抄録
Synthetic studies on biologically active and structurally unique unusual amino acids, isolated as a free form or a constituent of peptides, have been described. (1) The synthesis of neurotoxin, (-) -domoic acid (3) was achieved starting from L-glutamic acid via a stereospecific [4 + 2] cycloaddition of 5 followed by a construction of the C-1' side chain. (2) Optically pure 2-amino-3-butenol (15), prepared from L-or D-methionine, was used as the chiral serine equivalent as well as a building block for the syntesis of β-hydroxy-α-amino acid system. This was converted to the aspergillomarasmine A skeleton 24 and galantinic acid (28). (3) Significant 1, 2- and 1, 3-asymmetric induction of 2-amino-4-pentenoic acid system 17 (allylglycine) has been observed during the introduction of a hydroxyl group into its unsaturated side chain. For example, allylic oxidation of 35 provided the threo-β-hydroxyallylglycine derivative 36 as the major product, and halolactonization of 61 afforded the cis bromolactone 62, predominantly. These intermediates were efficiently transformed to the hydroxyproline analogues 40, 71, and 72. On the other hand, cyclopropylglycines (58) and (59) have been synthesized from the β-hydroxy-allylglycine derivative via a Pd (II) catalyzed [3, 3] sigmatropic rearrangement and a subsequent cyclopropanation. In addition, several useful transformations concerning amino protecting groups were also disclosed.
