Wittig reaction with partially protected sugar lactol derivatives. Preparation of highly cytotoxic goniofufurone analogues

Article abstract of DOI:10.1016/j.tetlet.2004.10.122

A new approach to the dephenyl goniofufurone analogue 2 and the corresponding (3S,4R)-stereoisomer 3 is reported. The resulting furanolactones 2 and 3 have shown a potent and selective in vitro cytotoxicity against certain human tumour cell lines.

Full text of DOI:10.1016/j.tetlet.2004.10.122

Tetrahedron
Letters
Tetrahedron Letters 45 (2004) 9409–9413
Wittig reaction with partially protected sugar lactol
derivatives. Preparation of highly cytotoxic
goniofufurone analogues
a
a
a
b
Velimir Popsavin,a, Sanja Grabezˇ, Mirjana Popsavin, Ivana Krstic, Vesna Kojic,
*
´
´
b
Gordana Bogdanovic and Vladimir Divjakovic
c
´
´
a
c
´
Department of Chemistry, Faculty of Sciences, University of Novi Sad, Trg D. Obradovica 3, 21000 Novi Sad, Serbia and Montenegro
bInstitute of Oncology Sremska Kamenica, Institutski put 4, 21204 Sremska Kamenica, Serbia and Montenegro
´
Department of Physics, Faculty of Sciences, University of Novi Sad, Trg D. Obradovica 4, 21000 Novi Sad, Serbia and Montenegro
Received 9 September 2004; revised 15 October 2004; accepted 20 October 2004
Available online 6 November 2004
Abstract—A new approach to the dephenyl goniofufurone analogue 2 and the corresponding (3S,4R)-stereoisomer 3 is reported.
The resulting furanolactones 2 and 3 have shown a potent and selective in vitro cytotoxicity against certain human tumour cell lines.
ꢀ 2004 Elsevier Ltd. All rights reserved.
Natural styryl lactones have received a great deal of
interest due to their widespread occurrence1 and their
varied antitumour activities.2 Notable among them is
(+)-goniofufurone (1, Scheme 1), a cytotoxic styryl lac-
tone that was isolated from the stem barkof Goniothal-
amus giganteus (Annonaceae).3 Due to the unique
structural features and significant biological activity,
(+)-1 and its stereoisomers have been synthesized by
many groups from different starting materials.4 Owing
to their potential as antitumour agents a number of gonio-
fufurone analogues have also been synthesized,5
including the recent preparation of furanolactones 2
and 3 (dephenyl goniofufurone analogues).6 However,
data related to their biological activities has not been re-
ported so far. Herein we report an alternative synthesis
of the lactones 2 and 3 for evaluation of their antiproli-
ferative activity against human tumour cell lines.
In 1993 Prakash and Rao7 reported an efficient synthesis
of 1 starting from D-glucose. The key step of the synthe-
sis was a spontaneous lactonisation and Michael ring
closure accompanying a Z-selective Wittig reaction8 of
ethoxycarbonylmethylenetriphenylphosphorane with a
furanose lactol 4 having a free hydroxyl group at C-2.
Accordingly it was assumed that a similar Wittig reac-
tion with D-xylo- and D-lyxofuranose lactol derivatives
of type 5 and 6 might provide access to the furanolact-
ones 2 and 3, respectively.
Although the furanolactone 2 can be obtained in a single
step by condensation of D-xylose with MeldrumÕs acid,9
we envisaged its preparation via the protected D-xylo-
furanose derivative 710 (Scheme 2) in order to explore
a possible divergent route that would be suitable not
only for the preparation of 2, but also for an alternative
synthesis of (+)-goniofufurone and 7-epi-goniofufurone.
The lactol 7 readily reacted with the stabilized ylide
Scheme 1. Goniofufurone (1) and analogues.
Keywords: Goniofufurone analogues; Furanolactones; Cytotoxicity; D-
Xylose; D-Lyxose; Wittig reaction; Michael ring closure.
