Synthesis of vulpinic acids from dimethyl tartrate

Article abstract of DOI:10.1016/j.tetlet.2009.03.011

A series of vulpinic acids differing by the aryl or heteroaryl groups placed in the ester α-position were prepared by Suzuki-Miyaura cross-coupling involving a common iodide and the corresponding aryl boronates. The preparation of the iodide precursor fro

Full text of DOI:10.1016/j.tetlet.2009.03.011

Tetrahedron Letters 50 (2009) 2430–2433
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Synthesis of vulpinic acids from dimethyl tartrate
Brice Nadal a, Pierre Thuéry b, Thierry Le Gall a,
*
a CEA, iBiTecS, Service de Chimie Bioorganique et de Marquage, Bât. 547, 91191 Gif-sur-Yvette, France
b CEA, IRAMIS, Service de Chimie Moléculaire (CNRS URA 331), Bât. 125, 91191 Gif-sur-Yvette, France
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of vulpinic acids differing by the aryl or heteroaryl groups placed in the ester
prepared by Suzuki–Miyaura cross-coupling involving a common iodide and the corresponding aryl bor-
a-position were
Received 21 January 2009
Revised 2 March 2009
Accepted 4 March 2009
Available online 9 March 2009
onates. The preparation of the iodide precursor from (+)-dimethyl -tartrate required four steps: the
L
esterification of one hydroxyl group, a Dieckmann cyclization allowing the construction of the tetronic
acid moiety, a dehydration leading to the installation of the exocyclic double bond and lastly, an N-iodo-
succinimide-mediated iodation of the alkene obtained.
Keywords:
Vulpinic acid
Ó 2009 Elsevier Ltd. All rights reserved.
Dimethyl tartrate
Dieckmann condensation
Iodination
Suzuki–Miyaura cross-coupling
Pulvinic acids and the corresponding methyl esters, vulpinic
acids, are pigments found in mushrooms and lichens.1,2 Antioxi-
dant activities of such compounds were recently shown in a study
in our laboratory.3,4 In the course of a study aimed at evaluating
the properties of various pulvinic acids derivatives, we have devel-
oped several routes leading to these compounds.5 It was especially
interesting to be able to prepare selectively series of compounds in
which one of the aryl groups will vary, while the other one would
remain unchanged. This would allow evaluating the respective
importance of the aryl groups on the activity of the synthesized
compounds. Two pathways leading to vulpinic acids 1 are depicted
in the Scheme 1. In the first one, already reported,5c–e compounds 1
substituted by various Ar groups were prepared via Suzuki–Miya-
ura couplings involving several arylboronates 4 and a single alke-
nyl triflate or iodide 5. We now report an alternative route
leading to unsymmetrical vulpinic acids in which a Suzuki–Miya-
ura coupling is employed at a late step for the introduction of var-
ious aryl and heteroaryl Ar0 groups, by combination of
arylboronates 4 with a single iodide precursor 6, in which Ar = 4-
methoxyphenyl.
O
X
O
O
O
Ar
B
+
RO
O
Ar'
Ar
MeO2C
O
5 (X = OTf or I)
4
HO
O
Ar'
MeO2C
Ar
RO
O
1
O
Ar'
B
+
O
I
MeO2C
6
4
Scheme 1. Routes to vulpinic acids.
and isolated in 65% and 17% yield, respectively. The use of the La-
cey version of the Dieckmann condensation for the synthesis of
tetronic acids is a well-established method.6–8 Brandänge et al. ap-
plied this method to the cyclization of the monoacetate derived
from dimethyl tartrate.9
Our initial goal was to prepare alkene 11, which would be con-
verted to the corresponding iodide. The synthesis of 11 from (+)-di-
Accordingly, the cyclization of 9 to tetronic acid 10 was realized
by treatment with 3 equiv of lithium hexamethyldisilazide
(LiHMDS) in THF at ꢀ78 °C.10 The crude tetronic acid was not puri-
fied, but directly submitted to dehydrating conditions, leading to a
mixture of alkenes (Z)-11 and (E)-110, isolated in 81% and 7% over-
all respective yield from alcohol 9 after silica gel chromatogra-
phy.11 The two isomers were readily separated, (E)-110 being
distinctly less polar, which may be attributed to a chelation of
methyl L-tartrate (7) is described in the Scheme 2. Treatment of
diol 7 with 4-methoxyphenylacetic acid in the presence of dicyclo-
hexylcarbodiimide (DCC) and 4-(dimethylamino)pyridine (DMAP)
led to a mixture of monoester 9 and the corresponding diester,
which were easily separated by silica gel column chromatography
* Corresponding author. Tel.: +33 1 69 08 71 05; fax: +33 1 69 08 79 91.
