99mTc Complexes Research Articles

Ligand-exchange reaction of labile “3+1” 99mTc(V) complexes with SH group-containing proteins

The reactivity of labile 3+1 mixed-ligand 99mTc complexes of the type [ 99mTcO(SES)(RS)] with SES being a tridentate dithiol ligand and glutathione or dimethylcysteamine as monodentate ligands RSH towards proteins was investigated in vitro and in vivo. It was found that the complexes undergo reversible transchelation reactions with SH group-containing components of blood such as albumin or haemoglobin. High labelling yields were obtained when 3+1 complexes with the tridentate SSS ligand were used. The biodistribution of blood proteins labelled by ligand-exchange reaction with the [ 99mTcO(SSS)] or [ 99mTcO(SNMeS)] core was studied and compared with the in vivo distribution of the labile 3+1 complexes containing glutathione as monodentate ligand.

Use of myocardial imaging agents for tumour diagnosis--a success story?

The search for new radiopharmaceuticals for tumour diagnosis usually proceeds on the basis of rational concepts drawing on the latest advances in molecular biology. Using this approach, radioactive peptide hormones, antibodies and oligonucleotides have been developed that are used increasingly in nuclear medicine for diagnostic and therapeutic purposes. This article, however, focusses on a group of radiopharmaceuticals whose use in tumour diagnosis was not the outcome of a methodical development programme but rather the result of a chance discovery. These radiopharmaceuticals, thallium-201 and technetium-99m labelled 2-methoxyisobutylisonitrile (MIBI), tetrofosmin and furifosmin, were first developed through extensive research efforts for cardiac imaging, but during their worldwide application for myocardial scintigraphy they were accidentally found to accumulate in tumours. Intensive studies were then begun on cell cultures in an attempt to discover the cause of their uptake into tumours. The aim was to compare the effectiveness of the radiopharmaceuticals for tumour diagnosis in a range of indications and to investigate the various mechanisms by which they are taken up into tumours. While the more favourable radiophysical properties of 99mTc-MIBI render it superior to 201Tl for many diagnostic purposes, neither 99mTc-tetrofosmin nor 99mTc-furifosmin has yet proved suitable for clinical routine examinations, although the former has found limited application. In the case of 99mTc complexes, the breakthrough came with the experimental finding that these substances are substrates of P-glycoprotein, a product of the human multidrug resistance gene (MDR1). The concentration of 99mTc complexes in tumour cells is a function of a passive, membrane potential-dependent influx into and a P-glycoprotein-controlled efflux out of the tumour cell. Preliminary studies suggest that in vivo detection of MDR may even be possible. There is also evidence that the P-glycoprotein-mediated transport system can be blocked competitively. However, it will be some time before a system can be developed for detection of MDR on a routine basis.

Glutathione Interaction with SNS/S Mixed-Ligand Complexes of Oxorhenium(V): Kinetic Aspects and Characterization of the Products

A series of oxorhenium(V) SNS/S mixed-ligand complexes [ReO(Ln/L)] carrying different types of tridentate ligands (Ln) and the same monodentate coligand (L) [L = C6H5S, L1 = C2H5N(CH2CH2S)2 (1), L2 = (C2H5)2NCH2CH2N(CH2CH2S)2 (2), L3 = C2H5SCH2CH2N(CH2CH2S)2 (3), and L4 = 2,6-(SCH2)2NC5H3 (4)] have been synthesized and characterized by spectroscopic methods and elemental analyses. X-ray structure determination was performed for complexes 3 and 4. Complex 3 adopts the expected distorted trigonal bipyramidal geometry around the metal in a syn configuration, while complex 4, due to the aromatic character of the nitrogen of the SNS donor-atom set, exhibits a distorted square pyramidal geometry. The interaction of complexes 1−4 with glutathione (GSH) was studied by high-performance liquid chromatography, revealing the rapid formation of the respective daughter complexes 5−8, wherein the L coligand has been substituted by GS. The daughter complexes 5−8 have been characterized by ES-MS and 2D NMR spectroscopy. Kinetic aspects of the interaction of complexes 1−3 with GSH have been studied by isothermal titration microcalorimetry providing direct measurements of the interaction rate constants as well as of the total enthalpy change. The reaction of complex 1 exhibits the slowest rate and that of complex 2 the fastest. This is in agreement with previously reported trends for analogous 99mTc complexes.

