Enantioselective synthesis of several natural virologins

Article abstract of DOI:10.1002/jccs.200400193

An enantioselective synthesis of Virologins 1-(S and R), 2-trans-(S and R) and 3-cis-(S and R) were achieved by Mitsunobu reaction to construct a chiral center and Ando reagent to form cis-olefin.

Full text of DOI:10.1002/jccs.200400193

Journal of the Chinese Chemical Society, 2004, 51, 1333-1337
1333
Enantioselective Synthesis of Several Natural Virologins
Ying Su (
), Xin-Feng Ren (
),
Xue-Gong She (
Department of Chemistry, State Key Laboratory of Applied Organic Chemistry, Lanzhou University,
) and Xin-Fu Pan* (
)
Lanzhou 730000, P. R. China
An enantioselective synthesis of Virologins 1-(S and R), 2-trans-(S and R) and 3-cis-(S and R) were
achieved by Mitsunobu reaction to construct a chiral center and Ando reagent to form cis-olefin.
Keywords: Virologins; Enantioselective synthesis; cis-olefin.
INTRODUCTION
Virologins 1, 2 and 3 were first isolated1 from the bark
strategy, selective demethylation of 3,4,5-trimethoxybenz-
aldehyde (4) with piperidine gave 4-hydroxy-3,5-dimeth-
oxybenzaldehyde (5),6 Mitsunobu reaction with (R)-6,4 the
absolute configuration of which was determined by Sharp-
less dihydroxylation,7 gave the key intermediate compound
(S)-1. Where the absolute configuration was inverted com-
pletely from the SN2 type nucleophilic displacement, then
(S)-1 reacted with monoethyl malonate8 to give the trans-ole-
fin (S)-7, which was reduced with LiAlH4 and AlCl39 to af-
ford the corresponding trans-alcohol (S)-8, followed by
Swern Oxidention,10 the target compound (S)-2 was ob-
tained. (S)-1 was treated with Ando reagent11 in dry THF giv-
ing cis-olefin (S)-9 in 85%; reduction of (S)-9 gave the corre-
sponding unsaturated alcohol (S)-3. In same way, using (S)-6
as a starting material, (R)-1, (R)-2 and (R)-3 were easily ob-
tained.
and fruit calyx of Licaria chrysophylla and determined to be a
new b-aryloxy-arylpropane type neolignan. This kind of neo-
lignan has a wide range of bioactivity, such as anti-cercaria
penetration, inhibition of the growth of silkworm larvae,
antileukemic and antifungal activity, anti-leishmanial activ-
ity2,3 and so on; these arouse the interest of chemists. To our
best knowledge, synthesis of Virologins 1, 2 and 3 have not
been reported in the literature. Herein we demonstrate the
enantioselective synthetic approach to Virologins (S and R)-
1, trans-(S and R)-2 and cis-(S and R)-3 on the basis of the
work in our group.4,5 In this work, SN2 type nucleophilic dis-
placement on the chiral carbon led to the complete inversion
of its absolute configuration, and the absolute configuration
of the final products could be confirmed.
In conclusion, chiral Virologins (S and R)-1, trans-(S
and R)-2 and cis-(S and R)-3 have been Enantioselective syn-
thesized, respectively. All spectral data were in agreement
with those found in the literature.1 The route presented herein
can be applied to asymmetric synthesis of this kind of neo-
lignan.
RESULTS AND DISCUSSION
As shown in Scheme I, adopting a convergent synthetic
OMe
OMe
OMe
MeO
OMe
O
MeO
OMe
O
MeO
OMe
O
OMe
OMe
OMe
MeO
MeO
MeO
CHO
HO
CHO
2
3
1
* Corresponding author. E-mail: panxf@lzu.edu.cn

1334 J. Chin. Chem. Soc., Vol. 51, No. 6, 2004
Su et al.