E-mail address: thierry.legall@cea.fr (T. Le Gall).
0040-4039/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2009.03.011

B. Nadal et al. / Tetrahedron Letters 50 (2009) 2430–2433
2431
MeO
MeO
MeO
MeO
CO2H
O
OH
O
I+
OH
O
CO2Me
6
8
MeO2C
CO2Me
O
O
MeO2C
CO2Me
CO2Me
DCC, DMAP
CH2Cl2
O
O
OH
OH
9
11
Scheme 4. Hypothesis concerning the reactivity of alkene 11.
(+)-dimethyl tartrate
65%
(7)
MeO
(CF3CO)2O
NEt3, CH2Cl2
LiHMDS
OH
CO2Me
OH
THF
-78 °C
O
10
O
MeO
MeO
OH
OH
CO2Me
+
O
O
CO2Me
O
O
(
)-11'
E
(Z)-11
81% (2 steps)
7% (2 steps)
Figure 1. Molecular structure of iodoalkene 6.
Scheme 2. Synthesis of alkene 11.
is also connected to another electron-withdrawing group, the ester
function, is thus not nucleophilic enough to react with iodine(I)
cation.
the hydroxyl group by the ester function in this compound. A
strong IR band at 2594 cmꢀ1 due to the chelated hydroꢀx1yl is ob-
served for (E)-110, while a strong IR band at 3524 cm due to
the nonchelated hydroxyl is observed for (Z)-11, which is in accor-
dance with previous observations for similar compounds.2c The
configuration of the major (Z)-isomer was also ascertained on the
basis of a single-crystal X-ray diffraction structural study.12 Only
this isomer was then employed in the next step. The synthetic se-
quence leading to 11 was easily performed on a multi-gram scale.
Attempts to iodinate alkene 11 using several conditions such as
N-iodosuccinimide in ethanol13 or in acetic acid,14 or I2/CAN15 did
not lead to the expected product. A small amount of iodide 6 was
identified in a reaction involving the treatment of 11 with N-iodo-
succinimide in the presence of acetic acid in THF. The reaction con-
ditions were then changed and we eventually showed that
iodoalkene 6 could be obtained in 50% yield in a reproducible
way, provided that compound 11 was treated with 1 equiv of so-
dium hydroxide prior to the reaction with N-iodosuccinimide
(Scheme 3).16 Thus, the substrate of the reaction was actually com-
pound 12, in which the enol function was converted to the corre-
sponding sodium enolate.
A single-crystal X-ray diffraction structural study of iodoalkene
6 allowed establishing the Z configuration of the exocyclic double
bond (Fig. 1).12 Thus, the iodination of alkene 11 proceeds with
inversion of the double bond configuration. However, due to a
change in priority order, both the substrate 11 and the product 6
are (Z)-configurated. The formation of iodoalkene 6 instead of the
corresponding (E)-isomer is probably favored because in 6, the ste-
rically demanding iodine atom is located in a less crowded
position.
Suzuki–Miyaura cross-couplings were then carried out using io-
dide 6 and several aryl- or heteroarylboronates 4 (Scheme 5, Table
1).
The conditions designed by Occhiato et al.,17 which make use of
PdCl2(PPh3)2 as the catalyst and 2 M Na2CO3 as the base, in reflux-
ing THF, were previously employed in related couplings involving
iodides such as 5.5d,e They were applied to the cross-couplings
involving iodide 6, and found to be also convenient in this case.
Boronates 4a–h were thus converted to the corresponding adducts
1a–h in 50–81% yield.18 The best yield was obtained from boronate
4a substituted with a phenyl group (entry 1), which led to the
known lichen pigment pinastric acid (1a).15 The physical and spec-
troscopic data for 1a are in good agreement with those reported in
the literature.2g,i,5e,19 Compounds in which the phenyl group is
substituted by Cl, CF3, or OH were also obtained in good yields
A hypothesis can then be drawn concerning the lack of reactiv-
ity of alkene 11. In alkene 11, the enol function is likely to present a
significant carbonyl character (Scheme 4). The double bond, which
MeO
MeO
0.5N NaOH
(1 equivalent)
OH
ONa
MeO
acetone, H2O
OH
O
CO2Me
O
CO2Me
O
O
CO2Me
I
O
O
11
Ar'
B
12
+
O
O
O
6
4
N
I
MeO
MeO
PdCl2(PPh3)2
2 M Na2CO3
OH
OH
O
CO2Me
I
CO2Me
Ar'
THF, reflux
AcOH, THF
50 ° C
O
O
O
O
50%
6
1
Scheme 3. Preparation of iodoalkene 6.
