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C2-Symmetric Bisoxazoline Ligands
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2,5-bis[m-[N-(10S)-(10 -isobutyl-20-hydroxyethyl)amido]phenyl]-1,3,4-
oxadiazole 2a. General Procedure I. A solution of 2,5-di-(m-carboxy-
phenyl)-1,3,4-oxadiazole 1 (1.17 g, 3.76 mmol) and SOCl2 (20 mL) was
refluxed for 10 h. The excess SOCl2 was removed under reduced pressure,
benzene (20 mL) was added and the solvent was removed again to dry-
ness to afford the diacyl dichloride. The above diacyl dichloride in
CH2Cl2 (50 mL) was added dropwise to a solution of S-leucinol (0.88 g,
7.52 mmol) and Et3N (2.82 mL) in CH2Cl2 (30 mL) at 0ꢀC and stirring at
room temperature for 24 h. The precipitate was filtered and washed with
diethyl ether to afford the colorless solid powder 2a 1.51 g (79.2% yield).
M.p. 163–169ꢀC. IR (KBr): 3470, 3320, 2920, 2840, 1640, 1570 cmÀ1
.
EI MS: 508 (Mþ). H NMR (DMSO): ꢁ 0.90 (6H, d, J ¼ 5.2 Hz, CH3),
0.92 (6H, d, J ¼ 5.2 Hz, CH3), 1.37–1.54 (4H, m, CH2), 1.62–1.67 (2H, m,
CH), 3.33–3.50 (4H, m, CH2), 4.09–4.15 (2H, m, CH), 4.75 (2H, t,
J ¼ 5.8Hz, OH), 7.74 (2H, t, J ¼ 7.8 Hz, ArH), 8.12 8.15 (2H, m, ArH),
8.28–8.31 (2H, m, ArH), 8.37 (2H, d, J ¼ 8.6 Hz, NH), 8.63 (2H, t,
J ¼ 1.4 Hz, ArH). Anal. calcd. C28H36N4O5: C, 66.14; H, 7.08; N,
11.02. Found: C, 66.12; H, 7.13; N, 10.93.
1
2,5-bis[m-[N-(10S)-(10-isopropyl-20-hydroxyethyl)amido]phenyl]-1,3,4-
oxadiazole 2b. Following general procedure I, from 2,5-di-(m-carboxy-
phenyl)-1,3,4-oxadiazole 1 (1.68 g, 5.3 mmol) , SOCl2 (30 mL), S-valinol
(1.09 g, 10.5 mmol) and Et3N (4.0 mL) to provide colorless solid 2b in
74.7% yield (1.9g). M.p. 240–242ꢀC. IR (KBr): 3400, 2950, 1650,
1530 cmÀ1. EI MS: 480 (Mþ). 1H NMR (DMSO): ꢁ 0.92 (6H, d,
J ¼ 6.8 Hz, CH3), 0.94 (6H, d, J ¼ 6.8 Hz, CH3), 1.92–2.00 (2H, m,
CH), 3.53–3.59 (4H, m, CH2), 3.83–3.90 (2H, m, CH), 4.63 (2H, t,
J ¼ 5.6, OH), 7.74 (2H, t, J ¼ 7.8 Hz, ArH), 8.15 (2H, d, J ¼ 7.8 Hz,
ArH), 8.28–8.31 (2H, m, ArH), 8.32 (2H, d, J ¼ 8.8 Hz, NH), 8.62 (2H,
s, ArH). Anal. calcd. C26H32N4O5: C, 64.98; H, 6.71; N, 11.67. Found: C,
64.85; H, 6.71; N, 11.52.
2,5-bis[m-[N-(10S)-(10-benzyl-20-hydroxyethyl)amido]phenyl]-1,3,4-oxa-
diazole 2c. Following general procedure I, from 2,5-di-(m-carboxy-
zphenyl)-1,3,4-oxadiazole
1
(0.82 g, 2.65 mmol), SOCl2(20 mL),
S-phenylalaninol (0.8 g, 5.3 mmol) and Et3N (2.0 mL) to give a colorless
solid 2c in 80.8% yield (1.24 g). M.p. 240–242ꢀC. IR (KBr): 3400, 3350,
1
1620, 1550 cmÀ1. FAB-MS: 577 (M þ 1). H NMR (DMSO): ꢁ 2.82 (2H,
dd, J ¼ 8.8, 13.0 Hz, CH2), 2.97 (2H, dd, J ¼ 5.2, 13.4 Hz, CH2), 3.23–3.40
(2H, m, CH2), 3.43–3.56 (2H, m, CH2), 4.15–4.28 (2H, m, NCH), 4.89
(2H, t, J ¼ 5.6 Hz, OH), 7.10–7.34 (10H, m, ArH), 7.72 (2H, t, J ¼ 7.4 Hz,
ArH), 8.05 (2H, dd, J ¼ 1.2, 7.4 Hz, ArH), 8.27 (2H, dd, J ¼ 1.2, 7.4 Hz,
ArH), 8.52 (2H, d, J ¼ 8.0 Hz, NH), 8.55 (2H, s, ArH). Anal. calcd.
C34H32N4O5: C, 70.82; H, 5.59; N, 9.72. Found: C, 70.97; H, 5.59; N, 9.50.