*
Corresponding author. Tel.: +381 21 350 122; fax: +381 21 454
065; e-mail: popsavin@ih.ns.ac.yu
0040-4039/$ - see front matter ꢀ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2004.10.122

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V. Popsavin et al. / Tetrahedron Letters 45 (2004) 9409–9413
Scheme 2. Reagents and conditions: (a) Ph3P:CHCO2Me, MeOH, rt, 24h, 61% of 8, 25% of 9; (b) imidazole, C6H6, reflux, 11h, 51% of 8, 17% of 10;
(c) H2, 10% Pd/C (0.1equiv), rt, 1.5h, 84%; (d) H2, 10% Pd/C (0.2equiv), rt, 24h, 87%.
Ph3P:CHCO2Me in dry methanol to give the expected
furanolactone 8 (61%) accompanied by a minor amount
of the corresponding E-enoate 9 (25%). Both 8 and 9
had been prepared earlier in our laboratory, but in a
rather different ratio (12% of 8; 74% of 9).11 The major
reaction product 8 was presumably formed from the
respective Z-enoate 7a through a sequential lactonisa-
tion—Michael cyclisation process.7,12 If the sequence
had proceeded otherwise (with Michael ring closure tak-
ing precedence over lactonisation) we would have de-
tected in the reaction mixture at least traces of b-C-
furanoside 10, which from steric reasons cannot lacton-
ise. In an alterative sequence, in which Michael ring clo-
sure preceded lactonisation, the E-enoate 9 was treated
with imidazole in boiling benzene for 11h. Under these
reaction conditions the lactone 8 was obtained in 51%
yield, along with a minor amount of the b-C-glycoside
1013 (17%) thus providing an indirect proof for the
mechanism of conversion of 7 to 8. The ÔanomericÕ con-
figuration of 10 (at C-3) was established by an NOE
experiment, which showed a through-space interaction
between H-3 and the 4-OH.
moval of the benzyl group from the primary position
to afford the alcohol 1114 in 84% yield. Compound 11
could presumably be converted to (+)-goniofufurone,
or to its 7-epimer, via a three-step sequence that would
comprise a selective oxidation of 11 to the correspond-
ing aldehyde, reaction with PhMgBr, followed by OH
group deprotection. When the hydrogenolysis of 8 was
repeated using an excess of the catalyst (0.2Mequiv of
Pd) and prolonging the reaction time to 24h, the
known6,9,15 goniofufurone analogue 2 was obtained
(87%), with physical constants and spectral data in good
agreement with those already reported.6,9,15
After the successful preparation of the goniofufurone
analogue 2, we were also interested in obtaining the cor-
responding (3S,4R)-stereoisomer 3. This was of interest
to us as several goniofufurone stereoisomers have been
shown to exhibit moderate to significant antitumour
activities.2,5 In our initial efforts to discover an expedient
route to 3, we first examined a Wittig reaction of the D-
lyxofuranose 1210 with Ph3P:CHCO2Me in dry metha-
nol (Scheme 3). Although these conditions were found
to be optimal for obtaining Z-selectivity in the D-xylo
series, the major product in the reaction of 12 was the
corresponding E-alkene 13, which was isolated in 34%
Catalytic reduction of 8 over 10% Pd/C (0.1Mequiv of
Pd) for 1.5h at room temperature effected selective re-
Scheme 3. Reagents and conditions: (a) Ph3P:CHCO2Me, MeOH, rt, 24h, 34% of 13, 14% of 8.

V. Popsavin et al. / Tetrahedron Letters 45 (2004) 9409–9413
9411
alternative route for the preparation of 3. The synthesis
started from the known19 D-lyxofuranose derivative 14,
which is readily available from D-lyxose in two steps
(Scheme 4). Thus, the lactol 14 reacted with
Ph3P:CHCO2Me in refluxing acetonitrile to form an
intermediate enoate (not shown in the Scheme), which
then underwent a spontaneous Michael ring closure,
affording a mixture of a- and b-C-glycosides 1520 and
1621 in a ratio of ca. 1:1. The stereochemistry at C-3 in
15 was assigned on the basis of a NOE interaction be-
tween H-2 and H-4. A NOE between the endo-orien-
tated methyl group (from the isopropylidene moiety)
and H-3, definitely confirmed the D-talo configuration
of the product. The stereochemistry of 16 at C-3 was re-
solved on the bases of a NOE interaction between H-2
and endo-Me protons. Treatment of purified 15 with
NaOMe in MeOH effected equilibration (via a ring-
opening and ring-closure mechanism)22 to give a 10:1
mixture of 16 and 15, with the b-C-glycoside 16 as the
major product. The overall yield of 16 was 74% calcu-
lated from the starting compound. Hydrolytic removal
of the isopropylidene protective group in 16 with aque-
ous trifluoroacetic acid occurred with concomitant lact-
onisation to give the target molecule 3 in 80% yield. The
physical constants, as well as the 1H and 13C NMR spec-
tral data of product 3 were in agreement with the re-
ported values.6
O7
O6
C4
C6
C7
C3
C2
O5
C5
C1
O1
O4
Figure 1. ORTEP drawing of the furanolactone 8 with non-H labelling
scheme. The displacement ellipsoids are drawn at 50% probability.
