PROCESS FOR THE PURIFICATION OF AN AMINOALCOHOL

Abstract: The present invention relates to a process for the preparation of 2-amino-1,3-propanediol, having a content of organic impurities lower than 0.1 % and inorganic impurities lower than 0.05 %, comprising the following steps: a) formation of a 2-amino-1,3-propanediol salt with an acid; b) crystallization of the salt resulting from step a) from an aqueous or a hydro-organic mixture with a solvent selected from the group consisting of an alcohol of the general formula R-OH, wherein R is a C1-C6 straight or branched alkyl chain, and a mono (C1-C3)alkylether of the (C3-C7)alkylcellosolve group; c) elution of the free base by using ion exchangers to give an aqueous solution of said base; d) precipitation or crystallization of the solid 2-amino-1,3-propanediol from a solvent as defined in step b).

Description: PROCESS FOR THE PURIFICATION OF AN AMINQALCOHOL 2-amino-l , 3-propanediol of formula (I), known as εerinol, is widely used as building-block in the synthesis of non-ionic iodinated X-ray contrast media. Great attention has been paid on its synthetic preparation, since the cost of such products is quite high, while its purification has been considered less interesting. The main industrial application of this product relies on the synthesis of many non-ionic X-ray contrast media, particularly ( S )-N,N' -bis-[2-hydroxy-l- (hydroxymethyl ) ethyl]-5- [ ( 2-hydroxy-l-oxopropyl )amino]- 2,4, 6-triiodo-l , 3-benzenedicarboxamide , known with the international denomination of Iopamidol (The Merck Index, XI Ed., page 799, n°4943). Physicians and authorities which grant drug market authorizations, require drugs with very low level of impurities in order to limit the number of side-effects experienced by patients. As far as iodinated contrast agents are concerned, particular care must be paid since the total amount of administered product is much higher than other drugs. As a matter of example, the injected contrast agent dose can reach or exceed 150 g. The high purity level of the compound of formula (I) is extremely important in order to avoid by-products and assure high purity standards in the final products. In literature there are various purification methods of compound (I) such as vacuum-diεtillation, which is the most widely used (for instance US 5053545, US 4221740), and a purification process which provideε for the use of styrene-divinylbenzene resins, such aε XAD-2 (see US- 342868) . Beyond serinol, two of its salts are commercially supplied, that's to say hydrochloride and oxalate which show a better stability and handling, compared to the free base. The syntheεiε and the crystallization of these salts has been already described in some patents (for instance EP 348223, US 5053545). The purity reported by manufacturers is 98%, therefore unsatisfactory. As already known in literature (F. Uggeri et al., Journal of Chromatography , 432, 1988) the main organic by-products of compound (I), whose purification is the object of this invention, are: N-methyl-l-amino-2 , 3- propanediol, ethanolamine , 2 , 3-diaminopropanol , 1,3- diaminopropanol , glycerine and 2-aminopropanol , but also some inorganic impurities, the structural iso er of compound of formula (I), that's to say 3-amino-l,2- propanediol, known as isoεerinol, must be considered. According to the type of industrial syntheεis of the compound of formula (I), percentages of the impurity main components can remarkably differ. Therefore it is important to have available selective purification processes for said impurities. This invention refers to a process for the purification of 2-amino-l , 3-propanediol to obtain a product characterized by a content of organic impurities lower than 0.1% and inorganic impurities lower than 0.05% comprising the following steps: a) formation of a 2-amino-l , 3-propanediol salt with an acid, preferably hydrochloric acid or oxalic acid; b) crystallization of the salt formed in step a) from an aqueous or, alternatively, hydro-organic mixture with a solvent selected from the group consisting of an alcohol of formula R-OH, wherein R is a (C1-C6) straight or branched alkyl chain, a mono(Cι-C3)- alkylether