Journal of Agricultural and Food Chemistry
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J = 8.5 Hz, 2H, OCH2O), 4.84 (d, J = 4.5 Hz, 1H, H-1), 4.54−4.57
(m, 1H, H-11), 4.33 (t, J = 9.5 Hz, 1H, H-11), 3.82 (s, 3H, 4′-OCH3),
3.75 (s, 6H, 3′-OCH3, 5′-OCH3), 3.48−3.55 (m, 1H, H-3), 3.26−3.30
(m, 1H, H-2). MS (ESI): m/z (%) 413 ([M + H]+, 30).
6.56 (s, 1H, H-8), 6.24 (s, 2H, H-2′, H-6′), 5.98 (s, 2H, OCH2O),
4.63 (t, J = 8.5 Hz, 1H, H-11), 4.37 (s, 1H, H-1), 3.85−3.89 (m, 1H,
H-11), 3.81 (s, 3H, 4′-OCH3), 3.75 (s, 6H, 3′-OCH3, 5′-OCH3),
3.43−3.51 (m, 2H, H-3, −CH2OH), 3.36−3.39 (m, 1H, −CH2OH),
2.37−2.38 (m, 1H, H-2). MS (ESI): m/z (%) 414.1 ([M + H]+, 73).
General Procedure for the Synthesis of Isoxazolopodophyllol-
Based Esters (11a−11h). A mixture of the corresponding carboxylic
acids R3CO2H (0.28 mmol), DIC (0.28 mmol), DMAP (0.04 mmol),
and compound 10 (0.2 mmol) in dry DCM (10 mL) was stirred at
room temperature. When the reaction was complete according to TLC
analysis, the mixture was diluted by DCM (40 mL), washed by water
(20 mL), aqueous HCl (0.1 mol/L, 20 mL), saturated aqueous
NaHCO3 (20 mL) and brine (20 mL), dried over anhydrous Na2SO4,
concentrated in vacuo, and purified by PTLC to give compounds 11a−
11h in 75−98% yields. The example data of compounds 11a and 11b
are shown as follows, whereas data of compounds 11c−11g can be
found in the Supporting Information.
Synthesis of Oxime of Podophyllotoxone (7) and Isoxazolopo-
dophyllic Acid (8). A mixture of podophyllotoxone (6, 206 mg, 0.5
mmol), hydroxylamine hydrochloride (44.5 mg, 0.64 mmol), and
pyridine (0.14 mL) in absolute ethanol (20 mL) was refluxed. When
the reaction was complete after 72 h, checked by TLC analysis, the
solvent was removed under reduced pressure and saturated aqueous
NaHCO3 (15 mL) was added to the residue, which was extracted with
ethyl acetate (3 × 30 mL). The combined organic phase was dried
over anhydrous Na2SO4, filtered, concentrated under reduced
pressure, and purified by silica gel column chromatography eluting
with DCM/methanol (98:2, v/v) to afford compound 7 (16.6 mg,
7.7% yield) and compound 8 (168.7 mg, 79% yield).
Data for Compound 7. White solid. mp = 104−106 °C [literature,
138−140 °C].24 [α]20D = −31 (c 3.2 mg/mL, acetone). 1H NMR (500
MHz, CDCl3) δ: 7.43 (s, 1H, H-5), 6.68 (s, 1H, H-8), 6.28 (s, 2H, H-
2′, H-6′), 6.06 (d, J = 9.5 Hz, 2H, OCH2O), 4.50 (t, J = 9.0 Hz, 1H,
H-11), 4.56 (d, J = 6.0 Hz, 1H, H-1), 3.82−3.86 (m, 1H, H-11), 3.80
(s, 3H, 4′-OCH3), 3.72 (s, 6H, 3′-OCH3, 5′-OCH3), 3.53−3.62 (m,
2H, H-2, H-3). MS (ESI): m/z (%) 428 ([M + H]+, 28).
Data for Compound 8. White solid. mp = 242−244 °C [literature,
246−248 °C].24 [α]20D = −66 (c 3.8 mg/mL, acetone). 1H NMR (500
MHz, CDCl3) δ: 7.42 (s, 1H, H-5), 6.56 (s, 1H, H-8), 6.21 (s, 2H, H-
2′, H-6′), 6.00 (s, 2H, OCH2O), 4.76 (s, 1H, H-11), 4.66 (s, 1H, H-1),
3.76 (s, 2H, H-3, H-11), 3.65 (s, 3H, 4′-OCH3), 3.62 (s, 6H, 3′-OCH3,
5′-OCH3), 3.13 (s, 2H, H-2). MS (ESI): m/z (%) 428 ([M + H]+,
98).
