Synthesis and characterization of five-coordinate rhenium(V) and technetium(V) mixed ligand bifunctional complexes carrying the SNS/S or the SNN/S donor atom set. Crystal structure of ReO{[(C2H5)2NCH2CH2N(CH2CH2S)2](p-H2N–PhS)} and ReO{[(CH2)4NCH2CH2NCH2CH2S](p-H2N–PhS)}

Synthesis and evaluation of technetium-99m labelled 1-(2-methoxyphenyl)piperazine derivative for single photon emission computed tomography imaging for targeting 5-HT1A

Quantitative changes in expression level of 5HT_1A are somewhere related to common neurological disorders such as anxiety, major depression and schizophrenia. We have designed EDTA conjugated SPECT imaging probe for localization of 5HT_1A receptor in brain. For designing SPECT probe we have employed the concept of bivalent approach and a homodimeric system with desirable pharmacokinetics of 5HT_1A imaging. ^99mTc-EDHT was also evaluated for its stability through serum stability assay and glutathione challenge experiment. Biodistribution study showed the highest accumulation of radioactivity in kidney which depicted the renal mode of excretion from the body. However in brain the uptake of 1.21% ID per gram was observed in initial 5 min of drug administration. On blocking the receptor this percent get decreased to 0.97% ID per gram. The regional distribution in brain was also performed which showed the accumulation of drug in cerebellum, cortex and hippocampus part, which are already known for 5HT_1A expression. Dynamic study in rabbit is also in support of results derived from biodistribution and blood kinetics experiment. These finding suggest that ^99mTc-EDHT holds promising place for further optimization before nuclear medicine applications in different animal species.

Synthesis, characterization and biological evaluation of novel neutral fac-M(CO)3(SNO) complexes (M=Re, 99mTc) bearing the o-methoxyphenylpiperazine moiety

The synthesis, characterization and biological evaluation of two new neutral tricarbonyl fac-M(CO)(3)(SNO) (M=Re, (99m)Tc) bearing o-methoxyphenylpiperazine as pharmacophore and S-functionalized cysteine or penicillamine as chelators are reported. Competition binding tests showed good affinity for the 5-HT(1A) receptor (8 and 54 nM for 4a and 4b, respectively). Biodistribution studies in healthy animals showed high initial blood and liver uptake, fast blood and tissue depuration and negligible brain uptake.

Rhenium Inhibitors of Cathepsin B (ReO(SYS)X (Where Y = S, py; X = Cl, Br, SPhOMe-p)): Synthesis and Mechanism of Inhibition

The synthesis of four new oxorhenium(V) complexes containing the "3 + 1" mixed-ligand donor set, ReO(SYS)X (where Y = S, py; X = Cl, Br), is described. All of the complexes tested exhibited selectivity for cathepsin B over K. Most notably, compound 6, ReO(SSS-2,2')Br (IC50(cathepsin B) = 1.0 nM), was 260 times more potent against cathepsin B. It was also discovered that complexes containing the same tridentate (SSS) ligand were more potent when the leaving group was bromide versus chloride (e.g., IC50(cathepsin B): ReO(SSS-2,2')Cl (4), 8.8 nM; ReO(SSS-2,2')Br (6), 1.0 nM). Mechanistic studies with cathepsin B showed that both compounds 2 (ReO(SpyS)(SPhOMe-p)) and 4 were active-site-directed. Compound 2 was determined to be a tight-binding, reversible inhibitor, while compound 4 was a time-dependent, slowly reversible inhibitor. The results described in this paper show that the oxorhenium(V) "3 + 1" complexes are potent, selective inhibitors of cathepsin B and have potential for the treatment of cancer.

Syntheses and oxidation of methyloxorhenium(V) complexes with tridentate ligands

Four new methyloxorhenium(V) compounds were synthesized with these tridentate chelating ligands: 2-mercaptoethyl sulfide (abbreviated HSSSH), 2-mercaptoethyl ether (HSOSH), thioldiglycolic acid (HOSOH), and 2-(salicylideneamino)benzoic acid (HONOH). Their reactions with MeReO(3) under suitable conditions led to these products: MeReO(SSS), 1, MeReO(SOS), 2, MeReO(OSO)(PAr(3)), 3, and MeReO(ONO)(PPh(3)), 4. These compounds were characterized spectroscopically and crystallographically. Compounds 1 and 2 have a five-coordinate distorted square pyramidal geometry about rhenium, whereas 3 and 4 are six-coordinate compounds with distorted octahedral structures. The kinetics of oxidation of 2 and 3 in chloroform with pyridine N-oxides follow different patterns. The oxidation of 2 shows first-order dependences on the concentrations of 2 and the ring-substituted pyridine N-oxide. The Hammett analysis of the rate constants gives a remarkably large and negative reaction constant, rho = -4.6. The rate of oxidation of 3 does not depend on the concentration or the identity of the pyridine N-oxide, but it is directly proportional to the concentration of water, both an accidental and then a deliberate cosolvent. The mechanistic differences have been interpreted as reflecting the different steric demands of five- and six-coordinate rhenium compounds.

