Journal of Natural Products
Article
1
m/z 367.1830 [M + H]+ (calcd for C23H27O4, 367.1909), 389.1730
[M + Na]+ (calcd for C23H26O4Na, 389.1729). 22: white, micro-
crystalline solid; mp 129.5−131.1 °C; 1H NMR (400 MHz, CDCl3) δ
7.50 (d, J = 8.4 Hz, 1H), 7.36 (d, J = 16.4 Hz, 1H), 6.94 (d, J = 16.4
Hz, 1H), 6.67 (d, J = 2.2 Hz, 2H), 6.52 (dd, J = 8.4, 2.4 Hz, 1H), 6.47
(d, J = 2.4 Hz, 1H), 6.36 (t, J = 2.2 Hz, 1H), 3.87 (s, 3H), 3.84 (s,
3H), 3.83 (s, 6H); 13C NMR (101 MHz, CDCl3) δ 160.9, 160.9,
160.6, 158.1, 140.4, 127.4, 127.0, 123.9, 119.3, 105.0, 104.4, 104.4,
99.4, 98.5, 55.5, 55.40, 55.35, 55.35; ESIMS (+) m/z 301.1 [M + H]+.
( )-Kuwanol E Heptamethyl Ether (2). Diene 7 (0.050 g, 0.136
mmol), dienophile 6 (0.052 g, 0.136 mmol), dry o-xylene (2 mL), and
1 M BH3·THF (0.6 μL, 0.006 mmol, d = 0.87 g/mL) were introduced
into a sealed tube. The mixture was heated at 100 °C for 60 h under an
inert atmosphere, and the reaction was monitored by analytical HPLC
(eluent: MeCN/H2O = 70/30). After the complete disappearance of
the starting materials, the reaction mixture was cooled and
concentrated in vacuo, and the crude residue was purified by
preparative MPLC (eluent: n-hexane/EtOAc = 80:20) to give the
target endo-isomer 2 (0.040 g, 5.44 mmol, 40% yield) and the exo-
isomer 3 (0.012 g, 0.016 mmol, 12% yield) as white solids. 2: white,
microcrystalline solid; mp 96.2−97.8 °C; 1H NMR (400 MHz,
CDCl3) δ 12.60 (s, 1H), 7.76 (d, J = 9.2 Hz, 1H), 7.47 (d, J = 8.8 Hz,
1H), 7.24 (d, J = 16.4 Hz, 1H), 6.98 (d, J = 8.0 Hz, 1H), 6.88 (d, J =
16.4 Hz, 1H), 6.54−6.48 (m, 1H), 6.50 (br ovrlp s, 2H), 6.46 (d, J =
2.4 Hz, 1H), 6.39−6.34 (m, 2H), 6.31 (dd, J = 8.4, 2.4 Hz, 1H), 5.47
(s, 1H), 5.12 (t, J = 7.2 Hz, 1H), 4.46 (br s, 2H), 4.15−4.05 (m, 1H),
3.86 (s, 3H), 3.85 (s, 3H), 3.83 (s, 3H), 3.75 (s, 3H), 3.72 (s, 3H),
3.47 (s, 6H), 3.24 (d, J = 7.2 Hz, 2H), 2.47 (dd, J = 17.8, 5.8 Hz, 1H),
2.30−2.16 (m, 1H), 1.79 (s, 3H), 1.71 (s, 3H), 1.64 (s, 3H); 13C NMR
(101 MHz, CDCl3) δ 206.2, 161.9, 161.4, 160.4, 159.2, 159.2, 158.7,
158.1, 158.0, 138.1, 132.9, 131.3, 129.2, 127.6, 127.3, 126.9, 126.9,
122.8, 122.4, 122.3, 119.6, 116.8, 116.6, 115.7, 104.9, 104.1, 102.4,
102.4, 101.0, 98.9, 98.5, 55.6, 55.49, 55.45, 55.4, 55.22, 55.22, 55.17,
48.5, 37.5, 35.1, 31.6, 25.8, 23.4, 21.5, 17.7; HRMS (ESI-Orbitrap) m/
z 771.3482 [M + Na]+ (calcd for C46H52O9Na, 771.3509), 787.3217
[M + K]+ (calcd for C46H52O9K, 787.3243).
