Deactivation mechanisms of iodo-iridium catalysts in chiral amine racemization

Toluene-Poisoning-Resistant High-Entropy Non-Noble Metal Anode for Direct One-Step Hydrogenation of Toluene to Methylcyclohexane

The direct one-step hydrogenation of toluene to methylcyclohexane facilitated by a proton-exchange membrane water electrolyzer driven by renewable energy has garnered considerable attention for stable hydrogen storage and safe hydrogen transportation. However, a persistent challenge lies in the crossover of toluene from the cathode to the anode chamber, which deteriorates the anode and decreases its energy efficiency and lifetime. To address this challenge, the catalyst-poisoning mechanism is systematically investigated using IrO2 and high-entropic non-noble-metal alloys as anodes in acidic electrolytes saturated with toluene and toluene-oxidized derivatives, such as benzaldehyde, benzyl alcohol, and benzoic acid. Benzoic acid plays an important role in polymer-like carbon-film formation by blocking the catalytically active sites on the anode surface. Moreover, Nb and the highly entropic state on the surface of the multi-element alloy lower the adsorbing ability of toluene and prevent polymer-like carbon film formation. This study contributes to the design of catalyst-poisoning-resistant anodes for organic hydride technology, advanced fuel cells, and batteries.

Low-Basicity 5-HT6 Receptor Ligands from the Group of Cyclic Arylguanidine Derivatives and Their Antiproliferative Activity Evaluation

The serotonin 5-HT6 receptor (5-HT6R), expressed almost exclusively in the brain, affects the Cdk5 signaling as well as the mTOR pathway. Due to the association of 5-HT6R signaling with pathways involved in cancer progression, we decided to check the usefulness of 5-HT6R ligands in the treatment of CNS tumors. For this purpose, a new group of low-base 5-HT6R ligands was developed, belonging to arylsulfonamide derivatives of cyclic arylguanidines. The selected group of molecules was also tested for their antiproliferative activity on astrocytoma (1321N1) and glioblastoma (U87MG, LN-229, U-251) cell lines. Some of the molecules were subjected to ADMET tests in vitro, including lipophilicity, drug binding to plasma proteins, affinity for phospholipids, drug-drug interaction (DDI), the penetration of the membrane (PAMPA), metabolic stability, and hepatotoxicity as well as in vivo cardiotoxicity in the Danio rerio model. Two antagonists with an affinity constant Ki < 50 nM (PR 68Ki = 37 nM) were selected. These compounds were characterized by very high selectivity. An analysis of pharmacokinetic parameters for the lead compound PR 68 confirmed favorable properties for administration, including passive diffusion and acceptable metabolic stability (metabolized in 49%, MLMs). The compound did not exhibit the potential for drug-drug interactions.

Continuous Flow Chiral Amine Racemization Applied to Continuously Recirculating Dynamic Diastereomeric Crystallizations

A new, dynamic diastereomeric crystallization method has been developed, in which the mother liquors are continuously separated, racemized over a fixed-bed catalyst, and recirculated to the crystallizer in a resolution-racemization-recycle (R³) process. Separating the racemization from crystallization overcomes problems of using catalysts in situ, that suffer conflicting sets of conditions, inhibition, and separation. Continuous racemization has been achieved through the covalent attachment of [IrCp*I₂]₂ SCRAM catalyst to Wang resin solid support to give a fixed-bed catalyst. One tertiary and a variety of secondary optically enriched amines have been racemized efficiently, with residence times compatible with the crystallization (2.25-30 min). The catalyst demonstrates lower turnover (TOF) than the homogeneous analogue but with reuse shows a long lifetime (e.g., 40 recycles, 190 h) giving acceptable turnover number (TON) (up to 4907). The slow release of methylamine during racemization of N-methyl amines was found to inactivate the catalyst, which could be partially reactivated using hydroiodic acid. Dynamic crystallization is achieved in the R³ process through the continual removal of the more soluble diastereomer and supply of the less soluble one. The solubility of the diastereomers was determined, and the difference correlates to the rate of resolution but is also affected by the rates of racemization, crystal growth, and dissolution. A variety of cyclic and acyclic amine salts were resolved using mandelic acid (MA) and ditoluoyl tartaric acid (DTTA) with higher resolvability (S = yield × d.e.) than the simple diastereomeric crystallization alone. Comparing resolvabilities, resolutions were 1.6-44 times more effective with the R³ process than batch, though one case was worse. Further investigation of this revealed an unusual thermodynamic switching behavior: rac-N-methylphenethylamine was initially resolved as an (S,S)-bis-alkylammonium tartrate crystal but over time became the equivalent (R,S) salt. Thermal, mixing, concentration, stoichiometry, and seeding conditions were all found to affect the onset of the switching behavior which is only associated with difunctional resolving reagents.