Scheme I
OMe
MeO
OH
OMe
MeO
OMe
i
CHO
CHO
4
5
OMe
OMe
OMe
MeO
OMe
MeO
MeO
OMe
MeO
MeO
OMe
MeO
v
iv
O
O
O
CO2Et
CHO
MeO
MeO
OH
MeO
iii
(S)-7
( S)-8
(S)-2
OMe
OMe
OMe
MeO
OMe
MeO
OMe
MeO
OMe
MeO
MeO
OMe
MeO
OMeii
iv
MeO
vi
O
CHO
5 +
O
O
OH
MeO
MeO
MeO
EtO2C
OH
(R)-6
(S)-1
(S)-9
(S)-3
(R)-2
(R)-3
(R)-1
5 +(S)-6
Reagents and conditions: (i) piperidine, H2O, reflux, 48 h, 80%; (ii) DIAD, PPh3, THF, 24 h, r.t., 48%; (iii) HO2CCH2CO2Et,
pyridine, piperidine, reflux, 6 h, 70%; (iv) LAH, AlCl3, diethyl ether, r.t., 3 h, 92%; (v) oxalyl chloride, DMSO, Et3N, CH2Cl2,
O
O
P
-78 °C, 2 h, 92%; (vi)
CH CO Et , NaH, THF, -78 °C, 2 h, 85%.
2 2
2
EXPERIMENTAL SECTION
on a ZAB-HS spectrometer. Optical rotations were deter-
mined on a Perkin Elmer 341 polarimeter. Chiral analysis
was performed on a Varian Dynamax SD-300 using chiralcel
column CDMPC (150 ´ 4.6 mm D) with hexane/isopropyl al-
cohol as eluent. Column chromatography was generally per-
formed on silica gel (200-300 mesh) eluting with petroleum
ether:ethyl acetate and TLC inspections on silica gel GF254
Melting points were measured on a Kofler apparatus
and were uncorrected. The 1H NMR and 13C NMR data were
recorded with Bruker AM-80 MHz, AM-200 MHz, AM-300
MHz or AM-400 MHz spectrometer. The chemical shifts are
reported in ppm relative to TMS. Mass spectra were recorded

Enantioselective Synthesis of Several Natural Virologins
J. Chin. Chem. Soc., Vol. 51, No. 6, 2004 1335
plates with petroleum ether:ethyl acetate, if not noted espe-
cially below.
were the same as those of (S)-1.
(S)-3-{3,5-Dimethoxy-4-[1-methyl-2-(3,4,5-trimethoxy-
phenyl)ethoxyl]phenyl}-(trans)-acrylic acid ethyl ester,
(S)-7
4-Hydroxy-3,5-dimethoxybenzaldehyde (5)
A solution of 3,4,5-trimethoxybenzaldehyde (4) (1.0 g,
5.09 mmol) in piperidine (10 mL) and water (10 mL) was
heated under reflux for 48 h and the cooled mixture was
poured into 4 N aqueous hydrochloric acid. The mixture was
extracted with ethyl acetate (3 ´ 20 mL). The combined or-
ganic layer was washed with 2 N hydrochloric acid, water,
and dried over Na2SO4. The solvent was distilled off and the
residue was flash chromatographed using petroleum ether
and ethyl acetate (4:1, v/v) as eluent to afford (5) as a white
solid (741 mg, 80%). Mp 113-114 °C. MS (EI): 182 (M+),
167, 139, 111, 96, 65. 1H NMR (80 MHz, CDCl3): d ppm 3.97
(s, 6H), 6.12 (br s, 1H), 7.17 (s, 2H), 9.83 (s, 1H).
