CO
R^2
R^1
re face (when looking at this face there is
a clockwise sequence of priorities)
si face (when looking at this face there is
a counterclockwise sequence of priorities
The re and si faces of a carbonyl group
(Where O > R^1 > R^2 in terms of Cahn-Inglod-Prelog priorities)
- The preference of many NADH-dependent enzymes for either re or si face of their
respective substrates is known ⇒ some of these enzymes become exceptionally
useful stereoselective reagents for synthesis.
- Yeast alcohol dehydrogenase is one of the most widely used enzymes.
- Extremozymes, enzymes from thermophilic bacteria, have become important in
synthetic chemistry.
i) Use of heat-stable enzymes allows reactions to be completed faster due to the
rate-enhancing factor of elevated temperature (over 100 °C in some cases),
although greater enantioselectivity is achieved at lower temperature.
O HO H
Thermoanaerobium brockii
95%enantiomeric excess
85% yield
- Chiral reducing agents:
- Chiral reducing agents derived from aluminum or boron reducing agents that
involve one or more chiral organic ligands.
- S-Alpine-borane and R-Alpine-borane are derived from either (–)-α-pinene or
(+)-α-pinene and 9-borabicyclo[3.3.1]nonane (9-BBN).
