Identification of a novel boron-containing antibacterial agent (AN0128) with anti-inflammatory activity, for the potential treatment of cutaneous diseases

Article abstract of DOI:10.1016/j.bmcl.2006.08.130

A series of borinic acid picolinate esters were synthesized and screened for their minimum inhibitory concentration (MIC) against Gram-positive and -negative bacteria. Our lead compounds were then screened for anti-inflammatory activity. From these studie

Full text of DOI:10.1016/j.bmcl.2006.08.130

Bioorganic & Medicinal Chemistry Letters 16 (2006) 5963–5967
Identification of a novel boron-containing antibacterial agent
(AN0128) with anti-inflammatory activity, for the potential
treatment of cutaneous diseases
Stephen J. Baker,a,* Tsutomu Akama,a Yong-Kang Zhang,a Vittorio Sauro,b
Chetan Pandit,b Rajeshwar Singh,b Maureen Kully,b Jehangir Khan,b Jacob J. Plattner,a
Stephen J. Benkovic,c Ving Leea, and Kirk R. Maplesa
aAnacor Pharmaceuticals, Inc., 1060 E. Meadow Circle, Palo Alto, CA 94303, USA
bNAEJA Pharmaceutical, Inc., 4290-91A Street, Edmonton, Alta., Canada T6E 5V2
c414 Wartik Laboratory, Pennsylvania State University, University Park, PA 16802, USA
Received 11 July 2006; revised 30 August 2006; accepted 31 August 2006
Available online 25 September 2006
Abstract—A series of borinic acid picolinate esters were synthesized and screened for their minimum inhibitory concentration (MIC)
against Gram-positive and -negative bacteria. Our lead compounds were then screened for anti-inflammatory activity. From these
studies, we identified 3-hydroxypyridine-2-carbonyloxy-bis(3-chloro-4-methylphenyl)borane (2g, AN0128) as having the best com-
bination of anti-bacterial and anti-inflammatory activities. This compound is now in clinical development for dermatological
conditions.
Ó 2006 Elsevier Ltd. All rights reserved.
Atopic dermatitis (AD), or eczema, is an inflammatory
disease affecting around 10–20% of children and 1–3%
of adults.1 It is commonly characterized by flaky, itchy
skin and sufferers will often scratch the affected area un-
til it bleeds, compromising skin barrier function and
causing bacterial infection. In 90% of cases there is a
bacterial component involving the Gram-positive bacte-
rium Staphylococcus aureus.2 AD is caused by type 2
helper T (Th2) cells involved in the allergic response
and is aggravated by allergens contacting the skin.2
Depending on the severity of the condition, the primary
treatment is management of environmental factors
along with administration of topical or systemic cortico-
steroids to reduce inflammation.3 However, steroids are
known to have a number of side effects and their chronic
use is not without risk. Other treatments include the cal-
cineurin inhibitors tacrolimus (FK-506)2 and picroli-
mus.2 These drugs inhibit production of Th2
cytokines, but also Th1 cytokines, which are involved
in immune response. Recently, the US-FDA issued a
public-health advisory for these treatments.4
Since a bacterial component exists in most cases of AD,
parallel treatment with antibacterial and anti-inflamma-
tory agents produced an improved clinical response.5
Therefore, it would be desirable to develop a single drug
that possesses both these activities and has a superior
safety profile.
We previously reported a new class of antibacterial
agents, borinic acid quinoline esters (1).6 In this report,
we describe a related class, borinic acid picolinate esters
(2) and the identification of a new antibacterial agent,
3-hydroxypyridine-2-carbonyloxy-bis(3-chloro-4-methyl-
phenyl)borane (2g), which has additional activity
against pro-inflammatory cytokines. This combination
of activities is ideal for the treatment of AD and
also acne, where the inflammatory response is mediated
by the anaerobic bacterium, Propionobacterium acnes
(Fig. 1).
Keywords: Atopic dermatitis; Antibacterial activity; Borinic acid pic-
olinate ester; Structure–activity relationship.
*
Corresponding author. Tel.: +1 650 739 0711; fax: +1 650 739
0139; e-mail: sbaker@anacor.com
Borinic acid picolinate esters (2), were synthesized as
outlined in Scheme 1. Symmetrical borinic acids (5,
Present address: Adesis, Inc., 27 McCullough Drive, New Castle, DE
19720, USA.
