Organic compounds -- part of the class 532-570 series – Organic compounds – Radioactive metal containing
Patent
1999-06-04
2000-10-03
McKane, Joseph
Organic compounds -- part of the class 532-570 series
Organic compounds
Radioactive metal containing
424 153, 424 111, 514777, 514778, 534 14, 536 46, 536103, A61K 5104, A61K 4706, C07F 1300
Patent
active
061275301
DESCRIPTION:
BRIEF SUMMARY
The present invention relates in general to a method for the reduction of oxygenated compounds of rhenium and technetium and in particular to the reduction of perrhenate or pertechnetate ions.
More particularly, the invention relates to reactions for the reduction of the said oxygenated compounds which are carried out in the course of the preparation of complexes of the radionuclides .sup.186 Re, .sup.188 Re and .sup.99m Tc; in these reactions, the radionuclide perrhenate or pertechnetate ion is reduced in the presence of a reducing agent and a ligand which can form a complex with the radionuclide in its reduced oxidation state.
It is known that the radionuclides .sup.186 Re, .sup.188 Re and .sup.99m Tc have nuclear properties which make their coordination compounds suitable for application in nuclear medicine as therapeutic and diagnostic agents. Although the similarity between the chemical properties of technetium and rhenium lead one to think that a method of synthesising .sup.99m Tc radiopharmaceuticals might simply be transferred to the preparation of similar tracers of .sup.186 Re and .sup.188 Re, there are, however, fundamental differences between the properties of the two elements such as to make the possible use of rhenium compounds in nuclear medicine subject to certain conditions.
In fact, since the metals technetium and rhenium in their highest oxidation states and, in particular, the tetraoxygenated anions [MO.sub.4 ].sup.- (M=Re, Tc) are the principal starting materials for the synthesis of radiopharmaceuticals of rhenium and technetium, the result is that the reduction potentials of these species play a very important role in determining the course of the synthesis reactions. In particular, it is known that the reduction potential of the pertechnetate anion is considerably greater than that of the perrhenate anion. This indicates that, once a given synthesis has been determined, it must be much easier to prepare a technetium complex than the analogous rhenium complex.
In general, it is possible for a given synthesis adopted to obtain a radiopharmaceutical from .sup.99m Tc give a very much lower reaction yield in the case of rhenium. This conclusion is even more significant when one considers that, in the therapeutic application of rhenium compounds, the final product must have a very high radiochemical purity to reduce radiological risks.
The considerations set out above show that, to produce radiopharmaceutical preparations involving metal complexes of the radionuclides .sup.186 Re and .sup.188 Re, it is necessary to provide a method of synthesis which is very efficient at reducing the perrhenate ion.
U.S. Pat. No. 4,455,291 discloses that various "accelerators" are useful to facilitate the preparation of cationic .sup.99m Tc complexes. Accelerators include oxalic acid, tartaric acid and ascorbic acid.
U.S. Pat. No. 4,871,836 discloses that .sup.186 Re/.sup.188 Re kits can usefully contain an "accelerator (catalyst)", preferably citric acid, tartaric acid and malonic acid. Example 9 discloses a freeze-dried kit for the preparation of .sup.186 Re complexes from perrhenate which includes both citric acid and cyclodextrin in the formulation. The cyclodextrin is described as a solubiliser.
U.S. Pat. No. 5,026,913 discloses that cyclodextrins can be used as solubilisers in kits for the preparation of .sub.99m Tc radiopharmaceuticals.
U.S. Pat. No. 5,300,280 discloses a method of stabilising radiopharmaceutical kits using cyclic oligosaccharides (cyclodextrins) to inhibit oxidation and/or volatilisation of the kit components. .sup.186 Re, .sup.188 Re and .sup.99m Tc are specifically claimed.
DD 265628 discloses a method for the production of in vivo stable .sup.99m Tc pertechnetate crown ether coordination compounds, wherein crown ethers are reacted stoichiometrically with Sn.sup.2+ cations and sodium .sub.99m Tc-pertechnetate is added in a stoichiometric amount.
A specific object of the present invention is to provide a more efficient method for the reduction of oxygenated compounds of rhenium a
REFERENCES:
patent: 5300280 (1994-04-01), Derosch et al.
Alberto et al., "New organometallic technetium complexes in high and low oxidation states, " Radiochimica Acta, 63, 153-161 (1993).
Hermann et al., "Mehrfachbindungen zwischen Hauptruppenelementen und Ubergangsmetallen, " Journal of Organometallic Chemistry, 372, 351-370 (1989).
Haby et al., "Development of a stable single-vial formulation for a new technetium complex using bilayer lyophilization, " PDA Journal of Pharmaceutical Science & Technology, vol. 51, No, 2, 68-71 (1997).
Bolzati Cristina
Boschi Alessandra
Duatti Adriano
Franceschini Rodolfo
Uccelli Licia
McKane Joseph
Nycomed Amersham Sorin S.r.l.
Sackey Ebenezer
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