NO178107B - Process for preparing nonionic polyol contrast media from ionic contrast media - Google Patents

Description

This invention relates to a process for synthesis

of a non-ionic contrast medium or an intermediate for this, from an ionic contrast medium.

Medical imaging with X-rays depends largely on the radiographic contrast media (CM). An ideal CM developed to mix with body fluids should be economically acceptable, chemically stable, highly water soluble, easily injectable and biologically inert. Previously known CM, generally based on

salts of derivatized triiodinated benzene vests satisfy the first four criteria, but they induce adverse clinical effects. Such toxicity stems from their ionicity, solution hyperosmolality vis-à-vis the body fluids and chemotoxicity, which shows their relatively high hydrophobicity.

Nonionic, less hyperosmolal, less hydrophobic, but more expensive compounds exist, of which Iohexol/Iopamidol/Metrizamide is used clinically in the United States. Metrizamide suffers from hydrolytic instability, and must therefore be dispensed in freeze-dried form and reconstituted before use. However, solutions of some other non-ionic, stable CM have a higher osmolality and can thus cause pain when injected into the arteries. Other compounds are not persistently water-soluble at higher concentrations. All current non-ionic CMs, although less toxic than the previously known ones, are much more expensive.

Consequently, despite the large number of compounds that have been prepared, there is considerable interest in producing a nonionic CM that is both pharmacologically and economically improved. For this reason, it is essential that when the ring has been iodinated,

the subsequent steps must be few and give high yields. Furthermore, the iodinated substrate, as well as the reactant used for further functionalization, should be cheap.

There is extensive patent literature regarding non-ionic contrast media and their production methods. See especially US patent no. 4,364,921; 4,341,756; 4,250,113;

4,021,481; 4,001,323; 3,702,866; 3,701,771 and 3,622,616. See

also "Radiocontrast Agents volume 73 of the Handbook of Experimental Pharmacology, Springer, New York, 1985", which gives a comprehensive overview of the field at the time of publication.

Non-ionic contrast media are produced according to the invention by reacting a 3-(amino- or carboxamido)-5-acylamino-2,4,6-triiodobenzoic acid with a halogehydrin with from 2 to 5 carbon atoms and 1 to 4 hydroxy groups in an aqueous medium at a pH higher than 9 and lower than 11 at a temperature from 60-100°C for a sufficient time to selectively N-alkylate the acylamido group and give a first intermediate; and optionally performing the following steps: acylating all hydroxyl groups with an acylating agent to a second intermediate;

forms acyl halide of the second intermediate with acid chloride; and

reacts the acyl chloride with an alkylamine to form the nonionic contrast medium.

The methodologies provide a new and efficient synthetic approach to both known and new non-ionic contrast media. The combination of low viscosity and low osmolality in the products has not been achieved before in a clinically applicable contrast medium.

Description of the preferred embodiments

The new methods use triiodopersubstituted acylomidobenzoic acids as starting materials, preferably available as an ionic contrast medium. The method involves selective and efficient alkylation of the nitrogen in the acylamido group with a halohydrin under weakly basic conditions in an aqueous medium, followed by protection of hydroxyl groups, activation of the benzoic acid group and amidation of the activated benzoic acid group. The synthetic strategy uses readily available reagents that are, for the most part, cheap and lead to high yields of easily purified intermediates and final product.

The starting materials are 5-acylamido-substituted triiodobenzoic acids, where the 3-position is substituted with a substituted amino group or a carboxamido group. The starting materials will normally have at least approx. 10 carbon atoms, and normally from 0 to 2, even more often from 0 to 1 hydroxyl group. The product will usually have less than 20 carbon atoms, even fewer than approx. 18 carbon atoms, and will have at least three nitrogen atoms, of which at least one will be a substituent on a ring carbon atom, while one or both hydrogen atoms can be amidohydrogen. Acyl groups attached to the nitrogen will generally have from 1 to 4 carbon atoms, normally from 2 to 3 carbon atoms and from 0 to 3 oxy substituents, even more often from 0 to 2 oxy substituents. Alkyl substituents will generally have from 1 to 3 carbon atoms, even more preferably from 1 to 2 carbon atoms and have from 0 to 3 hydroxy groups, even more preferably from 0 to 2 hydroxy groups.

The following flowchart shows a synthetic strategy. TIB means triiodobenzene where the vertical line shows the group in connection with the horizontal lines which are bound in the 1, 3 and 5 positions respectively. The numbers above the arrows show the reaction, while the legend shows the reagents and conditions for the reaction.

(1) Halohydrin with 2 to 5 carbon atoms and 1 to 4 hydroxy groups; aqueous base, pH 9-13, 60-100°C, 0.5-6 hours. (2) AcZ, Z = chlorine or AcO, where Ac is an acyl group having from 2 to 3 carbon atoms; tart. - amine, 50-80°C, 1-6 hours. (3) G-Cl (G-inorganic or organic acyl group); 50-80°C; 0.25-3 hours.

(4) HNR<8>R<9>; tart. - amine, 35-75°C.

(5) (a) OH~; (b) neutralization, comes into being

acid fermentation when acetonides are present.

The symbols are defined as follows:

TIB= 2,4,6-triiodobenzene;

Y- NR1R2 or CONR3R4 or CH2NR<2>COR<3>

R» an aliphatic group having from 1 to 3,

normally 2 to 3 carbon atoms with from 0 to 2, normally 0 to 1 hydroxy groups;

R1= hydrogen, an aliphatic group with from 1 to 3, normally 1 to 2 carbon atoms, with from 0 to 2, normally 0 to 1 oxy group, an aliphatic acyl group with from 1 to 3, normally 1 to 2 carbon atoms, and from 0 to 2, normally 0 to 1 oxy group;

R 2 = the same as or different from R 1 , normally R<2> will be hydrogen or an aliphatic group; at least one of R<1> and R 2 is different from hydrogen;

R<3>= hydrogen or an aliphatic group having from 1 to 3, normally 1 to 2 carbon atoms, having from 0 to 2, normally 0 to 1 hydroxy groups or acyloxy groups;

R 4 = the same as or different from R 3 , normally hydrogen;

R 5 = mono- or polyoxyalkyl from 2 to 5, normally

2 to 4, preferably 3 to 4 carbon atoms, with from 1 to 4, normally 1 to 2 hydroxy groups; 1 12' 34 Y = NR R or CONR R ; 21 2 9 R = the same as R with the proviso that when R is hydrogen and R is acyl or an aliphatic group, R contains mono- or polyoxyalkyl with from 2 to 5, normally 2 to 4, preferably 3 to 4 carbon atoms with from 1 to 3, normally 1 to 2 hydroxy groups;

c c .5 R = same as R , except that all hydroxyl groups in R

are acyloxy groups, where Ac is attached to the hydroxyloxygen;

R<7>= same as R, except that all hydroxyl groups in R5 are acyloxy groups, where Ac is bound to the hydroxyloxygen;

Y<2>= same as Y<1>, except that all hydroxyl groups in Y<1>

are acyloxy groups, where Ac is attached to the hydroxyloxygen;

R8 and R<9> = same or different and is hydrogen or alkyl with from 1 to 4 carbon atoms with 0 to 3, normally 1 to 3 hydroxy groups, the total number of carbon atoms not being greater than approx. 6-> normally not larger than approx. 4;

q ' q 1 8 9

R and R = the same as R and R except that they exclude alkoxy groups as substituents;

Ac= an aliphatic acyl group of 2 to 3 carbon atoms, especially acetyl;

X= halogen or 2-oxypyridyl, N-oxysuccinimidyl or isoureido;

Y4 = Y1 or Y.

Each of the steps will now be considered in detail. The starting compound will be an acylamidotriiodo-substituted benzoic acid,

where the second substituent is a carboxamido group or an amino group. If desired, the starting materials can be ionic contrast media or their iodinated precursors which are easy to

get bought and cheap. Such compounds include derivatives of triiodo-3,5-diaminobenzoic acid, diatrizoate, 3,5-diacetamido-2,4,6-triiodobenzoic acid and metrizoate, N-monomethyl derivative of diatri-

zoate and derivatives of 5-aminosophthalic acid, iothalamate, 5-acetamido-2,4,6-triiodo-N-methylisophthalamic acid; and ioxythalamic acid, 5-acetamido-2,4,6-triiodo-N-(2-hydroxyethyl)-isophthalamic acid or its immediate precursor, the corresponding N-(2-acetoxyethyl) compound. Although generally available ion-

isic contrast media are preferred as starting materials, all the triiodobenzoic acid derivatives which are substituted in the 3- and 5-positions with amino and carboxyl groups with various applicable substituents can be used.