of the ( C3-C7 )alkylcelloεolve group; c) elution of the free base by using ion exchangers to give an aqueous solution of said base; d) formation of the solid 2-amino-l , 3-propanediol by precipitation or crystallization from alcohols of formula R-OH. Crystallization of salts formed in step a) can be carried out in an aqueous or hydro-organic solution and particularly preferred are the alcohols of formula R-OH selected from the group conεisting of ethanol, ethanol, propanol, isopropanol, butanol, 2-butanol and t-butanol and 2-methoxyethanol . Particularly useful are the crystallization techniques of the already known hydrochloride and neutral oxalate of serinol, which are going to be illustrated in detail, since they can give directly marketable products. We have also found out that obtaining the free base from these salts according to step c), by using H + or Na + form cation exchangers, gives a free base furtherly purified by the chromatographic action carried out by the same resins. This technique is highly innovative with respect to the chemical methods using an alkaline or alkaline-earth base to free these salts, in particular sodium hydroxide, potassium hydroxide and calcium hydroxide, since the salt conversion to free base is quantitative and no traces of inorganic impurities are detected in the resulting product. The filtration step of the inorganic salt (for instance calcium oxalate, sodium chloride, potassium chloride), which causes product losses due to the troublesome washing of the panel of said salt on the filter, is thus avoided. The use of the process of this invention is particularly advantageous, on an industrial scale, even for the removal of the colour from the raw solutions and the eaεy automation of the process by meanε of a potentiometer, conductimeter and refracto eter equipped with flow cells. The preferred cation exchangers are selected from the group consisting of gel or macroporous polystyrene- based exchangers having sulphonic acid groups. For example: C 20 MB (Duolite), A berlite® IR 120 ( Rho & Haas), Amberjet® 1200 (Rhom & Haas) or alternatively C 100 E (Purolite) or C 350 MB (Dow). In any case analogous cationic exchangers by different manufacturers can be used. The compound of formula (I) is recovered through elution with aqueous ammonia, in particular the use of 4.7% aqueous ammonia allows the elimination of inorganic impurities. The exceeding ammonia is easily removed through evaporation before step d). When necessary the reaction can be monitored through pH and so it is very eaεy to diεcard the moεt impure fractions . Strong anion exchangers can be used to produce a free base from a crude solution containing a mixture of inorganic or organic acid which can be water-insoluble and able to εalify εerinol, therefore having a different action from that performed by cation exchangerε. Thiε method, even though it excludeε a chromatographic action on the compound of formula (I), gives a free base in a single εtep, exploiting the higher basicity of tertiary amines of the anion exchanger compared to serinol. The preferred anion exchangers are selected from the group consisting of strong anion exchangers such as gel or macroporous polystyrene- based exchangerε with diethyla monium or dimethylammonium groups. For example: Amberlite® IRA 420 or other typeε with analogouε featureε (for inεtance A 400 Purolite, SA 12 A Diaion, SBR-P Dowex ) . Alεo for thiε proceεs, control systemε, εuch as potentiometer, conductimeter and refractometer , can be used making the proceεs more easily exploitable and automated. As already cited the methods of the literature teach vacuum- distillation to give solid serinol, we have found out a simple and effective method to attain the εame aim, without submitting the product to a prolonged damaging thermal treatment. After elution of the free base through ion exchangers, an aqueous solution of the compound of formula (I) iε obtained which, after concentration, can cause the crystallization or precipitation of the free base. If water content is lower than 3% a precipitation occurε, otherwiεe it iε more profitable to operate with a maximum water content of 20% according to the type