Prins-type macrocyclizations as an efficient ring-closing strategy in natural product synthesis

Prins-type macrocyclizations have recently emerged as a successful strategy in the synthesis of polyketide-derived natural products. This reaction provides a concise and selective means to form tetrahydropyran-containing macrocyclic rings of varying size. A high degree of functionality within the macrocycle is tolerated and the yields for these transformations are typically good to excellent. Since the initial report of a Prins macrocyclization reaction in 1979, examples of this approach did not re-emerge until 2008. However, the use of this method in natural product synthesis has rapidly gained momentum in the synthetic community, with multiple examples of this macrocyclization tactic reported in the recent literature.     

The interaction of lipid modified pseudopeptides with lipid membranes

We have studied the structure of two lipopeptides based on the simple dipeptide building block L-Phe-D-Oxd. These peptides have been reported previously to form fiber-like materials. The lipopeptides synthesized here had the structures C(n)(2)H((2n+1))CO-L-Phe-D-Oxd-OBn or C(n)(2)H((2n+1))CO-D-Phe-L-Oxd-OBn with n = 5 or 11. Addition of the N-terminal lipid modification did not cause a major disturbance of the structures these molecules form. The lipid modifications themselves showed highly rigid structures as inferred from solid-state (2)H NMR. The peptide backbone showed (13)C NMR chemical shifts in agreement with β-sheet secondary structure. Addition of a lipid modification to the N-terminus is a common motif in biology to attach proteins to the membrane. Therefore, we also investigated the lipopeptides in the presence of synthetic POPC bilayers. Two different molecular species were detected under these circumstances: (i) lipopeptide monomers that showed chain order parameters similar to those of the host membrane, (ii) lipopeptide aggregates that exhibited very similar structures and dynamics as the crystalline aggregates. Overall, the lipopeptides showed a well defined and rigid secondary structure that is in agreement with fibrillar aggregates previously detected for those peptides without the lipid modification.     

Templating S100A9 amyloids on Aβ fibrillar surfaces revealed by charge detection mass spectrometry,microscopy, kinetic and microfluidic analyses

The mechanism of amyloid co-aggregation and its nucleation process are not fully understood in spite of extensive studies. Deciphering the interactions between proinflammatory S100A9 protein and Aβ₄₂ peptide in Alzheimer''s disease is fundamental since inflammation plays a central role in the disease onset. Here we use innovative charge detection mass spectrometry (CDMS) together with biophysical techniques to provide mechanistic insight into the co-aggregation process and differentiate amyloid complexes at a single particle level. Combination of mass and charge distributions of amyloids together with reconstruction of the differences between them and detailed microscopy reveals that co-aggregation involves templating of S100A9 fibrils on the surface of Aβ₄₂ amyloids. Kinetic analysis further corroborates that the surfaces available for the Aβ₄₂ secondary nucleation are diminished due to the coating by S100A9 amyloids, while the binding of S100A9 to Aβ₄₂ fibrils is validated by a microfluidic assay. We demonstrate that synergy between CDMS, microscopy, kinetic and microfluidic analyses opens new directions in interdisciplinary research.

Templating mechanism of S100A9 amyloids on Aβ fibrillar surfaces during amyloid co-aggregation process was revealed by synergy of biophysical methods including charge detection mass spectrometry, microscopy, kinetic and microfluidic analyses.     

Field and pressure response of Yb compounds close to a quantum critical point

YbCu_5−x Al _x provides the possibility to tune ground state properties by a change of the valence due to the Cu/Al substitution, by pressure as well as by the application of a magnetic field. Near to the critical concentration x _cr≈1.5 non-Fermi-liquid properties (NFL) are obvious, obeying hyperscaling. If magnetic order sets in for x>1.5, the application of moderate magnetic fields quenches order and again NFL features become evident. Hyperscaling in this case indicates strongly interacting spin fluctuations.