Synthesis and stability of two indomethacin prodrugs

Article abstract of DOI:10.1016/j.bmcl.2006.01.003

The purpose of this study was to synthesize and study the in vitro enzymatic and non-enzymatic hydrolysis of indomethacin-TEG ester and amide prodrugs. It was found that the ester conjugate 10 was comparatively stable between pH 3 and 6 (half-life >90 h),

Full text of DOI:10.1016/j.bmcl.2006.01.003

Bioorganic & Medicinal Chemistry Letters 16 (2006) 1874–1879
Synthesis and stability of two indomethacin prodrugs
Shyamala Chandrasekaran, Abeer M. Al-Ghananeem,
Robert M. Riggs and Peter A. Crooks*
Department of Pharmaceutical Sciences, College of Pharmacy, University of Kentucky, Lexington, KY 40536-0082, USA
Received 6 October 2005; revised 23 December 2005; accepted 4 January 2006
Available online 24 January 2006
Abstract—The purpose of this study was to synthesize and study the in vitro enzymatic and non-enzymatic hydrolysis of indometh-
acin–TEG ester and amide prodrugs. It was found that the ester conjugate 10 was comparatively stable between pH 3 and 6 (half-
life >90 h), with a half-life equal to 5.2 h in 80% buffered plasma. In contrast, the amide conjugate 12 appeared to be stable over the
entire pH range studied with the only observed degradation being cleavage of the indolic N-4-chlorobenzoyl moiety.
ꢀ 2006 Elsevier Ltd. All rights reserved.
Indomethacin (1-[4-chlorobenzoyl]-5-methoxy-2-methyl
indole-3-acetic acid) is a potent non-steroidal anti-in-
flammatory agent used primarily in the treatment of
rheumatoid arthritis.1 The compound also has potential
for use in uveitis, a common disease afflicting 0.5% of
the population2 and responsible for over 30,000 cases
of legal blindness in the U.S.3 Indomethacin may also
be used in the management of cystoid macular edema
(CME), a disease characterized by a build up of serous
fluid extracellular space in the retina caused by a disrup-
tion of the blood–retinal barrier. CME is a common
occurrence after cataract and vitreo–retinal surgeries4
and is frequently associated with diabetes.5 In 1979
Klein et al.6 showed that systemic indomethacin de-
creased the incidence of post surgical CME at 4–6
weeks, however, other investigators7,8 failed to substan-
tiate these findings. The blood–eye barrier restricts intra-
ocular penetration of drugs requiring high systemic
dosing to achieve therapeutic levels within the eye.9 In
the case of indomethacin, systemic toxicities including
dyspepsia, headache, and dizziness10 limit the dose that
can be administered, and in many studies therapeutic
concentrations may not have been achieved. The topical
application of non-steroidal anti-inflammatory agents
would avoid many of these problems, but is limited by
the low concentrations that can be tolerated in the eye,
and by poor ocular absorption.11,12 In the soluble form,
indomethacin is an ionic surface active compound, and
such compounds have long been known to be damaging
to biological membranes.13 However, a non-ionic pro-
drug of indomethacin could be expected to be less dam-
aging. Walters et al.14 studied the effect of surfactants
composed of a linear dodecyl chain linked to various
polyoxyethylene glycol (PEG) chains (Brij surfactants).
They found that surfactants composed of PEGs contain-
ing less than 8 ethylene oxide units caused little damage
to rat GI tissues, while those with PEGs containing
more than 10 units both decreased the barrier function
and stripped proteins from the surface of the gastric
mucosal membrane. Nishima and co-investigators15
examined the transdermal absorption of Brij type sur-
factants in the mouse model and found that maximal
absorption occurred with short ethylene oxide chains.
These findings suggest that a PEG prodrug of indometh-
acin may have increased absorption and decreased irri-
tancy compared to the parent compound. A further
advantage of PEG as a potential prodrug moiety is that
upon enzymatic cleavage, parent drug plus PEG would
be regenerated, and PEG is essentially biologically inert,
and is used as a marker substance to monitor GI absorp-
tion in human.16,17
The present research work focuses on the design and
strategy involved in the synthesis and in vitro enzymatic
and non-enzymatic hydrolysis of two prodrugs of
indomethacin conjugated with triethylene glycol
(TEG) at the carboxylic acid moiety via either an ester
or an amide linkage. The two prodrugs were the
indomethacin–TEG ester and amide conjugates.
Keywords: Indomethacin; Prodrug; Stability.
*
Solvents were obtained from Fischer Scientific Co.
(Fairlawn, NJ, USA). Indomethacin, borax, and
Corresponding author. Tel.: +1 859 257 1718; fax: +1 859 257
7585; e-mail: pcrooks@email.uky.edu
0960-894X/$ - see front matter ꢀ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2006.01.003

