3322
Y. Usuki et al. / Bioorg. Med. Chem. Lett. 16 (2006) 3319–3322
Table 3. Oxidative potential of 2, 7–9, UK-2A, AA, and QH2
structure or hydrophobicity of the dilactone ring, as cell
membrane permeability is necessary.
Compound
Ep (mV)
2
+1125
+1141
+1119
This research was partially supported by Grants-in-Aid
for Scientific Research from the Ministry of Education,
Culture, Sports, Science and Technology of Japan (No.
14580615).
7
8
9
+786, +1577
+1108
+1057
UK-2A
AA
QH2
+810, +1402
References and notes
permeability of 2 and 7. The activities of 8 and 9 were
about 1% of that of UK-2A, indicating that these ubi-
quinol analogues do not act as inhibitors of respiration,
even if they permeate into cells. This suggests the possi-
bility that ubiquinol analogues 8 and 9 serve as media-
tors of electron transport.
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Furthermore, cyclic voltammetric measurements were
performed with a BAS-50W electrochemical analyzer
using a conventional three-electrode system, in which a
glassy carbon disk (/ = 3 mm), an Ag|Ag+ (0.01 M) ace-
tonitrile, and a platinum electrode were the working, ref-
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Bu4NPF6 were degassed with Ar prior to the voltammet-
ric measurements at room temperature. The ferrocene/
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dard and the redox potential of the couple was
+200 mV under the above conditions. The voltammo-
grams for compounds 2, 7–9, UK-2A, AA, and ubiqui-
nol (QH2)19 show well-defined oxidation peak(s). The
oxidation potentials are summarized in Table 3. Com-
pounds 2, 7, 8, UK-2A, and AA gave one oxidation
peak at around +1100 mV and no significant correla-
tions between oxidative potential and structure/MIC
were observed. Compounds 9 and QH2 had two
oxidation peaks; the second oxidation potential of
QH2 (+1402 mV) was much lower than that of 9
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