Structure-activity relationship study of asiatic acid derivatives against beta amyloid (Aβ)-induced neurotoxicity

Article abstract of DOI:10.1016/S0960-894X(99)00658-7

8 Semi-synthetic derivatives of asiatic acid were prepared and their protective effect against Aβ-induced neurotoxicity was evaluated. Among them, asiatic acid (2), and 4, 16 showed 97, 92 and 87% of protective effect, respectively.

Full text of DOI:10.1016/S0960-894X(99)00658-7

Bioorganic & Medicinal Chemistry Letters 10 (2000) 119±121
Structure±Activity Relationship Study of Asiatic Acid Derivatives
Against Beta Amyloid (Aꢀ)-induced Neurotoxicity
Sang-sup Jew, a,* Chi-hyoung Yoo, a Doo-yeon Lim, a Heeman Kim, a
Inhee Mook-Jung, b Min Whan Jung, c Heesung Choi, d Young-hoon Jung, e
Heedoo Kim f and Hyeung-geun Park a,*
aCollege of Pharmacy, Seoul National University, San 56-1, Shillim-dong, Kwanak-gu, Seoul 151-742, South Korea
bBrain Disease Research Center, Ajou University, School of Medicine, Suwon, South Korea
cInstitute for Medical Science, Ajou University, School of Medicine, Suwon, South Korea
dDong Kook Pharmaceutical Co. Ltd., Central Research Institute, Jincheon-Gun, Choong Cheong Book-Do, South Korea
eCollege of Pharmacy, Sung Kyun Kwan University, Suwon, South Korea
fCollege of Pharmacy, Sookmyung Woman University, Seoul, South Korea
Received 7 October 1999; accepted 12 November 1999
AbstractÐ8 Semi-synthetic derivatives of asiatic acid were prepared and their protective e€ect against Ab-induced neurotoxicity
was evaluated. Among them, asiatic acid (2), and 4, 16 showed 97, 92 and 87% of protective e€ect, respectively. # 2000 Elsevier
Science Ltd. All rights reserved.
Dementia of Alzheimer's type in the elderly has become
the main social problem. Recently it has been reported
that the most important pathological hallmark of Alz-
heimer's disease (AD) is deposition of senile plaques in
the brain.1 The senile plaque consists of diverse mole-
cules but the major component is beta amyloid (Ab)
protein which is concentrated in the plaque core.2±4
Based on these results, the abnormal overproduction of
Ab has been proposed as a cause of AD.5,6
C(23); an ole®ne group at C(12); a carboxylic acid
group at C(28). Among these functional groups, the
unusual triol and C(28)-carboxylic acid were modi®ed
and the protective e€ect against Ab-induced neurotoxi-
city was evaluated.
Eight compounds were prepared from asiatic acid (2)
which could be easily obtained from the titrated extract
of Centella asiatica. We adapted the known procedure
5
for the synthesis of 3,13 4,13 14 and 6.15 C(2)-Ketoasiatic
Centella asiatica is one of the herbal plants used in dif-
ferent continents by diverse ancient culture and tribal
groups.7 Historically, the extract has been used as a
wound healing agent,8 and brain tonics for the mentally
retarded.9 The extract has three di€erent triterpenoid
ingredients; asiaticoside (1), asiatic acid (2), and made-
cassic acid (3) (Fig. 1).10,11 In 1992, the extract has been
patented as a dementia treating agent and cognitive
enhancer.12 In this paper, the primary structure activity
relationship (SAR) study of asiatic acid against Ab-
induced neurotoxicity were reported.
acid (9) was prepared from 6 in 3 steps. The direct
oxidation of 6 in the presence of C(28)-CO2H gave 9 in
poor yield, but the corresponding ester (7) could be
oxidized successfully. The treatment of 6 with ethoxy-
methyl chloride in basic condition gave 7. The oxidation
of 7 by using pyridinium chlorochromate followed by
simultaneous deprotection of acetonide and ethoxy-
methyl ester in acidic condition gave 9. C(2)-O-Acetyl-
asiatic acid (13) was prepared from 7 by acetylation
using acetic anhydride in basic condition and the fol-
lowing deprotection of acetonide and ethoxymethyl
ester. In case of octyloxymethyl ester of asiatic acid (11),
the octyloxymethyl ester formation from 6 by using
octyloxymethylchloride followed by deprotection of
acetonide in acidic condition gave 11 (Scheme 1).16
C(2)-Deoxyasiatic acid (16) and C(2),C(3),C(23)-tri-
deoxyasiatic acid (19) were prepared from 7 and 5,
Structurally, asiatic acid (2) has three kinds of func-
tional groups: three hydroxy groups at C(2), C(3) and
*Corresponding authors.
0960-894X/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(99)00658-7

