Coumarin-based prodrugs. Part 3: Structural effects on the release kinetics of esterase-sensitive prodrugs of amines

Article abstract of DOI:10.1016/S0968-0896(98)00014-5

To study the structural effects on the release kinetics of a coumarin- based esterase-sensitive prodrug system, two series of compounds with varying structural features of the ester 'trigger' part and the amine 'drug' part were synthesized. The half-lives of the nine model prodrugs in the presence of porcine liver esterase ranged from about 2 min to 190 min. The steric bulkiness of the acyl group seems to have only a very minor effect on the half-lives of the esterase-triggered release of amines from the model prodrugs. The rate of the lactonization depends on the steric and electronic properties of the amine moiety.

Full text of DOI:10.1016/S0968-0896(98)00014-5

BIOORGANIC &
MEDICINAL
CHEMISTRY
Bioorganic & Medicinal Chemistry 6 (1998) 417±426
Coumarin-based Prodrugs. Part 3: Structural E€ects on the
Release Kinetics of Esterase-sensitive Prodrugs of Aminesy
Binghe Wang,* Huijuan Zhang, Ailian Zheng and Wei Wang
Department of Chemistry, North Carolina State University, Raleigh, NC 27695-8204, USA
Received 29 July 1997; accepted 10 November 1997
AbstractÐTo study the structural e€ects on the release kinetics of a coumarin-based esterase-sensitive prodrug system,
two series of compounds with varying structural features of the ester `trigger' part and the amine `drug' part were
synthesized. The half-lives of the nine model prodrugs in the presence of porcine liver esterase ranged from about 2 min
to 190 min. The steric bulkiness of the acyl group seems to have only a very minor e€ect on the half-lives of the ester-
ase-triggered release of amines from the model prodrugs. The rate of the lactonization depends on the steric and elec-
tronic properties of the amine moiety. # 1998 Elsevier Science Ltd. All rights reserved.
Introduction
further understand the e€ects of di€erent structural
features on the release kinetics, we undertook this e€ort
to synthesize and evaluate the release kinetics of a series
of coumarin-based prodrugs of model amines. In
studying the structural e€ects, we were interested in
examining two factors. First, how the steric bulkiness of
the acyl group (R-) (Scheme 1) would a€ect the esterase-
catalyzed hydrolysis of the phenol ester bond. Second,
how the structural features of the amine `drug' part (X-)
(Scheme 1) would a€ect the release kinetics. Therefore,
we synthesized two series of compounds, one with
varying sizes of the acyl group (R-) and the other with
varying structural features of the `drug' part (X-). The
release rates of these prodrugs were studied using PLE
in a phosphate bu€er solution.
Earlier, we reported the chemical feasibility studies of a
coumarin-based esterase-sensitive prodrug system for
amines1 and its application for the preparation of ester-
ase-sensitive cyclic prodrugs of peptides.2 The design of
this prodrug system takes advantage of the facile lacto-
nization of coumarinic acid and its derivatives 2
(Scheme 1).3±6 Other similar systems have also been
used for the preparation of esterase-sensitive prodrugs
of amines7±10 and peptides.11,12 However, the coumarin-
based prodrug system has one major advantage, that is,
the toxicity pro®le of coumarin is well-known and cou-
marin has been found to be relatively nontoxic in many
clinical and laboratory studies.13±17 During the course of
our studies of the bioreversibility of the coumarin-based
prodrug system using puri®ed porcine liver esterase
(PLE) and pig plasma, we noticed that all the coumarin-
based prodrugs of either model amines or peptides did
not release the `drug' moiety at the same rate, due to
either di€erent rates of the esterase-catalyzed hydrolysis
of the phenol ester linkage or the lactonization.1,2,18 To
Results and discussion
Synthesis
The key to the synthesis was the preparation of cou-
marinic acid with proper acylation of the phenol
hydroxyl group 9 (Scheme 2). Due to the facile lacto-
nization of coumarinic acid and its derivatives 2
(Scheme 1), direct acylation of the phenol hydroxyl
group of 2 was not feasible. Therefore, the synthesis
started from coumarin (3). The lactone ring of coumarin
(3) was opened through reduction with LiAlH4 at low
Key words: Prodrug; coumarin; coumarinic acid; esterase;
structural e€ect.
*Corresponding author. Tel: (919) 515-2948; Fax: (919) 515-
2948; E-mail: binghe_wang@ncsu.edu
yPart of this work was performed at the University of Okla-
homa Health Sciences Center, College of Pharmacy.
0968-0896/98/$19.00 # 1998 Elsevier Science Ltd. All rights reserved
PII: S0968-0896(98)00014-5

418
B. Wang et al./Bioorg. Med. Chem. 6 (1998) 417±426
temperature (0 ꢀC) for 15 min to give the diol 4.19 It
should be noted that higher reaction temperature or
longer reaction time led to the formation of the over-
reduction product without the exo double bond. The
primary hydroxyl group of the diol 4 was then selec-
tively protected as the tert-butyldimethyl silyl (TBDMS)
ether through reaction with TBDMS-Cl at 0 ꢀC for 14 h.
Again, higher temperature and longer reaction time led
to the formation of the side product with TBDMS
attached to both the primary and the phenol hydroxyl
groups. The free phenol hydroxyl group of 5 was then
acylated in 76±100% yields through reactions with the
appropriate acid anhydrides in the presence of triethyl
amine (TEA) and 4-dimethylaminopyridine (DMAP).
The TBDMS protecting group was then cleaved in
almost quantitative yields using acetic acid to give 7a±d,
which were converted in a two-step oxidation to the key
intermediates 9a±d with a free carboxyl group. For the
oxidation of the allylic hydroxyl group of 7a±d to the
corresponding aldehydes 8a±d, either pyridinium chloro-
chromate (PCC) or manganese dioxide could be used to
accomplish this conversion. The aldehydes 8a±d were
then converted to the corresponding carboxylic acids
9a±d in high yields (over 95%) through oxidation with
hydrogen peroxide in the presence of sodium chlorite
under acidic conditions.20 The coupling of amines to the
free acids 9a±d to give 10a±d, g±i was accomplished
using 1,3-dicyclohexylcarbodiimide (DCC) as the acti-
vating agent in the presence of 1-hydroxybenzotriazole
(HOBt) and DMAP, and the yields ranged from 78%
for benzylamine to 33% for p-anisidine. Compounds
Scheme 1. The concept of a coumarin-based esterase-sensitive
prodrug system.
10e,f were obtained following
approach.21
a
photochemical
One thing worth special attention was the preparation
of the amide of aniline (10, R=CH3, R0=C6H5,
R00=H). When aniline was coupled with the protected
coumarinic acid 9a, no desired cis product was
obtained. Instead, the undesirable trans product 11 was
obtained in 40% isolated yield with the rest being the
starting material. We have also attempted to prepare the
cis amide of aniline without success using a photo-
chemical approach.21 It is not readily clear why the
preparation of this compound is particularly problem-
atic.
