Solution and Solid Phase Synthesis of Unusual a-Amino Acids From

group has ais0 added various substituted amines to 5.10 although yields were typically
less than SOS? Monne et al. have perfonned similar experiments with p-
methylaspartase in expanding the functionalities that may be incorporated?
X=Me,Et,nPr,
CI, Br
Scheme 5 J
RLH,
R*=H,M~,E~,
NH2, OH
Aspartate aminotransferase (EC 2.6.1.1) has also been used for the synthesis of
both threo- and erythro-L-B-hydroxyaspartic acid From dihydroxyfumarate and cysteine
sulfinate? It was necessary to separate the diastereomea by ion exchange
chromatography giving 72% of the etyfhro derivative and 26% of threo-L-P-
hydroxyaspartic acid.
5.1.4.2 PAnion Chemistry (including &Lactans)
The obvious, and indeed most popular, method for the stereoselective synthesis of
p-substituted aspartic acids is to utilize the inherent chirality of aspartic acid for 1,2-
aymrnetric induction reactions. This is most easily accomplished through the p-anion of
aspartic acid.
Seebach et al. first reported the stereoselective alkylation of aspartic acid
denvatives in 198 1 ? Di-t-butyl-N-formyl-itspartate 5.11 (P=CHO, R'=R~=~BU) was
doubly deprotonated with lithium diethylamide then alkylated with a variety of
electrophiles to give a mixture of a- and p-substituted aspartic acid denvatives in a ratio
254