The synthesis and evaluation of the 99mTc complexes of cyclic RGD-peptide antagonists of the integrin alphavbeta3

The synthesis and evaluation of the 99mTc complexes of cyclic RGD-peptide antagonists of the integrin alphavbeta3

Stability studies on 99mTechnetium(III) complexes with tridentate/monodentate thiol ligands and phosphine (‘3+1+1’ complexes)

The preparation and characterisation of 3+1+1 technetium complexes of the general formula [Tc(SES)(RS)(PMe 2Ph)] ( SES= tridentate dithiol ligand , E=S, O, NMe; RSH= monothiol ligand ) at the n.c.a. level is described. The Tc(III) complexes are prepared in a one-step procedure starting from pertechnetate in yields of 85–95% of radiochemical purity. A comparison of their chromatographic data with the fully characterised 99Tc complexes indicate the identity of the investigated compounds. Stability studies show that the 99mTc complexes undergo some alteration in solution. They are oxidised to the 3+1 oxotechnetium (V) complexes and/or decompose in aqueous solution. In challenge experiments performed with glutathione, exchange of the monothiolato ligand occurs in the same manner as known for the 3+1 complexes.

Oxorhenium and oxotechnetium [SNS/S] mixed ligand complexes having a pendant diisopropylaminoethyl-group. Synthesis, characterization and biodistribution studies

A novel SNS tridentate ligand, the N,N-bis(2-mercaptoethyl)-N′,N′-diisopropylethylenediamine was synthesized and the corresponding oxorhenium and oxotechnetium “mixed ligand” complexes using 3 monodentate aromatic thiols as coligands were prepared and characterized. Rhenium complexes were obtained as crystals with high yield by substitution of ligand and coligand on the trichlorobis(triphenylphosphine)-rhenium(V) oxide using a molar ratio ligand:coligand:precursor of 1. Characterization was performed by HPLC analysis, UV-vis and IR spectra, elemental analysis and X-ray diffraction. Results were consistent with the ReOLC structure. The complexes adopted a distorted trigonal bipiramidal geometry and were neutral due to ionization of all sulphur atoms upon complexation. Consequently 99mTc complexes were also prepared and evaluated in mice as potential brain imaging agents. Labelling was performed by substitution using 99mTc-glucoheptonate as precursor. The labelling yield was over 85% and the radiochemical purity of the complexes over 99%. Biodistribution in mice demonstrated high uptake and retention in brain. However comparison with previously reported “mixed ligand” complexes showed that the incorporation of the diisopropylaminoethyl group in the SNS/S backbone is not enhancing the biological characteristics of this type of complexes. Copyright © 2000 John Wiley & Sons, Ltd.

Synthesis and biological evaluation of the four isomers of technetium-99m labeled ethylenecysteamine cysteine ( 99mTc-ECC), the mono-acid derivative of 99mtc- L,L-ethylenedicysteine

