Attachment of Sugar Phosphates and Nucleotide Derivatives to Pyrazolylborate-Zinc Units

Modeling Zinc Enzyme Inhibition with Functional Thiolate Ligands

The blocking of zinc enzymes by thiolate-containing inhibitors was modeled by treating TpPh,MeZn-OH with functional thiols. The latter were chosen such that they contain an additional donor function (COOH, COOR, NH2, NHR, OH) in a position favorable for chelation. Of them, mercapto carboxylic acid esters were incorporated as thiolates. The corresponding mercapto carboxylic acids, however, used only their carboxylate function for coordination. Various mercapto amines, mercapto alcohols, and mercaptophenol were exclusively converted to thiolate ligands. The two modes of inhibitor attachment, terminal or chelating, were observed equally frequently. As a rule, they occur as alternatives for similar ligands. In case of 2-mercaptophenol they coexist in the crystalline state and in solution. Hydrogen bonding, both intra- and intermolecular, seems to be a decisive factor determining the inhibitor attachments. Its persistence in solution is underlined by the observation that TpPh,MeZn-hydroxythiophenolates are methylated about 2 orders of magnitude slower than TpPh,MeZn-SPh itself.

Macrocyclic copper(II) and zinc(II) complexes incorporating phosphate esters

Slow evaporation of solutions prepared by adding either Cu(ClO(4))(2).6H(2)O or Zn(ClO(4))(2).6H(2)O to solutions containing appropriate proportions of Me(3)tacn (1,4,7-trimethyl-1,4,7-triazacyclononane) and sodium phenyl phosphate (Na(2)PhOPO(3)) gave dark blue crystals of [Cu(3)(Me(3)tacn)(3)(PhOPO(3))(2)](ClO(4))(2).(1)/(2)H(2)O (1) and colorless crystals of [Zn(2)(Me(3)tacn)(2)(H(2)O)(4)(PhOPO(3))](ClO(4))(2).H(2)O (2), respectively. Blue crystals of [Cu(tacn)(2)](BNPP)(2) (3) formed in an aqueous solution of [Cu(tacn)Cl(2)], bis(p-nitrophenyl phosphate) (BNPP), and HEPES buffer (pH 7.4). Compound 1 crystallizes in the triclinic space group P1 (No. 2) with a = 9.8053(2) A, b = 12.9068(2) A, c = 22.1132(2) A, alpha = 98.636(1) degrees, beta = 99.546(1) degrees, gamma = 101.1733(8) degrees, and Z = 2 and exhibits trinuclear Cu(II) clusters in which square pyramidal metal centers are capped by two phosphate esters located above and below the plane of the metal centers. The trinuclear cluster is asymmetric having Cu...Cu distances of 4.14, 4.55, and 5.04 A. Compound 2 crystallizes in the monoclinic space group P2(1)/c (No. 14) with a = 13.6248(2) A, b = 11.6002(2) A, c = 25.9681(4) A, beta = 102.0072(9) degrees, and Z = 4 and contains a dinuclear Zn(II) complex formed by linking two units of [Zn(Me(3)tacn)(OH(2))(2)](2+) by a single phosphate ester. Compound 3 crystallizes in the monoclinic space group C2/c (No. 15) with a = 24.7105(5) A, b = 12.8627(3) A, c = 14.0079(3) A, beta = 106.600(1) degrees, and Z = 4 and consists of mononuclear [Cu(tacn)(2)](2+) cations whose charge is balanced by the BNPP(-) anions.

Pyrazolylborate-zinc-hydrosulfide complexes and their reactions

Four new hydrosulfide complexes Tp*Zn-SH of substituted pyrazolylborate ligands (Tp*) were prepared by reactions of Tp*Zn-OH with H(2)S, and three of them were structurally characterized. Unlike the Tp*Zn-OH complexes they do not react with esters, phosphates, or CO(2), e.g. for thiolytic cleavage reactions. They also cannot be deprotonated, as various bases induce precipitation of ZnS and release of anionic Tp*. Acidic organic X-OH compounds (carboxylic acids, trinitrophenol, hexafluoroacetylacetone) replace the SH groups with formation of Tp*Zn-OX. Thiols undergo an entropy-driven SH substitution to yield the Tp*Zn-SR complexes. Like the Tp*Zn-SR complexes the Tp*Zn-SH complexes are quite reactive toward alkylation with methyl iodide, yielding Tp*Zn-I and CH(3)SH. The kinetic investigation of the methylation of Tp(Ph,Me)Zn-SH has shown it to be a clean second-order reaction, thereby indicating that the SH group is alkylated in the zinc-bound state.