Synthesis of poinsettifolin A

Article abstract of DOI:10.1016/j.tet.2014.10.021

A synthesis of poinsettifolin A (1), a prenylated flavonol isolated from Dorstenia poinsettifolia, is described. Two routes starting from quercetin were explored, and 1 could be prepared if a prenyl group first was incorporated at C-6 of the protected quercetin followed by a condensation with citral at C-8. The key synthetic steps are a Mitsunobu reaction, an europium (III)-catalysed Claisen rearrangement coupled with cross-metathesis, and a benzopyran-forming geranylation. The two geranylated 3,5,3′,4′-tetrahydroxyflavonols prepared, 1 and 3, were assayed for antileishmanial activity against Leishmania amazonensis and Leishmania braziliensis, and found to be active. Compound 3 showed cytotoxic activity against leukaemia and lung cancer cells while 1 lacked cytotoxicity.

Full text of DOI:10.1016/j.tet.2014.10.021

Tetrahedron 70 (2014) 9052e9056
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Synthesis of poinsettifolin A
Zilma Escobar a, Carlos Solano a, Rikard Larsson a, Martin Johansson a,
b
b
c
a,
*
~
Efrain Salamanca , Alberto Gimenez , Eduardo Munoz , Olov Sterner
a Center for Analysis and Synthesis, Department of Chemistry, Lund University, P.O. Box 124, SE-22100 Lund, Sweden
b
ꢀ
ꢀ
Instituto de Investigaciones Farmaco Bioquímicas, Universidad Mayor de San Andres, P.O. Box 2932, La Paz, Bolivia
c
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
Instituto Maimonides de Investigacion Biomedica de Cordoba (IMIBIC), Universidad de Cordoba, Avda. de Menendez Pidal s/n 14004, Cordoba, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 4 August 2014
Received in revised form 26 September 2014
Accepted 6 October 2014
Available online 12 October 2014
A synthesis of poinsettifolin A (1), a prenylated flavonol isolated from Dorstenia poinsettifolia, is de-
scribed. Two routes starting from quercetin were explored, and 1 could be prepared if a prenyl group first
was incorporated at C-6 of the protected quercetin followed by a condensation with citral at C-8. The key
synthetic steps are a Mitsunobu reaction, an europium (III)-catalysed Claisen rearrangement coupled
with cross-metathesis, and a benzopyran-forming geranylation. The two geranylated 3,5,30,40-tetrahy-
droxyflavonols prepared, 1 and 3, were assayed for antileishmanial activity against Leishmania ama-
zonensis and Leishmania braziliensis, and found to be active. Compound 3 showed cytotoxic activity
against leukaemia and lung cancer cells while 1 lacked cytotoxicity.
Keywords:
Prenylated flavonols
Poinsettifolin A
Leishmania amazonensis
Leishmania braziliensis
Cytotoxicity
Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction
besides yielding larger amounts of 1 also can produce derivatives
and analogues for subsequent SAR studies.
All plants produce flavonoids, and more than 9000 individual
compounds have been described in the scientific literature. They
are secondary metabolites that have been proposed to have dif-
ferent functions in the plant, for example defending it, protecting it
from UV radiation, and giving the petals beautiful colours that at-
tract insects and birds.1 Some chemical properties and biological
activities of the flavonoids are considered to be beneficial for hu-
man health,2 which is highly relevant as we consume significant
amounts daily. Studies have shown that they, in general, are anti-
oxidants and free-radical scavengers,3 and possess anti-in-
flammatory,4 antiviral5 and anticancer properties.6 In recent years
prenylated flavonoids have attracted attention because the prenyl
groups increase the lipophilicity and thereby the ability to pene-
trate biological membranes. Prenylflavonoids display a series of
interesting biological activities such as leishmanicidal activity.7e9
A previous study of the extracts of the herb Dorstenia poinset-
tifolia, examined in a search for new antiparasitic agents, yielded
small amounts of the new geranylated flavonol poinsettifolin A
(1).10 The possibility to investigate different biological properties of
1, such as the antileishmania activity, which is considered impor-
tant for the Dorstenia genus,11 requires a synthetic procedure, that
2. Results and discussion
2.1. Retrosynthesis
Even if different synthetic approaches based on de novo syn-
thesis of 1 were considered, we decided to start from the closely
related and ready available flavonol quercetin (2). The two principal
routes examined, both depending on the selective reactivity of ring
A, are shown in Scheme 1.
