Margit Gruner

Maradolipids: Diacyltrehalose Glycolipids Specific to Dauer Larva in Caenorhabditis elegans

In response to harsh environmental conditions, such as overcrowding or starvation, the nematode C. elegans interrupts and arrests its reproductive life cycle by forming a specific dauer (enduring) larva. Dauer larvae have very distinct metabolism, morphology, and enhanced stress resistance for surviving unfavorable environmental conditions. They express high amounts of stress-protective proteins such as the heat-shock protein Hsp90, superoxide dismutase, and catalase . They also remodel their body surfaces—they build a dauer-specific cuticle and seal the pharynx with a cuticular block . Although, the dauer larva formation pathway is biologically well investigated, there is not much information about the chemical means by which dauer larvae resist the various kinds of environmental stresses. Similar to some other organisms, lipids might play an important role in the adaptation process of dauer larvae to harsh conditions. We asked whether the transition from reproductive stages to the dauer larva is associated with global changes in the lipid composition or metabolism. For this purpose we used a temperature-sensitive mutant of daf-2(e1370) that reproduces at 15 8C or 20 8C but forms dauer larvae at 25 8C . Lipids were extracted from daf-2(e1370) worms grown at 20 8C and 25 8C (Figures 1 a and b, respectively) and separated by two-dimensional (2D) thin-layer chromatography (TLC) that resolved the major lipid classes: glycerophospholipids, ceramides, glycosphingolipids, fatty acids, sterols, etc. The plates were sprayed with the Molisch reagent, which specifically stains carbohydrate-containing lipids in purple and all other lipid classes in yellow-brown on the same TLC plates. As seen, there is a significant difference between reproductive L3 larvae and dauer larvae (compare Figures 1a and b): In addition to two Molisch-positive (purple) forms of glucosylceramides (GlucCer), a spot that is visible exclusively on the TLC containing the dauer larvae is observed (arrowhead). This spot appeared to be specific to dauer larva; that is, it could not be detected either in the mixed population of wildtype worms grown at 20 8C and 25 8C, or in any other individual reproductive larval stages (L1 to L4, adults; not shown). Most importantly, dauer larvae obtained from starved plates of wild-type worms (N2) displayed a spot of comparable strength (see Figure 1 a (arrowhead) in the Supporting Information). Hence we conclude that the spot represents a genuine lipid component of the natural dauer larvae, which does not depend on the genetic background or temperature. Mobility of the dauer-larva-specific lipid on TLC and its positive reaction to the Molisch reagent suggested that it might be a dauer-specific glycosphingolipid. To test this possibility, we isolated neutral glycolipids (NGL) from dauer larvae (see Figure 2a in the Supporting Information). The dauer-larva-specific spot was indeed found in the glycolipid fraction (NGL, arrowhead). In contrast to glycosphingolipids, however, this lipid was susceptible to saponification (see Figure 1b in the Supporting Information; compare patterns before and after saponification—the spot indicated by arrowhead is absent after the saponification). Our observation indicates that this lipid does not belong to the class of glycosphingolipids and must contain at least one ester bond (amide bonds of glycosphingolipids cannot be cleaved by saponification). On the basis of its occurrence exclusively in dauer larvae and its chemical dissimilarity to glycosphingolipids, we call this lipid maradolipid (from maradi, enduring/ dauer in Georgian). [*] S. Penkov, F. Mende, V. Zagoriy, C. Erkut, K. Schuhmann, Dr. D. Schwudke, J. M ntler, Dr. A. Shevchenko, Prof. Dr. T. V. Kurzchalia Max Planck Institute for Molecular Cell Biology and Genetics Pfotenhauerstraße 108, 01307 Dresden (Germany) Fax: (+ 49)351-210-2000 E-mail: kurzchalia@mpi-cbg.de

Total synthesis of pamamycin-607☆

Abstract The macrodiolide antibiotic pamamycin-607 has been synthesized by coupling of the two hydroxy acid constituents using the Yamaguchi method. While the final lactonization with formation of the ester linkage between C(1) and the C(8′) oxygen proceeded with complete C(2) epimerization, the alternative ring closure involving the carboxylic acid of the smaller fragment and the hydroxyl group of the larger fragment yielded the target molecule.

Conformational behaviour and first crystal structures of a calix[4]arene featuring a laterally positioned carboxylic acid function in unsolvated and solvent-complexed forms

A detailed conformational analysis of a rarely investigated type of compound, a laterally monosubstituted calix[4]arene (1, which has a carboxylic acid function in the lateral position), is reported. 2D solution NMR techniques at various temperatures and in different solvents have been used, showing interesting aggregation behaviour for the different conformers. The first illustrations of crystal structures of this compound type are given, including the unsolvated carboxylic calix[4]arene and two mixed solvent complexes containing EtOH–H2O and EtOH–THF, respectively. Isostructurality calculations have been carried out, allowing detailed comparison of the investigated structures, and an unusual conformational chirality isomerism of the calixarene molecule is demonstrated.

First total synthesis of the biscarbazole alkaloid oxydimurrayafoline

We report the first total synthesis of oxydimurrayafoline via nucleophilic substitution at the benzylic position at C-3 of the carbazole framework.