(c 0.1, MeOH); H NMR (400 MHz, acetone-d6) δ 13.00 (s, 1H),
8.42 (d, J = 9.1 Hz, 1H), 7.34 (d, J = 8.5 Hz, 1H), 7.21 (d, J = 16.4 Hz,
1H), 6.99 (d, J = 8.4 Hz, 1H), 6.76 (d, J = 16.4 Hz, 1H), 6.50 (d, J =
2.3 Hz, 1H), 6.46−6.41 (m, 3H), 6.40 (d, J = 2.3 Hz, 1H), 6.34 (dd, J
= 8.5, 2.3 Hz, 1H), 6.30 (dd, J = 8.4, 2.3 Hz, 1H), 5.76 (s, 1H), 5.21−
5.14 (m, 1H), 4.63−4.59 (m, 1H), 4.10−4.05 (m, 1H), 3.75−3.70 (m,
1H), 3.27 (d, J = 7.2 Hz, 2H), 2.49 (br d, J = 17.4 Hz, 1H), 2.16 (d, J =
18.1 Hz, 1H), 1.92 (s, 3H), 1.72 (s, 3H), 1.58 (s, 3H); 13C NMR (101
MHz, acetone-d6) δ 209.8, 164.7, 163.7, 159.0, 157.9, 157.5, 157.5,
156.8, 156.4, 139.1, 133.4, 132.2, 131.4, 128.7, 128.2, 126.0, 124.9,
123.8, 123.3, 122.0, 117.4, 115.8, 115.1, 113.3, 108.4, 108.3, 107.4,
106.6, 106.6, 103.6, 103.5, 47.8, 36.5, 33.1, 32.2, 25.8, 23.9, 22.2, 17.9;
HRMS (ESI-Orbitrap) m/z 649.2460 [M − H]− (calcd for C39H37O9,
649.2446).
(+)-Kuwanol E Heptamethyl Ether (2). A purified sample of
naturally occurring (+)-kuwanol E (1) (4 mg, 6.15 μmol) was
dissolved in acetone (1.5 mL) in a round-bottom flask containing
K2CO3 (16.54 mg, 0.12 mmol) and (CH3)2SO4 (0.0058 mL, 0.061
mmol, d = 1.33 g/mL). The mixture was heated at reflux for 96 h. The
solvent was removed under reduced pressure, and H2O was added.
The aqueous solution was extracted with EtOAc (6 × 2 mL). The
organic layers were collected, dried over Na2SO4, and evaporated in
vacuo. The crude residue was purified by semipreparative HPLC
(eluent: n-hexane/EtOAc = 80/20) to give (+)-2 as a white solid (1.5
mg, 0.002 mmol, 33% yield). (+)-2: white, amorphous solid; [α]20
D
+23 (c 0.1, EtOH), +30 (c 0.1, CHCl3); 1H NMR (400 MHz, CDCl3)
δ 12.60 (s, 1H), 7.76 (d, J = 9.1 Hz, 1H), 7.46 (d, J = 8.4 Hz, 1H), 7.24
(d, J = 16.4 Hz, 1H), 6.98 (d, J = 8.4 Hz, 1H), 6.88 (d, J = 16.4 Hz,
1H), 6.53−6.47 (m, 1H), 6.49 (br ovrlp s, 2H), 6.46 (d, J = 2.4 Hz,
1H), 6.38−6.34 (m, 2H), 6.30 (dd, J = 8.4, 2.4 Hz, 1H), 5.46 (s, 1H),
5.11 (t, J = 7.2 Hz, 1H), 4.46 (s, 2H), 4.15−4.05 (m, 1H), 3.86 (s,
3H), 3.85 (s, 3H), 3.83 (s, 3H), 3.75 (s, 3H), 3.72 (s, 3H), 3.47 (s,
6H), 3.24 (d, J = 6.7 Hz, 2H), 2.47 (dd, J = 17.2, 6.3 Hz, 1H), 2.23 (s,
1H), 1.79 (s, 3H), 1.71 (s, 3H), 1.63 (s, 3H); HRMS (ESI-Orbitrap)
m/z 749.3671 [M + H]+ (calcd for C46H53O9, 749.3689), 771.3489
[M + Na]+ (calcd for C46H52O9Na, 771.3509), 787.3217 [M + K]+
(calcd for C46H52O9K, 787.3243).
