I. Hueso-Falcón et al. / Bioorg. Med. Chem. 18 (2010) 1724–1735
1733
4.1.15. Preparation of compounds 19–21
4.1.17. 15-Oxo-grandiflorenic acid (23)
To 277.2 mg of compound 17 (0.883 mmol) dissolved in 12 mL
of dry DCM under N2 atmosphere were added 250.8 mg of SeO2
(2.6 equiv) and the mixture was stirred for 17 h at room tempera-
ture. Then the mixture was treated following the same procedure
for compounds 10 and 11. The crude was purified by chromatotron
using 2 mm plate and n-Hex/AcOEt 10% as solvent to yield
152.2 mg of 19 (53%), 23.2 mg of 20 (8%), and 16.0 mg of 21 (6%)
as amorphous solids. Compound 19 showed identical spectroscopic
data to those reported.32
Compound 19 was oxidized following the same procedure de-
scribed for 12. Thus 42.3 mg of 19 (0.128 mmol) dissolved in
DCM were treated with 84.7 mg of PDC (1.9 equiv) under N2 atmo-
sphere. The reaction mixture was stirred at room temperature for
24 h. After filtration through florisil and evaporation of solvent
the residue was purified by preparative-TLC using n-Hex/AcOEt
15% to render 13.7 mg of compound 23 (33%) as amorphous pale
yellow solid. 23 showed. identical spectroscopic data to those
published.32
Compound 20 1H NMR (300 MHz, CDCl3) d: 9.58 (1H, s, H-17),
7.06 (1H, s, H-15), 5.13 (1H, s, H-11), 3.65 (3H, s, H-21), 3.14 (1H, s,
H-13), 1.21 (3H, s, H-18), 0.95 (3H, s, H-20), 2.50–0.77 (15H, m).13C
NMR (75 MHz, CDCl3) d: 189.4 (d, C-17), 177.3 (s, C-19), 160.4 (d,
C-15), 153.9 (s, C-16), 145.4 (s, C-9), 116.4 (d, C-11), 51.2 (q, C-21),
47.6 (d, C-5), 47.5 (t, C-14), 47.3 (s, C-4), 44.8 (s, C-8), 39.8 (t, C-1),
38.0 (t, C-3), 37.9 (s, C-10), 34.9 (d, C-13), 28.0 (q, C-18), 27.8 (t, C-
12), 25.9 (t, C-7), 22.8 (q, C-20), 19.8 (t, C-2), 18.1 (t, C-6). EIMS m/z
(%): 328 ([M]+, 45), 269 (29), 253 (81), 235 (25), 234 (100), 202
(19), 197 (23), 187 (21), 175 (37), 174 (69), 173 (21), 159 (80), 147
(39), 145 (22), 129 (24), 121 (27), 117 (26), 107 (28), 105 (40), 93
(20), 91 (50). HREIMS: 328.2039 (calcd for C21H28O3 [M]+
4.1.18. Grandiflorenic acid benzyl ester (24)
To a solution of 75 mg of KOH (4 equiv) in dry acetone (5 mL)
were added 100 mg (0.333 mmol) of grandiflorenic acid (16), and
82 lL of benzyl bromide (1 equiv). The reaction mixture was stir-
red at room temperature until disappearance of the starting acid
(6 h). Then 40 mL of H2O were added and the aqueous phase was
extracted several times with AcOEt. The organic phases were com-
bined, dried over MgSO4 and concentrated under reduced pressure.