of solvent used for cryεtallization. Particularly preferred are the crystallization εolventε selected from the group consisting of ethanol, 2-butanol, n-butanol, t-butanol, isobutanol, pentanol, iεopentanol . The method comprises a precipitation at temperatures ranging from -5°C to 30°C according to the solvent used. When the impurities are mainly inorganic or the compound of formula (I) is contaminated by a salt of 5- amino-2,4, 6-triiodoisophthalic acid, thiε invention alεo refers to a process for the purification of 2-amino-l, 3- propanediol with same previous characteristics of purity, said procesε comprising the following steps: a)' preparation of an aqueous solution of 2-amino-l, 3- propanediol and elution of said εolution on ion exchangers under the previously described conditions to give an aqueous solution of 2-amino-l, 3- propanediol; b)' precipitation or crystallization of εolid 2-amino- 1 , 3-propanediol from an alcohol of formula R-OH, under the previouεly deεcribed conditions. When the organic impurities in 2-amino-l, 3- propanediol amount to 2% and are the only oneε present, thiε invention also refers to a proceεε for the purification of a product with the same previous characteristics of purity, said procesε comprising only the step of precipitation or crystallization of the compound of formula (I) from an alcohol of formula R-OH, according to the previous conditions. The analytical methods used to evaluate the quality of a inopropanediols is reported in the previously cited publication (F. Uggeri et al . , Journal of Chromatography , 432, 1988). In order to have a clearer and simpler view of thiε invention, a list of the salts which can be used for the compound (I) is given below, while the methods are illustrated in the examples. 1) Serinol neutral oxalate The preparation of neutral salt with oxalic acid is known; it can be easily crystallized from water by working with solutions having a concentration ranging from 12.5% to 90% (w/w) in water. The resulting yieldε are higher than 80% with a high purity. In fact, εalts with a content of organic impurities lower than 0.3% and the practically complete removal of inorganic impuritieε, are obtained. In addition, the structural isomer iεoserinol is totally removed in a selective way with this method. The weight ratio between water and the salt ranges between 1:0.5 and 1:10, according to the desired purification level. As already cited, we have found out that the use of an organic solvent mixed with water during crystallization can analogously reduce by-products and overcomes the problem connected to the troublesome filtration of the εalt crystallized from water . In particular purifying activity is higher with respect to known and unknown by-products with lipophilic characteristics such as secondary and tertiary amines which can be present and the capacity of removing the isomer, isoserinol, is kept in a complete way or within residual values of 0.1%. The organic εolventε used are the alcohols of general formula R-OH, above described, as well as the particularly preferred alcohols and monoalkyether glycols. The water content in the caεe of the neutral oxalate of εerinol in the hydro-organic precipitation mixtureε can range from 0% to 95%. The weight ratio between the neutral oxalate of compound (I) and the εolvent can range between 1:1 to 1:10 parts by weight. Serinol hydrochloride Serinol is easily salified with hydrochloric acid. The salt is not cryεtallizable from water due to its high solubility. Different patents describe the preparation of εerinol hydrochloride aε crude final product, therefore the crystallization of such salt is a remarkable advantage, being the same salt a product commercially supplied. Some patents, such as US 5053545, illustrate hydrochloride aε synthetic intermediate which is converted into free base through reaction of the εalt with sodium hydroxide. Other patents, such as EP 348223, give examples of crystallization of saltε using low molecular weight alcohols for εerinol. The salt can be obtained through the action of aqueous hydrochloric acid in the final step or, alternatively, when this technique is used for purification, the free base