Synthesis and biological properties of a rhodacyanine derivative, SSJ-127, having high efficacy against malaria protozoa

Article abstract of DOI:10.3987/COM-08-S(F)35

One of rhodacyanine derivatives, SSJ-127 (1), showed a complete cure of a mouse model infected with Plasmodium berghei by subcutaneous administration. The synthesis, in vitro activities against several protozoa and in vivo antimalarial test and PK study o

Full text of DOI:10.3987/COM-08-S(F)35

HETEROCYCLES, Vol. 77, No. 1, 2009
207
HETEROCYCLES, Vol. 77, No. 1, 2009, pp. 207 - 210. © The Japan Institute of Heterocyclic Chemistry
Received, 2nd July, 2008, Accepted, 30th July, 2008, Published online, 31st July, 2008.
DOI: 10.3987/COM-08-S(F)35
SYNTHESIS AND BIOLOGICAL PROPERTIES OF A RHODACYANINE
DERIVATIVE, SSJ-127, HAVING HIGH EFFICACY AGAINST
MALARIA PROTOZOA#
Khanitha Pudhom,† Jian-Feng Ge,† Chika Arai,†,‡ Mei Yang,†,‡ Marcel
Kaiser,§ Sergio Wittlin,§ Reto Brun,§ Isamu Itoh,†,‡ and Masataka Ihara†,‡,*
†Research Centre of Medicinal Sciences, Hoshi University, 2-4-41 Ebara,
Shinagawa, Tokyo 142-8501, Japan, ‡Synstar Japan Co., Ltd., 2-18-3
Nishigotanda, Shinagawa, Tokyo 141-0031, §Swiss Tropical Institute,
Socinstrasse 57, CH-4002 Basel, Switzerland and e-mail address:
m-ihara@hoshi.ac.jp
Abstract – One of rhodacyanine derivatives, SSJ-127 (1), showed a complete
cure of a mouse model infected with Plasmodium berghei by subcutaneous
administration. The synthesis, in vitro activities against several protozoa and in
vivo antimalarial test and PK study of SSJ-127 (1) are reported.
Malaria is one of the most perilous infectious diseases caused by protozoan parasites in tropical and
subtropical regions. Each year, there are approximately 515 million cases of malaria, killing between one
and three million people, the majority of whom are young children.1 No vaccine is currently available for
malaria and the resistance of the protozoa to clinically used chemotherapeutic agents is increasingly
common. Therefore, the development of new classes of antimalarial medicines having a novel mechanism
of action is highly desired.2-7 Recently, we recorded that rhocyanine derivatives displayed potent in vitro
and in vivo activities against Plasmodium parasites.8-11 Further investigation of antimalarial activities of a
number of newly synthesized rhodacyanine derivatives has led us finding SSJ-127 (1), which exhibits a
complete cure of a mouse model infected with P. berghei. Here, we would like to communicate the
synthesis and biological properties of the rhodacyanine derivative, SSJ-127 (1).
--------------------------------------
#This paper is dedicated to Professor Emeritus Keiichiro Fukumoto as we celebrate his 75th birthday and
his significant contributions to the field of heterocyclic chemistry and The International Journal,
“Heterocycles”.