A few years ago 99mTc-ethylenedicysteine ( 99mTc- L,L-EC) had been proposed as an interesting substitute for technetium-99m labeled mercaptoacetyltriglycine (MAG3) as renal function tracer agent. It possesses in its structure two carboxylate functions and is in this respect different from other renal tracers such as 99mTc- N,N′-bis-(mercaptoacetyl)-2,3-diaminopropionate ( 99mTc-CO 2DADS), 99mTc-MAG3, and Hippuran, which have only one carboxylic group. To study whether both carboxylic acid groups of 99mTc- L,L-EC contribute to the efficient renal handling of this compound we synthesized and biologically evaluated the technetium-99m labeled isomers of L- and D-ethylenecysteamine cysteine (ECC), the mono-acid derivative of 99mTc- L,L-EC. Labeling of L-ECC or D-ECC with 99mTc using a direct or exchange labeling method yields for each of them two diastereomeric 99mTc complexes (A and B, in the order of elution during reversed phase high performance liquid chromatography) in relative amounts depending on the pH during labeling. In mice, all four isomers of 99mTc-ECC ( LA, LB, DA, and DB) are cleared rapidly from the blood, mainly by the renal system. The isomers LB and DB show the most efficient renal handling, but none of the mono-acid derivatives has a urinary excretion rate as high as that of 99mTc- L,L-EC. The renal handling of the isomers of 99mTc-ECC is partly due to tubular secretion because the urinary excretion of these compounds is significantly lower in mice pretreated with probenecid. In the baboon, isomers DA and DB show a plasma clearance comparable to that of 99mTc- L,L-EC. The plasma clearance of isomers LA and LB is lower but still comparable to or higher than that of 99mTc-MAG3. In a human volunteer, isomer DB shows a plasma clearance rate only slightly lower than that of 99mTc- L,L-EC. Thus, it appears that the presence of one carboxylate in 99mTc-EC-like compounds can be sufficient for efficient renal handling. However, it is also evident that the configuration at the chiral carbon atom and the orientation of the oxotechnetium core determine in a significant way the biological characteristics.

A multinuclear NMR study of the complexation of W(VI) with meso-2,3-dimercaptosuccinic acid (DMSA)

Meso-2,3-dimercaptosuccinic acid (DMSA), which is used as an antidote for heavy metal poisoning and in complexes of 99mTc for diagnostic purposes, forms several complexes with tungsten(VI) in aqueous solutions, as found by 1H, 13C, 17O and 183W NMR spectroscopy. In the pH range ∼4–7, there are four complexes in which the acid acts as a bidentate ligand through one carboxyl group and the adjacent sulfhydryl group (a dominant 2:2 species and three 1:2 metal–ligand isomers are proposed) and 2:1 complexes in which the ligand is twisted in order to use the four binding groups. It is proposed that in both the 2:2 and 2:1 cases the S atoms bridge the two W atoms. At lower pH, the acid is again predominantly a tetradentate ligand in m:n associations with the metal (m>n).

Syntheses and radiolabeling of cysteine-oximes and pharmacological behaviour of their 99mTc complexes

Synthesis of two novel ligands using 2-oximino-butan-3-one and l-ethyl cysteinate is described. The synthetic procedure involved the formation of Schiff's base by the condensation of the amino group of l-ethyl cysteinate with the carbonyl group of 2-oximino-butan-3-one to provide the ligand I, N′(butan-2-enyl-3-oximino)ethyl cysteinate, followed by reduction of the Schiff's base with sodium borohydride to ligand II, N′(3-oximinobutyl)ethyl cysteinate. The ligands were characterised by NMR spectroscopy. Complexation studies with 99mTc were carried out using stannous tartrate as the reducing agent. The complexes were characterised by paper chromatography, thin layer chromatography and paper electrophoresis techniques. The complexes are formed in high yields when the reactions were carried out at pH 7–9. The 99mTc complex with ligand I is formed instantaneously while the 99mTc complex with ligand II is formed at a slower rate. The complexes were found to be neutral but the lipophilicity of the complex with ligand I was higher than that of the complex of ligand II. The stability of the complex with ligand I was relatively poor as compared to that of the complex with ligand II. Biodistribution studies of the 99mTc complexes of ligand I and II showed rapid blood clearance with hepatobiliary uptake. Renal excretion of the complex of ligand II was more than that observed for the complex of ligand I. The complexes did not show significant uptake in brain in spite of their favourable properties such as neutrality, lipophilicity and structural similarity with both ECD and HMPAO.

