1,4-Dihydroxy-2,3-dioxatricyclo[8.4.0.04,9]tetradecane and derivatives with in vitro activity against Plasmodium falciparum, Trypanasoma b brucei, Trypanasoma cruzi, and Leishmaniasis infantum

Article abstract of DOI:10.1016/S0960-894X(03)00326-3

1,4-Dihydroxy-2,3-dioxatricyclo[8.4.0.0^4,9]tetradecane and derivatives have been synthesised and their in vitro activity against Plasmodium falciparum (malaria) Ghana, Trypanasoma b brucei (sleeping sickness) TB-1, and Trypanasoma cruzi (Chagas' disease) TC-1, and Leishmaniasis infantum (leishmaniasis) L1 parasite strains has been assessed.

Full text of DOI:10.1016/S0960-894X(03)00326-3

Bioorganic & Medicinal Chemistry Letters 13 (2003) 2013–2015
1,4-Dihydroxy-2,3-dioxatricyclo[8.4.0.04,9]tetradecane and
Derivatives with In Vitro Activity Against Plasmodium
falciparum, Trypanasoma b brucei, Trypanasoma cruzi, and
Leishmaniasis infantum
Joshua Howarth* and Darragh Wilson
School of Chemical Sciences, Dublin City University, Glasnevin, Dublin 9, Ireland
Received 2 December 2002; revised 10 February 2003; accepted 19 March 2003
Abstract—1,4-Dihydroxy-2,3-dioxatricyclo[8.4.0.04,9]tetradecane and derivatives have been synthesised and their in vitro activity
against Plasmodium falciparum (malaria) Ghana, Trypanasoma b brucei (sleeping sickness) TB-1, and Trypanasoma cruzi (Chagas’
disease) TC-1, and Leishmaniasis infantum (leishmaniasis) L1 parasite strains has been assessed.
# 2003 Elsevier Science Ltd. All rights reserved.
There are several human protozoal parasites that cause
devastating diseases in the regions of the World where
they are found. Four of these parasites are Plasmodium
falciparum, Trypanasoma b brucei, Trypanasoma cruzi,
and Leishmaniasis infantum, causative agents of malaria,
sleeping sickness, Chagas’ disease, and Leishmaniasis,
respectively. Over the last decade intense research
efforts have been directed towards the nonalkaloidal
trioxane, naturally occuring lactone, artemisinin 1, its
semisynthetic ether 2 and ester derivatives, and synthetic
analogues, for example BO7 31,2 (Fig. 1). The reason
behind this fervent investigation is that these trioxane
systems offer a very real chemotherapeutic alternative to
standard quinoline (e.g., chloroquine) and antifolate
antimalarial drugs to which the P.falciparum parasite
has become largely resistant.3
(ARTC) into the system will prompt the uptake of the
compound by the infected red blood cell. Should this
ARTC also contain the chemical composition required
to kill the parasite, then it may be possible to produce a
drug that is effective against malarial erythrocyte para-
sites. We have shown the plausibility of this hypothesis
through the use of quinine and azure A or proflavin
hybrids.6
One can view the nonalkaloidal trioxane drugs and
other peroxide systems as ARTCs, as the peroxide
component may be readily reduced. Mechanistic studies
on the action of trioxane systems both in vitro and in
vivo, and on how this action results in their potent
antimalarial activity have shown that the chemical
composition required to kill the parasite is produced on
the reduction of the peroxide by Fe(II) in iron-por-
phyrins.7 We believe that it is possible that the same
hypothesis for the HMS within erythrocytes, with
respect to ARTCs, outlined above, could be applied to
all protozoal parasites that at some stage of their life
cycle occupy cells of the host. If we are correct a per-
oxide based molecule that acts against the malarial
parasite P.falciparum could feasibly act against the T.b
brucei, T.cruzi, and L.infantum parasites. These para-
sites all fulfil the above criteria in so much as they
occupy cells of the host during their life cycle.8
We are investigating the possibility of using the fact that
infected red blood cells are under a high degree of
endogenous oxidative stress, stemming from the para-
sitic presence, to combat erythrocyte parasites. Various
physiological processes come into play to relieve this
stress, primarily in the provision of substrates for
reduction in a process known as the hexose monophos-
phate shunt (HMS).4,5 In infected cells HMS activity
increases 24-fold and our hypothesis is that the intro-
duction of an alternative reductive target compound
In pursuit of evidence for this theory we synthesised a series
of simple compounds containing a peroxide unit (loosely
*Corresponding author. Tel.: +353-1-700-5312; fax: +353-1-700-
5503; e-mail: joshua.howarth@dcu.ie
0960-894X/03/$ - see front matter # 2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0960-894X(03)00326-3

