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acid ester hydrochloride salts into the corresponding free amines, see:
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29
Typical Experimental
Procedure for 2a
To a stirred solution of Fmoc-Ala-OH
(1 mmol) in dry CH2Cl2, Et3N (2
mmol) and Deoxo-Fluor (1.4 mmol) were added at 0 ˚C.
After the addition of TMSN3 (1.3 mmol), the reaction
mixture was subjected to ultrasonication. After 10 min, H-Leu-OMe
(1.5 mmol) was added, and the ultrasonication was continued until
completion of the reaction. The reaction mixture was evaporated,
hexane was added, and the residue was filtered. It was washed with
H2O, hexane, and dried under vacuum. Finally, the compound
was recrystallized using DMSO-H2O to afford
the urea as a colorless crystalline solid.
30
Selected Spectroscopic
Data
Fmoc-Val-ψ(NH-CO-NH)-Leu-OBzl (2b): white solid, mp 184 ˚C. ¹H
NMR (300 MHz, DMSO): δ = 0.92 (12 H, m), 1.32-1.85
(4 H, m), 3.10 (2 H, s), 3.70-3.80 (2 H, m), 4.20 (1 H,
t), 4.42 (2 H, m), 5.10 (1 H, d), 6.60-6.70 (2 H, m), 7.20-7.85
(13 H, m). ¹³C NMR (200 MHz, DMSO): δ = 18.5,
19.5, 22.0, 23.1, 24.5, 29.2, 40.3, 47.2, 59.0, 66.6, 120.0, 125.1,
126.5, 127.0, 127.2, 128.4, 129.3, 137.6, 141.2, 144.0, 155.4, 156.8,
176.4. HRMS: m/z calcd for C33H39N3NaO5:
580.2787; found: 580.2774 [M + Na].
Z-Gly-ψ(NH-CO-NH)-Val-OMe (2d): Off-white solid, mp 159 ˚C. ¹H
NMR (300 MHz, DMSO): δ = 0.93 (6 H, d), 3.14 (1
H, m), 3.58 (3 H, s), 4.51 (3 H, m), 5.30 (2 H, s), 6.10 (2 H, m),
6.48 (1 H, t), 7.20-7.40 (5 H, m). ¹³C
NMR (200 MHz, DMSO): δ = 17.1, 31.1, 52.1, 56.2,
57.8, 65.4, 127.1, 127.2, 128.5, 141.2, 156.8, 157.5, 171.6. HRMS: m/z calcd for C16H23N3NaO5:
360.1535; found: 360.1513 [M + Na].
Boc-Glu(OBzl)-ψ(NH-CO-NH)-Ile-OMe
(2e): solid, mp 138 ˚C. ¹H
NMR (300 MHz, DMSO): δ = 0.91 (6 H, d), 1.30-1.45
(11 H, s), 1.65 (1 H, m), 2.55 (2 H, m), 2.90 (2 H, m), 3.65 (3
H, s), 3.80-3.90 (2 H, m), 5.15 (2 H, s), 5.30 (1 H, d),
6.35 (1 H, d), 6.50 (1 H, d), 7.30-7.40 (5 H, m). ¹³C NMR
(200 MHz, DMSO): δ = 22.1, 23.1, 24.7, 28.6, 37.9, 39.7,
419, 50.9, 51.7, 61.9, 63.1, 78.7, 126.7, 127.6, 128.9, 137.7, 155.3,
156.8, 157.5, 178.1. HRMS: m/z calcd
for C24H37N3NaO7: 502.2529;
found: 502.2543 [M + Na].
Fmoc-Val-ψ(NH-CO-NH)-2,3,4,6-tetra-O-acetyl-β-d-glucopyranoside
(3a): white solid, mp 179 ˚C. ¹H
NMR (300 MHz, DMSO): δ = 0.93 (6 H, d), 1.95 (12
H, s), 3.12 (1 H, m), 4.30-4.45 (3 H, m), 4.67 (2 H, d),
4.90-5.20 (5 H, m), 5.40 (1 H, m), 5.70 (2 H, br), 6.90-7.50
(8 H, m). ¹³C NMR (200 MHz, DMSO): δ = 15.1,
20.8, 21.1, 33.2, 47.5, 59.7, 67.8, 68.0, 69.1, 69.2, 73.0, 74.8,
81.0, 126.8, 128.2, 128.4, 128.6, 141.3, 142.5, 156.0, 158.1, 170.7.
HRMS: m/z calcd for C34H41N3NaO12:
706.2588; found: 706.2601 [M + Na].
(1,2),(3,4)-Diacetylgalactopyranosyl-6-NH-CO-NH-Phe-OMe
(4b): solid, mp 104 ˚C. ¹H
NMR (300 MHz, DMSO): δ = 1.25 (12 H, s), 3.21
(2 H, d), 3.85 (3 H, s), 4.30-4.53 (3 H, m), 4.80 (1 H,
m), 5.50-5.70 (2 H, m), 6.31 (2 H, s), 7.10-7.40
(5 H, m). ¹³C NMR (200 MHz, DMSO): δ = 23.5,
34.2, 50.8, 54.2, 67.4, 69.2, 76.8, 77.9, 89.2, 107.6, 113.5, 125.4, 126.7,
127.8, 137.0, 157.2, 171.8. HRMS: m/z calcd
for C22H30N2NaO8: 473.1900;
found: 473.1918 [M + Na].
31 First, a solution of α-d-galactose (5 mmol) and ZnBr2 (5.2 mmol)
in acetone (20 mL) was stirred for 12 h and filtered. The filtrate
was concentrated and after a simple workup, the resulting (1,2),(3,4)-diacetylgalactopyranose
was dissolved in MeCN. Then, TEMPO and Na3PO4 buffer
were added and the reaction mixture was warmed to 35 ˚C.
Sodium chlorite and bleach were added, and the reaction mixture
was stirred till completion of reaction. A simple workup lead to
the isolation of the desired sugar-6-acid. See: Jhao M.
Li J.
Mano E.
Song Z.
Tschaen DM.
Grabowski EJJ.
Reider PJ.
J.
Org. Chem.
1999,
64:
2564