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

173.8 c=O), 156.3 CONH), 137.6 ( Cbe), 128.4, 127.7, 127.7 (Cbz===), 108.5
(OB0 ester C-O), 72.4 (OB0 ester w20), 68.8 (CbzQ120), 65.7 (m, 5 1.6 (a-CH),
5 1.2 (C0&H3), 35.2 (OB0 ester CCH3). 30.3 (f3-m2), 13.5 (OB0 ester CGC3), -0.7
(Si(CH3)& ESI-MS (M + Ht) 468.32. Anal. calcd for CnH3&I@Si : C, 56.51; H, 7.11;
N, 3.00. Found : C, 56.71; H, 7.29; N, 3.04.
4.438 Methyl-(2S,4S)-2-[~~Ioxy)carbOnyl]~-
trioxa-bicyc1o[2.2.2]oct1-yl)pentan~~ Cbz-L-Glu(îi)H)(OMe)-OBO, 4.96.
n-Butyllithium (0.72 mL, 1 .O8 mrnol) was slowly added to diisopropylamine (0.165 mL,
1.18 mmol) in dry THF (5 mL) at 0°C under Ar. After 30 minutes the mixture was
transferred via cannula to a second flask containing Cbz-L-Giu(0Me)OBO 4-69 (0.135 g,
0.36 mmol) and (it)-~ranr-2-(phenylsuifonyl)-3-phenyloxaW 4.92 (0.47 g, 1.80
mmol) in dry THF (10 mL) at -78°C under Ar. After 3 h the mixture was poured into
ether (50 mL) and extracted with 3% NH&1 (2 x 10 mL), 10% NaHC03 (10 mL), brine
(10 rnL) and dried over MgSQ. The resulting light yeli~~ oil was purified by flash
chromatography (1: 1 Et0Ac:Hex) to yield O. 1 lg (79% yield) of a clear oil which could
be crystailized from Et0Ac:hexanes to give 95 mg (68 % yield) of clear needles.
m.p. 103-104°C; [alZoD = -29.3 (c = 1 .O 1, CWl2); TLC (1 : 1, EtOAc:Hex), Rr = 0.17; 'H
NMR (Acetone-&, 300 MHz) 6 7.36-7.25 (m, SH, ArH), 5.89 (d, 1H, J = 1 O.OHz, NH),
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