Route a starts with the selective condensation of 2 with citral to
produce the pyrano flavonol intermediate 3. A prenylation of this
intermediate at C-6 would yield the target compound 1. Route b is
based on the selective insertion of a prenyl group at C-6 of 2 to
produce the intermediate 4, prior to its condensation with citral to
give 1.
2.2. Route a, direct C-prenylation via benzopyran 3
It is known that selective aldol-type condensations of poly-
hydroxy aromatic compounds can yield the corresponding benzo-
pyran systems.12,13 Even if this has not been previously carried out
with flavonoids, several successful examples with skeletons as di-
verse as dihydroxyphtalides, dihydroxybenzoates and xanthones
* Corresponding author. Tel.: þ46 462228213; fax: þ46 462228209; e-mail ad-
dress: Olov.Sterner@chem.lu.se (O. Sterner).
http://dx.doi.org/10.1016/j.tet.2014.10.021
0040-4020/Ó 2014 Elsevier Ltd. All rights reserved.

Z. Escobar et al. / Tetrahedron 70 (2014) 9052e9056
9053
yield and decreased the reaction time, and 3 was obtained in 80%
yield from 2 and citral under such conditions. Only 3 was obtained,
the corresponding C-6 condensation product was not observed in
spite of the apparent similarity of the two positions. However, due
to the presence of 3-OH in flavonols the electron density of C-8 can
be expected to be higher than that of C-6, explaining the higher
reactivity of that position.
With the geranylated intermediate 3 at hand, we attempted the
introduction of the prenyl moiety at C-6. The direct prenylation of
electron-rich phenolic compounds has been reported, although it is
known to be a challenge to obtain selective prenylation at only one
position in a compound like 2. The use of prenyl halides in the
presence of a base, e.g. DBU,14 tetramethylammonium hydrox-
ide,15,16 potassium hydroxide17,18 or sodium hydride,19,20 failed as C-
prenylated products were obtained together with O-prenylated as
well as degradation products of 3 (2 is not stable in basic condi-
tions). Next, Lewis acid catalysed condensation of 2-methyl-3-
buten-2-ol was attempted. This procedure is known to show an
improved C/O-prenylation ratio,21 and is not hampered by the
stability problems of 3 in basic conditions. With boron trifluoride
etherate C-prenylation of 3 was observed, but at several positions
yielding inseparable mixtures. Attempts to overcome this problem
by selective deactivation of the B ring with electron withdrawing
protective groups failed. The cyclic carbonate in ring B involving the
two adjacent hydroxyl groups turned out to be unstable to the
conditions used for C-prenylation with boric trifluoride etherate,
while the 3,30,40-tritoluenesulfonic ester derivative only gave O-
prenylation at 5-O of 3.
Scheme 1. The two principal synthetic routes from quercetin (2) to poinsettifolin A (1)
investigated. Route a was an unsuccessful attempt to obtain 1 by C-prenylation of the
benzopyran 3 (see text for details), while route b is shown in Scheme 2.
2.3. Route b, Claisen/metathesis via 6-isoprenylquercetin 422
As the direct prenylation at C-6 proved considerably more dif-
ficult than we had anticipated, we instead turned our attention to
the procedure for selective C-6 prenylation of flavonoids developed
by Tischer and Metz.23 The synthetic sequence comprises the se-
lective acetylation of all hydroxyl groups except 5-OH, a Mitsunobu
reaction to create the 5 allyl ether, an europium(III)-catalysed
Claisen rearrangement to give the 6-allyl derivative, followed by
a
cross-metathesis reaction yielding the corresponding 6-
prenylated compound followed by a transesterification to depro-
tect the acetoxy groups. Following this approach, which by neces-
sity has to be carried out prior to the geranylation at C-8, the first
step is a partial protection of quercetin. This is achieved in ac-
ceptable yields as the intramolecular hydrogen bond between 5-OH
and the carbonyl oxygen makes this hydroxyl group less reactive.
