合成路线1

The synthesis of the intermediate (S,S)-3-(Fmoc-amino)-2-methyl-5-phenyl-4-pentenoic acid (XI) has been performed as follows: The Horner-Wadsworth-Emmons condensation of cinnamaldehyde (I) with phosphonate (II) by means of NaH in THF gives (E,E)-5-phenyl-2,4-pentadienoic acid ethyl ester (III), which is condensed with (S)-N-benzyl-N-(alpha-methylbenzyl)amine (IV) by means of BuLi in THF to yield the chiral adduct (V). The reaction of (V) with LDA affords the corresponding lithium enolate, which is methylated with methyl iodide in THF to afford the enantioselectively methylated compound (VI). The hydrogenation of (VI) with H2 over Pd(OH)2 in methanol/water/HOAc provides (S,S)-3-amino-2-methyl-5-phenylpentanoic acid methyl ester (VII), which is treated with Boc2O and NaHCO3 in dioxane/water to give the N-protected ester (VIII). The reaction of (VIII) with NBS in CCl4, followed by treatment with DBU at 60 C, yields the pentenoic ester derivative (IX), which is treated first with LiOH and then with TFA to provide (S,S)-3-amino-2-methyl-5-phenyl-4-pentanoic acid (X). Finally, this compound is N-protected by reaction with Fmoc-Cl and K2CO3 in dioxane/water to furnish the target pentenoic acid intermediate (XI).