Pyrazolylboratozinc Complexes of Nucleosides and Nucleoside Analogues

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.

Coinage metal complexes of tris(pyrazolyl)methanide [C(3,5-Me2pz)3]−: κ3-coordination vs. backbone functionalisation

Tris(pyrazolyl)methanides, [C(3,5-R2pz)3]-, contain an unassociated tetrahedral carbanionic centre in the bridgehead position. In addition to nitrogen donor centres for transition metal coordination, an accessible reactive site for further manipulations is available in the backbone of the ligand. The coordination variability of the ambidental C-/N ligand [C(3,5-Me2pz)3]- was elucidated by investigating its coinage metal complexes. Two principle coordination modes were found for complexes of general formula [LMPR3] (with M = Cu(I), Ag(I), Au(I); L =[C(3,5-Me2pz)3]-; R = Ph, OMe). While for Cu(I) (2,3) and Ag(I) (4) complexes the anionic ligand acts as a face-capping, six electron N3-donor, gold(I) (5) is coordinated by the bridging carbanion yielding a two coordinate Au(I) complex comprising a covalent Au-C bond. The complexes featuring the kappa3-coordinated N3-donor ligand were investigated by 31P CP (MAS) NMR in the solid state.

Pyrazolylborate−Zinc Alkoxide Complexes. 3. Acid−Base Reactions

The alkoxides TpPh,MeZn-OR (R = Me, Et, i-Pr) undergo acid-base reactions with all hydrogen compounds whose acidity is higher than that of the corresponding alcohol ROH. Thus, anion exchange occurs with the common acids acetic acid, acetohydroxamic acid, acetylacetone, phenol, and ethylmercaptan. Alkoxide exchange is observed using methanol, ethanol, and trifluoroethanol. With the NH acids cyanamide, trifluoroacetamide, and pyrazoles, the corresponding anions are attached to zinc, and likewise beta- and gamma-lactams, a thiazolidinedione, and the cyclic sulfimide saccharin are deprotonated. Of the CH acids acetonitrile forms the Tp*Zn-cyanomethanide. Acetone is deprotonated by the cyanomethanide complex and incorporated as the Tp*Zn-beta-ketoiminate.