However, acetyl groups, used originally, are not suitable for quer-
cetin (2) as it partially degrades during the final deprotection
conditions. Instead, the 3,7,30,40,-tetrahydroxyl groups were pro-
tected as the corresponding benzoic acid esters, compound 5, as the
benzoyl group should be possible to remove using milder condi-
tions. The subsequent Mitsunobu reaction of 5 with allyl alcohol
provided the allylated intermediate 6, while the Claisen rear-
rangement of 6 using Eu(fod)3 provided compound 7 as the sole
product in 73% yield. It should be noted that, apart from the critical
role of the catalyst for achieving this selectivity, the amount of
catalyst and the concentration of the starting materials play critical
roles. Thus, increasing the concentration of 6 from 50 mM to 80 mM
resulted in the formation of the isomeric compound allylated at C-
8. The metathesis reaction was carried out using 2-methyl-2-
butene to get compound 8 in 88% yield. The problem of the for-
mation of the corresponding 6-(2-butenyl) product as an in-
separable by-product when using the more practical 2-methyl-2-
butene instead of isobutylene was overcome by using a 100-fold
excess of 2-methyl-2-butene. Different conditions for the cleavage
of the benzoyl groups under basic conditions were tested, but
complete deprotection could not be achieved. The benzoic acid
Scheme 2. Synthesis of poinsettifolin A. Reagents and conditions: (i) DCM, Bz2O,
DMAP, Et3N, reflux, 4 h, 60%; (ii) THF, allyl alcohol, DIAD, PPh3, 0 ꢀCe20 ꢀC, overnight,
90%; (iii) chloroform, Eu(fod)3, rt, 15 h, 73%; (iv) DCM, Grubbs 2nd, 2-methyl-2-butene,
rt, 48 h, 88%; (v) Et3N, H2O, MeOH, 50 ꢀC, 2 h, 75%; (vi) citral, 140 ꢀC, 5 h, 70%.
can be found. The condensation with citral was first attempted
under thermal conditions and in the absence of a catalyst. Pro-
longed heating in an oil bath led to the formation of 3, a compound
that so far has not been reported as a natural product, in moderate
yields. However, the use of microwave irradiation improved the

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Z. Escobar et al. / Tetrahedron 70 (2014) 9052e9056
ester 9 was the main product in most of the cases, and using
a mixture of sodium methoxide and triethylamine gave 9 in 75%
yield. An increase in temperature and/or pH to force complete
deprotection resulted in decomposition, but 3-OBz was trans-
formed to 3-OH during the geranylation of 9 to form the target 1.
This thermal condensation with citral was carried out essentially as
discussed above, and poinsettifolin A (1) was obtained from in-
termediate 9 in 65% yield.
The use of other protective groups than benzoyl was also in-
vestigated. The MEM derivative corresponding to 5 was actually
obtained in a higher yield (92%), and during the Claisen rear-
rangement of the MEM derivative corresponding to 6 prenylation at
C-8 was not observed, independently of the concentration of
starting material or the relative concentration of Eu(fod)3. However,
the deprotection of the MEM derivative corresponding to 8 could
not be achieved without suffering from a 6-endo-trig cyclization
involving the prenyl group and 5-OH.
biological characterization of 1 will continue as it shows a better
selectivity. While appearing to be essentially non-toxic to mam-
malian cells it has a significant anti-leishmanial activity especially
towards L. braziliensis. It should be noted that the L. braziliensis
strain used here is associated with the muco-cutaneous manifes-
tation of the disease, for which the treatments available today are
more aggressive and not always effective.24 The synthesis described
here includes transformations, for example the metathesis, that
facilitate a systematic variation of the structure of 1 and the
preparation of libraries of analogues to be used in SAR studies.