The procedure will now be described in more detail. The first step is the reaction of the acylamido-substituted triiodobenzoic acid with a halohydrin of from 2 to 5 carbon atoms, normally 3 to 4 carbon atoms, especially a chloridine, especially where the chlorine group is a primary or secondary chlorine group, there being from 1 to 4 oxy groups, and in at least one of the oxy groups is hydroxy, to give a vicinal halohydrin. The reaction will be carried out in an aqueous base, normally a basic solution with at least pH 9 / generally from pH 9 to pH 14, even better from approx. pH 9.5 to pH 13.5. Stoichiometric amounts of the halohydrin can be used, normally a small excess not exceeding two molar excesses, normally not exceeding one molar excess. The pH is maintained during the course of the reaction. The temperatures will normally be at least approx. 45°C and do not exceed approx. 100°C, preferably between 45°C and 95°C. The reaction is carried out until complete, which can be checked by TLC or HPLC. Generally less than 2 hours is required, often less than 1 hour. An aqueous medium is used which may, but need not, have co-solvents. As an aqueous medium is sufficient, the co-solvent will not normally be used.

When the reaction is complete, the product does not need to be isolated and purified, on the contrary, the medium can be neutralized to a slightly acidic pH, normally from approx. pH 4 to pH 6 and the solvents are removed, for example distilled azeotropically with a corresponding co-solvent, for example pyridine or toluene. The rest can see

is used directly in the next step.

The next step is the protection step, where hydroxyl groups will be reacted with a corresponding reagent that is stable under the reaction conditions in the next successive steps. As the next successive steps will involve acidic reagents, the protecting groups will be such that they will be able to survive the subsequent reactions. The reagents used for the protection will of course be reactive, so that they react with the hydroxyl groups and all available amino groups, will not affect the reactions of the carboxyl group to form an amide, and will make it possible to extract the product easily free of the protective groups.

As economic considerations are important for the synthetic strategy, cheap groups will normally be used. However, other groups could be used less effectively and less economically.

Of particular interest is the use of acyl halides and acyl anhydrides with from 1 to 3, preferably 2 carbon atoms, especially acetic anhydride. In the case of acetic anhydride, the anhydride can serve as a solvent and will therefore be present in considerable excess, and the amount present will normally be at least approx. 2

to 3 times molar excess. With other reagents, the reagents can

itself is either used as a solvent if suitable, or an inert solvent can be used such as acetonitrile, ethyl acetate or dichloromethane. In addition to the anhydride, an activation catalyst will be used, especially a tertiary amino compound, especially pyridine. The temperatures will be higher than room temperature, generally in the area of approx. 40-60°C, and the reaction will normally require approx. 1-6 hours depending on the individual reagent and the size of the reaction rate. Reactions for the course can be followed by thin-layer chromatography (TLC).

Processing will normally entail the removal of solvents by evaporation and azeotropic distillation as required. The residue can then be dissolved in water, and the aqueous layer can be extracted with a non-water-miscible polar organic solvent, for example an ester, preferably ethyl acetate, in a mixture with a non-polar solvent such as toluene. The aqueous layer can then be acidified to precipitate the hydroxy-protected benzoic acid, and the precipitate is dissolved in an organic extractant, preferably the same organic extractant, and the organic extracts are combined. The product can then be isolated in the usual way.

The hydroxy-protected benzoic acid compound is then activated, so that it becomes reactive with an aliphatic amine. There are a number of methods for activating the carboxyl groups. O-acylureas can be formed by using carbodiimides or the like. Active esters can be prepared such as N-hydroxysuccinimide, 2-acyloxypyridyl, nitrophenyl, chlorophenyl or the like. Although the particular way in which the carboxyl group is activated is not critical to the invention, the preferred method is to prepare the acyl chloride using an inorganic or organic acid halide, especially an inorganic acid halide such as thionyl chloride, sulfuryl chloride, phosphorus pentachloride or the like. Of particular interest is the use of thionyl chloride, where the thionyl chloride can be used as a solvent and can be present in excess, normally at least approx. 1-4 molar excess, and the reactant is dissolved in the thionyl chloride. Alternatively, the compound can be dissolved in an inert solvent such as dichloromethane or ethyl acetate and thionyl chloride used in a small excess, normally 2-4 molar excess. The mixture will then be heated at a higher temperature, generally from approx. 50-75°C for sufficient time for the reaction to proceed completely, generally approx. 0.25-3 hours. The reaction can be checked by TLC. The thionyl chloride and other solvents present can then be removed by evaporation and corresponding azeotropic distillation of the residue to remove all remaining thionyl chloride, and the resulting product dissolved in an inert polar organic solvent, such as an ester, followed by washing with bicarbonate and drying the organic the layer.

The activated carbonyl, especially the acyl halide, can then be combined in an inert organic polar solvent, preferably an ether or an amide, even better dioxane or dimethylacetamide, ~ with an acid neutralizing compound, preferably a tertiary amino compound, or a mixture of an inert organic polar solvent , preferably acetone or dichloromethane (giving two phases) with water in the presence of an organic base, preferably a carbonate or bicarbonate such as Ua2C0^, J^CO^,

or NaHCO 3 . The amino compound can be ammonia or alkyl-amino with from 1 to 4 carbon atoms having from 0 to 3, normally from 0 to 2 hydroxy groups, which can be protected or unprotected, - if protected as ethers, especially acetals or ketals, even more acetonide. The reaction can be carried out under mild conditions at room temperature or at a higher temperature, generally from approx. 40-70°C until it is complete, which will normally require approx. 0.5 hours and less than 12 hours, normally less than 9 hours.

The work-up generally follows the same procedure as previous work-ups in that the solvents are evaporated, the product is dissolved in a suitable polar organic solvent and washed with water with or without added sodium chloride. The organic layer can then be dried and the solvent removed by evaporation. In each case, the isolation steps are common.

The hydroxyl groups can then be deprotected by using a basic medium, normally basic alkanol medium, especially methanol, the pH being at least approx. 10 and the hydroxyl concentration is less than 1 normal. The reaction can be carried out under mild conditions, normally room temperature is satisfactory, as the reaction is normally complete in less than approx. 2 hours. Volatile material can then be removed by evaporation and the remainder neutralized with aqueous acid, also under ambient conditions. Appropriately, a pH of 1 to 2 can be used to remove the acetonide functions when such are present. If desired, the product can also be further purified by desalination with a suitable ion exchange resin.

With regard to the height of the invention, the claimed method entails a relatively mild N-alkylation of a 3-(amino-or carboxamido)-5-acylamino-2,4,6-triiodobenzoic acid which is not known previously described. The mild reaction conditions used, namely pH in the range 9-11 and temperatures in the range 60-100"C, are very easy to work with and still give high yields of the N-alkylated product. In connection with this advantage, 3-( amino- or carboxamido)-5-acylamino-2,4,6-triiodobenzoic acid starting material itself be an existing ionic contrast medium which is a commercial product in large quantities and at a low price. The invention thus converts these relatively cheap, easily available ionic materials to nonionic contrast media (or intermediates thereof) using mild conditions while achieving high yields.Furthermore, the subsequent steps of acylation, formation of the acyl halide, and reaction with the alkylamine have also been found to proceed smoothly and also provide good yields in each step, so that the non-ionic contrast medium is finally obtained in a good total yield. In this context, it is very important that each step in such a synthesis series gives a high yield, according to if the loss of significant amounts of iodinated material at any point in the synthesis would reduce the success of the process.

In summary, the applicant has arrived at a very advantageous method for the production of non-ionic contrast media (or intermediates for these) which uses readily available starting materials and mild process conditions, while at the same time that good yields are achieved through all synthesis steps. Seen in the light of the unpredictable nature of chemistry, the advantageous synthesis route that the applicant has arrived at could not be expected based on the state of the art.

A number of compounds can be prepared according to the present invention. Of particular interest are the new compounds 5-(2,3-dihydroxypropylacetamido)-2,4,6-triiodo-N-(2,3-dihydroxypropyl)-N'-(2-hydroxyethyl)-isophthalamide (compound VIII in the experimental section) and 5-(N-2,3-dihydroxypropylacetamido)-2,4,6,-triiodo-N-methyl-N1-(1,3,4-trihydroxy-threo-but-2-yl)- isophthalamide (compound XVIII in the experimental part).

These particular compounds have been found to have excellent properties with respect to toxicity, water solubility, osmolality, stability, viscosity and the like, factors which are particularly important in angiography and urography.

It is also possible to prepare new nonionic polyol contrast agents by starting with noniodinated compounds. For example, a 5-amino-N-(mono or poly)hydroxyalkyl-N'-(mono

or poly)hydroxyalkyl isophthalamide is reacted with an iodine source such as KICl2 in an aqueous acid solution under heating. In this and the other compounds in this order, the substituents present on the benzene ring are preferably the same substituents indicated as preferred above. The product of this first reaction is a 5-amino-2,4,6-triiodo—N-(mono or poly)hydroxyalkyl-5'-(mono or poly)hydroxyalkyl isophthalamide.

