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

Cb2H
1
OsO,. NMO
acetone:H&
OH
m
2) ion exctrange
4.1OQ (from 4.1 00)
4.1- (frorn 4.101)
I 0~04. NMO
acetone:H20
Initially, dihydroxylation of 4.97 and 4.99 with stoichiometric amounts of Os04 in
pyridine and reduction with refluxing methanolic sodium sulfite or sodium bisulfite gave
a complex mixture of decomposed materials that were not is~lated.~ However, N-
methylmorpholine N-oxide catalyzed osmylationgg gave the cis-diols 4.100 and 4.101 in
54% and 48% yield respectively. Detennining the stereochemistry of dihydroxylation
proved to be problematic since attempts at crystallizing 4.102, its N-trityl derivative and
bis-3,s-dinitrobenzoyl ester derivative failed to give crystals capable of X-ray analysis.
With optical rotations reported for only two of the eight possible isomers of
dihydroxyglutamic a~id,6~." deprotection of 4.102 and 4.103 and cornparison of opticai
rotations held little promise for identiving the stereuchemistry of addition, especially due
to the small amount of materiai available. Efforts are continuing in an attempt to grow
cry stals for identification of stereochemistry b y X-ray anal y sis. Deprotection of the Cbz