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

Higher activity is usually observed for cationic Rh0 complexes and over 1 0 chiral bis-
phosphines have ken prepared, the most fiequenily used being DIPAMP ((Ra)- 1,2-
ethanedi y lbis[(o-methoxyphen y1)pheny lphospne]) 1.1 with enantioselectivities
typically in the range of 80% to >99%. For example. both 1.19 and 1.20 were generated
in 902 ee? P-Hydroxy-a-amino acids have also been synthesized using this
method~logy.~ Numerous reviews cover this topic in more detail?
As an alternative to chiral hydrogenation catalysts, reduction of the a$-
unsaturated amino acid can also be controlled by chiral auxiliaries or asymmetric centers
in the sidechain. This technique has been used extensively toward the synthesis of
substituted glutamic acids and will be covered in more detail in Chapter Four.
mT
Scheme 1.8
Q', [Rh(L*)COOpC C02H L*: Chiral Diphosphine
1 .17/H2 COD:
O O
1 .t 8 (R, R)-Dipamp 1.1 9 1.20
1.3.1.2 Reductive Amination of a-Ketoacids
1.5-Cyctoactadiene
X: CIO4, BF4, PF6
The reductive amination of a-ketoacids is a known biosynthetic step and the
corresponding enzymes have been used comprehensively in the spthesis of a-amino
acids. Phen y t alanine dehydrogenase from Badius sphaericus has ken used to
investigate the amination of various ammatic a-ketoacids with varying degrees of