The potent cytotoxicity of compound 3 should also be studied in
further detail. Interestingly, 30-O as well as 40-O prenylated side
products obtained during the attempts to transform 3 to 1 also
lacked cytotoxic activity, so the cytotoxicity of 3 does in fact not
depend on an unsubstituted position 6. Again, analogues of 3 would
be readily available for a SAR study.
4. Experimental
2.4. Biological activities
4.1. General information
2.4.1. Leishmanicidal activity. Compounds 1 and 3 were assayed for
antileishmanial activity against the promastigote forms of the
parasites Leishmania amazonensis and Leishmania braziliensis. Both
compounds exhibit good leishmanicidal activity against both the
tested strains, 3 being slightly more potent. It is possible that the
leishmanicidal activity is favoured by an unsubstituted position 6,
but the difference may also depend on the higher lipophilicty of 1
compared to 3 (Table 1).
Reagents was purchased from commercial suppliers and used
without further purification unless otherwise noted. THF was dis-
tilled from sodium under N2, while dichloromethane and chloro-
form were distilled from CaH2 under N2. All reactions were carried
out in standard dry glassware and atmospheric surroundings un-
less otherwise stated. Thin layer chromatography (TLC) was carried
out on Merck pre-coated silica gel aluminium sheets (60 F254),
detected under UV light and visualized with sulfuric acid or ferric
chloride. Column chromatography was performed on SiO2 (Matrex
ꢁ
LC-gel: 60 A, 35-70 MY, Grace). Melting points were obtained using
Table 1
SMP10 melting point apparatus. 1H and 13C NMR spectra were
recorded using a Bruker DR400 at room temperature. Chemical
shifts are given in ppm relative to TMS using the residual solvent
signal as internal standard (7.27 and 77.23, respectively for CDCl3,
3.31 and 49.05, respectively for CD3OD, 2.50 and 39.51, respectively
for (CD3)2SO). Mass spectra (HRESI) were recorded with a Micro-
mass Q-TOF Micro.
In vitro leishmanicidal activity of compounds 1 and 3 with Amphotericin B as
positive control (IC50
, mg/mL)
Compound
L. amazonensis
L. braziliensis
1
3
22.6
4.9
0.3
4.5
2.5
0.2
Amphotericin B
4.2. 2-(3,4-Dihydroxyphenyl)-3,5-dihydroxy-8-methyl-8-(4-
methyl-pent-3-en-1-yl)pyrano[2,3-f]chromen-4(8H)-one (3)
2.4.2. Cytotoxicity activity. Compound 1 lacked cytotoxic activity
against leukaemia (Jurkat) and lung cancer cells (A549) cells. In
contrast, 3 was a potent cytotoxic compound initially suggesting
that isoprenylation at C-6 was detrimental for the cytotoxic activity
of 3 (Table 2). Interestingly, Jurkat cells that grow in suspension are
more sensitive to the action of compound 3 than A549 cells, which
are adherent cancer epithelial cells.
Quercetin (3 g, 9.92 mmol), citral (17 mL, 99.2 mmol) and
methanol (3 mL) was added to a microwave vessel and mixed in
order to obtain a homogenous solution. The reaction mixture was
irradiate at 120 ꢀC for 30 min the mixture was then cooled to room
temperature and the residual solvent was removed using a Kugel-
rohr apparatus. The product was purified by chromatography (SiO2,
CH2Cl2:MeOH 8:1) to give the title compound 3 as greenish solid
(3.2 g, 80%). Mp 220e222 ꢀC; nmax (neat) 3500, 1650, 1592, 1533,
Table 2
In vitro cytotoxic activity of compounds 1 and 3 towards Jurkat and A549 cells (IC50
as mg/mL)
1357, 1279, 1160, 1001, 901, 821, 770 cmꢁ1
; dH (400 MHz (CD3)2SO)
12.61 (1H, s, 5-OH), 7.72 (1H, d, J 2.2 Hz, 20-H), 7.61 (1H, dd, J 2.2,
8.5 Hz, 60-H), 6.90 (1H, d, J 8.5 Hz, 50-H), 6.86 (1H, d, J 10.1 Hz, 100-H),
6.20 (1H, d, J 0.3 Hz, 6-H), 5.75 (1H, d, J 10.1 Hz, 200-H), 5.08 (1H, tqq,
J 7.1, 1.3, 1.3 Hz, 600-H), 2.04 (2H, ddd, J 7.1, 8, 8 Hz, 500-H2), 1.70 (2H,
m, 400-H2), 1.60 (3H, s, 800-H3), 1.51 (3H, s, 1000-H3), 1.40 (3H, s, 900-H3);