Esterase kinetics
The prodrugs 10a±i were designed to release the model
amine drugs after esterase-catalyzed hydrolysis of the
phenol ester bond (Scheme 1). We decided to study the
release kinetics using PLE as the enzyme trigger because
it has been widely used in similar studies.7,22,23 Because
of the complexity of the reaction kinetics, which
involves an enzymatic reaction and multi-step chemical
reactions (Scheme 3), no attempt was made to determine
the rate constants for each step of the reaction. Instead,
the kinetic studies were carried out in the context of
determining the overall reaction rates, which should
Scheme 2. Synthesis of the coumarin-based model prodrugs
10a±i. Reagents and conditions: (a) LAH, 0 ꢀC, 15 min; (b)
TBDMSCl, DMAP; (c) (RCO)2O, DMAP-TEA; (d)
H2O:THF:HOAc (1:1:3); (e) PCC or MnO2; (f) H2O2, NaClO2,
10 ꢀC; (g) DCC/HOBt, DMAP, HNR0R00.

B. Wang et al./Bioorg. Med. Chem. 6 (1998) 417±426
419
Scheme 3. Lactonization of coumarinic acid and its derivatives.
provide relevant information for the prediction of the
release rates of coumarin-based prodrugs of other amine
drugs. Therefore, only the pseudo-®rst-order rate con-
stants were determined for each compound in a phos-
phate bu€er (0.05 M, pH 7.4, 37‹0.5 ꢀC) in the
presence of PLE at an enzyme concentration of about
1 unit/mL.
Figure 1. Typical HPLC chromatographs. Panel A: coumarin
(3); panel B: starting material 10g; panel C: 90s after the
addition of esterase; panel D: 9 min after the additon of
esterase.
Upon incubation with PLE, all model prodrugs quickly
released the amine moiety with half-lives ranging from
about 2 min (10g) to about 190 min (10i), a di€erence of
almost two orders of magnitude. These results are sum-
marized in Table 1. We developed two methods for the
kinetic studies, one was an HPLC method and the other
was a UV method. Using the HPLC method, we were
able to monitor the formation of the intermediate 2,
coumarin (3), and the disappearance of the starting
material 10. However, this method was tedious and
required more than one week's time to perform a tripli-
cate experiment for a single compound. The UV method
was based on the di€erence in extinction coecients
between the starting material 10 and the ®nal product,
coumarin (3) at 276 nm. For example, coumarin (3) has
the formation and disappearance of the intermediates.
Therefore, each method has its advantages and dis-
advantages depending on the information desired from
the kinetic studies. Figure 1 shows a typical HPLC
reaction pro®le using 10g as an example. To validate the
consistency of the two methods in the determination of
the pseudo-®rst-order rate constants, we used both
methods in parallel for the studies of the release kinetics
of compounds 10a,g,h. The pseudo-®rst-order rate con-
stants were similar using these two methods for 10a and
10h indicating their consistency (Table 1). However, the
situation for 10g was di€erent (Table 1). For 10g, the
t1/2 determined using the HPLC method was about
1.63 min, whereas, the t1/2 determined using the UV
method was about 2.22 min. The over 30% di€erence in
1
an extinction coecient of 10,790 M 1 cm at 276 nm,
and 10a and 10d has an extinction coecient of 5245
and 4544, respectively, at the same wavelength. With the
UV method, we were able to perform the same kinetic
studies within a much shorter period of time, however,
without the ability of studying the detailed pro®le for
Table 1. Rates of the appearance of coumarin (3) from the esterase-triggered lactonization of 10a±i
R0
R00
kobs (Â104) (s
)
t1/2 (min)
pKa of the amine
Method
1
Model prodrug
R
10a
10a
10b
10c
10d
10e
10f
10g
10g
10h
10h
10i
Me
Me
Et-
PhCH2-
PhCH2-
PhCH2-
PhCH2-
PhCH2-
Pr-
H
H
7.24‹0.13
7.22‹0.54
6.50‹0.63
5.81‹0.10
5.71‹0.45
9.27‹0.74
2.28‹0.11
71.0‹0.4
15.95‹0.28
16.07‹1.20
17.88‹1.82
19.88‹0.32
20.32‹1.67
12.50‹0.98
50.73‹2.35
1.63‹0.02
9.33
9.33
9.33
9.33
9.33
10.60
10.66
5.34
5.34
9.54
9.54
11.02
HPLC
UV
UV
H
i-Pr-
t-Bu-
Me
Me
Me
Me
Me
Me
Me
H
UV
UV
H
H
UV
UV
Cyclohexyl-
p-MeO-Ph-
p-MeO-Ph-
PhCH2-
PhCH2-
Et-
H
H
HPLC
UV
H
52.5‹6.1
2.22‹0.25
Me
Me
Et-
3.72‹0.02
3.55‹0.02
0.616‹0.043
31.05‹0.15
32.53‹0.18
188.0‹12.85
HPLC
UV
HPLC

420
B. Wang et al./Bioorg. Med. Chem. 6 (1998) 417±426
this case was due to the inherent ¯aw of using the HPLC
method to study the kinetics of a very fast reaction.
Because the retention times on the HPLC column for
both the starting material 10g and the intermediate 2
were about 10 min, while the half-life of the compound
was about 2 min, lactonization during sample handling
and HPLC chromatography could signi®cantly a€ect
the experimental value. However, in using the UV
method, data were collected much more quickly than in
the HPLC method. Therefore, for a fast reaction, the
UV method is more reliable.
In studying the e€ects of the structural features of the
model amine moieties on the release kinetics, we exam-
ined compounds 10a,e±i. It seems that both steric and
electronic properties of the amine moiety play a role in
determining the rate of lactonization. With this series of
compounds, all the starting materials disappeared in less
than 2 min to form intermediates 2 as observed with
HPLC/UV. Therefore, any di€erence in the apparent
®rst-order rate constants was largely due to the di€er-
ence in their rates of lactonization. It has been shown
that for the lactonization of the coumarinic acid
(Scheme 1, 2, X= OH), the rate-limiting step was the
collapse of the tetrahedral intermediate 12 and the for-
mation of the tetrahedral intermediate was reversible.3±6
Therefore, the rate of the forward lactonization reaction
depends on the partition of the tetrahedral intermediate
and the ratio of k3/k 2. Whereas, the overall pseudo-
®rst-order rate constant depends on the combined e€ect
of k1, k2, k 2, and k3. If the pKas of the amines are used
as an approximate measurement of their leaving group
ability,24,25 the kinetic data in Table 1 indicate that with
a better leaving group ( X), the lactonization is faster.
For example, p-anisidine has the lowest pKa (5.34)
among all the model amines and the lactonization of its
prodrug 10g is the fastest with a half-life of about 2 min.
This is understandable because with a better leaving
We were interested in examining two factors that could
a€ect the rates of esterase-triggered release of the model
amines from the prodrugs 10a±i, namely the structural
e€ects of the acyl group and the model amine moiety.