The crude was purified by column chromatography using n-Hex/
AcOEt 5% to yield 119.5 mg of 24 (88%) as a pale yellow solid.1H
NMR (300 MHz, CDCl3) d: 7.34 (5H, m, H-23–H-27), 5.22 (1H, s,
H-11), 5.10 (2H, s, H-21), 4.91 (1H, s, H-17a), 4.79 (1H, s, H-17b),
2.76 (1H, s, H-13), 2.60 (1H, d, J = 15.6 Hz, H-15), 1.21 (3H, s, H-
18), 0.89 (3H, s, H-20), 2.50–0.96 (16H, m).13C NMR (75 MHz,
CDCl3) d: 176.9 (s, C-19), 158.2 (s, C-9), 155.7 (s, C-16), 136.0 (s,
C-22), 128.8 (d, C-25), 128.6 (d, C-24), 128.3 (d, C-26), 127.9 (d,
C-23), 127.8 (d, C-27), 114.6 (d, C-11), 105.3 (t, C-17), 65.9 (t, C-
21), 50.1 (t, C-15), 46.5 (d, C-5), 44.7 (t, C-14), 44.7 (s, C-4), 42.0
(s, C-8), 41.1 (d, C-13), 40.6 (t, C-1), 38.5 (s, C-10), 38.3 (t, C-3),
37.7 (t, C-12), 29.5 (t, C-7), 28.0 (q, C-18), 23.5 (q, C-20), 20.0 (t,
C-2), 18.4 (t, C-6). EIMS m/z (%): 390 ([M]+, 27), 375 (43), 299
(32), 239 (31), 211 (8), 173 (8), 155 (7), 145 (7), 131 (11), 117
(6), 105 (11), 91 (100). HREIMS: 390.2534 (calcd for C27H34O2
[M]+ 390.2559). IR mmax 2930, 2868, 1721, 1457, 1214, 1138, 874,
328.2038). IR
706 cmꢂ1: UV(EtOH) kmax (log
+61.26 (c 0.9, CHCl3). Compound 21.1H NMR (300 MHz, CDCl3)
m
max 2942, 2871, 1723, 1672, 1459, 1218, 1145, 981,
e
): 202.2 (3.55) and 251.0 (3.47) nm.
½ ꢃ
a 2D0
d: 5.19 (1H, s, H-17a), 5.17 (1H, s, H-17b), 4.22 (1H, s, H-15), 3.62 (3H,
s, H-21), 2.80 (1H, s, H-13), 2.42 (1H, d, J = 4.1 Hz, H-11), 2.26 (1H, d,
J = 4.6 Hz, H-14a), 2.22 (1H, m, H-3a), 2.07 (1H, m, H-12a), 1.95 (1H,
m, H-1a), 1.91 (1H, m, H-6a), 1.87 (1H, d, J = 3.8 Hz, H-7a), 1.82 (1H,
J = 3.8 Hz, H-7b), 1.79 (1H, m, H-2a), 1.76 (1H, m, H-6b), 1.69 (1H, m,
H-14b), 1.54 (1H, m, H-2b), 1.41 (1H, d, J = 10.8 Hz, H-12b), 1.32 (1H,
d, J = 12.1 Hz, H-5), 1.21 (1H, m, H-1b), 1.17 (3H, s, H-18), 1.03 (1H,
m, H-3b), 0.78 (3H, s, H-20).13C NMR (75 MHz, CDCl3) d: 177.8 (s,
C-19), 161.6 (s, C-16), 140.3 (s, C-9), 125.7 (s, C-8), 109.4 (t, C-17),
78.9 (d, C-15), 53.0 (d, C-5), 50.9 (q, C-21), 43.6 (s, C-4), 42.2 (d, C-
11), 41.2 (t, C-14), 40.4 (d, C-13), 38.6 (s, C-10), 37.6 (t, C-3), 35.5
(t, C-1), 32.9 (t, C-12), 31.6 (t, C-7), 28.1 (q, C-18), 20.3 (t, C-6), 19.0
(t, C-2), 16.9 (q, C-20). EIMS m/z (%): 330 ([M]+, 2); 315 (3), 235
(19), 189 (32), 175 (34), 173 (55), 159 (29), 145 (25), 135 (24), 129
(29), 117 (54), 105 (43), 95 (36). HREIMS 330.2184 (calcd for
C21H30O3 [M]+ 330.2195). IR mmax 3386, 2929, 1726, 1653, 1231,
696 cmꢂ1; UV(EtOH) kmax (log
CHCl3).
