Amino acids, stannyl derivatives

Chiral y-amino-acids (e.g. 180) have been prepared from the corresponding optically active /8-amino-acids by the addition of one carbon atom using the Arndt-Eistert reaction.w-Amino-acids are available from cyclic anhydrides by treatment with stannyl azide (to give an w-isocyanatocarboxylic acid) followed by addition of an alcohol. In contrast to simple enamines, oxidation of N-acyl-a-aminocrotonates with thallium nitrate leads to the corresponding a/8-dimethoxy derivatives. 

Transmetallation can be employed in order to avoid the use of strongly basic conditions. One such variant is the [2,3]-Wittig-Still rearrangement wherein stannyl ethers can be converted to homoallylic alcohols. Several examples of this tranformation in the synthesis of amino acid components of bioactive polyoxins have been reported by Ghosh. In their synthesis of 5-0-carbomylpolyoxamic acid, a bioactive amino acid nucleoside, E and Z-allylic stannyl ethers, such as 45, derived from an isopropylidene L-threitol derivative, were subjected to the [2,3]-Wittig-Still rearrangement. 

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