168.5, 171.4, 173.8. Anal. Calcd for C21H31N306: C, 59.84; H, 7.41; N, 9.97. Found: C,

60.13; H, 7.64; N, 9.94.

 (5S)-5-Benzyl-3,6,9-trioxo-l-phenyl-2-oxa-4,7,10-triazadodecan-12-oic acid (Z-

Phe-Gly-Gly-OH, 5.4c):[89CCC784] Colorless microcrystals (98%), mp 120-122 C.

(lit.[89CCC784] 122-125 oC): [a]25D = -21.40 (c 1.4, DMF) [lit.[89CCC784] [a]15D -

11.80 (c 1.0, DMF); H NMR (DMSO-d6) 6 2.76 (t, J= 12.3 Hz, 1H, CHCH2Ph),

3.03-3.08 (m, 1H, CHCH2Ph), 3.78 (s, 4H, NCH2COx2), 4.31 (br s, 1H, NCHCO), 4.94

(s, 2H, OCH2Ph), 7.25-7.40 (m, 11H, ArH and NH), 7.56 (d, J= 7.8 Hz, 1H, NH), 8.11

(br s, 1H, NH), 8.35 (br s, 1H, CO2H). 13C NMR (DMSO-d6) 6 37.4, 40.6, 41.9, 56.2,

65.3, 126.2, 127.4, 127.6, 128.0, 128.3, 129.2, 137.0, 138.1, 155.9, 169.0, 171.1, 171.8.

 (5S, 8S, llS)-5-Benzyl-8,1 1-dimethyl-3,6,9-trioxo-l-phenyl-2-oxa-4,7,10-tri-

azadodecan-12-oic acid (Z-Phe-Ala-Ala-OH, 5.4d):[69ABB311] Colorless

microcrystals (92%), mp 180-180 oC. (lit.[69ABB311] 187.5-188.5 oC): [a]25D = -15.00

(c 1.0, DMF). H NMR (DMSO-d6) 6 1.23-1.29 (m, 6H, CH3x2), 2.66-2.75 (m, 1H,

CHCH2Ph), 3.00-3.05 (m, 1H, CHCH2Ph), 4.17-4.35 (m, 3H, NCHCOx3), 4.93 (s, 2H,

OCH2Ph), 7.19-7.33 (m, 10H), 7.51 (d, J= 8.7 Hz, 1H, NH), 8.14 (br s, 1H, NH), 8.17

(br s, 1H, NH), One exchangeable proton is missing. 13C NMR (DMSO-d6) 6 17.1, 18.2,

37.3, 47.4, 47.8, 55.9, 65.1, 126.1, 127.3, 127.5, 127.9, 128.2, 129.1, 136.9, 138.1, 155.8,

171.1, 171.7, 173.9.

 (5S, 8S, 11S)-5-Benzyl-ll-(hydroxymethyl)-8-methyl-3,6,9-trioxo-l-phenyl-2-

oxa-4,7,10-triazadodecan-12-oic acid (Z-Phe-Ala-Ser-OH, 5.4e): Colorless

microcrystals (94%), mp 185.5-186.5 oC: [a]25D = -1.40 (c 1.1, DMF); 1HNMR

(DMSO-d6) 6 1.26 (d, J= 7.0 Hz, 3H, CHCH3), 2.68-2.76 (m, 1H, CHCH2Ph),