Monoethyl malonate (61 mg, 0.46 mmol) was added to
the solution of compound (S)-1 (90 mg, 0.23 mmol) in
pyridine (5 mL) and piperidine (0.10 mL). The mixture was
heated under reflux at 120 °C for 6 h, and then the pyridine
was evaporated. The crude product was dissolved in ethyl ac-
etate and the solution was washed with 5% sodium bicarbon-
ate and water, then dried over Na2SO4. The solvent was dis-
tilled off and the residue was flash chromatographed using
petroleum ether and ethyl acetate (7:1, v/v) as eluent. (S)-7
was obtained as a colorless oil (74 mg, 70%). [a]2D5 +6.4 (c
3.3, CHCl3). MS (EI): 460 (M+), 252, 224, 210, 209, 208, 194,
181, 177, 151, 135. 1H NMR (200 MHz, CDCl3): d ppm 1.24
(d, 3H, J = 6.2 Hz), 1.35 (t, 3H, J = 7 Hz), 2.77 (dd, 1H, J =
13.6, 7.4 Hz), 3.09 (dd, 1H, J = 13.6, 5.6 Hz), 3.83-3.85 (m,
15H), 4.26 (q, 2H, J = 7 Hz), 4.49 (m, 1H), 6.32 (d, 1H, J =
15.8 Hz), 6.48 (s, 2H), 6.77 (s, 2H), 6.58 (d, 1H, J = 15.8 Hz).
13C NMR (100 MHz, CDCl3) d 14.53, 20.06, 22.15, 43.89,
56.28, 60.68, 61.04, 70.22, 80.20, 105.47, 106.73, 108.25,
117.53, 129.96, 134.72, 136.61, 138.44, 144.81, 153.10,
154.10, 167.19. IR (KBr/cm-1): 1710, 1584, 1501, 1460,
1374, 1333, 1127, 1045, 1010, 982, 926.
(S)-3,5-Dimethoxy-4-[1-methyl-2-(3,4,5-trimethoxyphenyl)-
ethoxyl]benzaldehyde, (S)-1
A solution of PPh3 (464 mg, 1.77 mmol) and (R)-6 (0.2
g, 0.88 mmol) in dry THF (15 mL) was added dropwise to a
solution of (5) (322 mg, 1.77 mmol) and DIAD (diisopropyl
azodicarboxylate) (358 mg, 1.77 mmol) in dry THF at room
temperature under nitrogen. After stirring the mixture over-
night at room temperature, the mixture was evaporated in
vacuo. The residue was flash chromatographed using petro-
leum ether and ethyl acetate (6:1, v/v) as eluent. A bright yel-
low oil (S)-1 (0.17 g) was obtained in 48% yield. [a]2D5 +3 (c
3.0, CHCl3). MS (EI): 390 (M+), 224, 209, 208, 194, 193, 181,
165, 151, 135. 1H NMR (400 MHz, CDCl3): d ppm 1.26 (d,
3H, J = 6.4 Hz), 2.77 (dd, 1H, J = 13.6, 8 Hz), 3.11 (dd, 1H, J
= 13.6, 6 Hz), 3.82-3.92 (m, 15H), 4.59-4.64 (m, 1H), 6.46 (s,
2H), 7.13 (s, 2H), 9.87 (s, 1H). 13C NMR (100 MHz, CDCl3) d
19.86, 21.88, 43.67, 56.02, 56.14, 60.77, 69.97, 80.10,
106.47, 106.63, 131.54, 134.19, 136.42, 141.84, 152.85,
154.07, 190.99. IR (KBr/cm-1) 1691, 1587, 1460, 1386, 1327,
1126, 1045, 1009, 980, 923. HRFABMS m/z 408.2023 (calcd
for C21H30O7N, 408.2017).
(R)-3-{3,5-Dimethoxy-4-[1-methyl-2-(3,4,5-trimethoxy-
phenyl)ethoxyl]phenyl}-(trans)-acrylic acid ethyl ester,
(R)-7
By a procedure similar to the preparation of (S)-7, the
reaction of (R)-1 (92 mg, 0.24 mmol) with monoethyl mal-
onate (62 mg, 0.47 mmol) in pyridine (5 mL) gave (R)-7 (76
mg, 70%) as a colorless oil. [a]2D5 -3 (c 1.6, CHCl3). Other
spectral data were the same as those of (S)-7.
