Kava analogues as agents for treatment of periodontal diseases: Synthesis and initial biological evaluation

Article abstract of DOI:10.1016/j.bmcl.2018.05.026

Six kava analogues of the structural type 3-oxocyclohex-1-en-1-yl benzoates (and corresponding benzamides) were synthesized and evaluated for their affect on periodontal deconstruction in collagen anti-body primed oral gavage model of periodontitis. The c

Full text of DOI:10.1016/j.bmcl.2018.05.026

Accepted Manuscript
Kava Analogues as Agents for Treatment of Periodontal Diseases: Synthesis
and Initial Biological Evaluation
Bin Cai, James S. Panek, Salomon Amar
PII:
S0960-894X(18)30428-1
https://doi.org/10.1016/j.bmcl.2018.05.026
BMCL 25843
DOI:
Reference:
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Bioorganic & Medicinal Chemistry Letters
Received Date:
Revised Date:
Accepted Date:
6 February 2018
11 May 2018
12 May 2018
Please cite this article as: Cai, B., Panek, J.S., Amar, S., Kava Analogues as Agents for Treatment of Periodontal
Diseases: Synthesis and Initial Biological Evaluation, Bioorganic & Medicinal Chemistry Letters (2018), doi: https://
doi.org/10.1016/j.bmcl.2018.05.026
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Kava Analogues as Agents for Treatment of
Periodontal Diseases: Synthesis and Initial
Biological Evaluation
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Bin Cai, James S. Panek, and Salomon Amar

Bioorganic & Medicinal Chemistry Letters
Kava Analogues as Agents for Treatment of Periodontal Diseases: Synthesis and
Initial Biological Evaluation
Bin Cai , James S. Panek Salomon Amarb, 
a
a, 
a
Department of Chemistry, Boston University, Metcalf Center for Science and Engineering, 590 Commonwealth Avenue, Boston, Massachusetts 02215, United
States
b
Department of Pharmacology, New York Medical College, Valhalla, NY, United States
ARTICLE INFO
ABSTRACT
Article history:
Received
Revised
Accepted
Available online
Six kava analogues of the structural type 3-oxocyclohex-1-en-1-yl benzoates (and
corresponding benzamides) were synthesized and evaluated for their affect on periodontal
deconstruction in collagen anti-body primed oral gavage model of periodontitis. The compounds
were prepared through an acylation or amidation of the enolizable cyclic 1,3-diketone. We have
learned that three of the analogues are responsible for the reduction of inflammatory cell counts
within soft tissue. These novel kava-like molecules where the lactone is replaced by an α,β-
unsaturated ketone show promise in the prevention and treatment of inflammation and alveolar
bone loss associated with periodontitis.
Keywords:
Kava
Periodontal disease
Cyclohexene benzoate
Buchwald coupling
2
009 Elsevier Ltd. All rights reserved.
Periodontal disease caused by bacterial accumulations or
dental plaque on the teeth is highly prevalent in the United
States. Gingivitis which is the most popular and mild form of
periodontal disease affects 70%-80% of adults in the United
The difficulty with treatment of periodontal disease has been
the fact that there are no effective, orally available small
molecule drugs. Conventional periodontal therapy comprises
oral hygiene instruction and scaling and root planning.
However, systemic or local risk factors such as deep pockets or
1-3
States. The more advanced form is periodontitis with affected
4
9
US adult population over 47%. While gingivitis is
furcations of multirooted teeth may complicate the treatment.
characterized by inflammation of the gums, redness, swelling,
and frequent bleeding, periodontitis is more severe and leads to
To control the inflammation associated with periodontal
disease, many anti-TNF-α drugs have been used as additive
2,3
10,11
tissue damage and alveolar bone loss. Studies in the past 10
years have also indicated correlations between periodontal
disease and various systemic disorders and disease, including
cardiovascular disease, diabetes mellitus, preterm low birth
weight, and osteoporosis. The source of periodontal disease
comes from approximately 500 different bacterial entities and
therapies.
However, risks of such therapies outweigh
potential benefits. Additionally, all current TNF-α blockers are
protein therapeutics, which must be administered parenterally
and cost significantly higher than small molecule drug
formulations. Therefore, there is a pressing need for the
development of effective small
5-8
various human viruses. Among them, three microaerophilic
species (Actinobacillus actinomycetemcomitans, Campylobacter
rectus, and Eikenella corrodens) and seven anaerobic species
molecule therapeutics for the
definitive treatment of periodontal
diseases. In line with our continued
(
Porphyromonas gingivalis, Bacteroides forsythus, Treponema
interest in identifying a novel class of
oral TNF-α modulators, we recently
discovered that Kava, a natural
denticola, Prevotella intermedia, Fusobacterium nucleatum,
Eubacteria, and spirochetes) are frequently identified
periodontal pathogens.
product extract from the Piper
methysticum plant (in set), and its
—
——