Scheme 5. Synthesis of vulpinic acids 1.

2432
B. Nadal et al. / Tetrahedron Letters 50 (2009) 2430–2433
Chem. Soc. 1968, 2968–2974; (c) Weinstock, J.; Blank, J. E.; Oh, H. J.; Sutton, B.
Table 1
M. J. Org. Chem. 1979, 44, 673–675; (d) Knight, D. W.; Pattenden, G. J. Chem. Soc.,
Perkin Trans. 1 1979, 84–88; (e) Ramage, R.; Griffiths, G. J.; Sweeney, J. N. A. J.
Chem. Soc., Perkin Trans. 1 1984, 1547–1553; (f) Pattenden, G.; Turvill, M. W.;
Chorlton, A. P. J. Chem. Soc., Perkin Trans. 1 1991, 2357–2361; (g) Pattenden, G.;
Pegg, N.; Kenyon, R. J. Chem. Soc., Perkin Trans. 1 1991, 2363–2371; (h) Ahmed,
Z.; Langer, P. J. Org. Chem. 2004, 69, 3753–3757; (i) Ahmed, Z.; Langer, P.
Tetrahedron 2005, 61, 2055–2063.
Synthesis of compounds 1a–h
Entry
Ar0
Boronate
Product
Yield (%)
81
1
4a
1a
3. (a) Meunier, S.; Desage-El Murr, M.; Nowaczyk, S.; Le Gall, T.; Pin, S.; Renault, J.-
P.; Boquet, D.; Créminon, C.; Saint-Aman, E.; Valleix, A.; Taran, F.; Mioskowski,
C. ChemBioChem 2004, 5, 832–840; (b) Meunier, S.; Hanédanian, M.; Desage-El
Murr, M.; Nowaczyk, S.; Le Gall, T.; Pin, S.; Renault, J.-P.; Boquet, D.; Créminon,
C.; Mioskowski, C.; Taran, F. ChemBioChem 2005, 6, 1234–1241.
4. The antioxidant properties of variegatic acid were previously reported. See:
Kasuga, A.; Aoagi, Y.; Sugahara, T. J. Food Sci. 1995, 60, 1113–1115.
5. (a) Desage-El Murr, M.; Nowaczyk, S.; Le Gall, T.; Mioskowski, C.; Amekraz, B.;
Moulin, C. Angew. Chem., Int. Ed. 2003, 42, 1289–1293; (b) Heurtaux, B.; Lion, C.;
Le Gall, T.; Mioskowski, C. J. Org. Chem. 2005, 70, 1474–1477; (c) Desage-El
Murr, M.; Nowaczyk, S.; Le Gall, T.; Mioskowski, C. Eur. J. Org. Chem. 2006,
1489–1498; (d) Willis, C.; Bodio, E.; Bourdreux, Y.; Billaud, C.; Le Gall, T.;
Mioskowski, C. Tetrahedron Lett. 2007, 48, 6421–6424; (e) Bourdreux, Y.; Bodio,
E.; Willis, C.; Billaud, C.; Le Gall, T.; Mioskowski, C. Tetrahedron 2008, 64, 8930–
8937; (f) Mallinger, A.; Le Gall, T.; Mioskowski, C. J. Org. Chem. 2009, 74, 1124–
1129.
HO
2
3
4
4b
4c
4d
1b
1c
1d
73
60
64
Cl
F3C
CF3
6. Lacey, R. N. J. Chem. Soc. 1954, 832–839.
7. For recent syntheses of tetronic acids via Dieckmann condensation, see. ( )-
Stemonamine: (a) Zhao, Y.-M.; Gu, P.; Tu, Y.-Q.; Fan, C.-A.; Zhang, Q. Org. Lett.
2008, 10, 1763–1766; Pulvinones: (b) Bernier, D.; Moser, F.; Brückner, R.
Synthesis 2007, 2240–2248; Bernier, D.; Brückner, R. Synthesis 2007, 2249–
2272; Retipolide E, ornatipolide: (c) Ingerl, A.; Justus, K.; Hellwig, V.; Steglich,
W. Tetrahedron 2007, 63, 6548–6557; Abyssomicin C, atrop-abyssomicin C, and
abyssomicin D: (d) Nicolaou, K. C.; Harrison, S. T. J. Am. Chem. Soc. 2007, 129,
429–440.
