Loss of co-linearity by modular polyketide synthases: a mechanism for the evolution of chemical diversity

Modular polyketide synthases biosynthesise natural products through successive Claisen-type condensations, where one module is responsible for one round of chain extension. This review describes recent findings where this rule of co-linearity is broken, either by one module being bypassed (skipping) or through one module being used for multiple chain extension events (stuttering).     

Unprecedented chemistry of an aryloxychlorodiazirine: generation of a dihalodiazirine and diazirinone

The reaction of p-nitrophenoxychlorodiazirine with tetrabutylammonium fluoride follows three channels: (1) approximately 17% of p-nitrophenoxide/fluoride exchange to chlorofluorodiazirine and p-nitrophenol, (2) approximately 28% of Cl/F exchange to p-nitrophenoxyfluorodiazirine, and (3) approximately 55% of ipso fluoride attack, affording p-nitrofluorobenzene and the previously unknown diazirinone (diazacyclopropenone).     

A dimerization "switch" in the internalization mechanism of a cell-penetrating peptide

The internalization mechanism of a cell-penetrating peptide has been explored through combinatorial selection of a phage-displayed peptide dimer library, chemical synthesis, and biophysical characterization. Both energy-dependent and energy-independent modes for peptide uptake by the target mammalian cells were observed, suggesting a role for higher-order structure in modulating the action of this novel cell-penetrating peptide.     

Thermal rearrangement of divinylcyclopropane systems. A new formal total synthesis of (±)-quadrone

The key step of a new approach to the total synthesis of the structurally and physiologically interesting sesquiterpenoid (±)-quadrone (1) involves thermal (Cope) rearrangement of the highly functionalized divinylcyclopropane derivative 8. The product 9 of this process is converted into 19, thus completing a formal total synthesis of (±)-1.     

Hopping on a zig-zag course

We study the diffusion coefficient of Active Brownian particles in two dimensions. In addition to usual attributes of active motion we let the particles turn in preferred directions over random times. This angular motion is modeled by an effective Lorentz force with time dependent frequency switching between two values at exponentially distributed random times. The diffusion coefficient is calculated by the Taylor-Kubo formula where distributions found from a Fokker-Planck equation or from a continuous time random walk approach have been inserted for averaging. Eventually properties of the diffusion coefficient will be discussed.     

A palladium catalysed cyclisation-carbonylation of bromodienes: control in carbonylation over facile beta-hydride elimination

Conditions have been found for the efficient palladium mediated cyclisation-carbonylation of bromodienes to give gamma,lambda-unsaturated acids.     

Stereochemical study of phosphonothioate cleavage by a metallomicelle

[reaction: see text] The copper metallomicellar hydrolysis of O-methyl O-4-nitrophenyl phenylphosphonothioate to O-methyl phenylphosphonothioic acid takes place with effectively complete inversion at phosphorus.     

Synchronization of noisy systems by stochastic signals

We study, in terms of synchronization, the nonlinear response of noisy bistable systems to a stochastic external signal, represented by Markovian dichotomic noise. We propose a general kinetic model which allows us to conduct a full analytical study of the nonlinear response, including the calculation of cross-correlation measures, the mean switching frequency, and synchronization regions. Theoretical results are compared with numerical simulations of a noisy overdamped bistable oscillator. We show that dichotomic noise can instantaneously synchronize the switching process of the system. We also show that synchronization is most pronounced at an optimal noise level-this effect connects this phenomenon with aperiodic stochastic resonance. Similar synchronization effects are observed for a stochastic neuron model stimulated by a stochastic spike train.