Synthesis, Postmodification and Characterization of Linear Polystyrene-based Supports for the Interaction with Immobilized Biocatalysts

A series of linear polystyrene-based supports has been synthesized using conventional or controlled (reversible addition fragmentation chain transfer or nitroxide-mediated) free radical polymerizations, in order to modulate their molecular weight characteristics. Polymer post-modification via esterification of the primary hydroxyl alcohol functionalities, pendant from the polymer backbone, with a mandelic acid derivative introduces efficiently (>85% yield) racemic, enzyme-cleavable moieties. A study of the interactions of these polymeric substrates with immobilized penicillin G acylase, in mixed organic/aqueous buffer solvent systems, results in a modest enantioselectivity (comparable with that of racemicmandelic acid methyl ester), but reveals that the biocatalytically active moieties on the linear polymers can be cleaved with first-order rate kinetics, as observed with small molecules in solution; the reaction rates (which can differ by more than one order ofmagnitude) are influenced both by the synthetic polymer length and by the polymer structure resulting from themethod of polymerization used

Oxadiazole/Pyridine-Based Ligands: A Structural Tuning for Enhancing G-Quadruplex Binding

Non-macrocyclic heteroaryls represent a valuable class of ligands for nucleic acid recognition. In this regard, non-macrocyclic pyridyl polyoxazoles and polyoxadiazoles were recently identified as selective G-quadruplex stabilizing compounds with high cytotoxicity and promising anticancer activity. Herein, we describe the synthesis of a new family of heteroaryls containing oxadiazole and pyridine moieties targeting DNA G-quadruplexes. To perform a structure–activity analysis identifying determinants of activity and selectivity, we followed a convergent synthetic pathway to modulate the nature and number of the heterocycles (1,3-oxazole vs. 1,2,4-oxadiazole and pyridine vs. benzene). Each ligand was evaluated towards secondary nucleic acid structures, which have been chosen as a prototype to mimic cancer-associated G-quadruplex structures (e.g., the human telomeric sequence, c-myc and c-kit promoters). Interestingly, heptapyridyl-oxadiazole compounds showed preferential binding towards the telomeric sequence (22AG) in competitive conditions vs. duplex DNA. In addition, G4-FID assays suggest a different binding mode from the classical stacking on the external G-quartet. Additionally, CD titrations in the presence of the two most promising compounds for affinity, TOxAzaPy and TOxAzaPhen, display a structural transition of 22AG in K-rich buffer. This investigation suggests that the pyridyl-oxadiazole motif is a promising recognition element for G-quadruplexes, combining seven heteroaryls in a single binding unit

Cationic Pentaheteroaryls as Selective G-Quadruplex Ligands by Solvent-Free Microwave-Assisted Synthesis

A solvent-free and microwave-assisted synthesis of several water soluble acyclic penta-heteroaryls containing 1,2,4-oxadiazole moieties (1–7) has been achieved with good yields. Their binding interactions with DNA quadruplex structures were thoroughly investigated by FRET melting, fluorescent intercalator displacement assay (G4-FID) and CD spectroscopy. Among the G-quadruplexes considered, attention was focused on telomeric repeats together with the proto-oncogenic c-kit sequences and the c-myc oncogene promoter. Compound 1, and to a lesser extent 2 and 5, preferentially stabilise an antiparallel structure of the telomeric DNA motif, and exhibit an opposite binding behaviour to structurally related polyoxazole (TOxaPy), and do not bind duplex DNA. The efficiency and selectivity of the binding process was remarkably controlled by the structure of the solubilising moieties