Synthesis of Optically Active Polyguanidines by Polyaddition Reaction of Biscarbodiimides with Chiral Diamines

Gallium Hydride-Catalyzed Selective Hydroboration of Unsaturated Organic Substrates

The first examples of tetrasubstituted conjugated bis-guanidinate (CBG) supported monomeric and thermally stable gallium dihalides [LGaX2], (X=Cl (Ga-Cl), I (Ga-I)) and dihydride (Ga-H) [LGaH2] (where L={(ArHN)(ArN)-C=N-C=(NAr)(NHAr)}; Ar=2,6-Et2-C6H3) compounds are reported. The reaction of in situ generated LLi with 1.0 equiv. GaX3 (X=Cl, I) afforded compounds Ga-Cl and Ga-I. The reaction between Ga-Cl and Li[HBEt3] in benzene yielded the dihydride compound Ga-H. All reported compounds (Ga-Cl, Ga-I, and Ga-H) were characterized by NMR, HRMS, and single-crystal X-ray diffraction studies. Ga-H was probed for the hydroboration of carbodiimides (CDI), isocyanates, and isothiocyanates with HBpin. Compound Ga-H was also found effective for the catalytic hydroboration of imines, nitriles, alkynes, esters, and formates, affording the corresponding products in quantitative yields. Stoichiometric reactions with a CDI were performed to establish the catalytic cycle.

1,4-Diurea- and 1,4-Dithiourea-Substituted Aromatic Derivatives Selectively Inhibit α-Synuclein Oligomer Formation In Vitro

Parkinson's disease (PD) is the second most common neurodegenerative disease, affecting the elderly population worldwide. In PD, the misfolding of α-synuclein (α-syn) results in the formation of inclusions referred to as Lewy bodies (LB) in midbrain neurons of the substantia nigra and other specific brain localizations, which is associated with neurodegeneration. There are no approved strategies to reduce the formation of LB in the neurons of patients with PD. Our drug discovery program focuses on the synthesis of urea and thiourea compounds coupled with aminoindole moieties to abrogate α-syn aggregation and to slow down the progression of PD. We synthesized several urea and thiourea analogues with a central 1,4-phenyl diurea/thiourea linkage and evaluated their effectiveness in reducing α-syn aggregation with a special focus on the selective inhibition of oligomer formation among other proteins. We utilized biophysical methods such as thioflavin T (ThT) fluorescence assays, transmission electron microscopy (TEM), photoinduced cross-linking of unmodified proteins (PICUP), as well as M17D intracellular inclusion cell-based assays to evaluate the antiaggregation properties and cellular protection of our best compounds. Our results identified compound 1 as the best compound in reducing α-syn fibril formation via ThT assays. The antioligomer formation of compound 1 was subsequently superseded by compound 2. Both compounds selectively curtailed the oligomer formation of α-syn but not tau 4R isoforms (0N4R, 2N4R) or p-tau (isoform 1N4R). Compounds 1 and 2 failed to abrogate tau 0N3R fibril formation by ThT and atomic force microscopy. Compound 2 was best at reducing the formation of recombinant α-syn fibrils by TEM. In contrast to compound 2, compound 1 reduced the formation of α-syn inclusions in M17D neuroblastoma cells in a dose-dependent manner. Compound 1 may provide molecular scaffolds for the optimization of symmetric molecules for its α-syn antiaggregation activity with potential therapeutic applications and development of small molecules in PD.