Novel chromene derivatives as TNF-α inhibitors

Article abstract of DOI:10.1016/j.bmcl.2003.08.025

A novel series of chromene-based TNF-α inhibitors is described. These chromene derivatives inhibit bacterial lipopolysaccharide (LPS) stimulated production of TNF-α from human peripheral blood mononuclear cells (PBMC). Additionally, these compounds inhibit NF-kB mediated transcription activation.

Full text of DOI:10.1016/j.bmcl.2003.08.025

Bioorganic& Medicinal Chemistry Letters 13 (2003) 3647–3650
Novel Chromene Derivatives as TNF-ꢀ Inhibitors
Jie-Fei Cheng,a,* Akira Ishikawa,a,b Yoshinori Ono,a,b Thomas Arrheniusa
and Alex Nadzana
aDepartment of Chemistry, Chugai Pharma USA, 6275 Nancy Ridge Dr, San Diego, CA 92121, USA
bDepartment of Chemistry, Chugai Pharmaceuticals, Ltd., Japan
Received 10 June 2003; revised 12 August 2003; accepted 13 August 2003
Abstract—A novel series of chromene-based TNF-a inhibitors is described. These chromene derivatives inhibit bacterial lipopoly-
saccharide (LPS) stimulated production of TNF-a from human peripheral blood mononuclear cells (PBMC). Additionally, these
compounds inhibit NF-kB mediated transcription activation.
# 2003 Elsevier Ltd. All rights reserved.
Tumor Necrosis Factor a, or TNF-a, is a pro-inflam-
matory cytokine secreted by a variety of cells, including
monocytes and macrophages, in response to many
inflammatory stimuli or external cellular stress.1 It is a
key cytokine in the inflammation cascade causing the
production and/or release of other cytokines and
agents. TNF-a exerts its biological effects through
interaction with one of two ubiquitously expressed cell
surface receptors, TNFR1 (p55) and TNFR2 (p75).
Binding of TNF-a to its receptors initiates a series of
parallel protein serine/theroine kinase cascades which
lead to the activation of members of the MAP kinase
superfamily. It also causes activation of the transcrip-
tion factors NF-kB and Jun Kinase.2 NF-kB in turn
regulates the production of many proinflammatory
cytokines including TNF-a and related proteins that are
elevated in immunoinflammatory diseases.3 TNF-a level
and NF-kB transcriptional activity are controlled by a
reciprocal feedback loop. Since excessive or unregulated
TNF-a production has been implicated in mediating or
exacerbating a number of disease states, for example
cachexia and sepsis,4 decreasing TNF-a levels or inhib-
iting NF-kB transcriptional activation constitute valu-
able therapeuticstrategies for the treatment of many
inflammatory, infectious, immunological or malignant
diseases such as rheumatoid arthritis, psoriasis, and
inflammatory bowel disease.5
Macromolecular TNF-a inhibitors, such as soluble
TNF-a receptor6 Enbrel1 and the TNF-a specific
monoclonal antibody7 Remicade1 have been shown to
be useful for the treatment of inflammatory and auto-
immune diseases. They were approved for reducing the
sign and symptom of moderate to severe rheumatoid
arthritis, psoriaticarthritis, and Crohn’s disease. The
efficacy of a number of small molecules8 with anti-
inflammatory activity has been linked to their ability to
lower TNF-a level. Herein, we report a novel series of
chromene-based TNF-a inhibitors.
As part of our effort in searching for small molecule
TNF-a inhibitors, we have identified a novel series of
chromene derivatives as potential HTS leads. The gen-
eral synthesis of these chromene derivatives is shown in
Scheme 1. Knoevenagel condensation of an appro-
priately substituted 2-hydroxyl acetophenone 1, which
was obtained either from commercially available sour-
ces or prepared according to the literature procedure,9
with aryladehyde 2 in the presence of piperidine and
acetic acid provides benzopyrone products 3 in fair to
good yields.10 When R1=H, the condensation is carried
out using lithium hexamethyldisilylamide as a base.
Reduction of the benzopyrone 3 with NaBH4 followed
by acid-promoted dehydration of the resultant alcohol
intermediate give the desired chromene derivatives 4. It
was found that the substitution pattern in the chromene
benzene ring has an important influence on the ability
of the molecules to block TNF-a production. A meth-
oxyl group at the C-7 position and a 3,4,5-trimethoxy-
phenyl group at the C-2 position are the preferred
substituents (data not shown).
*Corresponding author. Tel.: +1-858-535-5903; fax: +1-858-535-
5994; e-mail: jcheng@chungai-pharm.com
0960-894X/$ - see front matter # 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2003.08.025

