A bifunctional ligand that is capable of forming Re and 99mTc complexes as complementary fluorescent and radioactive probes was developed. The tridentate bis(quinoline) amine ligand, which is referred to as the SAACQ system, was prepared in a single step from Fmoc protected lysine in high yield. Reaction of the SAACQ ligand with [Re(CO)3Br3]2- resulted in the formation of the SAACQ-(Re(CO)3)+complex which exhibits favorable fluorescence properties including a long lifetime and a large Stoke's shift. Because the SAACQ ligand is derived from an amino acid, it can readily be linked to or incorporated within peptides as a means of targeting the probe to specific receptors. To demonstrate this feature, the SAACQ ligand and the SAACQ-Re complex were incorporated into fMLFG, a peptide that binds to the formyl peptide receptor (FPR). Uptake of the fMLF[(SAACQ-Re(CO)3)+]G conjugate into human leukocytes in vitro was visualized by fluorescence microscopy, and the observed distribution of the peptide was similar to that of a well-established fluorescent FPR probe. The corresponding Tc complex, fMLF[(SAACQ-99mTc(CO)3)+]G, was prepared in excellent yield from [99mTc(CO)3(OH2)3]+, which affords the opportunity to correlate the results of the microscopy experiments with in vivo radioimaging studies because the probes are isostructural.

The reactions of the Re(V) starting material [ReO(PPh(3))(2)Cl(3)] with ligands of the type XN(Y)Z [X = Y = 2-pyridylmethyl, Z = -CH(2)CO(2)Et (L(1)Et), -CH(2)CH(2)CO(2)Et (L(2)Et), -CH(2)CH(2)CH(2)CH(2)CH(NHCO(2)Bu(t))CO(2)H (L(3)H); X = 2-pyridylmethyl, Y = 2-(1-methylimidazolyl)methyl, Z = -CH(2)CO(2)Et (L(4)Et)] yielded the Re(III) trichloride complexes of the type [ReCl(3)(L(n)R)]. The complexes are mononuclear, paramagnetic species with a facial geometry of the chloride ligands. The nitrogen donors of the tridentate L(n)()R ligands complete the distorted octahedral coordination spheres of the complexes. Crystal data: [ReCl(3)(L(1)Et)] (1), monoclinic, C2/m, a = 16.088(3) A, b = 9.980(2) A, c = 12.829(2) A, beta = 91.384(3) degrees, Z = 4, D(calc) = 1.967 g/cm(-)(3); [ReCl(3)(L(4)Et)] (4), monoclinic, C2/c, a = 22.880(1) A, b = 7.4926(4) A, c = 22.560(1) A, beta = 94.186(1) degrees, Z = 8, D(calc) = 2.001 g/cm(-3).

The reactions of a series of potentially tridentate ligands, derived from single amino acids or amino acid analogues, with [NEt(4)](2)[ReBr(3)(CO)(3)] have been investigated. The model compounds [Re(CO)(3)Br[(2-pyridylmethyl)NH(2)]] (1) and [Re(CO)(3)[(2-pyridylmethyl)(2)NH]]Br (2) were also prepared and structurally characterized. With ligands possessing two pyridyl appendages, (2-pyridylmethyl)(2)NX (X = -CH(2)CO(2)H, -CH(2)CO(2)Et, -CH(2)CH(2)CO(2)H, -CH(2)CH(2)CO(2)Et, -CH(2)CH(2)CH(2)CH(2)CH(NHCO(2)(t)Bu)CO(2)H), complexes of the type [Re(CO)(3)(ligand)]Br (3-6) were isolated. All possess the fac-[Re(CO)(3)N(3)] coordination geometry in the cationic molecular unit. Similarly, the ligands with the imidazolyl arms (2-pyridylmethyl)[2-(1-methylimidazolyl)methyl]NCH(2)CO(2)Et and [2-(1-methylimidazolyl)methyl](2)NCH(2)CO(2)Et, complexes 7 and 8 of the same [Re(CO)(3)(ligand)]Br type, were prepared. Replacement of one pyridyl arm with a thiophene group yielded the complex [Re(CO)(3)[(2-pyridylmethyl)N(CH(2)CO(2))(2-thiophenemethyl)]] (9), while additional substitution of X = -H for -CH(2)CO(2)H yielded [Re(CO)(3)Br[(2-pyridylmethyl)NH(2-thiophenemethyl)]] (10). In both 9 and 10, the thiophene is uncoordinated and pendant, and the derivatives display fac-[Re(CO)(3)N(2)O] and fac-[Re(CO)(3)N(2)Br] coordination geometries, respectively. Crystal data: C(9)H(8)BrN(2)O(3)Re (1), triclinic P1, a = 8.156(1) A, b = 12.077(1) A, c = 12.945(2) A, alpha = 92.183(3) degrees, beta = 107.848(3) degrees, gamma = 100.955(7) degrees, V = 1185.1(3) A, Z = 4; C(15)H(13)BrN(3)O(3)Re (2), tetragonal P4(1), a = 8.6095(3) A, c = 22.228(1) A, V = 1646.9(1) A(3), Z = 4; C(17)H(14)BrN(3)O(5)Re.CH(3)OH (3), monoclinic P2(1)/m, a = 7.4425(3) A, b = 9.7596(4) A, c = 14.0646(6) A, beta = 97.753(1) degrees, V = 1012.26(7) A(3), Z = 2; C(19)H(19)BrN(3)O(5)Re (4), tetragonal P42(1)c, a = 16.895(3) A, c = 15.042(3) A, V = 4293.7(13) A(3), Z = 8; C(18)H(20)BrN(4)O(5)Re.CH(3)OH.H(2)O (7), monoclinic P2(1)/c, a = 10.2816(4) A, b = 30.386(1) A, c = 14.5810(6) A, beta = 99.868(1) degrees, V = 4488.03(3) A(3), Z = 8; C(17)H(21)BrN(5)O(5)Re.0.5CH(2)Cl(2).0.5H(2)O (8), triclinic P1, a = 11.5363(6) A, b = 13.1898(6) A, c = 16.4933(8) A, alpha = 89.356(1) degrees, beta = 74.907(1) degrees, gamma = 76.216(1) degrees, V = 2349.8(2) A(3), Z = 4; C(16)H(13)N(2)O(5)ReS (9), monoclinic P2(1)/c, a = 17.2072(7) A, b = 8.5853(4) A, c = 11.5607(5) A, beta = 101.73(1) degrees, V = 1672.2(1) A(3), Z = 4; and C(14)H(12)N(2)O(3)BrReS (10), triclinic P1, a = 7.5585(3) A, b = 9.7713(4) A, c = 11.7103(4) A, alpha = 109.566(1) degrees, beta = 98.298(1) degrees, gamma = 100.925(1) degrees, V = 779.73(5) A(3), Z = 2.