Rational design of hydrogen-free catalytic active sites

Materials that are organic-based and exhibit oxidative catalytic activity, including free-radical pathways, while being refractory to the activated oxygen species are not known. The synthesis of several classes of such materials, their electronic and structural characterizations as well as catalytic properties are reported. Their rational molecular design and biologically inspired reactivity are based on enzymatic active sites, which are reengineered into robust metal-organic fluoroalkylated scaffolds that, for the first time, exhibit structural asymmetry and tunable π-π interactions both in solution and solid state. In these complexes, labile C-H bonds are replaced with chemically and thermally resistant C-F bonds to create a Teflon coating ; of the metal active site, keeping it open for catalysis while protecting the molecule against self-decomposition. The first part presents the synthesis, spectroscopic and X-ray structural characterization of new, mixed alkyl-perfluoroalkyl trispyrazolylborate (Tp) ligands and several of their sodium and silver derivatives. These complexes are subject to an N3-coordinating agent bearing a -1 charge. The metal is encapsulated in a fluorine-rich environment and exhibits a high Lewis acidity, allowing additional coordination by toluene, triphenylphosphine, methyldiphenylphosphine and triphenylphosphine oxide. X-ray crystallographic analysis of the new materials allows for the development of a structural model that predicts interatomic distances and the relative stability of this class of compounds. The balancing of electronic and steric effects of substituents on the Tp and additional ligands can lead to remarkably stable compounds in solution and the solid state, even when metals particularly prone to reduction (such as silver) are involved. Examples among the new complexes are provided. The second part describes the design of two new classes of macrocyclic organic chromophores with enhanced N4-coordinating ability and -2 charges, belonging to the family of fluoroalkylated phthalocyanines and produced as their zinc and cobalt complexes. The first class, bearing trifluoromethyl groups, exhibits reduced steric hindrance and solvent-dependent aggregation. A direct correlation between the degree of dimerization and the solvent\u27s hydrogen bond donor ability is established. The second class constitutes the first asymmetric perfluorinated phthalocyanines, a property imparted by a combination of fluorine atoms and perfluoroisopropyl groups. X-ray crystal structures reveal tunable π-π stacking in the solid state for representatives of both classes. The new compounds\u27 ability to catalytically activate oxygen from air and consequently oxidize substrates is tested on two processes of industrial importance: the environmentally benign conversion of corrosive thiols to disulfides and the photocatalytic oxidation of (S\u27)-citronellol. The extreme electronic deficiency imparted on the metal complexes supports a new strategy for broadening catalytic activity to include thiols with poor basicity, which under normal circumstances cannot be oxidized. Quantitative substrate conversion and virtual immunity of the catalysts to chemical attacks is demonstrated for the first time in a metal-organic assembly through oxygen consumption and stability studies, thus opening pathways for development of new materials

Reaction-Based Probes for Imaging Mobile Zinc in Live Cells and Tissues

Chelatable, or mobile, forms of zinc play critical signaling roles in numerous biological processes. Elucidating the action of mobile Zn(II) in complex biological environments requires sensitive tools for visualizing, tracking, and manipulating Zn(II) ions. A large toolbox of synthetic photoinduced electron transfer (PET)-based fluorescent Zn(II) sensors are available, but the applicability of many of these probes is limited by poor zinc sensitivity and low dynamic ranges owing to proton interference. We present here a general approach for acetylating PET-based probes containing a variety of fluorophores and zinc-binding units. The new sensors provide substantially improved zinc sensitivity and allow for incubation of live cells and tissue slices with nM probe concentrations, a significant improvement compared to the μM concentrations that are typically required for a measurable fluorescence signal. Acetylation effectively reduces or completely quenches background fluorescence in the metal-free sensor. Binding of Zn(II) selectively and quickly mediates hydrolytic cleavage of the acetyl groups, providing a large fluorescence response. An acetylated blue coumarin-based sensor was used to carry out detailed analyses of metal binding and metal-promoted acetyl hydrolysis. Acetylated benzoresorufin-based red-emitting probes with different zinc-binding sites are effective for sensing Zn(II) ions in live cells when applied at low concentrations (∼50–100 nM). We used green diacetylated Zinpyr1 (DA-ZP1) to image endogenous mobile Zn(II) in the molecular layer of mouse dorsal cochlear nucleus (DCN), confirming that acetylation is a suitable approach for preparing sensors that are highly specific and sensitive to mobile zinc in biological systems.National Institutes of Health (U.S.) (NIH grant GM065519)National Institutes of Health (U.S.) (NIH grant R01-DC007905)National Institutes of Health (U.S.) (NIH Fellowship (F32- EB019243))National Institutes of Health (U.S.) (NIH Fellowship (T32-DC011499))National Institutes of Health (U.S.) (NIH Fellowship (F32-DC013734)