dC (101 MHz (CD3)2SO) 176.1, 160.2, 158.7, 150.0, 147.9, 146.9, 145.2,
136.1, 131.1, 126.6, 123.8, 122.0, 120.2, 115.8, 114.8, 114.7, 103.8, 100.5,
98.4, 80.6, 40.8, 26.5, 25.4, 22.2, 17.5; HRMS (ES): MþHþ, found
437.1590. C25H25O7 requires 437.1600.
Compound
Jurkat
A549
1
3
>40
2.1
>40
9.7
3. Conclusion
In summary, the first total synthesis route to poinsettifolin A (1)
has been accomplished in six steps and with an acceptable overall
yield, starting from commercially available materials. The selec-
tivity of the condensation of 2 with citral is remarkable, and po-
tentially useful for the synthesis of other geranylated flavonols.
Although 3 is more potent than 1 in the assays reported here, the
4.3. 4-(3,7-bis(Benzoyloxy)-5-hydroxy-4-oxo-4H-chromen-2-
yl)-1,2-phenylene dibenzoate (5)
Triethylamine (5.8 mL, 40.86 mmol) was added to a solution of
quercetine (2) (4.00 g, 13.23 mmol), 4-dimethylaminopyridine

Z. Escobar et al. / Tetrahedron 70 (2014) 9052e9056
9055
(DMAP, 0.17 g, 1.39 mmol) and benzoic anhydride (12.90 g,
57.02 mmol) in anhydrous CH2Cl2 (40 mL). The reaction was heated
to reflux for 4 h, allowed to cool to room temperature, quenched
with water and extracted with EtOAc (90 mL). The organic phase
was dried and evaporated in vacuo to give the crude product, which
was purified by chromatography (SiO2, ethyl acetate:toluene 1:50)
to obtain the pure title compound 5 as yellowish crystals (6.00 g,
60%). Mp 197e199 ꢀC; nmax (neat) 1741,1655,1600,1450,1346,1233,
108.7,101.8, 27.4; HRMS (ES): MþNaþ, found 781.1686. C46H30O11Na
requires 781.1671.
4.6. 4-(3,7-bis(Benzoyloxy)-5-hydroxy-6-(3-methylbut-2-en-
1-yl)-4-oxo-4H-chromen-2-yl)-1,2-phenylene dibenzoate (8)
A mixture of 7 (3 g, 3.96 mmol) and Grubbs’ second generation
catalyst (100 mg, 0.12 mmol), was dissolved in anhydrous CH2Cl2
(70 mL) under a nitrogen atmosphere. After 30 min 2-methyl-2-
butene (45 mL, 424 mmol) was added, and the solution was stir-
red for 48 h at room temperature. The solvent was evaporated in
vacuo to give the crude product, which was purified by chroma-
tography (SiO2, ethyl acetate:toluene 1:50) to give the title com-
pound 8 as a yellowish solid (2.75 g, 88%). Mp 207e208 ꢀC; nmax
1194, 1172, 1145, 1042, 1019, 917, 862, 794, 697 cmꢁ1
; dH (400 MHz
CDC13) 12.17 (1H, s, 5-OH), 8.26e8.20 (4H, m, Bz), 8.05e8.01 (5H,
m, Bz), 7.95 (1H, dd, J 8.6, 2.2 Hz, 60-H) 7.69e7.64 (2H, m, Bz),
7.58e7.50 (7H, m, Bz, 20-H and 50-H), 7.40e7.35 (4H, m, Bz), 7.07
(1H, d, J 2.0 Hz, 8-H), 6.77 (1H, d, J 2.0 Hz, 6-H); dC (100.6 MHz,
CDCl3) 176.3, 164.0, 163.8, 163.6, 163.6, 161.8, 156.7, 156.0, 155.5,
145.3, 142.9, 134.2, 134.1, 134.0, 133.9, 132.6, 130.7 (2C), 130.3 (2C),
130.2 (4C), 128.7 (2C), 128.7 (2C), 128.6,128.5 (2C), 128.5 (2C), 128.2,
128.2, 127.9, 127.7, 126.8, 124.1, 123.9, 108.9, 105.7, 101.4; HRMS (ES):
MþNaþ, found 741.1373. C43H26O11Na requires 741.1351.
