A Highly Convergent Total Synthesis of (+)-Myxovirescine M2. Preliminary Communication

The antibiotic myxovirescine M₂ was synthesized from seven building blocks ( 1 – 7 , Scheme 1), with the following chiral starting materials being employed: (S)-malic acid, (+)-D -ribonolactone, (S)-2-(hydroxymethyl)butanoate, and (2R,4S)-5-hydroxy-2,4-dimethylpenLanoate. Three new nucleophilic reagents, 8 – 10 , for C-C bond formation have been used. The key steps of the synthesis are: a Suzuki coupling between an alkyl borane and a vinyl bromide ( 4 + 12e → 13 ), a Julia olefinalion ( 14 + 17 → 18 ), and a Yamaguchi macrolactonizalion to form the 28-membered lactone ( 18 → 19 ), This extremely convergenl synthetic approach will allow the preparation of a number of the 31 known myxovirescine molecules.     

Preparation of Oxazolidine-Containing Peptides: Unusual effects in RhIII-catalyzed acetalizations of aldehydes with urethane-protected serine and threonine esters and with dipeptides containing serine or threonine residues at the N-terminus

The cyclization reaction of aldehydes with Z- and Boc-protected β-hydroxyamino-acid esters (Tables 1 and 2), or of dipeptides containing serine or threonine at the N-terminus (Table 3), to give oxazolidine derivatives, occurs in the presence of isopropyl orthoformate and catalytic amounts of [Rh(MeCN)₃(triphos)](CF₃SO₃)₃. The reaction may be carried out under kinetic or under thermodynamic control, so that the ratio of the two possible epimeric products can be changed. The protecting group can be removed from the 3-position of the oxazolidine ring, and the resulting NH group can be coupled with another amino acid. Thus, a new method for the preparation of peptides containing β-hydroxy-amino acid-derived oxazolidines (‘pseudo-prolines’) is available. N-Neopentyl-substituted tripeptides are also described.     

Physics reach with CMS at high and super-high luminosities

The European Physical Journal C - The physics reach of the Compact Muon Solenoid, under construction to study proton-proton collisions at a centre-of-mass energy of 14 TeV, is presented at design...     

Iron(II) Spin‐Crossover Complexes in Ultrathin Films: Electronic Structure and Spin‐State Switching by Visible and Vacuum‐UV Light

The electronic structure of the iron(II) spin crossover complex [Fe(H₂bpz)₂(phen)] deposited as an ultrathin film on Au(111) is determined by means of UV‐photoelectron spectroscopy (UPS) in the high‐spin and in the low‐spin state. This also allows monitoring the thermal as well as photoinduced spin transition in this system. Moreover, the complex is excited to the metastable high‐spin state by irradiation with vacuum‐UV light. Relaxation rates after photoexcitation are determined as a function of temperature. They exhibit a transition from thermally activated to tunneling behavior and are two orders of magnitude higher than in the bulk material.     

Emergent criticality through adaptive information processing in boolean networks

We study information processing in populations of boolean networks with evolving connectivity and systematically explore the interplay between the learning capability, robustness, the network topology, and the task complexity. We solve a long-standing open question and find computationally that, for large system sizes N, adaptive information processing drives the networks to a critical connectivity K(c)=2. For finite size networks, the connectivity approaches the critical value with a power law of the system size N. We show that network learning and generalization are optimized near criticality, given that the task complexity and the amount of information provided surpass threshold values. Both random and evolved networks exhibit maximal topological diversity near K(c). We hypothesize that this diversity supports efficient exploration and robustness of solutions. Also reflected in our observation is that the variance of the fitness values is maximal in critical network populations. Finally, we discuss implications of our results for determining the optimal topology of adaptive dynamical networks that solve computational tasks.     

On the E1 partial wave sum rule and the WKB approximation

The electric dipole (E1) partial wave sum rule, relevant to Coulomb scattering, is derived semiclassically within the WKB theory. Limiting expressions are presented according to the values of the angular momentum l of the colliding particle, the Sommerfeld number and the adiabaticity parameter ξ = ν _? - ν _i. A comparison with the quantal results, of the WKB sum rule and the classical orbital integrals, shows that the WKB approximation is extremely accurate even in the case of light and/or fast particles (ν ? 1). An algorithm is presented for the calculation of the modified Bessel function of the second kind with imaginary argument K _iξ(x) and its derivative dK _iξ(x)/dx.