can be dissolved in organic εolventε and therefore hydrogen chloride is added up to εaturation. Salt crystallization, according to the method of this invention, is performed through hydro-organic mixtures in which water content ranges, for serinol hydrochloride, from 0% to 10% (w/w) while the salt/solvent ratio can range from 1:0.5 to 1:10 (w/w) at a crystallization temperature ranging from -5°C to 15°C. Preferred organic solvents are ethanol and 2- ethoxyethanol . The following examples are intended to illustrate the best experimental conditions to carry out the process of this invention. EXAMPLE 1 Purification of εerinol neutral oxalate. 300 g of crude εerinol neutral oxalate containing 2% of organic by-productε and 8% of inorganic by-products (εodiu chloride, sodium sulfate) are diluted in 600 g of water at 80°C. The εolution is kept at 80°C for Ih. 10 g of active carbon are added and the mixture was kept under stirring at the same temperature for lh. Then the mixture is filtered at 80°C and carbon is removed by washing with 120 g of water preheated to 80°C. Then the solution is slowly cooled to 30°C in 2h then to 0-l°C, keeping the temperature for 2h. It is filtered under vacuum (20 mmHg ) and washed with 300 g of 50%aqueous methanol (w/w) precooled at 0-l°C. After drying at 70°C for 12h at 12 mmHg 250 g of dry product were obtained. Elution of the free base The resulting product is dissolved in water thus giving a 15%-weight solution. The solution is percolated on 1200 mL of H + -form cation exchanger Amberjet® 1200, obtained by washing the resin at a neutral pH . Serinol is eluted with 1200 mL of 4.7% aqueous ammonia at appr. 2 BV/h. The reεin iε waεhed to neutral pH with deionized water ( approx . 2L). The reεulting εolution is evaporated to a residue then dissolved with 200 g of anhydrous 2-butanol and evaporated to a reεidue through under vacuum concentration (7 mmHg) to give a reεidue with a water content < 0.3%. Precipitation of the free baεe The reεidue is disεolved with 1150 g of 2-butanol then cooled to -3°C, the temperature iε kept for 3 h. Serinol iε filtered and washed with 120 g of 2-butanol precooled at 0°C, dried at 30°C under vacuum (3 mmHg) for 12 h to give 240 g of dry εerinol. Total yield 70%. Total organic by-products 0.05% ashes-free . EXAMPLE 2 Alternative to Example 1 using methanol as solvent. 300 g of serinol neutral oxalate containing 1% of organic by-products are dissolved in 1000 g of water at 80°C. The solution is decolorized with 1.5 g of active carbon and filtered at 80°C then cooled to 60°C and 1000 g of anhydrous methanol are added. The temperature is kept to 17°C for 5 h. The reεulting product iε filtered and washed with 150 g of methanol then dried at 60°C (12 mmHg) for 12 h in order to give 285 g of dry product. The free base is obtained according to Example 1. Free base crystallization The residue iε disεolved with 1150 g of 5%-water 2- butanol. Then it is cooled to -3°C, and the temperature is kept for 3 h. The product is filtered and washed with 120 g of 2-butanol precooled at 0°C, dried at 30°C under vacuum (3 mmHg) for 12 h. Total yield 90%. Total organic by-products 0.06% asheε-free . EXAMPLE 3 Alternative to Example 1 using ethanol as solvent. 300 g of serinol neutral oxalate containing 1.5% of organic by-products and 3% of inorganic by-products are disεolved in 800 g of water at 80°C. The solution iε decolorized with 1.5 g of active carbon and filtered at 80°C, then cooled to 60°C and 800 g of anhydrouε ethanol are added. The temperature is lowered to 17°C for 5 h. The resulting product is filtered and washed with 200 g of 95% methanol (w/w), then dried at 60°C (12 mmHg) for 12 h to give 285 g of dry product. The free baεe is obtained according to the Example 1 uεing n-butanol aε anhydrification εolvent . Free base crystallization The reεidue iε dissolved with 1000 g of n-butanol (water content 5%) then cooled to -3°C, and the temperature is kept for 3 h. Serinol is filtered and washed with 120 g of n-butanol precooled at 0°C, dried at 30 °C under vacuum (3 mmHg) for 12 h. Total yield 90%. Total organic by-products 0.06% asheε-free . EXAMPLE 4 Purification of serinol hydrochloride. 