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HETEROCYCLES, Vol. 77, No. 1, 2009
S
O
N
N+
Me
Cl–
S
N
N
Me
Et
O
1
Synthesis: SSJ-127 (1) was prepared starting with the right hand segment, benzo[d]thiazol-3-ium part, as
shown in Scheme 1. Reaction of 2,3-dimethylbenzo[d]thiazol-3-ium tosylate (2) and ethyl isothiocyanate
in the presence of triethylamine in pyridine at 110 oC for 1 h gave the thioamide 3 in 55% yield. Without
o
purification, 3 was treated with bromoacetic acid in acetic acid at 90 C for 30 min to afford the
4-oxothiazolidine 4 in 77% yield. Treatment of 4 with N,N’-diphenylformimidamide in acetic anhydride
o
at 140 C for 30 min provided the phenylacetamidomethylenethiazolidine 5 in 97% yield. Reaction of 5
o
with 2,4-dimethyloxazolo[4,5-b]pyridinium iodide in the presence of triethyamine in acetnitrile at 80 C
for 2.5 h, followed by eluation of the product through IRA-400 (Cl), gave SSJ – 127 (1)12 in 49% overall
yield. Thus, SSJ-127 (1) was easily synthesized in five steps from known compounds using a standard
synthetic procedure.13,14
Me
N+
Me
N+
S
Et
NH
BrCH2CO2H
AcOH, 90 oC
–OTs
Me
EtNCS, NEt3
pyridine, 110 oC
–OTs
S
S
2
3
O
Me
N+
N
Ac
Ph
S
I–
PhNHCH=NPh
Ac2O, 140 oC
Me
S
N
N+
Me
6
N+
Me
S
S
1
1) Et3N, MeCN, 80 oC
2) IRA-400 (Cl)
N
Br–
N
Br–
Et
O
Et
O
5
4
Scheme 1. Synthesis of SSJ – 127 (1)
Antiprotozoal Activities: IC50 values of SSJ-127 (1) against P. falciparm K1, Trypanosoma cruzi, T.
brucei rhodesiense, Leishmania donovani and L-6 rat skeletal myoblast cell line together with the
selective indexes, determined at Swiss Tropical Institute (STI), are shown in Table 1. SSJ-127 (1)
showed activities at ten ng/mL concentrations against P. falciparm K1 and T. brucei rhodesiense with
good selectivity.

HETEROCYCLES, Vol. 77, No. 1, 2009
209
Table 1. Antiprotozoal and Cytotoxic Activities (IC50 values, µg/mL) of SSJ-127 (1).a
Cytotox.
P. falc.K1
T. cruzi
T. b. rhod.
L. don., axenic
L6
IC50
0.029
SI b
420
IC50
2.41
SI b
5.1
IC50
SI b
554
IC50
SI b
40.1
IC50
0.022
0.304
12.2
aValues indicate the inhibitory concentration of SSJ – 127 in µg/mL that is necessary to achieve 50% growth
inhibition (IC50). Data shown are values from two replicate experiments.
bSelectivity index = (IC50 value for L6)/(IC50 value for P. falciparum, T. cruzi, T. b. rhodesiense, or L. donovani).
Next, in vivo experiments of SSJ-127 (1) were studied using P. berghei, GFP ANKA strain at STI and
using P. berghei, NK 65 strain at Hoshi University, respectively. Single subcutaneous (sc) administration
of 100 mg/kg of SSJ-127 (1) to NMRI mice (femeles) infected with P. berghei, GFP ANAK exhibited
95% suppression after 4 days. A positive result, 40 % suppression, was also obtained by single po
administration of 100 mg/kg of 1 to the infected mice. It was very pleased for us to observe the complete
cure on in vivo test dosing SSJ-127 (1). Namely, tree time sc administrations of 40 mg/kg/d of 1 to ICR
mice (males) infected with P. berghei, NK 65 strain provided 100% suppression and all treated mice have
survived after 18 months. They have grown well and are now very active at Hoshi University.
PK Study: A preliminary pharmacokinetic study using male rats, Crl:CD(SD), was carried out by
intravenous (iv) and sc administrations. The results, analyzed by two-compartmental methods using the
computer program 3P87, are summarized in Table 2. The sc bioavailability of 1 was determined to be
excellent.
Table 2. Pharmacokinetic Parameters of ID-127 (1)
T1/2α
(h)
T1/2β CL
(h) (L/h·kg)
V
T(peak)
(h)
AUC0-24h
(ng×h/mL)
88.08
route
(L/kg)
4.45
66.09
iva
scb
0.055 4.17 11.35
0.79
5.22 4.34
5.36
4606.3
adosage: 1 mg/kg, n=2
bdosage: 20 mg/kg, n=2
SSJ-127 (1) showed characteristic features such as the accumulation into a specific organelle of malaria
parasites with fluorescence and further results of investigation will be published in a future.
ACKNOWLEDGEMENTS
We thank Professor Terumi Nakajima and Professor Toshio Honda, Hoshi University, for their kind
encouragement. We also express our gratitude to Sekisui Medical Co., Ltd. for the PK study.

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1
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7.28-7.08 (m, 1H), 6.72 (s, 1H), 5.52 (d, J = 13.7 Hz, 1H), 4.17 (q, J = 7.0 Hz, 2H), 4.08 (s, 6H),
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