This first intermediate is then reacted with an acylation compound, preferably an acyl halide or acyl anhydride, most preferably an acyl halide such as acetyl chloride to give the 5-acylamino derivative. This derivative can also be prepared from an ionically iodinated compound (for example ioxythalamic acid)1 by protecting the hydroxyls by acetylation, by activating the carboxyl, especially with an acyl halide and by reacting with a corresponding hydroxyalkylamine, especially l-amino-2,3- propanediol. See examples 3 and 25 for details of the corresponding reactions. This derivative is then reacted with an epihalohydrin as previously described. A preferred method is to dissolve the derivative in 1,2-propanediol containing sodium bicarbonate and epichlorohydrin. This reaction is usually completed in approx. 1 hour at 90°C.

A preferred starting material for use in this aspect

of the invention is 5-amino-N-(2-hydroxyethyl)-N<1->(2,3-dihydroxy-propyl) isophthalamide which is available for purchase. By carrying out the reactions described above with KIC12 acetyl chloride and epichlorohydrin, 5-(2,3-dihydroxypropylacetamido)-2,4,6-triiodo-N-(2,3-

dihydroxypropyl)-N'-(2-hydroxyethyl)isophthalamide (compound VIII) in the experimental part, which can also be prepared by

the previously described techniques. However, this particular method provides the desired compound in only three steps from a commercially available source.

The sodium bicarbonate is typically present in excess to ensure capture of all acid formed in the alkylation reaction. Example 37 in the following examples sets forth a complete example of this reaction including times, temperatures and molar ratios.

The prepared compounds can be used as contrast media for angiography, urography and opacification of body spaces.

The following examples are given as an illustration of the invention.

EXPERIMENTAL

Example 1. Alkylation of ioxythalamic acid 5-Acetamido-2,4,6-triiodo-N-(2-hydroxyethyl)-

Isophthalamic acid (I) to: 5-(N- 2, 3- Dihydroxypropylacetamido)- 2, 4, 6-,- triiodo - N.-( 2-Hydroxyethyl)- isophthalamic acid ( II)

To ioxythalamic acid (161g), 0.25 mol) was added

1 N sodium hydroxide (250 ml) and adjusted the pH with 5 N NaOH to 10.5-10.6 at 85-90°C. 3-Chloro-1,2-propanediol (30.41g, 0.275 mol) was added and the pH readjusted to 10.5-10.6 with 5N NaOH, followed by further additions at 1 hour (2.76, 0.025 mol) and at 2 hours (2.76g, 0.025 mol). The reaction was complete at 2.5 hours by TLC. Glacial acetic acid (5ml) was added to pH 5, the solvents were evaporated and the residue azeotropically distilled with toluene (150ml) to give 294g of a mixture which was used without product isolation in the next step. Example 2. Acetylation of N-alkylated ioxythalamic acid 5-(N-2,3-Dihydroxypropylacetamido)-2,4,6,-triiodo —N-(2-hydroxyethyl)-isophthalamic acid (II) to: 5-( N- 2, 3- Diacetoxypropylacetamido)- 2, 4 , 6-triiodo — N-(2-acetoxyethyl)- isophthalamic acid ( III)

The crude mixture (290g) from step one, containing the title compound (250mmol) was slurried in acetic anhydride (500ml) with pyridine (19.76g, 250mmol) and mechanically at 65°C.

According to TLC, the acetylation was complete after 3 hours.

The acetic anhydride and acetic acid were evaporated, and the residue azeotropically distilled with toluene (100 ml x 2). The residue was dissolved in saturated aqueous sodium bicarbonate (500ml) and ethyl acetate (200ml). The layers were separated and the bicarbonate layer re-extracted with ethyl acetate (200ml x 2). The aqueous layer was acidified with concentrated hydrochloric acid to pH 0-1 which gave a white precipitate which was extracted with ethyl acetate (3x200ml). The organic extracts were combined and washed with brine (100 ml) and dried over MgSO 4 . Removal of the solvent gave 206g of the product (III)

as a white foam (97% yield).

Example 3. Acyl chloride formation of N-alkylated, acetylated

ioxythalamic acid

5-( N-2, 3-Diacetoxypropylacetamido)-2,4, 6-triiodo-.. r-N-(2-acetoxyethyl)-isophthalamic acid (III) to: 5-( N- 2, 3- Diacetoxypropylacetamido)- 2 , 4 , 6- tri iodo- T- N- ( 2-acetoxyethyl)- isophthalamic acid chloride ( IV)

The title compound (III) (250g, 243mmol) was dissolved in thionyl chloride (400ml) and the reaction heated at 60-65°C for 1 hour until complete (according to TLC). The thionyl chloride was evaporated on a rotary evaporator, and the residue azeotropically distilled with acetyl acetate (250ml x 2), the product dissolved in - ethyl acetate (400ml), extracted with aqueous saturated bicarbonate (150ml x 2) and dried over MgSO 4 , giving 202g of an off-white foam (96% yield).

Example 4. Amidation of alkylated, acetylated ioxythalamic acid chloride with trans-dioxepane

(protected aminothreitol)

5-(N-2,3-Diacetoxypropylacetamido)-2,4,6-triiodo-N-(2-acetoxyethyl)-isophthalamic acid chloride (IV) to: 5-( N- 2, 3- Diacetoxypropylacetamido)- 2, 4, 6- triiodo- N- 2 acetoxyethyl- N'-( trans- 2, 2- dimethyl- 6- hydroxy- 1, 3- dioxepan- 5- yl)- isophthalamide ( V)

The title compound (86.25g, 100mmol) was dissolved in dimethylacetamide (200ml) to which had been added triethylamine (13.9ml, 100mmol) and trans-5-amino-2,2-dimethyl-6-hydroxy-1,3-dioxepane (19 ,3g, 120mmol). The reaction mixture was stirred at room temperature for 8 h until complete (according to TLC). The solvent was evaporated in vacuo and the residue dissolved in ethyl acetate (200ml). The solution was washed with water (3x50ml) and saline (2x50ml). Drying (MgSO 4 ) followed by solvent removal gave the product (V) (96g) as an off-white foam (97% yield).

Example 5. Deprotection of alkylated acetylated ioxythalamic acid amidated with trans-dioxepane

to aminothreitol deriv

5-(N-2,3-Diacetoxypropylacetamido)-2,4,6-triiodo-N-(2-acetoxyethyl)-N(trans-2,2-dimethyl-6-hydroxy-1,3-dioxepane-5- yl)-isophthalamide (V) to: 5-( N- 2, 3- Dihydroxypropylacetamido)- 2, 4, 6- triiodo- N-( 2-hydroxyethyl)- N'-( 1, 3, 4- trihydroxy- threo - but- 2- yl)-

isophthalamide (VI)

The title compound (V) (4.94g, 5mmol) was dissolved in methanol (20ml), the pH was adjusted to 12-13 with 5N sodium hydroxide and the mixture was stirred for 1 hour at 25°C to achieve complete deacetylation (according to TLC). After evaporation to dryness, 15ml of 0.1N HC1 was added (to pH 1-1.5), the solution stirred for 30 minutes at 25°C to obtain the product (according to HPLC) which, after evaporation of acid and redissolution in water, was desalted with AG -501 mixed layer ion exchange resin. The solution was decolorized with bone charcoal and the solvent was removed in vacuo to give the product (VI) as a white powder (3.2g) (78% yield).

Example 6. Amidation of alkylated, acetylated ioxythalamic acid with 3-amino-1,2-propanediol 5-(N-2,3-Diacetoxypropylacetamido)-2,4,6-triiodo-N-(2-acetoxyethyl)-isophthalarnic acid chloride (IV) to: 5-( N- 2, 3- Diacetoxypropylacetamido)- 2 , 4 , 6- trijo6V.- N-( 2-acetoxyethyl)- N'-( 2, 3- dihydroxypropyl)- isophthalamide

(VIII)

The title compound (IV) (86.25g, 100mmol) was dissolved

in dimethylacetamide (200ml) to which have been added triethylamine (13.9g, 100mmol) and 3-amino-1,2-propanediol' (10.93g, 120mmol). The reaction was stirred at room temperature for 8 hours until complete by TLC. The solvent was evaporated in vacuo and the product dissolved in tetrahydrofuran (75ml) and partitioned with water saturated with sodium chloride. The organic extract was washed with brine.- IN hydrochloric acid (9:1, 50ml x 2) followed by brine: water (1:1) (50ml x 2) and finally brine (40ml x 1). The organic layer was dried over MgSO 4 and the solvent was removed to give 80.6g of the product (VII) as an off-white foam (87.9% yield).

