title: Synthesis and characterization of an unsymmetrical cobalt(III) active site analogue of nitrile hydratase.
abstract: The design, synthesis, and characterization of an unsymmetrical diamidato-dithiol ligand (H(4) 1, where the hydrogen atoms represent deprotonatable amide and thiol protons) and its cobalt(III) complex, a synthetic analogue of the cobalt-containing nitrile hydratase enzyme family, are reported. The ligand was prepared in 24% yield from an overall eight-step synthetic pathway following a modified protocol established in our laboratory that includes two peptide couples using O-(1H-benzotriazol-1-yl)-N,N,N',N'-tetramethyluronium hexafluorophosphate as the coupling agent. The ligand and all precursors were characterized by NMR spectroscopy and elemental analysis. The cobalt nitrile hydratase synthetic analogue complex [NBu(4)][Co(1)] was prepared on deprotonating ligand H(4) 1 to [1](4-) on addition of 5 equiv of NaH in N,N-dimethylformamide and adding 1 equiv of CoCl(2) at -40 °C under a N(2) atmosphere followed by oxidizing the complex by stirring it overnight open to dry air. The complex [NBu(4)][Co(1)] was isolated after counterion exchange with 1 equiv of NBu(4)Cl followed by crystallization from MeCN/Et(2)O in 71% yield. The structure of the complex was confirmed by X-ray diffraction analysis. Cyclic voltammetry studies on [NBu(4)][Co(1)] in a 0.1 M [NBu(4)][PF(6)]/MeCN solution showed a quasi-reversible reduction potential at -1.1 V (vs. Ag/AgCl), and magnetic susceptibility investigations indicated the complex is paramagnetic in both the solid and the solution states as determined from inverse-Gouy and Evans NMR methods, respectively.
authors.affiliation: Department of Chemistry, Western Washington University, 516 High Street, Bellingham, WA 98225, USA.
authors.forename: Jennifer K
authors.initials: JK
authors.lastname: Angelosante
authors.forename: Lauren M
authors.initials: LM
authors.lastname: Schopp
authors.forename: Breia J
authors.initials: BJ
authors.lastname: Lewis
authors.forename: Amber D
authors.initials: AD
authors.lastname: Vitalo
authors.forename: Dustin T
authors.initials: DT
authors.lastname: Titus
authors.forename: Rebecca A
authors.initials: RA
authors.lastname: Swanson
authors.forename: April N
authors.initials: AN
authors.lastname: Stanley
authors.forename: Brendan P
authors.initials: BP
authors.lastname: Abolins
authors.forename: Michelle J
authors.initials: MJ
authors.lastname: Frome
authors.forename: Lisa E
authors.initials: LE
authors.lastname: Cooper
authors.forename: David L
authors.initials: DL
authors.lastname: Tierney
authors.forename: Curtis
authors.initials: C
authors.lastname: Moore
authors.forename: Arnold L
authors.initials: AL
authors.lastname: Rheingold
authors.forename: Christopher J A
authors.initials: CJ
authors.lastname: Daley
mesh_terms: D020134:Catalytic Domain; D003035:Cobalt / Q000737:chemistry*; D018360:Crystallography, X-Ray; D006836:Hydro-Lyases / Q000138:chemical synthesis* / Q000737:chemistry* / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D015394:Molecular Structure
chemical_list: D003035:Cobalt; D006836:Hydro-Lyases; C048831:nitrile hydratase