Residual dipolar couplings (RDCs) have revolutionized the NMR-based structure determination of large biomolecules [1][2][3][4] and lately demonstrated their potential in the field of small molecules. [5][6][7][8][9][10][11][12] The measurement of RDCs relies on the partial orientation of the molecule of interest, for which a socalled alignment medium is necessary. In aqueous solution a variety of alignment media are known, for example,[*] Dr.
Three distinct four-component supramolecular nanorotors, prepared by varying the rotator's structure and keeping all other components constant, exhibit rotational frequencies that differ by almost 2 orders of magnitude. When the rotors were used as catalyst for two click reactions, the product yield correlated with the speed of the machine, e.g., 20% at 0.50 kHz, 44% at 20 kHz and 62% at 42 kHz. The kinetic effect on the product yield is attributed to the ability of the rotating catalysts to displace the product more efficiently from the active site at higher speed (anchimeric assistance). This mechanistic hypothesis was convincingly corroborated by a linear correlation between product yield and product liberation.
Polyketomycin is a tetracyclic quinone glycoside produced by Streptomyces diastatochromogenes Tü6028. It shows cytotoxic and antibiotic activity, in particular against Gram-positive multi-drug-resistant strains (for example, MRSA). The polyketomycin biosynthetic gene cluster has been sequenced and characterised. Its identity was proven by inactivation of a alpha-ketoacyl synthase gene (pokP1) of the "minimal polyketide synthase II" system. In order to obtain valuable information about tailoring steps, we performed further gene-inactivation experiments. The generation of mutants with deletions in oxygenase genes (pokO1, pokO2, both in parallel and pokO4) and methyltransferase genes (pokMT1, pokMT2 and pokMT3) resulted in new polyketomycin derivatives, and provided information about the organisation of the biosynthetic pathway.
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