Example 7. Deprotection of alkylated, acetylated ioxythalamic acid amidated with 3-amino-1,2-propanediol 5-(N-2,3-Diacetoxypropylacetamido)-2,4,6-triiodo-N-(2-acetoxyethyl)-N '-(2,3-dihydroxypropyl)-isophthalamide (VII) to: 5-( N- 2, 3- Dihydroxypropylacetamido)- 2, 4, 6- triiodo - N-( 2, 3- dihydroxypropyl)-N'-( 2- hydroxyethyl)-

isophthalamide (VIII)

The title compound (VII) (9.17g, 10mol) was dissolved

in methanol (20ml), pH adjusted to 13 with 5N sodium hydroxide and stirred at room temperature for 30 minutes to achieve complete deacetylation (according to TLC and HPLC). The solution was neutralized with Dowex 50 H+ resin and evaporated to give 7.8g of an off-white foam (99% yield). The product was dissolved in water and decolorized with bone charcoal. Removal of the solvent gave the product (VIII) as a white foam (6.3g) (80% yield).

NMR: (<1>H, 80 MHz, DMSO-d6): 8.6 (2 H, broad multiplet, carbamoyl N-H); 4.9-4.0 (5 H, broad singlet, exchangeable, hydroxyl protons); 4.1-2.8 (14 H, multiplet, protons on carbon with nitrogen and hydroxyl functions); 2.25 and 1.8

(3 H, pair of singlets, acetanilide methyl protons).

TLC: silica gel 70:30 CHCl3:MeOH: r_f (acetylated compound VII) 0.84; r_f (product compound VIII) 0.20.

HPLC: aminopropyl Alltech, 10u, 31ml/min 87% acetonitrile/water.

rf: 6.1 and 7.5 for two isomers.

Elemental analysis: calculated for C^gf^^I^N^Ogf^O: C,26.71; ff, 3, 26; 1.47.05; N,5.19%; Found: C,26.45, H,3.30; 1,46,71; 11.4.80%.

ALTERNATIVE SYNTHESIS OF COMPOUND ( VIII)

Step 1. Alkylation of ioxythalamic acid

5-Acetamido-2,4,6-triiodo — N-(2-hydroxyethyl)-

isophthalamic acid (I) to: 5-( N- 2, 3- dihydroxypropylacetamido)- 2, 4, 6- triiodo- N-(2-hydroxyethyl)- isophthalamic acid ( II)

To the ioxythalamic acid (161g, 0.25mol) was added 1N sodium hydroxide (250ml) followed by calcium hydroxide (13.4g, 0.181mol) and the suspension was heated to 90°C. 1-Chloro-2,3-propanediol (37.3g, 0.338mol) was added over 2 hours. The reaction was complete at 2.5 hours according to TLC.

Concentrated hydrochloric acid was added until pH 5.0, the solvents were evaporated and the residue azeotropically distilled with acetic acid (200ml), giving a mixture which was used without product isolation in the next step.

Step 2. Acetylation of N- alkylated

ioxythalamic acid

5-(N-2,3-Dihydroxypropylacetamido)-2,4,6-triiodo— N-(2-hydroxyethyl)-isophthalamic acid (II) to: 5-(N-2, 3- Diacetoxypropylacetamido)- 2, 4, 6-triiodo-N-(2-acetoxyethyl)-isophthalamic acid (III)

The crude mixture from step 1 containing the title compound (II) (185g, 0.25mol) was mixed with pyridine (19/76g, 0.25mol) and acetic anhydride (240ml, 2.54mol) was added while maintaining the temperature at 70° c. According to TLC was

acetylation complete after 3 hours.

The acetic anhydride and acetic acid were mostly evaporated, and the residue was dissolved in water (250ml). The aqueous mixture was washed with butyl acetate (50mlx3) and then acid-

made with concentrated hydrochloric acid to pH 0 to 1, which gave a white precipitate which was extracted with dichloromethane (3x200ml).

The organic extracts were combined, the solvent

removed and replaced with 1,2-dichloroethane (350ml). Partial removal of the solvent gave a viscous solution that was dry enough for chlorination (containing product in 93% yield).

Step 3. Acyl chloride formation of N-alkylated,

acetylated ioxythalamic acid

5-(N-2,3-Diacetoxypropylacetamido)-2,4,6-triiodo - N-(2-acetoxyethyl)-isophthalamic acid (III) to:

5-( N- 2, 3- Diacetoxypropylacetamido)- 2, 4, 6- triiodo - N-( 2-acetoxyethyl- isophthalamic acid chloride ( IV) The title compound (III) (205g, 0.243mol) in 1,2-dichloroethane (total volume 250ml ) was mixed with thionyl chloride (53.2 mL, 0.79 mol) at 70 °C, and the reaction mixture was held at 70 °C for 2 h until complete (by TLC). The solvents were evaporated on a rotary evaporator, and the residue azeotropically distilled with 1,2-dichloroethane (100ml x 2). The product was dissolved in 1,2-dichloroethane (200ml), washed with aqueous saturated bicarbonate (150ml x 1) and the solvent removed to give a viscous solution (containing product IV in 96% yield).Step 4. Amidation of 3-(N-2-acetoxyethyl)-carbomoyl-5-(N-2,3-diacetoxypropyl)-acetyl-amino-2,4,6- triiodobenzoyl chloride (IV) with 3-propane-1,2-diol to: 5-( N- 2, 3- Diacetoxypropylacetamido)- 2, 4, 6- triiodo- N-( 2-acetoxyethyl)- N'-( 2, 3-dihydroxypropyl)-isophthalamide

(VIII)

The title compound (IV) (240g, 0.27mol) in 1,2-dichloro-

ethane (total volume 160ml) was diluted with acetone (270ml) and added to a mixture of 3-amino-1,2-propanediol (30.4g, 0.334mol), water (65ml) and sodium bicarbonate (23.4g, 0.278mol) . The mixture was heated at 55°C for 8 hours, when TLC showed that the reaction

had passed completely. Water (500ml) was added and the solution was extracted with 1,2-dichloroethane containing 15 vol% acetone (2 x 40ml). The aqueous layer was salted with sodium sulfate (140g) and extracted with a mixture of dichloromethane:n-propanol (9:1, 300ml). The dichloromethane was removed at atmospheric pressure, n-propanol (300ml) was added and the solution was concentrated to a volume of 250ml. This solution was treated with Dowex-50-H+ resin to remove excess 3-amino-1,2-propanediol, and the solution was treated with bone charcoal overnight under reflux. The bone char was removed and the filtrate was freed of solvent to give an off-white foam (VII) (220g).

TLC: (silica gel, 90% chloroform/10%

methanol). RF (IV): 0.78 and 0.70. RF (V): 0.28.

Step 5. Deacetylation of 5-(N-2,3-diacetoxypropyl)-acetamido)-2,4,6-tri iodo-N-(2-acetoxyethyl)-N'-(2,3-dihydroxypropyl)-isophthalamine ( VII) to: 5-( N- 2, 3- dihydroxypropylacetamido)- 2, 4, 6- triiodo- N-( 2-hydroxyethyl)- N'-( 2, 3- dihydroxypropyl)- isophthalamine

(VIII)

The product of the preceding amidation reaction (V)

(220g) was dissolved in methanol (450ml) and 1M sodium methoxide in methanol (50ml) was added. The solution was stirred for 30 minutes during which methyl acetate was removed as an azeotrope with methanol. The final solution was neutralized to pH 7.0 by addition of Dowex-50-H+. The solution was freed from solvent to give (VIII) as an off-white foam (184g, 0.232mol) (yield: 84%

from the corresponding acid chloride). An aqueous solution of (VIII)

(0.5 mol) was treated with bone charcoal (5% wt) at 80°C for 4 h, filtered, water removed and the product recrystallized from 5% aqueous ethanol to give 87% (VIII) 99.2% pure. (Analytical data: see Example 7).

Example 8. Amidation of alkylated, acetylated

ioxythalamic acid chloride with diethanolamine

5-(N-2,3-Diacetoxypropylacetamido)-2,4,6-triiodo— N-(2-acetoxyethyl)-isophthalamic acid chloride (IV) to: 5-( N- 2, 3- Dihydroxypropylacetamido)- 2, 4, 6- triiodo— N, N-bis-( 2- hydroxyethyl)- N'-( 2- hydroxyethyl)- isophthalamide

(IX)

The title compound (IV) (4.31g, 5mmol) was dissolved in dimethylacetamide (10ml) and triethylamine (0.7ml, 5mmol) and diethanolamine (0.79g, 7.5mmol) were added. The reaction mixture was kept at room temperature for 8 hours until complete by TLC. After evaporation of the solvent in vacuo, the residue was partitioned between tetrahydrofuran (50ml) and saline (50ml). The organic layer was washed with brine: conc. HCl (9:1, 15ml x 1) followed by 75% saturated saline (20ml x 3). The organic extracts were dried over MgSO 4 and the solvent removed to give 4.5g of an off-white foam (94% yield). The material was deprotected as described in example 7 and desalted on mixed layer resin (AG-501) which gave 4.2g of final product (IX).