5
6
4e
4f
1e
1f
80
50
O
8. Reviews on tetronic acids synthesis: (a) Tejedor, D.; García-Tellado, F. Org. Prep.
Proc. Int. 2004, 36, 33–59; (b) Zografos, A. L.; Georgiadis, D. Synthesis 2006,
3157–3188; (c) Schobert, R.; Schlenk, A. Bioorg. Med. Chem. 2008, 16, 4203–
S
7
8
4g
4h
1g
1h
61
61
4221.
0
9. Brandänge, S.; Flodman, L.; Norberg, ÅA J. Org. Chem. 1984, 49, 927–928.
10. Synthesis of compound 10: A solution of LiHMDS (109 mL, 1 M in THF) was
added to THF (220 mL) under nitrogen. The solution was cooled to ꢀ78 °C and
then a solution of compound 9 (11.9 g, 36.5 mmol) in THF (120 mL) was added
dropwise. The reaction mixture was stirred for 1 h at ꢀ78 °C and then allowed
to warm to room temperature over 2 h. After cooling at 0 °C, aqueous 2 N HCl
(140 mL) was added. The two layers were separated, and the aqueous layer
was extracted with AcOEt (2 ꢁ 200 mL). The combined organic layers were
dried (MgSO4) and filtered. Concentration under vacuum afforded tetronic acid
10 (10.7 g) as a pale yellow solid, which was used directly in the next step.
O
(entries 2–5). As could have been expected, the reaction involving
boronate 4f, in which the phenyl group is substituted in the para
position by the electron-withdrawing acetyl group was less effi-
cient (entry 6). Compounds 1g and 1h derived from heterocyclic
boronates 4g and 4h, containing a 3-thienyl and a 3-furanyl group,
respectively, were also prepared uneventfully (entries 7 and 8). It is
worthy of note that these cross-couplings were carried out using
iodide 6, in which the enol function was left unprotected. The anti-
oxidant properties of products 1a–h are under investigation and
will be reported in due course.
Compound 10: Mp 179–181 °C; TLC: Rf 0.35 (9:1 CH2Cl2/MeOH); ½a D20
ꢂ
+132.9 (c
1.00, MeOH); IR (KBr pellet) mmax: 3324, 3016, 2957, 2843, 2645, 1747, 1696,
1637, 1613, 1517, 1447, 1428, 1391, 1312, 1294, 1259, 1213, 1125,1032, 992,
832, 628 cmꢀ1 1H NMR (400 MHz, acetone-d6, d): 7.87 (d, 2H, J = 9.0 Hz, Ar-H),
;
6.94 (d, 2H, J = 9.0 Hz, Ar-H), 5.27 (d, 1H, J = 1.9 Hz, CHOC(O)), 4.79 (d, 1H,
J = 1.9 Hz, CHOH), 3.82 (s, 3H, OCH3), 3.80 (s, 3H, OCH3); 13C NMR (100 MHz,
acetone-d6, d): 172.4, 172.3, 170.5, 159.6, 129.5 (2C), 123.6, 114.3 (2C), 102.7,
78.6, 69.7, 55.5, 52.9; HRMS (ESI-TOF) calcd for C14H14NaO7 [M+Na]+ 317.0637,
found 317.0633.
11. Synthesis of compounds (E)-110, (Z)-11: A solution of tetronic acid 10 (1.5 g,
5.06 mmol), obtained from the previous reaction, and DMAP (91 mg,
0.253 mmol, 5 mol %) in dry CH2Cl2 (45 mL) was cooled to ꢀ18 °C.
Triethylamine (4.23 mL, 30.4 mmol, 6 equiv) was added, then trifluoroacetic
anhydride (2.15 mL, 15.2 mmol, 3 equiv) was added dropwise over 15 min. The
reaction mixture was allowed to warm to room temperature. After stirring for
16 h, 3 N HCl (15 mL) was added. After stirring for 1 h at room temperature, the
two layers were separated, and the aqueous layer was extracted with AcOEt
(2 ꢁ 15 mL). The combined organic layers were dried (MgSO4), filtered, and
concentrated under vacuum. Silica gel chromatography (90:10, then 50:50,
then 30:70 cyclohexane/acetone) afforded alkenes (E)-110 (106 mg, 7%) as a
yellow solid and (Z)-11 as an orange solid (1.13 g, 81%). (E)-110: Mp 159–
In summary, a novel synthetic access to a series of vulpinic
acids was developed. In these vulpinic acids, the lactone ring is
substituted by a 4-methoxyphenyl group, and they differ by the
nature of the aryl or heteroaryl group located in the a-ester posi-
tion. The approach relied on a convenient preparation of alkene
11 from dimethyl tartrate, involving a Dieckmann condensation,
the preparation of iodide 6 under particular conditions, and the
use of a Suzuki–Miyaura cross-coupling as the last step. This ap-
proach is complementary to the methods that we described
previously.
