Process for the preparation of complex compounds

There is disclosed a process for the preparation of analytically pure chelate complexes which can be used in diagnostic medicine, for example as contrast media or radiopharmaceuticals. The process comprises transcomplexing a complex of a .beta.-dicarbonyl compound and a metal ion, for example a metal acetylacetonate, which is readily soluble in an organic solvent that is not miscible in all proportions with water, with a stoichiometric amount or with a less than equivalent amount of a chelating agent whose binding affinity for the metal ion is greater than that of the .beta.-dicarbonyl compound.

The present invention relates to a novel process (methodological process) 
for the preparation of metal complexes, in particular of paramagnetic 
and/or radioactive chelate complexes, in especially pure form, to the 
complexes prepared by said process, and to novel chelate complexes with 
known chelating agents. 
Paramagnetic and/or radioactive chelate complexes are used mainly in 
diagnostic medicine, for example in X-ray, radionuclide, ultrasonic and/or 
magnetic nuclear resonance diagnostics, as contrast medium. For this 
utility, it is essential to prepare the chelate complexes in the greatest 
possible purity. In the known processes of the prior art for the 
preparation of chelate complexes, an inorganic metal compound, usually a 
halide, for example a chloride, is reacted with the chelating agent. The 
complexes so obtained, however, do not have the desired purity. On the 
contrary, they are contaminated by the counterion present in the inorganic 
metal compound, by excess or unreacted educt and by products that are 
formed when neutralising acid, for example hydrohalic acid or sulfuric 
acid, that forms during the chelation. The neutralisation is necessary, 
because the chelate complexes used for medicinal purposes must have a 
physiologically tolerable pH value. The impurities can only be separated 
with difficulty and incompletely. 
It is the object of the present invention to provide a simple process for 
the preparation of chelate complexes in purer form, wherein the 
neutralisation step is dispensed with. 
The invention relates more particularly to a process for the preparation of 
a complex of a metal ion and a chelating agent, which comprises 
transcomplexing a complex of a .beta.-dicarbonyl compound and the said 
metal ion, which complex is readily soluble in an organic solvent that is 
not miscible in all proportions with water, with a stoichiometric amount 
or with a less than equivalent amount of a chelating agent whose binding 
affinity for the metal ion is greater than that of the .beta.-dicarbonyl 
compound, or of a salt, preferably a pharmaceutically acceptable salt, of 
such a chelating agent containing at least one salt-forming group. 
The metal ions to be complexed are, in particular, paramagnetic metal ions 
of the series of the transition metals including the lanthanides and 
actinides, as well as metal ions of the third main group of the periodic 
table, and radionuclide ions. 
Metal ions of the series of the paramagnetic transition metal ions, 
exclusive of the lanthanides and actinides, to be singled out for special 
mention are the iron ions Fe.sup.2+ and, in particular, Fe.sup.3+, and 
also the copper ion Cu.sup.2+, the cobalt ion Co.sup.2+, the nickel ion 
Ni.sup.2+, the manganese ions Mn.sup.2+ and Mn.sup.3+, the chromium ions 
Cr.sup.2+ and Cr.sup.3+ and the vanadinium ion V.sup.2+. 
A particularly suitable metal ion of the series of the lanthanide ions is 
the gadolinium ion Gd.sup.3+, but the europium ion Eu.sup.2+, the 
lanthanum ion La.sup.3+ and the ytterbium ion Yb.sup.3+ may also be 
mentioned. 
A preferred metal ion of the series of the actinides is the protactinium 
ion Pa.sup.4+. 
Metal ions of the third main group of the periodic table are aluminium ions 
and, preferably, gallium and indium ions. In the case of gallium and 
indium the ions of the radioactive isotopes are preferred, for example 
.sup.67 Ga and .sup.111 In. 
Radionuclide ions are, in particular, the ions of the radioactive isotopes 
of the above metals, for example of the metastable technetium 99, .sup.99m 
Tc, or .sup.140 La, .sup.168 Yb, .sup.67 Ga or .sup.111 In. 
