Platinum phenanthroline complexes inhibit amyloid-β (Aβ) aggregation and reduce Aβ-caused neurotoxicity [Proc. Natl. Acad. Sci., 2008, 105, 6813-6818]. In this study, we investigated the interactions of Aβ(1-16) with [PtCl(2)(phen)] (phen=1,10-phenanthroline) using HPLC, ESI-MS, and NMR spectroscopy , and characterized the identity of products using tandem mass spectrometry. Results indicated that the phenanthroline ligand could induce noncovalent interactions between Aβ peptide and platinum complexes, leading to rapid Aβ platination. Multiple products were generated in the reaction, in which His6/His14 chelation was preferentially formed. Coordination of Asp7, His13, and Lys16 was also detected in other products. The majority of products were monoplatinated adducts with binding of the {Pt(phen)} scaffold, which impeded intermolecular interactions between Aβ peptides. Moreover, noncovalent interactions were confirmed by the interaction between Aβ peptide and [Pt(phen)(2)]Cl(2). The synergistic roles of the phen ligand and platinum(II) atom in the inhibition of Aβ aggregation are discussed.
Two novel bifunctional primary amine catalysts 1 (R A ,S,S) and 2 (R A ,R,R), which bear both central and axial chiral elements, have been developed to promote highly diastereoselective and enantioselective aldol reactions of arylaldehydes with cyclic and acyclic ketones in the presence of water at room temperature. The catalyst 2 (R A ,R,R) afforded the desired products with high levels of anti diastereoselectivity (up to 99:1) and enantioselectivity (up to 98%), showing that the two chiral elements of catalyst 2 (R A ,R,R) are matched, and enhance the stereochemical control. In addition, the catalyst 2 (R A ,R,R) was found to catalyze the direct aldol reaction of 4-nitrobenzaldehyde with 2-cyclohexanone under neat reaction conditions at room temperature with the high anti diastereoselectivity (98:2) and enantioselectivity (98%).
Bifunctional chiral tertiary amine thioureas derived from both α-amino acids and carbohydrates were developed. These organocatalysts promoted the enantioselective conjugate addition of acetylacetone to various aromatic and aliphatic nitroolefins at room temperature in good yields (up to 93 %) and with good enantioselectivity (up to 90 % ee). Furthermore, an interesting matched-mismatched effect of
Lewis acid catalyzed isomerization of 7-oxabicyclic alkenes into 1-naphthol derivatives in high yields (87-98%) under mild reaction conditions has been developed. The mechanism of this reaction is briefly postulated.Brønsted acid catalyzed isomerization of 7-oxabicyclic alkenes into 1-naphthol derivatives is one of the most fundamental reactions in organic synthesis. [2][3][4] This process has proven to be effective for incorporating the naphthol fragment into complex molecules; 5-8 however, the use of strong protic acids has limited the utilization of this reaction, especially in Brønsted acid sensitive substrates. Furthermore, the use of strong protic acids leads to highly acidic waste streams, which pose an environmental problem for industrial processes. For these reasons, several alternative approaches to 1-naphthol derivatives that do not require the presence of strong protic acids have been developed. Unfortunately, these methods suffer from drawbacks such as the use of expensive palladium catalysts, high reaction temperatures and limited substrate scope. Miura et al. 9 reported a palladium-catalyzed annulation of o-bromobenzaldehydes with 2-substituted 2-alkenals, however, high temperature (120°C) is required in this reaction. Furthermore, yields are generally moderate due to the production of 1,3-disubstituted naphthalenes accompanied by decarbonylation. Recently, Martin et al. 10 reported an elegant palladium-catalyzed ring-opening of 7-oxabicyclic alkenes with aryl and vinyl halides followed by oxidation of the intermediate dihydronaphthols with 2-iodoxybenzoic acid (IBX). This protocol provides 2-substituted 1-naphthol derivatives in good yields, however, it suffers from drawbacks such as the use of expensive palladium catalyst and excess IBX (3 equiv). From a practical point of view, it is thus highly desirable to develop a novel method for the preparation of 1-naphthol derivatives.During the past decades, metal-based Lewis acids have found many applications in organic synthesis. 11 Nevertheless, they have largely been neglected as effective catalysts for the isomerization of 7-oxabicyclic alkenes into 1-naphthol derivatives, probably due to the reaction with the bridging oxygen of 7-oxabicyclic alkenes, which reduces the reactivity of Lewis acids. Metal triflates are unique Lewis acids that are currently of great research interest. 12-17 Metal triflates are generally stable and still active in the presence of many substrates containing heteroatoms such as nitrogen, oxygen and sulfur. Due to these advantages, they are widely used in organic synthesis. 18 We envisioned that metal triflates with suitable cations and anions might be effective catalysts for the isomerization of 7-oxabicyclic alkenes into 1-naphthol derivatives. In this paper, we report the first example of Cu(OTf) 2 -catalyzed isomerization of 7-oxabicyclic alkenes into 1-naphthol derivatives under mild conditions. 19This methodology has the following features: (i) it differs from the isomerization catalyzed by Brønsted acids in having a ...
In the title complex, [Cu(C17H15NO5)(C12H8N2)]·2H2O, the central CuII ion is five-coordinate, bound to one N atom and two O atoms from the Schiff base ligand and by two N atoms from a 1,10-phenanthroline ligand in a distorted square-pyramidal configuration. In the crystal, intermolecular O—H⋯O and C—H⋯O hydrogen bonds form a two-dimensional network parallel to (001).
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