2014
J.Howarth, D.Wilson / Bioorg.Med.Chem.Lett.13 (2003) 2013–2015
Figure 1.
based on the artemisinin trioxane substructure),9,10
(Scheme 1). In choosing our peroxide containing
structures we also took into account current theories
on the mode of action of endoperoxides, that is the
ability of active endoperoxides to undergo cleavage to
form an Fe(IV)¼O species and an oxygen radical that
subsequently undergoes a 1,5-H shift to produce a
carbon-centred radical.11 Our choice of peroxide theo-
retically had the potential to satisfy these require-
ments. Using LDA and FeCl3 we dimerised
cyclohexanone 4a to form the bis(cyclohexyl)-2,20-
dione 5a, similarly we coupled 2-methylcyclohexanone
4b to form bis(3,30-dimethylcyclohexyl)-2,20-dione 5b.
On subsequent reaction with 30% aqueous hydrogen
peroxide the diones 5a and 5b gave 1,4-dihydroxy-2,3-
dioxatricyclo[8.4.0.04,9]tetradecane 6a, and 5,14-dimethyl-
1,4-dihydroxy-2,3-dioxatricyclo[8.4.0.04,9]tetradecane 6b,
respectively. Reaction of 5a with 30% aqueous hydrogen
peroxide in the presence of methanol gave 1-methoxy-4-
hydroxy-2,3-dioxatricyclo[8.4.0.04,9]tetradecane 6c. The
1,4-dihydroxy-2,3-dioxatricyclo[8.4.0.04,9]tetradecane 6a
was then reacted with four diacid chlorides 7 to form
the esters 8a–d.12 Compounds 6a–c and 8a–d were then
assayed in vitro against the P.falciparum Ghana, T.b
brucei TB-1, T.cruzi TC-1, and L.infantum L1 strains,
and cytoxicity was tested on the cell line MRC-5. The
results of the biological in vitro testing are given in
Table 1.
As can be seen from the results given in Table 1 for the
initial in vitro biological assessment of compounds 6a–c
and 8a–d they are all active against the protozoal para-
Scheme 1.

J.Howarth, D.Wilson / Bioorg.Med.Chem.Lett.13 (2003) 2013–2015
2015
Table 1.
Compd IC50 (mM) IC50 (mM) IC50 (mM) IC50 (mM) IC50 (mM)
Acknowledgements
The Authors would like to acknowledge the contribution
to this research by the Tropical Disease Research section
of the World Health Organisation and Enterprise Ireland.
Ghana
TB-1
TC-1
L1
MRC-5
6a
6b
6c
8a
8b
8c
8d
0.1
>32.0
5.0
6.0
1.0
19.0
>32
13.0
<64.0
16.0
10.0
4.0
24.0
>32.0
8.0
>32.0
13.0
15.0
>32.0
>32.0
>32.0
>32.0
>32.0
>32.0
>32.0
10.0
>32.0
8.0
>32.0
13.0
References and Notes
16.0
17.0
>32.0
>32.0
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J. N.; Klinedinst, D.; Shapiro, T. Tetrahedron Lett. 1996, 37,
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19.0
sites for which they were assayed. The anti-protazoal
parasite activities of these molecules are not potent in
comparison to other compounds currently used to treat
the corresponding disease. For example artemether has
an activity of 0.025 mM against P.falciparum Ghana
strain, Suramin 0.043 mM against T.b brucei TB-1
strain, Nifurtimox 0.39 mM against T.cruzi
TC-1
strain, and PX-6518 0.019 mM against L.infantum L1
strain.13 However, the fact that they are active
against all of these parasites, that at some point in
their life cycle invade cells of the host, indicates that
the HMS and the use of ARTCs may provide a
route to delivery of active anti-protazoal parasite
compounds. This approach may lead to a pan-anti-
protazoal drug.
7. Posner, G. H.; Cumming, J. N.; Ploypradith, P.; Oh, C. H.
J.Am.Chem.Soc. 1995, 117, 5885.
8. Mason-Bahr, P. E. C.; Apted, F. I. C. Mason’s Tropical
Diseases, 8th ed; Bailiere Tindall: London, 1982.
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Starostin, E. K.; Ignatenko, A. V.; Nikishin, G. I. Russ.Chem.
Bull. 1995, 44, 907.
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D.; Shapiro, T. A. Tetrahedron Lett. 1997, 53, 37.
12. All compounds 6a–c and 8a–d gave correct microanalysis,
1H and 13C NMR analytical data.
13. Data supplied by the Tropical Disease Research unit of
the World Health Organisation, Geneva, Switzerland.
The synthesis of the peroxide systems 6 that we have
assayed for biological activity is relatively simple and
open to adaptation to form numerous analogues that
may show greater efficacy against the aforementioned
parasites. We are currently investigating this option.