12.6 Hz, 1H, OCH2Ph), 7.36 (s, 5H), 7.55 (d, J= 7.0 Hz, 1H, NH), 7.91 (d, J= 7.8 Hz,

1H, NH), 8.17 (br s, 1H, NH), One exchangeable proton is missing. 13C NMR (DMSO-

d6) 6 17.8, 21.3, 22.7, 24.1, 41.7, 50.0, 65.3, 127.7, 127.7, 128.2, 136.8, 155.7, 168.5,

172.6, 173.8. Anal. Calcd for C19H27N306: C, 58.00; H, 6.92; N, 10.68. Found: C, 58.21;

H, 7.01; N, 10.59.

 (11S)-l11-Isobutyl-5-methyl-3,6,9-trioxo-1-phenyl-2-oxa-4,7,10-triazadodecan-

12-oic acid (Z-DL-Ala-Gly-Leu-OH, 5.4a+5.4a'): Colorless microcrystals (94%), mp

101-105 oC. 1HNMR (DMSO-d6) 6 0.83 (d, J= 6.2, 3H), 0.88 (d, J= 6.3 Hz, 3H), 1.21

(d, J= 7.2 Hz, 3H), 1.52-1.62 (m, 3H), 3.72 (d, J= 5.1 Hz, 2H), 4.02-4.07 (m, 1H),

4.24-4.26 (m, 1H), 4.99 (d, J = 12.6 Hz, 1H), 5.05 (d, J= 12.6 Hz, 1H), 7.28-7.46 (m,

5H), 7.55 (d, J= 7.0 Hz, 1H), 7.90-7.97 (m, 1H), 81.4-8.17 (m, 1H). 13C NMR

(DMSO-d6) 6 17.8, 21.3, 22.7, 24.1, 41.7, 50.1, 50.2, 65.4, 127.7, 127.7, 128.3, 136.8,

155.8, 168.6, 172.7, 173.8. Anal. Calcd for C19H27N306: C, 58.00; H, 6.92; N, 10.68.

Found: C, 58.43; H, 6.99; N, 10.66.

 (5S, 11S)-l1-Isobutyl-5-isopropyl-3,6,9-trioxo-l-phenyl-2-oxa-4,7,10-triaza-

dodecan-12-oic acid (Z-Val-Gly-Leu-OH, 5.4b): Colorless microcrystals (85%), mp

131.5-132.5 oC: [a]25D = -17.10 (c 1.4, MeOH); H NMR (DMSO-d6) 6 0.82-0.88 (m,

12H, CH3x4), 1.49-1.66 (m, 3H, CH2CH(CH3)2), 1.93-2.02 (m, 1H, CHCH(CH3)2), 3.73

(d, J= 5.4 Hz, 2H, NCH2CO), 3.85 (apparent t, J& 7.7 Hz, 1H, NCHCO), 4.25 (apparent

q, J& 7.7 Hz, 1H, NCHCO), 5.01 (d, J= 12.6 Hz, 1H, OCH2Ph), 5.07 (d, J= 12.6 Hz,

1H, OCH2Ph), 7.30-7.40 (m, 6H, ArH and NH), 7.95 (d, J= 8.0 Hz, 1H, NH), 8.21 (t, J

= 5.4 Hz, 1H, NH), One exchangeable proton is missing. 13C NMR (DMSO-d6) 6 18.1,

19.1, 21.3, 22.7, 24.1, 29.9, 41.6, 50.0, 60.3, 65.3, 127.6, 127.7, 128.2, 136.9, 156.2,