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

Scheme 6.12
Grignard addition to aldehyde 6.34 and ketone 6.35 was performed using
essentially identical conditions as those reported in chapter two. Prolonged reaction
times and a twenty-fold excess of Grignard reagent was required. The appearance of the
desired resin-bound B-hydroxy-a-amino acids 636-6.44 was monitored using MAS 'H
NMR to follow the disappearance of the aidehyde peak 6.34 at 6 9.67 ppm and the
methyl ketone 6.35 at 6 2.30 ppm (Scheme 6.12). MAS I3c NMR was used to follow
6.37 and 6.43, labeled by ' 3 ~ ~ (Figure 3 ~ g 6.4). ~ The use of EtzO in the reaction
mixture was also minimized since it caused significant shnnkage of the resin, particularly
TentaGel PHB? Mer approximately 6 h, acetone was added and the solvents were
removed under anhydrous conditions. The min was then washed with dry CH2C12 and
Et20.