Esterification of Cyclic N6-Threonylcarbamoyladenosine During RNA Sample Preparation.

The continuous deciphering of crucial biological roles of RNA modifications and their involvement in various pathological conditions, together with their key roles in the use of RNA-based therapeutics, has reignited interest in studying the occurrence and identity of non-canonical ribonucleoside structures during the past years. Discovery and structural elucidation of new modified structures is usually achieved by combination of liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) at the nucleoside level and stable isotope labeling experiments. This approach, however, has its pitfalls as demonstrated in the course of the present study: we structurally elucidated a new nucleoside structure that showed significant similarities to the family of (c)t6A modifications and was initially considered a genuine modification, but subsequently turned out to be an in vitro formed glycerol ester of t6A. This artifact is generated from ct6A during RNA hydrolysis upon addition of enzymes stored in glycerol containing buffers in a mildly alkaline milieu, and was moreover shown to undergo an intramolecular transesterification reaction. Our results demand for extra caution, not only in the discovery of new RNA modifications, but also with regard to the quantification of known modified structures, in particular chemically labile modifications, such as ct6A, that might suffer from exposure to putatively harmless reagents during the diverse steps of sample preparation.

Complementary mechanochemical and biphasic approaches for the synthesis of organic thiocyanates using hexacyanoferrates as non-toxic cyanide sources.

Herein, we describe two complementary approaches towards various organic thiocyanates that are affordable, reliable and follow the principles of sustainable chemistry, starting from commercially available thiols or disulfides. Additionally, the application of this mild method to the first total synthesis of psammaplin B is demonstrated. Non-toxic and inexpensive ferricyanide is used as the cyanide source, which can be activated either in a mechanochemical, solvent-free approach, or in a biphasic solvent system allowing easier work-up. A total of 27 examples is demonstrated, with up to quantitative yields.

Cell Adhesion on UV-Crosslinked Polyurethane Gels with Adjustable Mechanical Strength and Thermoresponsiveness.

Temperature-responsive polyurethane (PU) hydrogels represent a versatile material platform for modern tissue engineering and biomedical applications. However, besides intrinsic advantages such as high mechanical strength and a hydrolysable backbone composition, plain PU materials are generally lacking bio-adhesive properties. To overcome this shortcoming, the authors focus on the synthesis of thermoresponsive PU hydrogels with variable mechanical and cell adhesive properties obtained from linear precursor PUs based on poly(ethylene glycol)s (pEG) with different molar masses, isophorone diisocyanate, and a dimerizable dimethylmaleimide (DMMI)-diol. The cloud point temperatures of the dilute, aqueous PU solutions depend linearly on the amphiphilic balance. Rheological gelation experiments under UV-irradiation reveal the dependence of the gelation time on photosensitizer concentration and light intensity, while the finally obtained gel strength is determined by the polymer concentration and spacing of the crosslinks. The swelling ratios of these soft hydrogels show significant changes between 5 and 40 °C whereby the extent of this switch increases with the hydrophobicity of the precursor. Moreover, it is shown that the incorporation of a low amount of catechol groups into the networks through the DMMI dimerization reaction leads to strongly improved cell adhesive properties without significantly weakening the gels.