Example 9. Amidation of alkylated, acetylated ioxythalamic acid chloride with serinol

5-(N-2,3-Diacetoxypropylacetamido)-2,4,6-triiodo~ N-(2-acetoxyethyl)-isophthalamic acid chloride (IV) to: 5-( N- 2, 3- Dihydroxypropylacetamido)- 2, 4, 6- triiodo— N-( 1, 3- dihydroxypropyl)- N'-( 2- hydroxyethyl)-

isophthalamide (X)

To the solution of the title compound (IV) (12.3g, 14.3mmol) in diethylacetamide (54ml) was added triethylamine (2.0ml; 14.3mmol) and serinol (1.56g, 17.2mmol). The reaction mixture was stirred at room temperature for 8 h until complete by TLC. The solvent was removed in vacuo and tetrahydrofuran (20ml) and salt water (20ml) were added to the residue. The aqueous layer was extracted with tetrahydrofuran (2 x 10 ml). The organic layer was dried (MgSO 4 ) and removal of the solvent gave an off-white solid (11.45g) which was deacetylated as described in Example 38. Desalting of the crude product on Dowex mixed bed resin (AG-501) followed by decolorization with bone charcoal and evaporation gave the product (X) (10.lg) (77% yield).

Example 10. Alkylation of sodium iothalamate 5-Acetamido-2,4,6-triiodo-N-methylisophthalamic acid

(XI) to:

5-( N- 2, 3- Dihydroxypropylacetamido)- 2, 4, 6- triiodo — N-methylisophthalamic acid ( XII)

Sodium iothalamate (XI) (146g, 229.5mmol) was dissolved in

IN sodium hydroxide (380ml) followed by addition (over 30 minutes) of 3-chloro-1,2-propanediol (28.75ml, 344mmol), pH was adjusted with 5N NaOH to 11.5-12.0. The mixture was brought to 85°C and stirred for 2 hours until complete by TLC. The pH was adjusted to 6-7 with concentrated hydrochloric acid and the water removed on an evaporator. The residue was azeotropically distilled with toluene (100ml x 1) and gave 215g (including inorganic salts) of an off-white product (XII) which was acetylated without isolation in the next reaction.

Example 11. Acetylation of the alkylated

iothalamic acid

5-(N-2,3-Dihydroxypropylacetamido)-2,4,6-triiodo- N-methylisophthalamic acid chloride (XII) to: 5-( N- 2, 3- Diacetoxypropylacetamido)- 2, 4, 6- triiodo - N -methylisophthalamic acid ( XIII)

To the crude product (XII) (215g) from Example 10, pyridine (25ml) was added followed by acetic anhydride (400ml), keeping the temperature below 50°C. The mixture was heated at 50°C for 1 hour and the solvents were removed in vacuo. The residue was co-evaporated with toluene (2 x 100ml) and dissolved

in a mixture of ethyl acetate (300ml) and aqueous sodium bicarbonate (750ml). The aqueous layer was extracted with ethyl acetate (2 x 200ml) and acidified with concentrated hydrochloric acid to pH 0.5. The mixture was extracted with ethyl acetate (3 x 300ml) and the combined organic layer was washed with water (2 x 100ml) and brine (2 x 50ml) and dried (MgSO 4 ). Removal of the solvent gave the product (XIII), a pale yellow foam (I63g) (92% yield from sodium iotalate (XI)).

Example 12. Acylchlorination of the alkylated,

acetylated iothalamic acid

.</ >5-(N-2,3-Diacetoxypropylamido)-2,4,6-triiodo - N-methylisophthalamic acid (XIII) to: 5-( N- 2, 3- Diacetoxypropylacetamido)- 2, 4, 6- triiodo-N-methylisophthalamic acid chloride (XIV)

The product (XIII) from Example 11 (163g, 0.21mol)

was dissolved in thionyl chloride (500ml), stirred and refluxed for 1 hour, after which TLC showed that the reaction was complete. thionyl-

chloride was distilled from at 50-60°C at 100 Torr and the residue dried by coevaporation with ethyl acetate (2 x 100ml). The off-white foamy product was dissolved in ethyl acetate (700ml), washed with saturated aqueous sodium bicarbonate (4 x 200ml) and brine (2 x 250ml). The organic layer was dried (MgSO 4 ) and the solvent removed to give the product (XIV) as an off-white foam (143.3g) representing 79% yield based on iothalamic acid.

Example 13. Amidation of the chloride of the alkylated,

acetylated iothalamic acid with cis-dioxepane

5-(N-2,3-Diacetoxypropylacetamido-2,4,6-triiodo— N-methylisophthalamic acid chloride (XIV) to: 5-( N- 2, 3- Diacetoxypropylacetamido)- 2, 4, 6- triiodo- N-( cis- 2, 2- dimethyl- 6- hydroxy- 1, 3- dioxepan- 5- yl)- N'-methylisophthalamide ( XV)

The title compound (XIV) (10g, 12.65mmol) was dissolved

in dimethylacetamide (25ml) to which was added triethylamine (1.8ml, 12.65mmol) and cis-5-amino-2,2-dimethyl-6-hydroxy-1,3-dioxepane (2.44g, 15.2mmol). The solution was stirred at room temperature for 8 hours, after which the reaction was complete. The solvent was removed in vacuo and the residue was dissolved in ethyl acetate (50ml). The solution was washed with water (3 x 25ml) and saline (2 x 25ml). Drying (MgSO 4 ) followed by solvent removal gave the product (XV) as an off-white foam.

Example 14. Deprotection of alkylated, acetylated iothalamic acid amidated with cis-dioxepane

to D, L- aminoerythritol derivative 5-(N-2,3-Diacetoxypropylacetamido)-2,4,6-triiodo- N-(cis-2,2-dimethyl-6-hydroxyv-1,3-dioxepan-5-vl )-N'-methylisophthalamide (XV) to: 5-( N- 2, 3- Dihydroxypropylacetamido)- 2, 4, 6- triiodo- N-methyl- N'-( 1, 3, 4- trihydroxy- erythrobut - 2-yl)-

isophthalamide (XVI)

To a solution of the title compound (XV) (7.9g, 8.63mmol) in methanol (30ml) was added 5N NaOH to pH 13. According to TLC, the deacetylation was complete after 30 minutes at 24°C. The solution was treated with Dowex 50 H+ resin and the solvent was removed on a rotary evaporator to give 6.78g of foam (96% yield), which was dissolved in H 2 O (30ml). 1N HCl (3ml) was added and the mixture stirred for 1 hour at 25°C. The solvents were removed on a rotary evaporator and the remaining acid removed with Dowex mixed bed resin (AG-501). Bone charcoal treatment and evaporation gave 5.9g of product (XVI) as a white foam (5.9g) (86% yield).

Example 15. Amidation of alkylated, acetylated iothalamic acid chloride with protected D, L-aminothreitol

5-(N-2,3-Diacetoxypropylacetamido)-2,4,6-triiodo— N-methylisophthalamic acid chloride (XIV) to: 5-( N- 2, 3- Diacetoxypropylacetamido)- 2, 4, 6- triiodo- N- ( trans- 2, 2- dimethyl- 6- hydroxy- 1, 3- dioxepan- 5- yl)- N'-methylisophthalamide ( XVII)

To the solution of the title compound (XIV) (11g, 13.9mmol) in dimethylacetamide (25ml) was added trimethylamine (1.9ml, 13.9mmol) and trans-5-amino-2,2-dimethyl-6-hydroxy-1 ,3-dioxepane (2.69g, 16.7mmol). The reaction mixture was stirred at room temperature for 8 h until complete by TLC. The solvent was removed in vacuo and the residue dissolved in ethyl acetate (50ml). The solution was washed with water (3 x 25ml) and saline (2 x 25ml). Drying (MgSO 4 ) followed by solvent extraction gave the product (XVII) as a pale yellow foam.

Example 16. Deprotection of alkylated, acetylated iothalamic acid amidated with

trans-dioxepane to the D,L-aminothreitol derivative 5-(N-2,3-Diacetoxypropylacetamido)-2,4,6-triiodo— N-(trans-2,2-dimethyl-6-hydroxy-1,3-dioxepane- 5-yl)-N'-methylisophthalamide (XVII) to: 5-( N- 2, 3- Dihydroxypropylacetamido)- 2, 4, 6- tri iodo- N-methyl- N'-( 1, 3, 4- trihydroxy- threo- but- 2- yl)-

isophthalamide ( XVIII

To a solution of the title compound (XVII) (4.5g, 4.92mmol) in methanol (15ml) was added 5N NaOH to pH 13. According to TLC, the diacetylation was complete after 30 minutes at 24°C. The solution was treated with Dowex 50 H+ resin and the solvent removed on a rotary evaporator yielding 4.30g of foam, which was dissolved in H 2 O (30ml). IN HCl (30ml) was added and the solution stirred for 1 hour at 25°C. The solvent was removed on a rotary evaporator and the remaining acid removed with Dowex mixed bed resin (AG-501). Bone charcoal treatment and evaporation gave the product (XVIII) as a white foam (3.6g) (93% yield).

