K. Hiroya et al. / Bioorg. Med. Chem. 10 (2002) 3229–3236
3233
over MgSO4 and concentrated. The residue was purified
by silica gel chromatography eluting with hexane–ethyl
acetate (9:1–4:1) to yield 5 (12.1 mg, 69%) as a white
solid. IR n(film) cmꢀ1: 3447, 2943, 2870, 1738, 1240,
mixture was refluxed for 3 h. The reaction was cooled to
room temperature and the solvent was removed in
vacuo. The residue was extracted with Et2O. The
organic solution was washed with brine and dried over
MgSO4. The solvent was evaporated and the crude
product was purified by silica gel chromatography
(hexane–ethyl acetate, 4:1) to afford 6 (38.4 mg, 98%) as
a white solid. IR n (film) cmꢀ1: 3421, 2945, 2872, 1732,
1246, 1028. 1H NMR (300 MHz) d: 0.78 (1H, d,
J=10.4 Hz), 0.83 (3H, s), 0.84 (6H, s), 0.97 (3H, s), 1.02
(3H, s), 0.97–2.03 (24H, m), 1.68 (3H, s), 2.03 (3H, s),
2.38 (1H, td, J=10.6, 6.0 Hz), 3.33 (1H, d, J=10.7 Hz),
3.79 (1H, d, J=10.7 Hz), 4.46 (1H, dd, J=5.5, 10.7 Hz),
4.58 (1H, s), 4.67 (1H, s). 13C NMR (75 MHz) d: 14.5,
15.8, 16.0, 16.3, 18.0, 18.9, 20.7, 21.1, 21.2, 23.6, 25.0,
26.9, 27.8, 29.0, 29.6, 33.8, 34.0, 36.9, 37.2, 37.7, 38.2,
40.8, 42.6, 47.7, 48.6, 50.2, 55.3, 60.4, 80.9, 109.7, 150.6,
171.1. MS m/z (relative intensity): 484 (30, M+). HRMS
calcd C32H52O3: 484.3916. Found: 484.3913.
1
1034. H NMR (500 MHz) d: 0.66 (1H, d, J=9.2 Hz),
0.74 (3H, s), 0.80 (3H, s), 0.82–0.91 (1H, m), 0.94 (3H,
s), 0.95 (3H, s), 1.01–1.09 (6H, m), 1.15–1.26 (4H, m),
1.34–1.40(5H, m), 1.49–1.69 (11H, m), 1.74 (1H, dd,
J=12.2, 7.3 Hz), 1.80–1.84 (1H, m), 1.90–1.98 (1H, m),
2.05 (3H, s), 2.42 (1H, td, J=11.2, 5.7 Hz), 3.16 (1H, dd,
J=11.2, 4.9 Hz), 3.84 (1H, d, J=11.2 Hz), 4.23 (1H, dd,
J=11.2, 1.8 Hz), 4.56 (1H, s), 4.67 (1H, d, J=1.8 Hz).
MS m/z (relative intensity): 484 (37, M+). HRMS calcd
C32H52O3: 484.3916. Found: 484.3904.
28-tert-Butyldimethylsiloxybetulin
(16).
Imidazole
(31.4 mg, 0.46 mmol) and DMAP (17.6 mg, 0.16 mmol)
were added to a solution of betulin (1) (61.5 mg,
0.14 mmol) in anhydrous DMF (2.5 mL) at room tem-
perature. After being stirred for 20min, the mixture was
cooled to 0 ꢁC then TBSCl (41.0mg, 0.27 mmol) was
added. The mixture was warmed to room temperature
and stirred for 7 h. Water was added to the mixture and
the aqueous phase was extracted with Et2O. The com-
bined organic solution was washed with brine and dried
over MgSO4. The solvent was removed in vacuo and
purified by silica gel chromatography (hexane–ethyl
acetate, 9:1) to afford 16 (64.3 mg, 86%) as a white
solid. IR n (film) cmꢀ1: 3385, 2943, 2860, 1088. 1H NMR
(500 MHz) d: 0.02 (6H, s), 0.67 (1H, d, J=9.2 Hz), 0.74
(3H, s), 0.81 (3H, s), 0.88 (9H, s), 0.84–1.38 (22H, m),
1.49–1.66 (11H, m), 1.95–1.86 (3H, m), 2.37 (1H, td,
J=10.8, 5.9 Hz), 3.17 (1H, dd, J=11.6, 4.9 Hz), 3.23
(1H, d, J=9.5 Hz), 3.65 (1H, d, J=9.5 Hz), 4.54 (1H, s),
4.65 (1H, d, J=1.8 Hz). MS m/z (relative intensity): 556
(7, M+). HRMS calcd C36H64O2Si: 556.4676. Found:
556.4709.