Corresponding author. Tel.: +1-617-353-2484; fax: +1-617-353-6466; e-mail: panek@bu.edu
Corresponding author. Tel.: +1-914-594-3036; fax: +1-914-594-4362; e-mail: salomon_amar@nymc.edu
1

several analogues exhibited significant TNF-α reduction in vitro
and 2), and through these structural modifications we have
gained enhanced bioactivity.
2
,12
and in vivo. Moreover, our recent study of kava on a
conventional oral gavage model of periodontitis has indicated
kava as a useful compound in reducing alveolar bone loss and
The synthetic approach towards compounds 13 and 14 is
19
3
based on the O-acylation of the highly enolizable cyclic 1,3-
inflammation in P. gingivalis-induced periodontitis. The major
diketones. Accordingly, treatment of 1,2-dichloroethane
solution of commercially available 1,3-cyclohexanedione with
various benzoyl chlorides in the presence of pyridine efficiently
provided the O-acylated enol derivatives 13 and 14 (Scheme 1).
They were further transformed to β-ketoesters through the C-
acylation of in situ generated lithium enolate using Mander’s
chemical components of kava are seven lactones (Figure 1A)
and three chalcones (Figure 1B). Although previous studies
1
3
2,12
have demonstrated kava, a mixture of the ten major compounds,
as a potent agent on TNF-α reduction, limitations including
hepatic, neurologic, and dermatological toxicity, solubility and
14
stability in vivo and cell permeability present opportunity for
further medicinal chemistry optimization.
20
reagent (ethyl cyanoformate). Thus, compound 14 was treated
with lithium bis(trimethylsilyl)amide solution (LHMDS) to
generate lithium enolates. The subsequent nucleophilic attack
Figure 1. The major components of kava. The relative
(C-acylation) of the enolate with ethyl cyanoformate was
facilitated by additive 1,3-Dimethyl-3,4,5,6-tetrahydro-2(1H)-
pyrimidinone (DMPU), cleanly providing compound 15
(Scheme 1) without trace of O-acylation products.
Scheme 1. Synthesis of compounds 13-15. Reagents and
conditions: (i) pyridine, DCE, rt; (ii) ethyl cyanoformate,
o
abundance of the major constituents are shown in parentheses.
DMPU, LHMDS, THF, -78 C, 1h.
A widely used and well-established method for early-stage
discovery chemistry to optimize potent compounds to achieve
drug-like properties is the structure–activity-relationship (SAR)
study. In the present study, the correlations between the
structural features of designed analogues and biological
properties and/or activities of targets are presented. These
correlations often provide useful information for specific
interactions between the substructures of compounds and
biological systems. More importantly, efforts are directed to
identify sites of the molecules that can tolerate modifications
without losing significant activities while displaying a range of
potencies. Through the chemical modifications of these sites,
compounds are modified in order to improve potency and
Encouraged by the screening results that electron-donating
group on the aryl ring plays a beneficial role in TNF-α
2
reduction and the assumption that amide would be more stable
in vivo, we synthesized three enamides (17-19) utilizing
21-25
Buchwald’s copper-mediated coupling
between vinyl iodide
16 and commercially available benzamides. Treatment of
commercially available 5,5-dimethylcyclohexane-1, 3-dione
with triphenylphosphine, iodine, and triethylamine in
acetonitrile efficiently afforded vinyl iodide 16, which
subsequently participated in a copper-mediated cross-coupling
reaction (Scheme 2). Thus, 16 and the benzamides were
successfully coupled in the presence of substoicometric
2 3
amounts of CuI, N, N-dimethylglycine, and CS CO to produce
2
pharmaceutical properties. Our previous efforts on the initial
three enamides 17-19 respectfully. Unfortunately the series of
SAR study generated a set of kavain analogues. Interestingly,
among them, one ring-opened analogue which bears an α,β-
unsaturated ester surprisingly showed ≥ 50% suppression of
15-17
TNF-α secretion. Additionally, medicinal chemistry
efforts
have pointed out the effect of the methyl group (and 4,4-
dimethyl substitution in compounds 13-15) in improving
potency in drug discovery. In light of these findings, the present
work details our synthesis of newly designed analogues to
explore the above factors, preliminary structure-activity-
relationship (SAR) study, evaluation of these analogues (not
sure about biological term), and identification of a potent
18
compound kava-241. In that regard, we sought to enhance the
hydrolytic stability of the second generation of kava analogues
by replacing the lactone with an α,β-unsaturated ketone
(Scheme 1). The structural variations allowed the rapid
production of six cyclohexanones substituted with a benzoate or
benzamide at the C6-position of the cyclic enone (Schemes 1
2

vinyl amides proved to be inactive in the initial TNF-
production. assay, which of course requires further evaluation.
Acknowledgments
We gratefully acknowledge financial support from the NIH
grants RO1HL076801 and RO1DE014079 to SA. We thank Dr.
Paul Ralifo and Dr. Norman Lee at the Boston University
Chemical Instrumentation Center for helpful discussions and
assistance with NMR and HRMS experiments.
Scheme 2. Synthesis of vinyl amides 17-19. Reagents and
conditions: (i) PPh
CuI, N, N-dimethylglycine, CS
3
, I
2
, NEt
3
, CH
3
CN, rt, 3d. (ii) benzamide,
3
o
2
CO , dioxane, 60 C, 12h.
Given that kava was found to be anti-inflammatory, we
selected our screening strategy involving a cell-based assay
wherein control experiments cells were exposed to P. gingivalis
and responded by producing a potent pro-inflammatory
cytokine TNF-. The analogs in schemes 1 and 2 were screened
using our cell-based assay with two optimal concentrations of
the given compound at concentration depicted in Figure 2 using
parent Kava as a positive control. Briefly, bone-marrow
Supplementary data
Supplementary data associated with this article can be found,
in the online version
References
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3

Highlights



New kava analogues as agents for treatment of
periodontal diseases.
15 was found to significantly reduce P.
gingivalis induced TNF-α production.
Corresponding vinyl amide analogues were
inactive.
4