 7 carbon atoms, N,N-dimethylformamide, N,N-dimethylacetamide or dimethylsulphoxide. A method as claimed in claim 3, characterised in that said functionalization is conducted with a molar ratio of chitosan to chlorohydrin compound or epoxy compound of between 1:0.5 and 1:6. A method as claimed in claim 3, characterised in that said functionalization is conducted at a temperature of between 60°C and 120°C for a time of between 6 and 16 hours. A method as claimed in claim 3, characterised in that said treatment with the Fe II , Fe III , Mg, Ca or Bi salt is conducted in aqueous solution at a compound (IV) concentration of between 8% and 13% w/v with a molar ratio of monomer unit of (IV) to metal ion of between 1:1 and 1:1.5. A method as claimed in claim 12, characterised in that said treatment is conducted at a temperature of between 10°C and 25°C for 15-20 hours. A method as claimed in claim 3, characterised in that said neutralization of the sulphonic group is conducted in aqueous solution or in organic solvent or in mixed organic/aqueous solvent at a compound (IV) concentration of between 8% and 13% w/v with alkaline or alkaline-earth hydroxide or another strong base up to a pH value exceeding 7.5. A method as claimed in claim 14, characterised in that said neutralization is conducted at ambient temperature. The use of compounds of general formula (I) where M is Fe II or Fe III for the preparation of pharmaceutical compounds suitable for sideropenia therapy. Pharmaceutical compositions containing, in solution, compounds of compounds of general formula (I) where M is Fe II or Fe III . Claims for the following Contracting States : GR, ES A method for preparing complexes of iron or other metals with sulphonated derivatives of chitosan, having the following general formula (I): in which: R is H or a C₁-C₅ alkyl group, or an arylalkyl group; A is H or an alkaline metal or an alkaline earth metal; X is a sulphate, nitrate, acetate or chloride anion; m is a whole number from 50 to 1000; n is zero or a whole number from 1 to 10; M is Fe II , Fe III , Mg, Ca or Bi; characterised by the following steps: a) hydrolyzing-activating commercial chitosan by treatment with an organic acid, possibly mixed with an alkaline nitrite, and later with alkaline hydroxyde; b) functionalizing by treatment in an organic solvent or in water or in a mixed organic-aqueous solvent with a chlorhydrin or epoxy compound having the general structure (II) or (III): where n is between 0 and 10, and carrying at one end of the chain a sulphonated group where M is hydrogen or an alkaline or alkaline-earth metal; c) treating with an Fe II , Fe III , Mg, Ca or Bi salt in aqueous solution and precipitating the complex by adding a water-soluble organic solvent; d) neutralizing the sulphonic group with an alkaline or alkaline-earth hydroxide or other strong base in aqueous and/or organic or mixed organic/aqueous solution and recovering the neutralized complex by adding a water-soluble organic solvent if operating in water, or by filtration in the remaining cases. A method as claimed in claim 1, characterised in that said hydrolysis-activation is conducted by treating commercial chitosan firstly with 0.1 M acetic or formic acid and then with 5N NaOH. A method as claimed in claim 2, characterised in that said treatment with acetic or formic acid is conducted under reflux for 24 hours. A method as claimed in claim 1, characterised in that said hydrolysis-activation is conducted by treating commercial chitosan firstly with 0.4-0.5 M acetic acid and sodium nitrite and then with 5N NaOH. A method as claimed in claim 4, characterised in that said treatment is conducted at ambient temperature. A method as claimed in claim 1, characterised in that said functionalization is conducted in an aqueous medium or in an organic solvent or in a mixed organic/aqueous solvent. A method as claimed in claim 6, characterised in that said organic solvent is ethylene glycol, methanol or higher homologous alcohols up to 7 carbon atoms. N,N-dimethylformamide, N,N-dimethylacetamide or dimethylsulphoxide. A method as claimed in claim 1, characterised in that said functionalization is conducted with a molar ratio of chitosan to chlorohydrin compound or epoxy compound of between 1:0.5 and 1:6. A method as claimed in claim 1, characterised in that said functionalization is conducted at a temperature of between 60°C and 120°C for a time of between 6 and 16 hours. A method as claimed in claim 1, characterised in that said treatment with the Fe II , Fe III , Mg, Ca or Bi salt is conducted in aqueous solution at a compound (IV) concentration of between 8% and 13% w/v with a molar ratio of monomer unit of (IV) to metal ion of between 1:1 and 1:1.5 A method as claimed in claim 10. characterised in that said treatment is conducted at a temperature of between 10°C and 25°C for 15-20 hours. A method as claimed in claim 1, characterised in that said neutralization of the sulphonic group is conducted in aqueous solution or in organic solvent or in mixed organic/aqueous solvent at a compound (IV) concentration of between 8% and 13% w/v with alkaline or alkaline-earth hydroxide or another strong base up to a pH value exceeding 7.5 A method as claimed in claim 12, characterised in that said neutralization is conducted at ambient temperature. The use of compounds of general formula (I) where M is Fe II or Fe III for the preparation of pharmaceutical compounds suitable for sideropenia therapy.

Inventors: BUTELMAN FEDERICO, BUTELMAN, FEDERICO
Applicants: TEXCONTOR ETS, ETABLISSEMENT TEXCONTOR
Application year: 1990
Main classification: C08B37
IPC codes: A61K33, C08B37, A61K31, A61P7, C07F9, C07F15