Study on the formation of mixed ligand oxorhenium and oxotechnetium complexes (SNS/S combination)

Theoretically, several complexes can be formed during the reaction between the tridentate aminedithiol ligand EtN(CH 2CH 2SH) 2, L1H 2, the monodentate thiol p-ClC 6H 4SH, L2H, and the Re VOCl 3(PPh 3) 2. Three main possibilities are: (i) neutral mixed ligand complexes ReOL1L2, the syn isomer, complex 1 and the anti isomer, complex 2; (ii) binuclear complex of the tridentate ligand, (ReO) 2(L1) 3, complex 3 and (iii) anionic complex of the monothiol [ReO(L2) 4] −, complex 4. When a mixture of L1H 2/L2H, 1/1 ratio, is applied, the major product of the reaction is the syn isomer 1. A small amount of the anti isomer 2 is also isolated (yield <2%) while none of the complexes 3 and 4 are formed under the above reaction conditions. The oxorhenium complexes 3 and 4 have been synthesized by the reaction of L1H 2 or L2H respectively with the precursor ReOCl 3(PPh 3) 2. The crystal structures of 1, 3, and 4 are determined by X-ray crystallography. The corresponding 99mTc complexes have been prepared by exchange reaction using 99mTc-glucoheptonate as precursor. Similarly the major reaction product is the syn isomer, complex 1′, while none of the other complexes are formed during the reaction at tracer level. The above studies demonstrate that simultaneous action of a tridentate SNS ligand and a monodentate thiol in equimolar quantities on Re VOCl 3(PPh 3) 2 or 99mTc-glucoheptonate leads to a single rhenium or technetium-99m species, the syn MOL1L2.

A ‘preformed chelate approach’ model for coupling amine-modified rhenium and technetium ‘3+1’ mixed ligand complexes to carboxylate residues: Crystal structure of ReO[CH 3SCH 2CH 2N(CH 2CH 2S) 2][ p-SC 6H 4NH 2] and ReO[CH 3SCH 2CH 2N(CH 2CH 2S) 2][ p-SC 6H 4NHCOC 6H 5

Selected ‘3+1’ mixed ligand oxorhenium and oxotechnetium complexes containing the SNS/S donor atom set have been modified by introduction of a bifunctional amine anchor on the p-position of the thiophenolato monodentate ligand. A representative series of complexes containing several tridentate ligands was prepared both at macromolar (Re complexes) and nanomolar ( 99mTc complexes) amounts. Coupling of these complexes to activated carboxylate groups was performed according to the ‘preformed chelate approach’ using benzoyl chloride as a model molecule. Coupling yields were high both at nanomolar and millimolar metal concentration, as revealed by high-performance liquid chromatographic analysis of 99mTc and Re species adopting parallel radiometric and photometric detection modes. All Re compounds have been characterized by classical analytical methods. In addition, the structures of representative parent ReO[CH 3SCH 2CH 2N(CH 2CH 2S) 2][ p-SC 6H 4NH 2] and daughter ReO[CH 3SCH 2CH 2N(CH 2CH 2S) 2][ p-SC 6H 4NHCOC 6H 5] complexes were solved by X-ray crystallography. Both compounds adopt a distorted trigonal bipyramidal geometry around rhenium, wherein the oxo group and the sulfur atoms of the SNS ligand occupy the equatorial plane and the nitrogen atom and the sulfur of the monothiol are located at the apical positions trans to each other.

The integrity of the disulfide bond in a cyclic somatostatin analog during 99mtc complexation reactions

Recent development of a variety of thiol-free chelating agents has facilitated the design of 99mTc-labeled somatostatin analogs suitable for receptor imaging of somatostatin-positive tumors. However, it remains ambiguous whether the disulfide bonds in cyclic peptides are stable during 99mTc complexation reactions, and contradictory results have been reported regarding the integrity of disulfide bonds in cyclic somatostatin analogs. To estimate the stability of the disulfide bond in a synthetic somatostatin analog at low peptide concentrations, [ 125I]I-RC-160, in which radioiodine was incorporated into the 3-Tyr residue, was synthesized and the integrity of the disulfide bond of the peptide was investigated in the presence of reducing agents such as ascorbic acid, dithionite, and stannous ions. The disulfide bond in [ 125I]I-RC-160 remained stable in the presence of ascorbic acid in boiling water. The disulfide bond was also stable when treated with stannous ions at concentrations sufficient to reduce 99mTc for complexation with a thiol-free chelating agent, bis(hydroxamamide) analog when the 99mTc complexation reaction was performed at room temperature. However, the disulfide bond of [ 125I]I-RC-160 was slightly cleaved in the presence of a small amount of stannous ions when the reaction was performed in boiling water. Treatment of [ 125I]I-RC-160 with dithionite in boiling water markedly reduced the disulfide bond of the parental peptide. These findings indicated that synthetic somatostatin analogs may be labeled with 99mTc with stannous ions as the reducing agent without impairing their structure after conjugation of thiol-free chelating agents that provide 99mTc chelates under mild reaction conditions.

