Molecules 2020, 25, 1315
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evaporation under reduced pressure, and washed with petroleum ether (40–60 C) to obtain the
product as white crystals (0.32 g, 79%). Further purification was performed using a CombiFlash
EZ Prep system (Teledyne-ISCO, Lincoln, NE, USA, eluent: gradient: dichloromethane – methanol
0–30%). The reaction and the work up were monitored by TLC (eluent: ethyl acetate, Rf: 0.11). Mp:
191–193 ◦C; 1H-NMR (300 MHz, DMSO-d6) δH 16.21 (1H, brs, 8.72 (1H, d, J = 7.5 Hz, 4-H), 7.44 (1H, d,
J = 8.7 Hz, 12-H), 7.33 - 7.24 (10H, m, 9,10,11,17,18,19-H), 5.27 (1H, quint, 6.9 Hz, 2-H), 4.96 (1H, d,
J = 13.5 Hz, 15a-H), 4.92 (1H, d, J = 13.5 Hz, 15b-H), 4.30 (1H, m, 6-H), 3.03 (1H, dd, J = 3.3 Hz, J =
13.8 Hz, 7a-H), 2.72 (1H, dd, J = 10.8 Hz, J = 13.5 Hz, 7b-H), 1.52 (3H, d, J = 6.9 Hz, 3-H); 13C-NMR
(75.5 MHz, DMSO-d6) δC 171.7 (5-C), 158.7 (1-C), 156.3 (14-C), 138.5 (8-C), 137.5 (16-C), 129.6, 128.7,
128.5, 128.1, 127.9, 126.7 (9,10,11,17,18,19-C), 65.7 (15-C), 56.5 (6-C), 40.0 (2-C), 37.8 (7-C), 19.7 (3-C);
ν
max/cm–1 3300 (N-H), 2984, 2874, 2741, 2615 (tetrazole), 1684 (C=O), 1651 (C=O), 1531 (N-H), 1234
(C-O); MS(ESI) m/z 417.2 (M + Na)+; CHN [Found: C, 60.78; H, 5.68; N, 20.92. C20H22N6O3 requires C,
60.90; H, 5.62; N, 21.31%].
(2S)-2-Amino-3-phenyl-N-[(1S)-1-(1H-1,2,3,4-tetrazol-5-yl)ethyl]propanamide (14j-LL): Cbz-l-phenylalanyl-
1-l-aminoethyltetrazole (13j-LL, 0.30 g, 0.8 mmol) was deprotected by general method E. Following
filtration, the solid residue was washed with ethanol, which was discarded. The residue was washed
with water, which was freeze dried, then purified by column chromatography (eluent: dichloromethane
– ethanol 10:1, 8:1, 6:1, 1:1 then 0:1 ratio) to give the pure product as a white solid (40 mg, 20%). Further
purification was performed by Prep HPLC method A. The reaction and the work up were monitored
by TLC (eluent: ethanol, Rf: 0.39). Mp: 152–155 ◦C; 1H-NMR (300 MHz, D2O) δH 7.15 (3H, m, 10,11-H),
7.01 (2H, m, 9-H), 5.24 (1H, quart, J = 6.9 Hz, 2-H), 3.77 (1H, m, 6-H), 2.97 (1H, dd, J = 6.0, J = 13.5 Hz,
7a-H), 2.89 (1H, dd, J = 7.8, J = 13.5 Hz, 7b-H), 1.43 (3H, d, J = 7.2 Hz, 3-H); 13C-NMR (75.5 MHz, D2O)
δC 163.5 (1-C), 150.6 (5-C), 135.5 (8-C), 129.2 (9-C), 128.6 (10-C), 127.1 (11-C), 55.5 (6-C), 41.3 (2-C), 39.3
(7-C), 19.3 (3-C); ν
max/cm–1 3217 (N-H), 1651 (C=O), 1528 (N-H); MS(ESI) m/z 283.2 (M + Na)+. HRMS
(Found (M + H)+ 261.1462. Calcd. for C12H17ON6: (M + H)+ 261.1458.); (Purity test: HPLC method A).
Benzyl-N-[(1S)-1-{[(1S)-1-(1H-1,2,3,4-tetrazol-5-yl)propyl]carbamoyl}ethyl]carbamate (13b-LL): Prepared
using general method G. The Fmoc group of the Fmoc-1-l-aminopropyltetrazole attached to
2-chlorotrityl chloride resin (resin:loading; 1:1 ratio; 2.9 mmol) was removed. After coupling of
Cbz-l-alanine with the resin, the title compound was cleaved off. The cleaving mixture (TFA/DCM/TIS,
ratio 5:95:1 eq) was removed by evaporation under reduced pressure. The crude product was
subsequently washed with petroleum ether (40–60 ◦C) to obtain the product as white crystals (0.49 g,
52%). Mp: 174–175 ◦C; 1H-NMR (300 MHz, DMSO-d6) δH 8.44 (1H, d, J = 7.5 Hz, 5-H), 7.41 (1H, d, J =
7.2 Hz, 9-H), 7.34 (5H, m, 14,15,16-H), 5.06 (1H, m, 2-H), 5.02 (2H, s, 12-H), 4.10 (1H, quint, J = 6.9 Hz,
7-H), 1.88 (2H, m, 3-H), 1.19 (3H, d, J = 7.2 Hz, 8-H), 0.87 (3H, t, J = 7.2 Hz, 4-H); 13C-NMR (75.5 MHz,
DMSO-d6) δC 173.0 (6-C), 156.8 (1-C), 156.1 (11-C), 137.5 (13-C), 128.8 (15-C), 128.2 (16-C), 128.1 (14-C),
65.8 (12-C), 50.4 (7-C), 45.8 (2-C), 26.8 (3-C), 18.4 (8-C), 10.6 (4-C); ν
max/cm–1 3300 (N-H), 3265 (N-H),
2976, 2876, 2735, 2617 (tetrazole), 1691 (C=O), 1651 (C=O), 1533 (N-H), 1246 (C-O); MS(ESI) m/z 333.1
(M + H)+; CHN [Found: C, 54.20; H, 6.11; N, 24.91. C15H20N6O3 requires C, 54.21; H, 6.07; N, 25.29%].
(2S)-2-Amino-N-[(1S)-1-(1H-1,2,3,4-tetrazol-5-yl)propyl]propanamide
(
14b-LL):
Cbz-l-alanyl-1-l-
aminopropyltetrazole (13b-LL, 0.40 g, 1.2 mmol) was deprotected by general method E. Following
filtration, the solid residue was washed with ethanol, which was discarded. The residue was washed
with water, which was freeze dried to give the product as a white solid (206 mg, 86%). Due to poor
solubility, the corresponding hydrochloride salt was prepared using 2M HCl in diethyl ether solution
(20 mL) for characterization (hygroscopic solid). Further purification was performed by Prep HPLC
1
method A. The reaction and the work up were monitored by TLC (eluent: ethanol, Rf: 0.12). H-NMR
(300 MHz, DMSO-d6) δH 9.17 (1H, d, J = 7.6 Hz, 5-H), 8.34 (3H, brs, 9-H), 5.09 (1H, quart, J = 7.8 Hz,
2-H), 3.93 (1H, quart, J = 6.7 Hz, 7-H), 1.92 (2H, m, 3-H), 1.38 (3H, d, J = 7.0 Hz, 8-H), 0.90 (3H, t, J = 7.4
Hz, 4-H); 13C-NMR (75.5 MHz, DMSO-d6) δC 170.0 (6-C), 158.0 (1-C), 48.6 (7-C), 46.4 (2-C), 26.8 (3-C),