Synthesis of norlignans and in vitro inhibitory activity of antigen-induced degranulation

Article abstract of DOI:10.1016/j.bmcl.2012.04.033

The synthesis and biological evaluation of a series of novel norlignans are described. Norlignans were evaluated for their inhibitory activity on the release of β-hexosaminidase, a marker of degranulation, from RBL-2H3 cells induced by the IgE-antigen com

Full text of DOI:10.1016/j.bmcl.2012.04.033

Bioorganic & Medicinal Chemistry Letters 22 (2012) 3653–3655
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Bioorganic & Medicinal Chemistry Letters
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Synthesis of norlignans and in vitro inhibitory activity of antigen-induced
degranulation
Eonjeong Park a, Yoon Jung Yang b, Aejin Kim a, Jong Hwan Kwak c, Young Hoon Jung c,
a,
Se Chan Kang b, , In Su Kim
⇑
⇑
a College of Pharmacy, Kyung Hee University, Seoul 130-701, Republic of Korea
b Department of Life Science, Gachon University, Seongnam 461-701, Republic of Korea
c School of Pharmacy, Sungkyunkwan University, Suwon 440-746, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
The synthesis and biological evaluation of a series of novel norlignans are described. Norlignans were
evaluated for their inhibitory activity on the release of b-hexosaminidase, a marker of degranulation,
from RBL-2H3 cells induced by the IgE–antigen complex. The results showed that norlignans 4c and
Received 21 March 2012
Revised 4 April 2012
Accepted 7 April 2012
Available online 13 April 2012
4e potently inhibited degranulation, with IC50 values of 18.3 and 17.9 lM, respectively.
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
Norlignan
Degranulation
Allergy
IgE
Derivative
Mast cells and basophils play crucial roles in type I allergy in-
duced by antigens such as foods, dust, mites, pollen, cosmetics
and medicines.1–3 When the human body is stimulated by anti-
gens, B cells and plasma cells produce and release antigen-specific
immunoglobulin E (IgE) antibodies that bind to high affinity IgE
Norlignans are abundant in the heartwood of many coniferous
trees and in some monocotyledonous plants,9 and possess a wide
spectrum of biological activities such as anti-cancer/anti-inflam-
matory,10 anti-complement,11 anti-fungal activity,12 testosterone
5a
-reductase inhibition,13 and cyclic AMP phosphodiesterase
receptors (Fc
phils.4 The interactions of multivalent antigens with IgE on the sur-
faces of mast cells lead to cross-linking of the Fc RI–IgE complex,
eRI) on the surface membranes of mast cells or baso-
inhibition.14
Naturally occurring norlignan are a class of natural phenolic
e
compounds with diphenylpentane carbon skeletons (C6–C5–C6).
Hinokiresinol (1a), the E-isomer of nyasol (2), is a typical example
of such a norlignan (Fig. 1). Hinokiresinol (1a) was first isolated
from the heartwood of Chamaecyparis obtuse in 1965,15 and was
found to display appreciable estrogen receptor binding activity16
and some antiplasmodial activity.17
We recently found that nyasol (2) and its derivatives, isolated
from Anemarrhena asphodeloides, act as powerful inhibitors of anti-
gen-induced degranulation, and have the potential to be useful ther-
apies for allergic disorders such as asthma and atopic dermatitis.18
In view of these interesting biological activities of norlignans, we re-
port here the inhibitory activity of hinokiresionol derivatives includ-
ing synthetic intermediates on antigen-induced degranulation.
General routes for the preparation of hinokiresinol derivatives
are outlined in Scheme 1. Chalcones 3a–d, prepared from the
corresponding acetophenones and aldehydes through Claisen–
Schmidt condensation, were smoothly converted to b-vinyl
ketones 4a–d by the addition of Grignard reagent in the presence
of CuI. The reduction of the ketones 4a–d with NaBH4 yielded
the alcohols 5a–d, which were reacted with 1 M HCl to produce
and triggers degranulation, the immediate release of granules con-
taining histamine and serotonin as potent inflammatory media-
tors.5 These mediators induce a variety of biological processes,
including inflammation of surrounding tissues, vasodilation,
mucous secretion, and bronchoconstriction. b-Hexosaminidase
enzyme, which is stored in the secretory granules of mast cells,
is released concomitantly with histamine when mast cells are
immunologically activated.6 The activity of b-hexosaminidase re-
lease into the medium has therefore been used as a marker of mast
cell degranulation.7 Rat basophilic leukemia 2H3 (RBL-2H3) cells,
tumor analog of mast cells, have been used as mast cell models
in vitro for screening the effects of unknown compounds on hista-
mine release and b-hexosaminidase release activity.8
⇑
Corresponding authors. Tel.: +82 31 750 8826; fax: +82 31 750 8984 (S.C.K.);
tel.: +82 2 961 0475; fax: +82 2 966 3885 (I.S.K.).
E-mail addresses: sckang73@gachon.ac.kr (S.C. Kang), insukim@khu.ac.kr (I.S.
Kim).
0960-894X/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bmcl.2012.04.033