We were interested in studying how the steric hindrance
of the acyl group would a€ect the esterase-catalyzed
hydrolysis to give 2 as re¯ected in the pseudo-®rst-order
rate constants (Scheme 1). We expected no e€ect of
the acyl group on the lactonization step of the reaction
of 2 (Scheme 1). Therefore, any di€erence in the pseudo-
®rst-order rate constants among 10a±d would be due to
the di€erent rates of hydrolysis of the phenol ester.
We ®rst studied the release kinetics of compounds 10a±
d, which had the same amine moiety, but di€erent acyl
groups (R-) attached to the phenol hydroxyl group.
Figure 2 shows the UV reaction pro®les of the esterase-
catalyzed hydrolysis of the prodrugs 10a and 10d. Much
to our surprise, variations of the steric bulkiness of the
acyl group did not seem to have signi®cantly a€ected
the rate of the esterase-triggered release of the amine
moiety. As can be seen from the data presented in
Table 1, the release rates decreased only slightly when
the acyl group changed from a simple methyl group
(10a) to a bulky t-butyl group (10d). However, it should
be emphasized that we did not determine the rate for the
®rst step (k1) of the reaction, namely, the esterase-cata-
lyzed hydrolysis of the phenol ester linkage. Therefore,
the magnitude of the di€erence in the release rates (kobs
)
among 10a±d (Table 1) should not be viewed as the
same as the magnitude of the di€erence in the rates of
esterase-catalyzed ester hydrolysis (k1). In another
word, the di€erence in the esterase-catalyzed hydrolysis
(k1) of the phenol ester linkage could be far greater.
However, because the subsequent lactonization (k2 and
k3) with concomitant release of the model amine was the
rate-limiting step, the e€ect of the hydrolysis rate (k1)
di€erence was not readily apparent by analyzing the
pseudo-®rst-order rate constants (kobs
) (Table 1).
Therefore, as long as the hydrolysis of the ester is so fast
that the lactonization is the rate-limiting step, the dif-
ference in the esterase-catalyzed phenol ester hydrolysis
rates would not have any signi®cant e€ect on the half-
lives of the prodrugs.
Figure 2. Typical UV reaction pro®les of the esterase-catalyzed
hydrolysis of the prodrugs 10a and 10d.

B. Wang et al./Bioorg. Med. Chem. 6 (1998) 417±426
421
group, k3 would be faster and, therefore, the lactoniza-
tion is faster. The data also indicate that steric hin-
drance slows down the lactonization. This is evident
when comparing the rates (Table 1) of 10f (X=cyclo-
hexylamine) versus 10e (X=propylamine), 10h (X=N-
methylbenzylamine) versus 10a (X=benzylamine).
Cyclohexylamine and propylamine have very similar
pKa's (Table 1). However, their release rates were dif-
ferent by about fourfold. N-methylbenzylamine and
benzylamine also have similar pKas (Table 1) and their
release rates were di€erent by about twofolds. It is not
readily clear how steric hindrance would a€ect the
release rates. One possible, but unproved explanation is
that there is a change of the rate-determining step.
Although, for the lactonization of coumarinic acid (2,
X=OH), the rate-limiting step is the collapse of the
tetrahedral intermediate, this is not necessarily true for
bulky amides of coumarinic acid (2, X=NRR0). Steric
hindrance could make the attack of the phenol hydroxyl
group on the amide carbonyl group so dicult that the
formation (k2) of the tetrahedral intermediate 12 could
be the rate-limiting step for the amides of sterically hin-
dered amines. This would help to explain why the half-
life of 10f (X=cyclohexylamine) was much longer than
that of 10e (X=propylamine) and the half-life of the
amide of a secondary amine (10h) was much longer than
that of a primary amine (10a). For those compounds
where the electronic e€ect and the steric e€ect work in
opposite direction, the explanation of the overall
pseudo-®rst-order constants was more dicult. For
example, a p-methoxyphenyl group (10g) is bulkier than
a propyl group (10e). However, because anisidine is a
better leaving group, the release was faster for 10g. Both
the electronic and steric e€ects need to be considered in
explaining the reaction rates of 10a (X=benzylamine)
vs. 10e (X=propylamine) and 10h (X=N-methyl-
benzylamine) versus 10i (X=N,N-diethylamine). It
should be noted that the elucidation of the detailed
mechanism(s) of these release reactions will require
much more studies than what is presented in this report
and is beyond the scope of this study.
facilitate the lactonization and steric hindrance tends to
hinder the lactonization. With all the compounds stud-
ied, the release time was relatively short, making the
coumarin-based prodrug system practical for the prep-
aration of coumarin-based prodrugs of amines with a
variety of structural features. Work is underway to use
the same system for the preparation of cyclic prodrugs
of biologically important peptides or peptide mimetics.
Experimental
General methods
All 1H NMR spectra were recorded at 300 MHz with
TMS as the internal standard. Column chromatography
was performed using silica gel (200±400 mesh) from
Aldrich. Elemental analyses were performed by Mid-
west Microlab, Indianapolis, Indiana. Mass spectral
analyses were conducted by North Carolina State Uni-
versity Mass Spectrum Laboratory. Commercially
available starting materials and reagents were purchased
from Aldrich. THF was distilled from Na and benzo-
phenone. Methylene chloride (CH2Cl2) was distilled
from CaH2. A Shimadzu 1601 UV-visible spectro-
photometer was used for the esterase kinetics study.
HPLC assay conditions
A Shimadzu HPLC system consisting of a SCL-10A
system controller, two LC-10AS pumps, an SPD-10AV
UV-VIS detector, and an SIL-10A auto injector was
used for the kinetic studies. A reversed-phase C-18 col-
umn (L=15 cm, ID=4.6 mm, particle size=5 mm) was
used. The mobile phase consisted of HPLC grade
methanol (Fisher Scienti®c) and distilled water ®ltered
through a Millipore Milli-Q water puri®cation system.
A detection wavelength of 285 nm was used. All pH
values were determined with an Accumet 1003 Hand-
hold pH/mV/Ion Meter (Fisher Scienti®c).
