S. Hanessian et al. / Tetrahedron 59 (2003) 995–1007
1003
(Hþ) was added in small portions until the solutions became
neutral. The resin was filtered and the filtrate was
evaporated to dryness to yield the corresponding 300-
amino-N-hydroxy analogues: 18a0 (FAB MS cal0cd for
C45H60N6O19 (MþNaþ) 1011.4; found 1011.4), 18b (FAB
MS calcd for C46H62N6O19 (MþNaþ) 1025.4; found
1025.4), 18c0 (FAB MS calcd for C47H64N6O19 (MþNaþ)
1039.4; found 1039.6), 18d0 (FAB MS calcd for
C48H66N6O19 (MþNaþ) 1051.4; found 1051.3), 18e0
(FAB MS calcd for C46H62N6O19 (MþNaþ) 1025.4;
found 1025.4) as white solids. These were hydrogenolyzed
over H2 (balloon) in the presence of 10% Pd/C (7 mg) in
dioxane–H2O–acetic acid (20:20:1) for 40 min. Filtration
followed by lyophilization of the solvent gave pure
N-hydroxyureas 8a–e as white solids.
(3 mL) was treated with Ra-Ni (5 mg of 50% dispersion in
H2O/AcOH). The mixture was stirred over H2 (balloon) for
5 h at rt, then filtered and lyophilized to give pure 19
1
(14 mg, 70%). H NMR (D2O) d 5.50 (d, J¼3.9 Hz, 1H),
5.18 (d, J¼3.9 Hz, 1H), 4.10–3.99 (m, 2H), 3.88–3.52 (m,
16H), 3.45–3.30 (m, 7H), 3.18 (dd, J¼10.3, 6.7 Hz, 1H);
13C NMR (D2O) d 160.5, 98.8, 97.1, 82.2, 81.5, 73.7, 73.0,
72.5, 71.7, 71.6, 69.4, 69.2, 66.5, 60.3, 55.9, 50.4, 48.7,
41.0, 40.6, 38.1, 33.0; FAB MS calcd for C53H66N6O20
(MþNaþ) 1129.4; found 1129.4.
4.4.7. Compound 20. To the mixture of N-Cbz-4-amino-
butyric acid (1 g, 4.22 mmol) and N-hydroxysuccinimide
(0.49 g, 4.22 mmol) in dioxane (15 mL) was added DCC
(0.87 g, 4.22 mmol) at 08C. The mixture was stirred
overnight, filtered, the solvent was removed in vacuo, the
residue was dissolved in benzene (40 mL) and ether
(40 mL), washed with NaHCO3, dried (MgSO4) and
evaporated to dryness. The NOS ester was sufficiently
pure for coupling with the aminoglycoside. A solution
containing 65 mg (0.2 mmol of ester) was added to 16
(85 mg, 0.1 mmol) in THF–H2O (2:1, 3 mL). The resulting
solution was stirred for 24 h, then evaporated and
chromatographed (CH2Cl2–MeOH, 4:1) to give 22 mg the
amide (FAB MS calcd for C48H60F3N5O19 (MþHþ)
1068.38; found 1068.3).
1
4.4.1. Compound 8a (95%). H NMR (D2O) d 5.50 (d,
J¼4.2 Hz, 1H), 5.18 (d, J¼4.4 Hz, 1H), 4.09–3.49 (m,
20H), 3.42–3.29 (m, 4H), 2.21 (m, 1H), 1.96 (s, 12H), 1.74
(dd, J¼14.2, 1.2 Hz, 1H); 13C NMR (D2O) d 180.5, 165.0,
98.5, 96.3, 81.5, 80.0, 73.1, 73.0, 72.6, 71.5, 69.4, 68.8,
66.2, 60.3, 56.0, 50.3, 48.7, 40.9, 38.2, 31.6, 25.9, 23.0;
MALDI-FTMS calcd for C21H42N6O13Na (MþNaþ)
609.2702; found 609.2714.
1
4.4.2. Compound 8b (98%). H NMR (D2O) d 5.49 (d,
J¼4.4 Hz, 1H), 5.14 (d, J¼4.3 Hz, 1H), 4.08–3.24 (m,
24H), 3.14 (dd, J¼10.2, 6.8 Hz, 1H), 2.9 (t, J¼5.2 Hz, 2H),
2.17 (m, 1H), 1.94 (s, 12H), 1.92 (m, 2H), 1.72 (dd, J¼14.1,
7.4 Hz, 1H); 13C NMR (D2O) d 181.2, 177.8, 162.0, 98.6,
96.3, 81.4, 79.9, 73.1, 72.9, 72.5, 71.5, 69.4, 68.8, 66.2,
63.2, 60.2, 55.9, 50.3, 48.5, 47.9, 40.9, 37.8, 25.8, 25.3,
23.4; ES-MS calcd for C22H45N6O13 (MþHþ) 601.3; found
601.3.
A portion of the above amide (15 mg, 0.015 mmol) was
dissolved in the solution of 1 M NH3 in THF–H2O (3:1,
1.5 mL). The mixture was stirred for 44 h, after which time
it was evaporated to dryness. The resulting N-Cbz
intermediate (FAB MS calcd for C46H61N5O18 (MþHþ)
972.4; found 972.4) was subjected to hydrogenolysis with
Pd/C 10% (5 mg) over H2 (balloon) in H2O–dioxane–
AcOH (20:20:1, 1.5 mL) to give 11 mg of pure 20 (96%).
