Exploration of head-to-tail and head-to-head isomers of a guanine quadruplex platinum-based binder

Organic–inorganic hybrid mixed-halide ZnII and CdII tetrahalometallates with the 2-methylimidazo[1,5-a]pyridinium cation

The three isomorphous hybrid salts are assembled from discrete 2-methyl­imidazo[1,5-a]pyridinium cations and Zn^II or Cd^II tetra­halometallate anions that show disorder involving partial substitution of Br by Cl and Cl by I in the [CdBr_2.42Cl_1.58]^2–, [CdCl_3.90I_0.10]^2– and [ZnCl_3.19I_0.81]^2– anions.

Three isomorphous 0-D hybrid salts, namely, 2-methyl­imidazo[1,5-a]pyridinium tri­chlorido­iodido­zincate(II), (C₈H₉N₂)₂[ZnCl_3.19I_0.81] or [L]₂[ZnCl_3.19I_0.81], (I), 2-methyl­imidazo[1,5-a]pyridinium di­bromido­dichlorido­cadmate(II), (C₈H₉N₂)₂[CdBr_2.42Cl_1.58] or [L]₂[CdBr_2.42Cl_1.58], (II), and 2-methyl­imidazo[1,5-a]pyridinium tri­chlorido­iodido­cadmate(II), (C₈H₉N₂)₂[CdCl_3.90I_0.10] or [L]₂[CdCl_3.90I_0.10], (III), are assembled from discrete 2-methyl­imidazo[1,5-a]pyridinium cations, L⁺, and mixed-halide tetra­halometallate anions. In the three structures, there are two crystallographically non-equivalent cations that were modelled as being rotationally disordered by 180°. In the lattices of the three compounds, a disordered state exists involving partial substitution of Cl by I for sites 2–4 in (I), Br by Cl for all four sites in (II) and Cl by I for site 2 in (III). In the solid state, the organic and inorganic sheets alternate parallel to the bc plane in a pseudo-layered arrangement. In the organic layer, pairs of centrosymmetic­ally related trans-oriented cations form π-bonded chains. The adjacent tetra­halometallate anions in the inorganic layer show no connectivity with the shortest M⋯M separations being greater than 7 Å. A variety of C—H⋯X—M (X = Cl, Br, I) contacts between the organic and inorganic counterparts provide additional structural stabilization. The title structures are isomorphous with the previously reported structures of the chloride analogues, [L]₂[ZnCl₄] and [L]₂[CdCl₄].

Portrait of a Family of Highly Stabilizing and Selective Guanine Quadruplex Platinum(II)-Based Binders

The long-standing history of platinum coordination complexes in nucleic acid recognition attests to the unique suitability of such species for therapeutic applications. Here, we report the synthetic exploration and development of a family of di-imine ligands, and their platinum(II) complexes, elaborated on a 3-(2-pyridyl)-[1,2,4]triazolo[4,3-a]pyridine platform which, in its unsubstituted form, has recently been shown to display exceptional capabilities for guanine quadruplex (G4) targeting. The identification of facile, high-yielding synthetic methods for the derivatization of this platform for the incorporation of additional sites of interactions with guanine quadruplex loops and grooves, along with the optimization of platinum(II) complexation methods, are discussed. Gratifyingly, preliminary biophysical screening of this novel family of binders validates all but one family members as robust G4 binders and highlights enhanced selectivity for quadruplex versus duplex DNA compared to the parent compound. These results bear promise for practical developments based on this platform.