合成路线1

Racemic amine (I) can be resolved by the following alternative procedures: An alternative procedure to compound (VII) begins by condensating amine (II) with N-Boc-L-alanine (IV) in the presence of HOBt.H2O, DIEA and EDC in THF to yield the N-Boc-L-alaninamide derivative (IX) . Similarly, the hydrochloride of amine (II) reacts with N-Boc-L-alanine (IV) in the presence of HOBt.H2O, DIEA and EDC in THF . Intermediate (IX) is then deprotected with either HCl in EtOAc or 1,4-dioxane , or concentrated HCl , and the resulting amine (VII) is obtained as the free base or employed without isolation, respectively. Finally, either hydrochloride (VII) or the nonisolated species obtained from compound (IX) is condensed with 2(S)-hydroxy-3-methylbutyric acid (X) by means of HOBt.H2O, NMM and EDC.HCl in H2O to give semagacestat . Under related conditions, the free base of (VII) couples with acid (XI) in the presence of HOBt.H2O, DIEA and EDC in THF . Alternatively, silylation of 2(S)-hydroxy-3-methylbutyric acid (X) with HMDS in the presence of (NH4)2SO4 at reflux gives trimethylsilyl 3-methyl-2(S)-(trimethylsilyloxy) butanoate (XI), which is first reacted with (COCl)2 in the presence of DMF in CH2Cl2 and then with the mesylate salt (VIII) by means of NMM in CH2Cl2 .