Preparation and characterization of technetium complexes with Schiff base and phosphine coordination. 1. complexes of technetium-99g and -99m with substituted acac 2en and trialkyl phosphines (where acac 2en = N,N′-ethylenebis[acetylacetone iminato

A series of 23 technetium(III) complexes of the type [TcL(PR 3) 2]+, where L represents a tetradentate Schiff base ligand in the equatorial plane and PR 3 represents the axial phosphine ligands, are reported. Full ligand syntheses and characterizations are included. The technetium complexes were prepared with 99mTc to study the organ distribution in guinea pigs at 5 and 60 min postinjection. Four prototypical complexes of the series were also prepared with either 99gTc or 99gTc/99mTc (designated as carrier-added) to allow macroscopic characterization. Equivalence of the 99gTc and 99mTc complexes was demonstrated by dual detection high performance liquid chromatography (HPLC) techniques. The development of a one-step preparation from the standard two-step method is discussed for some complexes. Biodistribution data are related to structure and lipophilicity. None of the complexes in the series exhibited a tendency for in vivo reduction. Myocardial uptake was favorable for a number of complexes. The optimal agent from this series for further imaging development was chosen based on myocardial uptake, rapid blood and liver clearance, and ability to be formulated as a one-step kit.

The potential for myocardial imaging with hypoxia markers

Direct "hot spot" imaging of myocardial tissue hypoxia is potentially of great clinical importance because available noninvasive approaches for the detection of myocardial ischemia have generally been based on the detection of flow heterogeneity or identification of regional alterations of myocardial metabolism. These existing approaches provide only an indirect assessment of regional myocardial ischemia, and may be affected by either sympathetic activation or substrate availability. The assessment of tissue oxygenation with hypoxic compounds may be the best indicator of the balance of flow and oxygen consumption. These compounds may provide a means of identifying dysfunctional chronically ischemic but viable "hibernating" myocardium and find a critical place in the assessment of angiogenesis. Nitroimidazole compounds hold promise for positive imaging of hypoxia in the heart. However, refinement of these compounds is needed to improve target specificity. The potential of technetium-99m (Tc99m) complexes derived from removal of the nitroimidazole moiety from a nitroimidazole-containing ligand is interesting and warrants further investigation. Experimental studies support the possibility of identifying myocardial hypoxia with the positron-emitting compound F18-fluoromisonidazole noninvasively. The potential of a Tc99m labeled nitroimidazole for positive imaging of myocardial ischemia is tremendous because single-photon imaging is more widely available. The true clinical potential of these nitroimidazole compounds can only be defined with future experimental and clinical studies. Ideally, these studies should include comparisons of tracer uptake with independent measures of regional ischemia or measures of oxygen tension, potentially using magnetic resonance imaging.

Synthesis and Binding Affinities of Novel Re-Containing 7alpha-Substituted Estradiol Complexes: Models for Breast Cancer Imaging Agents.