Puri®ed esterase kinetics
Puri®ed PLE (carboxylic-ester hydrolase; EC 3.1.1.1; E-
2884) was obtained from Sigma as a suspension in a
3.2 M (NH4)2SO4 solution (pH 8). Then 1.5 microliters
of this suspension (containing 6800 units of enzyme per
mL) was diluted with 9.9 mL of phosphate bu€er
(0.05 M, pH 7.4). One hundred microliters of the 0.01 M
stock solution of the model prodrug 10 in dimethylsulf-
oxide was then combined with above-mentioned bu€er-
PLE solution. It was shaken for 30s, then kept in a
water bath at 37‹0.5 ꢀC. Due to the rapid rate of con-
version of 10 under these conditions, aliquots were
withdrawn from the reaction mixture at various times
and immediately frozen in a dry ice/acetone bath, which
Conclusion
The structural e€ects on the release kinetics of the cou-
marin-based esterase-sensitive prodrug system have
been studied with nine model compounds. The struc-
tural e€ects of the acyl group were studied using sub-
stituted acetic acid with varying steric bulkiness. This
structural variation seems to have a very minor e€ect on
the overall half-lives of the model prodrugs 10a±d in the
presence of porcine liver esterase. For the structural
e€ects of the amine part, factors that could stabilize a
developing negative charge on the nitrogen during the
collapse of the tetrahedral intermediate 12 tend to

422
B. Wang et al./Bioorg. Med. Chem. 6 (1998) 417±426
instantaneously stopped the reaction. These samples
were later analyzed by the above-described HPLC or
UV method. The areas of the appearance of coumarin 3
in the HPLC method or the absorbency at the wave-
length of 276 nm in the UV method were used to calcu-
late the half-lives. The endpoints were obtained at about
seven half-lives, at which point the reaction was over
water (15 mL). The solution was dried over MgSO4, ®l-
tered, and evaporated to a€ord 6a as a white solid
(1.67 g, 100%). H NMR (CDCl3) d 0.03 (6 H, s), 0.89
(9 H, s), 2.28 (3 H, s), 4.30 (2 H, d, J=6.0 Hz), 5.90 (1
H, m), 6.39 (1 H, d, J=11.7 Hz), 7.07 (1 H, d,
J=8.7 Hz), 7.21±7.33 (3 H, m); MS (EI) m/z 306 (M+, 1),
249 (10), 175 (68), 133 (100), 117 (10). Anal. calcd for
C17H26O3Si: C, 66.62; H, 8.55. Found: C, 66.74; H, 8.48.
1
99% complete. Then Ln (A
At) for four half-lives
was plotted against time and k and t1/2 (0.693/k) were
1
calculated based on the slope of the linear curve.
2-[(Z)-3-{[1-(tert-Butyl)-1,1-dimethylsilyl]oxy}-1-propenyl]
phenyl propionate (6b). In a manner similar to the prep-
aration of 6a, 5 (2.19 g, 8.29 mmol), propionic anhydride
(1.27 mL, 9.95 mmol), DMAP (202 mg, 1.66 mmol), and
triethylamine (2.07 mL, 14.92 mmol) were treated to
a€ord 6b as a colorless oil (2.65 g, 100%). 1H NMR
(CDCl3) d 0.00 (6 H, s), 0.86 (9 H, s), 1.23 (3 H, t,
J=7.5 Hz), 2.55 (2 H, q, J=7.5 Hz), 4.27 (2 H, d,
J=7.5 Hz), 5.86 (1 H, m), 6.36 (1 H, d, J=1.7 Hz), 7.03
(1 H, d, J=7.8 Hz), 7.18±7.30 (3 H, m); MS (FAB) m/z
320 (M+, 3), 263 (80), 189 (99), 133 (100), 131 (100), 115
(23). Anal. calcd for C18H28O3Si: C, 67.46; H, 8.80.
Found: C, 67.22; H, 8.69.
2-[(Z)-3-Hydroxy-1-propenyl] phenol (4). A solution of
coumarin (3) (1.46 g, 10 mmol) in ether (40 mL) was
treated at 0 ꢀC with a suspension of lithium aluminum
hydride (0.76 g, 20 mmol) in ether (20 mL). After stirring
for 15 min, 1 N HCl (70 mL) was dropwise added to the
reaction at 0 ꢀC, then the solution was extracted with
ether (3Â30 mL). The combined ether layer was dried
over MgSO4 and concentrated to give a slightly yellow
solid (1.44 g). Crystallization from methylene chloride/
ethyl acetate (7:1) gave 4 (0.66 g, 44%) as white crystals.
1H NMR (CD3OD) d 4.26 (2 H, d, J=6.6 Hz), 5.80 (1
H, m), 6.63 (1 H, d, J=11.7 Hz), 6.77±7.11 (4 H, m);
MS (EI) m/z 150 (M+, 26), 132 (20), 131 (100), 77 (20).
Anal. calcd for C9H10O2: C, 71.98; H, 6.71. Found: C,
71.58; H, 6.68.
2-[(Z)-3-{[1-(tert-Butyl)-1,1-dimethylsilyl]oxy}-1-propenyl]
phenyl 2-methylpropanoate (6c). In a manner similar to
the preparation of 6a, 5 (198 mg, 0.75 mmol), isobutyric
anhydride (149 mL, 0.90 mmol), DMAP (18 mg,
0.15 mmol), and triethylamine (188 mL, 1.35 mmol) were
2-[(Z)-3-{[1-(tert-Butyl)-1,1-dimethylsilyl]oxy}-1-propenyl]
phenol (5). To a stirred solution of 4 (3.87 g, 25.8 mmol)
in dry THF (40 mL) was added a solution of tert-butyl-
dimethylsilyl chloride (4.28 g, 28.4 mmol) in dry THF
(30 mL) at 0 ꢀC. This was followed by the dropwise
addition of DMAP (4.73 g, 38.7 mmol) in dry THF
(50 mL). After stirring at 0 ꢀC for 14 h, the solution was
®ltered and evaporated to remove the THF. Ethyl acet-
ate (50 mL) was added and the solution was washed
with 1 N HCl (2Â30 mL), 5% NaHCO3 (25 mL), and
water (25 mL). The ethyl acetate layer was dried over
MgSO4, ®ltered, and evaporated to give a yellow oil
(7.63 g). The oil was chromatographed on a silica gel
column with ethyl acetate/hexanes (1:15) to a€ord 5 as a
1
reacted to give 6c as a colorless oil (250 mg, 100%). H
NMR (CDCl3) d 0.00 (6 H, s), 0.89 (9 H, s), 1.31 (6 H,
d, J=6.9 Hz), 2.80 (1 H, m), 4.30 (2 H, d, J=6.9 Hz),
5.88 (1 H, m), 6.39 (1 H, d, J=11.7 Hz), 7.05 (1 H, d,
J=7.8 Hz), 7.27±7.33 (3 H, m); MS (FAB) m/z 335
[(M+H)+, 8], 277 (36), 203 (57), 145 (46), 133 (100),
131 (30). Anal. calcd for C19H30O3Si: C, 68.22; H, 9.04.
Found: C, 68.27; H, 8.91.
2-[(Z)-3-{[1-(tert-Butyl)-1,1-dimethylsilyl]oxy}-1-propenyl]
phenyl pivalate (6d). In a manner similar to the pre-
paration of 6a, 5 (1.97 g, 7.46 mmol), trimethylacetic
anhydride (1.67 mL, 8.21 mmol), DMAP (182 mg,
1.49 mmol), and triethylamine (1.87 mL, 13.43 mmol)
were reacted for 24 h to a€ord a colorless oil, which was
chromatographed on a silica gel column with hexanes,
then ethyl acetate/hexanes (1:8) to give 6d as a colorless
oil (1.97 g, 76%). 1H NMR (CDCl3) d 0.03 (6 H, s), 0.89
(9 H, s), 1.36 (9 H, s), 4.31 (2 H, d, J=6.9 Hz), 5.88 (1
H, m), 6.39 (1 H, d, J=11.7 Hz), 7.03 (1 H, d,
J=8.1 Hz), 7.20±7.31 (3 H, m); MS (FAB) m/z 349
[(M+H)+, 4], 347 [(M-H)+, 11], 291 (42), 217 (51), 133
(100), 131 (59), 115 (39). Anal. calcd for C20H32O3Si: C,
68.92; H, 9.25. Found: C, 68.87; H, 9.34.
