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H.-Y. Lee et al. / Bioorg. Med. Chem. Lett. 18 (2008) 4670–4674
COOEt
OH
N
N
COOH
a-c
Br
j-m
a-i
f-i
N
N
Boc
N
H
OH
52
49
50
22
24
N
N
N
OH
j-l
m, n
j, r, s
h, n-q, o
Br
N
N
Boc
N
H
N
COOEt
51
23
25
Scheme 2. Reagents and conditions: (a) (trimethylsilyl)diazomethane, benzene,
MeOH, rt, 1 h; (b) di-tert-butyl dicarbonate, DIPEA, DMAP, MeOH, rt, 16 h; (c) DIBAL,
THF, 0 °C to rt, 100 min; (d) MsCl, Et3N, CH2Cl2, 0 °C, 30 min; (e) LiBr, acetone,
reflux, 12 h; (f) carbazole, Cs2CO3, DMF, 70 °C, 1 day; (g) TFA, CH2Cl2, rt, 45 min; (h)
trans-cinnamaldehyde, AcOH, MeOH, rt, 1 h; (i) NaBH(OAc)3, rt, 1 day. (j) di-tert-
butyl dicarbonate, Et3N, CH2Cl2, rt, 16 h; (k) oxalyl chloride, DMSO, Et3N, CH2Cl2,
À78 °C to rt, 5 h; (l) diethyl bezylphosphonate, NaH, DMF, 0 °C to rt, 17 h; (m) TFA,
CH2Cl2, rt, 1 h; (n) N-(4-bromobutyl)carbazole, TBAB, CH2Cl2, 50% aq. NaOH, rt, 1
day.
Scheme 3. Reagents and conditions: (a) TBSCl, NaH, THF, 0 °C to reflux, 3 days; (b)
MsCl, Et3N, CH2Cl2, 0 °C, 20 min; (c) diethylmalonate, NaH, TBAI, THF, 0 °C to rt, 1
day; (d) NaCl, DMF, reflux, 38 h; (e) TBAF, THF, rt, 90 min; (f) MsCl, Et3N, CH2Cl2,
0 °C, 20 min; (g) LiBr, acetone, reflux, 9 h; (h) PPh3, CH3CN, reflux, 1 day; (i)
benzaldehyde, t-BuOH, benzene, 70 °C, 10 h; (j) LiAlH4, THF, 0 °C, 20 min; (k) MsCl,
Et3N, CH2Cl2, 0 °C, 20 min; (l) LiBr, Acetone, reflux, 4 h; (m) carbazole, Cs2CO3, DMF,
80 °C, 14 h; (n) 1,4-cyclohexanedione monoethylene acetal, n-BuLi, THF, À78 °C to
rt; (o) Pd/C, H2(1 atm), ethylacetate, 7 h, rt; (p) 1 N HCl, acetone, 50 °C, 1 h; (q)
(carbethoxymethylene) triphenylphosphorane, benzene, reflux, 3 days; (r) PCC,
CH2Cl2, rt, 1 h; (s) diethyl benzylphosphonate, NaH, DMF, 0 °C to rt, 19 h.
as the importance of the carbazole ring in 1. These analogs were
readily synthesized from amine, monosubstituted piperazine and
dibromoalkanes (or epibromohydrin) (Scheme 1).7 The cell prolifer-
ation inhibitory activities of compounds 1–21 are summarized in
Table 1.
Compared to racemic Incentrom A (1), separately prepared
enantiomers (2, 3) did not show any changes in activity, nor did
the protection of the hydroxyl group (4). However, a group bigger
than hydroxyl (5, 7) or the sp2 center in the chain (6) was not tol-
erable for activity. Actually, the hydroxyl group was not necessary
because the compound without hydroxyl group improved the
activity (8). Moreover, the butyl and pentyl chains showed better
activities than other chain lengths (9–12), suggesting that the opti-
mal moiety between carbazole and piperazine rings was a 4-car-
bon chain with no substituent in the middle.
attachment of carbazole produced 24. Compound 25 was prepared
from cyclohexanedione monoethyleneketal. A butylcarbazole unit
was introduced through Wittig olefination followed by hydrogena-
tion of the olefin product. After deprotection of the ketal, two-car-
bon extension was achieved using Wittig olefination reductions,
thus leading to the trans isomer as the major form of disubstituted
cyclohexane.
Finally, the cinnamyl unit was introduced in the same manner
as in the synthesis of 24.
The activities of these compounds were unusual: Both 22 and
23 exhibited undiminished inhibitory activities (MIC of 11–13
and 4–5 lM, respectively), whereas neither 24 nor 25 showed
When indole ring was introduced in place of carbazole (13) or
the rigid carbazole ring was dismantled (14), the inhibitory activity
was completely lost. On the other hand, ring expansion (16) or par-
tially hydrogenated carbazole was tolerated (15, 17), whereas an
introduction of the electron-withdrawing spacer was not (18). Of
the substituted carbazoles (19–21), only the parent 3-nitrocarba-
zole improved the inhibitory activity.
Based on these results, we kept carbazole, fixed the C4 chain
length between carbazole and piperazine rings, and explored the
other parts of Incentrom A to place a photo-affinity tag.
We prepared piperidine analogs of Incentrom A to test the
importance of two nitrogen atoms. Compound 22 was prepared
from 4-piperidinyl butanoic acid (49) by converting 49 into the
corresponding bromide (50) and by attaching carbazole and cin-
namyl groups to 49. The other piperidine analog 23 was prepared
from 4-piperidinyl ethanol (51) as shown in Scheme 2. All carbon
analogs (24, 25) were prepared as shown in Scheme 3. The selec-
tive protection of 52 followed by two carbon extension on one side
using malonate ester synthesis produced a butyl chain for attach-
ment of a carbazole unit and the other ethyl alcohol was extended
to the cinnamyl group through Wittig olefination reaction. Final
inhibitory activity. These results manifested that the presence of
nitrogen in the molecule was crucial for the inhibitory activity.
However, the position of the nitrogen atom was not critical. The
nitrogen atom could play a role either in establishing electrostatic
interaction with target proteins or in retaining the solubility in
aqueous solution or both.
Next, we varied the cinnamyl group. An epoxide analog 26 was
prepared similarly to the preparation of 9 using epoxycinnamyl
bromide rather than cinnamyl bromide. Hydrogenolysis of 26 pro-
duced 27 and its ester analogs 28 and 29 were prepared from 27.
Hydrogenation of the double bond of 9 produced 30. Conforma-
tionally restricted naphthyl compound (31), compounds with vary-
ing chain length (compounds 32-35), and fully saturated
cyclohexyl compound (36) were also prepared, and their activities
are summarized in Table 2. An introduction of epoxide in place of
olefin (26) slightly improved the activity, and the opening of epox-
ide to alcohol (27) retained the activity. The hydroxyl group offered
a site for attaching other functional groups because the acetate
form 28 was still active. However, the activity was lost when a lar-
ger group was attached (29). The saturation of the double bond of
cinnamyl group (30) slightly reduced the activity.