e
): 202.8 (3.67). ½a D20
ꢃ
+27.47 (c 0.9,
4.1.19. Preparation of compound 25
The reduction of grandiflorenic acid was achieved following the
same experimental procedure described for the obtention of deriv-
ative 9. 61 mg (0.20 mmol) of grandiflorenic acid (16) were treated
with a large excess of LiAlH4 (250 mg, 32.4 equiv) to obtain 47 mg
(81%) of the hydroxylated derivative 25 which showed identical
spectroscopic data to those published.30
1159, 1015, 897 cmꢂ1. UV(CHCl3) kmax (log
ꢂ35.85 (c 0.5, CHCl3).
e
): 203.0 (3.62). ½a D20
ꢃ
4.1.16. 15
17.7 mg (0.054 mmol) of compound 19 dissolved in the mini-
mum amount of pyridine (105 L) was treated with an excess of
a-Acetoxy-grandiflorenic acid methyl ester (22)
l
4.1.20. 15a-Hydroxy-kaurenoic acid (27)
Ac2O (1 mL, 197 equiv) in the presence of catalytic amount of
DMAP. The reaction mixture was stirred for 24 h, after elimination
of solvent, compound 22 (19.9 mg, 100%) was obtained as an amor-
phous solid.1H NMR (300 MHz, CDCl3) d: 5.45 (1H, s, H-15), 5.37
(1H, s, H-11), 5.20 (1H, s, H-17a), 5.16 (1H, s, H-17b), 3.63 (3H, s,
H-21), 2.77 (1H, s, H-13), 2.07 (3H, s, OCOCH3), 1.17 (3H, s, H-
18), 0.94 (3H, s, H-20), 2.42–0.99 (15H, m). 13C NMR (75 MHz,
CDCl3) d: 177.8 (s, C-19), 170.3 (s, OCOCH3), 158.1 (s, C-9), 153.4
(s, C-16), 118.1 (d, C-11), 112.0 (t, C-17), 79.1 (d, C-15), 51.0 (q,
C-21), 46.3 (d, C-5), 45.1 (s, C-4), 44.5 (s, C-8), 41.0 (t, C-14), 40.9
(t, C-1), 39.1 (d, C-13), 38.3 (s, C-10), 37.8 (t, C-3), 37.4 (t, C-12),
27.8 (q, C-18), 23.7 (q, C-20), 23.2 (t, C-7), 21.1 (q, OCOCH3), 20.0
(t, C-2), 17.7 (t, C-6).EIMS m/z (%): 372 ([M]+, 18), 357 (32), 313
(28), 312 (100), 297 (85), 253 (54), 237 (61), 197 (23), 183 (21),
173 (36), 172 (40), 157 (20), 145 (26), 143 (20), 131 (21), 129
(25), 105 (28), 93 (15). HREIMS: 372.2311 (calcd for C23H32O4
[M]+ 372.2301). IR mmax 2926, 2873, 1731, 1457, 1370, 1235,
To a solution of 172.4 mg of 26 (0.461 mmol) in 3 mL of MeOH
was added 1.28 mL of 0.5 M Na2CO3 solution (1.5 equiv). The reac-
tion mixture was refluxed for 24 h. Then the MeOH was removed,
brine was added to the aqueous solution and it was extracted with
DCM (3x 10 mL). The organic phases were collected and dried over
anhydrous MgSO4, then were filtered and concentrated. The result-
ing product (27) was obtained as an amorphous white solid
(132.0 mg, 90%) and it showed spectroscopic data identical to gran-
difloric acid.33
4.1.21. 15-Oxo-kaurenoic acid (28)
To 149.0 mg of 27 (0.469 mmol) in 10 mL of acetone at 0° C
were added 180 lL of Jones reagent. The reaction was followed
by TLC and it was quenched after 6 h with 2 mL of isopropanol.
The reaction mixture was filtered through florisil and washed sev-
eral times with AcOEt. Then the solvent was removed and the res-
idue was purified by preparative-TLC using n-Hex/AcOEt (30%) to
yield 42.3 mg of 28 (29%) as an amorphous white solid. 28 showed
identical spectroscopic data to those reported.17
1146, 1016, 979, 903 cmꢂ1. UV(EtOH) kmax (log
+49.24 (c 0.8, CHCl3).
e): 201.8 (3.71).
½ ꢃ
a 2D0