General Procedure for the Synthesis of Isoxazolopodophyllic-
Acid-Based Esters (9a−9i). A mixture of the corresponding alcohols
R2OH (0.28 mmol), diisopropylcarbodiimide (DIC, 0.2 mmol), 4-
dimethylaminopyridine (DMAP, 0.04 mmol), and compound 8 (0.2
mmol) in dry DCM (10 mL) was stirred at room temperature. When
the reaction was complete according to TLC analysis, the mixture was
diluted by DCM (40 mL), washed by water (20 mL), aqueous HCl
(0.1 mol/L, 20 mL), saturated aqueous NaHCO3 (20 mL), and brine
(20 mL), dried over anhydrous Na2SO4, concentrated in vacuo, and
purified by PTLC to give compounds 9a−9i in 74−89% yields. The
example data of compounds 9a and 9b are shown as follows, whereas
data of compounds 9c−9i can be found in the Supporting
Information.
Data for Compound 11a. Yield = 81%, white solid. mp = 136−137
°C. [α]20 = −56 (c 3.0 mg/mL, acetone). 1H NMR (500 MHz,
D
CDCl3) δ: 8.10 (s, 1H, −CHO), 7.47 (s, 1H, H-5), 6.56 (s, 1H, H-8),
6.16 (s, 2H, H-2′, H-6′), 5.99 (s, 2H, OCH2O), 4.64 (t, J = 8.5 Hz,
1H, H-11), 4.31 (d, J = 4.5 Hz, 1H, H-1), 4.02−4.06 (m, 1H,
−CH2OCHO), 3.89−3.93 (m, 1H, H-11), 3.81−3.85 (m, 4H,
−CH2OCHO, 4′-OCH3), 3.75 (s, 6H, 3′-OCH3, 5′-OCH3), 3.50−
3.57 (m, 1H, H-3), 2.53−2.60 (m, 1H, H-2). HRMS (ESI): calcd for
C23H24NO8 ([M + H]+), 442.1496; found, 442.1493.
Data for Compound 11b. Yield = 98%, white solid. mp = 83−84
°C. [α]20 = −57 (c 3.2 mg/mL, acetone). 1H NMR (500 MHz,
D
CDCl3) δ: 7.47 (s, 1H, H-5), 6.55 (s, 1H, H-8), 6.15 (s, 2H, H-2′, H-
6′), 5.99 (s, 2H, OCH2O), 4.64 (t, J = 9.0 Hz, 1H, H-11), 4.28 (d, J =
4.0 Hz, 1H, H-1), 4.00−4.03 (m, 1H, −CH2OCOC3H7), 3.88−3.92
(m, 1H, H-11), 3.81 (s, 3H, 4′-OCH3), 3.69−3.74 (m, 7H, 3′-OCH3,
5′-OCH3, −CH2OCOC3H7), 3.49−3.57 (m, 1H, H-3), 2.52−2.54 (m,
1H, H-2), 2.29 (t, J = 7.5 Hz, 2H, OCOCH2C2H5), 1.62−1.69 (m, 2H,
OCOCH2CH2CH3), 0.95 (t, J = 7.0 Hz, 3H, CH3). HRMS (ESI):
calcd for C26H30NO8 ([M + H]+), 484.1966; found, 484.1958.
Synthesis of Isoxazolopodophyllic-Acid-Based n-Butylamide (12).
A mixture of n-butylamine (0.28 mmol), DIC (0.20 mmol), DMAP
(0.04 mmol), and compound 8 (0.2 mmol) in dry DCM (10 mL) was
stirred at room temperature. When the reaction was complete after 14
h according to TLC analysis, the mixture was diluted by DCM (40
mL), washed by water (20 mL), aqueous HCl (0.1 mol/L, 20 mL),
saturated aqueous NaHCO3 (20 mL), and brine (20 mL), dried over
anhydrous Na2SO4, concentrated in vacuo, and purified by PTLC to
Data for Compound 9a. Yield = 86%, white solid. mp = 150−152
°C [literature, 82−84 °C].24 [α]20D = −77 (c 3.4 mg/mL, acetone). 1H
NMR (500 MHz, CDCl3) δ: 7.46 (s, 1H, H-5), 6.56 (s, 1H, H-8), 6.13
(s, 2H, H-2′, H-6′), 6.00 (s, 2H, OCH2O), 4.82 (t, J = 8.5 Hz, 1H, H-
11), 4.63 (d, J = 5.0 Hz, H-1), 3.88−3.95 (m, 1H, H-11), 3.78−3.82
(m, 4H, H-3, 4′-OCH3), 3.73 (s, 3′-OCH3, 5′-OCH3), 3.67 (s, 3H,
−CO2CH3), 3.19 (dd, J = 5.0, 12.5 Hz, 1H, H-2). MS (ESI): m/z (%)
442.27 ([M + H]+, 100).
give compound 12 in 88% yield as a white solid. mp = 182−183 °C.