1
white solid (5.63 g, 83%). H NMR (CDCl3) d 0.07 (6
H, s), 0.90 (9 H, s), 4.18 (2 H, d, J=7.2 Hz), 6.02 (1 H,
m), 6.52 (1 H, d, J=11.7 Hz), 6.87±7.21 (4 H, m); MS
(FAB) m/z 264 (M+, 6), 207 (48), 177 (44), 133 (100),
131 (18). Anal. calcd for C15H24O2Si: C, 68.13; H, 9.15.
Found: C, 67.95; H, 9.15.
2-[(Z)-3-{[1-(tert-Butyl)-1,1-dimethylsilyl]oxy}-1-propenyl]
phenyl acetate (6a). To
a solution of 5 (1.44 g,
5.45 mmol) in dry CH2Cl2 (30 mL) was added dropwise
acetic anhydride (0.62 mL, 6.54 mmol), then DMAP
(133 mg, 1.09 mmol) and triethylamine (1.36 mL,
9.81 mmol). After stirring at room temperature under
N2 atmosphere for 1 h, the reaction mixture was washed
with 1 N HCl (2Â20 mL), 5% NaHCO3 (15 mL), and
2-[(Z)-3-Hydroxy-1-propenyl]phenyl acetate (7a). To a
solution of 6a (1.09 g, 3.56 mmol) in THF (10 mL) was
added water (10 mL). This was followed by the dropwise

B. Wang et al./Bioorg. Med. Chem. 6 (1998) 417±426
423
addition of acetic acid (30 mL). The mixture was stirred
at room temperature for 3 h and then evaporated to
remove THF, water, and acetic acid. Ethyl acetate
(40 mL) was added to the residue, which was washed
with 5% NaHCO3 (2Â20 mL) and water (20 mL). The
ethyl acetate solution was dried over MgSO4, ®ltered,
and evaporated to a€ord 7a as a colorless oil (682 mg,
gel column and eluted with CH2Cl2 to remove the
chromium salts. The black residue was washed several
times with CH2Cl2 and the solution was run through the
same column. The solution was then evaporated to give
a green oil (275 mg). The crude product was chromato-
graphed on a silica gel column with ethyl acetate/hex-
1
anes (1:8) to a€ord 8a as a green oil (153 mg, 51%). H
1
100%). H NMR (CDCl3) d 2.20 (3 H, s), 4.13 (2 H, d,
NMR (CDCl3) d 2.28 (3 H, s), 6.20 (1 H, dd, J=8.4,
11.4 Hz), 7.16 (1 H, d, J=7.5 Hz), 7.30±7.54 (4 H, m),
9.80 (1 H, d, J=8.4 Hz); MS (EI) m/z 190 (M+, 9), 147
(100), 131 (66), 43 (17). Anal. calcd for C11H10O3: C,
69.46; H, 5.30. Found: C, 69.40; H, 5.26.
J=6.9 Hz), 5.87 (1 H, m), 6.37 (1 H, d, J=11.7 Hz),
6.97 (1 H, d, J=7.2 Hz), 7.11±7.26 (3 H, m); MS (EI)
m/z 192 (M+, 2), 132 (11), 131 (100), 77 (14), 43 (41).
Anal. calcd for C11H12O3: C, 68.74; H, 6.29. Found: C,
68.90; H, 6.30.
2-[(Z)-3-Oxo-1-propenyl]phenyl propionate (8b). To a
solution of 7b (122 mg, 0.592 mmol) in dry CH2Cl2
(20 mL) in a ¯ask equipped with a drying tube contain-
ing anhydrous CaSO4 was added in one portion 85%
activated manganese(IV) oxide (121 mg, 1.184 mmol).
The reaction solution was kept stirring and more man-
ganese(IV) oxide was added at one hour intervals in one
121 mg-portion for a period of 5 h. The reaction mixture
was ®ltered through Celite (5 g), washed with CH2Cl2
and evaporated to a€ord 8b as a brown oil (111 mg,
92%). 1H NMR (CDCl3) d 1.25 (3 H, t, J=7.5 Hz), 2.58
(2 H, q, J=7.5 Hz), 6.20 (1 H, dd, J=8.4, 11.1 Hz), 7.17
(1 H, d, J=7.8 Hz), 7.27±7.55 (4 H, m), 9.81 (1 H, d,
J=8.4 Hz); MS (FAB) m/z 204 (M+, 6), 149 (72), 148
(11), 147 (28), 131 (100). Anal. calcd for C12H12O3: C,
70.58; H, 5.92. Found: C, 70.28; H, 5.94.
2-[(Z)-3-Hydroxy-1-propenyl]phenyl propionate (7b). In
a manner similar to the preparation of 7a, the silyl
group of 6b (214 mg, 0.669 mmol) was cleaved by reac-
tion in THF (4 mL), water (4 mL), and acetic acid
1
(12 mL) to a€ord 7b as a yellow oil (138 mg, 100%). H
NMR (CDCl3) d 1.26 (3 H, t, J=7.8 Hz), 2.58 (2 H, q,
J=7.8 Hz), 4.22 (2 H, d, J=6.9 Hz), 5.96 (1 H, m), 6.46
(1 H, d, J=11.7 Hz), 7.06 (1 H, d, J=7.8 Hz), 7.17±7.35
(3 H, m); MS (EI) m/z 206 (M+, 2), 150 (23), 132 (100),
131 (71), 57 (3). Anal. calcd for C12H14O3: C, 69.88; H,
6.84. Found: C, 69.77; H, 6.90.
2-[(Z)-3-Hydroxy-1-propenyl]phenyl 2-methylpropanoate
(7c). In a manner similar to the preparation of 7a, the
silyl group of 6c (250 mg, 0.75 mmol) was cleaved by
reaction in THF (4 mL), water (4 mL), and acetic acid
1
(12 mL) to a€ord 7c as a yellow oil (165 mg, 100%). H
2-[(Z)-3-Oxo-1-propenyl]phenyl 2-methylpropanoate (8c).
In a manner similar to the preparation of 8b, 7c (1.12 g,
5.10 mmol) was treated with 85% activated mangane-
se(IV) oxide (6Â1.04 g, 6Â10.2 mmol) to a€ord 8c as a
NMR (CDCl3) d 1.31 (6 H, d, J=7.2 Hz), 2.80 (1 H, m),
4.21 (2 H, d, J=6.0 Hz), 5.96 (1 H, m), 6.46 (1 H, d,
J=11.4 Hz), 7.04 (1 H, d, J=7.5 Hz), 7.16±7.34 (3 H,
m); MS (EI) m/z 220 (M+, 2), 150 (8), 132 (100), 131
(63), 71 (5). Anal. calcd for C13H16O3: C, 70.88; H, 7.32.