Example 17. Alkylation of metrizonic acid with

chloropropanediol

3-Acetamido-5-(N-methylacetamido)2,4,6-triiodobenzoic acid (XIX) to: 3-( N- 2, 3- Dihydroxypropylacetamido)- 5-( N-methylacetamido)- 2, 4, 6- triiodobenzoic acid (XX)

The title compound (XIX) as sodium salt (15g, 23.lmmol) was dissolved in 100ml of water to which was added 5N sodium hydroxide to pH 12-13. 3-Chloro-1,2propanediol (2.81g, 25.4mmol) was added dropwise over 15 minutes, and the pH adjusted to 12-13 with additional 5N sodium hydroxide. After 1.5 hours at 50-60°C, the reaction mixture was shown to be complete by TLC; 2N HCl was added by co-evaporation with pyridine. The resulting foamy product (XX) weighing 26.1g and containing inorganic salt was used directly in Example 18.

Example 18: Acetylation of N-alkylated

metrizonic acid

3-(N-2,3-Dihydroxypropylacetamido)-5-(N-methyl-acetamido)-2,4,6-triiodobenzoic acid (XX) to: 3-( N- 2, 3- Diacetoxypropylacetamido)- 5-( N - methyl-acetamido )- 2, 4, 6- triiodobenzoic acid ( XXI)

The crude product (26.lg) prepared in Example 17 was slurried in acetic anhydride (26.2ml, 277mmol) to which pyridine (25ml) had also been added. After stirring at 50°C for 1 hour, the reaction was complete according to TLC. The solvents were removed in vacuo and the residue coevaporated with toluene (2 x 20ml) and dissolved in a mixture of ethyl acetate (100ml) and aqueous sodium bicarbonate (100ml). The aqueous layer was extracted with ethyl acetate (2 x 25ml) and acidified with concentrated hydrochloric acid to pH 0.5. The mixture was extracted with ethyl acetate containing 10% tetrahydrofuran (3 x 50ml), and the combined organic layers were washed with water (2 x 25ml) and brine (2 x 25ml) and dried (MgSO 4 ). Removal of the solvent gave the product (XXI) as an off-white solid (17.5g) (96% yield relative to metrizonic acid).

Example 19. Acylchlorination of acetylated,

alkylated metrizonic acid

3- (N-2, 3-"Diacetoxypropylacetamido)-5-(N-methyl-acetamido)-2,4,6-triiodobenzoic acid (XXI) to: 3-( N- 2, 3- Diacetoxypropylacetamido)- 5-( N- methyl-acetamido)- 2, 4, 6- triiodobenzoyl chloride ( XXII)

The title compound (XXI) (15g, 19.lmmol) was slurried in thionyl chloride (40ml) and heated to reflux with stirring. After 1 hour, TLC showed that the reaction was complete. Thionyl chloride was distilled away in vacuo. After resolution

in 40ml chloroform and extraction with 40ml saturated bicarbonate, washing with water and brine, the organic layer was dried over MgSO4, filtered and the solvent evaporated on

a Rotavap to give the product (XXII) (14.6g) (95% yield) as a yellow solid. Melting point 145-150°C (decomposition).

Example 20. Amidation of metrizonic acid chloride

(previously acetylated and alkylated) with

trans- dioxepan

3-(N-2,3-Diacetoxypropylacetamido)-5-(N-methyl-acetamido)-2,4,6-triiodobenzoyl chloride (XXII) to: 3-( N- 2, 3- Diacetoxypropylacetamido)- 5-( N - methyl-acetamido)- 2, 4, 6- triiodo.- N-( trans- 2, 2- dimethyl- 6-hydroxy- 1, 3- dioxepan- 5- yl- benzamide ( XXIII)

The title compound (XXII) (8g, 9.94 mmol) was dissolved in dimethylacetamide (20ml) and to this solution was added triethylamine (1.4ml, 9.96mmol) and trans-5-amino-2,2-dimethyl-6-hydroxy -1,3-dioxepane (1.9g, 11.9mmol). The reaction mixture was stirred at room temperature for 8 hours, whereby the reaction mixture was complete according to TLC. The solvent was removed in vacuo and the residue dissolved in dichloromethane (40ml). The solution was washed with water (3 x 25ml) and saline (2 x 25ml). Drying (MgSO 4 ) followed by solvent extraction gave the product (XXIII) as a yellow foam (9.20g) (99% yield).

Example 21. Deprotection of alkylated

metrizonic acid with trans- dioxepan to

D, L- amino tree toll derivative

3-(N-2,3-Diacetoxypropylacetamido)-5-(N-methyl-acetamido)-2,4,6-triiodo-N-(trans-2,2-dimethyl-6-hydroxy-1,3-dioxepane -5-yl)-benzamide (XXIII) to: 3-( N- 2, 3- Dihydroxypropylacetamido)- 5-( N- methyl-acetamido)- 2, 4, 6- triiodo- N-( 1, 3, 4 - trihydroxy-threo-but-2-yl)-benzamide (XXIV)

The title compound (XXIII) (5g, 5.38mmol) was dissolved in 23ml of methanol, and 2.7ml of 0.2M sodium hydroxide in methanol was added. After 1.5 hours, the solution was evaporated to dryness (4.3g, 94% yield), to which was added 13ml of water and 0.025ml of concentrated HCl (0.3mmol). After stirring for 2 hours, the solution was neutralized with 1.6ml of 1N sodium hydroxide and desalted on a mixed bed AG-501 ion exchange resin, giving the product (XXIV) as an off-white solid (3.27g) (75% yield).

Example 22. Alkylation and subsequent

acetylation of diatrizonic acid

3,5-Diacetamido-2,4,6-triiodobenzoic acid (diatrizonic acid)

(XXV) to:

3, 5- bis-(N- 2, 3,- Diacetoxypropylacetamido)- 2, 4, 6-triiodobenzoic acid ( XXVI)

Diatrizonic acid (XXV) (205.6g, 0.33mol) was dissolved in 6.45N aqueous sodium hydroxide (160ml). The solution was heated to 45°C and, under mechanical stirring, 3-chloro-1,2-propanediol (77.9g, 0.7mol) was added dropwise over 15 minutes. The reaction mixture was heated at 45°C for 5 hours and then neutralized to pH 7.0 by the addition of concentrated hydrochloric acid (2.4ml). The solvent was removed in vacuo at 50°C and the residue was dried by azeotropic distillation with pyridine (3 x 150ml). To the resulting white foam (345g) was added pyridine (100ml, 1.27mol) and acetic anhydride (260ml, 2.76mol) with cooling to maintain the temperature at 40°C. The mixture was heated at 40°C for 1 hour and then treated with water (100 ml) under ice-cooling for 30 minutes. The solution was diluted with water (500ml) and extracted with a mixture of ethyl acetate/toluene (1:3)

(4 x 200ml). The aqueous layer was acidified to pH 0-1 with concentrated hydrochloric acid, the product taken up in ethyl acetate (500ml)

and the organic solution was washed with 10% sodium chloride (5 x 300ml) followed by brine (2 x 100ml). Drying (MgSO 4 ) followed by solvent extraction gave the product (XXVI) as a white foam (260g) (85% yield from diatrizonic acid) (XXV).

Example 23. Amidation of alkylated, acetylated ioxythalamic acid chloride with diethanolamine 5-(N-2,3-Diacetoxypropylacetamido)-2,4,6-triiodo-N-(2-acetoxyethyl)-isophthalamic acid chloride (IV) to: 5-( N- 2, 3- Diacetoxypropylacetamido)- 2, 4, 6- triiodo - N- N-bis-( 2- hydroxyethyl)- N'-( 2- acetoxyethyl)- isophthalamide

(XXVII)

(Also refer to example 8)

To a solution of (IV) (4.31g, 5mmol) in dioxane (1Oml) and water (2ml) was added solid potassium carbonate (0.691g, 5mmol), diethanolamine (0.790g, 7.5mmol) and the mixture was heated to 50 -55°C for 2-3 hours, whereby the reaction was complete according to TLC.

The reaction mixture was partitioned between tetrahydrofuran (50ml) and brine (50ml) and the layers were separated. The organic layer was washed with brine: conc. HC1 (9:1, 15ml x 1), followed by 75% saturated saline (20ml x 3). The THF extracts were dried over MgSO 4 and the solvent was removed to give 4.2 g (XXVII) (90% yield).

Example 24. Deprotection of alkylated, acetylated ioxythalamic acid amidated with diethanolamine 5-(N-2,3-Diacetoxypropylacetamido)-2,4,6-triiodo—N,N-bis-(2-hydroxyethyl)-N'-(2- acetoxyethyl)-isophthalamide (XXVII) to: 5-( N- 2, 3- Dihydroxypropylacetamido)- 2, 4, 6- triiodo— N, N-bis-( 2- hydroxyethyl)- N'-( 2- hydroxyethyl)- isophthalamide

(IX)

A solution of (XXVII) (3.8g, 4.lmmol) in methanol (20ml) was treated with sodium methoxide (1M in methanol, 2ml) at 25°C. The methyl acetate formed was continuously distilled off in vacuo. After 30 minutes, the solution was neutralized with Dowex 50H+ resin and the solvent removed to give (IX) (2.85g, 87% yield).

