Chiral pool

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The chiral pool is a "collection of abundant enantiopure building blocks provided by nature" used in synthesis. [1] [2] In other words, a chiral pool would be a large quantity of common organic enantiomers. Contributors to the chiral pool are amino acids, sugars, and terpenes. 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.

Contents

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

Use of verbenone (in red) as precursor to the drug paclitaxel. (Wrong arrow - not a retrosynthesis) WenderTaxol.svg
Use of verbenone (in red) as precursor to the drug paclitaxel. (Wrong arrow - not a retrosynthesis)

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. [3]

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 resolving agents. [4]

Chiral ligands from the chiral pool

Synth-Chiraphos.png

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: [5]

Chiral reagents from the chiral pool

Synth-Chiraphos.png Structural formula of (+)-Diisopinocampheylborane.svg
Synth-Chiraphos.png

Diisopinocampheylborane is an organoborane that is useful for asymmetric synthesis of secondary alcohols. It is derived by hydroboration of α-pinene, a common diterpene member of the chiral pool. [6]

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. [7]

Related Research Articles

<span class="mw-page-title-main">Hydrazone</span> Organic compounds - Hydrazones

Hydrazones are a class of organic compounds with the structure R1R2C=N−NH2. They are related to ketones and aldehydes by the replacement of the oxygen =O with the =N−NH2 functional group. They are formed usually by the action of hydrazine on ketones or aldehydes.

<span class="mw-page-title-main">Imine</span> Organic compound or functional group containing a C=N bond

In organic chemistry, an imine is a functional group or organic compound containing a carbon–nitrogen double bond. The nitrogen atom can be attached to a hydrogen or an organic group (R). The carbon atom has two additional single bonds. Imines are common in synthetic and naturally occurring compounds and they participate in many reactions.

In organic chemistry, the Mannich reaction is a three-component organic reaction that involves the amino alkylation of an acidic proton next to a carbonyl functional group by formaldehyde and a primary or secondary amine or ammonia. The final product is a β-amino-carbonyl compound also known as a Mannich base. Reactions between aldimines and α-methylene carbonyls are also considered Mannich reactions because these imines form between amines and aldehydes. The reaction is named after Carl Mannich.

The Bouveault–Blanc reduction is a chemical reaction in which an ester is reduced to primary alcohols using absolute ethanol and sodium metal. It was first reported by Louis Bouveault and Gustave Louis Blanc in 1903. Bouveault and Blanc demonstrated the reduction of ethyl oleate and n-butyl oleate to oleyl alcohol. Modified versions of which were subsequently refined and published in Organic Syntheses.

The Strecker amino acid synthesis, also known simply as the Strecker synthesis, is a method for the synthesis of amino acids by the reaction of an aldehyde with ammonia in the presence of potassium cyanide. The condensation reaction yields an α-aminonitrile, which is subsequently hydrolyzed to give the desired amino acid. The method is used commercially for the production of racemic methionine from methional.

<span class="mw-page-title-main">Favorskii rearrangement</span> Chemical reaction

The Favorskii rearrangement is principally a rearrangement of cyclopropanones and α-halo ketones that leads to carboxylic acid derivatives. In the case of cyclic α-halo ketones, the Favorskii rearrangement constitutes a ring contraction. This rearrangement takes place in the presence of a base, sometimes hydroxide, to yield a carboxylic acid but most of the time either an alkoxide base or an amine to yield an ester or an amide, respectively. α,α'-Dihaloketones eliminate HX under the reaction conditions to give α,β-unsaturated carbonyl compounds.

<span class="mw-page-title-main">Camphorsulfonic acid</span> Chemical compound

Camphorsulfonic acid, sometimes abbreviated CSA or 10-CSA is an organosulfur compound. Like typical sulfonic acids, it is a relatively strong acid that is a colorless solid at room temperature and is soluble in water and a wide variety of organic substances.

<span class="mw-page-title-main">Isoborneol</span> Chemical compound

Isoborneol is a bicyclic organic compound and a terpene derivative. The hydroxyl group in this compound is placed in an exo position. The endo diastereomer is called borneol. Being chiral, isoborneol exists as enantiomers.

α-Halo ketone

In organic chemistry, an α-halo ketone is a functional group consisting of a ketone group or more generally a carbonyl group with an α-halogen substituent. α-Halo ketones are alkylating agents. Prominent α-halo ketones include phenacyl bromide and chloroacetone.

Chiral resolution, or enantiomeric resolution, is a process in stereochemistry for the separation of racemic compounds into their enantiomers. It is an important tool in the production of optically active compounds, including drugs. Another term with the same meaning is optical resolution.

<span class="mw-page-title-main">Benzyl cyanide</span> Chemical compound

Benzyl cyanide (abbreviated BnCN) is an organic compound with the chemical formula C6H5CH2CN. This colorless oily aromatic liquid is an important precursor to numerous compounds in organic chemistry.

<span class="mw-page-title-main">Cyclohexenone</span> Chemical compound

Cyclohexenone is an organic compound which is a versatile intermediate used in the synthesis of a variety of chemical products such as pharmaceuticals and fragrances. It is colorless liquid, but commercial samples are often yellow.

<span class="mw-page-title-main">1-Phenylethylamine</span> Chemical compound

1-Phenylethylamine is the organic compound with the formula C6H5CH(NH2)CH3. This primary amine is a colorless liquid is often used in chiral resolutions. Like benzylamine, it is relatively basic and forms stable ammonium salts and imines.

