Why a complementary analytical toolbox is essential for correct siRNA duplex content determination.

Small interfering RNAs (siRNAs) have emerged as a highly promising class of therapeutics, capable of effectively treating a wide range of indications, including previously challenging targets. To correctly characterize the duplex content of siRNA therapeutics, a careful design of the analytical conditions is required. This is due to the weak interactions governing the duplex formation and thermal stability of these double-stranded oligonucleotides.

Optimization of elution conditions and comparison of emerging biocompatible columns on the resolving power and detection sensitivity of oligonucleotides by ion-pairing reversed-phase liquid chromatography mass spectrometry.

A generic performance comparison strategy has been developed to evaluate the impact of mobile-phase additives (ion-pairing agent / counter ion systems), distinct stationary phases on resulting resolving power, and MS detectability of oligonucleotides and their critical impurities in gradient IP-RPLC. Stationary-phase considerations included particle type (core-shell vs. fully porous particles), particle diameter, and pore size.

Evaluation of micropillar array columns for chromatographic separation of phosphorothioated oligonucleotides and their diastereomers.

Chromatographic analysis of therapeutic oligonucleotides is challenging due to the presence of closely related impurities, degradants or metabolites and due to the presence of phosphorothioate bonds, which introduce chiral centers. In the present study, ion pair reversed phase chromatography of oligonucleotides on micropillar array columns was investigated. Two commonly used mobile phase conditions were included.

Reinvestigation of the Branimycin Stereochemistry at Position 17-C.

A conformational study of branimycin was performed using single-crystal X-ray crystallography to characterize the solid-state form, while a combination of NMR spectroscopy and molecular modeling was employed to gain information about the solution structure. Comparison of the crystal structure with its solution counterpart showed no significant differences in conformation, confirming the relative rigidity of the tricyclic system. However, these experiments revealed that the formerly proposed stereochemistry of branimycin at 17-C should be revised.

Large-scale and chromatography-free synthesis of an octameric quinoline-based aromatic amide helical foldamer.

The synthesis of helical aromatic oligoamide foldamers derived from 8-amino-2-quinolinecarboxylic acid is described. The precursors are commercially available and products up to and including the octamer are obtained. The procedure covers the synthesis of the monomer, reduction of N-terminal nitro groups into amines, saponification of C-terminal methyl esters to form carboxylic acids, and coupling of amines and acids to form amides via acid chloride activation.