Chelating agents are organic compounds that contain at least two potential 
ligands, as in particular the desferrioxamines containing free OH groups 
disclosed, for example, in U.S. Pat. No. 3,634,407, preferably the 
desferrioxamines of the B-series, most particularly desferrioxamine B 
commercially available in the form of the methane-sulfonate under the 
trade name Desferal.RTM., or derivatives thereof containing an acylated 
amino group, and also desferrioxamine E. Other preferred chelating agents, 
especially for Fe.sup.3+, Al.sup.3+ and Cr.sup.3+, are, for example, 
2-(3'-hydroxyprid-2'-yl)-3-methyl-3-thiazoline-4-carboxylic acid disclosed 
in European patent 45 281 and referred to hereinafter as desferrithiocine, 
and the demethyl derivative thereof also disclosed therein, as well as 
further siderophores formed from microorganisms, for example rhodotorula 
acid. 
Numerous other chelating agents are suitable, for example 
3-hydroxy-2-methyl-4H-pyran-4-one (maltol), 
(L)-2-amino-3-[3-hydroxypyrid-4-on-1-yl]propionic acid (L-mimosine), and 
other 3-hydroxy-4-pyridone derivatives, the specific choice of said 
chelating agents being determined by the desired properties of the chelate 
complex to be prepared (see below). 
Salt-forming groups in a chelating agent are acid groups, for example 
carboxylic acid, phosphoric acid or sulfonic acid groups, or basic groups, 
for example amino groups. 
Salts of chelating agents which, like desferrithiocine, contain at least 
one acid group, are preferably alkali metal salts, mainly sodium or 
potassium salts. Salts of chelating agents which, like desferrioxamin B, 
contain at least one basic group, are acid addition salts, preferably 
pharmaceutically acceptable acid addition salts, for example with 
inorganic acids such as hydrochlorid acid, sulfuric acid or phosphoric 
acid, or with suitable organic carboxylic or sulfonic acids, for example 
trifluoroacetic acid or methylsulfonic acid. 
A .beta.-dicarbonyl compound is an organic compound which carries two 
carbonyl groups in 1,3-position to each other and which may also be in 
enol form, with the proviso that the two carbonyl groups must be available 
for complexing a metal ion and may not be sterically hindered. A preferred 
1,3-dicarbonyl compound is 2,4-pentanedione (acetylacetone), because the 
acetylacetonates of numerous metals are commercially available. 
An organic solvent which is not miscible in all proportions with water is, 
for example, a suitable carboxylate such as ethyl acetate, a suitable 
cyclic or, in particular, acyclic ether such as tetrahydrofuran or diethyl 
ether, or an unsubstituted or halogenated hydrocarbon, for example an 
aromatic hydrocarbon such as benzene or toluene, an aliphatic hydrocarbon 
such as pentane or heptane, or a halogenated hydrocarbon such as 
chloroform or dichloromethane. 
In which of the above mentioned solvents a specific metal complex 
containing a .beta.-dicarbonyl compound is readily soluble depends on the 
specific complex. Metal acetylacetonates, for example, are readily soluble 
in ethyl acetate, diethyl ether, benzene or toluene. 
The binding affinity of the chelating agent for the metal ion must be 
sufficiently greater than the binding affinity of the .beta.-dicarbonyl 
compound for the appropriate metal ion, i.e. the negative decadic 
logarithm of the disassociation constant (pK) must be greater for the 
complex consisting of chelating agent and metal ion than for the complex 
consisting of .beta.-dicarbonyl compound and metal ion, as otherwise the 
process of this invention will not run or will not proceed quantitatively. 
In analogy to the customary naming of the iron(III) complex, the metal 
complexes of a desferrioxamine will hereinafter be designated as 
"ferrioxamine", stating the name of the complexed metal and, if necessary, 
denoting its oxidation state, followed by the suffix "oxamine". By 
analogy, the complexes formed by desferrithiocine will be named using the 
suffix "thiocine". 
If the chelate complex prepared by the process of this invention is to be 
used in diagnostic medicine, it must have, for example, the following 
properties: 
Especially if the metal ion in the free form is toxic, the complex must be 
substantially stable so that as few metal ions as possible will pass into 
the organism. If the metal ion in question is endogenous and non-toxic in 
the respective concentration, a lower stability of the complex may be 
tolerated. As endogenous ions it is preferred to use iron ions for the 
process of this invention. It goes without saying that the chelate complex 
as a whole should also be substantially non-toxic and be sufficiently 
soluble for most uses, and it should also be excreted from the organism as 
soon as possible after the diagnosis has been performed. The above 
requirements are admirably fulfilled, for example, by the iron(III) 
complexes of desferrioxamine B and desferrithiocine. 