0960-894X/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2006.08.130

5964
S. J. Baker et al. / Bioorg. Med. Chem. Lett. 16 (2006) 5963–5967
In general, these borinic acid picolinate esters (2) were
R1
found to be easy to handle and required no specialized
equipment. We could purify the intermediate borinic
acids (5) using standard column chromatography condi-
tions and we found their esters (2) to be very stable un-
der most conditions. These esters (2) can be stored at
room temperature for prolonged periods.
R2
B
O
N
O
N
O
B
R1
R1
R3
2
1
Figure 1. Diphenylborinic acid ester complexes.
Compounds were screened for their minimum inhibitory
concentration (MIC) against Gram-positive and -nega-
tive bacteria. The results are given in Table 1. We iden-
tified two initial lead compounds. Both possessed a
symmetrical borinic acid moiety containing a 3- or 4-
chloro-substituent on each ring and a 3-hydroxy group
on the picolinic acid unit giving 2a or 2b, respectively.
These had reasonable activity against all pathogens.
The bis(4-chlorophenyl) derivative was slightly more ac-
tive against Staphylococcus epidermidis, P. acnes, and
Bacillus subtilis, however, the bis(3-chlorophenyl) deriv-
ative was more active against S. aureus (Table 1). We
first set out to determine the SAR of the diphenyl bori-
nic acid unit by substituting R2 with various groups.
Substitution of one chlorophenyl group of either 2a or
2b with a pyridin-3-yl group to give 2c and 2d, respec-
tively, essentially eliminated all activity against Gram
positive bacteria, even when the chloro group was intro-
duced back in the same place on the pyridine ring (2e).
Interestingly, when R2 was thiophen-3-yl (2f) activity
was lost only against S. aureus and S. epidermidis. When
methyl groups were added to the 4-position of 2a, to
give 2g, activity was increased against most strains
except Haemophilus influenzae, where activity was lost
(Table 1). Since activity against Gram-positive patho-
gens was most important to us, 2g became our new lead
compound. We investigated the effect of adding alkyl
groups at R2 and synthesized the methyl (2h) and phen-
ethyl (2i) derivatives of 2g. The methyl derivative (2h)
was less active but showed the similar activity profile
to the thiophene derivative (2f). The phenethyl deriva-
tive showed remarkably similar activity to 2g, however,
stability studies found that these alkyl derivatives were
not as stable as the diphenyl borinic acid picolinate ester
R2 = R1–Ph) were synthesized by Method A. Two molar
equivalents of an arylmagnesium bromide (3,
X = MgBr) was treated with one molar equivalent of
trimethylborate under anhydrous conditions. Alterna-
tively, 5 (R2 = R1–Ph) was synthesized by treating two
molar equivalents of an arylhalide (3, X = Br or I) with
either butyllithium or isopropylmagnesium chloride fol-
lowed by one molar equivalent of trimethylborate under
anhydrous conditions to give the borinic acid (5,
R2 = R1–Ph). Non-symmetrical borinic acids (5,
R2 5 R1–Ph) were prepared using Method B. Boronic
acid esters (4, R 5 H) were either purchased commer-
cially or prepared by treating the corresponding boronic
acid (4, R = H) with ethylene glycol and heating to re-
flux in THF or toluene to yield boronic acid ethylene
glycol esters. If the boronic acid (4, R = H) was not
commercially available then it was prepared by treating
the arylanion of 3 with an equimolar amount of trimeth-
ylborate. The boronic acid esters of (4) were treated with
Grignard reagents or aryllithiums to give the borinic
acid (5). When R2 of the borinic acid (5) was (substitut-
ed)pyridyl then butyllithium was added slowly to the
corresponding bromopyridine in the presence of the gly-
col esters of 4 at À78 °C.7 The borinic acids (5) were
usually taken onto the final step as a crude mixture,
but occasionally they were purified by column chroma-
tography. In the final step the borinic acid (5) was heat-
ed to reflux with a picolinic acid in a mixture of ethanol/
water to give the borinic acid picolinate esters (2a–x),
which usually precipitated from the solution upon
cooling.8
X
(a) or (b)
Method A
Method B
R1
R2
B
3
X = MgBr, Br, or I
OH
R1
OR
B
5
(c) or (d)
R2
OR
4
R2
B
O
N
O
(e)
R1
R3
2
Scheme 1. Synthesis of borinic acid picolinate esters (2). Reagents and conditions: (a) B(OMe)3 (0.5 equiv), THF, 0 °C to rt (when X = MgBr); (b)
BuLi, B(OMe)3 (0.5 equiv), THF, À78 °C to rt (when X = Br); (c) 3 (X = MgBr), THF, 0 °C to rt; (d) 3 (X = Br), BuLi, THF, À78 °C to rt; (e) R3-
picolinic acid, EtOH, water, reflux.

