Chemical Biology 3OA3, September 2009 Page 26 equivalent to malachite green. The dihydronicotinamide returns to the oxidized form. In experiment 4, whole cells of yeast are used as a reducing agent to reduce a carbonyl compound. This application of biology to chemistry avoids the expense of NADH and purified enzymes discussed above, but still proceeds with very high selectivity (the product is a single enantiomer produced in >98% enantiomeric excess (e.e.)), unlike the product using the chemical reagent, NaBH4. So what’s the downside? Unfortunately, not all carbonyl compounds will enter the yeast cells, and of those that do, some will not be substrates for the yeast enzyme. In that case, it’s back to sodium borohydride, or else a more sophisticated chemical reagent. As with all of organic chemistry, the choice of reagent is not as obvious as it might appear! ProcedurePrepare a solution of 2.1 g of sodium carbonate monohydrate and 2.6 g (about 0.015 mole) of
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