The process is carried out by adding a solution of the complex of the 
.beta.-dicarbonyl compound and the metal ion in a suitable solvent in 
which it is readily soluble, preferably an organic solvent that is 
immiscible or sparingly miscible with water, for example a suitable ester 
such as ethyl acetate, or a suitable ether such as diethyl ether, to a 
solution of the chelating agent in a suitable solvent, and efficiently 
stirring the mixture. If the solubility of the chelating agent, for 
example desferrioxamine B mesylate, permits it, the solvent for the 
chelating agent is conveniently water. If the chelating agent is only 
sparingly soluble in water, it is also possible to use an aqueous 
suspension of the chelating agent. The chelating agent can, however, also 
be used in a non-aqueous solvent, for example an alcohol such as methanol, 
ethanol or isopropanol. The reactants can be used in equivalent amounts. A 
small excess, for example 10-20%, of the complex with the 
.beta.-dicarbonyl compound can also be used. The reaction is preferably 
carried out in the temperature range from ca. -20.degree. to ca. 
+150.degree. C., more particularly from 0.degree. to +100.degree. C., 
preferably from +10.degree. to +70.degree. C., especially from +15.degree. 
to +40.degree. C. and, most preferably, at room temperature (ca. 
+20.degree. C.). The reaction temperature in any given case will depend, 
inter alia, on the melting and boiling points of the solvent or mixture of 
solvents, on the stability of the reactants and of the chelate complex, 
and on the desired reaction rate. If desired or necessary, the reaction 
can be carried out under pressure, for example under the inherent pressure 
of the system and/or in an inert gas atmosphere, for example under 
nitrogen or argon. The isolated yields of pure product are ca. 80-100% of 
theory. 
To isolate the desired metal complex and to separate unreacted educt and 
by-product, i.e. the complex of the .beta.-dicarbonyl compound and the 
metal ion as well as the liberated .beta.-dicarbonyl compound, use is made 
of differences in the relative solubility between the desired metal 
complex and the educt and the by-product. In this connection, it will be 
expedient to choose for the reaction a solvent system that is suitable for 
the easy isolation of the desired metal complex. 
The complexes with the .beta.-dicarbonyl compound, for example the metal 
acetylacetonates, are insoluble in water, but are soluble in a 
substantially water-immiscible solvent such as ethyl acetate or diethyl 
ether. In contrast, the complexes formed in the process of this invention, 
for example the desferrioxamine B chelate complexes, are virtually 
insoluble in at least one substantially water-immiscible organic solvent, 
for example ethyl acetate, diethyl ether, benzene, toluene or 
tetrahydrofuran. This virtual insolubility makes it easy to isolate and 
purify them. The desferrithiocine complexes are preferably prepared in a 
system consisting of water and a less polar solvent than ethyl acetate, 
for example in diethyl ether. 
In the normal case of the reaction mixture containing water, the aqueous 
phase is separated after completion of the transcomplexing reaction and 
extracted with an organic solvent in which the desired metal complex has 
as low a solubility as possible and in which the impurities are as readily 
soluble as possible. The aqueous phase, if necessary after first 
concentrating it, is subsequently lyophilised. If, exceptionally, the 
reaction mixture does not contain water, it is strongly concentrated, for 
example to dryness, and the residue is then extracted with an organic 
solvent in which the desired metal complex has as low a solubility as 
possible and in which the impurities are as readily soluble as possible. 
The complexes with the .beta.-dicarbonyl compound are commercially 
available, for example numerous acetylacetonates, or they can be prepared 
in a manner known per se, for example by reacting the .beta.-dicarbonyl 
compound with a salt of the corresponding metal, for example a chloride. 
It is also possible to react metal salts of 2-ethylcaproic acid 
(octoates), metal naphthenates or metal stearates with the 
.beta.-dicarbonyl compound [G. Stockelmann et al., Angew. Chem. 79, 530 
(1967)] or to bring cation exchangers charged with the desired metal ion, 
in an organic solvent, into contact with the .beta.-dicarbonyl compound 
[K. Ohzeki et al., Bull. Chem. Soc. Jap. 48, 67-68 (1975)]. 
