Rational Design of Dinitroxide Polarizing Agents for Dynamic Nuclear Polarization to Enhance Overall NMR Sensitivity.

We evaluate the overall sensitivity gains provided by a series of eighteen nitroxide biradicals for dynamic nuclear polarization (DNP) solid-state NMR at 9.4 T and 100 K, including eight new biradicals. We find that in the best performing group the factors contributing to the overall sensitivity gains, namely the DNP enhancement, the build-up time, and the contribution factor, often compete with each other leading to very similar overall sensitivity across a range of biradicals. NaphPol and HydroPol are found to provide the best overall sensitivity factors, in organic and aqueous solvents respectively. One of the new biradicals, AMUPolCbm, provides high sensitivity for all three solvent formulations measured here, and can be considered to be a "universal" polarizing agent.

Trehalose matrices for high temperature dynamic nuclear polarization enhanced solid state NMR.

Dynamic nuclear polarization (DNP) at cryogenic temperatures has proved to be a valuable technique to enhance the sensitivity of solid-state NMR spectroscopy. Over the years, sample formulations have been optimized for experiments at cryogenic temperatures. At 9.4 T, the best performing polarizing agents are dinitroxides such as AMUPol and TEKPol that lead to enhancement factors of around 250 at 100 K. However, the performance of these radicals plummets at higher temperatures. Here we introduce trehalose-based DNP polarizing matrices, suitable to embed biomolecular assemblies. Several formulation protocols are investigated, in combination with various polarizing agents, including a new biradical structure chemically tethered to a trehalose molecule. The DNP efficiency of these new polarizing media is screened as a function of the radical concentration, the hydration level of the matrix and the protein content. Sizeable enhancement factors are reported at 100 K and 9.4 T. More importantly, we show that the DNP performance of these new polarizing media outperform the conventionally used water/glycerol mixture at temperatures above 180 K. This study establishes trehalose matrices as a promising DNP medium for experiments at temperatures >150 K where conventional water-based formulations soften and are no longer viable, thus opening new avenues for DNP enhanced solid-state NMR spectroscopy at temperatures close to ambient temperature.

Intermolecular Addition of Carbon-Centered Radicals to Ynamides. A Regio- and Stereoselective Route to Persubstituted α-Iodo-enamides.

Rather surprisingly, C-C bond formation through "intermolecular" radical addition to internal ynamides has never been reported. Actually, ynamides are excellent acceptors for "electrophilic" carbon-centered radicals. These processes enable the introduction of functionalized alkyl chains at Cß, groups that have not yet been introduced via the addition of organometallics. Radical carboiodination affords persubstituted α-iodo-enamides in moderate to high yield. The addition is totally stereoselective. Theoretical support to the mechanism and the scope and limitation of the reaction are discussed.

Enediynes bearing polyfluoroaryl sulfoxide as new antiproliferative agents with dual targeting of microtubules and DNA.

A novel series of enediynes possessing pentafluorophenylsulfoxide have been developed. The innovative compounds possess antiproliferative activity against a broad panel of human cancer cells originating from breast, blood, lung, kidney, colon, prostate, pancreas or skin with IC50 ranging from 0.6 to 3.4 µM. The antiproliferative activity of enediynes in darkness is associated to their ability to compromise microtubule network. In addition, exposure to UV leads to double-stranded DNA cleavage caused by the newly synthesized molecules reducing further their IC50 in nanomolar range against human tumor cells, including chemo-resistant pancreatic cancer cells. Taken together, the examined data demonstrate that enediynes possessing pentafluorosulfoxide are promising molecules in the cancer therapy.