F. Amblard et al. / Bioorg. Med. Chem. Lett. 17 (2007) 4428–4431
4429
using 1.5 equiv of a 1 M solution of BCl3 to give the de-
sired 3,30-bis-allylbiphenol 5a–i (Scheme 1).
tions (10 and 15 lg/ml) of honokiol analogs (from a
10 mg/ml stock) and observed for morphology changes
after 24 h.
The biphenols 3b–i were commercially available but,
biaryl 3a was synthesized through a Pd-catalyzed Su-
zuki-Miyaura reaction (Scheme 2). Thus the coupling
between 2-iodophenol 6 and the phenol 4-boronic
acid 7 was achieved by using Pd(OAc)2 (10 mol%),
dppf (diphenylphosphino ferrocene) (10 mol%) in
presence of K2CO3 (3.0 equiv) in THF at room
temperature.
Modifying the position of allyl and hydroxyl groups
around the simple biphenyl skeleton, as with
compounds 5b and 5c, reduced the cellular growth
(Table 1), but did not demonstrate any activity
enhancement compared with honokiol (57% and 56%
inhibition at 15 mg/ml, respectively, for 5b and 5c,
compared to 85% inhibition for honokiol). The
mono-allylated compound 10 was almost completely
inactive in all cell lines. Introduction of a linker be-
tween the two phenyl rings, making larger, but also
more ‘flexible’ molecules, is an interesting way to
determine the influence of the size of the compound
on the target. Initial results indicated that introduction
of a one-carbon bridge bearing a dimethyl (5e) or a
pyridine group (5h) significantly decreased cytotoxicity
in SVR cells. On the other hand, the presence of
groups such as methylene (5d), methylenecyclohexyl
(5f) or dichloroalkene (5g) provided similar anti-prolif-
erative activities, but without selectivity compared to
normal human lymphocytes [peripheral blood mono-
nuclear (PBM) cells]. Compound 5i was quite potent
and showed an excellent anti-proliferative response
in SVR cells (68% and 89% inhibition at 10 and
15 lg/mL) and an IC50 of 3.4 lM in human T-cell
lymphoma cells (CEM). At the same time, no toxicity
was detected in normal human PBM cells. This selec-
tivity made this compound a good candidate for fur-
Interestingly, the allylation/Claisen procedure applied
to the 2-(4-hydroxyphenyl)-5-pyrimidinol 8 did not
give the expected diallylated derivative, but produced
the monoallylated compound 10 (Scheme 3). In fact,
if the migration of the allyl group is generally the
main product of the Claisen reaction,8 the cleavage
can be the dominant reaction mode in particular
with electron deficient rings such as the case of
pyrimidine.
Cytotoxic activities. The anti-tumoral activities of
compounds 5a–i and 10 were determined by measur-
ing their effect on the survival and proliferation of
the immortalized endothelial cell line SVR.9 Briefly,
SVR cells (104) were plated in 24-well dishes. The next
day, the medium was replaced with fresh medium con-
taining the inhibitors or controls. Cells were incubated
at 37 °C for 72 h,10 and cell number was determined
in triplicate using a Coulter Counter (Hialeah, FL).
Immortalized and K-Ras transformed rat epithelial
cells (RIEpZip and RIEpZipK-Ras12V) were main-
tained at 37 °C, 5% CO2, in Dulbecco’s modified Ea-
gle’s medium supplemented with 10% fetal calf
serum (RIE).11,12 Cells were plated at 105/well in six-
well plates. Cells were treated with either vehicle
(60.05% DMSO in medium) or increasing concentra-
ther evaluation in
a
small animal model. To
determine whether compound 5i exhibits anti-tumor
activity in vivo, SVR cells were injected into flank
of 6-week-old nude male mice. When tumors became
visible at approximately 1 week after inoculation, mice
received 3 mg/day compound 5i or vehicle control
intraperitoneally. Treatment up to 100 mg/kg for 30
days did not inhibit the tumor growth, but also did
not result in any toxicity compared with vehicle
control.
OH
OH
OH
Pd(OAc)2
dppf
Antiviral activities. Since honokiol 2 itself is a modest
antiviral agent against HIV-1, the activities of analogs
5a–i and 10 were also evaluated and the results ex-
pressed as a median effective concentration or EC50
(Table 1). The antiviral13 and cytotoxicity14 assays
were performed as previously described. Compared
to honokiol 2, compounds 5a–d, 5f–h, and 10 ap-
peared less potent against HIV-1 in human PBM cells
and only compounds 5e and 5i showed moderate
activities close to honokiol’s activity (EC50 of 4.1
and 9.5 lM, respectively, compared to 3.3 lM for
honokiol).
I
+
OH
K2CO3
THF
60%
B(OH)2
3a
7
6
N
N
N
allyl bromide
HO
OH
O
O
K2CO3, acetone
N
In conclusion, the discovery of the anti-proliferative po-
tency of compounds 5d, 5f, 5g, and especially 5i provides
new insights into the synthesis and the evaluation of new
biphenyl-linked compounds. As a result of the above
studies, further modifications between the two phenol
moieties would be envisaged in order to generate more
potent and selective analogs with improved in vivo
activity.
8
9
N
N
BCl3
CH2Cl2
HO
OH
10
Scheme 3.
Amblard, Franck
