First total synthesis of piperodione and analogs

Article abstract of DOI:10.1016/j.tetlet.2014.09.079

Piperodione (3), a secondary metabolite previously isolated from the Javanese pepper plant Piper retrofractum in 0.0002% isolated yield was synthesized in a convergent strategy utilizing a Mannich and a Stetter reaction. An over-all yield of 76% could be achieved. Several analogs were prepared by this synthetic sequence. None of the compounds showed a significant cytotoxicity for human tumor cells (photometric sulforhodamine B assay).

Full text of DOI:10.1016/j.tetlet.2014.09.079

Tetrahedron Letters 55 (2014) 6243–6244
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Tetrahedron Letters
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First total synthesis of piperodione and analogs
⇑
Sven Sommerwerk, Simone Kern, Lucie Heller, René Csuk
Martin-Luther-Universität Halle-Wittenberg, Organische Chemie, Kurt-Mothes-Str. 2, D-06120 Halle (Saale), Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 23 July 2014
Revised 10 September 2014
Accepted 16 September 2014
Available online 20 September 2014
Piperodione (3), a secondary metabolite previously isolated from the Javanese pepper plant Piper
retrofractum in 0.0002% isolated yield was synthesized in a convergent strategy utilizing a Mannich
and a Stetter reaction. An over-all yield of 76% could be achieved. Several analogs were prepared by this
synthetic sequence. None of the compounds showed a significant cytotoxicity for human tumor cells
(photometric sulforhodamine B assay).
Ó 2014 Elsevier Ltd. All rights reserved.
Keywords:
Piperodione
Mannich reaction
Stetter reaction
Cytotoxicity
SRB assay
The pantropical plant family of Piperaceae, shrubs or small trees
also known as the pepper family, contains almost 2000 different
species in 13 genera.1 Some of these peppers are extensively used
not only in spicing food but also in Ayurvedic medicine.2 The main
alkaloid of black pepper (Piper nigrum) as well as of long pepper
(Piper longum) is piperine (1, Fig. 1). This compound is also respon-
sible for the pungency of these peppers by activating the heat and
acidity sensing TRPV ion channel TRPV1 on pain sensing nerve
cells.3 The interest in pepper-plant derived natural products was
growing steadily within the last decade. This interest, however,
was focused on the search of new lead structures for the develop-
ment of drugs to treat infections and cancer.
Figure 1. Structure of piperine (1), piperlongumine (2), and piperodione (3).
Recently, plants of the genus Piper came again in the focus of
interest of scientific research, and many physiologically active
compounds have been identified and isolated from different spe-
cies of the genus Piper. The presence of unsaturated amides4 seems
quite typical for these plants. Thus, piperine (1) was found to pos-
sess not only anti-angiogenic properties5 but also to improve6
memory impairment and neurodegeneration in rats. Piperlongu-
mine7 (2) is toxic selectively to cancer cells in vitro and in vivo
by elevating the cellular levels of reactive oxygen species.7
Recently, piperodione (3) was isolated from the dried fruits of Piper
retrofractum albeit in very low yields.8 Thus, the extraction and
exhaustive chromatography of 1 kg of dried plant material afforded
2.1 mg of 3, only. Piperodione is a very interesting compound since
it enhances the outgrowth of neurites of NGF-mediated PC12 cells
interested in obtaining this compound in larger quantities to per-
form extended biological screening. Its extraction from natural
sources, however, has some major drawbacks. Firstly, only small
amounts of 3 (0.0002%) can be obtained from the fruits of Piper
retrofractum, and authentic specimen of this Javanese long pepper
is very difficult to obtain, since it is often confused (and mixed)
with Piper longum, common long pepper.
Our synthetic strategy (Scheme 1) started from commercially
available 3,4-methylenedioxy-acetophenone (4) whose Mannich
reaction9,10 with paraformaldehyde/diisopropylammonium trifluo-
roacetate followed by acidic work-up gave propenone 5;10 as a side
product. As a side reaction the formation of 3-chloro-1-propanone
at low concentrations ranging from 0.1 to 10 l
M.8 We became
6
11 was observed. Compound 5 was characterized by 13C NMR; the
spectrum showed the presence of two signals at d = 132.5 and
129.9 ppm that were assigned to the olefinic carbons.
⇑
Corresponding author. Tel.: +49 (0) 345 5525660; fax: +49 (0) 345 5527030.
E-mail address: rene.csuk@chemie.uni-halle.de (R. Csuk).
http://dx.doi.org/10.1016/j.tetlet.2014.09.079
0040-4039/Ó 2014 Elsevier Ltd. All rights reserved.