( )-exo-Kuwanol E Heptamethyl Ether (3). Diene 7 (0.050 g,
0.136 mmol), dienophile 6 (0.052 g, 0.136 mmol), dry o-xylene (2
mL), and 1 M BH3·THF (0.6 μL, 0.006 mmol, d = 0.87 g/mL) were
introduced into a sealed tube. The mixture was heated at 160 °C for
24 h under an inert atmosphere, and the reaction was monitored by
analytical HPLC (eluent: MeCN/H2O = 70/30). After the complete
disappearance of the starting materials, the reaction mixture was
cooled and concentrated in vacuo, and the crude residue was purified
by preparative MPLC (eluent: n-hexane/EtOAc = 80:20) to give the
target exo-isomer 3 (0.043 g, 0.057 mmol, 42% yield) and the endo-
isomer 2 (0.014 g, 0.019 mmol, 14% yield) as white solids. 3: white,
microcrystalline solid; mp 96.9−98.2 °C; 1H NMR (400 MHz,
CDCl3) δ 12.96 (s, 1H), 7.45 (d, J = 8.4 Hz, 1H), 7.20 (d, J = 9.6 Hz,
1H), 7.19 (d, J = 16.4 Hz, 1H), 7.00 (d, J = 8.4 Hz, 1H), 6.82 (d, J =
16.4 Hz, 1H), 6.60 (br s, 1H), 6.50 (dd, J = 8.4, 2.4 Hz, 1H), 6.46 (d, J
= 2.0 Hz, 1H), 6.31 (d, J = 2.0 Hz, 1H), 6.27 (d, J = 2.0 Hz, 1H), 6.26
(dd, J = 8.4, 2.4 Hz, 1H), 5.97 (d, J = 9.2 Hz, 1H), 5.30 (s, 1H), 5.27
(br s, 1H), 5.07 (t, J = 7.2 Hz, 1H), 4.61 (br s, 1H), 4.36 (d, J = 10 Hz,
1H), 3.93 (br s, 3H), 3.87 (s, 3H), 3.83 (s, 3H), 3.80 (s, 3H), 3.69 (s,
3H), 3.67 (s, 3H), 3.53 (br s, 3H), 3.16 (d, J = 6.4 Hz, 2H), 2.40 (br s,
1H), 2.21 (br d, J = 13.2 Hz, 1H), 1.73 (s, 3H), 1.69 (s, 3H), 1.62 (s,
3H); 13C NMR (101 MHz, CDCl3) δ 209.0, 162.3, 161.1, 160.4,
159.3, 159.3 158.8, 158.1, 157.9, 137.8, 131.2, 131.1, 129.6, 127.4,
127.2, 124.4, 122.7, 122.5, 119.5, 119.4, 115.9, 115.7, 104.9, 104.2,
103.3, 103.3, 102.2, 102.2, 100.9, 98.8, 98.4, 56.2, 55.6, 55.44, 55.39,
55.2, 53.4, 53.4, 46.8, 38.1, 37.3, 31.6, 25.7, 23.2, 21.5, 17.7; HRMS
(ESI-Orbitrap) m/z 771.3490 [M + Na]+ (calcd for C46H52O9Na,
771.3509), 787.3224 [M + K]+ (calcd for C46H52O9K, 787.3243).
