Total Syntheses of 11-Acetoxy-4-deoxyasbestinin D, 4-Deoxyasbestinin C,Asbestinin-10, -20, -21 and -23

Six members of the asbestinin family of marine diterpene natural products have been synthesized in an efficient and stereoselective manner from a single oxa-bridged intermediate. Five of these natural products have not been synthesized previously and the structures of four of them have been confirmed as those proposed originally or following revisions to the original structures. The fifth natural product—asbestinin-21—has been shown to be a diastereomer of the compound that had been proposed previously.     

Discovery of Chemicals to Either Clear or Indicate Amyloid Aggregates by Targeting Memory‐Impairing Anti‐Parallel Aβ Dimers

Amyloid‐β (Aβ) oligomers are implicated in Alzheimer disease (AD). However, their unstable nature and heterogeneous state disrupts elucidation of their explicit role in AD progression, impeding the development of tools targeting soluble Aβ oligomers. Herein parallel and anti‐parallel variants of Aβ(1–40) dimers were designed and synthesized, and their pathogenic properties in AD models characterized. Anti‐parallel dimers induced cognitive impairments with increased amyloidogenesis and cytotoxicity, and this dimer was then used in a screening platform. Through screening, two FDA‐approved drugs, Oxytetracycline and Sunitinib, were identified to dissociate Aβ oligomers and plaques to monomers in 5XFAD transgenic mice. In addition, fluorescent Astrophloxine was shown to detect aggregated Aβ in brain tissue and cerebrospinal fluid samples of AD mice. This screening platform provides a stable and homogeneous environment for observing Aβ interactions with dimer‐specific molecules.     

Design of Oligourea-Based Foldamers with Antibacterial and Antifungal Activities

There is an urgent need to develop new therapeutic strategies to fight the emergence of multidrug resistant bacteria. Many antimicrobial peptides (AMPs) have been identified and characterized, but clinical translation has been limited partly due to their structural instability and degradability in physiological environments. The use of unnatural backbones leading to foldamers can generate peptidomimetics with improved properties and conformational stability. We recently reported the successful design of urea-based eukaryotic cell-penetrating foldamers (CPFs). Since cell-penetrating peptides and AMPs generally share many common features, we prepared new sequences derived from CPFs by varying the distribution of histidine- and arginine-type residues at the surface of the oligourea helix, and evaluated their activity on both Gram-positive and Gram-negative bacteria as well as on fungi. In addition, we prepared and tested new amphiphilic block cofoldamers consisting of an oligourea and a peptide segment whereby polar and charged residues are located in the peptide segment and more hydrophobic residues in the oligourea segment. Several foldamer sequences were found to display potent antibacterial activities even in the presence of 50% serum. Importantly, we show that these urea-based foldamers also possess promising antifungal properties.     

Theoretical and empirical approaches to understanding the effect of phosphonate groups on the thermal degradation for two chemically modified PMMA

The influence of phosphonated groups on thermal degradation and flammability has been investigated in the case of two chemically modified PMMA. Thermogravimetric analysis as well as pyrolysis combustion flow calorimetry have been used to define the efficiency of phosphorus in both condensed and vapor phases. A theoretical study was also performed to determine the contribution of phosphonated groups to the effective heat of combustion, residue content and heat release capacity. Empirical and theoretical approaches agreed to highlight that PMMA modified with monophosphonated comonomer is more efficient in both condensed and vapor phases in terms of flammability and char formation. These results were attributed to the ability of phosphonate groups to interact with ester groups and also to the weakness of the P–C–N bonds. Moreover, this study proposes a method for designing the chemical environment of phosphonate group in polymers to achieve better flame retardancy.     

Ligand trans-effect: using an old concept as a novel approach to bis(dipolar) NLO-phores

In plane parallel arrangement and enhancement of NLO-activity are observed upon coordination of heteroditopic dipoles containing a phosphole ring on square-planar d8-palladium centre.     

One-step stereoselective synthesis and NMR chiral shift properties of a novel hexacoordinated phosphorus cation

[reaction: see text] Tropolone, binol, and PCl(5) react in CH(2)Cl(2) at reflux to generate in one step a novel C(2)-symmetric hexacoordinated phosphorus cation of configuration controlled by the binol ligand. It behaves as an efficient NMR chiral shift agent for chiral anionic phosphate and borate anions.     

Double-quantum filtered MAS NMR in the presence of chemical shielding anisotropies and direct dipolar and J couplings

Double-quantum filtered MAS NMR spectra of an isolated homonuclear spin-1/2 pair are considered, at and away from rotational resonance conditions. The pulse sequence used is the solid-state NMR equivalent of double-quantum filtered COSY, known from solution-state NMR. The 119Sn spin pair in [(chex3Sn)2S] is characterized by a difference in isotropic chemical shielding smaller than the two chemical shielding anisotropies and by direct dipolar and isotropic J-coupling constants of similar magnitudes. At rotational resonance, one-dimensional double-quantum filtered 119Sn lineshapes yield the relative orientation of the two 119Sn chemical shielding tensors. Good double-quantum filtration efficiencies are found at and away from rotational resonance conditions, despite the presence of large chemical shielding anisotropies. Numerical simulations illustrate the interplay of the direct dipolar and J-coupling pathways and identify the latter as the main pathway even at rotational resonance conditions.