The diagnosis and staging of breast cancer could be improved by the development of imaging radiopharmaceuticals that provide a noninvasive determination of the estrogen receptor status in the tumor cells. Toward this goal, we have synthesized a number of novel Re-containing 7alpha-substituted estradiol complexes. The introduction of the 7alpha side chain involves the alkylation of tetrahydropyranyloxy-protected 6-keto estradiol. The methods used to introduce the rhenium metal involve "3 + 1" and "4 + 1" mixed ligand complexes (2a-c and 5, respectively), tricarbonyl dithioether complexes (3), and the cyclopentadienyltricarbonylmetal organometallic system (4ab, 6, 7). These complexes showed binding affinities for the estrogen receptor (as high as 45% for the "3 + 1" complex 2c) when compared to the native ligand estradiol. The polarity of some complexes (4ab) was modified to improve biodistribution properties by introducing (poly)ether linkages into the 7alpha side chain (6, 7). These complexes provide a further refinement of our understanding of ligand structure-binding affinity correlations for the estrogen receptor, and they furnish the synthetic groundwork for the synthesis of the analogous Tc-99m complexes for evaluation as breast tumor imaging agents.

Synthesis of new N2S ligands, preparation of 99mTc complexes and their preliminary biodistribution in mice

Two new N 2 S ligands of MPBDA (N-(2-mercapto-propyl)-1,2-benzenediamine) and MEBDA (N-(2-mercapto-ethyl)-1,2-benzenediamine) were synthesized, and their lipophilic complexes of 99m Tc-MPBDA and 99m Tc-MEBDA were prepared in high yield (>92%) by stannous reduction of 99m TcO 4 - . Effects of pH, reaction temperature and time on the formation of 99m Tc complexes were investigated. Potential use of 99m Tc-MPBDA and 99m Tc-MEBDA in cerebral and myocardial imaging were evaluated in mice. High uptakes are demonstrated in both brain and heart, and residence times within heart are long. Two minutes following i.v. Administration, 1.85%ID of 99m Tc-MPBDA and 1.49%ID of 99m Tc-MEBDA appear in brain, and 1.64%ID of 99m Tc-MPBDA and 1.63%ID of 99m Tc-MEBDA are in heart. At 1hr after injection, 1.17%ID and 1.26%ID of 99m Tc-MPBDA remain respectively in brain and heart, and 0.67%ID and 1.18%ID of 99m Tc-MEBDA remain in brain and heart respectively. The activity in blood clears rapidly and the clearance half-life is less than 15 minutes. The properties of 99m Tc-MPBDA make it a potential useful agent for cerebral and myocardial perfusion imaging.

Radiochemical studies of 99mTc complexes of modified cysteine ligands and bifunctional chelating agents

The synthesis of four novel ligands using the amino-acid cysteine and its ethyl carboxylate derivative is described. The synthetic method involves a two-step procedure, wherein the intermediate Schiff base formed by the condensation of the amino group of the cysteine substrate and salicylaldehyde is reduced to give the target ligands. The intermediates and the final products were characterized by high resolution nuclear magnetic resonance spectroscopy. Complexation studies of the ligands with 99mTc were optimized using stannous tartrate as the reducing agent under varying reaction conditions. The complexes were characterized using standard quality control techniques such as thin layer chromatography, paper electrophoresis, and paper chromatography. Lipophilicities of the complexes were estimated by solvent extraction into chloroform. Substantial changes in net charge and lipophilicity of the 99mTc complexes were observed on substituting the carboxylic acid functionality in ligands I and II with the ethyl carboxylate groups (ligands III and IV). All the ligands formed 99mTc complexes in high yield. Whereas the complexes with ligands I and II were observed to be hydrophilic in nature and not extractable into CHCl 3, ligands III and IV resulted in neutral and lipophilic 99mTc complexes. The 99mTc complex with ligand III was not stable and on storage formed a hydrophilic and nonextractable species. The biodistribution of the complexes of ligands I and II showed that they cleared predominantly through the kidneys, whereas the complexes with ligands III and IV were excreted primarily through the hepatobiliary system. No significant brain uptake was observed with the 99mTc complexes with ligands III and IV despite their favorable properties of neutrality, lipophilicity, and conversion into a hydrophilic species. These ligands offer potential for use as bifunctional chelating agents.