<span class="mw-page-title-main">Diphenylethylenediamine</span> Chemical compound

1,2-Diphenyl-1,2-ethylenediamine, DPEN, is an organic compound with the formula H2NCHPhCHPhNH2, where Ph is phenyl (C6H5). DPEN exists as three stereoisomers: meso and two enantiomers S,S- and R,R-. The chiral diastereomers are used in asymmetric hydrogenation. Both diastereomers are bidentate ligands.

<span class="mw-page-title-main">Oxazoline</span> Chemical compound

Oxazoline is a five-membered heterocyclic organic compound with the formula C3H5NO. It is the parent of a family of compounds called oxazolines, which contain non-hydrogenic substituents on carbon and/or nitrogen. Oxazolines are the unsaturated analogues of oxazolidines, and they are isomeric with isoxazolines, where the N and O are directly bonded. Two isomers of oxazoline are known, depending on the location of the double bond.

In nitrile reduction a nitrile is reduced to either an amine or an aldehyde with a suitable chemical reagent.

<span class="mw-page-title-main">Enders SAMP/RAMP hydrazone-alkylation reaction</span>

The Enders SAMP/RAMP hydrazone alkylation reaction is an asymmetric carbon-carbon bond formation reaction facilitated by pyrrolidine chiral auxiliaries. It was pioneered by E. J. Corey and D. Enders in 1976, and was further developed by D. Enders and his group. This method is usually a three-step sequence. The first step is to form the hydrazone between (S)-1-amino-2-methoxymethylpyrrolidine (SAMP) or (R)-1-amino-2-methoxymethylpyrrolidine (RAMP) and a ketone or aldehyde. Afterwards, the hydrazone is deprotonated by lithium diisopropylamide (LDA) to form an azaenolate, which reacts with alkyl halides or other suitable electrophiles to give alkylated hydrazone species with the simultaneous generation of a new chiral center. Finally, the alkylated ketone or aldehyde can be regenerated by ozonolysis or hydrolysis.

<span class="mw-page-title-main">Valinol</span> Chemical compound

Valinol is an organic compound named after, and commonly produced from, the amino acid valine. The compound is chiral and is produced almost exclusively as the S‑isomer, due to the abundant supply of S-valine. It is part of a broader class of amino alcohols.

<i>N</i>-Sulfinyl imine

N-Sulfinyl imines are a class of imines bearing a sulfinyl group attached to nitrogen. These imines display useful stereoselectivity reactivity and due to the presence of the chiral electron withdrawing N-sulfinyl group. They allow 1,2-addition of organometallic reagents to imines. The N-sulfinyl group exerts powerful and predictable stereodirecting effects resulting in high levels of asymmetric induction. Racemization of the newly created carbon-nitrogen stereo center is prevented because anions are stabilized at nitrogen. The sulfinyl chiral auxiliary is readily removed by simple acid hydrolysis. The addition of organometallic reagents to N-sulfinyl imines is the most reliable and versatile method for the asymmetric synthesis of amine derivatives. These building blocks have been employed in the asymmetric synthesis of numerous biologically active compounds.

In organic chemistry, the Keck asymmetric allylation is a chemical reaction that involves the nucleophilic addition of an allyl group to an aldehyde. The catalyst is a chiral complex that contains titanium as a Lewis acid. The chirality of the catalyst induces a stereoselective addition, so the secondary alcohol of the product has a predictable absolute stereochemistry based on the choice of catalyst. This name reaction is named for Gary Keck.

References

  1. 1 2 Brill, Zachary G.; Condakes, Matthew L.; Ting, Chi P.; Maimone, Thomas J. (2017). "Navigating the Chiral Pool in the Total Synthesis of Complex Terpene Natural Products". Chemical Reviews. 117 (18): 11753–11795. doi:10.1021/acs.chemrev.6b00834. PMC   5638449 . PMID   28293944.
  2. Casiraghi, Giovanni.; Zanardi, Franca.; Rassu, Gloria.; Spanu, Pietro. (1995). "Stereoselective Approaches to Bioactive Carbohydrates and Alkaloids-With a Focus on Recent Syntheses Drawing from the Chiral Pool". Chemical Reviews. 95 (6): 1677–1716. doi:10.1021/cr00038a001.
  3. Ulrich Klar; et al. (2005). "Efficient Chiral Pool Synthesis of the C1-C6 Fragment of Epothilones". Synthesis . 2005 (2): 301–305. doi:10.1055/s-2004-834936.
  4. Blaser, Hans Ulrich (1992). "The chiral pool as a source of enantioselective catalysts and auxiliaries". Chemical Reviews. 92 (5): 935–952. doi:10.1021/cr00013a009.
  5. M. D. Fryzuk, B. Bosnich (1977). "Asymmetric synthesis. Production of optically active amino acids by catalytic hydrogenation". J. Am. Chem. Soc. 99 (19): 6262–6267. doi:10.1021/ja00461a014. PMID   893889.
  6. Lane, C. F.; Daniels, J. J. (1972). "(−)-Isopincampheol". Organic Syntheses. 52: 59. doi:10.15227/orgsyn.052.0059.
  7. A. W. Ingersoll (1937). "D- and l-α-Phenylethylamine". Organic Syntheses. 17: 80. doi:10.15227/orgsyn.017.0080.