S. J. Baker et al. / Bioorg. Med. Chem. Lett. 16 (2006) 5963–5967
5965
Table 1. Minimum inhibitory concentration (MIC, lg/mL) results for compounds 2 containing a 3-hydroxypicolinic acid moiety
R2
O
N
O
B
OH
R1
Compound
Method of synthesisa R1
R2
S. aureus S. epidermidis P. acnes B. subtilis H. influenzae
Erythromycin
0.5
0.15
8
0.1
10
0.1
16
4
16
2a
2b
2c
2d
2e
2f
A
A
B
B
B
B
A
B
B
A
B
B
A
A
A
B
A
3-Cl
4-Cl
3-Cl–Ph
4-Cl–Ph
60.125
4
16
64
32
32
1
1
32
1
1
16
32
3-Cl
4-Cl
Pyridin-3-yl
Pyridin-3-yl
nt
nt
nt
nt
nt
nt
32
32
32
16
32
4-Cl
3-Cl
2-Cl-pyridin-5-yl
Thiophen-3-yl
3-Cl–4-Me–Ph
4-Me
10
16
1
32
2g
2h
2i
3-Cl–4-Me
3-Cl–4-Me
3-Cl–4-Me
3-F
0.5
0.3
>64
32
32
0.5
>64
8
32
1
10
1
16
1
Phenethyl
3-F–Ph
>64
>64
>64
>64
4
2j
>64
8
>100
3
>64
4
2k
2l
3-Cl
3-Cl
3-SMe–Ph
2-Me–Ph
8
8
3
4
2m
2n
2o
2p
2q
3-Cl–4-F 3-Cl–4-F–Ph
3-Cl–4-OEt 3-Cl–4-OEt–Ph
3-Cl–4-NMe2 3-Cl–4-NMe2–Ph
1
8
3
8
2
2
1
nt
2
>64
>64
>64
16
32
4
32
2
64
2
3-Cl–4-Me
4-Cl–2-Me
4-Me–Ph
4-Cl–2-Me–Ph
3
0.3
4
2
0.5
a Refer to Scheme 1; nt, not tested.
(2g) (unpublished data) and so this substitution was not
considered for further development. From these results
we concluded that a phenyl group at R2 would be the
best for activity.
substituent on both phenyl rings gave the most potent
activity.
In a final study, we investigated the importance of the
substituent on the pyridine ring of picolinic acid. The
results are shown in Table 2. We kept the bis(3-chlo-
ro-4-methyl)borinic acid unit constant while modifying
the 3-hydroxy group on the picolinic acid part of 2g.
Removal of the 3-hydroxy group, to give 2r, led to
a loss of activity except against S. aureus, where the
activity remained approximately equal. Since the 3-hy-
droxy group of 2g can form a 6-membered hydrogen
bonded ring with the carbonyl group at the 2-position,
we synthesized the 3-acteoxy derivative (2s) to disrupt
this potential ring structure and to determine if a pro-
ton donor was important for activity. This derivative
was approximately as active as the lead compound
(2g), implying that this hydrogen bonding and the
proton on the 3-hydroxy group may not be important
for activity. Next we increased steric bulk at the 3-po-
sition with a benzoyl group to give 2t. This modifica-
tion was not tolerated by most bacteria tested with a
loss of activity of 30-fold or greater. Placement of a
3-amino group also led to a dramatic loss in activity
except against P. acnes and B. subtilis. Lastly, we were
able to determine the importance of the position of
the substituent using a carboxylic acid group as a
probe. The 3-carboxy derivative (2v) showed better
activity than 2g against S. aureus, and also showed
surprisingly good activity against H. influenzae, how-
ever, it was not so effective against S. epidermidis
and P. acnes. As the carboxy group was moved to
the 4- and 5-positions, giving 2w and 2x, respectively,
activity was approximately equivalent to 2v. We con-
cluded that the 3-hydroxy group was optimal for
Next, we investigated the SAR of substituents on the
diphenylborinic acid moiety, using the bis(3-chlorophe-
nyl) (2a) and bis(3-chloro-4-methylphenyl) (2g) deriva-
tives as leads. Initially, we replaced the 3-chloro- groups
of 2a with fluoro groups, to give 2j, however, this simple,
homologous substitution led to a total eradication of
antibacterial activity against all strains tested. Replace-
ment of one 3-chloro group of 2a with either 3-methylth-
iol group, to give 2k, or 2-methyl, to give 2l, resulted in
reduced activity against S. aureus and H. influenzae, but
increased activity against P. acnes and B. subtilis by
3- to 4-fold. Turning our attention to the bis(3-chloro-
4-methylphenyl) derivative (2g), we replaced the methyl
groups with fluoro groups to give 2m. This showed an 8-
to 16-fold reduction in activity against S. epidermidis, P.