A preferred embodiment of the process of this invention comprises 
transcomplexing an acetylacetonate of a radionuclide ion or of a 
paramagnetic metal ion selected from the series of the transition metals, 
including the lanthanides, preferably an acetylacetonate of Fe.sup.2+, 
Fe.sup.3+, Cu.sup.2+, Co.sup.2+, Ni.sup.2+, Mn.sup.2+, Mn.sup.3+, 
Cr.sup.2+, Cr.sup.3+, V.sup.2+, Gd.sup.3+, Eu.sup.2+, La.sup.3+ or 
Yb.sup.3+, with a chelating agent selected from desferrioxamine B, 
desferrioxamine E and desferrithiocine and a pharmaceutically acceptable 
salt thereof. 
Another preferred embodiment of the process of this invention comprises 
reacting an acetylacetonate of iron(III), manganese(III), indium(III) or 
gallium(III) with desferrioxamine B, desferrioxamine E, desferrithiocine, 
maltol, L-mimosine, 3-hydroxy-1,2-dimethyl-4-pyridone, 
3-hydroxy-2-methyl-N-propyl-4-pyridone or rhodotorula acid in water/ethyl 
acetate or water/diethyl ether at room temperature. 
The invention also relates to the chelate complexes obtained by the process 
of this invention, to novel chelate complexes, i.e. those not belonging to 
the prior art, especially the novel chelate complexes described in the 
Examples, and to the use of said chelate complexes in diagnostic medicine. 
The chelate complexes containing radioactive metal ions, for example 
.sup.99m Tc, .sup.111 In, .sup.67 Ga, .sup.140 La or .sup.168 Yb, can be 
used, for example, as radiopharmaceuticals. Chelate complexes with stable 
isotopes that have a higher atomic weight than iodine absorb X-rays and 
can therefore be used as X-ray contrast media. A number of these last 
mentioned chelate complexes absorb, reflect or scatter ultrasonic waves 
and hence can also be used in ultrasonic diagnosis. Chelate complexes that 
contain a paramagnetic metal ion, for example Gd.sup.3+, Mn.sup.2+, 
Cr.sup.3+ or Fe.sup.3+, with symmetrical electronic ground state, 
accelerate the spin relaxation and can be used in NMR spectroscopy as 
contrast media. Chelate complexes that contain a paramagnetic metal ion 
with unsymmetrical electronic ground state can be used in NMR spectroscopy 
or in magnetic in vivo resonance spectroscopy as displacement reagents. 
Aluminium complexes can be used as reference compounds for the evaluation 
(for example toxicity studies) of chelating agents. 
The dose to be administered to a mammal will depend, inter alia, on the 
chelate complex, on the nature of the mammal, and on the envisaged use, 
and is, for example, in the order of 0.001-1 millimole per kilogram of 
body weight. Administration is preferably made parenterally, more 
particularly intravenously, or enterally, for example orally.

The invention is illustrated by the following non-limitative Examples. 
ABBREVIATIONS 
DMSO: dimethyl sulfoxide 
FAB: fast atom bombardment 
HPLC: high pressure liquid chromatography 
EXAMPLE 1 
With efficient stirring, a solution of 3.38 kg (5.15 mol) of deferrioxamine 
B mesylate in 20 liters of water is added at room temperature to a solution 
of 2.20 kg (5.66 mol) of commercial iron(III) acetylacetonate in 25 liters 
of ethyl acetate. The mixture is stirred efficiently for 1 hour and turns 
red immediately. The aqueous phase is extracted with 4.times.10 liters of 
ethyl acetate, then concentrated somewhat at 55.degree. C. and 85 000 Pa 
(0.85 bar) to remove residual ethyl acetate, and thereafter lyophilised. 
The lyophilisate is digested with ethyl acetate and dried under a high 
vacuum, affording 3.54 kg (98% of theory) of deep red, hygroscopic 
ferrioxamine B mesylate that contains 1 mol of water. 