(S)-3-{3,5-Dimethoxy-4-[1-methyl-2-(3,4,5-trimethoxy-
phenyl)ethoxyl]phenyl}-(trans)-prop-2-en-1-ol, (S)-8
To a suspension of LiAlH4 (15 mg, 0.4 mmol) in dry di-
ethyl ether, AlCl3 (18 mg, 0.13 mmol) was added portionwise
at room temperature. After the suspension was stirred for 10
min, a solution of compound (S)-7 (62 mg, 0.13 mmol) in dry
diethyl ether was added dropwise to the suspension. The re-
action mixture was stirred at room temperature for 3 h. Then
the reaction was quenched with ice water, extracted with
ethyl acetate and the combined organic layers were washed
(R)-3,5-Dimethoxy-4-[1-methyl-2-(3,4,5-trimethoxyphenyl)-
ethoxyl]benzaldehyde, (R)-1
By a procedure similar to the preparation of (S)-1, the
reaction of (S)-6 (0.2 g, 0.88 mmol) with PPh3 (464 mg, 1.77
mmol), DIAD (358 mg, 1.77 mmol), (5) (322 mg, 1.77 mmol)
in dry THF stirring overnight gave (R)-1 (0.16 g, 45%) as a
bright yellow oil. [a]2D5 -5 (c 2.0, CHCl3). Other spectral data

1336 J. Chin. Chem. Soc., Vol. 51, No. 6, 2004
Su et al.
with brine, and then dried with Na2SO4. The solvent was dis-
tilled off and the residue was flash chromatographed using
petroleum ether and ethyl acetate (2:1, v/v) as eluent. Com-
pound (S)-8 was obtained as a colorless oil (52 mg, 92%).
[a]2D5 +8 (c 1.0, CHCl3). MS (EI): 418 (M+), 225, 210, 209,
208, 194, 181, 177, 151, 135. 1H NMR (200 MHz, CDCl3): d
ppm 1.24 (d, 3H, J = 5.6 Hz), 2.75 (dd, 1H, J = 13.6, 6 Hz),
3.15 (dd, 1H, J = 13.6, 6 Hz), 3.83-3.85 (m, 15H), 4.16 (dd,
2H, J = 14.4, 7.2 Hz), 4.42 (m, 1H), 6.34 (m, 1H), 6.48 (s,
2H), 6.60 (d, 1H, J = 16.0 Hz), 6.63 (s, 2H). 13C NMR (75
MHz, CDCl3) d 19.78, 29.68, 36.31, 43.66, 56.07, 60.84,
63.64, 79.84, 103.68, 106.54, 109.77, 127.89, 131.20,
132.16, 134.74, 152.88, 153.82. IR (KBr/cm-1) 3470, 1724,
1584, 1503, 1460, 1375, 1331, 1122, 1051, 1010, 969, 925.
(R)-3-{3,5-Dimethoxy-4-[1-methyl-2-(3,4,5-trimethoxy-
phenyl)ethoxyl]phenyl}-(trans)-prop-2-en-1-al, (R)-2
By a procedure similar to the preparation of (S)-2, the
reaction of (R)-8 (40 mg, 0.096 mmol) with oxlyl chloride (13
mg, 0.11 mmol), DMSO (19 mg, 0.23 mmol), TEA (29 mg,
0.29 mmol) in CH2Cl2 gave (R)-2 (36 mg, 91%) as a bright
yellow oil. [a]2D5 -5 (c 1.0, CHCl3). Other spectral data were
the same as those of (S)-2.
(S)-3-{3,5-Dimethoxy-4-[1-methyl-2-(3,4,5-trimethoxyphen-
yl)ethoxyl]phenyl}-(cis)-acrylic acid ethyl ester, (S)-9
To a solution of ethyl (di-o-tolylphosphono)acetate (51
mg, 0.15 mmol) in dry THF (1 mL) was added NaH (4 mg,
0.16 mmol) at 0 °C and stirred for 15 min at this temperature.