1
[α]20 = −95 (c 3.1 mg/mL, acetone). H NMR (500 MHz, CDCl3)
D
δ: 7.45 (s, 1H, H-5), 6.55 (s, 1H, H-8), 6.12 (s, 2H, H-2′, H-6′), 6.00
(s, 2H, OCH2O), 5.26 (s, 1H, NH), 4.75 (t, J = 7.5 Hz, 1H, H-11),
4.50 (d, J = 4.5 Hz, H-1), 3.79−3.88 (m, 4H, H-3, 4′-OCH3), 3.65−
3.69 (m, 7H, H-11, 3′-OCH3, 5′-OCH3), 3.15−3.19 (m, 1H,
−NHCH2), 3.04 (dd, J = 5.0, 12.0 Hz, 1H, H-2), 1.36−1.42 (m,
2H, −CH2CH2CH3), 1.25−1.30 (m, 2H, −CH2CH2CH3), 0.89 (t, 3H,
J = 7.5 Hz, −CH2CH2CH3). HRMS (ESI): calcd for C26H31N2O7 ([M
+ H]+), 483.2125; found, 483.2116.
Data for Compound 9b. Yield = 75%, white solid. mp = 181−182
°C. [α]20 = −59 (c 3.3 mg/mL, acetone). 1H NMR (500 MHz,
D
CDCl3) δ: 7.46 (s, 1H, H-5), 6.57 (s, 1H, H-8), 6.15 (s, 2H, H-2′, H-
6′), 6.00 (s, 2H, OCH2O), 4.82 (t, J = 8.5 Hz, 1H, H-11), 4.64 (d, 1H,
J = 5.0 Hz, H-1), 4.02−4.15 (m, 2H, −CO2CH2CH3), 3.87−3.96 (m,
1H, H-11), 3.79−3.83 (m, 4H, H-3, 4′-OCH3), 3.73 (s, 3′-OCH3, 5′-
OCH3), 3.17 (dd, J = 5.0, 12.5 Hz, 1H, H-2), 1.21 (t, J = 7.0 Hz, 3H,
CH3). HRMS (ESI): calcd for C24H26NO8 ([M + H]+), 456.1653;
found, 456.1646.
Biological Assay. The insecticidal activity of compounds 1, 3, 4,
5a−5i, 6−8, 9a−9i, 10, 11a−11h, and 12 against the pre-third-instar
larvae of northern armyworm, M. separata (Walker), was assessed by
the leaf-dipping method, as described previously.25 For each
compound, 30 larvae (10 larvae per group) were used. Acetone
solutions of compounds 1, 3, 4, 5a−5i, 6−8, 9a−9i, 10, 11a−11h, 12,
and toosendanin (used as a positive control) were prepared at the
concentration of 1 mg/mL. Fresh wheat leaves were dipped into the
corresponding solution for 3 s, then taken out, and dried in a room.
Leaves treated with acetone alone were used as a blank control group.
Several treated leaves were kept in each dish, where every 10 larvae
were raised. If the treated leaves were consumed, additional treated
leaves were added to the dish. After 48 h, untreated fresh leaves were
added to all dishes until adult emergence. The experiment was carried
out at 25 2 °C and relative humidity (RH) of 65−80% on a 12 h/12
h (light/dark) photoperiod. The insecticidal activity of the tested
Synthesis of Isoxazolopodophyllol (10). Compound 9a (100 mg,
0.23 mmol) in dry THF (5 mL) was slowly added to a suspension of
LiAlH4 (120 mg, 3.16 mmol) in dry THF. The reaction mixture was
stirred at room temperature under nitrogen for 3 h. Then, ethyl acetate
(10 mL) was added to the mixture, which was filtered, dried over
anhydrous Na2SO4, concentrated in vacuo, and purified by silica gel
column chromatography eluting with petroleum ether/ethyl acetate
(2:5, v/v) to afford compound 10 (76 mg, 80% yield) as a white solid.
mp = 200−202 °C [literature, 146−148 °C].24 [α]20 = −44 (c 3.1
D
mg/mL, acetone). 1H NMR (500 MHz, CDCl3) δ: 7.46 (s, 1H, H-5),
8437
dx.doi.org/10.1021/jf303069v | J. Agric. Food Chem. 2012, 60, 8435−8443