160 °C; TLC: Rf 0.7 (1:1 cyclohexane/acetone); IR (KBr pellet)
2923, 2845, 2594, 1780, 1680, 1635, 1604, 1513, 1440, 1353, 1280, 1251, 1188,
1157, 1093, 1042, 927, 833 cmꢀ1 1H NMR (400 MHz, CDCl3): d 13.15 (s, 1H,
mmax: 3071, 2960,
;
OH), 8.11 (d, 2H, J = 8.6 Hz, Ar-H), 6.96 (d, 2H, J = 8.6 Hz, Ar-H), 5.98 (s, 1H,
@CHCO2Me), 3.91 (s, 3H, OCH3), 3.84 (s, 3H, OCH3); 13C NMR (100 MHz, CDCl3):
d 171.5, 166.6, 159.9, 158.7, 158.2, 129.5 (2C), 121.4, 114.1 (2C), 105.6, 100.2,
55.4, 53.9; HRMS (ESI-TOF) calcd for C14H12NaO6 [M+Na]+ 299.0532, found
299.0542. (Z)-11: Mp 184-185 °C; TLC: Rf 0.1 (1:1 cyclohexane/acetone); IR
Acknowledgment
Financial support of this work by the Délégation Générale pour
l’Armement (DGA) is gratefully acknowledged.
(KBr pellet)
m
max: 3524, 3102, 3009, 2954, 2838, 1710, 1665, 1571, 1517, 1436,
1357, 1288, 1219, 1147, 1031, 957, 903, 836, 781, 651, 590 cmꢀ1
;
1H NMR
(400 MHz, acetone-d6, d): d 7.89 (d, 2H, J = 9.1 Hz, Ar-H), 7.01 (d, 2H, J = 9.1 Hz,
Ar-H), 5.91 (s, 1H, @CHCO2Me), 3.84 (s, 3H, OCH3), 3.76 (s, 3H, OCH3); 13C NMR
(100 MHz, acetone-d6, d): 168.1, 164.2, 160.8, 160.5, 153.3, 130.6 (2C), 121.9,
114.8 (2C), 106.0, 95.8, 55.7, 52.1; HRMS (ESI-TOF) calcd for C14H12NaO6
[M+Na]+ 299.0532, found 299.0524.
References and notes
1. For reviews on pulvinic acid derivatives, see: (a) Gill, M.; Steglich, W. Prog.
Chem. Org. Nat. Prod. 1987, 51, 1–317; (b) Rao, Y. S. Chem. Rev. 1976, 76, 625–
694.
2. For selected pulvinic acid derivatives syntheses, see: (a) Volhard, J. Liebigs Ann.
Chem. 1894, 282, 1–21; (b) Beaumont, P. C.; Edwards, R. L.; Elsworthy, G. J.
12. Crystallographic data (excluding structure factors) have been deposited with
the Cambridge Crystallographic Data Centre as supplementary publication
numbers CCDC 717486 for alkene (Z)-11 and CCDC 717485 for iodide 6. Copies

B. Nadal et al. / Tetrahedron Letters 50 (2009) 2430–2433
2433
of the data can be obtained, free of charge, on application to CCDC, 12 Union
156.2, 129.5 (2C), 121.4, 114.1 (2C), 107.0, 69.6, 55.9, 55.4; HRMS (ESI-TOF)
calcd for C14H11INaO6 [M+Na]+ 424.9498, found 424.9493.
17. Occhiato, E. G.; Trabocchi, A.; Guarna, A. J. Org. Chem. 2001, 66, 2459–2465.
18. Representative procedure for the Suzuki–Miyaura cross-coupling: All the solvents
were degassed. To a solution of iodide 6 (150 mg, 0.373 mmol) in THF (19 mL)
Road, Cambridge CB2 1EZ, UK, (fax: +44
deposit@ccdc.cam.ac.uk).