Example 25. Amiderinq of alkylated, acetylated ioxythalamic acid chloride with

3- N- methylamino- 1, 2- propanediol 5-(N-2,3-diacetoxypropylacetamido)-2,4,6-triiodo- N-(2-acetoxyethyl)-isophthalamic acid chloride (IV) to: 5-( N- 2, 3- diacetoxypropylacetamido)- 2, 4, 6- triiodo- N-methyl- N-( 2, 3- dihydroxypropyl)- N'-( 2- acetoxyethyl)-

isophthalamide ( XXVIII)

The chloride (IV) (43.13g, 50mmol) was dissolved in a mixture of acetone (70ml) and water (20ml), sodium bicarbonate (4.20g, 50mmol) and 3-(N-methyl)-amino-1,2- propanediol (5.78g, 55mmol).

The reaction mixture was heated at 50°C for 4 hours,

then poured into water (400ml) and 1,2-dichloroethane (50ml), giving two layers. The 1,2-dichlorotan layer was back-extracted with water (50ml x 1). Anhydrous sodium sulfate (200g) was added to the combined aqueous extracts, which were extracted with dichloromethane (250ml x 1). Evaporation of the solvent gave 35.5g of a white solid (XXVIII) (77% yield).

Example 26. Deprotection of alkylated, acetylated ioxythalamic acid amidated with

3- N- methyl- 1, 2- propanediol

5-(N-2,3-Diacetoxypropylacetamido)-2,4,6-triiodo- N,N-(methyl-2,3-dihydroxypropyl)-N'-(2-acetoxyethyl)-

isophthalamide (XXVIII)•to: 5-( N- 2, 3- Dihydroxypropylacetamido)- 2, 4, 6- triiodo- N-methyl- N-( 2, 3- dihydroxypropyl)- N'-( 2- hydroxyethyl)-

isophthalamide (XXIX)

The title compound (XXVIII) (0.8g, 0.86mmol) was dissolved

in methanol (lml) to which was added 0.5ml IN sodium methoxide-

solution at 25°C with stirring. The resulting methyl acetate was distilled off continuously. After 30 minutes, the mixture was neutralized with Dowex 50 H+ resin and evaporated to give 0.677g of a solid (XXIX) (98% yield).

Example 27. Amidation of alkylated, acetylated ioxythalamic acid chloride with

3-amino-1,2-propanediol

5-(N-2,3-Diacetoxypropylacetamido)-2,4,6-triiodo- N-(2-acetoxyethyl)-isophthalamic acid chloride (IV) to: 5-( N- 2, 3- Diacetoxypropylacetamido)- 2, 4, 6- triiodo- N-( 2, 3- dihydroxypropyl)- N'-( 2- acetoxyethyl)-

isophthalamide (VII)

(Reference also to example 7, alternative synthesis).

"The title compound (IV) (240g, 0.27mmol) in 1,2-dichloroethane (total volume 160ml) was diluted with acetone (270ml) and added to a mixture of 3-amino-1,2-propanediol (30.4g, 0.334 mmol)

water (65ml) and sodium bicarbonate (23.4g, 0.278mmol). The mixture was heated to 55°C for 8 hours, after which TLC showed that the reaction was complete. Water (500ml) was added and the solution was extracted with 1,2-dichloroethane (2 x 40ml) containing 15% acetone by volume. The aqueous layer was salted with sodium sulfate (140g) and extracted with a mixture of dichloromethane: n-propanol (9:1, 300ml). The dichloromethane was distilled from, n-propanol (300ml) was added, the solution concentrated to 250ml and treated with Dowex 50-H+ resin, and treated with bone char for 6 hours under reflux. Filtration and solvent removal gave (VII) (220g, 86% yield).

Example 28. Deprotection of alkylated, acetylated ioxythalamic acid amidated with

3-amino-1,2-propanediol

5-(N-2,3-Diacetoxypropylacetamido)-2,4,6-triiodo - N-(2,3-dihydroxypropyl)-N'-(2-acetoxyethyl)-

isophthalamide (VII) to: 5-( N- 2, 3- Dihydroxypropylacetamido)- 2, 4, 6- triiodo*- N-( 2, 3- dihydroxypropyl)- N'-( 2- hydroxyethyl)-

isophthalamide (VIII)

(Reference also to example 7, alternative synthesis).

The product of the preceding amidation reaction (VII)

(220g) was dissolved in methanol (450ml) and 1M sodium methoxide in methanol (50ml) was added. The solution was stirred for 30 minutes while methyl acetate was continuously removed in vacuo, then neutralized to pH 7.0 with Dowex-50-H+. Solvent removal

a solid (VIII) (184g, 0.232mol) (yield: 84% from (IV) acid chloride).

Example 29. Acetylation of 5-amino-2,4,6-triiodo—N-(2,3-dihydroxypropyl)-isophthalamic acid

5-amino-2,4,6-triiodo-N-(2,3-dihydroxypropyl)-

isophthalamic acid (XXX) to:

5- acetamido- 2, 4 , 6- tr i iodo — N-( 2 , 3- diacetoxypropyl) - isophthalamic acid (XXXI) ~The title compound (XXX) (252.8g, 0.4mol) was mixed with glacial acetic acid (150ml) and acetic anhydride (350ml, 3.7mol). Concentrated sulfuric acid was added (1Oml) and the solution was heated for 6 hours at 40°C. The slurry was completely . in a mixture of ice and salt water (2:1, 1.51) stirred for 30 minutes and filtered off. The solid was washed with cold water (200ml x 1) and dried, giving 274g (90% yield of (XXXI). Example 30. Alkylation, followed by acetylation of 5-acetamido-2,4,6-triiodo— N - (2, 3-dihydroxypropyl)- isophthalamic acid 5-acetamido-2,4,6-triiodo-N-(2,3-diacetoxypropyl)-isophthalamic acid (XXXI) to: 5-( N- 2, 3- diacetoxypropylacetamido)- 2, 4, 6- triiodo— N- ( 2, 3- diacetoxypropyl)- isophthalamic acid ( XXXII)

The title compound (XXXI) (227.4g, 0.3mol) was dissolved in 1N sodium hydroxide (300ml) and the pH was adjusted to 12.0

with the addition of 5N sodium hydroxide.

Calcium hydroxide (97%, 17g, 0.223mol) and 3-chloro-1,2-propanediol (44.76g, 0.405mol) were added at 85-90°C for two hours. After 2.5 hours the reaction was complete according to TLC.

The pH was brought to 6.0 with concentrated hydrochloric acid (4ml)

and the water was removed to give an oil which was dissolved in glacial acetic acid (500ml). The solution was concentrated to 50% and pyridine (24.2ml, 0.3mol) and acetic anhydride (311ml, 3.3mol) were added over 45 minutes. After 6 hours at 70°C, TLC showed that the reaction was complete.

After the volume reduction to 50%, ice-cold water (500ml) and ethyl acetate (250ml) were added, the layers separated and the aqueous layer acidified to pH 1.0 with concentrated hydrochloric acid (60ml). The product was extracted into dichloromethane (500ml), which was then replaced with 1,2-dichloroethane (400ml) to give 211.6g, 0.231mol (XXXII) (77% yield).

Example 31. Chlorination of alkylated, acetylated 5-acetamido-2,4,6,-triiodo-N-(2,3-dihydroxypropyl)-isophthalamide)

5-N-(2,3-diacetoxypropylacetamido)-2,4,6-tr iodo«-N-(2,3-diacetoxypropyl)-isophthalamic acid (XXXII) to: 5-N-(2,3-diacetoxypropylacetamido) - 2, 4, 6- triiodo- N-( 2, 3- diacetoxypropyl)- isophthalamic acid chloride

(XXXIII)

To a solution of the title compound (XXXII) (169.5g, 0.185mol) in 1,2-dichloroethane (total volume 450ml) at 55°C was added thionyl chloride (51.25ml, 0.702mol). The solution was heated at 70°C for 3 hours, whereupon TLC showed that the reaction was complete.

The solution was concentrated to 250ml and the remainder azeo-

distilled with 1,2-dichloroethane (200ml x 2). 700ml of 1,2-dichloroethane was added and the mixture washed with saturated sodium bicarbonate (500ml x 1) to give (XXXIII) (165.25g, 96% yield).

