H. E. Master et al. / Bioorg. Med. Chem. Lett. 13 (2003) 1249–1251
1251
Table 1. Inhibition of complement (classical pathway) and hemolytic activity of target molecules
a
b
Compd
R
R1
Complement inhibition IC50 (mM )
Hemolytic activity EC50 (mM)
2
3
4
5
6
7
CHO
CHO
CHO
COOH
COOH
COOH
Me
Et
Ph
Me
Et
Ph
Me
Et
919
1000
1388
NA
>4411
>4000
>3030
2960
NA
2530
1401
1562
631
>2803
>3409
2210
14
15
16
Tetrazole-5-yl
Tetrazole-5-yl
Tetrazole-5-yl
Ph
798
954
Ursolic acid
Oleanolic acid
54.7
76.6
NA, not active (at the highest concentration tested in the assay, 600 mg/mL).
The concentration of compound required to inhibit complement mediated hemolysis of sensitized sheep RBCs by 50% compared to vehicle control.
a
IC50 values were obtained from dose–response curves of percent inhibition.
b
The concentration of compound effective to cause 50% hemolysis in the absence of complement. Values were obtained from dose–response curves
of percent hemolysis.
matic ethers, 5 and 6, show hemolytic activity with no
inhibition of complement activity. However, the m-phen-
oxy benzoic acid (7) showed inhibition of complement
activity with an IC50 of 1400 mM and the compound was
not as effective as 5 and 6 in causing complement inde-
pendent hemolysis. Although, the bioisosteric tetrazoles
Acknowledgements
We thank Dr. Larry Walker, Director, National Centre
for Natural Products Research, School of Pharmacy,
University of Mississippi, MS 38677, USA for the
bioassays.
(
14–16;R=tetrazole-5-yl) caused significant inhibition of
complement activity, m-ethoxy and m-phenoxy (15–16)
were more potent among all the target molecules. They
also showed intrinsic hemolytic property;however, the
EC50 value of hemolysis was several-fold higher than
IC50 value of complement inhibition in the case of 15.
Among these, m-methoxy phenyl tetrazole (14) was not
as active as 15 and 16 in inhibiting complement and did
not have hemolytic activity, unlike 15 and 16.
References and Notes
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Thus, it is evident from the results that the hemolytic
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7
4
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This whole exercise thus reveals the necessary criterion
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In earlier studies, most of the compounds reported to
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9
5
,7,9À11
have cytotoxic properties.
The compounds screened
in this study did not demonstrate any cytotoxic activity, in
vitro, towards human cell lines (cancer as well as normal
noncancerous cells, data not shown) thereby confirming
their safety. Further study is in progress to find safe,
stronger and specific inhibitors of complement activity.
1
1
992;p 199.
0. Patrick, R. A., Johnson, R. E., In Annual Reports in
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