volume of H2O and freeze-dried to afford the pure product 1b
(80 mg, 84%) as a white powder (MeOH:NH4OH/3 : 2, Rf 0.54):
1H NMR (500 MHz, D2O) d 3.71–3.77 (m, 2H, CH2 of N-glycinyl),
Ring I: 1.82–1.97 (m, 1H, H3ax), 2.15 (ddd, 1H, J1 = 4.2, J2 = 8.2,
J3 = 12.8 Hz, H3eq), 3.43–3.49 (m, 1H, H6), 3.49–3.61 (m, 2H, H2
and H5), 3.63–3.78 (m, 2H, H4 and H6¢), 5.45 (d, 1H, J = 2.8 Hz,
H1), Ring II: 1.85–2.00 (m, 1H, H2ax), 2.44 (ddd, 1H, J1 = 4.3,
J2 = 8.4, J3 = 12.5 Hz, H2eq), 3.38–3.52 (m, 1H, H3), 3.48–3.52
(m, 1H, H1), 3.67–3.79 (m, 2H, H4 and H6), 3.84–3.90 (m, 1H,
H5), Ring III: 3.35–3.43 (m, 1H, H3ax), 3.55–3.61 (m, 1H, H4),
3.63–3.68 (m, 1H, H6), 3.70–3.75 (m, 1H, H6¢), 3.77–3.83 (m, 1H,
H5), 3.78–3.90 (m, 1H, H2), 5.03 (d, 1H, J = 3.4 Hz, H1) (Fig.
S1†); 13C NMR (100 MHz, D2O) d 34.7, 35.7, 40.7, 44.1, 49.7,
50.2, 51.0, 54.9, 61.0, 66.6, 69.7, 72.2, 72.6, 72.9, 75.1, 87.7, 88.4,
100.4 (anomeric C), 100.7 (anomeric C), 175.9 (C O) (Fig. S2†);
ESI-MS m/z calcd for C20H40N6O10Na 547.2704, found 547.2695
[M + Na]+; Retention time on HPLC: 3.53 min.
1H NMR (500 MHz, D2O) d 1.75–1.88 (m, 1H, AHB), 2.04 (m,
1H, AHB), 3.00–3.16 (m, 2H, AHB), 3.93–4.01 (q, 1H, J = 4.0 Hz,
AHB), Ring I: 1.84–1.95 (m, 1H, H3ax), 2.17 (ddd, 1H, J1 = 3.9,
J2 = 8.4, J3 = 12.8 Hz, H3eq), 3.37–3.45 (m, 1H, H6¢), 3.49–3.57
(m, 2H, H5 and H6), 3.49–3.69 (m, 1H, H2), 3.74–3.80 (m, 1H,
H4), 5.43 (d, 1H, J = 2.7 Hz, H1), Ring II: 1.80–1.95 (m, 1H,
H2ax), 2.41–2.45 (m, 1H, H2eq), 3.36–3.53 (m, 2H, H1 and H3),
3.68–3.79 (m, 2H, H4 and H6), 3.78–3.87 (m, 1H, H5), Ring III:
3.35–3.44 (m, 1H, H3ax), 3.55–3.64 (m, 1H, H4), 3.64–3.70 (m,
1H, H6), 3.70–3.77 (m, 1H, H6¢), 3.78–3.87 (m, 1H, H5), 3.79–3.87
(m, 1H, H2), 5.03 (d, 1H, J = 3.0 Hz, H1) (Fig. S4†); 13C NMR
(100 MHz, D2O) d 28.4, 29.9, 31.6, 37.3, 47.4, 48.6, 49.3, 50.4,
55.6, 59.2, 60.5, 64.8, 66.1, 68.8, 70.1, 73.5, 74.5, 79.3, 84.2, 95.3
(anomeric C), 101.2 (anomeric C), 176.7 (C O) (Fig. S5†); ESI-
MS m/z calcd for C22H45N6O11 569.3146, found 569.3146 [M +
H]+; Retention time on HPLC: 4.89 min.
6¢¢¢-N-Azidoacetyl paromomycin (2a)
6¢-N-CbzAHB tobramycin (1c)
To paromomycin sulfate (2) (200 mg, 0.28 mmol) dissolved
in MeCN : H2O/2 : 1 (5 mL) were added K2CO3 (80 mg,
0.56 mmol) and azidoacetyl-N-hydroxysuccinimiyl ester (3)
(82 mg, 0.42 mmol). The reaction mixture was stirred at rt
for 16 h. The progress of the reaction was monitored by
TLC (MeOH:NH4OH/3 : 2, Rf 0.64). The reaction mixture was
concentrated under reduced pressure and further purified by
flash chromatography (SiO2, MeOH→MeOH:Et3N/90 : 10). The
fractions containing the pure product were concentrated under
reduced pressure. The residue was dissolved in a minimal volume
of H2O and freeze-dried to afford the pure product 2a (109 mg,
67%) as white powder: 1H NMR (500 MHz, D2O) d 3.45–3.51 (m,
2H, CH2 of azidoacetyl), Ring I: 3.34 (m, 1H, H2), 3.36–3.39 (m,
1H, H4), 3.60–3.66 (m, 1H, H6), 3.69–3.71 (m, 1H, H5), 3.80–3.90
(m, 2H, H3 and H6¢), 5.74 (d, 1H, J = 3.3 Hz, H1), Ring II: 1.83
(ddd, 1H, J1 = J2 = J3 = 12.7 Hz, H2ax), 2.43 (dt, 1H, J1 = 4.1, J2 =
12.4 Hz, H2eq), 3.28–3.30 (m, 1H, H1), 3.45–3.51 (m, 1H, H3),
3.69–3.71 (m, 1H, H5), 3.80–3.90 (m, 1H, H6), 3.97–4.01 (m, 1H,
H4), Ring III: 3.60–3.66 (m, 1H, H5), 3.80–3.90 (m, 1H, H5¢), 4.12
(m, 1H, H4), 4.25 (m, 1H, H2), 4.32 (t, 1H, J = 5.2 Hz, H3), 5.31
(s, 1H, H1), Ring IV: 3.45–3.51 (m, 1H, H2), 3.57–3.60 (m, 1H,
H4), 3.69–3.71 (m, 1H, H6), 3.80–3.90 (m, 1H, H6¢), 3.97–4.01
(m, 1H, H5), 4.16 (m, 1H, H3), 5.12 (s, 1H, H1); 13C NMR (100
MHz, D2O) d 28.8, 40.4, 49.5, 50.4, 51.7, 52.6, 54.6, 59.2, 61.1,
67.1, 68.4, 69.4, 70.0, 73.0, 73.3, 74.3, 74.5, 76.5, 77.9, 82.3, 84.9,
96.4 (anomeric C), 96.7 (anomeric C), 110.5 (anomeric C), 171.4
(C O); ESI-MS m/z calcd for C25H46N8O15Na 721.3004, found
721.2994 [M + Na]+.