(neat) 1737, 1599, 1450, 1241, 1175, 1043, 1019, 798, 700 cmꢁ1
; dH
(400 MHz CDC13) 12.46 (1H, s, 5-OH), 8.26e8.21 (4H, m, Bz),
8.04e8.01 (5H, m, Bz), 7.94 (1H, dd, J 8.6, 2.2 Hz, 60-H), 7.70e7.64
(2H, m, Bz), 7.58e7.50 (7H, m, Bz, 20-H and 50-H), 7.40e7.35 (4H, m,
Bz), 7.02 (1H, s, 8-H), 5.18 (1H, m, 200-H), 3.41 (2H, d, J 6.8 Hz, 100-H2),
1.61 (3H, s, 400-H3), 1.59 (3H, s, 500-H3); dC (100.6 MHz, CDCl3) 176.5,
164.2, 163.9, 163.8, 163.7, 159.5, 155.3, 155.1, 153.9, 145.2, 142.9,
134.2, 134.1, 134.0, 133.9, 132.8, 132.5, 130.7 (2C), 130.3 (2C), 130.2
(4C), 128.9, 128.8 (2C), 128.7 (2C), 128.6 (2C), 128.6 (2C), 128.3,
128.3, 128.1, 127.9, 126.8, 124.1, 123.9, 120.9, 118.1, 108.7, 101.8, 25.7,
22.4, 17.9; HRMS (ES): MþNaþ, found 809.1999. C48H34O11Na re-
quires 809.1992.
4.4. 5-(Allyloxy)-2-(3,4-bis(benzoyloxy)phenyl)-4-oxo-4H-
chro-mene-3,7-diyl dibenzoate (6)
A
solution of diisopropylazodicarboxylate DIAD (1.92 mL,
9.51 mmol) in THF (10 mL) was added to a cooled (ice bath) solution
of 5 (4.30 g, 5.95 mmol), allyl alcohol (0.6 mL, 8.92 mmol) and
triphenylphosphine (2.03 g, 7.73 mmol) in anhydrous THF (100 mL).
The resulting yellow solution was allowed to warm to room tem-
perature and stirred overnight. The title compound 6 had then
precipitated and was filtered off and washed with cold diethyl
ether. After drying 6 was obtained as white crystals (4.08 g, 90%).
