title: Formation of a metal-to-nitrogen bond of normal length by a neutral sufonamide group within a tridentate ligand. A new approach to radiopharmaceutical bioconjugation.
abstract: We demonstrate that a tertiary sulfonamide group, N(SO2R)R'2, can rehybridize to form a M-N bond of normal length even when the group is in a linear tridentate ligand, such as in the new tridentate N(SO2R)dpa ligands derived from di-(2-picolyl)amine (N(H)dpa). N(SO2R)dpa ligands were used to prepare fac-[Re(CO)3(N(SO2R)dpa)](PF6 or BF4) complexes. Structural characterization of the new complexes established that the tertiary sulfonamide nitrogen atom binds to Re with concomitant sp(2)-to-sp(3) rehybridization, facilitating facial coordination. The new fac-[Re(CO)3(N(SO2R)dpa)]X structures provide the only examples for any metal with the sulfonamide as part of a noncyclic linear tridentate ligand and with a normal metal-to-nitrogen(tertiary sulfonamide) bond length. Rare previous examples of such normal M-N bonds have been found only in more constrained situations, such as with tripodal tetradentate ligands. Our long-term objectives for the new tridentate N(SO2R)dpa ligands are to develop the fundamental chemistry relevant to the eventual use of the fac-[M(I)(CO)3](+) core (M = (99m)Tc, (186/188)Re) in imaging and therapy. The sulfonamide group uniquely contributes to two of our goals: expanding ways to conjugate the fac-[M(I)(CO)3](+) core to biological molecules and also developing new symmetrical tridentate ligands that can coordinate facially to this core. Tests of our conjugation method, conducted by linking the fac-[Re(I)(CO)3](+) core to a new tetraarylporphyrin (T(N(SO2C6H4)dpa)P) as well as to a dansyl (5-(dimethylamino)naphthalene-1-sulfonyl) group, demonstrate that large molecular fragments can be tethered via a coordinated tertiary sulfonamide linkage to this core.
authors: Department of Chemistry, Louisiana State University , Baton Rouge, Louisiana 70803, United States.
authors: Theshini
authors: T
authors: Perera
authors: Pramuditha
authors: P
authors: Abhayawardhana
authors: Patricia A
authors: PA
authors: Marzilli
authors: Frank R
authors: FR
authors: Fronczek
authors: Luigi G
authors: LG
authors: Marzilli
mesh_terms: D002248:Carbon Monoxide / Q000737:chemistry; D018360:Crystallography, X-Ray; D008024:Ligands; D008958:Models, Molecular; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D019275:Radiopharmaceuticals / Q000138:chemical synthesis / Q000737:chemistry*; D012211:Rhenium / Q000737:chemistry*; D013449:Sulfonamides / Q000737:chemistry*
chemical_list: D008024:Ligands; D009942:Organometallic Compounds; D019275:Radiopharmaceuticals; D013449:Sulfonamides; D012211:Rhenium; D002248:Carbon Monoxide