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The yield of target compound IIae l depended both on the absolute con figuration of initial N -Boc-phenylalanine and nature of substituents present in the phenyl ring and phosphonate moiety respectively. The structures of all the compounds were confi rmed by IR1H NMR,13C NMR,31P NMR,19F NMR spectra, and elemental analysis. The IR spectra of products IIael exhibited absorption bands at 3281-3289 cm-1, indicating the presence of amidic N-H.The stretching frequency at 1653-1684 cm-1was assigned to C=O vibrations and the characteristic absorptions at 1207-1224 cm-1and 1005-1024 cm-1 were attributed to the presence of P=Oand the P-O-C group, respectively. In 1H NMR spectra, all phenyl protons showed multiplet at 7.49-6.71 ppm. The main character-istic of the 1H NMR spectra of IIael is the presence of high-frequency down field broad singletδH8.84 -8.43 for amidic N-H protons. The broad doublets atδH8.12-7.97 presumably arise due to the presence of deshielded N-H proton of thiourea linked to the phosphonate moiety and benzene ring through an intervening carbon atom. While the broad doublets atδH6.45-6.32 are assigned to the N-H proton of thiourea directly attached to the asymmetric carbon atom, another adjacent doublet atδH6.33-6.12 appeared due to the C-H proton of N-C-P. The multiplet atδH5.28-5.14 was assigned to the C-H of N-C-C group. The typical low intense carbon resonance frequencies atδc183.8-182.9 andδc171.2-170.4 in the 13C NMR spectra of IIa-l also con firmed the presence of C=S and C=O double bond respectively. As expected, fluorine and phosphorus resonance appeared atδF -118.8 to 115.2 andδP20.3-22.6 in their corresponding fluorine and phosphorus NMR spectra, respectively. According to the31P NMR spectra of all target compounds, phosphorus atom of the phosphonate moiety was coupled to adjacent CH.  |
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