Found: C, 70.78; H, 7.42.
1
brown oil (953 mg, 86%). H NMR (CDCl3) d 1.30 (6
H, d, J=6.9 Hz), 2.80 (1 H, m), 6.20 (1 H, dd, J=8.1,
11.4 Hz), 7.15 (1 H, d, J=8.1 Hz), 7.26±7.54 (4 H, m),
9.81 (1 H, d, J=8.1 Hz); MS (EI) m/z 218 (M+, 1), 148
(15), 147 (100), 132 (97). Anal. calcd for C13H14O3: C,
71.54; H, 6.46. Found: C, 71.75; H, 6.58.
2-[(Z)-3-Hydroxy-1-propenyl]phenyl pivalate (7d). In a
manner similar to the preparation of 7a, the silyl group
of 6d (170 mg, 0.489 mmol) was cleaved by reaction in
THF (3 mL), water (3 mL), and acetic acid (9 mL) to
a€ord 7d as a colorless oil (114 mg, 100%). 1H NMR
(CDCl3) d 1.36 (9 H, s), 4.22 (2 H, d, J=6.9 Hz), 5.96 (1
H, m), 6.46 (1 H, d, J=11.4 Hz), 7.02 (1 H, d,
J=7.8 Hz), 7.15±7.34 (3 H, m); MS (FAB) m/z 234
(M+, 2), 217 (75), 133 (100), 132 (30), 131 (30), 115 (11).
Anal. calcd for C14H18O3: C, 71.77; H, 7.74. Found: C,
71.60; H, 7.67.
2-[(Z)-3-Oxo-1-propenyl]phenyl pivalate (8d). In a man-
ner similar to the preparation of 8b, 7d (103 mg,
0.44 mmol) was treated with 85% activated mangane-
se(IV) oxide (4Â90 mg, 4Â0.88 mmol) to a€ord 8d as a
yellow oil (96 mg, 94%). 1H NMR (CDCl3) d 1.27 (9 H,
s), 6.13 (1 H, dd, J=8.1, 11.7 Hz), 7.06 (1 H, d,
J=7.8 Hz), 7.19±7.48 (4 H, m), 9.74 (1 H, d, J=8.1 Hz);
MS (FAB) m/z 233 [(M+H)+, 13], 149 (24), 147 (16),
131 (100). Anal. calcd for C14H16O3: C, 72.39; H, 6.94.
Found: C, 72.09; H, 6.91.
2-[(Z)-3-Oxo-1-propenyl]phenyl acetate (8a). To a solu-
tion of PCC (677 mg, 3.14 mmol) in dry CH2Cl2 (35 mL)
was added dropwise
a
solution of 7a (302 mg,
(Z)-3-[2-(Acetyloxy)phenyl]-2-propenoic acid (9a). A
1.57 mmol) in dry CH2Cl2 (20 mL) during 20 min. After
stirring at room temperature under N2 atmosphere for
30 min, the black solution was poured onto a short silica
solution of 80% sodium chlorite (648 mg, 5.73 mmol) in
water (5.73 mL) was added dropwise within 2 h period
to a stirred mixture of 8a (777 mg, 4.09 mmol) in

424
B. Wang et al./Bioorg. Med. Chem. 6 (1998) 417±426
acetonitrile (4.09 mL), sodium phosphate (132 mg,
1.10 mmol) in water (1.64 mL), and 30% hydrogen per-
oxide (0.48 mL). During the addition, the reaction tem-
perature was kept at 10 ꢀC with an ice-water bath.
Oxygen evolution from the solution was observed until
the end of the reaction (about 2 h) with a bubbler con-
nected to the apparatus. A small amount of sodium
sul®te was added to destroy the unreacted HOCl and
H2O2. The solution was acidi®ed with 1 N HCl to pH 1-
2. The mixture was extracted with ethyl acetate (80 mL).
The ethyl acetate layer was washed with saturated
sodium chloride solution (2Â30 mL) and dried over
MgSO4. Filtration and evaporation of the solvent
a€orded 9a as a white solid (834 mg, 99%). 1H NMR
(CD3OD) d 2.25 (3 H, s), 6.05 (1 H, d, J=12.6 Hz), 6.91
(1 H, d, J=12.6 Hz), 7.07±7.52 (4 H, m); MS (FAB) m/z
207 [(M+H)+, 45], 148 (18), 147 (100), 146 (49). Anal.
calcd for C11H10O4: C, 64.07; H, 4.89. Found: C, 63.80;
H, 4.74.
(FAB) m/z 249 [(M+H)+,10], 147 (100), 146 (28). Anal.
calcd for C14H16O4: C, 67.72; H, 6.50. Found: C, 67.54;
H, 6.57.
2-[(Z)-3-(Benzylamino)-3-oxo-1-propenyl]phenyl acetate
(10a). To a solution of 9a (123 mg, 0.597 mmol) in dry
CH2Cl2 (3 mL), DCC (148 mg, 0.716 mmol) was added
at 0 ꢀC and the solution was stirred for 10 min. Then
HOBt (89 mg, 0.657 mmol) was added and the solution
was stirred for an additional 10 min. To the mixture was
added dropwise benzylamine (70 mg, 0.657 mmol), then
DMAP (14.5 mg, 0.119 mmol). After stirring at 0 ꢀC
under N2 atmosphere for 1 h, the ice-bath was with-
drawn and the reaction was kept stirring at room tem-
perature for 3 h. Then the reaction was cooled in a
freezer ( 20 ꢀC) for 15 min and ®ltered to remove the
1,3-dicyclohexylurea (DCU) white precipitate. After the
addition of CH2Cl2 (50 mL), the organic layer was
washed with saturated NaHCO3 solution (3Â15 mL),
10% citric acid (2Â15 mL), and water (20 mL) and then
dried over MgSO4. Filtration and evaporation gave a
light yellow oil (212 mg), which was chromatographed
on a silica gel column with ethyl acetate/hexanes (1:4) to
give 10a as a white solid (137 mg, 78%). 1H NMR
(CDCl3) d 2.26 (3 H, s), 4.27 (2 H, d, J=5.4 Hz), 6.15 (1
H, d, J=12.0 Hz), 6.59 (1 H, brs), 6.72 (1 H, d,
J=12.0 Hz), 6.92±7.31 (9 H, m); MS (EI) m/z 295 (M+,
5), 236 (81), 147 (61), 106 (100), 91 (78), 43 (22). Anal.
calcd for C18H17NO3: C, 73.20; H, 5.80; N, 4.74. Found:
C, 73.15; H, 5.90; N, 4.75.
