Tobias Braxmeier

Efficient Inhibition of the Alzheimer's Disease β-Secretase by Membrane Targeting

β-Secretase plays a critical role in β-amyloid formation and thus provides a therapeutic target for Alzheimers disease. Inhibitor design has usually focused on active-site binding, neglecting the subcellular localization of active enzyme. We have addressed this issue by synthesizing a membrane-anchored version of a β-secretase transition-state inhibitor by linking it to a sterol moiety. Thus, we targeted the inhibitor to active β-secretase found in endosomes and also reduced the dimensionality of the inhibitor, increasing its local membrane concentration. This inhibitor reduced enzyme activity much more efficiently than did the free inhibitor in cultured cells and in vivo. In addition to effectively targeting β-secretase, this strategy could also be used in designing potent drugs against other membrane protein targets.

Isocyanates — Part 3.7 Synthesis of carbamates by DMAP-catalyzed reaction of amines with di-tert-butyldicarbonate and alcohols

Abstract Carbamates are prepared by DMAP-catalyzed reaction of amines with di-tert-butyldicarbonate and subsequent trapping of the intermediate isocyanates with alcohols.

Isocyanates Part 5. Synthesis of chiral oxazolidin-2-ones and imidazolidin-2-ones via DMAP-catalyzed isocyanation of amines with di-tert-butyl dicarbonate

Abstract Oxazolidin-2-ones and imidazolidin-2-ones are prepared under mild reaction conditions by DMAP-catalyzed isocyanation of 1,2-aminoalcohols and 1,2-diamines with di-tert-butyl dicarbonate and subsequent cyclization.

Computational screening for membrane-directed inhibitors of mast cell activation

Receptor-mediated signaling events frequently depend on the integrity of their membrane environments. Only a limited number of compounds are currently available that are known or thought to modulate membrane environments and affect signaling events without disrupting membrane structure. Among these are alkylphospholipids including the drug miltefosine that is approved for the treatment of breast cancer and leishmaniasis. In addition, miltefosine has recently been shown to block immunoglobulin E receptor-dependent mast cell activation. On the basis of these findings, we have explored other alkylphospholipids as potential inhibitors of mast cell activation and confirmed the inhibitory activity of five molecules. By comparing the head groups of these alkylphospolipids common pharmacophore features were determined. Through computational screening utilizing this pharmacophore information a new lipid-like inhibitory chemotype was identified that blocked mast cell activation with potency comparable to miltefosine.

Evaluation of steroidal amines as lipid raft modulators and potential anti-influenza agents.

The influenza A virus (IFV) possesses a highly ordered cholesterol-rich lipid envelope. A specific composition and structure of this membrane raft envelope are essential for viral entry into cells and virus budding. Several steroidal amines were investigated for antiviral activity against IFV. Both, a positively charged amino function and the highly hydrophobic (ClogP≥5.9) ring system are required for IC50 values in the low μM range. An amino substituent is preferential to an azacyclic A-ring. We showed that these compounds either disrupt or augment membrane rafts and in some cases inactivate the free virus. Some of the compounds also interfere with virus budding. The antiviral selectivity improved in the series 3-amino, 3-aminomethyl, 3-aminoethyl, or by introducing an OH function in the A-ring. Steroidal amines show a new mode of antiviral action in directly targeting the virus envelope and its biological functions.

Lipid-like sulfoxides and amine oxides as inhibitors of mast cell activation.

The drug miltefosine is a prototypic lipid-like compound thought to modulate membrane environments and thereby indirectly prevent receptor-mediated signaling events. In addition to its primary therapeutic indications in cancer and leishmaniasis, miltefosine has also been shown to block immunoglobulin E receptor-dependent mast cell activation. Miltefosine and other alkylphospholipids that are active in mast cell degranulation assays contain a positively charged nitrogen and a phosphate group that are important for activity. In addition to alkylphospholipids, ceramides are also known to act on membrane environments and inhibit mast cell activation. We have systematically searched a very large compound collection for other lipid-like inhibitors of mast cell activation. Analogs of an initially identified screening hit were synthesized and preliminary SAR information was collected, leading to the identification of sulfoxide and amine oxide containing lipid-like compounds as new inhibitors of mast cell activation. Sulfoxide and amine oxide derivatives were found to be only slightly less active than miltefosine.

Tert-butyl isocyanate, a non-rigid molecule

Abstract The geometric structure of tert-butyl isocyanate, (CH 3 ) 3 CNCO, was determined by gas electron diffraction. The scattering intensities are fitted best with a non-rigid model which possesses a large-amplitude torsional motion of the tert-butyl group around the NC bond and an equilibrium structure with staggered orientation of the tert-butyl group with respect to the NCO group. The nitrogen bond angle [CNC = 137(2)°] is equal to that estimated from rotational constants. It is very similar to CNC angles in methyl and ethyl isocyanate and is not affected by steric interactions.