Example 32. Amidation of alkylated, acetylated 5-acetamido-2,4,6-triiodo-N-(2,3-dihydroxypropyl)-isophthalamic acid chloride with 2-aminoethanol

5-(N-2,3-diacetoxypropylacetamido)-2,4,5-triiodo-N-(2,3-diacetoxypropyl)-isophthalamic acid chloride

(XXXIII) to: 5-( N- 2, 3- diacetoxypropylacetamido)- 2, 4, 6- triiodo- N-( 2-hydroxyethyl)- N'-( 2, 3- diacetoxypropyl)- isophthalamide

(xxxiv)

The title compound (XXXIII), (132g, 0.141mol) was dissolved in acetone (300ml) and water (75ml), and to this was added sodium bicarbonate (11.85g, 0.141mol) and 2-aminoethanol (10.35g, 0.170mol) ). The reaction mixture was heated at 50°C for 6 hours, after which TLC showed that the reaction was complete.

The reaction mixture was diluted with water (500ml) and toluene (200ml) and the layers were separated. The organic layer was back-extracted with water (100 ml x 1), the aqueous extract was combined and saturated with sodium chloride, and the product was extracted with dichloromethane (400 ml). The dichloromethane layer was washed. The dichloromethane layer was washed with 50% brine solution (50mlx1), the layers separated and the dichloromethane removed, giving XXXIV (120.6g, 89% yield).

Example 33. Deprotection of alkylated, acetylated 5-(N-2,3-dihydroxypropylacetamido)-

2, 4, 6-trijo-isophthalamic acid

amidated with 2-aminoethanol

5-(N-2,3-diacetoxypropylacetamido)-2,4,6-triiodo-N-(2-hydroxyethyl)-N1 -(2,3-diacetoxypropyl)-isophthalamine (XXXIV) to: 5-( N- 2 , 3- dihydroxypropylacetamido)- 2, 4, 6- triiodo— N-( 2-hydroxyethyl)- N'-( 2, 3- dihydroxypropyl)- isophthalamide

(VIII)

The title compound (XXXIV) (60.3g, 0.063mol) was dissolved in methanol (total volume 250ml). 15ml of an IM solution of sodium methoxide was added and the solution stirred for 30 minutes at 25°C, while the methyl acetate formed was continuously distilled off in vacuo. The solution was then neutralized with Dowex 50-H+ and the solvent removed to give VIII (49.lg, 99% yield).

Example 34. Alkylation of acetylated ioxythalamic acid

5-acetamido-2,4,6-triiodo-N-<2-acetoxyethyl)-

isophthalamic acid (XXXV) to: 5-( N- 2, 3- dihydroxypropylacetamido)- 2, 4 , 6- triiodo»- N-( 2-hydroxyethyl)- isophthalic acid ( II)

The title compound (XXXV) (6.86g, 0.01mol) was dissolved in 1N sodium hydroxide (10ml) and 1N sodium hydroxide (1ml) was added to saponify the ester.

The solution was heated to 90°C and calcium hydroxide (97%, 0.556g, 0.0075mol) was added followed by 3-chloro-1,2-propanediol (1.5g, 0.0135mol) over 1 hour. The reaction was heated for an additional 30 minutes until it was complete according to

TLC.

Glacial acetic acid was added to pH 5.0, the solvents were evaporated and the residue azeotropically distilled with toluene (20ml) to give 11.7g of a mixture amenable to acetylation as shown in Example 2.

ALTERNATIVE SYNTHESIS OF COMPOUND VIII:

EXAMPLES 35-37

Example 35. Iodination of 5-amino-N-(2-hydroxyethyl-N'-(2,3-dihydroxypropyl)-

isophthalamide (hydrochloride)

5-amino-N-(2-hydroxyethyl)-N'-(2,3-dihydroxypropyl)-isophthalamide (hydrochloride) (XXXVI) to: 5- amino- 2, 4, 6- triiodo - N-( 2- hydroxyethyl)-N'-(2,3-dihydroxypropyl)-isophthalamide (XXXVII): The title compound (XXXVII, 600mg, 1.80mmol) was dissolved in water (8.9ml) and concentrated hydrochloric acid (0.15ml). 1, 84M KIC12 (3.3ml) was added and the reaction mixture was heated at 80°C for 3 hours. The pH of the reaction mixture was adjusted with sodium bicarbonate, rotary evaporated to dryness and dissolved in 8ml ethanol. Inorganic salts were filtered off, the filtrate acidified with conc. HCl. and evaporated to give 918g of an orange solid (79% yield).

Example 36: Acetylation of 5- amino- 2, 4, 6-

triiodo N-(2- hydroxytetyl )- N'-( 2, 3- dihydroxypropyl)- isophthalamide

5-amino-2,4,6-triiodo-N-(2-hydroxyethyl)-N'-(2,3-dihydroxypropyl)-isophthalamide (XXXVII) to: 5-acetamido-2, 4, 6- tr in iodo — N-,( 2- acetoxyethyl) -N' - ( 2, 3-diacetoxypropyl)- isophthalamide ( XXXVIII): The title compound (600mg, 0.89mmol) was dissolved in glacial acetic acid (lml), pyridine (72ul, 0.89mmol) and acetyl chloride (620 µL, 8.9 mmol) was added and the reaction was heated at 50°C for 2 hours until complete by TLC.

The excess of acetyl chloride was removed by distillation, the product dissolved in tetrahydrofuran (10 ml) and the solution was washed with a saline-0.1 N HCl mixture (5 ml x 1). The THF was removed to give 650mg of the product (XXXVIII) (87% yield). Example 37: alkylation of 5-acetamido-2,4,6-triiodo-N-(2-acetoxyethyl)-N'-(2,3-diacetoxypropyl)-isophthalamide with epichlorohydrin

5-acetamido-2,4,6-triiodo-N-(2-acetoxyethyl)-N'-(2,3-diacetoxypropyl)-isophthalamide (XXXVIII) to: 5- N-(2,3-dihydroxypropyl)- acetamido-2,4,6-triiodo1-1H 2-hydroxyethyl)-N'-(2,3-dihydroxypropyl)-isophthalamide

(VIII)

The title compound (XXXVIII, 650mg, 0.77mmol) was dissolved in ~1,2-propanediol (3ml), sodium bicarbonate (1.29mg, 1.54mmol) and epichlorohydrin (1.2ml, 15.4mmol) were added and the reaction mixture was heated at 90°C. TLC and HPLC showed that the reaction was complete after 1 hour and gave compound VIII, in 73% yield.

Example 38. Deacetylation of alkylated, acetylated

ioxythalamic acid chloride (IV) amidated with serinol

5-(N-2,3-diacetoxypropylacetamido)-2,4,6-triiodo—N-(2-acetoxyethyl)-N'-(1,3-dihydroxyisopropyl)-

isophthalamide (XXXIX) to: 5-( N- 2, 3- dihydroxypropylacetamido)- 2, 4, 6- triiodo N^

( 1, 3. dihydroxyisopropyl1- N'-( 2- hydroxyethyl)-

isophthalamide (X)

The title compound (XXXIX, 11.45g, 0.125mol) was

dissolved in methanol (25ml), pH adjusted to 13 using 5N sodium hydroxide and the solution was stirred at room temperature for 30 minutes to achieve complete deacetylation as shown by HPLC and TLC. The solution was neutralized with Dowex 50 H+ resin, and the solvent was removed to give an off-white foam. Desalting of the crude product on Dowex mixed layer resin (AG-501) followed by decolorization with bone charcoal and evaporation gave the product tX, 8.7g,

77% yield).

The above procedure demonstrated the simple, rapid and effective synthesis strategy of the present invention. The economy of the method is shown by high yields and the use of intermediate products without further purification. In addition, only simple, cheap and easily removable reagents are used, and the resulting product is essentially free of contaminants. The number of steps from the starting material is minimal, which further minimizes separations and purifications.

Claims (5)

1. Process for the synthesis of a non-ionic contrast medium or an intermediate for this, from an ionic contrast medium, characterized by the fact that one reacts a 3-(amino- or carboxamido)-5-acylamino-2,4,6-triiodobenzoic acid with a halohydrin having from 2 to 5 carbon atoms and 1 to 4 hydroxy groups in an aqueous medium at a pH higher than 9 and lower than 11 at a temperature from 60-100°C for a sufficient time to selectively N-alkylate the acylamido group and give a first intermediate; and optionally performing the following steps: acylating all hydroxyl groups with an acylating agent to a second intermediate; forms acyl halide of the second intermediate with acid chloride; and reacts the acyl chloride with an alkylamine to form the nonionic contrast medium. 2. Method according to claim 1, characterized in that the halohydrin is a chlorohydrin with from 2 to 5 carbon atoms and from 1 to 4 hydroxy groups. 3. Method according to claim 1, characterized in that all acyl groups have from 2 to 3 carbon atoms. 4. Method according to claim 1, characterized in that the base is calcium or barium hydroxide. 5. Method according to claim 1, characterized in that the reaction occurs in a mixture of an inert organic polar solvent and water in the presence of an inorganic base.