Then it was cooled to -78 °C and compound (S)-1 (48 mg,
0.12 mmol) was added in dry THF at this temperature. And
the resulting mixture was stirred for 2 h at this temperature.
The reaction was quenched with saturated NH4Cl, and the
mixture was extracted with AcOEt; the combined extracts
were washed with water, followed by brine, and then dried
(MgSO4). The solvent was distilled off and the residue was
flash chromatographed using petroleum ether and acetone
(15:1, v/v) as eluent. (S)-9 was obtained as a colorless oil (48
mg, 85%). [a]2D5 +2 (c 1.0, CHCl3). MS (EI): 460 (M+), 252,
224, 210, 209, 208, 194, 181, 177, 151, 135. 1H NMR (300
MHz, CDCl3): d ppm 1.27 (m, 6H), 2.71 (dd, 1H, J = 13.5, 7
Hz), 3.08 (dd, 1H, J = 13.5, 7 Hz), 3.81-3.83 (s, 15H), 4.18 (q,
2H, J = 4.2 Hz), 4.46 (m, 1H), 5.90 (d, 1H, J = 12.8 Hz), 6.46
(s, 2H), 6.81 (d, 1H, J = 12.9 Hz), 7.07 (s, 2H). 13C NMR (75
MHz, CDCl3) d 14.16, 19.79, 43.65, 56.04, 60.29, 60.79,
79.92, 106.46, 107.98, 118.59, 129.86, 134.60, 136.28,
137.29, 143.04, 152.84, 153.10, 166.34. IR (KBr/cm-1) 1713,
1583, 1502, 1459, 1372, 1331, 1127, 1049, 1010, 976, 926.
(R)-3-{3,5-Dimethoxy-4-[1-methyl-2-(3,4,5-trimethoxy-
phenyl)ethoxyl]phenyl}-(trans)-prop-2-en-1-ol, (R)-8
By a procedure similar to the preparation of (S)-8, the
reaction of (R)-7 (60 mg, 0.13 mmol) with LiAlH4 (15 mg,
0.39 mmol), AlCl3 (17 mg, 0.13 mmol) in dry diethyl ether
gave (R)-8 (49 mg, 89%) as a colorless oil. [a]2D5 -9 (c 1.0,
CHCl3). Other spectral data were the same as those of (S)-8.
(S)-3-{3,5-Dimethoxy-4-[1-methyl-2-(3,4,5-trimethoxy-
phenyl)ethoxyl]phenyl}-(trans)-prop-2-en-1-al, (S)-2
To a stirred solution of oxlyl chloride (12 mg, 0.097
mmol) in 1 mL of CH2Cl2 at -78 °C was added DMSO (17 mg,
0.21 mmol) dropwise; 30 min later (S)-8 (37 mg, 0.089
mmol) in 1 mL of CH2Cl2 was added via cannula. After the
solution was stirred for 40 min, TEA (triethylamine) (27 mg,
0.27 mmol) was added and the mixture was allowed to warm
to room temperature and stirred for 2 h. Water was added and
the phases were separated; the organic layer was washed with
brine, then dried with Na2SO4. The solvent was distilled off
and the residue was flash chromatographed using petroleum
ether and ethyl acetate (4:1, v/v) as eluent. (S)-2 was obtained
as a bright yellow oil (34 mg, 92%). [a]2D5 +4 (c 1.7, CHCl3).
(R)-3-{3,5-Dimethoxy-4-[1-methyl-2-(3,4,5-trimethoxyphen-
yl)ethoxyl]phenyl}-(cis)-acrylic acid ethyl ester, (R)-9
By a procedure similar to the preparation of (S)-9, the
reaction of (S)-1 (59 mg, 0.15 mmol) with ethyl (di-o-tolyl-
phosphono)acetate (63 mg, 0.18 mmol), NaH (5 mg, 0.2
mmol) in THF, gave (R)-9 (59 mg, 85%) as a colorless oil.