(Z)-3-[2-(Propionyloxy)phenyl]-2-propenoic acid (9b). In
a manner similar to the preparation of 9a, 80% sodium
chlorite (76 mg, 0.672 mmol) in water (0.672 mL), 8b
(98 mg, 0.48 mmol) in acetonitrile (0.48 mL), sodium
phosphate (15.5 mg, 0.13 mmol) in water (0.194 mL),
and 30% hydrogen peroxide (0.06 mL) were reacted to
a€ord 9b as a white solid (101 mg, 96%). 1H NMR
(CDCl3) d 1.20 (3 H, t, J=7.5 Hz), 2.50 (2 H, q,
J=7.5 Hz), 5.97 (1 H, d, J=12.6 Hz), 6.93 (1 H, d,
J=12.6 Hz), 7.00±7.43 (4 H, m); MS (FAB) m/z 221
[(M+H)+, 12], 149 (12), 148 (12), 147 (100), 146 (24).
Anal. calcd for C12H12O4: C, 65.45; H, 5.49. Found: C,
65.48; H, 5.59.
2-[(Z)-3-(Benzylamino)-3-oxo-1-propenyl]phenyl propionate
(10b). In a manner similar to the preparation of 10a, 9b
(387 mg, 1.76 mmol), DCC (472 mg, 2.29 mmol), HOBt
(285 mg, 2.11 mmol), benzylamine (340 mg, 3.17 mmol),
and DMAP (65 mg, 0.53 mmol) were reacted at room
temperature for 5.5 h to give 10b as a white solid
(332 mg, 61%). 1H NMR (CDCl3) d 1.26 (3 H, t,
J=7.5 Hz), 2.58 (2 H, q, J=7.5 Hz), 4.29 (2 H, d,
J=6.0 Hz), 6.15 (1 H, d, J=11.7 Hz), 6.54 (1 H, brs),
6.72 (1 H, d, J=11.7 Hz), 6.92±7.32 (9 H, m); MS (EI)
m/z 309 (M+, 1), 236 (65), 147 (45), 106 (100), 91 (73),
57 (10). Anal. calcd for C19H19NO3: C, 73.77; H, 6.19;
N, 4.53. Found: C, 73.34; H, 6.44; N, 4.72.
(Z)-3-[2-(Isobutyryloxy)phenyl]-2-propenoic acid (9c). In
a manner similar to the preparation of 9a, 80% sodium
chlorite (594 mg, 5.25 mmol) in water (5.25 mL), 8c
(817 mg, 3.75 mmol) in acetonitrile (3.75 mL), sodium
phosphate (121 mg, 1.01 mmol) in water (1.52 mL), and
30% hydrogen peroxide (0.44 mL) were reacted to
a€ord 9c as a white solid (877 mg, 100%). 1H NMR
(CDCl3) d 1.29 (6 H, d, J=7.2 Hz), 2.79 (1 H, m), 6.03
(1 H, d, J=12.3 Hz), 7.00 (1 H, d, J=12.3 Hz), 7.05±
7.50 (4 H, m); MS (FAB) m/z 234 (M+, 3), 149 (54), 147
(100), 131 (10). Anal. calcd for C13H14O4: C, 66.66; H,
6.02. Found: C, 66.26; H, 6.13.
2-[(Z)-3-(Benzylamino)-3-oxo-1-propenyl]phenyl 2-methyl-
propanoate (10c). In a manner similar to the prepara-
tion of 10a, 9c (107 mg, 0.457 mmol), DCC (113 mg,
0.548 mmol), HOBt (68 mg, 0.503 mmol), benzylamine
(54 mg, 0.503 mmol), and DMAP (11 mg, 0.091 mmol)
were reacted to give 10c as a colorless oil (98 mg, 66%).
1H NMR (CDCl3) d 1.30 (6 H, d, J=6.9 Hz), 2.83 (1 H,
m), 4.29 (2 H, d, J=6.0 Hz), 6.15 (1 H, d, J=12.3 Hz),
6.58 (1 H, brs), 6.71 (1 H, d, J=12.3 Hz), 6.91±7.32 (9 H,
m); MS (FAB) m/z 324 [(M+H)+, 100], 254 (97), 236
(33), 147 (36), 106 (29). Anal. calcd for C20H21NO3: C,
(Z)-3-{[2-(2,2-Dimethylpropanoyl)oxy]phenyl}-2-propenoic
acid (9d). In a manner similar to the preparation of 9a,
80% sodium chlorite (526 mg, 4.65 mmol) in water
(4.65 mL), 8d (770 mg, 3.32 mmol) in acetonitrile
(3.32 mL), sodium phosphate (108 mg, 0.90 mmol) in
water (1.35 mL), and 30% hydrogen peroxide
(0.39 mL) were reacted to a€ord 9d as a light yellow
solid (822 mg, 100%). 1H NMR (CDCl3) d 1.34 (9 H, s),
6.03 (1 H, d, J=12.3 Hz), 6.99±7.49 (5 H, m); MS

B. Wang et al./Bioorg. Med. Chem. 6 (1998) 417±426
425
74.28; H, 6.55; N, 4.33. Found: C, 73.89; H, 6.49;
N, 4.45.
2-[(E)-3-Anilino-3-oxo-1-propenyl]phenyl acetate (11). In
a manner similar to the preparation of 10a, 9a (122 mg,
0.592 mmol), DCC (146 mg, 0.710 mmol), HOBt (88 mg,
0.651 mmol), aniline (61 mg, 0.651 mmol), and DMAP
(14 mg, 0.118 mmol) were reacted at room temperature
2-[(Z)-3-(Benzylamino)-3-oxo-1-propenyl]phenyl pivalate
(10d). In a manner similar to the preparation of 10a, 9d
(93 mg, 0.375 mmol), DCC (100 mg, 0.487 mmol), HOBt
(61 mg, 0.450 mmol), benzylamine (72 mg, 0.675 mmol),
and DMAP (14 mg, 0.112 mmol) were reacted at room
temperature for 9.5 h to give 10d as a white solid (98 mg,
1
for 4.5 h to give 11 as white crystals (67 mg, 40%). H
NMR (CDCl3) d 2.27 (3 H, s), 6.53 (1 H, d, J=15.6 Hz),
7.00±7.60 (9 H, m), 7.76 (1 H, d, J=15.6 Hz), 8.45 (1 H,
brs); MS (EI) m/z 281 (M+, 11), 239 (17), 147 (100), 93
(72), 43 (26). Anal. calcd for C17H15NO3: C, 72.58; H,
5.37; N, 4.98. Found: C, 72.23; H, 5.36; N, 4.93.
1
78%). H NMR (CDCl3) d 1.34 (9 H, s), 4.29 (2 H, d,
J=6.0 Hz), 6.14 (1 H, d, J=12.0 Hz), 6.64 (1 H, brs),
6.71 (1 H, d, J=12.0 Hz), 6.92±7.32 (9 H, m); MS (EI)
m/z 337 (M+, 1), 236 (60), 147 (39), 106 (100), 91 (70),
57 (44). Anal. calcd for C21H23NO3: C, 74.75; H, 6.87;
N, 4.15. Found: C, 74.48; H, 6.94; N, 4.34.
