(3R)-3-(4-chlorophenyl)-4-[[(1S)-2-methyl-1-(2-methylpropanoyloxy)propoxy]carbonylamino]butanoic acid
(3R)-3-(4-chlorophenyl)-4-[[[(1S)-2-methyl-1-(2-methyl-1-oxopropoxy)propoxy]-oxomethyl]amino]butanoic acid
(3R)-3-(4-chlorophenyl)-4-[[(1S)-1-isobutyryloxy-2-methyl-propoxy]carbonylamino]butyric acid