- Synthetic cascades are enabled by combining biocatalysts with artificial metalloenzymes
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Enzymatic catalysis and homogeneous catalysis offer complementary means to address synthetic challenges, both in chemistry and in biology. Despite its attractiveness, the implementation of concurrent cascade reactions that combine an organometallic catalyst with an enzyme has proven challenging because of the mutual inactivation of both catalysts. To address this, we show that incorporation of a d 6 -piano stool complex within a host protein affords an artificial transfer hydrogenase (ATHase) that is fully compatible with and complementary to natural enzymes, thus enabling efficient concurrent tandem catalysis. To illustrate the generality of the approach, the ATHase was combined with various NADH-, FAD- and haem-dependent enzymes, resulting in orthogonal redox cascades. Up to three enzymes were integrated in the cascade and combined with the ATHase with a view to achieving (i) a double stereoselective amine deracemization, (ii) a horseradish peroxidase-coupled readout of the transfer hydrogenase activity towards its genetic optimization, (iii) the formation of L-pipecolic acid from L-lysine and (iv) regeneration of NADH to promote a monooxygenase-catalysed oxyfunctionalization reaction.
- Koehler,Wilson,Duerrenberger,Ghislieri,Churakova,Quinto,Knoerr,Haeussinger,Hollmann,Turner,Ward
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- Ring-Chain Tautomerism of Pseudooxynicotine and Some Other Iminium Compounds
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The ring-chain tautomerism in aqueous solution of the nicotine metabolite pseudooxynicotine (1) has been studied.Of the four possible forms of 1, only the chain form 1a and the iminium form 1c could be observed by NMR spectroscopy.The chain form 1a was strongly preponderant at high or low pH.The proportion of 1c reached a maximum level of 52-53 percent in a neutral solution of 1.These results differ strongly from those published by other workers.Some analogous compounds (e.g. 5 and 6) have also been investigated.
- Brandaenge, Svante,Lindblom, Lars,Pilotti, Ake,Rodriguez, Benito
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p. 617 - 622
(2007/10/02)
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