C.sub.25 H.sub.45 FeN.sub.6 O.sub.8.CH.sub.3 SO.sub.3 H.H.sub.2 O 
(727.633): Cal: C 42.92, H 7.06, Fe 7.68, N 11.55, S 4.41. Found C 43.15, 
H 7.19, Fe 7.81, N 11.60, S 4.44. 
HPLC: column: Hypersil ODS, 5 .mu.m, 120.times.4.6 mm systems: solution 
A=2.5 mmol of phosphate buffer pH 3.0 solution B=20% of solution A and 80% 
of acetonitrile 
______________________________________ 
Gradient: 
Minutes % A % B flow: ml/min 
______________________________________ 
0 100 0 2.3 
10 70 30 2.3 
12 0 100 2.3 
15 100 0 2.3 
______________________________________ 
R.sub.f value: 7 minutes, 
Mass spectrum [(+) FAB in thioglycerol]: (M+H).sup.+ =614. 
EXAMPLE 2 
With efficient stirring, 16.80 g (48 mmol) of manganese(III) 
acetylacetonate are added to 26.40 g (40 mmol) of desferrioxamine B 
mesylate in 400 ml of water and the mixture is efficiently stirred for 2 
hours at room temperature. Working up as in Example 1 gives a deep green, 
slightly hygroscopic manganese(III) oxamine B mesylate that contains 0.5 
mol of water. 
C.sub.25 H.sub.45 MnN.sub.6 O.sub.8.CH.sub.3 SO.sub.3 H.1/2H.sub.2 O 
(717.708): Cal. C 43.51, H 7.02, N 11.71, S 4.46, Mn 7.66. Found: C 43.38, 
H 7.02, N 11.50, S 4.29, Mn 8.16. 
HPLC (conditions as in Example 1): R.sub.f value=5.5 minutes 
Solubilities: readily soluble in water. 
EXAMPLE 3 
In accordance with the procedure described in Example 2, but stirring for 
only 1 hour and digesting the lyophilisate with diethyl ether/n-heptane, 
white, hygroscopic aluminiumoxamine B mesylate that contains 1.5 mol of 
water is obtained from 13.12 g (20 mmol) of desferrioxamine B mesylate in 
250 ml of water and 7.78 g (24 mmol) of aluminium acetylacetonate in 200 
ml of ethyl acetate. 
C.sub.25 H.sub.45 AlN.sub.6 O.sub.8.CH.sub.3 SO.sub.3 H.1,5H.sub.2 O 
(707.773): Cal: C 44.12, H 7.40, N 11.87, S 4.53, Al 3.81. Found: C 44.11, 
H 7.29, N 11.65, S 4.47, Al 3.70. 
HPLC (conditions as in Example 1): R.sub.f value=7 minutes. 
Solubilities: readily soluble in water. 
EXAMPLE 4 
In accordance with the procedure of Example 3, but without digestion of the 
lyophilisate with diethyl ether/n-heptane, white, slightly hygroscopic 
indiumoxamine B mesylate is obtained from 6.56 g (10 mmol) of 
desferrioxamine B mesylate in 100 ml of water and 4.94 g (12 mmol) of 
indium(III) acetylacetonate in 100 ml of ethyl acetate. 
C.sub.25 H.sub.45 InN.sub.6 O.sub.8.CH.sub.3 SO.sub.3 H (768.593): Cal. C 
40.63, H 6.43, N 10.93. Found: C 40.50, H 6.40, N 10.90. 
Mass spectrum [(+) FAB, thioglycerol]: (M+H).sup.+ =673. 
HPLC: column: Hypersil ODS, 5 .mu.m, 120.times.4.6 mm. systems: solution 
A=2.5 mmol of phosphate buffer pH 3.0; solution B=20% of solution A and 
80% of acetonitrile. 
______________________________________ 
Gradient: 
Minutes % A % B flow: ml/min 
______________________________________ 
0 100 0 2.3 
10 60 40 2.3 
12 0 100 2.3 
15 100 0 2.3 
______________________________________ 
R.sub.f value: 9 minutes, 
Solubilities: readily soluble in water and DMSO. 
EXAMPLE 5 
In accordance with the procedure described in Example 4, white, slightly 
hygroscopic galliumoxamine B mesylate is obtained from 3.28 g (5 mmol) of 
desferrioxamine B mesylate in 50 ml of water and 2.20 g (6 mmol) of 
gallium(III) acetylacetonate in 50 ml of ethyl acetate. 