Influence of laterally attached alkyl groups on the conformational behaviour of a basic calix[4]arene: combined NMR, molecular mechanics and X-ray study

Three new calixarenes 3–5 featuring an alkyl residue of different chain lengths attached to one of the central ring methylene groups of the basic calix[4]arene 1 have been prepared. A systematic study that includes also the lower homologous compound 2 showing the effect of the alkyl substitution on the conformational behaviour of the calixarene framework in comparison with the unsubstituted parent compound 1 is reported. The application of special 2D NMR techniques, 2D-EXSY and ROESY methods at various temperatures establishes that calixarenes 2–5 adopt the partial cone conformation of lower symmetry and far less the symmetric cone and 1,2-alternate conformations. In solution, they undergo a fast interconversion with relatively low activation energies of about 15 kcal/mol at room temperature. The conformer distribution is well reproduced by molecular mechanistic calculations (MMFF94), indicating the present conformers to assume the lowest steric energies. A single-crystal X-ray structure of the lateral ethyl derivative 2 corroborates these results, showing the molecule in a sterically favourable partial cone conformation.

Synthesis and photophysical properties of colloids fabricated by the layer-by-layer polyelectrolyte assembly onto Eu(III) complex as a core

The luminescent colloids have been synthesized through the layer-by-layer assembly of poly(sodium 4-styrenesulfonate) (PSS) and polyethyleneimine (PEI) onto the luminescent core. The latter has been obtained by the reprecipitation of complex Eu[(TTA)(3)1] (where TTA(-) and 1 are thenoyltrifluoroacetonate and 2-(5-chlorophenyl-2-hydroxy)-2-phenylethenyl-bis-(2-methoxyphenyl)phosphine oxide, respectively) from organic solvent to aqueous solution. The variation of Eu(III) complexes indicates the role of the complex core in the development of such core-shell colloids. Complex Eu[(TTA)(3)1] is most convenient precursor of Eu-doped luminescent nanocomposites. The fluorometric measurements at each step of the layer-by-layer polyelectrolyte assembly onto Eu[(TTA)(3)1] core, at various pHs and additives reveal the quenching of Eu-centered luminescence as a result of the interfacial interaction of the core and the dye. The AFM images and electrochemical behavior of PSS-(PEI-PSS)(n)-Eu[(TTA)(3)1] colloids deposited on the surface indicate the stability of the polyelectrolyte multilayer in the dried state.

Enantioselective synthesis of the larger fragment of pamamycin-607☆

Abstract The enantiomerically pure methyl ester of the complete larger hydroxy acid (C(1)C(18)) of the macrodiolide antibiotic pamamycin-607 has been synthesized using a general sultone route to actic acids and analogs. The requisite N , N -dimethylamino moiety was introduced by Mitsunobu inversion with hydrazoic acid followed by a reaction cascade involving hydrogenation and double reductive methylation.

Synthesis and isolation of homeomorphous isomers of P-containing cryptands

The novel isomeric phosphite cryptands 2, 3, and 4 could be synthesized by a simple one-pot tripod capping method starting from bisphenol 1 and PCl3. The assembling of five components led to the formation of a macrobicyclic structure, which probably requires an appropriate preorganization of the reactants. In contrast to the NMR spectra of 2, 3, and 4 in solution, the X-ray structures of 2 and 3 reveal that these molecules have no C3 symmetry in the solid state. In the 31P NMR spectra, both in- and out-P atoms have remarkably different chemical shifts due to a distorted geometry around the in-phosphorus. Phosphorus atoms in the inposition have a decreased reactivity. They are, therefore, more slowly oxidized by cumene hydroperoxide than out-P atoms. A stepwise synthesis was developed for phosphite/phosphatecryptands (5, 7, 9, and 15) via the monoprotected bisphenol 11 and the phosphate 14. In addition, the cylindrical macrotricycle 16 was isolated as a mixture of diastereomers from the crude product of this reaction.

Zur Ringumwandlung von 2-Amino-thiophen-3-carbonsäureestern: Pyridon- und Pyridazinon-Derivate

Whereas treatment of the ethyl 5-acetyl-2-amino-4-methyl-thiophene-3-carboxylate (1) with potassium hydroxide yields the 2-hydroxy-thiophene-3-carbonitrile4 its hydrazone2 is converted into the 1-amino-5-mercapto-2-pyridone derivative6. The transformation of the 2-amino-5-phenylazo-thiophene derivative9 by potassium hydroxide yields the substituted 3-mercapto-pyridazin-6(1H)one10, with sodium ethoxide the 5-phenylhydrazono-2-oxo-thiolen-3-carbonitrile11 is formed. From6 the 5-mercapto-2-pyridone derivatives7 d,e can be obtained.

Structural Design, Solid‐Phase Synthesis and Activity of Membrane‐Anchored β‐Secretase Inhibitors on Aβ Generation from Wild‐Type and Swedish‐Mutant APP

Covalent coupling of β-secretase inhibitors to a raftophilic lipid anchor via a suitable spacer by using solid-phase peptide synthesis leads to tripartite structures displaying substantially improved inhibition of cellular secretion of the β-amyloid peptide (Aβ). Herein, we describe a series of novel tripartite structures, their full characterization by NMR spectroscopy and mass spectrometry, and the analysis of their biological activity in cell-based assays. The tripartite structure concept is applicable to different pharmacophores, and the potency in terms of β-secretase inhibition can be optimized by adjusting the spacer length to achieve an optimal distance of the inhibitor from the lipid bilayer. A tripartite structure containing a transition-state mimic inhibitor was found to be less potent on Aβ generation from Swedish-mutant amyloid precursor protein (APP) than from the wild-type protein. Moreover, our observations suggest that specific variants of Aβ are generated from wild-type APP but not from Swedish-mutant APP and are resistant to β-secretase inhibition. Efficient inhibition of Aβ secretion by tripartite structures in the absence of appreciable neurotoxicity was confirmed in a primary neuronal cell culture, thus further supporting the concept.