0 1223 336033 or e-mail:
13. Ge, P.; Kirk, K. L. J. Org. Chem. 1997, 62, 3340–3343.
14. Iwaoka, T.; Murohashi, T.; Katagiri, N.; Sato, M.; Kaneko, C. J. Chem. Soc., Perkin
Trans. 1 1992, 1393–1397.
were added Pd(PPh3)2Cl2 (13 mg, 0.019 mmol, 5 mol %),
a solution of 3-
15. Zhang, F. J.; Li, Y. L. Synthesis 1993, 565–567.
hydroxyphenylboronic acid pinacol ester (123 mg, 0.559 mmol, 1.5 equiv) in
THF (7 mL), and 2 M aqueous Na2CO3 (8.2 mL). The reaction mixture was
refluxed for 2 h under argon. After cooling to room temperature, water (5 mL)
and saturated aqueous 3 N HCl (3 mL) were added. The aqueous layer was
extracted with ethyl acetate (3 ꢁ 50 mL). The combined organic layers were
dried (MgSO4), filtered, and concentrated under vacuum. Silica gel
chromatography (70:30 cyclohexane/AcOEt) afforded 1b as a yellow solid
(100 mg, 73%). Compound 1b: Mp 180–181 °C; TLC: Rf 0.65 (AcOEt); IR (KBr
16. A 0.5 M NaOH aqueous solution (14.48 mL, 7.24 mmol, 1 equiv) was added to a
solution of alkene 11 (2 g, 7.24 mmol, 1 equiv) in acetone (120 mL) and water
(40 mL). The reaction mixture was stirred at room temperature for 2 h. After
concentration under vacuum, N-iodosuccinimide (3.26 g, 14.48 mmol,
2 equiv), THF (72 mL) and acetic acid (1.25 mL, 21.72 mmol, 3 equiv) were
added successively. The solution obtained was heated at 50 °C for 16 h under
nitrogen. After cooling to room temperature, saturated aqueous Na2S2O3
(50 mL) and AcOEt (50 mL) were added. The two layers were separated, and
the aqueous layer was extracted with AcOEt (2 ꢁ 50 mL). The combined
organic layers were dried (MgSO4), filtered, and concentrated under vacuum.
Silica gel chromatography (80:20, then 50:50 cyclohexane/CH2Cl2) afforded
iodide 6 (1.6 g, 50%) as an orange solid. Compound 6: mp 174–175 °C; TLC: Rf
pellet)
m
max: 3366, 2958, 2839, 2408, 1746, 1671, 1600, 1475, 1439, 1374, 1310,
1280, 1254, 1182, 1070, 838 cmꢀ1
;
1H NMR (400 MHz, CDCl3, d): 13.56 (s, 1H,
OH), 8.12 (d, 2H, J = 9.1 Hz, Ar-H), 7.27 (t, 1H, J = 7.9 Hz, Ar-H), 6.97 (d, 2H,
J = 9.1 Hz, Ar-H), 6.86 (ddd, 1H, J = 7.9, 2.4, 0.9 Hz, Ar-H), 6.81 (ddd, 1H, J = 7.9,
1.6, 0.9 Hz, Ar-H), 6.74 (dd, 1H, J = 2.4, 1.6 Hz, Ar-H), 3.87 (s, 3H, OCH3), 3.85 (s,
3H, OCH3); 13C NMR (100 MHz, CDCl3, d): 171.7, 166.4, 159.7, 158.7, 155.4,
155.1, 133.5, 129.5 (3C), 122.6, 121.7, 117.2, 115.8, 115.0, 114.1 (2C), 105.5,
55.4, 54.5; HRMS (ESI-TOF) calcd for C20H16NaO7 [M+Na]+ 391.0794, found
391.0793.
0.45 (1:1 cyclohexane/AcOEt); IR (KBr pellet)
1773, 1673, 1583, 1512, 1464, 1439, 1367, 1294, 1252, 1184, 1064, 1024, 941,
896, 836, 805, 756, 577 cmꢀ1 1H NMR (400 MHz, CDCl3, d): 13.18 (s, 1H, OH),
mmax: 3018, 2952, 2838, 2521,
;
8.09 (d, 2H, J = 9.1 Hz, Ar-H), 6.95 (d, 2H, J = 9.1 Hz, Ar-H), 3.98 (s, 3H, OCH3),
3.84 (s, 3H, OCH3); 13C NMR (100 MHz, CDCl3, d): 168.9, 165.2, 160.2, 159.9,
19. Dias, D.; White, J. M.; Urban, S. Nat. Prod. Res. 2007, 21, 366–376.