3-hydroxy-a-amino acids

For example, N-(2-hydroxyphenyl)imines 9 (R = alkyl, aryl) together with chiral zirconium catalysts generated in situ from binaphthol derived ligands were used for the asymmetric synthesis of a-amino nitriles [17], the diastereo- and/or enantioselective synthesis of homoallylic amines [18], the enantioselective synthesis of simple //-amino acid derivatives [19], the diastereo- and enantioselective preparation of a-hydroxy-//-amino acid derivatives [20] or aminoalkyl butenolides (aminoalkylation of triisopropylsilyloxyfurans, a vinylogous variant of the Mannich reaction) [21]. A good example for the potential of the general approach is the diastereo- and enantioselective synthesis of (2R,3S)-3-phenylisoserine hydrochloride (10)... 

The following aspects of this structural component are important in relation to control and recognition mechanisms first, a hydroxy-amino acid is located on the carboxyl side of the asparagine residue that forms the site of attachment second, there is a spacer residue (B) in the polypeptide chain and third, the polarity of residue B appears to control the type of oligosaccharide side-chain that becomes attached to asparagine. If residue B is polar, a complex type of poly-... 

The condensation of organolithium reagents (2 equiv.) with glyoxylate-derived oxime ethers (182) provides a direct method for the synthesis of a- -hydroxy amino acids (equation 22). Both glyoxylic acid and glyoxylamide oxime ethers are compatible with this process. A(>hydroxyaminoacetamides are also product in low/moderate yields by the addition of isonitriles to oximes (oxime ethers) analogous to the four component condensation described by Ugi. ... 

High enantioselectivity for a-amino acids and a-hydroxy amino acids ... 

These results suggest that the initiator is a glucoprotein, which may be glucosylated at several sites and in which glucose may well be attached directly to protein. While the presence of other sugars cannot be excluded it is not necessary to postulate them on this evidence. The nature of the attachment to protein is not clear, but it may well be through a hydroxy-amino acid. 

Although not specifically related to the taxol side chain, two other publications deserve mention. Williams and his colleagues have developed a general stereocontrolled asymmetric synthesis of a-hydroxy-/ -amino acids (558) while Verdine has published a concise stereoselective synthesis of a-hydroxy-a-methyl-/ -amino acids (559). 

Wan, Y. et al.. Synthesis and target identification of hymeiualdisine analogs, Chem. Biol., 11, 247, 2004. Kobayashi, J., Madono, T., and Shigemori, H., Nakijiquinones C and D, new sesquiterpenoid quinones with a hydroxy amino acid residue from a marine sponge inhibiting c-erbB-2 kinase. Tetrahedron, 51, 10867, 1995. 

S,4R,2 l 5)-4-hydroxyl-l-92 -hydroxydodecylproline (Chiralplate) a-Hydroxy amino acids... 

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