Concise Article
MedChemComm
Conclusions
Among the tested UA analogs in the DPPH radical scavenging
assay, the common structure of active compounds was
hydroxybenzimidazoline or hydroxyindoline. As a result, the
moiety required for the antioxidant activity of UA was 2-CO and
7-NH or 9-NH because 5 and 6 had greater antioxidant activity
than UA. Introduction of 3-NH, 8-CO, and 9-NH moieties to 5
increased the activity. Most active analog was 2a, whose activity
was 150 times higher than that of UA. It is noteworthy that all of
the active compounds in this series were designed as p-ami-
nophenol 10 and hydroquinone 11 derivatives. These data
suggested that the pyrimidine-trione moiety of UA was not
essential and the hydroquinone/p-aminophenol-equivalent
structure was effective to have the antioxidant activity. Among
the synthetic analogs, compounds 1a, 2a and 3a showed
remarkable radical scavenging activity with low cytotoxicity and
sufficient solubility in a neutral buffer solution. These could be
good candidates for preparing a novel potent antioxidant.
Fig. 3 The radical scavenging activity of regioisomer(s) of 2a and 3a. Numbers
3
À1 À1
depict the second-order rate constants (Â 10
M
s
). The relative activity ratio
of 2a and 3a of each isomer(s) was shown in parenthesis.
(Table 1) were within 10–12; thus, we expected that the active
form of these compounds was not an anion.
Although p-aminophenol 10 was most effective on the
radical scavenging ability, most of the phenolic compounds and
1
0 were highly toxic. To show the utility of these synthetic
Acknowledgements
analogs as bioactive antioxidants, cytotoxicity under physio-
logical conditions using human promyeloid leukemia cell lines
This work was supported by Platform for Drug Discovery,
Informatics, and Structural Life Science from the Ministry
of Education, Culture, Sports, Science and Technology,
Japan (MEXT), and High-Tech Research Center project from
MEXT.
9
(HL-60) was investigated. HL-60 cells were exposed to test
compounds for 24 h, and the number of viable cells was
counted using the trypan blue dye method with a Vi-CELL
10
counter. Compounds 1a, 2a, and 3a and UA did not exert
potent cytotoxicity up to 120 mM. In contrast, p-aminophenol 10
and hydroquinone 11 showed remarkable cytotoxicity.
The radical scavenging activity of 1a, 2a, and 3a was higher Notes and references
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1
1 PBS buffer: pH 7.4, aqueous solution containing KCl (200 mg
À1
À1
À1
L
), NaCl (8000 mg L ), KH
2
PO
4
(200 mg L ), and
À1
Fig. 4 Cytotoxicity on the HL-60 cell line.
Na
HPO
(1150 mg L ).
2
4
This journal is ª The Royal Society of Chemistry 2013
Med. Chem. Commun., 2013, 4, 527–529 | 529