120
S. Jew et al. / Bioorg. Med. Chem. Lett. 10 (2000) 119±121
respectively as shown in Scheme 2.16 The treatment of 7
with CS2, CH3I in basic condition gave the xantate (14).
The reduction of 14 with n-Bu3SnH, followed by
deprotection of acetonide gave 16. Compound 19 could
be obtained by similar method. Compound 5 was con-
verted to trixantate (17) by addition of excess CS2 and
CH3I in basic condition. The reduction of 17, followed
by hydrolysis with lithium bromide in collidine gave 19.
In order to determine the lead compound, the in vitro
protective e€ect against Ab-induced neurotoxicity for
the above asiatic acid derivatives (4±6, 9, 11, 13, 16, 19)
Figure 1.
Scheme 1. Conditions and reagents: (a) DHP, PTSA (cat.), THF, 0 ꢀC, 1 h, 90%, (b) Ac2O, Et3N, CH2Cl2, rt, 3 h, 90%, (c) K2CO3, EtOH, rt, 2 h,
85%, (d) excess CH2N2, 0 ꢀC, 1 h, 100%, (e) 2,2-dimethoxy propane, PTSA (cat.), DMF, rt, 5 h, 95%, (f) EtOCH2Cl, (i-Pr)2NEt, CH2Cl2, rt, 1 h,
95%, (g) PCC, CH2Cl2, rt, 4 h, 82%, (h) 6 N-HCl (cat.), CH3OH, H2O, rt, 2 h, 85%, (i) C8H17OCH2Cl, (i-Pr)2Net, CH2Cl2, rt, 1 h, 90%, (j) 1 N-HCl
(cat.), CH3OH, H2O, 0 ꢀC, 0.5 h, 85%, (k) Ac2O, Et3N, CH2Cl2, rt, 3 h, 85%, (l) 6 N-HCl (cat.), CH3OH, H2O, rt, 2 h, 85%.
Scheme 2. Conditions and reagents: (a) CS2, CH3I, NaH, THF, rt, 2 h, 77%, (b) n-Bu3SnH, toluene, re¯ux, 2 h, 85%, (c) 6 N-HCl (cat.), CH3OH,
H2O, rt, 2 h, 85%, (d) CS2, CH3I, NaH, THF, rt, 2 h, 64%, (e) n-Bu3SnH, toluene, re¯ux, 2 h, 82%, (f) LiBr, collidine, re¯ux, 3 h, 75%.

