End‐On Nitrogen Insertion of a Diazo Compound into a Germanium(II) Hydrogen Bond and a Comparable Reaction with Diethyl Azodicarboxylate

A happy ending : The germanium(II) hydride [LGeH], where L=[HC{(CMe)(2,6‐iPr₂C₆H₃N)}₂], reacts with a diazoalkane to form the hydrazone derivative (see picture). The reaction proceeds through the unprecedented end‐on nitrogen insertion of the diazo compound.

     

Hydrogen-bond-mediated enantio- and regioselectivity in a Ru-catalyzed epoxidation reaction

A chiral epoxidation catalyst based on a tricyclic octahydro-1H-4,7-methanoisoindol-1-one scaffold, in which a hydrogen bonding site and the catalytically active ruthenium center are spatially separated, was synthesized. It was shown that epoxidation reactions in such a supramolecular catalyst occur with high enantio- and regioselectivity because the hydrogen bonds expose the substrate to the ruthenium porphyrin complex with a clear conformational preference. The epoxidation of 3-vinylquinolone proceeded in up to 95% ee (71% yield).     

Isolation and structure elucidation of a novel yellow pigment from the marine bacterium Pseudoalteromonas tunicata

The marine environment is a major source for many novel natural compounds. A new yellow pigment has been isolated from the marine bacterium P. tunicata and identified as a new member of the tambjamine class of compounds. The structural identification was achieved by a combination of 1D and 2D-NMR spectroscopy and high resolution mass spectrometry data.     

Molecular libraries in liquid phase via UGI-MCR

Standard chemistry prescribes the conversion of one or two compounds into their products. In contrast, Eintopf (one-pot) multicomponent reactions (MCRs) involve at least three different compounds. One-pot MCRs are a useful tool in combinatorial chemistry: From a mixture of educts a large number of products can be simultaneously formed in liquid phase, called a soluble molecular library. The member compounds of such libraries are investigated simultaneously for desired properties, e.g. antibiotic activity. The main constraint is, that the underlying chemistry must not produce unknown side reactions and must lead to a broad spectrum of stable products with high yields. Isocyanide multicomponent chemistry allows the generation of soluble libraries of very different sizes, which are easy to screen for biological or pharmaceutical efficacy using the algorithms presented. Products can easily be enumerated and the kinetics of the isocyanide chemistry is simple to investigate. Combinatorial chemistry is capable of generating and optimizing leads faster and with fewer resources than by conventional means. Combinatorial chemistry based on isocyanide chemistry is by far the most important and most impressive technique in use today to reducing time and costs associated with lead generation and optimization during the drug discovery process. The simplicity of the reaction conditions involved means that the generation and screening of libraries can be automated.     

Applying an edit distance to the matching of tree ring sequences in dendrochronology

In dendrochronology wood samples are dated according to the tree rings they contain. The dating process consists of comparing the sequence of tree ring widths in the sample to a dated master sequence. Assuming that a tree forms exactly one ring per year a simple sliding algorithm solves this matching task.

But sometimes a tree produces no ring or even two rings in a year. If a sample sequence contains this kind of inconsistencies it cannot be dated correctly by the simple sliding algorithm. We therefore introduce a algorithm for dating such a sample sequence against an error-free master sequence, where n and m are the lengths of the sequences. Our algorithm takes into account that the sample might contain up to missing or double rings and suggests possible positions for these kind of inconsistencies. This is done by employing an edit distance as the distance measure.     

Redox control of a polymerization catalyst by changing the oxidation state of the metal center

The activity of cerium alkoxide complexes supported by a Schiff base ligand was controlled using redox reagents during the ring-opening polymerization of L-lactide. The rate of L-lactide polymerization was modified by switching in situ between the cerium(III) and cerium(IV) species.     

Redox control of a ring-opening polymerization catalyst

The activity of an yttrium alkoxide complex supported by a ferrocene-based ligand was controlled using redox reagents during the ring-opening polymerization of L-lactide. The oxidized complex was characterized by X-ray crystallography and (1)H NMR, XANES, and M?ssbauer spectroscopy. Switching in situ between the oxidized and reduced yttrium complexes resulted in a change in the rate of polymerization of L-lactide. Synthesized polymers were analyzed by gel permeation chromatography. Polymerization of trimethylene carbonate was also performed with the reduced and oxidized forms of an indium alkoxide complex. The indium system showed the opposite behavior to that of yttrium, revealing a metal-based dependency on the rate of polymerization.     

Product ion mobility as a promising tool for assignment of positional isomers of drug metabolites

Travelling wave ion mobility spectrometry - mass spectrometry (TWIMS-MS) was evaluated as a tool for structural identification of metabolites of small molecule drugs in cases where the exact position of the biotransformation could not be identified by conventional tandem mass spectrometry. Test sets of compounds containing biotransformations at aromatic positions were analyzed. These present a problem for traditional MS methods since an atomic level localization of the biotransformation cannot normally be determined from MS(n) spectra. In addition to ion mobility measurements of the intact metabolite ions, ion mobility measurements of product ions were also made and the results compared with calculated values. This approach reduces the complexity of the problem, making theoretical calculations easier and more predictable when a modeled collision cross section (CCS) is required. A good relative correspondence between theoretical and measured CCSs was obtained allowing the identification of the exact position of the biotransformation. It was also demonstrated that authentic standards with substructures identical to those in the unknown can be used to assign the exact position of the biotransformation. In this approach the identification was based on the comparison of the drift times or CCSs for product ions of the standard, with those of the same product ions in the unknown.