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

250 MHz) 6 5.47 (br ci, lH, J = S.OH& NH), 4.47 (d, LH, I = 6.1Hz, &CHH), 4.43 (d,
1 H, J = 6. lHz, B-CHH), 4.354.27 (m, 4H, 2 oxetane CH&)), 4.07-3.57 (m, 3H, a-CH,
C02CH2), 3.01 (br s, lH, OH), 1.36 (s, 9H, (CH3)3C), 1.24, (s, 3H, oxetane CCH3); 13c
NMR (CDClp, 63 MHz) G 17 1 .O (C=O), 155.6 (CONH), 80.1 ((C&)3C) , 79.8 (oxetane
-
CH20), 68.8 (CO~H~), 663.1 ($-=), 55.8 (a-CH), 39.3 (oxetane cCH3), 28.2
(GH3)3C), 20.7 (oxetane CcH3); IR (neat) 3386, 2970, 1746, 17 13, 1509, 1367, 1 163,
1060; HRMS (FAB) calculated for (M + H+) Cl3H2m6 290.1604, found 290.1594.
Anal. calcd for C13Ha06: C, 53.78; H, 8.33; N, 4.83. Found: C, 53.97; H, 8.62; N,
5.06.
2AS (2-Methyl-2.oxetanyl)methyl-(2SJR)-t[(?e~-buto~~bnyI)~o]-3-
hydroxybutanoate, Boc-Thr oxetane ester, 2.43.
Boc-L-Thr 2.41 (5.0 g, 0.023 mol) and Cs2C03 (4.65 g, 0.014 mol, 0.6 eq) were
combined and dissolved in H20 (50 mL). The water was then removed in vacuo and the
resulting oil was lyophilized for 12 hours to give a white foam. To this foam was added
oxetane tosylate 2.38 (6.41 g, 0.024 mol) and Nd (0.71 g, 4.7 mmol, 0.2 eq) which was
then taken up in DMF (250 rnL) and allowed to stir under Ar for 48 hours. The DMF
was then removed in vacuo and the resuIting sofid dissolved in EtOAc (300 mL) and
H20 ( 100 mL) and extracted with 10% NaHC03 (2 x 50 mi,), saturated NaCl ( 1 x 50
mL) and dried over MgS04. The solvent was removed under reduced pressure to yield a
yellow oil which was purified by flash chromatography (1: 1, Et0Ac:Hex) to yield the
ester 2*43 as a white solid in 73% yield (4.32g).