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

Generai Procedure for Removd of Rotecting Grwpc. Cbz-GGlu(y-Me)(OMe)-OB0
ester 4.73 (72 mg, 0.18 rnmol) was combined with doubly distilled 6N HCI (2 ml) and
refluxed for 4 hours. The solvent was then removed in vacuo, rinsed with distilled water,
reduced again and then lyophilized to a white powder. The white powder was disso!ved
in a minimum of distilled water and placed on Dowex 50x8- 100 ion-exchange resin.
The column was then rinsed with 5 column lengths of distilled water then 5 column
lengths of 0.5 N N&OH that were collected. The solvent was removed under reduced
pressure and lyophilized to give a white powder which was then crystallized from
acetone:water or ethanol: water.
4.4.1 (ZS)-2-[@eazyloxy)~bonyI]amin01S=me~ acid, Cbz-L-
Glu-(0Me)-OH, 4.61.
Glutamic acid 4.60 (20.0 g, 0.136 mol) was suspended in freshly distilled MeOH (400
mL) and cooled to 0°C whilst stimng under Ar. Chlorotrimethylsilane (15 mL, 0.1 19
mol) was slowly added by dropping funnel and after 30 min allowed to warm to ambient
temperature. After 2 hours the mixture was cooled to 0°C and a second aliquot of
chlorotrimethylsilane (15 mL, 0.119 mol) slowly added. After 24 hours the solvent was
removed in vacuo, revealing an oil which was placed under high vacuum. De-ionized
water (200 mL) was added to the oil followed by slow addition of Na2C03 (20.23 g,
0.163 mol) to prevent excessive frothing. Once the oil was completely in solution it was
cooled to 0°C and N-(benzyoxycarbony1)-succinimide (33.89 g, 0.136 mol), pre-