1,2-Amino alcohols, which have a broad spectrum of biological activities,23 can be categorized as adrenaline-like with one chiral center at C-1 or as ephedrine-like with two chiral centers at C-1 and C-2 (Scheme 7). Although a variety of methods have been developed for the stereoselective preparation of 1,2-amino alcohols,24 in most cases it is easier and more efficient to prepare these important compounds stereoselectively starting from chiral cyanohydrins (Scheme 7).25,26
Scheme 7: Synthesis of (1R)- and (1R, 2S)-1,2-amino alcohols starting from
Although it is known that only adrenaline-like compounds with (1 Reconfiguration and ephedrine-like compounds with (1R, 2S)-configuration are responsible for the desired biological activity, in most cases racemates are still applied as pharmaceuticals. (1R, 2S)-ephedrine is produced by a fermentation process, which is limited to very specific substrates. When starting from non-racemic cyanohydrins, however, almost any structural variation for the stereoselective synthesis of 1,2-amino alcohols is possible. One interesting example for this possibility of structural variation is the preparation of heteroaromatic analogues of L-ephedrine.27 Follow-up reactions of optically active 1,2-amino alcohols enable the stereoselective preparation of other interesting compounds. 2-Hydroxy-3-amino carboxylic acids, for example, can be prepared stereoselectively from furyl-1,2-amino alcohols by ozonization of the furyl group to give the carboxyl group.28
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