Selective chemical imaging of static actin in live cells

We have characterized rationally designed and optimized analogues of the actin-stabilizing natural products jasplakinolide and chondramide C. Efficient actin staining was achieved in fixed permeabilized and non-permeabilized cells using different combinations of dye and linker length, thus highlighting the degree of molecular flexibility of the natural product scaffold. Investigations into synthetically accessible, non-toxic analogues have led to the characterization of a powerful cell-permeable probe to selectively image static, long-lived actin filaments against dynamic F-actin and monomeric G-actin populations in live cells, with negligible disruption of rapid actin dynamics.     

Templated Total Synthesis of Cu(I)-Methanobactin OB3b**

Methanobactin OB3b (Mbn-OB3b) is a unique natural product with stunning affinity for copper ions (K_a≈Cu(I) 10³⁴). Here, we report the first total synthesis of Cu(I)-bound methanobactin OB3b featuring as key transformations a cyclodehydration-thioacylation sequence, to generate the conjugated heterocyclic systems, and a copper-templated cyclization, to complete the caged structure of the very sensitive target compound.     

Zur F?llung des vier- und sechswertigen Selens mit SO2

Zusammenfassung Selen läßt sich, sofern es vierwertig vorliegt, mit SO₂ aus 0,5–1 n salzsauren Lösungen quantitativ fällen, wenn man bei etwa 100° C und im verschlossenen Gefäß arbeitet. Aus Selenatlösungen läßt sich Selen durch Erhitzen der wenigstens 4n salzsauren Lösung mit überschüssigem SO₂ auf etwa 100° C im verschlossenen Gefäß quantitativ ausfällen. Eine Bestimmung von Se^IV und SeVI nebeneinander ist dadurch möglich, daß man zunächst das Se^IV aus 0,5 n salzsaurer Lösung mit SO₂ fällt und dann aus dem wenigstens 4n salzsauer gemachten Filtrat das in Lösung gebliebene SeVI mit SO₂ als Selen ausfällt.     

On the relationship between fluorescnece and molecular geometry. The effect of intermolecular shift on the excimer emission of crystalline dianthronylidene ethane.

The existence of two luminescent excimer geometries in polymorphic dianthronylidene ethane has been verified by X-ray structure determinations of three crystal modifications. The different excimer emission energies are interpreted in terms of variations in transannular π-orbital interaction resulting from an intermolecular shift of adjacent molecules across the log axis of the anthronylidene moiety.     

Solubilisierende Schutzgruppen für enzymatische Peptidsynthesen Untersuchungen mit Polyoxyethylen-gebundenen Substraten

The utility of amino acids and dipeptides esterified to solubilizing polyoxyethylene supports as substrates for protease-mediated peptide bond formation was studied using free and immobilized -chymotrypsin as a catalyst. Poor yields were obtained with N-protected amino acid or dipeptide polyoxyethylene esters as carboxyl components, most probably due to a shielding of the active site of the acyl enzyme intermediate by the polymer favouring hydrolytic cleavage. Experiments with polyoxyethylene esters as nucleophiles gave good results with free chymotrypsin, immobilized chymotrypsin predominantly caused hydrolysis of the ester carboxyl component due to unfavourable interactions between the soluble and insoluble polymers.

Abkürzungen: Die IUPAC/IUB-Regeln für Aminosäure- und Peptidderivate wurden befolgt; vgl. Eur. J. Biochem.53, 1 (1975). Die verwendeten Aminosäuren hattenL-Konfiguration.BOC =tert.-Butyloxycarbonyl,Z = Benzyloxycarbonyl,Ac = Acetyl, –OMe = Methylester, –OPOE = Polyoxyethylenester,POE = -Hydroxy--hydroxypoly(oxyethylen) = Polyoxyethylen,DCC =N,N-Dicyclohexylcarbodiimid,NEM =N-Ethylmorpholin.