By two separate routes were prepared four diastereoisomers of (2R or 2S,5R or SS)-3-benzyI-5-{(1S)[(tert-butoxycarbonyl)amino]-2-phenylethyl}tetrahydrofuran-2-one (11, 12, 17 and 18). Since the furanones were derived from (S)-phenylalanine, absolute configurations of all chiral carbon atoms could be deduced from their H-1 NMR spectra. The furanones were easily hydrolyzed to four (2R or 2S,4R or 4S,5S)-2-benzyl-5-[(tert-butoxycarbony)amino]-4-hydroxy-6-phenylbutanoic acids (20-23), hydroxyethylene isosteres of Phe-Phe peptide bond.