300 g of crude serinol hydrochloride containing 1% of organic by-products comprising 0.2% of iεoεerinol and 0.3% of methylεerinol are dissolved in 450 g of 2- methoxyethanol at 90°C. The resulting solution iε gradually cooled to 15°C and the temperature iε kept for 2 h. The precipitate iε filtered and waεhed with 40 g of 2-methoxyethanol precooled at 0°C. First crop yield: 90%. Mother liquors are concentrated to 750 g and the second crop iε precipitated by repeating the procedure. Second crop yield: 10%. 285 g of product between the first and the second crop are given and dried at 60°C (12 mmHg) for 12h. Hydrochloride is converted into free base following the procedure of Example 1. Total yield 87%. Total organic by-products 0.1% asheε-free . EXAMPLE 5 Serinol purification containing 5-amino-2 , 4 , 6-triiodoiso- phthalic acid. 200 g of serinol containing 10% of 5-amino-2 , 4 , 6- triiodoiεophthalic acid, 10% of inorganic substances and 0.4% of organic impurities are diεεolved in 2000 g of water. The solution is percolated on 1200 mL of Na+-form cation exchanger C 350 MB, obtained by washing the bed up to neutral pH . Serinol iε eluted with 1200 mL of 4.7% (w/w) aqueous ammonia at approx . 2 BV/h. The resin is washed to neutral pH with deionized water (approx. 2L ) . The reεulting εolution iε concentrated to a reεidue and dissolved with 400 g of iso-butanol. Precipitation of the free base The residue is dissolved with 1000 g of iso-butanol then cooled to -3°C, and the temperature is kept for 3 h. Serinol is filtered and washed with 100 g of solvent precooled at 0°C, dried at 30°C under vacuum (3 mmHg) for 12 h. Total yield 85%. Total organic by-products 0.08% asheε-free . EXAMPLE 6 Alternative to Example 4. 300 g of εerinol εalified with hydrochloric acid and 5% of εodium εulfate and 1.0% of organic impurities are dissolved in 3000 g of water. The εolution iε percolated on 2000 L of anion exchanger IRA 420 and the bed is washed up to neutral pH, at approx. 2 BV/h. Serinol iε recovered reducing the eluate to a residue of approximately 220 g with 10% (w/w) of water. Precipitation of the free base The residue iε dissolved with 1000 g of iso- pentanol. Then it iε cooled to -3°C, and the temperature iε kept for 3 h. Serinol iε filtered and washed with 100 g of isopentanol precooled at 0°, dried at 30°C under vacuum (3 mmHg) for 12 h. Total yield 85%. Total organic by-products 0.08% ashes-free. EXAMPLE 7 Free base cryεtallization. 200 g of εerinol containing 1% of inorganic εubεtances and 1% of organic impurities are dissolved in 600 g of 10%-water iso-pentanol heating to 40°C if desired. Then it is cooled to -3°C, and the temperature is kept for 6h. Serinol is filtered and washed with 120 g of anhydrous solvent precooled at 0°C, dried at 30°C under vacuum (3 mmHg) for 12h. Total yield 78%. Total organic by-products 0.01% ashes-free. EXAMPLE 8 Preparation of lopamidol using the serinol purified as previously described 680 g of S-(- )-5- ( ( 2-acetyloxy )-l-oxopropyl )amino )- 2 , 4 , 6-triiodo-l , 3-benzendicarboxylic acid dichloride (prepared as described in WO 96/37460) are disεolved in 1360 g of dimethylacetamide at room temperature and after cooling at 15°C [Solution A ]. 181 g of 2-ammino-l , 3-propanediol purified with the method deεcribed in the previouε Example 1 are diεεolved in 1360 g of dimethylacetamide and added to the εolution A in one hour at 8-15°C whilεt εtirring. The reaction is completed after ten hours at room temperature. The reaction mixture is concentrated at 100°C at 10 mbar until 98% of the solvent is distilled. 1700 g of water are added to the reεidue and the εolution iε purified uεing the method described in WO 97/30735. Yield on dry lopamidol: 94% Contents of by-products determined with HPLC method (according to the method described in USP XXIII-NF, 1996, Vsuppl. ) = 0.11% The by-product N- [2-hydroxy-l- ( hydroxymethyl )ethyl]- N' -( 2 , 3-dihydroxypropyl )-5-( 2-hydroxy-l-oxopropyl )-2 ,4, 6- triiodo-1 , 3-benzenedicarboxamide , coming from isoserinol, iε under the detection limit. No preεence of other by-productε derived from 3- amino-1 , 2-propanediol are detected (see as ref Pharmeuropa, 6, 343-345, 19949.

