Valine Valinol

The main disadvantages of Evans auxiliaries 22 and 23 are that they are expensive to purchase and inconvenient to prepare, as the preparation involves the reduction of (5 )-valine 24 to water-soluble (b )-valinol, which cannot be readily extracted to the organic phase. The isolation of this water-soluble vali-nol is difficult and requires a high vacuum distillation, which is not always practical, especially on an industrial scale. Therefore, an efficient synthesis of Evans chiral auxiliary 25 has been developed, as depicted in Scheme 2-1930 ... 

These observations imply that the Cu oxidant is little sensitive to the steric surroundings of the hydroxyl function. The scope of the reaction can be further extended to protected primary p-amino alcohols with equal efficiency. The oxidation of dibenzyl valinol (Entry 6), which contains a tertiary nitrogen atom, proceeds in excellent yield. Moreover, the involvement of a neutral medium is ideally demonstrated by the lack of racemization of both dibenzyl valinal and Boc-prolinal (Entries 6 and 7). Purification of this latter product, which was prepared on a gramm-scale, necessitated only a simple filtration (32). 

By similar reduction procedures, amino alcohols can be derived from almost every amino acid. (S)-Valinol [(S)-4], (S)-leucinol [(S)-5], and (S -zm-leucinol [(S) ] are prominent examples of these compounds. A detailed procedure for the reduction of (S)-valine to (S)-valtnol by borane-dimethyl sulfide/boron trifluoride-diethyl ether complex has been reported6, as well as details on the preparation of (5)-leucinol2 and (S)-/m-leucinol ... 

Valine, A4 Valinol, A4 Vallesamidine, K13 Veatchine, K32 Venoterpine, K9 Venturicidins, Y13 Veprisone, TS2 Veralkamine, K34 Verapamil, A36 ... 

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