Neutral Re(V) and Tc(V) oxo complexes of the peptide dimethylglycyl-L-seryl-L-cysteinylglycinamide (RP294) were prepared and characterized by HPLC, spectroscopic techniques, and X-ray crystallographic analysis. The peptide was prepared as a single peptide chain using solid phase methods and characterized by HPLC and various spectroscopic techniques. The water-soluble Re(V) oxo complex of dimethylglycyl-L-seryl-L-cysteinylglycinamide [ReO(RP294)] was prepared from the reaction of the peptide with either [ReO(2)(en)(2)]Cl or ReOCl(3)(PPh(3))(2) in the presence of base. The complex exists as two isomers, the serine CH(2)OH group being in the syn oranti conformation with respect to the Re-oxo bond. The ratio of the isomers at room temperature is 1:1.1. The isomers were separated by reverse-phase HPLC, but the isolation of each isomer was complicated by their rapid interconversion in aqueous solution at room temperature. The molecular structure of the syn isomer of the Re complex was determined by X-ray crystallography. Crystals of syn-[ReO(RP294)] (C(12)H(20)N(6)O(5)ReS) are orthorhombic, of space group P2(1)2(1)2(1), with a = 6.954(1) Å, b = 8.0472(1) Å, c = 32.9183(4) Å, and Z = 4. The structure was solved by direct methods and was refined by full-matrix least-squares procedures to R = 0.0327 (R(w) = 0.0838) for 10 447 reflections with I > 2sigma(I). The Re metal was coordinated in a distorted square pyramidal geometry with the oxo moiety in the apical position. The peptide coordinated to ReO(3+) via the N(amine) atom of dimethylglycine, the S(thiolate) atom of cysteine, and the two N(amide) atoms of serine and cysteine (an N(2)N'S donor atom set). The Re atom lies approximately 0.74 Å above the distorted plane formed by the N(2)N'S donor atom set. Variable-pH (1)H NMR spectral data showed the Re complex was stable from pH 5 to 8.5. The reaction of (99)TcO(4)(-) with SnCl(2), sodium gluconate, and RP294 produced the (99)Tc(V) oxo RP294 complex, [(99)TcO(RP294)]. Like the [ReO(RP294)] complex, [(99)TcO(RP294)] also exists in the syn and anti conformations in a ratio of approximately 1:1. The (99m)Tc complex of RP294 was prepared at the tracer level from the reaction of Na[(99m)TcO(4)] with excess SnCl(2), sodium gluconate, and RP294. The (99m)Tc and Re RP294 complexes behaved similarly under identical HPLC conditions.

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Several linear N4O2 amine phenols based on triethylenetetramine (trien) were prepared and characterized by spectroscopic techniques (Hzbad = 1,10-bis(2-hydroxybenzy1)-1,4,7,10-tetraazadecane; HzClbad = 1 ,lO-bis(2hydroxy-5-chlorobenzy1)-1,4,7,10-tetraazadecane; HzBrbad = 1,10-bis(2-hydroxy-5-bromobenzy1)-1,4,7,10-tetraazadecane). These amine phenols were prepared by the in situ reduction of the corresponding Schiff bases, which were in tum derived from condensation reactions of trien with the appropriately substituted salicylaldehyde. Characterization of the amine phenols revealed two hydroxybenzyl groups connected to the trien backbone via the terminal primary amine nitrogen atoms. There are six potential sites for coordination to a metal ion: four amine nitrogens and two phenolate oxygens. Acetone adducts, prepared by refluxing the amine phenols in acetone, contained two imidazolidine rings, each of which was formed by the reaction of acetone with one inner and one terminal amine nitrogen. Monocationic metal complexes were obtained from the reactions of Ga3+ and In3+ with the N402 amine phenols in the presence of 2 equiv of base (acetate). The molecular structure of [Ga(Brbad)]-C104-(CH3)2SO (C22H32Br2ClGaN407S, MW = 761.6) was determined by X-ray methods: orthorhombic space group Pbca; a = 14.777(4), b = 22.221(5), c = 17.410(7) A; V = 5717(5) A3, 2 = 8. The structure was solved by the Patterson method and was refined by full-matrix least squares procedures to R = 4.81%, R, = 5.22% for 2230 reflections with Fo2 I 30(FO2). Ga3+ was coordinated by four neutral amine nitrogens and two anionic phenolate oxygens to give an N4O2 donor set in a distorted octahedral geometry. The two phenolate oxygen atoms and each pair of sequential N donor atoms were coordinated cis to each other. The perchlorate anion suffers from a 2-fold disorder around a pseudo-3-fold 0-C1 axis, and there is a DMSO solvate molecule. 'H NMR spectral data of the metal complexes showed rigid solution structures for all the Ga and In complexes; no evidence of fluxional behavior was observed at solution temperatures as high as 120 "C.

A new series of linear N4O2 amine phenols (H2 badd, H2 Brbadd, and H2 Clbadd) based on N,N‘-bis(3-aminopropyl)ethylenediamine (tnentn) were prepared and characterized by spectroscopic techniques. Monocationic hexadentate metal complexes with the tnentn-based amine phenols were obtained from the reactions of Ga3+ and In3+ with the linear amine phenol in the presence of a weak base (acetate). The molecular structure of [Ga(Brbadd)]ClO4 has been determined by X-ray crystallography; crystals of [Ga(Brbadd)][ClO4] (C22H30Br2ClGaN4O6) are orthorhombic:  a = 12.462(1) Å, b = 21.835(2) Å, c = 9.961(2) Å, Z = 4, space group P212121. The structure was solved by the Patterson method and was refined by full-matrix least-squares procedures to R = 0.031 (R w = 0.029) for 1924 reflections with I ≥ 3σ(I). The Ga3+ ion is coordinated in a distorted octahedral geometry by an N4O2 donor atom set. The four nitrogen atoms of the tetraamine backbone form the equatorial plane of the octahedron, and the two phenolate oxygen atoms are coordinated trans to each other. Water-soluble 1,10-bis(2-hydroxy-5-sulfonylbenzyl)-1,4,7,10-tetraazadecane (H6 Sbad 2+), 1,12-bis(2-hydroxybenzyl-5-sulfonylbenzyl)-1,5,8,12-tetraazadodecane (H6 Sbadd 2+), and N,N‘-bis-(2-hydroxy-5-sulfonylbenzyl)-N,N‘-bis(2-methylpyridyl)ethylenediamine (H6 Sbbpen 2+) were also prepared and characterized; potentiometric titrations of these three ligands, in the absence and presence of Ga3+ and In3+, were performed to determine deprotonation constants of the ligands and the thermodynamic stabilities of Ga and In amine phenol complexes. The formation constants of the Ga3+ and In3+ complexes with Sbad 4- (Ga3+, log β = 28.33(8); In3+, log β = 24.54(2)), Sbadd 4- (Ga3+, log β = 28.27(5); In3+, log β = 24.56 (5)), and Sbbpen 4- (Ga3+, log β = 35.33(8); In3+, log β = 34.85(5)) were obtained. All six of the Ga and In hexadentate amine phenol complexes were found to be very stable in aqueous solution. With the exception of [In(Sbadd)]-, all the complexes were calculated to be thermodynamically stable with respect to demetalation by transferrin at physiological pH. The linear amine phenols showed a selectivity for Ga3+ over In3+, while the Sbbpen 4- derivative was indiscriminate in binding the Ga3+ and In3+ ions.

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