Chemistry Letters Vol.35, No.11 (2006)
1273
Table 1. Surface properties of C10AS and C10NS at air–water
interface
exponentially at the higher concentrations and approaches to
53% inhibition, as shown in Figure 2. C10AS exhibits the higher
antipeptic activity than a reference compound C3AS below the
cmc and the IC50 (concentration which inhibits peptic activity
by 50%) values are 0.31 and 0.91 mmol kgꢁ1, respectively. This
would be caused by a hydrophobic binding of amphiphilic
C10AS to the hydrophobic active pocket of pepsin.11 It is known
that native BSA is unfolded by a cooperative binding of sodium
dodecyl sulfate around a half of its cmc.12 C10AS can also
unfold BSA around 0.55 mmol kgꢁ1. The unfolded BSA can
be digested more easily by pepsin than native BSA. This may
be the cause of decrease in percentage inhibition at the higher
concentrations.
In summary, the surfactant having an azulene moiety,
C10AS, newly synthesized are slightly less surface-active than
its structural isomer, C10NS, probably due to the dipole moment
of azulene moiety. C10AS exhibits the higher antipeptic activity
than its propyl derivative, C3AS, below a half of the cmc, above
which the antipeptic activity of C10AS are weaken probably by
the unfolding of BSA which promotes its digestion by pepsin.
cmc
ꢀcmc
pC20
Acmc
/nm2
Compounds
/mmol kgꢁ1 /mN mꢁ1
C10AS(25 ꢂC)
C10NS(30 ꢂC)9
1.06
0.52
39.8
37.4
3.69 0.620
3.98 0.646
at cmc (ꢀcmc), efficiency in surface tension reduction (pC20: the
negative logarithm of the surfactant concentration required to re-
duce the surface tension of solvent by 20 mN mꢁ1), and surface
area per surfactant molecule (Acmc) obtained from Figure 1 were
summarized in Table 1. These data show that C10AS exhibits
the weaker surface-activity than C10NS. This would be attribut-
ed to the higher hydrophilicity of C10AS due to the dipole mo-
ment of azulene ring. The smaller Acmc may be caused by the at-
tractive interaction between the azulene ring dipole moments.
The antipeptic activity of C10AS was measured with the
same method as Yanagisawa et al.10 A mixture of 1.0 mL of
5 mg/mL bovine serum albumin (BSA), 0.3 mL of 1 M HCl
and 2.0 mL of C10AS solution with various concentrations
was preincubated at 37 ꢂC for 5 min. Zero point five mL of pep-
sin derived from porcine stomach mucosa (10 mg/mL of
0.5 M HCl) was added to the mixture and incubated at 37 ꢂC
for 10 min. Two point zero mL of 10% trichloroacetic acid
was then added to stop the enzyme reaction. Zero point one
mL of a supernatant obtained after centrifugation at 3000–
3500 rpm for 10 min was added to 2.0 mL of 0.2 M borate buffer
solution (pH 9.0). To determine the amount of digested BSA
(that is, hydrolysed BSA) fluorescence intensity at 475 nm was
measured 5 min after 1.0 mL of fluorescamine solution
(0.3 mg/mL of acetone) was added to the supernatant solution.
The percentage inhibition was calculated by
A part of this work was supported by Foundation of
Nagano Prefecture for Promoting Science, Japan. We thank
Mr. T. Yamada for melting point measurements.
References and Notes
1
2
3
¨
4
5
S. Okabe, K. Takeuchi, K. Honda, K. Takagi, Pharmacomet-
rics 1975, 9, 31.
%inhibition ¼ 100 ꢃ ðA ꢁ BÞ=A
ð1Þ
where A and B is the amount of digested BSA without and with
C10AS, respectively.
The percentage inhibition of C10AS increases linearly
with its concentration below 0.55 mmol kgꢁ1, but it decreases
6
7
T. Yanagisawa, S. Wakabayashi, T. Tomiyama, M. Yasunami,
K. Takase, Chem. Pharm. Bull. 1988, 36, 641.
Mp 140–142 ꢂC (dec.). 1H NMR (D2O, 400 MHz) ꢁ 0.85 (3H,
t, CH2CH2(CH2)7CH3), 1.09 (14H, brs, CH2CH2(CH2)7CH3),
1.40 (2H, quint, CH2CH2(CH2)7CH3), 2.58 (2H, t, CH2CH2-
(CH2)7CH3), 6.43 (1H, dd, H-5), 6.96–7.06 (2H, m, H-6 and
H-7), 7.68 (1H, d, H-4), 7.90 (1H, s, H-2), 8.68 (1H, d, H-8).
13C NMR (D2O, 100 MHz) ꢁ 16.8, 25.5, 29.6, 32.3, 32.6,
34.1, 34.8, 126.4, 128.1, 129.3, 131.1, 137.1, 137.7, 138.6,
139.2, 140.5, 141.7. IR (KBr) 2921, 2850, 1573, 1390, 1180,
1064, 887, 744, 730 cmꢁ1. MS m/z (relative intensity) 268
(8.6), 141 (100), 43 (23.5).
100
80
60
40
20
0
8
Mp 160–162 ꢂC (dec.). 1H NMR (D2O, 400 MHz) ꢁ 0.91 (3H,
t, CH2CH2CH3), 1.72 (2H, sext, CH2CH2CH3), 2.97 (2H, t,
CH2CH2CH3), 7.36 (1H, dd, H-5), 7.43 (1H, dd, H-7), 7.81
(1H, dd, H-6), 8.02 (1H, s, H-2), 8.49 (1H, d, H-4), 8.92
(1H, d, H-8). 13C NMR (D2O, 100 MHz) ꢁ 16.1, 26.8, 31.1,
127.9, 128.3, 132.3, 137.7, 138.6, 139.0, 139.2, 141.2, 142.7.
IR (KBr) 2950, 2923, 2865, 1573, 1463, 1450, 1419, 1409,
1388, 1178, 1145, 1089, 1035, 877, 728 cmꢁ1
.
9
X. Tan, L. Zhang, S. Zhao, J. Yu, J. An, J. Surfact. Deterg.
2004, 7, 135.
10 T. Yanagisawa, K. Kosakai, C. Izawa, T. Tomiyama, M.
Yasunami, Chem. Pharm. Bull. 1991, 39, 2429.
11 N. S. Andreeva, A. S. Zdanov, A. E. Gustchina, A. A. Fedorov,
J. Biol. Chem. 1984, 259, 11353.
12 T. Takagi, K. Tsujii, K. Shirahama, J. Biochem. 1975, 77, 939.
0
1
2
3
4
5
m / mmol kg−1
Figure 2. Antipeptic activity of C10AS ( ) and C3AS ( ). The
dashed line represents the cmc of C10AS at 25 ꢂC.