Solid-phase synthesis provides a modular, lysine-based platform for fluorescent discrimination of nitroxyl and biological thiols

We describe a modular, synthetically facile solid-phase approach aimed at separating the fluorescent reporter and binding unit of small-molecule metal-based sensors. The first representatives contain a lysine backbone functionalized with a tetramethylrhodamine fluorophore, and they operate by modulating the oxidation state of a copper ion ligated to an [N4] (cyclam) or an [N2O] (quinoline-phenolate) moiety. We demonstrate the selectivity of their Cu(II) complexes for sensing nitroxyl (HNO) and thiols (RSH), respectively, and investigate the mechanism responsible for the observed reactivity in each case. The two lysine conjugates are cell permeable in the active, Cu(II)-bound forms and retain their analyte selectivity intracellularly, even in the presence of interfering species such as nitric oxide, nitrosothiols, and hydrogen sulfide. Moreover, we apply the new probes to discriminate between distinct levels of intracellular HNO and RSH generated upon stimulation of live HeLa cells with ascorbate and hydrogen sulfide, respectively. The successful implementation of the lysine-based sensors to gain insight into biosynthetic pathways validates the method as a versatile tool for producing libraries of analogues with minimal synthetic effort.National Institutes of Health (U.S.) (NIH Grant 1S10RR13886-01)National Science Foundation (U.S.) (NSF Grant CHE-1265770

Chiral bicyclo[3.3.1]-3,7-dioxanonane derivatives: Study of crystallization mode and conformational dynamics in solution

International audienc

Fully automated fast-flow synthesis of antisense phosphorodiamidate morpholino oligomers

Rapid development of antisense therapies can enable on-demand responses to new viral pathogens and make personalized medicine for genetic diseases practical. Antisense phosphorodiamidate morpholino oligomers (PMOs) are promising candidates to fill such a role, but their challenging synthesis limits their widespread application. To rapidly prototype potential PMO drug candidates, we report a fully automated flow-based oligonucleotide synthesizer. Our optimized synthesis platform reduces coupling times by up to 22-fold compared to previously reported methods. We demonstrate the power of our automated technology with the synthesis of milligram quantities of three candidate therapeutic PMO sequences for an unserved class of Duchenne muscular dystrophy (DMD). To further test our platform, we synthesize a PMO that targets the genomic mRNA of SARS-CoV-2 and demonstrate its antiviral effects. This platform could find broad application not only in designing new SARS-CoV-2 and DMD antisense therapeutics, but also for rapid development of PMO candidates to treat new and emerging diseases

Synthesis of proteins by automated flow chemistry

Ribosomes can produce proteins in minutes and are largely constrained to proteinogenic amino acids. Here, we report highly efficient chemistry matched with an automated fast-flow instrument for the direct manufacturing of peptide chains up to 164 amino acids long over 327 consecutive reactions. The machine is rapid: Peptide chain elongation is complete in hours. We demonstrate the utility of this approach by the chemical synthesis of nine different protein chains that represent enzymes, structural units, and regulatory factors. After purification and folding, the synthetic materials display biophysical and enzymatic properties comparable to the biologically expressed proteins. High-fidelity automated flow chemistry is an alternative for producing single-domain proteins without the ribosome.National Science Foundation (Grant 1122374