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 ( /ɪˈnænti.əmər, ɛ-, -oʊ-/ ''ih-NAN-tee-ə-mər''; from Ancient Greek ἐνάντιος ''(enántios)'' 'opposite', and μέρος ''(méros)'' 'part') – also called optical isomer, antipode, or optical ant ...

. Contributors to the chiral pool are

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha ...

s, sugars, and

terpene Terpenes () are a class of natural products consisting of compounds with the formula (C5H8)n for n > 1. Comprising more than 30,000 compounds, these unsaturated hydrocarbons are produced predominantly by plants, particularly conifers. Terpenes ar ...

s. Their use improves the efficiency of

total synthesis Total synthesis is the complete chemical synthesis of a complex molecule, often a natural product, from simple, commercially-available precursors. It usually refers to a process not involving the aid of biological processes, which distinguishes i ...

. 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 from i ...

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 molecu ...

, 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 (PTX), sold under the brand name Taxol among others, is a chemotherapy medication used to treat a number of types of cancer. This includes ovarian cancer, esophageal cancer, breast cancer, lung cancer, Kaposi's sarcoma, cervical can ...

(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 A ...

(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 organic synthesis. In man ...

, 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 bananas, tamarinds, and citrus. Its salt Salt is a mineral composed primarily of sodium chloride (NaCl), a c ...

, is used to synthesize chiraphos, a component of catalysts used for asymmetric hydrogenation: ;Chiral reagents from the chiral pool : Diisopinocampheylborane is an

organoborane Organoborane or organoboron compounds are chemical compounds of boron and carbon that are organic derivatives of BH3, for example trialkyl boranes. Organoboron chemistry or organoborane chemistry is the chemistry of these compounds. Organoboron ...

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 carbon atom. The term ''alcohol'' originally referred to the primary alcohol ethanol (ethyl alcohol), which i ...

s. It is derived by

hydroboration In organic chemistry, hydroboration refers to the addition of a hydrogen- boron bond to certain double and triple bonds involving carbon (, , , and ). This chemical reaction is useful in the organic synthesis of organic compounds. Hydroboration ...

α-pinene α-Pinene is an organic compound of the terpene class, one of two isomers of pinene. It is an alkene and it contains a reactive four-membered ring. It is found in the oils of many species of many coniferous trees, notably the pine. It is als ...

, a common

diterpene Diterpenes are a class of chemical compounds 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 ...

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