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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.
Chiral pool synthesis is especially attractive for target molecules having similar chirality to a relatively inexpensive naturally occurring building-block such as a sugar or amino acid. However, the number of possible reactions the molecule can undergo is restricted and tortuous synthetic routes may be required (e.g. Oseltamivir total synthesis ).
Chiral auxiliaries are incorporated into synthetic routes to control the absolute configuration of stereogenic centers. David A. Evans' synthesis of the macrolide cytovaricin, considered a classic, utilizes oxazolidinone chiral auxiliaries for one asymmetric alkylation reaction and four asymmetric aldol reactions, setting the absolute stereochemistry of nine stereocenters.
A chiral substance is enantiopure when only one of two possible enantiomers is present so that all molecules within a sample have the same chirality sense. Use of homochiral as a synonym is strongly discouraged. [22] A chiral substance is enantioenriched or heterochiral when its enantiomeric ratio is greater than 50:50 but less than 100:0. [23]
The second strategy is asymmetric synthesis: the use of various techniques to prepare the desired compound in high enantiomeric excess. Techniques encompassed include the use of chiral starting materials (chiral pool synthesis), the use of chiral auxiliaries and chiral catalysts, and the application of asymmetric induction.
Chiral resolution, or enantiomeric resolution, [1] is a process in stereochemistry for the separation of racemic mixture into their enantiomers. [2] It is an important tool in the production of optically active compounds, including drugs . [ 3 ]
Aza-BH reactions are known in asymmetric synthesis by making use of chiral ligands. In one study, [4] for the first time, successful use was made of a chiral solvent based on an ionic liquid (IL). This solvent is a condensation product of L-(−)-malic acid (available from the chiral pool), boric acid catalyzed by sodium hydroxide.
Dihydrolevoglucosenone can be used as a renewable building block to produce valuable chemicals such as drugs, flavours and fragrances and specialty polymers. [8]As dihydrolevoglucosenone is produced as a single enantiomer, it can be used for chiral pool synthesis.