J. Med. Chem. 2007, 50, 595-598
Chart 1. Title and Reference Compoundsa
595
Design and Synthesis of Potent Antimalarial
Agents Based on Clotrimazole Scaffold:
Exploring an Innovative Pharmacophore
Sandra Gemma,†,‡ Giuseppe Campiani,*,†,‡ Stefania Butini,†,‡
Gagan Kukreja,†,‡ Bhupendra P. Joshi,†,‡ Marco Persico,‡,§
Bruno Catalanotti,‡,§ Ettore Novellino,‡,
Ernesto Fattorusso,‡,§ Vito Nacci,†,‡ Luisa Savini,†,‡
Donatella Taramelli,‡,| Nicoletta Basilico,‡,| Giulia Morace,|
Vanessa Yardley,‡,# and Caterina Fattorusso‡,§
Dipartimento Farmaco Chimico Tecnologico and European
Research Centre for Drug DiscoVery and DeVelopment, UniVersita’
di Siena, Via Aldo Moro, 53100 Siena, Italy, Dipartimento di
Chimica delle Sostanze Naturali and Dipartimento di Chimica
Farmaceutica e Tossicologica UniVersita’ di Napoli Federico II, Via
D. Montesano 49, 80131 Napoli, Italy, Dipartimento di Sanita’
Pubblica-Microbiologia-Virologia, UniVersita’ di Milano, Via
Pascal 36, 20133 Milano, Italy, and Department of Infectious and
Tropical Diseases, London School of Hygiene and Tropical
Medicine, Keppel Street, London WC1E 7HT, United Kingdom
ReceiVed December 13, 2006
Abstract: Identification of new molecular scaffolds structurally un-
related to known antimalarials may represent a valid strategy to
overcome resistance of P. falciparum (Pf) to currently available drugs.
We describe herein the investigation of a new polycyclic pharmaco-
phore, related to clotrimazole, to develop innovative antimalarial agents.
This study allowed us to discover compounds characterized by a high
in vitro potency, particularly against Pf CQ-resistant strains selectively
targeting free heme, which are easy to synthesize by low-cost synthetic
strategies.
a R, R1, R2, X, Y, and n are as defined in Table 1.
heme, prevents its detoxification into hemozoin, causing oxida-
tive stress in the parasite.4 Consequently, the induction of
oxidative stress may represent a promising rationale for anti-
malarial chemotherapy. Accordingly, free heme represents a
valuable target in the design of new antimalarial agents as the
lack of interaction with a specific protein target can decrease
the potential of inducing resistance under drug pressure.
Furthermore, the absence of free heme in the human host could
guarantee Pf specificity.
The increasing resistance of the malaria parasite Plasmodium
falciparum (Pf) to currently available drugs and especially to
chloroquine (CQ, 1, Chart 1) demands a continuous effort to
develop new effective therapeutic options.1 Identification of new
molecular scaffolds structurally unrelated to existing antimalarial
agents represents a valuable strategy to bypass resistance
phenomena.
During the intraerythrocytic life cycle of Pf, toxic free heme
is released into the parasite acidic food vacuole (FV) following
host hemoglobin degradation. As a result of its high toxicity,
disposal of free heme represents a crucial step for Pf survival,
and even small perturbations of its detoxification mechanisms
could lead to Pf death due to the generation of reactive oxygen
species. The main pathway of free heme detoxification is the
crystallization into inert hemozoin, which accounts for most of
the heme clearance in the FV.2 The remaining heme diffuses
through the FV membrane into the cytoplasm where it is
inactivated by reduced glutathione.3
Clotrimazole (CLT, 2), a well-known antimycotic drug, is
endowed with low in vitro antimalarial activity (W2, IC50
)
0.55 µM).5,6 Several studies, aimed at clarifying its mechanism
of action, demonstrated that CLT is able to inhibit the crystal-
lization of free Fe(III)-protoporphyrine (FP; ꢀ400) into â-hematin
and that, in the same conditions, it forms in vitro complexes
with heme in which the imidazole ring results to be a Fe(III)
axial ligand.7 Interestingly, it has also been reported that CLT,
interacting with free heme, induces a 10-fold potentiation of
heme-dependent hemolysis with respect to CQ.8 Finally, a recent
report suggests that in the presence of H2O2, CLT inhibits Pf
hemoperoxidase, which contains heme as a prosthetic group,
by a mechanism based on CLT-one electron oxidation product.9
Based on the above-mentioned CLT properties, we used its
scaffold to develop novel antimalarial agents, characterized by
the lack of interaction with a definite Pf or host target protein
and with improved pharmacological profile over CLT.
Interaction with free heme is thought to be responsible for
the activity of two of the most potent classes of antimalarial
agents known to date, namely, 4-aminoquinolines and endop-
eroxides. Indeed, the production of reactive radical species as
a direct consequence of endoperoxide interaction with Fe(II)-
heme, and the formation of complexes between CQ and free
It is known that CLT elicits its antimycotic activity through
the inhibition of fungi cytochrome P450 14R-lanosterol-dem-
ethylase (14-LD). On the other hand, interaction with human
P450 cytochromes, and the subsequent interference with its own
metabolism and that of a number of endogenous and exogenous
chemicals, represents a critical issue for CLT systemic admin-
istration. Inhibition of cytochrome P450 is linked to the
coordination of the nucleophilic nitrogen of the azole hetero-
cyclic ring to the P450 heme iron in the ferric state. Accordingly,
the main goal of this work was the design of CLT-related free
heme selective ligands, with improved antimalarial potency and
* To whom correspondence should be addressed. Phone: 0039-0577-
† Dipartimento Farmaco Chimico Tecnologico, Universita’ di Siena
‡ European Research Centre for Drug Discovery and Development.
§ Dip. Chimica delle Sostanze Naturali, Universita’ di Napoli.
Dip. Chimica Farmaceutica e Tossicologica, Universita’ di Napoli.
| Universita’ di Milano.
# London School of Hygiene and Tropical Medicine.
10.1021/jm061429p CCC: $37.00 © 2007 American Chemical Society
Published on Web 01/31/2007