acnes, and B. subtilis but, interestingly, this compound
had greatly increased activity against the Gram-negative
bacterium H. influenzae. Replacement of the 4-methyl
group of 2g with ethoxy groups, to give 2n, showed only
a marginal decrease in activity, while replacement with
dimethylamino groups, to give 2o, rendered the mole-
cule almost inactive. Removal of one 3-chloro group
of 2g, to give 2p, showed reduction in activity of 2- to
10-fold, confirming the importance of both chloro
groups. Finally, moving the methyl- and chloro- groups
to the 2- and 4-positions, respectively, to give 2q,
showed an increase in activity against B. subtilis and
H. influenzae, at the expense of activity against Staphy-
lococcus species, which decreased 4-fold. From this
study we concluded that one methyl and one chloro

5966
S. J. Baker et al. / Bioorg. Med. Chem. Lett. 16 (2006) 5963–5967
Table 2. Minimum inhibitory concentration (MIC, lg/mL) results for compounds 2 containing a bis-(3-chloro-4-methylphenyl) borinic acid moiety
Me
Cl
O
N
O
Cl
B
R3
Me
Compound
R3
S. aureus
S. epidermidis
P. acnes
B. subtilis
H. influenzae
2r
2g
2s
2t
H
3-OH
0.5
1
>64
0.5
1
nt
0.3
1
nt
1
nt
>64
>64
>64
>64
8
3-OAc
3-COPh
3-NH2
3-CO2H
4-CO2H
5-CO2H
2
0.5
64
2
0.5
>64
0.125
2
32
>64
4
30
1
2u
2v
2w
2x
3
8
4
3
nt
8
nt
0.5
8
3
8
nt, not tested.
activity against the major cutaneous bacterial patho-
gens S. aureus and P. acnes.
or IL-4 release. Compounds 2q and 2x showed a similar
profile to that of compound 2g. By comparison, the anti-
biotic erythromycin showed no inhibition of pro-inflam-
matory cytokines. From these studies, compound 2g was
shown to have the best combination of anti-bacterial
and anti-inflammatory activities.
In order to test for concomitant anti-inflammatory
activity, compounds 2g, 2s, 2q, and 2x were evaluated
for their ability to inhibit release of inflammatory cyto-
kines from human peripheral blood mononuclear cells
(PBMCs). Either lipopolysaccharide (LPS, 1 lg/mL),
Concanavalin A (1 lg/mL) or phyto-hemagglutinin
(PHA, 2 lg/mL) was used to induce the release of cyto-
kines from the PBMCs. These compounds were screened
at a concentration of 10 lM. ELISA kits were used to
measure for two pro-inflammatory cytokines, TNF-a
and IL-1b, a Th1 cytokine, IFN-c, and a Th2 cytokine,
IL-4. The inhibition of cytokine release for each com-
pound was recorded as a percent of untreated control9
and the results are shown in Table 3. Compound 2g
showed strong inhibition of the release of pro-inflamma-
tory cytokines but no inhibition of IFN-c or IL-4 re-
lease. Compound 2s showed no inhibition of IL-1b
release, so this was not tested for inhibition of IFN-c
In conclusion, we report the identification and struc-
ture–activity relationship of a new class of antibacterial
agents, diphenylborinic acid picolinate esters. These
compounds primarily show activity against Gram-posi-
tive bacteria and SAR showed the diphenyl borinic acid
moiety was essential for activity. Potency was increased
with the positioning of methyl- and chloro-substituents
on the diphenyl borinic acid moiety in combination with
a 3-hydroxyl group on the pyridine ring. The most po-
tent derivative from this effort was 2g, which was also
found to inhibit the production of pro-inflammatory
cytokines. As a result, 2g (AN0128) was selected as a
clinical candidate and is currently in clinical develop-
ment for the treatment of dermatological diseases
Table 3. Percent inhibition of cytokine release from PBMCs, stimulated with either LPS, Concanavalin A, or PHA, by selected borinic acid
picolinate ester screened at 10 lM
R1
O
N
O
B
R1
R3
a
Compound
R1
R3
TNF-aa
IL-1b (%)
IFN-cb (%)
IL-4c (%)
Erythromycin
3-Cl–4-Me–
3-Cl–4-Me–
4-Cl–2-Me–
3-Cl–4-Me–
22
100
101
101
100
À32
99
nt
nt
2g
2s
3-OH
À20
nt
À21
nt
3-OAc
3-OH
5-CO2H
À49
103
80
2q
2x
15
24
57
9
nt, not tested.
