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

175.1 CC-O), 155.8 (CONH), 136.1 (Cbz===), 128.1, 127.8, 127.7 (a%=), 108.2
(OB0 ester c-O), 72.3 (OB0 ester azO), 66.6 (Cbzm20), 53.7 (a-CH), 51.9
(corn,), 43.3 (Ba), 36.1 (Ph-), 3 1.0 (OB0 ester CCH3), 13.3 (OB0 ester CcH3);
ESI-MS (M + H?) 456.22; Anal. calcd for Caz9N@: C, 65.92; H, 6.42; N, 3.07.
Found: C, 66.27; H, 6.77; N, 3.13.
5.4.14 (S29-2-Amia013-metbylbutanedioic acid, Asp(p-Me)OE, 5.47.
Cbz-Asp(fbMe)(OMe)OBO ester 5.41 (O. 189 g, 0.49 mmol) was taken-up in doubl y
distilled 6N HCI (5 rnL) and refluxed for 4 hours. The solvent was removed under
reduced pressure, rinsed with distilled water, reduced again and lyophilized to give 0.048
g of a white powder (68% yield). The white powder was dissolved in a minimum of
water and placed on Dowex 50x8- 100 ion-exchange min. The column was nnsed with
5 colurnn lengths of water then ehted with 0.5 N WOH. The fractions were collected
and combined then reduced in vocuo, lyophilized to give a white powder which was then
crystallized from acetone:water to give 0.02 1 g of clear crystals.
3"
2S,3S-5.47: mp 270-274 (dec.); [a]20t, = +12.8 (c = 0.5, 1N HCl), (lit.s9 [alZoD = +i3.6 (c
= 0.46, 1N HCl); 'H NMR @*O, 300 MHz) 6 3.97 (d, 1 H, / = 3.6Hz, a-CH), 3.15 (dq,
IH, J = 3.6,7.4Hz, p-CH), 1.18 (d, 3H, J = 7.5Hz. bCH3); 13c NMR OZO, 75 MHz) 6
177.2 c=O), 172.9 (CsO), 55.5 (W-I), 39.1 (B-CH), 1 1.6 ($-w3); ESI-MS 147.89.