Chiral cyanohydrin hydroxyl function

Therefore, the chiral cyanohydrins are valuable and versatile synthons as their single hydroxyl asymmetric centre is accompanied by at least one other chemical functionality. Thus with careful functional group protection, differential and selective chemical transformations can be performed. Such synthetic techniques lead to production of interesting bioactive compounds and natural products. These products include intermediates of j3-blockers 15 1117], j3-hydroxy-a-amino acids 16 [118],chiral crown ethers 17 [lll],coriolic acid 18 [120], sphingosines 19 [121], and bronchodilators such as salbutamol 20 [122] (Fig. 3). 

Due to the nitrile and hydroxyl functionality, enantiomerically pure cyanohydrins are useful building blocks for synthesis of chiral drugs and having enzymes available that make either the (R)- or (S)-enantiomer is very versatile. Scheme 4.12A illustrates the selectivity and substrate scope of Prunus amygdalus R-HNL and Hevea brasiliensis S-HNL. For most aldehyde and ketone substrates tested, high e.e.s can be reached [51a, 52]. 

Chiral cyanohydrins can be valuable chiral building blocks in organic syntheses [2,179] (Fig. 5). The interconversion of the hydroxyl functionality for example... 

Croton aldehyde (2-butenal), like many other a,p-unsaturated aldehydes, is a good substrate for almond HNL [98,125]. The unsaturated cyanohydrin (/ , )-2-hydroxy-3-pen-tenenitrile can be used, after protection of the hydroxyl group, as a potential chiral C3-synthon in which the double bond serves as a masked oxygen functionality. 

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