Purification of Naturally Occurring (+)-Kuwanol E (1). A crude
MeOH extract of cell cultures from Morus nigra (100 mg) was purified
by semipreparative reversed-phase HPLC (for conditions, see the
General Experimental Procedures) to afford (+)-1 as a white solid.
Recovery: 8 mg (94% purity, checked by analytical HPLC, see the
( )-Kuwanol E (1). Compound 2 (20 mg, 0.027 mmol), dry
CH2Cl2 (1.8 mL), and 1 M BBr3 in CH2Cl2 (0.094 g, 0.376 mmol, d =
1.467 g/mL) were introduced into a sealed tube. The mixture was
stirred at −78 °C for 120 h under an inert atmosphere. The reaction
was quenched with H2O (1 mL), extracted with EtOAc (3 × 5 mL),
dried over MgSO4, filtered, and concentrated. The resultant dark red
solid was purified by semipreparative reversed-phase HPLC (same
conditions used for (+)-1) to afford 1 as a white solid (3.51 mg,
1
0.0054 mmol, 20% yield). ( )-1: white, amorphous solid; H NMR
(400 MHz, acetone-d6) δ 13.00 (s, 1H), 8.42 (d, J = 9.1 Hz, 1H), 7.34
(d, J = 8.5 Hz, 1H), 7.21 (d, J = 16.4 Hz, 1H), 6.99 (d, J = 8.5 Hz,
1H), 6.76 (d, J = 16.4 Hz, 1H), 6.50 (d, J = 2.6 Hz, 1H), 6.46−6.41
(m, 3H), 6.40 (d, J = 2.6 Hz, 1H), 6.34 (dd, J = 8.5, 2.6 Hz, 1H), 6.30
(dd, J = 8.4, 2.6 Hz, 1H), 5.76 (s, 1H), 5.22−5.13 (m, 1H), 4.64−4.58
(m, 1H), 4.05 (d, J = 7.2 Hz, 1H), 3.76−3.69 (m, 1H), 3.27 (d, J = 7.2
Hz, 2H), 2.59−2.45 (m, 1H), 2.16 (d, J = 17.5 Hz, 1H), 1.92 (s, 3H),
1.72 (s, 3H), 1.58 (s, 3H); 13C NMR (101 MHz, acetone-d6) δ 209.8,
164.7, 163.7, 159.0, 157.9, 157.5, 157.5, 156.8, 156.4, 139.1, 133.4,
132.2, 131.4, 128.7, 128.2, 126.0, 124.9, 123.8, 123.3, 122.0, 117.4,
115.8, 115.1, 113.3, 108.4, 108.3, 107.4, 106.6, 106.6, 103.6, 103.5,
47.8, 36.5, 33.1, 32.2, 25.8, 23.9, 22.2, 17.9; HRMS (ESI-Orbitrap) m/
z 649.2443 [M − H]− (calcd for C39H37O9, 649.2446), 1299.4952
[2M − H]− (calcd for C78H75O18, 1299.4953).
( )-Kuwanon Y Heptamethyl Ether (5). Diene 7 (0.050 g, 0.136
mmol), dienophile 9 (0.043 g, 0.136 mmol), dry o-xylene (2 mL), and
1 M BH3·THF (0.6 μL, 0.006 mmol, d = 0.87 g/mL) were introduced
into a sealed tube. The mixture was kept at 100 °C for 72 h under an
inert atmosphere, and the reaction progress was monitored by
analytical HPLC (eluent: MeCN/H2O = 70/30). After the complete
disappearance of the starting materials, the reaction mixture was
cooled and concentrated in vacuo, and the crude residue was purified
by preparative MPLC (eluent: n-hexane/EtOAc = 80:20) to give the
endo-isomer 5 as a pale yellow solid (0.039 g, 0.054 mmol, 40% yield).
H
J. Nat. Prod. XXXX, XXX, XXX−XXX