1H NMR (D2O) d 5.52 (d, J¼5.4 Hz, 1H), 5.13 (d,
J¼5.6 Hz, 1H), 4.12–3.99 (m, 3H), 3.91–3.62 (m, 11H),
3.48–3.32 (m, 3H), 3.18 (dd, J¼8.0, 13.2 Hz, 1H) 3.05 (dd,
J¼7.4, 7.2 Hz, 2H), 2.39 (t, J¼7.0 Hz), 1.93 (s, 12H); 13C
NMR (D2O) d 182.1, 175.5, 99.0, 96.6, 81.8, 80.5, 73.3,
73.0, 72.7, 71.6, 71.5, 69.4, 68.8, 66.3, 60.3, 55.9, 49.4,
48.6, 41.0, 39.6, 33.3, 31.4, 25.7, 23.9, 23.4
1
4.4.3. Compound 8c (96%). H NMR (D2O) d 5.49 (d,
J¼4.3 Hz, 1H), 5.16 (d, J¼4.4 Hz, 1H), 4.09–3.19 (m,
24H), 3.13 (dd, J¼10.4, 6.6 Hz, 1H), 3.0 (m, 2H), 2.18 (m,
1H), 1.92 (s, 12H), 1.71 (dd, J¼14.0, 7.4 Hz, 1H), 1.62 (m,
4H); 13C NMR (D2O) d 180.3, 161.9, 98.5, 96.2, 81.0, 79.9,
73.0, 72.9, 72.6, 71.5, 69.4, 68.8, 66.1, 63.2, 60.3, 55.9,
50.3, 49.9, 48.5, 40.9, 39.8, 24.7, 24.7, 24.0, 22.9; ES-MS
calcd for C23H47N6O13 (MþHþ) 615.3; found 615.3.
4.4.8. Compound 21. To a stirred suspension of tobramycin
(200 mg, 0.43 mmol) in DMSO (3 mL) was added
Zn(OAc)2·2H2O (0.37 g, 1.7 mmol, washed with THF
prior to use). The mixture was stirred for 12 h, after which
time N-benzyloxycarbonyloxy succinimide (0.36 g,
1.46 mmol) was added in one portion. The reaction mixture
was stirred for 2 h, diluted with dioxane (3 mL), Amberlite
IR-120 (Hþ) (2 g) was added and the mixture was stirred for
another hour. The resin was poured onto a porous glass filter
containing 1 g of the same resin, which was washed with a
mixture of dioxane–H2O (1:1) until N-hydroxysuccinimide
was no longer detectable by TLC. The product was then
eluted with 1 M NH3 in dioxane–H2O (1:1); (TLC: CHCl3–
MeOH–5N NH4OH), and the fractions containing 3,20,60-
tris-N-benzyloxycarbonyl tobramycin (Rf 0.2) were
collected and pooled, the solution was saturated with
carbon dioxide (by bubbling gas through the solution for
30 min) and lyophilized to give 21 as a white fluffy solid,
(62–70 mg, 18–25%). 1H NMR (DMSO) d 8.42 (br s, 1H),
7.42–6.38 (m, 15H), 5.15–4.82 (m, 8H), 3.62–3.29 (m,
1
4.4.4. Compound 8d (97%). H NMR (D2O) d 5.48 (d,
J¼4.3 Hz, 1H), 5.14 (d, J¼4.2 Hz, 1H), 4.06–3.25 (m,
24H), 3.11 (dd, J¼10.5, 6.6 Hz, 1H), 2.93 (t, J¼5.1 Hz, 2H),
2.16 (m, 1H), 1.95 (s, 12H), 1.58 (m, 4H), 1.35 (m, 2H); 13C
NMR (D2O) d 179.8, 161.9, 98.5, 96.2, 81.0, 79.9, 73.0,
72.5, 71.5, 69.4, 68.7, 66.1, 63.2, 60.3, 55.9, 50.3, 50.2,
48.5, 40.9, 40.0, 31.7, 27.1, 26.3, 25.9, 23.4, 22.6; ES-MS
calcd for C24H49N6O13 (MþHþ) 629.3; found 629.3.
1
4.4.5. Compound 8e (97%). H NMR (D2O) d 5.48 (d,
J¼3.9 Hz, 1H), 5.15 (d, J¼3.9 Hz, 1H), 4.10–3.32 (m,
24H), 3.28 (t, J¼3.8 Hz, 2H), 3.12 (dd, J¼10.5, 6.7 Hz, 1H),
2.71 (s, 3H), 2.19 (m, 1H), 1.92 (s, 12H), 1.72 (dd, J¼14.0,
7.5 Hz, 1H); 13C NMR (D2O) d 180.7, 161.9, 98.8, 96.2,
81.4, 80.0, 73.0, 72.6, 71.5, 69.4, 68.8, 66.2, 60.3, 55.9,
50.4, 48.5, 47.5, 40.9, 33.6, 31.6, 23.1; ES-MS calcd for
C22H45N6O13 (MþHþ) 601.3; found 601.2.
4.4.6. Compound 19. A solution of 8a (20 mg) in H2O