and Helmut V o r b r i i g g e n [ * ] New synthetic methods (25)The synthesis of 4-dialkylaminopyridines can be accomplished in two steps starting from pyridine. Compared to pyridine, these derivatives are approximately lo4 times more active when used as acylation catalysts. Dialkylaminopyridines are being used with ever-increasing frequency for acylation reactions which proceed either incompletely or not at all in pyridine. This article reviews the various possible applications of 4-dialkylaminopyridines in terpene, steroid, carbohydrate and nucleoside chemistry as well as in the transformation of amino acids into a-acyl aminoketones and polymerization of isocyanates. In addition, N-substituted 4-dialkylaminopyridinium salts can be used for the transfer of sensitive groups to nucleophiles in aqueous medium. The exceptional catalytic effect of these derivatives, even in non-polar solvents, is due, in part, to the formation of high concentrations of N-acylpyridinium salts which are present in solution as loosely-bound, highly reactive ion pairs. DMAP PPY[*] Priv.-Doz.

An antifungal activity against Mucorhiemalis was detected in the culture broth of Sorangium cellulosum (Myxococcales) strain So ce90. The activity was excreted into the supernatant during the log and early stationary phase. Whenthe adsorber resin XAD-16was added to the culture, the active metabolites were quantitatively bound to the resin. The epothilons showed a high cytotoxicity for animal cells and mimic the biological effects oftaxol (Bollag et al, Cancer Res. 55: 2325~2333, 1995).In our screening program for secondary metabolites from myxobacteria, we detected metabolites with a narrowantifungal spectrum: they were inhibitory for Mucor hiemalis only. They were first seen in the culture broth of Sorangium cellulosum strain So ce90 and turned out to be novel macrocyclic polyketides1}.

How similar must a compound be to taxol in order to displace it from its binding site on microtubules? The microbial secondary metabolites epothilones A (1a) and B (1b) provide an answer to this question. These comparatively small, simply constructed, and highly cytotoxic macrolides surprisingly show no similarity to taxol, according to X‐ray and NMR spectroscopic results.

further stirring and filtration most of the solvent is removed in a vacuum. The bluish-black leaflets precipitated are washed with a little cold chloroform and dried in a vacuum.After dissolution in, and recovery from, chloroform the yield is 51 % (310mg). (2b) (66%, 460mg) is obtained analogously from ( l b ) (1 mmole, 490 mg); and (Zc) (364 mg, 1 mmole) affords (4) (260 mg, 59 %), a yellow powder, on dissolution of the crude product in carbon disulfide, concentration, and rubbing of the residue with methanol.

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