Enantioselective synthesis high-performance liquid

A new hydroxynitrile lyase (HNL) was isolated from the seed of Japanese apricot Prunus mume). It accepts benzaldehyde and a large number of unnatural substrates for the addition of HCN to produce the corresponding (7 )-cyanohydrins in excellent optical and chemical yields. A new high-performance liquid chromatography (HPLC)-based enantioselective assay technique was developed for the enzyme, which promotes the addition of KCN to benzaldehyde in a buffered solution (pH 4.0). Asymmetric synthesis of (7 )-cyanohydrins by a new HNL is described (Figure 8.4). ... 

Separations of enantiomers can be achieved by chiral chromatography. Even, when the enantioselective synthesis of drugs and pharmaceuticals is possible, a major part of chiral compounds is still produced as a racemate and needs to be separated into the enantiomers by chiral high performance liquid chromatography. 

There are many other useful analytical methods. Chromatographic methods such as gas chromatography (GC) and high-performance liquid chromatography (HPLC) are used daily for identification and estimation of the purity of a synthetic product. Chiroptical methods, such as circular dichroism (CD) spectroscopy, are also important especially in studying the relationships between absolute configuration and bioactivity of biofunctional molecules. In later chapters I will give some examples of application of CD spectroscopy in enantioselective synthesis. 

In 1999, both enantiomers of the fluorinated analog were obtained using LiHMDS and perchloryl fluoride as an electrophilic source of fluorine in 71% yield. After several steps, the enantiomers were separated using chiral high-performance liquid chromatography (HPLC) and biologically evaluated. More recently, the first enantioselective synthesis of both enantiomers of thalidomide was described with the aid of a chiral [N-F]+ reagent obtained by combination of a cinchona alkaloid, dihydroquinine (DHQ), and... 

The synthesis of lineatin, a pheromone of the insect Trypodendron lineatum, involves the enantioselective addition of methane to the double bond of alkene A in the presence of a chiral rhenium catalyst on silica (Re /silica see Figure 2.19). Michael performed eight separate experiments for this reaction in a 500 mL high-pressure stirred autoclave reactor using liquid methane as a solvent and 0.05 mmol catalyst. The results are shown in Table 2.2. 

Until recently organic photochemistry has only partially focused on stereoselective synthesis, one of the major challenges and research areas in modern organic synthesis. This situation has dramatically changed in the last decade and highly chemo-, regio-, diastereo- as well as enantioselective reactions have been developed. Chemists all over the world became aware of the fascinating synthetic opportunities of electronically excited molecules and definitely this will lead to a new period of prosperity. Photochemical reactions can be performed at low temperatures, in the solid or liquid state or under gas-phase conditions, with spin-selective direct excitation or sensitization, and even multi-photon processes start to enter the synthetic scenery. 

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