Synthesis and characterization of mixed-ligand oxorhenium complexes with the SNN type of ligand. Isolation of a novel ReO[SN][S][S] complex

A new series of mixed-ligand oxorhenium complexes 4-9, with ligands 1-3 (L1H2) containing the SNN donor set and monodentate thiols as coligands (L2H), is reported. All complexes were synthesized using ReOCl3(PPh3)2 as precursor. They were isolated as crystalline products and characterized by elemental analysis and IR and NMR spectroscopy. The ligands 1 and 2 (general formula RCH2CH2NHCH2CH2SH, where R = N(C2H5)2 in 1 and pyrrolidin-1-yl in 2) act as tridentate SNN chelates to the ReO3+ core, leaving one open coordination site cis to the oxo group. The fourth coordination site is occupied by a monodentate aromatic thiol which acts as a coligand. Thus, three new "3 + 1" [SNN][S] oxorhenium complexes 4-6 (general formula ReO[RCH2CH2NCH2CH2S][SX], where R = N(C2H5)2 and X = phenyl in 4, R = N(C2H5)2 and X = p-methylphenyl in 5, and R = pyrrolidinlyl and X = p-methylphenyl in 6) were prepared in high yield. Complex 4 adopts an almost perfect square pyramidal geometry (tau = 0.07), while 6 forms a distorted square pyramidal geometry (tau = 0.24). In both complexes 4 and 6, the basal plane is formed by the SNN donor set of the tridentate ligand and the S of the monodentate thiol. On the other hand, the ligand 3, [(CH3)2CH]2NCH2CH2NHCH2CH2SH, acts as a bidentate ligand, probably due to steric hindrance, and it coordinates to the ReO3+ core through the SN atoms, leaving two open coordination sites cis to the oxo group. These two vacant positions are occupied by two molecules of the monodentate thiol coligand, producing a novel type of "2 + 1 + 1" [SN][S][S] oxorhenium mixed-ligand complexes 7-9 (general formula ReO[[(CH3)2CH]2NCH2CH2NHCH2CH2S][SX][SX], where X = phenyl in 7, p-methylphenyl in 8, and benzyl in 9). The coordination sphere about rhenium in 7 and 8 consists of the SN donor set of ligand 3, two sulfurs of the two monodentate thiols, and the doubly bonded oxygen atom in a trigonally distorted square pyramidal geometry (tau = 0.44 and 0.45 for 7 and 8, respectively). Detailed NMR assignments were determined for complexes 5 and 8.

Synthesis and characterization of complexes of the {ReO} core with SNS and S donor ligands

The reaction of [ReOCl(3)(PPh(3))(2)] with N,N-bis(2-mercaptoethyl)benzylamine and 4-bromobenzenethiol allowed for the isolation of [ReO{eta(3)-(SCH(2)CH(2))(2)N(CH(2)C(6)H(5))}-(eta(1)-C(6)H(4)Br-4-S)] (1). The reaction of [ReOCl(3)(PPh(3))(2)] with [(HSCH(2)CH(2))(2)N(CH(2)C(5)H(4)N)] and the appropriate thiol in chloroform treated with triethylamine has led to the isolation of a series of neutral rhenium complexes of the type [ReO{eta(3)-(SCH(2)CH(2))(2)N(CH(2)C(5)H(4)N)}(eta(1)-C(6)H(4)X-4-S)] (X = Br (2), Cl (3), F (4), and OCH(3) (5)) and [ReO{eta(3)-(SCH(2)CH(2))(2)N(CH(2)C(5)H(4)N)}(eta(1)-C(6)H(4)OCH(3)-4-CH(2)S)] (6). Likewise, under similar reaction conditions, the use of the related tridentate ligand, [(HSCH(2)CH(2))(2)N(CH(2)CH(2)C(5)H(4)N)], has led to the isolation of a series of rhenium complexes of the type [ReO{eta(3)-(SCH(2)CH(2))(2)N(CH(2)CH(2)C(5)H(4)N)}(eta(1)-C(6)H(4)X-4-S)] (X=Br (7), Cl (8), OCH(3) (9)), as well as [ReO{eta(3)-(SCH(2)CH(2))(2)N(CH(2)CH(2)C(5)H(4)N)}(eta(1)-C(6)H(4)Cl-4-CH(2)S)].0.5CH(3)(CH(2))(4)CH(3) (10). These compounds are extensions of the '3+1' approach to the synthesis of materials with the {MO}(3+) core (M=Tc and Re), which have applications in nuclear medicine. The ligands chosen allow systematic exploration of the consequences of para-substitution on the monodentate thiolate ligand [S] and of derivatization of the substituent R on the tridentate aminodithiol ligand [SNS] of the type (HSCH(2)CH(2))(2)NR. Such modifications can influence lipophilicity, charge, size and molecular weight of the complex and consequently the biodistribution.