Synthesis of new N2S ligands, preparation of 99mTc complexes and their preliminary biodistribution in mice

Two new N2S ligands of MPBDA (N-(2-mercapto-propyl)-1,2-benzenediamine) and MEBDA (N-(2-mercapto-ethyl)-1,2-benzenediamine) were synthesized, and their lipophilic complexes of 99mTc-MPBDA and 99mTc-MEBDA were prepared in high yield (>92%) by stannous reduction of 99mTcO4−. Effects of pH, reaction temperature and time on the formation of 99mTc complexes were investigated. Potential use of 99mTc-MPBDA and 99mTc-MEBDA in cerebral and myocardial imaging were evaluated in mice. High uptakes are demonstrated in both brain and heart, and residence times within heart are long. Two minutes following i.v. Administration, 1.85%ID of 99mTc-MPBDA and 1.49%ID of 99mTc-MEBDA appear in brain, and 1.64%ID of 99mTc-MPBDA and 1.63%ID of 99mTc-MEBDA are in heart. At 1 hr after injection, 1.17%ID and 1.26%ID of 99mTc-MPBDA remain respectively in brain and heart, and 0.67%ID and 1.18%ID of 99mTc-MEBDA remain in brain and heart respectively. The activity in blood clears rapidly and the clearance half-life is less than 15 minutes. The properties of 99mTc-MPBDA make it a potential useful agent for cerebral and myocardial perfusion imaging Copyright © 1999 John Wiley & Sons, Ltd.

On the synthesis, isolation, and radiochemical studies for the preparation of in-house kits for 99mTc- meso- and d,l-HMPAO: a few additional observations

The simple procedure documented for the synthesis of d,l-hexamethyl propylene amineoxime ( d,l-HMPAO), the widely used radiopharmaceutical precursor for cerebral perfusion studies, has provided no clue to the inherent difficulties associated with the isolation of this desired isomer in moderate yields from the diastereomeric mixture. In addition, determination of the diastereomeric purity of the isolated fractions with the help of suitable analytical techniques has posed a major challenge. Herein, we report the protocol standardized for the purification and isolation of d,l-HMPAO in significantly improved yields from the crude diastereomeric mixture by fractional crystallization using a dual solvent system. In addition to the use of high resolution 1H-NMR, 13C-NMR as a suitable analytical tool for conclusive determination of the diastereomeric composition of HMPAO is being reported for the first time. Intermediate stages of crystallisation in the process of purification yielded a third product resulting in reduction of the yield of the desired product. Attempts made to characterize this product are discussed. Labelling of d,l-HMPAO with 99mTc was standardized in our laboratory using stannous tartrate as the reducing agent. The radiochemical studies of the meso isomer, which is also isolated in the process of crystallization in adequate amounts, have been standardized with a view to investigating its potential use for leukocyte labelling studies. The biodistribution studies of the 99mTc complexes prepared from the pure meso and d,l isomer in Swiss mice are reported. Diastereomeric forms of HMPAO were isolated in increased yields using an improved protocol by fractional crystallization involving a dual solvent system. High resolution 13C-NMR spectroscopy has been utilized to provide a conclusive analytical tool for efficient and simple screening of the diastereomeric composition. An additional compound exhibiting a different crystal habit and spectroscopic features was isolated in the process of crystallization. 99mTc complexes of both the diastereomers were standardized and used in animal biodistribution studies.

Chemistry of technetium radiopharmaceuticals 1: Chemistry behind the development of technetium-99m compounds to determine kidney function

The chemistry behind the development of technetium-99m (Tc-99m) complexes useful for determining renal (kidney) function is discussed. The design of these compounds so that they will be (1) stable in vivo, (2) actively taken up by the kidney and (3) excreted from the body without being metabolized is also discussed. Such issues as the purity of the product (>90% yield required), in vitro stability, and the requirement for ease of preparation are also mentioned. The development and chemistry of commercialized Tc-99m renal function radiopharmaceuticals are covered as are the interplay of the chemistry of Tc-99m and it macroscopic daughter isotope, Tc-99g. Basic technetium chemistry as well as renal physiology and function are also discussed briefly. An attempt is made to highlight areas where further work is needed.