Proton NMR Spectroscopy Data

The proton NMR spectra of **5** and **7** showed a doublet signal in the region between 8.73 and 8.99 ppm, attributed to deshielded H-3 proton. The 1H NMR spectrum of **5** revealed a signal assigned to the H-4 proton at 4.29 ppm as a doublet of doublets due to the vicinal coupling to H-3 and H-18 protons. The proton NMR spectra of α-acylamino ketones **7a** and **7b** showed the H-4 signal at 5.36 (**7b**) or 5.38 ppm (**7a**) as a triplet, due to the coupling to H-3 and H-18. The 1H NMR spectra of **5**, **7a**, and **7b** also highlighted characteristic signals for the isopropyl substituent, i.e., an octet (**5**) or a multiplet (**7a**,**b**) signal registered in the range of 2.17–2.28 ppm assigned to the methine proton (H-18) and two strongly shielded doublet signals, the first in the interval of 0.89–0.94 ppm and the second at 0.92 or 0.95 ppm, due to the non-equivalent protons (H-19, H-20) of the two methyl groups. The signal of proton of the carboxyl group of *N*-acyl-α-amino acid **5** was not recorded in the 1H NMR spectrum probably due to hydrogen-deuterium exchange, but the presence of the COOH group was confirmed both by IR and 13C NMR spectral data.

The 1H NMR spectrum of **6** displayed the H-4 doublet signal at 4.32 ppm due to the coupling only to the H-18 proton (with <sup>3</sup>*J* = 4.7 Hz). The methine proton of the 1-methylethyl group was revealed by the presence of a septet of doublets signal at 2.40 ppm due to coupling to protons H-19, H-20 (with <sup>3</sup>*J* = 6.9 Hz), and to H-4 proton (with <sup>3</sup>*J* = 4.7 Hz). The 1H NMR spectra of **8a** and **8b** showed for the isopropyl substituent a signal as septet at 3.26 (**8b**) or 3.29 ppm (**8a**) attributed to the H-18 proton, and a shielded doublet at 1.35 (**8b**) or 1.36 ppm (**8a**), due to the two CH3 groups' protons.
