Mild complexation protocol for chiral CpxRh and Ir complexes suitable for in situ catalysis.

A practical complexation method for chiral cyclopentadienyl (Cpx) iridium and rhodium complexes is described. The procedure uses the free CpxH with stable and commercially available rhodium(i) and iridium(i) salts without base or additive. The conditions are mild and do not require the exclusion of air and moisture. A salient feature is the suitability for in situ complexations enhancing the user-friendliness of Cpx ligands in asymmetric catalysis. DFT-calculations confirm an intramolecular proton abstraction pathway by either the bound acetate or methoxide. Furthermore, the superior facial selectivity of the proton abstraction step enabled the development of TMS-containing trisubstituted Cpx ligands which display improved enantioselectivities for the benchmarking dihydroisoquinolone synthesis.

A ß-Carbon elimination strategy for convenient in situ access to cyclopentadienyl metal complexes.

The electronic and steric properties of tailored cyclopentadienyl (Cp) ligands are powerful handles to modulate the catalytic properties of their metal complexes. This requires the individual preparation, purification and storage of each ligand/metal combination. Alternative, ideally in situ, complexation protocols would be of high utility. We disclose a new approach to access Cp metal complexes. Common metal precursors rapidly react with cyclopentadienyl carbinols via ß-carbon eliminations to directly give the Cp-metal complexes. An advantage of this is the direct and flexible use of storable pre-ligands. No auxiliary base is required and the Cp complexes can be prepared in situ in the reaction vessel for subsequent catalytic transformations.

In contrast to specific B cells, human basophils are unaffected by the toxic activity of an allergen toxin due to lack of internalization of immunoglobulin E-bound allergen.

BACKGROUND: Specific immunotherapy is the only curative therapy for type I allergies and the alarming increase in allergy prevalence emphasizes the need for additional/alternative strategies for curative treatment. Allergen toxins (AT), fusion products of an allergen with an apoptosis inducing cytotoxin, are a new kind of immunotoxin. OBJECTIVE: AT should allow allergen-specific targeting and elimination of allergy-relevant cells, with B cells being the primary target. An important question is the fate of the effector cells, e.g. mast cells and basophils, which carry allergen-specific IgE: the immunotoxin might even prove to be harmful. METHODS: We established a reliable in vitro B cell model (using two mouse hybridoma cell lines) for testing specificity and toxicity of P5-ETA', a fusion protein of the major timothy grass pollen allergen Phl p 5b and truncated Pseudomonas Exotoxin A. In a second step, we investigated the impact of the AT on human basophils. RESULTS: P5-ETA' reliably eliminated Phl p 5-specific cells in the in vitro B cell model, leaving unspecific B cells unharmed. Human basophils of grass pollen allergic donors specifically bound P5-ETA', released IL-4 and up-regulated the activation marker CD203c, but were not subject to the toxic effect because of lack of internalization of IgE-bound allergen. CONCLUSION: According to our data, basophils are pure effector cells in the context of IgE-bound allergen and not involved in classical antigen presentation.

How large is the conjugative stabilization of diynes?

The conjugation stabilization energies of dienes and diynes are considerably larger than estimates based on heat of hydrogenation differences between 1,3-butadiyne and 1-butyne as well as between 1,3-butadiene and 1-butene. Such comparisons do not take into account the counterbalancing hyperconjugative stabilization of the partially hydrogenated products by their ethyl groups. When alkyl hyperconjugation is considered, the conjugation stabilization of diynes ( approximately 9.3 kcal/mol) is found by two methods (involving isomerization of nonconjugated into conjugated isomers and heats of hydrogenation) to be larger than that of dienes ( approximately 8.2 kcal/mol).