C.sub.25 H.sub.45 GaN.sub.6 O.sub.8.CH.sub.3 SO.sub.3 H (723.493): Cal. C 
43.16, H 6.83, N 11.62. Found C 43.1, H 6.8, N 11.5. 
Mass spectrum [(+) FAB, thioglycerol]: (M+H).sup.+ =627. 
HPLC (conditions as in Example 4): R.sub.f -value=7.3 minutes. 
Solubilities: in water--30%, in DMSO--20%, in polyethylene glycol 400--2%. 
EXAMPLE 6 
A solution of 5.29 g (15 mmol) of iron(III) acetylacetonate in 300 ml of 
ethyl acetate is added to a suspension of 5.26 g (10 mmol) of 
desferrioxamine E in 500 ml of water, and the mixture is efficiently 
stirred for 5 hours at room temperature. The aqueous phase is then 
extracted repeatedly with ethyl acetate and then lyophilised to give 
ferrioxamine E. 
HPLC (conditions as in Example 11): R.sub.f value=3.92 minutes (educt: 4.70 
minutes). 
C.sub.27 H.sub.45 FeN.sub.6 O.sub.9.2,5H.sub.2 O (698.58): Cal: C 46.42, H 
7.21, Fe 7.99, N 12.03. Found: C 46.35, H 7.15, Fe 8.02, N 11.77. 
Mass spectrum [(+) FAB in thioglycerol]: (M+H).sup.+ =654. 
Solubility: in water 30%, in DMSO 20%, in polyethylene glycol 400 2%. 
EXAMPLE 7 
In accordance with the procedure described in Example 6, ferrithiocine is 
obtained from a suspension of 4.76 g (20 mmol) of desferrithiocine (free 
acid) in 200 ml of water and 7.00 g (20 mmol) of manganese(III) 
acetylacetonate in 300 ml of ethyl acetate after stirring for 6 hours. 
R.sub.f value=0.50 (methylene chloride/methanol/water=130:50:8), for 
comparison: R.sub.f of desferrithiocine=0.40. 
Solubility: readily soluble in water. 
EXAMPLE 8 
In accordance with the procedure of Example 7, green manganese thiocine is 
obtained from a suspension of 4.76 g (20 mmol) of desferrithiocine (free 
acid) in 200 ml of water and 7.00 g (20 mmol) of manganese(III) 
acetylacetonate in 300 ml of ethyl acetate. 
R.sub.f =0.45 (methylene chloride/methanol/water=130:50:8) for comparison: 
R.sub.f of desferrithiocine=0.40. 
EXAMPLE 9 
14.10 g (40 mmol) of iron(III) acetylacetonate in 400 ml of diethyl ether 
are added to a suspension of 9.52 g (40 mmol) of desferrithiocine and 
10.41 g (40 mmol) of desferrithiocine sodium salt in 400 ml of water, and 
the mixture is efficiently stirred for 1 hour at room temperature. The red 
aqueous phase is extracted repeatedly with diethyl ether and then 
lyophilised to give ferrithiocine sodium salt. 
C.sub.20 H.sub.16 FeN.sub.4 NaO.sub.6 S.sub.2.2H.sub.2 O (587.369): Cal: C 
40.90, H 3.43, N 9.54, S 10.92. Found: C 41.12, H 3.47, N 9.66, S 11.15. 
EXAMPLE 10 
5.29 g (15 mmol) of iron(III) acetylacetonate in 500 ml of ethyl acetate 
are added to a suspension of 3.78 g (30 mmol) of 
3-hydroxy-2-methyl-4-pyrone (maltol) in 500 ml of water, and the mixture 
is efficiently stirred for 3 hours at room temperature. The aqueous phase 
is then extracted repeatedly with ethyl acetate and thereafter lyophilised 
to give the iron(III) maltol complex. 
C.sub.18 H.sub.15 FeO.sub.9 (431.163): Cal: C 49,96, H 3.57, Fe 12.91, 
H.sub.2 O 0.37. Found: C 49,77, H 3.64, Fe 13.10, H.sub.2 O 0.37. 