Mp 220e222 ꢀC; nmax (neat) 1743, 1653, 1600, 1459, 1242, 1173,
4.7. 2-(3,4-Dihydroxyphenyl)-5,7-dihydroxy-6-(3-methylbut-
2-en-1-yl)-4-oxo-4H-chromen-3-yl benzoate (9)
A solution of NaOMe in MeOH (7 mL, 28% wt) was added to
a solution of 8 (2.7 g, 3.43 mmol) in 200 mL triethylamine/MeOH
(1:1) and the mixture was heated to 60 ꢀC for 1 h. The reaction
mixture was then poured into 1 M HCl (250 mL) and extracted with
EtOAc (400 mL). The organic phase was washed with brine, dried,
and evaporated in vacuo to give the title compound 9 as a yellowish
solid (1.2 g, 74%). Mp 150e152 ꢀC; nmax (neat) 3300, 1600, 1440,
1058, 1019, 700 cmꢁ1
; dH (400 MHz CDC13) 8.24e8.20 (4H, m, Bz),
8.04e8.00 (5H, m, Bz), 7.94 (1H, dd, J 8.6, 2.2 Hz, 60-H), 7.69 (1H, m,
Bz), 7.63 (1H, m, Bz), 7.56e7.47 (7H, m, Bz, 20-H and 50-H), 7.40e7.35
(4H, m, Bz), 7.15 (1H, d, J 2.1 Hz, 8-H) 6.75 (1H, d, J 2.1 Hz, 6-H), 6.10
(1H, m, 200-H), 5.59 (1H, dt, J 17.3, 1.7 Hz, 300-Ha) 5.33 (1H, dt, J 10.6,
1.4 Hz, 300-Hb), 4.72 (2H, ddd, J 4.9, 1.7, 1.4 Hz, 100-H2); dC (100.6 MHz,
CDCl3) 170.4, 164.1, 163.8, 163.8, 163.7, 160.1, 157.9, 155.2, 152.2,
144.7, 142.7, 134.9, 134.1, 133.9, 133.8, 133.8, 131.7, 130.7 (2C), 130.3
(2C), 130.2 (4C), 128.7 (2C), 128.6, 128.5 (2C), 128.5 (4C), 128.4,
128.4, 128.3, 128.2, 126.6, 123.9, 123.5, 118.5, 112.4, 103.4, 102.5,
70.2; HRMS (ES): MþNaþ, found 781.1681. C46H30O11Na requires
781.1671.
1266, 1153, 1084, 789, 704 cmꢁ1
; dH (400 MHz CD3OD) 8.18 (2H, dd,
J 8.4, 1.3 Hz, Bz), 7.71 (1H, m, Bz), 7.57 (2H, m, Bz), 7.37 (1H, d, J
2.2 Hz, 20-H), 7.31 (1H, dd, J 8.4, 2.2 Hz, 60-H), 6.80 (1H, d, J 8.4 Hz, 50-
H), 6.49 (1H, s, 8-H), 5.25 (1H, m, 200-H), 3.33 (2H, m, 100-H2), 1.78
(3H, s, 400-H3), 1.67 (3H, s, 500-H3); dC (100.6 MHz, CD3OD) 177.1,
165.5, 164.5, 159.8, 158.2, 156.6, 150.6, 146.8, 135.2, 132.2, 131.6,
131.5 (2C), 130.0, 129.9 (2C), 123.4, 122.1, 122.0, 116.5, 116.1, 113.4,
105.0, 94.4, 26.0, 22.3, 18.0; HRMS (ES): MþHþ, found 475.1323.
C27H23O8 requires 475.1299.
4.5. 6-Allyl-2-(3,4-bis(benzoyloxy)phenyl)-5-hydroxy-4-oxo-
4H-chromene-3,7-diyl dibenzoate (7)
4.8. 2-(3,4-Dihydroxyphenyl)-5,7-dihydroxy-6-(3-methylbut-
A solution of 6 (4 g, 5.28 mmol), Eu(fod)3 (500 mg, 0.53 mmol)
and anhydrous CHCl3 (100 mL) was heated in a sealed tube to 75 ꢀC
for 15 h. The solvent was evaporated in to give the crude product,
which was purified by chromatography (SiO2, ethyl acetate:toluene
1:50) to give the title compound 7 as yellowish crystals (3.4 g, 80%).
Mp 199e201 ꢀC; nmax (neat) 1737, 1599, 1450, 1243,1154, 1018, 1047,
2-en-1-yl)-4-oxo-4H-chromen-3-yl benzoate, poitsettifolin A
(1)
A solution of 9 (580 mg, 1.22 mmol) in citral (2.5 mL, 12 mmol)
was stirred at 140 ꢀC for 5 h. Thereafter the excess citral was dis-
tilled of (kugelrohr) and the resulting crude product purified by
chromatography (SiO2, CH2Cl2:MeOH 35:1) to give the title com-
pound 1 as a yellow oil. Solidification of the product was achieved
by adding 50 mL of a 1:5 EtOAc:hexane mixture into the round
bottom flask containing the compound. The solvent was then
evaporated in vacuo to get 1 as yellowish powder (450 mg, 70%).
