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

Before being purified by flash chromatography, an aliquot (0.093 mg, 0.31 mrnol) of the
reaction mixture described in section 2.4.1 1 was dissolved C&C12 (20 mL), cooled to
-20°C and NaB& (0.012 g, 0.3 1 mmol) then added. The mixture was allowed to warm
to room temperature and after 2 h poured into 3% -1 (10 m.) which was then
extracted with CHsl2 (3 x 10 mL). The organic fractions were pooled, extracted with
brine (15 mL) then dned over MgS04 and evaporated to dryness. After purification by
flash chromatography the optical rotation of Boc-Ser-OB0 ester 2-44 was determined.
[a120na = -40.2; (c = 0.98, EtOAc).
2.4.20 Addition of MeMgBr to Boc..Tùr(ket)OBO ester 2.47: 1-[Nfert-
Butoxy~bonyl-(lS)-l-amin0-2-bufanol]4met~yl-2,6,7-~o~bicyclo[2~2.2]~~e,
Boc-L-Thr(Me)-OB0 ester, 2.57.
Cnide Boc-L-Thr(ket)-OB0 ester 2.47 (0.561g, 1.86 mmol) was dissolved in dry EtzO
(15 mL) and CH2C12 (15 mL) under N2. A solution of MeMgBr in Et20 (1.86 mL, 5.58
mrnol) was added quiclcly by syringe at -78°C and the mixture stirred vigorously. Mer 2
h the reaction was quenched by pounng into 25 mL of 3% WCl. CH2C12 (120rnL) was
added and the organic layer was separated, washed with 3% N u l (50 mL) and brine
(50 mL), dried (MgS04), and evaporated to dryness. The product was purified by flash
chromatography (4: 1, CH2Cl5:EtOAc) to yield 0.4248 (72%) of a white solid.