By two separate routes were prepared four diastereoisomers of (2R or 2S,5R or 5S)-3-benzyl-5-(1S)- [(tert-butoxycarbonyl)amino]-2-phenylethyl}tetrahydrofuran-2-ones (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 1H NMR spectra. The furanones were easily hydrolyzed to four (2R or 2S,4R or 4S,5S)-2-benzyl-5- [(tert-butoxycarbonyl)amino]-4-hydroxy-6-phenylbutanoic acids (20-23), hydroxyethylene isosteres of Phe-Phe peptide bond.
通过两条不同的途径,制备了四个对映异构体(2R或2S,5R或5S)-3-苄基-5-(1S)-[(叔丁氧羰基)氨基]-2-苯乙基}四氢呋喃-2-酮(11、12、17和18)。由于呋喃酮是由(S)-苯丙氨酸衍生而来的,所有手性碳原子的绝对构型可以从它们的1H NMR谱中推断出来。这些呋喃酮容易水解成四个(2R或2S,4R或4S,5S)-2-苄基-5-[(叔丁氧羰基)氨基]-4-羟基-6-苯基丁酸(20-23),是Phe-Phe肽键的羟基乙烯同分异构体。