3648
J.-F. Cheng et al. / Bioorg. Med. Chem. Lett. 13 (2003) 3647–3650
The synthesized compounds were evaluated in LPS-
challenged human peripheral blood mononuclear cells
(PBMC) for their ability to inhibit TNF-a production
using an ELISA assay. The cells were cultured in
RPMI1640 medium supplemented with 5% heat-inacti-
vated fetal calf serum and antibiotics. PBMC (5ꢀ105
cells/mL) in 0.2 mL aliquot are pretreated with drugs in
DMSO for 60 min at 37 ꢁC in 96-well round-bottomed
tissue culture plates. Thereafter, the PBMC in the pre-
sence or absence of compound are stimulated with 1
mg/mL lipopolysaccharide (LPS) from Salmonella min-
nesota R595 at a final concentration of 100 ng/mL.
After overnight culture, the supernatants are harvested
and assayed immediately for TNF-a level. The concen-
tration of TNF-a in the supernatant is determined using
a human TNF-a ELISA Kit. A secondary assay using a
reporter gene system confirmed that these compounds
inhibit NF-kB activation.11 However, a clear correlation
between NF-kB inhibition and TNF-a inhibition was
not observed.
Reduction of the ester 4a with LiAlH4 affords the cor-
responding alcohol derivative 5. Subsequent treatment
with EtBr in the present of NaH provides the ethyl ether
6. Both compounds showed improved inhibitory activ-
ity relative to the parent compounds (Table 1). Amide
or ester formation of the carboxylic acid 7 are accom-
plished using the method of Yamaguchi.12 As can be
seen from Table 1, large groups in the ester or amides
portion are not tolerated. Primary amide (8a) and
methyl ester (9a) are the two best compounds in this
series. Interestingly, the carboxylic acid compound 7
itself is not active in the TNF-a inhibition assay.
Based on the results obtained from the amide and ester
series, the carboxyl acid was converted into other small
groups as shown in Scheme 3. Weinreb amide 10 is
prepared from the carboxylic acid 7. Reduction of the
Weinreb amide with DIBAL affords the corresponding
3-aldehyde derivative 13, which is subsequently con-
verted into its oxime derivative. Similarly, reaction of
Weinreb amide 10 with organolithium reagents or
Gringard reagent furnish the corresponding ketone
derivatives 12. On the other hand, reaction of carboxylic
acid compound 7 with ClSO2NCO affords the corre-
sponding 3-cyano compound 11. The latter is about ten
Starting from compound 4a, a moderate TNF-a inhib-
itor with an IC50 about 7 mM, a series of analogues are
prepared through the carboxylic acid intermediate 7 or
by direct reduction of the ester functionality (Scheme 2).
Scheme 1. General synthesis of chromenes. Reagents and conditions: (a) piperidine/HOAc or lithium hexamethyldisilylamide, THF; (b) (i) NaBH4/
MeOH, rt; (ii) HCl.
Scheme 2. Synthesis of chromene amides and esters. Reagents and conditions: (a) LiAlH4, Ether, rt; (b) EtBr, NaH, THF, rt; (c) NaOH aq rt;
(d) 2,4,6-tricholorobenzoyl chloride, R2R3NH or R4OH.

J.-F. Cheng et al. / Bioorg. Med. Chem. Lett. 13 (2003) 3647–3650
3649
Scheme 3. Synthesis of 3-substituted chromene derivatives. Reagents and conditions: (a) (COCl)2, DMF, CH2Cl2; (b) ClSO2NCO, toluene, reflux;
(c) DIBAL, toluene, ꢂ78 ꢁC–rt; (d) RLi or RMgX, THF, rt; (e) NH2OHHCl, MeOH, Et3N, rt.
Table 1. Representative chromene derivatives as TNF-a inhibitors
examples. A hydrogen bond acceptor may also con-
tribute to the enhancement of the activity at this posi-
tion (e.g., 4b vs 13). It will be interesting to see how the
chirality at C-2 position affects the potency. Given the
roles of TNF-a in inflammatory, infectious, immunolo-
gical or malignant diseases, these compounds may serve
as leads for novel therapeuticagents. Antioxidant such
as 10,11-dihydroxyapporphine13 and caffeic acid ester14
have long been known to inhibit the activation of tran-
scription factors including NF-kB as well as TNF-a
production. These chromene derivatives, with structural
features similar to some of the known antioxidants may
also be useful for elucidating the TNF-a signaling
pathway.
Compd
R
IC50 (mM)
(NF-kB)
IC50 (mM)
(TNF-a)
4a
10
12a
12b
11
13
14
5
–COOEt
–CON(Me)OMe
–COMe
25
11.7
14.1
11.7
3.4
7
31.1
0.1
4.7
0.6
0.6
4.1
2.4
1.1
11.6
2
12
13
>50
0.6
8.1
17.9
41.6
31.3
550
>50
48
–COPr-n
–CN
–CHO
–CH¼NOH
13.5
14.1
>50
21.3
17.7
13.8
11.8
14.1
16.2
>50
>50
>50
>50
25.5
28.4
17.5
>50
>50
>50
–CH2OH
–CH2OEt
Acknowledgements
6
4b
9a
9b
9c
9d
8a
8b
8c
8d
8e
8f
–H
–COOMe
We would like to thank Dr. Peter Simms and Ms.
Cynthia Jeffery at Chugai Pharma USA, LLC for ana-
lytical assistance.
–COOPr-i
–COOBu-t
–COOCH2CH2Ph
–CONH2
–CONHMe
–CONHEt
–CONHPr-i
–CONHBu-n
–CONHBu-t
–CONHPh
–CO–N–Piperidinyl
–CONMe2
–COOH
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