3,28-Diacetoxybetulin (7). To a solution of betulin (1)
(16.5 mg, 0.037 mmol) and catalytic amount of DMAP
in pyridine (0.4 mL) was added acetic anhydride
(11.3 mg, 0.11 mmol) at 0 ꢁC and warmed slowly to
room temperature. After being stirred for 5 h, Et2O was
added to the mixture and the solution was washed with
saturated NH4Cl solution. The aqueous phase was
extracted with Et2O. The combined organic solution
was washed with brine and dried over MgSO4. The sol-
vent was removed in vacuo and the residue was purified
by column chromatography on silica gel (hexane-ethyl
acetate, 9:1) to give 7 (19.0mg, 97%) as a white solid.
IR n (film) cmꢀ1: 2945, 2872, 1736, 1244, 1023. 1H NMR
(500 MHz) d: 0.76 (1H, d, J=9.2 Hz), 0.81 (3H, s), 0.82
(3H, s), 0.82 (3H, s), 0.94 (3H, s), 1.01–1.08 (6H, m),
1.15–1.28 (4H, m), 1.34–1.39 (5H, m), 1.48 (1H, m),
1.54–1.68 (10H, m), 1.74 (1H, dd, J=12.5, 7.6 Hz),
1.80–1.83 (1H, m), 1.98–1.89 (1H, m), 2.01 (3H, s), 2.04
(3H, s), 2.41 (1H, td, J=11.0, 6.1 Hz), 3.83 (1H, d,
J=11.0Hz), 4.23 (1H, d, J=11.0Hz), 4.44 (1H, dd,
J=11.0, 5.5 Hz), 4.56 (1H, s), 4.66 (1H, d, J=1.8 Hz).
MS m/z (relative intensity): 526 (7, M+). HRMS calcd
C34H54O4: 526.4022. Found: 526.4020.
3-Acetoxy-28-tert-butyldimethylsiloxybetulin (17). Ace-
tic anhydride (13.3 mg, 0.13 mmol) was added to a
solution of 16 (49.3 mg, 0.089 mmol) and DMAP
(0.7 mg, 6.2 mmol) in pyridine (0.9 mL) at 0 ꢁC and
warmed slowly to room temperature. After being stirred
for 16 h, Et2O was added to the mixture and the organic
solution was washed with water and the aqueous phase
was extracted again with Et2O. The combined organic
solution was washed with brine and dried over MgSO4.
The solvent was removed in vacuo and the residue was
purified by silica gel chromatography (hexane–ethyl
acetate, 9:1) to yield 17 (64.3 mg, 94%) as a white solid.
IR n (film) cmꢀ1: 2949, 2858, 1734, 1246, 1088. 1H
NMR (300 MHz) d: 0.01 (6H, s), 0.81 (3H, s), 0.82 (6H,
s), 0.87 (9H, s), 0.94 (3H, s), 0.99 (3H, s), 0.75–1.65
(21H, m), 1.65 (3H, s), 1.81–2.01 (3H, m), 2.01 (3H, s),
2.36 (1H, td, J=10.7, 6.1 Hz), 3.23 (1H, d, J=9.6 Hz),
3.64 (1H, d, J=9.6 Hz), 4.45 (1H, dd, J=5.8, 10.4 Hz),
4.54 (1H, dd, J=2.2, 1.4 Hz), 4.65 (1H, d, J=2.5 Hz).
MS m/z (relative intensity): 598 (5, M+). HRMS calcd
C38H66O3Si: 598.4781. Found: 598.4743.
28-Capryloxybetulin (8). A few drops of TMSCl was
added to a solution of betulin (1) (14.0 mg, 0.032 mmol)
in caprylic acid (0.32 mL) at room temperature. After
being stirred for 19 h, saturated NaHCO3 solution was
added and extracted with Et2O. The combined organic
solution was washed with brine and dried over MgSO4.
The solution was concentrated and the residue was
purified by chromatography on alumina (1.3 g) and
silica gel (3.0g) (hexane–ethyl acetate, 9:1) to afford 8
(15.5 mg, 84%) as a white solid. IR n (film) cmꢀ1: 3396,
2930, 2870, 1734, 1456. 1H NMR (300 MHz) d: 0.68
(1H, d, J=9.3 Hz), 0.76 (3H, s), 0.82 (3H, s), 0.88 (3H,
t, J=6.7 Hz), 0.97 (3H, s), 0.98 (3H, s), 1.03 (3H, s),
0.86–2.04 (34H, m), 1.68 (3H, s), 2.32 (2H, t, J=7.6 Hz),
2.45 (1H, td, J=10.9, 6.0 Hz), 3.18 (1H, dd, J=11.0,
5.2 Hz), 3.84 (1H, d, J=11.0Hz), 4.26 (1H, d,
J=11.0Hz), 4.59 (1H, s), 4.69 (1H, d, J=1.9 Hz). MS
m/z (relative intensity): 568 (13, M+). HRMS calcd
C38H64O3: 568.4855. Found: 568.4840.
3-Acetoxybetulin (6). To a solution of 17 (48.8 mg,
0.081 mmol) in THF (0.3 mL) was added TBAF (1.0 M
THF solution, 0.5 mL) at room temperature and the