a LPS stimulation (1 lg/mL) for 24 h (%).
b PHA stimulation (2 lg/mL) for 24 h.
c Concanavalin A stimulation (20 lg/mL) for 48 h.

S. J. Baker et al. / Bioorg. Med. Chem. Lett. 16 (2006) 5963–5967
5967
evaporation of the solvent gave 3-chloro-4-methylphenylbo-
ronic acid ethylene glycol ester (5.42 g, 27.6 mmol, 94%),
which was then treated with p-tolylmagnesium bromide
(28 mL, 1.0 M THF solution, 28 mmol) in anhydrous THF
(100 mL) at À78 °C. The cooling bath was removed and the
reaction mixture was stirred for 1 h before a room temper-
ature water bath was placed for additional 2 h of stirring.
The reaction was quenched with 6 M HCl and the resulting
solution was rotary evaporated. The residue was extracted
with ethyl acetate and purified by flash column chromatog-
raphy over silica gel eluted with a mixed solvent of ethyl
acetate and hexane (1:5) giving the desired (3-chloro-4-
methylphenyl)(p-tolyl)borinic acid as a yellow liquid (6.35 g,
26 mmol, 94%). This material was mixed with 3-hydroxypi-
colinic acid (3.07 g, 22.1 mmol) in pure ethanol (150 mL)
and stirred overnight at room temperature. The precipitates
formed were collected by filtration and washed with hexane
to give 2p as a cream solid (6.99 g, 87%): mp 192–194 °C;
ESI-MS (m/z) = 366 (M+H)+, 364 (MÀH)À; 1H NMR
(300 MHz, DMSO-d6) d(ppm) 2.22 (s, 3H), 2.25 (s, 3H), 7.03
(d, J = 7.5 Hz, 2H), 7.09–7.13 (m, 3H), 7.19 (d, J = 6.0 Hz,
2H), 7.90 (d, J = 3.0 Hz, 2H), 8.48–8.49 (m, 1H), 12.10 (br s,
1H). (c) Preparation of 3-hydroxypyridine-2-carbonyloxy-
(3-chlorophenyl)(3-pyridynyl)borane (2c): 3-chloro-phen-
ylboronic acid (1.00 g, 6.09 mmol) was heated to reflux with
ethylene glycol (0.340 mL, 6.09 mmol) in toluene using a
Dean–Stark trap. Rotary evaporation of the solvent gave 3-
chlorophenylboronic acid ethylene glycol ester (3.66 g,
20.0 mmol 91%), which was mixed with 3-bromopyridine
(2.64 g, 16.7 mmol) and THF (100 mL), and treated with n-
BuLi (1.6 M, 12 mL) over 4 h at À78 °C. The mixture was
stirred overnight and allowed to warm to room temperature.
Water was added and the pH was adjusted to 7 with
hydrochloric acid. The mixture was extracted with Et2O
several times. The organic extracts were combined and dried
on anhydrous MgSO4. The solvent was removed under
reduced pressure to give the crude borinic acid (2.05 g),
which was used for the next step without purification. To a
heated solution of the borinic acid (2.05 g, 9.43 mmol) in
EtOH (10 mL) was added 3-hydroxypicolinic acid (1.04 g,
7.50 mmol) in EtOH (7 mL) and water (5 mL). The mixture
was stirred for 4 h while cooling down to room temperature.