Mp 199e201 ꢀC; nmax (neat) 3350, 1648, 1597, 1532, 1416, 1357,
1018, 907, 795, 698 cmꢁ1
; dH (400 MHz CDC13) 12.46 (1H, s, 5-OH),
8.26e8.21 (4H, m, Bz), 8.04e8.01 (5H, m, Bz), 7.95 (1H, dd, J 8.6,
2.2 Hz, 60-H), 7.70e7.64 (2H, m, Bz), 7.58e7.50 (7H, m, Bz, 20-H and
50-H), 7.40e7.35 (4H, m, Bz), 7.07 (1H, s, 8-H), 5.93 (1H, m, 200-H),
5.00 (1H, m, 300-Ha) 4.97 (1H, m, 300-Hb), 3.47 (2H, d, J 6.1 Hz,100-H2);
dC (100.6 MHz, CDCl3) 176.5, 164.1, 163.8, 163.7, 163.6, 159.5, 155.4,
155.1, 154.1, 145.2, 142.9, 134.6, 134.2, 134.1, 134.0, 133.9, 132.5, 130.7
(2C), 130.3 (2C), 130.2 (4C), 128.8 (2C), 128.8 (2C), 128.7, 128.6 (2C),
128.5 (2C), 128.3, 128.3, 128.0, 127.9, 126.8, 124.1, 123.9, 116.1, 115.6,
1280, 1183, 820, 770 cmꢁ1
; dH (400 MHz CD3OD) 7.76 (1H, d, J
2.1 Hz, 20-H), 7.66 (1H, dd, J 8.5, 2.2 Hz, 60-H), 6.89 (1H, d, J 8.5 Hz, 50-
H), 6.88 (1H, d, J 10.2 Hz, 100-H), 5.62 (1H, d, J 10.2 Hz, 200-H), 5.19

9056
Z. Escobar et al. / Tetrahedron 70 (2014) 9052e9056
(1H, m, 2000-H), 5.10 (1H, m, 600-H), 3.29 (2H, m, 1000-H2), 2.12 (2H, m,
500-H2), 1.79 (3H, s, 4000-H3), 1.73 (2H, m, 400-H2), 1.66 (3H, s, 5000-H3),
1.64 (3H, s, 900-H3), 1.55 (3H, s, 800-H3), 1.42 (3H, s, 1000-H3); dC
(100.6 MHz, CD3OD) 177.5, 158.9, 158.6, 150.5, 149.0, 147.8, 146.4,
137.4, 132.7, 132.1, 126.9, 125.1, 124.3, 123.5, 121.7, 116.6, 116.4, 115.8,
112.4, 104.6, 101.8, 81.8, 42.8, 27.5, 26.0, 25.9, 24.0, 22.1, 18.2, 17.8;
HRMS (ES): MþNaþ, found 527.2046. C30H32O7Na requires
527.2033.
absorbance was measured at 550 nm using a TriStar LB 941 (Bert-
hold Technologies, GmbH & Co. KG). The IC50 values calculated
using Microsoft Excel 2000 program.25
Acknowledgements
This work was supported by the Swedish Science Research
Council, grant number VR-621.2011.3729.
4.9. Biological assays
Supplementary data
4.9.1. Leishmanicidal test. The activity was measured on in vitro
cultures of Leishmania parasite in promastigote forms of complex L.
amazonensis (clon 1: Lma, MHOM/BR/76/LTB-012) and complex L.
braziliensis (strand M2904 C192 RJA), cultivated at 26 ꢀC in
Schneider medium (pH 6.8) supplemented with inactivated
(56 ꢀCꢂ30 min) calf bovine serum (10%). Parasites in logarithmic
phase of growth, at a concentration of 1ꢂ106 parasites mLꢁ1, were
distributed on a 96 micro well plates and different concentration of
1H and 13C NMR data associated with this article. Supplemen-
tary data related to this article can be found at http://dx.doi.org/
10.1016/j.tet.2014.10.021.
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