合成路线1

Alkylation of the benzophenone imine of ethyl glycinate (XV) with bromomethylcyclobutane (XVI) by means of t-BuOK in THF at –78 °C, followed by acidic hydrolysis of the imine intermediate (XVII) gives 3-cyclobutyl-DL-alanine ethyl ester (XVIII). Subsequent protection of the amino ester (XVIII) with Boc2O in CH2Cl2 yields the N-Boc derivative (XIX), which upon alkaline hydrolysis of its ethyl ester group with LiOH in THF/H2O gives the N-Boc-protected amino acid (XX). After coupling amino acid (XX) with N,O-dimethylhydroxylamine in the presence of BOP and NMM in CH2Cl2, the resulting Weinreb amide (XXI) is reduced to aldehyde (XXII) using LiAlH4 in cold THF. Aldehyde (XXII) is then reacted with 2-hydroxyisobutyronitrile and Et3N to give cyanohydrin (XXIII), which by treatment with methanolic hydrochloric acid yields amino ester (XXIV), and subsequently reprotection with Boc2O leads to the N-Boc-protected amino ester (XXV). Hydrolysis of methyl ester (XXV) using LiOH followed by coupling of the resulting carboxylic acid (XXVI) with NH4Cl in the presence of EDC, HOBt and NMM in DMF affords carboxamide (XXVII) . Alternatively, carboxamide (XXVII) also results from direct hydrolysis of nitrile (XXIII) using LiOH and H2O2 in MeOH . Finally, acidic N-Boc group cleavage in compound (XXVII) provides the key amino hydroxyamide intermediate (II) . The analogous amino ketoamide (VI) is obtained by Swern oxidation of alcohol (XXVII) with DMSO and EDC in the presence of dichloroacetic acid in i-PrOH/EtOAc followed by acidic Boc group cleavage with HCl/i-PrOH at 40-50 °C .