合成路线1

Alternatively, compound (R)-(IX) can be obtained as follows: treatment of butylmalonic acid (XI) with formaldehyde (XII) in ethanol in the presence of piperidine provides 2-butyl acrylic acid (XIII), which is converted into oxazolidinone derivative (XVI) by first reaction with pivaloyl chloride (XIV) and Et3N in THF followed by treatment with derivative (XV) and BuLi in THF. Oxazolidinone (XVI) is then enantioselectively condensed with O-benzylhydroxylamine (XVII) and treated with p-TsOH to afford a single diastereoisomer (XVIII), which is then hydrolyzed with LiOH in THF to yield (XIX). Finally, hexanoic acid (XIX) is coupled to tert-Leucine-N,N-dimethylamide (VII) by means of EDC and HOBt in DMF.