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

enantiomers In chemistry, an enantiomer (Help:IPA/English, /ɪˈnænti.əmər, ɛ-, -oʊ-/ Help:Pronunciation respelling key, ''ih-NAN-tee-ə-mər''), also known as an optical isomer, antipode, or optical antipode, is one of a pair of molecular entities whi ...

. Contributors to the chiral pool are

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although over 500 amino acids exist in nature, by far the most important are the 22 α-amino acids incorporated into proteins. Only these 22 a ...

sugar Sugar is the generic name for sweet-tasting, soluble carbohydrates, many of which are used in food. Simple sugars, also called monosaccharides, include glucose Glucose is a sugar with the Chemical formula#Molecular formula, molecul ...

s, and

terpene Terpenes () are a class of natural products consisting of compounds with the formula (C5H8)n for n ≥ 2. Terpenes are major biosynthetic building blocks. Comprising more than 30,000 compounds, these unsaturated hydrocarbons are produced predomi ...

s. Their use improves the efficiency of

total synthesis Total synthesis, a specialized area within organic chemistry, focuses on constructing complex organic compounds, especially those found in nature, using laboratory methods. It often involves synthesizing natural products from basic, commercially ...

. Not only does the chiral pool contribute a premade carbon skeleton, their

chirality Chirality () is a property of asymmetry important in several branches of science. The word ''chirality'' is derived from the Greek (''kheir''), "hand", a familiar chiral object. An object or a system is ''chiral'' if it is distinguishable fro ...

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 Enantioselective synthesis, also called asymmetric synthesis, is a form of chemical synthesis. It is defined by IUPAC as "a chemical reaction (or reaction sequence) in which one or more new elements of chirality are formed in a substrate molecul ...

, 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 Paclitaxel, sold under the brand name Taxol among others, is a chemotherapy medication used to treat ovarian cancer, esophageal cancer, breast cancer, lung cancer, Kaposi's sarcoma, cervical cancer, and pancreatic cancer. It is administered b ...

(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 Epothilones are a class of potential cancer drugs. Like taxanes, they prevent cancer cells from dividing by interfering with tubulin, but in early trials, epothilones have better efficacy and milder adverse effects than taxanes. Epothilones were ...

(an alternative to paclitaxel) from readily available enantiopure (–)-pantolactone.

Other uses of the chiral pool

In addition to serving as building blocks in

, the chiral pool is tapped to produce asymmetric catalysts, chiral

protecting groups A protecting group or protective group is introduced into a molecule by chemical modification of a functional group to obtain chemoselectivity in a subsequent chemical reaction. It plays an important role in multistep synthesis, multistep organic ...

, and resolving agents.

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 2,3-Butanediol is the organic compound with the formula (CH3CHOH)2. It is classified as a ''vic''-diol (glycol). It exists as three stereoisomers, a chiral pair and the meso isomer. All are colorless liquids. Applications include precursors to ...

, derived from abundantly available

tartaric acid Tartaric acid is a white, crystalline organic acid that occurs naturally in many fruits, most notably in grapes but also in tamarinds, bananas, avocados, and citrus. Its salt (chemistry), salt, potassium bitartrate, commonly known as cream of ta ...

, is used to synthesize chiraphos, a component of catalysts used for asymmetric hydrogenation:

Chiral reagents from the chiral pool

: Diisopinocampheylborane is an

organoborane Organoboron chemistry or organoborane chemistry studies organoboron compounds, also called organoboranes. These chemical compounds combine boron and carbon; typically, they are organic derivatives of borane (BH3), as in the trialkyl boranes. Or ...

that is useful for

secondary alcohol In chemistry, an alcohol (), is a type of organic compound that carries at least one hydroxyl () functional group bound to a Saturated and unsaturated compounds, saturated carbon atom. Alcohols range from the simple, like methanol and ethanol ...

s. It is derived by hydroboration of α-pinene, a common

diterpene Diterpenes are a class of terpenes composed of four isoprene units, often with the molecular formula C20H32. They are biosynthesized by plants, animals and fungi via the HMG-CoA reductase pathway, with geranylgeranyl pyrophosphate being a primary ...

member of the chiral pool.

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 Malic acid is an organic compound with the molecular formula . It is a dicarboxylic acid that is made by all living organisms, contributes to the sour taste of fruits, and is used as a food additive. Malic acid has two stereoisomeric forms ( ...

, a dicarboxylic acid that is found in apples. It is used to resolve α-phenylethylamine, a versatile resolving agent in its own right.

References

{{Organic reactions Organic chemistry