S. Jew et al. / Bioorg. Med. Chem. Lett. 10 (2000) 119±121
121
Table 1. In vitro protective e€ect against Ab-induced neurotoxicity
for asiatic acid derivatives17
Acknowledgements
This research was supported by the Research Center of
New Drug Development of Seoul National University
and Dong Kook Pharmaceutical Co. Ltd.
Compound
Protective
activity (%)
Compound
Protective
activity (%)
1
2
3
4
5
6
24
97
56
92
58
66
9
50
22
22
87
40
11
13
16
19
References and Notes
1. Hyman, B. T.; Tanzi, R. E. Curr. Op. Neurol. Neurosurg.
1992, 5, 88.
2. Selkoe, D. J. Neuron 1991, 6, 487.
3. Haass, C.; Schlossmacher, M. G.; Hung, A. Y.; Vigi, P. C.;
Mellon, A.; Ostaszewki, B. L.; Lieburg, I.; Koo, E. H.; Shenk,
D.; Teplow, D. B.; Selkoe, D. J. Nature 1992, 359, 322.
4. Furcht, S. J.; Koo, E. H. J. Neuropath. Exp. Neurol. 1994,
52, 640.
5. Gravina, D.; Ho, L.; Eckman, C. B.; Long, K. E.; Otvos, L.;
Younkin, L. H.; Suzuki, N.; Younkin, S. G. J. Biol. Chem.
1995, 270, 7013.
6. Guilian, D.; Haverkamp, L. J.; Yu, J.; Karshin, W.; Torn,
D.; Li, J.; Kazanskaia, A.; Kirkpatric, J.; Rocher, A. E. J.
Biol. Chem. 1998, 273, 29719.
7. Bontems, J. E. Bull. Sci. Pharmacol. 1941, 49, 186.
8. Beljanski, M.; Vapaille, N. Rev. Eur. Etud. Clin. Biol. 1971,
16, 897.
9. Appa Rao, M. V. R.; Srinivasan, K.; Koteshwara Rao, T.
Indian J. Psychiatry 1977, 19, 54.
10. Rastogi, R. P.; Sarka, B.; Dhar, M. L. J. Sci. Industr. Res.
1960, 19B, 252.
11. Inamdar, P. K.; Yeole, R. D.; Ghogare, A. B.; de Souza,
N. J. J. Chromatography 1996, 742, 127.
12. European Patent Application, Hoechst Akitiengesellschaft,
EP 0 383171 A2, 1992.
13. Shim, P.-J.; Park, J.-H.; Chang, M.-S.; Lim, M.-J.; Kim,
D.-H.; Jung, Y.-H.; Jew, S.-s.; Park, E.-H.; Kim, H.-D.
Bioorg. Med. Chem. Lett. 1996, 6, 2937.
14. Singh, B.; Rastogil, R. P. Phytochemistry 1968, 7, 1385.
15. Dong Kook Pharmaceutical Co. Ltd. US Patent 9,308,876,
1999.
16. All new compounds gave satisfactory spectroscopic data
consistent with the proposed structures.
17. The general assay method was as the following: after the
pretreatment of asiatic acid derivatives (1 mM) to B103 cells
for 1 h at 37 ꢀC, cell death was induced by addition of Ab25±35
(50 mM) to the culture for 24 h at 37 ꢀC. MTT assay was
employed to quantitify cell survival. The degree of cell survival
was measured based on the absorbance at O.D. 570±630 nm,
using plate reader.
along asiaticoside (1), asiatic acid (2), and madecassic
acid (3) were investigated (Table 1). Inspection of Table
1 revealed several patterns in structure versus activity.
First of all, the free C(28)-CO2H derivative (2, 97%)
showed higher protective activity than methyl, octyloxy-
methyl, and glycosyl ester derivatives (5, 58%; 11, 22%;
1, 24%, respectively). But the tetrahydropyranyl ester
derivative (4, 92%) showed comparable activity with 2
(97%). The dramatic di€erence between 4 and 11 which
both have similar alkyloxymethyl ester group might be
due to the hydrolysis of 4 inside the neuronal cell. Sec-
ondly, the triol group is very important for biological
activity, especially C(3)-OH and C(23)-OH. The C(2)-
O-acetyl derivative (13, 22%) and C(2)-keto derivative
(9, 50%) showed decreased activity versus 2 (97%), but
the C(2)-deoxy derivative (16, 87%) showed comparable
activity. This result suggested that the C(2)-OH is not
quite critical but there is spatial constraint in the bind-
ing process. In case of C(3)-OH and C(23)-OH, the
protection with C(3),C(23)-acetonide (6, 66%) reduced
activity compared with 2 (97%). Deoxygenation of
C(3)-OH and C(23)-OH of 16 reduced the activity by
50% (16, 87%; 19, 40%). The additional hydroxy group
at C(5) in madecassic acid (3, 56%) decreased activity.
These cumulating results indicate that hydrogen bond
interactions might play an important role in binding
process with receptor in neuronal cell. In conclusion,
SAR study was performed with semi-synthetic deriva-
tives of asiatic acid. Among them, 2 (97%), 4 (92%)
and 16 (87%) showed high protective activity against in
vitro Ab-induced neurotoxicity. This ®nding gives us
valuable information to develop new drug for the treat-
ment against Alzheimer's disease. Based on the in vitro
result, the further detailed SAR study and in vivo study
are currently being investigated.