To tobramycin sulfate (1) (300 mg, 0.53 mmol) dissolved in
MeCN : H2O/2 : 1 (5 mL) were added K2CO3 (165 mg, 1.26 mmol)
and L-(-)-g-benzyloxycarbonylamino-a-hydroxybutyric acid (4)
(660 mg, 1.89 mmol). The reaction mixture was stirred at
rt for 16 h. The progress of the reaction was monitored by
TLC (MeOH:NH4OH/3 : 2, Rf 0.73). The reaction mixture was
concentrated under reduced pressure and further purified by
flash chromatography (SiO2, MeOH→MeOH:Et3N/90 : 10). The
fractions containing the pure product were concentrated under
reduced pressure. The residue was dissolved in a minimal volume
of H2O and freeze-dried to afford the pure product 1c (340 mg,
91%) as a white powder: 1H NMR (500 MHz, D2O) d 1.63–1.68
(m, 1H, AHB), 1.80–1.87 (m, 1H, AHB), 3.15–3.22 (m, 2H, AHB),
4.06 (dd, 1H, J1 = 4.0, J2 = 8.0 Hz, AHB), 4.97 (m, 2H, benzyl),
7.23–7.33 (m, 5H, aromatic), Ring I: 1.59–1.72 (m, 1H, H3ax),
2.02 (ddd, 1H, J1 = 4.2, J2 = 9.1, J3 = 11.5 Hz, H3eq), 3.14–3.23
(m, 1H, H2), 3.29–3.36 (m, 1H, H6), 3.37–3.44 (m, 1H, H6¢),
3.40–3.45 (m, 1H, H4), 3.59–3.65 (m, 1H, H5), 5.11 (s, 1H, H1),
Ring II: 1.23 (q, 1H, J = 11.9 Hz, H2ax), 1.95 (ddd, 1H, J1 = 4.1,
J2 = 9.4, J3 = 13.0 Hz, H2eq), 2.77–2.85 (m, 1H, H1), 2.95–3.03
(m, 1H, H3), 3.23–3.32 (m, 2H, H4 and H6), 3.49–3.56 (m, 1H,
H5), Ring III: 3.00–3.10 (m, 1H, H3ax), 3.30–3.38 (m, 1H, H4),
3.52–3.58 (m, 1H, H2), 3.61–3.64 (m, 1H, H6), 3.66–3.68 (m, 1H,
H6¢), 3.75–3.80 (m, 1H, H5), 4.91 (d, 1H, J = 3.8 Hz, H1); 13C
NMR (100 MHz, D2O) d 23.9, 32.5, 34.1, 37.2, 40.2, 49.4, 49.9,
55.2, 59.7, 60.9, 65.9, 67.5, 68.5, 69.8, 71.0, 72.9, 73.2, 74.9, 86.1,
87.2, 98.0 (anomeric C), 100.8 (anomeric C), 128.3, 129.0, 129.5,
159.0 (C O), 177. 5 (C O); ESI-MS m/z calcd for C30H51N6O13
703.3514, found 703.3510 [M + H]+.
6¢¢¢-N-Glycinyl paromomycin (2b)
Compound 2a (35 mg, 0.05 mmol) was dissolved in
MeOH : H2O/1 : 1 (2 mL) and catalytically hydrogenated using
H2 and 5% Pd/C (20 mg) as the catalyst at rt for 2 h. The
reaction mixture was filtered through Celite and concentrated
under reduced pressure. The residue was dissolved in minimal
volume of H2O and freeze-dried to afford the pure product 2b
(27 mg, 82%) as a white powder (MeOH:NH4OH/3 : 2, Rf 0.34):
1H NMR (500 MHz, D2O) d 3.48–3.51 (m, 2H, CH2 of N-glycinyl),
Ring I: 3.35 (dd, 1H, J1 = 3.7, J2 = 10.9 Hz, H2), 3.41 (d, 1H,
6¢-N-AHB tobramycin (1d)
Compound 1c (34 mg, 0.05 mmol) was dissolved in
MeOH : H2O/1 : 1 (2 mL) and catalytically hydrogenated using
H2 and 5% Pd/C (20 mg) as the catalyst at rt for 2 h. The
reaction mixture was filtered through Celite and concentrated
under reduced pressure. The residue was dissolved in minimal
volume of H2O and freeze-dried to afford the pure product 1d
(27 mg, 95%) as a white powder (MeOH:NH4OH/3 : 2, Rf 0.38):
This journal is
The Royal Society of Chemistry 2011
Org. Biomol. Chem., 2011, 9, 4057–4063 | 4061
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