The Total Synthesis of the Bioactive Natural Product Plantazolicin A and Its Biosynthetic Precursor Plantazolicin B

Herein, we describe our full investigations into the synthesis of the peptide‐derived natural product plantazolicin A, a compound that demonstrates promising selective activity against the causative agent of anthrax toxicity, and its biosynthetic precursor plantazolicin B. This report particularly focuses on the challenging preparation of the arginine containing thiazole fragment, including the development of a robust, high yielding procedure that avoids the use of sulfurating agents. Extensive studies on the design of a coherent protecting group strategy and the establishment of a step‐efficient dicyclization/oxidation approach allowed high levels of convergence for the construction of the oxazole fragments. This has led to a unified, highly convergent synthesis for both plantazolicin A and B.     

[1,3‐Bis(4‐nitrophenyl)triazenido](triphenylphosphine)gold(I)

In the title complex, [Au(C₁₂H₈N₅O₄)(C₁₈H₁₅P)], the coordination geometry about the Au^I ion is linear, with one deprotonated 1,3‐bis(4‐nitro­phenyl)­triazenide ion, [O₂NC₆H₄N=N–NC₆H₄NO₂]⁻, acting as a monodentate ligand (two‐electron donor), and one neutral tri­phenyl­phosphine mol­ecule completing the metal coordination. The triazenide ligand is almost planar (r.m.s. deviation = 0.0767 Å), with the largest interplanar angle being 11.6 (7)° between the phenyl ring of one of the terminal 4‐nitro­phenyl substituents and the plane defined by the N=N—N triad. The Au—N and Au—P distances are 2.108 (5) and 2.2524 (13) Å, respectively. Pairs of mol­ecules generated by centrosymmetry are associated into a supramolecular array via intermolecular C—H⋯O inter­actions, and N⋯C and N⋯O π–π interactions.     

Recognizing connectedness from vertex‐deleted subgraphs

Let G be a graph of order n. The vertex‐deleted subgraph G ? v, obtained from G by deleting the vertex v and all edges incident to v, is called a card of G. Let H be another graph of order n, disjoint from G. Then the number of common cards of G and H is the maximum number of disjoint pairs (v, w), where v and w are vertices of G and H, respectively, such that G ? v?H ? w. We prove that if G is connected and H is disconnected, then the number of common cards of G and H is at most ?n/2? + 1. Thus, we can recognize the connectedness of a graph from any ?n/2? + 2 of its cards. Moreover, we completely characterize those pairs of graphs that attain the upper bound and show that, with the exception of six pairs of graphs of order at most 7, any pair of graphs that attains the maximum is in one of four infinite families. © 2010 Wiley Periodicals, Inc. J Graph Theory 67:285‐299, 2011     

On local solutions to non-Newtonian slow viscous flows

The eigenfunction expansion method is used to obtain local solutions to some non-Newtonian slow viscous flows. The forms of viscosity variation amenable to such analysis are restricted but do include power-law fluids. Power-law flow near a sharp corner between plane boundaries is analysed and results are obtained for the critical corner angle for eddy formation. Flows near a 90° corner with either a moving boundary or a finite flow rate at the corner are also considered. The “stick-slip” behaviour of a power-law fluid at a plane solid boundary is shown to obey a simple law.     

Literatur

Ohne Zusammenfassung     

On the model dependence of the determination of the strong coupling constant in second order QCD from e+e−-annihilation into hadrons

Hadronic events obtained with the CELLO detector at PETRA are compared with second order QCD predictions using different models for the fragmentation of quarks and gluons into hadrons. We find that the model dependence in the determination of the strong coupling constant persists when going from first to second order QCD calculations.