[a]2D5 -3 (c 1.2, CHCl3). Other spectral data were the same as
those of (S)-9.
1
MS (EI): 416 (M+), 224, 209, 208, 181, 179, 167, 149. H
NMR (300 MHz, CDCl3): d ppm 1.16 (d, 3H, J = 5.7 Hz),
2.69 (dd, 1H, J = 13.5, 7.5 Hz), 3.01 (dd, 1H, J = 13.5, 6 Hz),
3.68-3.75 (m, 15H), 4.45 (dq, 1H, J = 7.5, 6 Hz), 6.50 (s, 2H),
6.55 (dd, 1H, J = 15.6, 7.5 Hz), 6.69 (s, 2H), 7.32 (d, 1H, J =
15.9 Hz), 9.59 (d, 1H, J = 7.8 Hz). 13C NMR (75 MHz,
CDCl3) d 20.09, 43.92, 56.26, 56.36, 61.07, 80.32, 105.95,
106.70, 128.02, 129.45, 134.61, 139.36, 153.04, 153.11,
154.24, 193.67. IR (KBr/cm-1) 1674, 1583, 1501, 1460, 1374,
1332, 1127, 1050, 1009, 974, 924. HRFABMS m/z 417.1912
(calcd for C23H29O7, 417.1908).
(S)-3-{3,5-Dimethoxy-4-[1-methyl-2-(3,4,5-trimethoxyphen-
yl)ethoxyl]phenyl}-(cis)-prop-2-en-1-ol, (S)-3
To a suspension of LiAlH4 (9 mg, 0.25 mmol) in dry di-
ethyl ether, AlCl3 (11 mg, 0.083 mmol) was added portion-
wise at room temperature. After the suspension was stirred

Enantioselective Synthesis of Several Natural Virologins
J. Chin. Chem. Soc., Vol. 51, No. 6, 2004 1337
for 10 min, a solution of compound (S)-9 (38 mg, 0.083
mmol) in dry diethyl ether was added dropwise to the suspen-
sion. The reaction mixture was stirred at room temperature
for 3 h. Then the reaction was quenched with ice water ex-
tracted with ethyl acetate and the combined organic layers
were washed with brine, and then dried with Na2SO4. The sol-
vent was distilled off and the residue was flash chromato-
graphed using petroleum ether and ethyl acetate (2:1, v/v) as
eluent. Compound (S)-3 was obtained as a bright yellow oil
(39 mg, 91%). [a]2D5 +5 (c 2.6, CHCl3). MS (EI): 418 (M+),
224, 210, 209, 208, 194, 193, 181, 179, 167, 165, 154, 149,
135. 1H NMR (300 MHz, CDCl3): d ppm 1.24 (d, 3H, J = 6.6
Hz), 2.75 (dd, 1H, J = 14, 8 Hz), 3.10 (dd, 1H, J = 14, 6 Hz),
3.81-3.83 (m, 15H), 4.08-4.15 (m, 1H), 4.46 (d, 2H, J = 6.6
Hz), 5.79-5.88 (m, 1H), 6.49 (m, 5H). 13C NMR (75 MHz,
CDCl3) d 19.85, 29.67, 43.68, 56.06, 59.66, 60.82, 79.72,
103.71, 106.18, 106.49, 130.45, 131.37, 134.73, 152.84,
153.42. IR (KBr/cm-1) 3478, 1724, 1585, 1503, 1460, 1429,
1374, 1329, 1237, 1186, 1127, 1047, 1009, 960, 922.
HRFABMS m/z 436.2333 (calcd for C23H34O7N, 436.2330).
for ROCS.SEM, Gansu Science Foundation (No. YS031-A21-
001) and Lanzhou University Foundation (No. 5715220101).
Received January 2, 2004.
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By a procedure similar to the preparation of (S)-3 the
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ACKNOWLEDGMENTS
This work was supported by NSFC (QT program), SRF