yield, along with the furanolactone 8 (14%) as a minor
product. The expected stereoisomer 12a was not de-
tected in the reaction mixture. Compound 8 could be
formed by inversion of configuration at C-4 in the
unsaturated lactone 12b, which is a possible intermedi-
ate in this reaction. A similar epimerisation has been ob-
served with D-mannose in the Wittig reaction,16 as well
as with D-galactose9 and D-mannose17 in reaction with
MeldrumÕs acid. The structure of compound 8 was con-
firmed by 1H and 13C NMR spectra, which displayed the
same signals as a sample of 8 prepared from the D-xylo-
lactol 7, as well as by a single crystal X-ray diffraction
analysis.18
The synthesized analogues 2 and 3 were assayed in vitro
for their antiproliferative activity against human myelo-
genous leukaemia K562, colon adenocarcinoma HT29,
estrogen receptor negative breast adenocarcinoma
MDA-MB-231, and normal foetal lung MRC-5 cells.
In vitro cytotoxicity was evaluated after 24h cell treat-
ment using the MTT assay.23 The results, including
the data for the reference compound, doxorubicin
(DOX), are presented in Table 1.
The X-ray analysis of furanolactone 8 (Fig. 1) obtained
from D-lyxofuranose derivative 12, reveals a cis junction
between the five-membered rings, as well as a trans ori-
entation of the lactone ring with respect to the substitu-
ents at C-5 and C-6. The tetrahydrofuran ring exists in
an envelope conformation, with C-5 above the plane
that contains the C-3, C-4, C-6 and O-6 atoms. The lac-
tone ring also adopts an envelope conformation, but
with C-3 below the plane formed by the remaining ring
atoms. The values of the torsion angles C2–C3–C4–
O4 = ꢀ25.2ꢁ, O4–C4–C5–O5 = 168.6ꢁ, O5–C5–C6–
C7 = 168.6ꢁ and O5–C5–C6–O6 = 81.6ꢁ are consistent
with the D-ido configuration of 8.
As shown in the Table 1, the analogue 2 was active only
against the K562 cell line, but was more than 6-fold
less active than the reference compound, doxorubicin.
Table 1. In vitro cytotoxicity of target compounds
Compds
IC50, lMa
MDA-MB-231
K562
HT-29
MRC-5
2
5.02
0.0074
0.82
>100
0.21
0.51
>100
0.39
0.29
>100
>100
0.32
3
DOX
a IC50 is the concentration of compound required to inhibit cell growth
by 50% compared to an untreated control.
The undesired outcome of the previous reaction (at-
tempted conversion of 12 to 12a) forced us to find an
Scheme 4. Reagents and conditions: (a) Ph3P:CHCO2Me, MeCN, reflux, 24h, 48% of 15, 43% of 16; (b) NaOMe, MeOH, reflux, 48h, 61% of 16, 6%
of 15; (c) 2:1 TFA–H2O, rt, 18h, 80%.

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V. Popsavin et al. / Tetrahedron Letters 45 (2004) 9409–9413
10. Popsavin, V.; Grabezˇ, S.; Stojanovic, B.; Popsavin, M.;
´
Pejanovic, V.; Miljkovic, D. Carbohydr. Res. 1999, 321,
However, the (3S,4R)-stereoisomer 3 showed a remark-
able cytotoxicity towards the K562 and HT29 cell lines,
being approximately 110- and 2.5-fold, respectively,
more potent than doxorubicin. In experiments with
MDA-MB-231 cells, the analogue 3 exhibited a strong
cytotoxicity similar to that observed for the reference
compound. Neither furanolactone 2 or 3 exhibited any
significant cytotoxicity towards normal foetal lung
MRC-5 cells.
