The
chiral pool is a "collection of abundant enantiopure building blocks provided by nature" used in synthesis.
In other words, a chiral pool would be a large quantity of common organic
Enantiomer. Contributors to the chiral pool are
,
, and
. Their use improves the efficiency of
total synthesis. Not only does the chiral pool contribute a premade carbon skeleton, their chirality is usually preserved in the remainder of the reaction sequence.
This strategy is especially helpful if the desired molecule resembles cheap enantiopure natural products. Many times, suitable enantiopure starting materials cannot be identified. The alternative to the use of the chiral pool is asymmetric synthesis, whereby achiral precursors are employed or racemic intermediates are resolved.
Examples
The use of the chiral pool is illustrated by the synthesis of the anticancer drug
paclitaxel (Taxol). The incorporation of the C10 precursor verbenone, a member of the chiral pool, makes the production of paclitaxel more efficient than most alternatives.
Chiral pool synthesis is used to build a part of epothilone (an alternative to paclitaxel) from readily available enantiopure (–)-pantolactone.
Other uses of the chiral pool
In addition to serving as building blocks in
total synthesis, the chiral pool is tapped to produce asymmetric catalysts, chiral protecting groups, and
.
Chiral ligands from the chiral pool
Asymmetric catalysis relies on chiral ligands, which in turn are generally derived from the chiral pool. For example enantiopure 2,3-butanediol, derived from abundantly available
tartaric acid, is used to synthesize
chiraphos, a component of catalysts used for asymmetric hydrogenation:
Chiral reagents from the chiral pool
Diisopinocampheylborane is an
organoborane that is useful for asymmetric synthesis of secondary alcohols. It is derived by
hydroboration of
alpha-Pinene, a common
diterpene member of the chiral pool.
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]
Resolving agents from the chiral pool
Many if not most of the common resolving agents are natural products or derivatives thereof. Illustrative is l-
malic acid, a dicarboxylic acid that is found in apples. It is used to resolve α-phenylethylamine, a versatile resolving agent in its own right.