6244
S. Sommerwerk et al. / Tetrahedron Letters 55 (2014) 6243–6244
Acknowledgments
Thanks are due to Dr. R. Kluge for measuring the ESI-MS spectra,
Dr. D. Ströhl for numerous NMR spectra, and to Ms. Jana Wiese for
taking the IR und UV–vis spectra. The cell lines were kindly
provided by Dr. Thomas Müller (Dept. of Haematology/Oncology,
Martin-Luther Universität Halle-Wittenberg). Support by the
‘Gründerwerkstatt—Biowissenschaften’ is gratefully acknowledged.
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.tetlet.2014.
09.079.
References and notes
Scheme 1. Synthesis of piperodione (3) and analogs (3b and 3c). Reagents and
conditions: (a) (CH2O)n, iPr3N+CF3CO2À, reflux, 6 h; dil HCl, 5 (83.8%), and 6 (3%); (b)
piperidine, reflux, 12 h, 67.2% (for 7a); pyrrolidine, reflux, 12 h, 91% (for 7b);
azetidine, reflux, 12 h, 64% (for 7c); (c) NaIO4 (silica gel supported), DCM, 25 °C, 78%
(for 8a), 74% (for 8b), 65% (for 8c); (d) 5-(2-hydroxyethyl)-4-methyl-3-(phenyl-
methyl)-thiazolium chloride, NEt3, microwaves, 80 °C, 15 h, 92% (for 3), 89% (for
3b), 61% (for 3c).
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Reaction of
D
-(À)diethyl tartrate with piperidine12,13 gave dia-
mide 7a whose cleavage with silica supported NaIO4 furnished
aldehyde 8a.13,14 Similarly, amides 7b and 7c were obtained; their
cleavage yielded aldehydes 8b and 8c, respectively. Compound 8a
is characterized in its IR spectrum by the presence of two strong
signals at
m
= 1640 and 1450 cmÀ1 (CO stretch vibrations); the cor-
responding signals are found in the 13C NMR spectrum at d = 187.7
and 162.1 ppm, respectively.
From the microwave assisted15 Stetter reaction16 of 5 with alde-
hyde 8a in the presence of 5-(2-hydroxyethyl)-4-methyl-3-(phen-
ylmethyl)-thiazolium chloride and triethylamine piperodione (3)
was obtained in 92% isolated as a slightly yellowish oil. Similarly
from 8b and 8c analogs 3b and 3c were obtained.
Compounds 3, 3b, and 3c were tested for their cytotoxicity
using a photometric sulforhodamine B (SRB) assay.17,18 None of
these compounds showed any significant cytotoxicity employing
eight different human cancer cell lines, and the IC50 values were
12. Seebach, D.; Kalinowski, H. O.; Bastian, B.; Crass, G. Helv. Chim. Acta 1977, 60,
301–325.
13. Nottingham, M.; Bethel, C. R.; Pagadala, S. R. R.; Harry, E.; Pinto, A.; Lemons, Z.
A.; Drawz, S. M.; van en Akker, F.; Carey, P.; Bonomo, R. A.; Buynak, J. D. Bioorg.
Med. Chem. Lett. 2011, 21, 387–393.
14. Zhong, Y.-L.; Shing, T. K. M. J. Org. Chem. 1997, 62, 2622–2624.
15. Aupoix, A.; Vo-Tanh, G. Synlett 2009, 1915–1920. conventional reaction
without microwave assistance gave 3 in 41% isolated yield (reflux, 24 h).
16. Stetter, H.; Skobel, H. Chem. Ber. 1987, 120, 643–645.
17. Skehan, P.; Storeng, R.; Scudiero, D.; Monks, A.; Mcmahon, J.; Vistica, D.;
Warren, J. T.; Bokesch, H.; Kenney, S.; Boyd, M. R. J. Natl. Cancer Inst. 1990, 82,
1107–1112; Siewert, B.; Csuk, R. Eur. J. Med. Chem. 2014, 74, 1–6; Siewert, B.;
Obernauer, A.; Csuk, R. Bioorg. Med. Chem. 2014, 22, 594–615; Siewert, B.;
Wiemann, J.; Köwitsch, A.; Csuk, R. Eur. J. Med. Chem. 2014, 72, 84–101.
18. Full experimental procedures and characterization of all compounds are given
in the Supplementary material to this publication.
>30 lm (cut-off of the assay). This seems of importance for an
advanced biological screening of these compounds, since com-
pound 2 was shown to be highly cytotoxic, and 3 and analogs are
interesting candidates for screening their ability to enhance the
outgrowth of neurites; thus they must not show any cytotoxicity
at all.
To sum up, we have developed a short convergent synthesis of
piperodione and three unnatural analogs. None of these com-
pounds exhibited significant cytotoxicity.