´
´
110–115.
11. Popsavin, V.; Grabezˇ, S.; Krstic, I.; Popsavin, M.;
´
Djokovic, D. J. Serb. Chem. Soc. 2003, 68, 795–804.
´
12. Prakash, K. R. C.; Rao, S. P. Tetrahedron Lett. 1991, 32,
7473–7476.
23
13. Selected data for 10 (syrup): ½aꢁD ꢀ18.7 (c 1.0, CHCl3); 1H
NMR (250MHz, CDCl3): d 2.68 (dd, 1H, J2a,3 = 9.6,
J2a,2b = 17Hz, H-2a), 2.97 (dd, 1H, J2b,3 = 5, J2a,2b
=
17Hz, H-2b), 3.12 (br s, 1H, OH), 3.60–3.80 (m, 5H,
2 · H-7 and CO2CH3), 3.93 (m, 1H, H-3), 3.99 (dd, 1H,
J4,5 = 2.3, J5,6 = 5.1Hz, H-5), 4.08 (dd, 1H, J3,4 = 4.9,
J4,5 = 2.3Hz, H-4), 4.23 (m, 1H, H-6), 4.48–4.72 (4d, 4H,
In summary, we have synthesized dephenyl goniofufu-
rone analogues 2 and 3, which have shown significant
antiproliferative activity against certain human neoplas-
tic cells. The furanolactone 3 showed strong cytotoxicity
towards the K562 and HT29 cell lines, being much more
potent than doxorubicin, an approved drug for treat-
ment of these malignant diseases, while both analogues
2 and 3 did not exhibit any cytotoxicity towards the nor-
mal MRC-5 cell line. In addition, this approach pro-
vided a convenient procedure for selective removal of
the primary benzyl group in 8, thus enabling access to
11, a postulated intermediate in the synthesis of (+)-gonio-
fufurone 1 or 7-epi-goniofufurone, which is also a nat-
ural product.24
Jgem = 12Hz, 2 · CH2Ph), 7.24–7.39 (m, 10H, 2 · Ph); 13
C
NMR (62.5MHz, CDCl3): d 38.3 (C-2), 52.0 (CO2CH3),
68.7 (C-7), 71.6 and 73.4 (2 · CH2Ph), 79.7 (C-6), 80.8 (C-
3), 81.1 (C-4), 85.3 (C-5), 127.5, 127.6, 127.8, 128.3, 128.4,
137.9 and 138.1 (Ph), 172.9 (C-1).
23
14. Selected data for 11 (syrup): ½aꢁD +4.3 (c 1.0, in CHCl3);
1H NMR (250MHz, CDCl3): d 2.52 (br s, 1H, OH), 2.58–
2.78 (m, 2H, 2 · H-2), 3.76 (dd, 1H, J6,7a = 4.3,
J7a,7b = 12Hz, H-7a), 3.84 (dd, 1H, J6,7b = 5.1,
J7a,7b = 12Hz, H-7b), 4.17 (m, 1H, H-6), 4.25 (d, 1H,
J5,6 = 4.9Hz, H-5), 4.56 and 4.71 (2d, 2H, Jgem = 12Hz,
CH2Ph), 4.91–5.01 (m, 2H, H-3 and H-4), 7.26–7.42
(m, 5H, Ph); 13C NMR (62.5MHz, CDCl3): d 35.8 (C-2),
61.1 (C-7), 72.7 (CH2Ph), 76.7 (C-3), 80.7 (C-6), 82.1
(C-5), 85.7 (C-4), 127.6, 128.2, 128.6 and 136.7 (Ph), 175.2
(C-1).
Acknowledgements
15. Dmitriev, B. A.; Chernyak, A. Y.; Kochetkov, N. K.
Zhur. Org. Khim. 1972, 41, 2754–2760.
16. Collins, P. M.; Overend, W. G.; Shing, T. S. J. Chem. Soc.,
Chem. Commun. 1982, 297–298.
