Synthesis and Molecular Structure of a Rhenium Complex Derived from 8a-Amino-6-methyl-ergoline

Tc and Re chelates of 8alpha-amino-6-methyl-ergoline: synthesis and affinity to the dopamine D2 receptor

The influence of structural changes at the 8alpha-amino position of 8alpha-amino-6-methyl-ergoline on the lipophilicity and affinity to the D2 receptor was studied. 8alpha-amino-6-methyl-ergoline (1) was converted into the derivatives (2a-f) by mercaptoacetylation of the amino group to make it possible to prepare the rhenium and technetium complexes (3, 4a,b). Binding tests on cloned human dopamine D2 receptors show that the affinities of the coordination compounds (IC50 values between 50 and 240 nM) are less than those of the derivatives 2a-f (IC50=3-50 nM) but more than those of the parent compound 1. Biodistribution studies of the Tc complexes 4a,b performed on Wistar rats show a slow blood clearance with substantial accumulation and retention in the liver and kidneys and low brain uptake.

Synthesis and characterization of novel trigonal bipyramidal technetium(III) mixed-ligand complexes with SES/S/P coordination (E = O, N(CH3), S)

Five-coordinate oxotechnetium(V) mixed-ligand complexes [TcO(SES)(S-p-C6H4-OMe)], where SES is a tridentate dithiolato fragment of the type -S(CH2)2E(CH2)2S- (E = O, 1; E = S, 2; E = NMe, 3) are converted via reduction-substitution reactions in the presence of PMe2Ph into the corresponding five-coordinate Tc(III) complexes [Tc(SES)(S-p-C6H4-OMe)(PMe2Ph)] (E = O, 4; E = S, 5; E = NMe, 6). Rearrangement of the original square pyramidal "3 + 1" oxo species to the trigonal bipyramidal "3 + 1 + 1" Tc(III) complexes occurs by placing the three thiolate donors on the basal plane, the phosphine phosphorus, and the heteroatom of the tridentate ligand at the apexes of the bipyramid. These Tc(III) complexes are diamagnetic species, thereby allowing multinuclear NMR characterization in solution, which confirm their structures to be identical to those observed in the solid state via X-ray determinations.

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.