Concerning the Baker's Yeast (Saccharomyces cerevisiae) Mediated Reduction of Nitroarenes and Other N-O Containing Functional Groups
✍ Scribed by Josie A. Blackie; Nicholas J. Turner*; Andrew S. Wells
- Publisher
- Elsevier Science
- Year
- 1997
- Tongue
- French
- Weight
- 537 KB
- Volume
- 38
- Category
- Article
- ISSN
- 0040-4039
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✦ Synopsis
Nitro-and nitrosoarenescanbe reducedusingbaker'syeast(Saccharomyces cerevkiae) under two distinctsets of conditions,one of whichis in fact a well establishednon-enzymicprocess. In orderto clarify reportsin the literaturea comparisonof the two methedshas beenmade.@ 1997Elsevier ScienceLtd.
Recently there have been a number of reports concerning the use of baker's yeast (Saccharomyces cerevisiae) for the reductive cleavage of N-O bonds in a variety of functional groups including nitro arenes', nitroalkenesz, nitrosoarenes', isoxazoles4 and N-oxides5. In general the reactions proceed under mild conditions and may present synthetic advantages in terms of chemo-and regioselectivity. Typically yeast catalysed reactions are carried out at neutral pH in aqueous media with a substrate concentration of 1-2 mg ml-l. However, inspection of the literature relating to yeast catalysed N-O reductions revealed that two distinct sets of reaction conditions could be employed for this biotransformation. Whereas most of the papers la-d. zb,4, sa describe the use of S, Cerevjsiae at pH 5.5-6.0 and 30 'C with fermenting Or non- fermenting yeast (thereafter called type I conditions), the group of Baik et aL,''"f'2''5b5b report quite different reaction conditions, namely reaction temperatures of 70-80 "C and even reflux (sic)5b, high pH (> 12) and the inclusion of methanol/ethanol in the reaction medium (type II conditions). Even with respect to the reduction of nitroarenes (vide infra), the two different reaction conditions result in different selectivity, e.g. under type I conditions electron-withdrawing groups are required for successful reduction '"b whereas with type II conditions electron-donating groups can be tolerated." This discrepancy suggested to us a difference in reaction mechanism, especially in view of the fact that the yeast is unlikely to be stable at high pH and temperature. In this letter we report on our investigations into the likely mechanisms of these two reductions. po2 r)o ~HOH