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

Since Cbz cleavage is quantitive, purification on an anion exchange column
instead of cation exchange column ailows for the easy separation of any non-hydrolyzed
ester. The anion exchange column also has the advantage that the base-sensitive
vinylglycine is only briefly exposed to base dunng the period the sample is loaded ont0
the colurnn and is not prone to racernization as previously reported in section 2.2.3.3.
Optical purity was assessed by derivatization of the fiee amino acid with OPA
2m63 and N-i-Bu-L-Cys 2.64 as described previously (section 2.2.4) and indicated the
vinylglycine synthesize via Takai olefination
olefination >95% ee (Figure 3.2).
possessed 86% ee and via Peterson
Figure 3m2: Assessrnent of ennntiomeric purity atGer ion exchange putif.~cation
of L-
vinylglycine obtained after deprotection of Cbz-L-Ser(CH;rTMS)OBO ester 3.45
(left) and Cbz-L=Gly(CH=CH2)0BO ester 3.3û. Amino acid samples prepareà as
described in Section 2.4.15a.