Precipitates formed were collected by filtration and dried to
give 2c (1.56 g, 28% overall) as a tan solid: mp > 250 °C;
ESI-MS (m/z) 339, 341, 343 (M+H)+; 1H NMR (300 MHz,
DMSO-d6) d (ppm) 7.07 (m, 1H), 7.16 (dd, J = 7.9, 7.2 Hz,
1H), 7.3–7.4 (m, 4H), 7.86 (dd, J = 7.6, 5.6 Hz, 1H), 8.01
(dd, J = 3.9, 1.9 Hz, 1H), 8.49 (d, J = 7.9 Hz, 1H), 8.6–8.7
(m, 2H).
including acne and atopic dermatitis. Results of these
trials will be described in future publications.
References and notes
1. Schultz-Larsen, F.; Hanifin, J. M. Immunol. Allergy Clin.
North Am. 2002, 22, 1.
2. Yeung, D. Y. M.; Bieber, T. Lancet 2003, 361, 151.
3. Hoare, C.; Li Wan Po, A.; Williams, H. Health Technol.
Assess. 2000, 4(37), 1.
4. <www.fda.gov/cder/drug/advisory/elidel_protopic.htm/>.
5. Leyden, J. J.; Kligman, M. M. Br. J. Dermatol. 1977, 96,
179.
6. Benkovic, S. J.; Baker, S. J.; Alley, M. R. K.; Woo, Y. H.;
Zhang, Y. K.; Akama, T.; Mao, W.; Baboval, J.; Rajag-
opalan, P. T. R.; Wall, M.; Kahng, L. S.; Tavassoli, A.;
Shapiro, L. J. Med. Chem. 2005, 48, 7468.
7. Li, W.; Nelson, D. P.; Jensen, M. S.; Hoerrner, R. S.; Cai,
D.; Larsen, R. D.; Reider, P. J. J. Org. Chem. 2002, 67,
5394.
8. Typical procedures for the synthesis of borinic acid picoli-
nate esters: (a) Preparation of 3-hydroxypyridine-2-carbon-
yloxy-bis(3-chloro-4-methylphenyl)borane (2g, AN0128):
2-chloro-4-iodotoluene (50 g, 200 mmol) was dissolved in
THF (250 mL) at 0 °C and treated with isopropyl magne-
sium chloride (122 mL, 2.0 M in THF, 244 mmol) for 5 h.
Trimethylborate (9.7 g, 93 mmol) was added and the reac-
tion mixture was stirred overnight allowing to warm to
room temperature. The reaction was quenched with 3 N
HCl (100 mL) and the resulting mixture was extracted into
ethyl acetate giving the crude intermediate, bis(3-chloro-4-
methylphenyl)borinic acid, as a white solid in quantitative
yield. A portion of this intermediate (14.6 g, 52.5 mmol) was
dissolved in ethanol (120 mL) and heated to reflux. 3-
Hydroxypicolinic acid (5.83 g, 42 mmol) was added in
portions to the hot solution. The reaction mixture was
stirred at reflux for 15 min after the addition of the last
portion of 3-hydroxypicolinic acid and then cooled to room
temperature. The reaction mixture was concentrated by
removal of some ethanol and the product precipitated from
the solution. The solid was removed by filtration and
recrystallized from ethanol to give the title product (2g) as
white crystals (13.4 g, 64%): mp 165.0–166.5 °C; ESI-MS
(m/z) = 400, 402, 404 (M+H)+; 1H NMR (300 MHz,
DMSO-d6) d (ppm) 2.25 (s, 6 H), 7.08–7.11 (d, J = 7.5 Hz,
2H), 7.19–7.21 (m, 4H), 7.91–7.92 (d, J = 3.3 Hz, 2H), 8.56
(t, J = 2.9 Hz, 1H). (b) Preparation of 3-hydroxypyridine-2-
carbonyloxy-
(2p): 3-chloro-4-methylphenylboronic
29.3 mmol) was heated to reflux with ethylene glycol (1:1
molar ratio) in toluene using a Dean–Stark trap. Rotary
(3-chloro-4-methylphenyl)(p-tolyl)borane
acid (5.0 g,
9. Dexamethasone was used as a positive control for inhib-
iting release of TNF-a, IFN-c, and IL-4, and cyclohexa-
mide was used as a positive control for inhibiting release of
IL-1b.