HPLC (conditions as in Example 1, but gradient after 14 minutes, 100% of A 
and 0% of B): 4.85 minutes (educt: 3.75 minutes), solubilities: 10% in 
DMSO, 3% in water. 
EXAMPLE 11 
3.2 g (9 mmol) of iron(III) acetylacetonate in 200 ml of ethyl acetate are 
added to a suspension of 1.5 g (7.5 mmol) of L-mimosine 
[(L)-2-amino-3-[3-hydroxypyrid-4-on-1-yl]propionic acid q.v. The Merck 
Index, 10th Edition, monograph number 6065] in 500 ml of water, and the 
mixture is efficiently stirred for 3 hours at room temperature. The 
aqueous phase is then extracted repeatedly with altogether 2000 ml of 
ethyl acetate and then lyophilised to give the iron(III) mimosine complex. 
C.sub.24 H.sub.27 FeN.sub.6 O.sub.12.2H.sub.2 O (683.393): Cal: C 42.18, H 
4.57, N 12.30. Found: C 41.95, H 4.56, N 12.00. 
HPLC (apart from the gradients given below, the conditions are as indicated 
in Example 1): 
______________________________________ 
Gradient: 
Minutes % A % B flow: ml/min 
______________________________________ 
0 100 0 2.3 
12 0 100 2.3 
14 100 0 2.3 
15 100 0 2.3 
______________________________________ 
R.sub.f -value: 0.54 minutes (educt: 0.62 minutes) 
Solubility: ca. 5% in water. 
EXAMPLE 12 
5.29 g (15 mmol) of iron(III) acetylacetonate in 300 ml of ethyl acetate 
are added to a suspension of 4.17 g (30 mmol) of 
3-hydroxy-1,2-dimethyl-4-pyridone (described in European patent 93 498, 
Example 3) in 300 ml of water, and the mixture is efficiently stirred for 
3 hours at room temperature. The aqueous phase is then extracted 
repeatedly with ethyl acetate and subsequently lyophilised. For further 
purification, the lyophilisate is digested in 300 ml of ethyl acetate to 
give the iron(III)-3-hydroxy-1,2-dimethyl-4-pyridone complex. 
C.sub.21 H.sub.24 FeN.sub.3 O.sub.6.1,3H.sub.2 O (493.709): Cal: C 51.09, H 
5.43, N 8.51. Found: C 51.03, H 5.38, N 8.34. 
HPLC (conditions as in Example 11): R.sub.f =4.10 minutes (educt: 13.63 
minutes). 
Solubility: 10% in DMSO, 20% in water. 
EXAMPLE 13 
4.3 g (12 mmol) of iron(III) acetylacetonate in 40 ml of ethyl acetate are 
added to 2.0 g (10 mmol) of 3-hydroxy-2-methyl-N-propyl-4-pyridone 
hydrochloride (described in European patent 93 498, Example 4) in 400 ml 
of water, and the mixture is efficiently stirred for 3 hours at room 
temperature. The aqueous phase is then extracted repeatedly with altogther 
3000 ml of ethyl acetate and subsequently lyophilised to give the 
iron(III)-3-hydroxy-2-methyl-N-propyl-4-pyridone hydrochloride complex. 
HPLC (conditions as in Example 1): R.sub.f =6.51 minutes (educt: 6.33 
minutes) 
Solubility: 10% in DMSO, 20% in water. 
EXAMPLE 14 
In accordance with the procedure described in Example 12, 3.44 g (10 mmol) 
of rhodotorula acid (sold by Sigma Chem. Company, P.O. Box 14508, St. 
Louis, Mo., USA) in 500 ml of water are reacted with 3.53 g (10 mmol) of 
iron(III) acetylacetonate in 500 ml of ethyl acetate. Working up as 
described in Example 12 gives the iron(III) rhodotorula acid complex. 
C.sub.42 H.sub.66 Fe.sub.2 N.sub.12 O.sub.18.1H.sub.2 O (1156.77): Cal: C 
43.61, H 5.93, N 14.53. Found: C 43.68, H 5.84, N 14.41. 
HPLC (conditions as in Example 11): R.sub.f =1.22 minutes (educt: 3.22 
minutes) 
Solubility: 10% in DMSO, 5% in water.