Claims: CLAIMS 1. Proceεε for the preparation of 2-amino-l, 3- propanediol, having a content of organic impuritieε lower than 0.1% and inorganic impuritieε lower than 0.05%, comprising the following steps: a) formation of a 2-amino-l , 3-propanediol salt with an acid; b) crystallization of the salt resulting from step a) from an aqueous or a hydro-organic mixture with a solvent εelected from the group conεisting of an alcohol of general formula R-OH, wherein R is a C1-C6 straight or branched alkyl chain, and a mono(Cι-C3 )alkylether of the (C3-C7 )alkylcellosolve group; c) elution of the free base by using ion exchangers to give an aqueous solution of said base; d) precipitation or crystallization of the solid 2- amino-1 , 3-propanediol from a solvent as defined in step b) . 2. Process according to claim 1, in which the salt of step a) is formed by hydrochloric acid or oxalic acid. 3. Proceεε according to claim 1, in which the crystallization of the salt in step b) is carried out in hydro-organic solution and the solvent is selected from the group consiεting of methanol, ethanol, propanol, isopropanol, butanol, 2-butanol, t-butanol and 2- methoxyethanol . 4. Process according to claim 1, in which the elution of the free baεe in εtep c) iε carried out through the uεe of Na + or H + form cation exchangers. 5. Proceεs according to claim 4, in which the cation exchangers are selected from the group consiεting of gel or macroporouε polyεtyrene- baεed exchangers having εulphonic acid groups. 6. Procesε according to claim 4 , in which 2-amino-l, 3- propanediol iε recovered through elution with aqueous ammonia . 7. Process according to claim 1, in which the elution of 2-amino-l, 3-propanediol is monitored through pH and carried out so that the fractions having the highest content of impurities are discarded. 8. Proceεε according to claim 1, in which the elution of 2-amino-l , 3-propanediol in εtep c) iε carried out through the use of strong anion exchangerε. 9. Proceεε according to claim 8, in which the anionic exchangers are εelected from the group consiεting of gel or macroporouε polystyrene- baεed exchangerε with diethylammonium or dimethylammonium groupε . 10. Proceεε according to claim 1, in which the precipitation of 2-amino-l , 3-propanediol of the aqueouε εolution obtained after εtep c) is carried out through solvent treatment, when water content is maximum 3%, at a temperature ranging between -5°C and 30°C. 11. Process according to claim 1, in which the crystallization of 2-amino-l , 3-propanediol of the aqueous solution obtained after step c) iε carried out through εolvent treatment, when water content iε maximum 20%, at a temperature ranging between -5"C and 30"C. 12. Process according to claim 11, in which the solvent is selected from the group conεiεting of methanol, ethanol, propanol, iεopropanol, butanol, 2-butanol, t- butanol and 2-methoxyethanol . 13. Process for the preparation of 2-amino-l, 3- propanediol, having a content of organic impurities lower than 0.1% and inorganic impurities lower than 0.05%, when said impurities are mainly inorganic or said 2-amino-l, 3- propanediol iε contaminated by a salt of 5-amino-2 ,4 , 6- triiodoiεophthalic acid, εaid proceεs comprising the following εtepε: a)' preparation of an aqueouε solution of 2-amino-l, 3- propanediol and elution of εaid εolution on ion exchangerε according to εtep c) in claim 1, to give an aqueouε εolution of 2-amino-l , 3-propanediol; b) 1 precipitation or crystallization of solid 2-amino- 1 , 3-propanediol from the solvent according to step d) of claim 1. 14. Procesε for the preparation of 2-amino-l , 3- propanediol, having a content of organic impurities lower than 0.1% and inorganic impurities lower than 0.05%, when the organic impurities amount to 2% and are the only ones present, εaid proceεε compriεing only the εtep of precipitation or cryεtallization of 2-amino-l, 3- propanediol from the solvent according to step b) of claim 1. 15. Proceεε according to claim 1, in which in order to cryεtallize 2-amino-l , 3-propanediol neutral oxalate from the hydro-organic mixture, the water content ranges between 0% and 95% and the weight ratio between the salt and the mixture ranges from 1:1 to 1:10 parts by weight. 16. Procesε according to claim 1, in which in order to crystallize 2-amino-l , 3-propanediol hydrochloride from the hydro-organic mixture, the water content ranges from 0% to 10%% (w/w), the weight ratio between the εalt and the mixture rangeε from 1:0.5 to 1:10 partε by weight. 17. Process according to claim 16, in which the organic solvent of the hydro-organic mixture iε εelected from the group conεisting of ethanol and 2-methoxyethanol . 18. Use of the 2-amino-l , 3-propanediol prepared with the procesε of claimε 1, 13 and 14, for the preparation of iodinated non-ionic X-ray contraεt agentε. 19. Uεe of the 2-amino-l , 3-propanediol prepared with the process of claimε 1, 13 and 14, for the preparation of lopamidol .

Inventors: DESANTIS NICOLA, FEDELI FRANCO, DESANTIS, NICOLA, FEDELI, FRANCO
Applicants: DESANTIS NICOLA, DIBRA SPA, FEDELI FRANCO, DESANTIS, NICOLA, DIBRA S.P.A., FEDELI, FRANCO
Application year: 1997
Main classification: C07C213
IPC codes: A61K49, C07C213, C07C215, C07C231, C07C237