Synthesis of a 4-Deoxy-4-C-Methylene Analog of Glucosylceramide

Abstract

D-Glucose was transformed into 2,3:5,6-di-O-isopropylidene dithioacetal 1; its oxidation to ketone 2 and subsequent Wittig reaction afforded 4-deoxy-4-C-methylene derivative 3. Hydrolytic removal of the protective groups, then O-acetylation, selective anomeric O-deacetylation, and base catalyzed trichloroacetonitrile addition furnished 4-deoxy-4-C-methylene substituted glycopyranosyl donor 7 as an anomeric mixture. Reaction of 7 with azidosphingosine derivative 8 under BF₃-OEt₂ catalysis gave β-glycopy-ranoside 9. Azido group reduction with triphenylphospnine in the presence of palmitic anhydride and water afforded directly O-acyl protected glycosphingolipid derivative 10 which yielded after Zemplen O-deacylation target molecule 11     

Chemoinformatik

Cheminformatics is a very interdisciplinary and fascinating field with various computer‐based methods intended to support molecular scientists. This article gives an introduction and a broad overview of several application areas to non‐experts. A main and basic application area in Cheminformatics is target on a proper 2D or 3D chemical structure representation. Additionally, the huge amount of chemical data is managed electronically. Computer‐based methods allow to large scale analyze this data to build models and to make predictions, in order to create new compounds with new properties.     

Excited and ground state vibrational dynamics revealed by two-dimensional electronic spectroscopy

Broadband two-dimensional electronic spectroscopy (2DES) can assist in understanding complex electronic and vibrational signatures. In this paper, we use 2DES to examine the electronic structure and dynamics of a long chain cyanine dye (1,1-diethyl-4,4-dicarbocyanine iodide, or DDCI-4), a system with a vibrational progression. Using broadband pulses that span the resonant electronic transition, we measure two-dimensional spectra that show a characteristic six peak pattern from coherently excited ground and excited state vibrational modes. We model these features using a spectral density formalism and the vibronic features are assigned to Feynman pathways. We also examine the dynamics of a particular set of peaks demonstrating anticorrelated peak motion, a signature of oscillatory wavepacket dynamics on the ground and excited states. These dynamics, in concert with the general structure of vibronic two-dimensional spectra, can be used to distinguish between pure electronic and vibrational quantum coherences.     

Fragment momentum distributions obtained from coupled electron-nuclear dynamics

We theoretically investigate fragmentation processes induced by femtosecond laser pulses within a model which incorporates electronic and nuclear motion. Single-pulse excitation leads to diffraction patterns in the electron momentum distribution which depend on the nature of the electronic state and also on the nuclear charge distribution. Additional structures appear in the nuclear momentum distribution if two time-delayed pulses produce fragments in the same dissociation channel. It is shown that these functions are modified by the electronic degree-of-freedom. A simultaneous excitation of two different electronic states results in further interferences which are related to electronic wave-packet dynamics on the attosecond time-scale.     

On the accuracy of explicitly correlated coupled-cluster interaction energies--have orbital results been beaten yet?

The basis set convergence of weak interaction energies for dimers of noble gases helium through krypton is studied for six variants of the explicitly correlated, frozen geminal coupled-cluster singles, doubles, and noniterative triples [CCSD(T)-F12] approach: the CCSD(T)-F12a, CCSD(T)-F12b, and CCSD(T)(F12*) methods with scaled and unscaled triples. These dimers were chosen because CCSD(T) complete-basis-set (CBS) limit benchmarks are available for them to a particularly high precision. The dependence of interaction energies on the auxiliary basis sets has been investigated and it was found that the default resolution-of-identity sets cc-pVXZ/JKFIT are far from adequate in this case. Overall, employing the explicitly correlated approach clearly speeds up the basis set convergence of CCSD(T) interaction energies, however, quite surprisingly, the improvement is not as large as the one achieved by a simple addition of bond functions to the orbital basis set. Bond functions substantially improve the CCSD(T)-F12 interaction energies as well. For small and moderate bases with bond functions, the accuracy delivered by the CCSD(T)-F12 approach cannot be matched by conventional CCSD(T). However, the latter method in the largest available bases still delivers the CBS limit to a better precision than CCSD(T)-F12 in the largest bases available for that approach. Our calculations suggest that the primary reason for the limited accuracy of the large-basis CCSD(T)-F12 treatment are the approximations made at the CCSD-F12 level and the non-explicitly correlated treatment of triples. In contrast, the explicitly correlated second-order Mo?ller-Plesset perturbation theory (MP2-F12) approach is able to pinpoint the complete-basis-set limit MP2 interaction energies of rare gas dimers to a better precision than conventional MP2. Finally, we report and analyze an unexpected failure of the CCSD(T)-F12 method to deliver the core-core and core-valence correlation corrections to interaction energies consistently and accurately.     

An efficient route to the musk odorant (R,Z)-5-muscenone via base-metal-catalysis

Muscenone^® is a valuable perfume ingredient consisting of a mixture of the E- and Z-isomers of 1 in racemic form as the major constituents. Among them, it is the (R,Z)-isomer, which exhibits the most favorable musk character and by far the lowest threshold; for these superior olfactory properties, pure (R,Z)-1 has recently been commercialized too. We present an efficient route to this precious compound based on an iron-catalyzed cross coupling reaction, a molybdenum-catalyzed alkyne metathesis for the formation of the macrocyclic ring, and a nickel-catalyzed semi-hydrogenation.