This workwas supported by a research grant from the
Ministry of Science and Environment Protection of the
Republic of Serbia (Grant No. 1896). The authors are
´
17. Mata, F. Z.; Martinez, M. B.; Perez, J. A. G. Carbohydr.
Res. 1992, 225, 159–161.
ˇ
grateful to Professor Ljubo Golic (Faculty of Chemistry
and Chemical Technology, University of Ljubljana,
Slovenia) for collecting the X-ray data.
18. Crystallographic data for 8 have been deposited with the
Cambridge Crystallographic Data Centre as supplemen-
tary publication number CCDC 249584. Copies of the
data can be obtained, free of charge, on application to
CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK [fax:
+44(0)-1223-336033 or e-mail: deposit@ccdc.cam.ac.uk.
19. Lin, C.-C.; Fan, G.-T.; Fang, J.-M. Tetrahedron Lett.
2003, 44, 5281–5283.
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23
20. Selected data for 15: mp 138ꢁC (from MeOH); ½aꢁD ꢀ21.7
1
(c 0.8, CHCl3); H NMR (250MHz, CDCl3): d 1.31 and
1.35 (2s, 3H each, CMe2), 2.47 (dd, 1H, J2a,3 = 7.9,
J2a,2b = 15.3Hz, H-2a), 2.57 (dd, 1H, J2b,3 = 7.4, J2a,2b
=
15.3Hz, H-2b), 3.37 (dd, 1H, J7a,7b = 9.5, J6,7a = 6.3Hz,
H-7a), 3.45 (dd, 1H, J7a,7b = 9.5, J6,7b = 5.7Hz, H-7b),
3.73 (s, 3H, CO2CH3), 3.97 (m, 1H, H-6), 4.47 (ddd, 1H,
J3,4 = 1.1, J2a,3 = 7.9, J2b,3 = 7.4Hz, H-3), 4.61 (dd, 1H,
J3,4 = 1.1, J4,5 = 6.1Hz, H-4), 4.78 (dd, 1H, J4,5 = 6.1, J5,6
3.9Hz, H-5), 7.19–7.54 (m, 15H, 3 · Ph); 13C NMR
(62.5MHz, CDCl3): d 25.3 and 26.2 (CMe2), 36.3 (C-2),
51.9 (CO2CH3), 61.7 (C-7), 79.5 (C-6), 80.3 (C-3), 81.0 (C-
5), 84.8 (C-4), 86.8 (CPh3), 112.7 (CMe2), 126.9, 127.7,
128.8 and 144.0 (Ph), 170.8 (C-1).
23
21. Selected data for 16 (syrup): ½aꢁD ꢀ26.3 (c 1.0, CHCl3); 1H
NMR (250MHz, CDCl3): d 1.34 and 1.36 (2 · s, 3H each,
CMe2), 2.78 (dd, 1H, J2a,3 = 6.6, J2a,2b = 16.7Hz, H-2a),
2.83 (dd, 1H, J2b,3 = 7, J2a,2b = 16.7Hz, H-2b), 3.42 (dd,
1H, J7a,7b = 9.5, J6,7a = 6.4Hz, H-7a), 3.49 (dd, 1H,
J7a,7b = 9.5, J6,7b = 6Hz, H-7b), 3.70 (ddd, 1H, J5,6 = 2.9,
J6,7a = 6.4, J6,7b = 6Hz, H-6), 3.72 (s, 3H, CO2CH3), 3.94
(ddd, 1H, J3,4 = 2.9, J2a,3 = 6.6, J2b,3 = 7Hz, H-3), 4.78 (m,
2H, H-4 and H-5), 7.17–7.58 (m, 15H, 3 · Ph); 13C NMR
(62.5MHz, CDCl3): d 25.2 and 25.8 (CMe2), 33.4 (C-2),
51.7 (CO2CH3), 61.3 (C-7), 77.4 (C-3), 80.6 (C-6), 81.0 and
´
9. Mata, F. Z.; Martinez, M. B.; Perez, J. A. G. Carbohydr.
Res. 1990, 201, 223–231.

V. Popsavin et al. / Tetrahedron Letters 45 (2004) 9409–9413
9413
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127.6, 128.8 and 144.0 (Ph), 171.5 (C-1).
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