Acknowledgements
Partial ®nancial support from the Presbyterian Health
Foundation (PHF-987) is gratefully acknowledged.
2-[(Z)-3-(4-Methoxyanilino)-3-oxo-1-propenyl]phenyl ace-
tate (10g). In a manner similar to the preparation of
10a, 9a (136 mg, 0.660 mmol), DCC (163 mg, 0.792
mmol), HOBt (98 mg, 0.726 mmol), p-anisidine (122 mg,
0.990 mmol), and DMAP (16 mg, 0.132 mmol) were
reacted to give 10g as a white solid (68 mg, 33%). 1H
NMR (CDCl3) d 2.35 (3 H, s), 3.72 (3 H, s), 6.23 (1 H,
d, J=11.7 Hz), 6.73 (2 H, d, J=8.7 Hz), 6.83 (1 H, d,
J=11.7 Hz), 7.06±7.37 (6 H, m), 7.93 (1 H, brs); MS
(EI) m/z 311 (M+, 76), 252 (60), 147 (90), 123 (100), 108
(49), 43 (29). Anal. calcd for C18H17NO4: C, 69.44; H,
5.50; N, 4.50. Found: C, 69.18; H, 5.53; N, 4.64.
References
1. Wang, B.; Zhang, H.; Wang, W. Bioorg. Med. Chem. Lett.
1996, 6, 945.
2. Wang, B.; Wang, W.; Zhang, H.; Shan, D.; Smith, T. D.
Bioorg. Med. Chem. Lett. 1996, 6, 2823.
3. Hersh®eld, R.; Schmir, G. L. J. Am. Chem. Soc. 1973, 95,
7359.
4. Hersh®eld, R.; Schmir, G. L. J. Am. Chem. Soc. 1973, 95,
8032.
5. Lippold, B. C.; Garrett, E. R. J. Pharm. Sci. 1971, 60, 1019.
2-{(Z)-3-[Benzyl(methyl)amino]-3-oxo-1-propenyl}phenyl
acetate (10h). In a manner similar to the preparation of
10a, 9a (135 mg, 0.655mmol), DCC (162 mg, 0.786 mmol),
HOBt (97 mg, 0.720 mmol), N-benzylmethylamine
(87 mg, 0.720 mmol), and DMAP (16 mg, 0.131 mmol)
were reacted at room temperature for 3.5 h to a€ord 10h
as a white solid (135 mg, 67%). 1H NMR (CDCl3) d
2.27 (3 H, d, J=7.2 Hz), 2.67/2.85 (3 H, ss), 4.33/4.56 (2
H, ss), 6.17 (1 H, dd, J=6.9, 12.6 Hz), 6.66 (1 H, d,
J=12.6 Hz), 6.97±7.62 (9 H, m); MS (EI) m/z 309 (M+,
20), 250 (54), 147 (62), 120 (100), 91 (73), 43 (21). Anal.
calcd for C19H19NO3: C, 73.77; H, 6.19; N, 4.53. Found:
C, 73.52; H, 6.19; N, 4.47.
6. Garrett, E. R.; Lippold, B. C.; Mielck, J. B. J. Pharm. Sci.
1971, 60, 396.
7. Amsberry, K. L.; Gerstenberger, A. L.; Borchardt, R. T.
Pharm. Res. 1991, 8, 455.
8. Amsberry, K. L.; Borchardt, R. T. Pharm. Res. 1991, 8, 323.
9. Shan, D.; Nicolaou, M. G.; Borchardt, R. T.; Wang, B. J.
Pharm. Sci. 1997, 86, 765.
10. Amsberry, K. L.; Borchardt, R. T. J. Org. Chem. 1990, 55,
5867.
11. Wang, B.; Gangwar, S.; Pauletti, G. M.; Siahaan, T.;
Borchardt, R. T. J. Org. Chem. 1997, 62, 1362.
12. Pauletti, G. M.; Gangwar, S.; Wang, B.; Borchardt, R. T.
Pharm. Res. 1997, 14, 11.
13. Coumarins. Biology, Applications and Mode of Action;
O'Kennedy, R.; Thornes, R. D., Eds.; John Wiley & Sons: New
York, 1997.
2-[(Z)-3-(Diethylamino)-3-oxo-1-propenyl]phenyl acetate
(10i). In a manner similar to the preparation of 10a, 9a
(111 mg, 0.539 mmol), DCC (133 mg, 0.647 mmol),
HOBt (80 mg, 0.593 mmol), diethylamine (51 mg,
0.701 mmol), and DMAP (13 mg, 0.108 mmol) were
reacted at room temperature for 4.5 h to give 10i as a
14. Cox, D.; O'Kennedy, R.; Thornes, R. D. Human Toxicol.
1989, 8, 501.
15. Thornes, R. D. In Coumarins. Biology, Applications and
Mode of Action; O'Kennedy, R.; Thornes, R. D., Eds.; John
Wiley & Sons: New York, 1997; p 255.
1
white solid (56 mg, 40%). H NMR (CDCl3) d 0.90 (3
H, t, J=6.9 Hz), 1.11 (3 H, t, J=6.9 Hz), 2.33 (3 H, s),
3.18 (2 H, q, J=6.9 Hz), 3.42 (2 H, q, J=6.9 Hz), 6.12 (1
H, d, J=12.6 Hz), 6.61 (1 H, d, J=12.6 Hz), 7.03±7.60
(4 H, m); MS (EI) m/z 261 (M+, 13), 219 (55), 202 (100),
147 (72), 43 (25). Anal. calcd for C15H19NO3: C, 68.94;
H, 7.33; N, 5.36. Found: C, 68.89; H, 7.29; N, 5.15.
16. Marshall, M. E.; Butler, K.; Fried, A. Mol. Biother. 1991,
3, 170.
17. Mohler, J. L.; Gomella, L. G.; Crawford, E. D.; Glode, L.
M.; Zippe, C. D.; Fair, W. R.; Marshall, M. E. Prostate 1992,
120, 123.
18. Wang, B.; Zheng, A. Chem. Pharm. Bull. 1997, 45, 715.

426
B. Wang et al./Bioorg. Med. Chem. 6 (1998) 417±426
19. Tius, M. A.; Fauq, A. H. J. Am. Chem. Soc. 1986, 108,
1035.
23. Tamm, C. Indian J. Chem. 1993, 32B, 190.
24. Handbook of Physical Properties of Organic Chemicals;
Howard, P. H.; Meylan, W. M., Eds.; CRC: Boca Raton, FL,
1997, p 161.
20. Dalcanale, E.; Montanari, F. J. Org. Chem. 1986, 51, 567.
21. Wang, B.; Zheng, A.; Zhang, H. Manuscript in preparation.
25. CRC Handbook of Chemistry and Physics; 75th ed.; Lide,
D. R., Ed.; CRC: Boca Raton, FL, 1994, pp 8-46.
22. Seki, H.; Kawaguchi, T.; Higuchi, T. J. Pharm. Sci. 1988,
77, 855.