3654
E. Park et al. / Bioorg. Med. Chem. Lett. 22 (2012) 3653–3655
determined by the characterization of spectroscopic data (1H and
13C NMR) and mass spectroscopy analysis.
HO
The inhibitory activity of antigen-induced degranulation by
synthesized norlignans was tested in an in vitro b-hexosaminidase
release inhibition assay using RBL-2H3 cells stimulated by DNP-
BSA, according to described protocols,19 and the results of their
inhibitory activities are summarized in Figure 2. 1,3-Bis(4-
hydroxyphenyl)pent-4-en-1-one (4a) inhibited 50% of b-hexosa-
HO
OH
OH
hinokiresinol (1a)
nyasol (2)
Figure 1. Structures of hinokiresinol (1a) and nyasol (2).
minidase release activity at a concentration of 34.6 lM. On the
hinokiresinol derivatives 1a–d with high trans-stereoselectivity
(trans:cis = 20 > 1). The structures of synthesized compounds were
other hand, compound 4b with a conversion of the bis-hydroxyl
groups in 4a to bis-methoxy groups had lower activity
O
O
NaBH4
vinylMgBr, CuI
R2
R2
R1
R1
THF, 0 oC
EtOH, rt
4a-d
3a-d
OH
1 M HCl
R2
R2
R1
R1
MeOH, 60 oC
5a-d
1a-d
Scheme 1. Strategy for the synthesis of hinokiresinol derivatives.
A-ring
HO
B-ring
OH
O
OH
HO
OH
HO
OH
4a, IC50 = 34.6 µM
5a, IC50 > 200 µM
1a, IC50 = 55.2 µM
O
OH
MeO
OMe MeO
OMe MeO
OMe
OH
4b
µ
5b
µ
M
1b
µ
, IC50 > 200 M
, IC50 = 88.5
O
M
, IC50 > 200
OH
OH
OH
HO
HO
HO
4c, IC50 = 18.3 µM
5c, IC50 = 34.1 µM
1c, IC50 = 55.6 µM
O
OH
OMe
MeO
OMe
MeO
OMe
MeO
4d,
5d,
1d
, IC50 > 200 µM
IC50 = 85.4 µM
IC50 > 200 µM
O
S
ketotifene (6)
IC50 = 35.2 µM
N
H3C
Figure 2. Structures and inhibitory activities of norlignans (1a–d, 4a–d, and 5a–d) and ketotifene (6) on b-hexosaminidase release from RBL-2H3 cells stimulated by DNP–
BSA.

E. Park et al. / Bioorg. Med. Chem. Lett. 22 (2012) 3653–3655
3655
Acknowledgments
O
O
OMe
OH
This work was supported by National Research Foundation of
Korea (No. 2010-0002465) funded by the Ministry of Education,
Science and Technology.
HO
MeO
4e, IC50 = 17.9 µM
4f, IC50 = 90.5 µM
Figure 3. Structures and inhibitory activities of compounds 4e and 4f on b-
hexosaminidase release from RBL-2H3 cells stimulated by DNP–BSA.
Supplementary data
Supplementary data associated with this article can be found,
in the online version, at http://dx.doi.org/10.1016/j.bmcl.
2012.04.033.
(IC50 = 88.5
sponding compounds 4a and 4b, showed no activity, even though
at a high concentration (>200 M). Hinokiresinol (1a) and dimeth-
lM). The alcohols 5a and 5b, prepared from the corre-
l
ylhinokiresinol (1b) were relatively less effective than norlignan 4a
for b-hexosaminidase release inhibition. To investigate the effects
of B-ring substituents of 4a, m-hydroxylated derivatives (1c, 4c
and 5c) and m-methoxylated derivatives (1d, 4d and 5d) were
examined for inhibitory activity of b-hexosaminidase release. As
shown in Figure 2, norlignan 4c displayed the most potent activity
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In conclusion, we synthesized various norlignans and evaluated
their inhibitory activities against b-hexosaminidase release from
RBL-2H3 cells stimulated by DNP-BSA. In general, the b-vinyl
ketone series were more potent than the b-vinyl alcohol and
hinokiresinol series. In particular, b-vinyl ketones 4c and 4e
showed about twofold stronger inhibitory activity than the well-
known anti-allergic drug ketotifen. These results show that b-vinyl
ketones represent a new class of strong b-hexosaminidase release
inhibitors. Further synthesis and biological evaluation of function-
alized b-vinyl ketones are currently under way to elucidate their
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