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

provided crystals of sufficient quality for X-ray analysis which assigned the
stereochemistry of addition as 2S,3S (Figure 5.1). Crystallization also removed the minor
diastereomer to give optically pure 2S,3S-5.50 in 73% yield. Subsequent deprotection of
the purified 2S,3S-p-methylaspartate denvative 5.41 with refiuxing 6N HCI (vide infia)
gave p-methylaspartate 5.47 in 68% yield after purification by cation exchange,
confirming the stereochemical assignment by comparïson of optical rotation to literature
values.
Scheme 5.17
Figure 5.1: X-Ray Crystal st~chue of Tr-GAsp(B-Me)(OMe)OBO ester 5.50.
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