S. Chandrasekaran et al. / Bioorg. Med. Chem. Lett. 16 (2006) 1874–1879
1875
chemicals used in synthetic procedures were obtained
from Sigma–Aldrich Chemicals (St. Louis, MO, USA).
Lithium azide and palladium on 5% carbon were ob-
tained from Eastman-Kodak (Rochester, NY, USA).
Chromatographic silica (grade 62) was purchased from
Davison Chemical, Baltimore, MD. PkF6 silica gel
preparative TLC plates (1000 lm) with fluorescent
indicator were obtained from Whatman Labsales Inc.
(Hillsoboro, OR, USA).
buffer was maintained at a constant value of 0.5, by
addition of an appropriate amount of potassium chlo-
ride. Tubes were sealed and immersed in a water bath
at 37 2 ꢁC. A sample of 200 lL was withdrawn period-
ically, quenched in an ice bath and assayed by HPLC.
Both the disappearance of the prodrug and the appear-
ance of indomethacin were measured. For the enzymatic
hydrolysis studies; fresh human blood was withdrawn
and allowed to stand for about 15 min. Fresh plasma
was generated by centrifugation at 3000 rpm for
15 min. The supernatant plasma was carefully with-
drawn and an 80% solution was prepared by addition
of 20% of 0.1 M phosphate buffer (pH 7.4). Standard
solutions of indomethacin prodrugs were prepared by
dissolving the appropriate prodrug in methanol. The
methanolic solution of the prodrug (50 ll) was added
to 5 mL of fresh human buffered plasma to give a final
concentration of 4.85 · 10ꢀ4 M. Tubes were sealed and
immersed in a water bath at 37 2 ꢁC. In triplicate,
100 ll of the sample was periodically removed and add-
ed to 100 ll acetonitrile to precipitate plasma proteins in
a microcentrifuge tube. Tubes were vortexed and
centrifuged at 14,000 rpm for 8 min. Hundred microliter
of the supernatant solution was analyzed by the HPLC
for both the prodrug and indomethacin content.
High-performance liquid chromatographic (HPLC)
analyses were carried out on a Hitachi System consisting
of an L-4000 UV detector, L-6200 intelligent pump, and
AS-2000 Autosampler (Hitachi, Tokyo, Japan). The
chromatographic column used was C18 reverse-phase
column (250 mm · 4.5 mm · 5 lm) fitted with a precol-
umn (Hamilton, Reno, Nevada). Chromatograms were
recorded on a D-2500 Chromatointegrator. The flow
rate for the entire part of the analytical study was main-
tained at 1 mL/min, and detection was by UV absorp-
tion at 270 nm. All nuclear magnetic resonance
(NMR) spectra were carried out in deuterated chloro-
form, unless otherwise stated, on a Varian VXR-300
spectrometer operating at 300 MHz (Varian Associates,
Palo Alto, CA). Chemical shifts are recorded as d values
(ppm) downfield from TMS as an internal standard; all
signals are classified as singlet (s), broad singlet (br s),
doublet (d), triplet (t), multiplet (m), and apparent dou-
blet (app d). Ultraviolet (UV) spectra were recorded on
a Hewlett Packard 9153C spectrophotometer, connected
to a Hewlet Packard 8452A diode array detector and a
Hewlet Packard Thick Jet Printer.
The indomethacin prodrugs 10 and 12 were successfully
synthesized according to Schemes 1 and 2 and carefully
characterized. In summary, monotritylation of triethyl-
ene glycol (TEG) to give 2 was best achieved by utilizing
a 1:1 molar ratio of trityl chloride and TEG (Scheme 1).
Only a small amount of ditritylated TEG contaminated
the final product and was efficiently removed by silica
gel column chromatography. Activation of indometha-
cin by reaction with carbonyl diimidazole, and coupling
of the resulting reactive intermediate 8 with the monotri-
tyl TEG afforded the protected conjugate 9 in low yield
(8–10%). O-detritylation of 9 was carried out using
20 % TFA in dichloromethane to afford the indometha-
cin–TEG ester prodrug 10 in 64% yield (Scheme 2).
For the non-enzymatic hydrolysis studies; a stock
methanolic solution of each prodrug was prepared. In
triplicate, 0.1 mL of this solution was added to 5 mL
of 0.1 M buffer (pH 1–11) in a culture tube to give a final
concentration of 1.28 · 10ꢀ5 M. The buffers used were
hydrochloric acid, sodium acetate, potassium phos-
phate, and sodium borate. Ionic strength (l) for each
C6H5
O
OH Pyridine
O
OH
HO
O
C6H5
O
O
Trityl chloride
45 oC/N2 gas
24 hours
(1)
(2)
C6H5
Mesyl chloride
0-5 oC/N2 gas
24 hours
Pyridine
O
C6H5
O
O
S
CH3
C6H5
O
O
O
LiN3
C6H5
(3)
DMF/N2 45oC/24 hours
C6H5
LAH
O
N3
Dry THF
0oC/45 min
C6H5
O
O
C6H5
(4)
C6H5
O
O
NH2
C6H5
O
C6H5
(5)
Scheme 1. Synthesis of 1-hydroxy-8-trityloxy-3,6-dioxaoctane (2) and 1-amino-8-trityloxy-3,6-dioxaoctane (5).

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S. Chandrasekaran et al. / Bioorg. Med. Chem. Lett. 16 (2006) 1874–1879
chloroform. The eluent fractions containing the desired
compound were combined and stripped to yield an oily
mass (2.47 g, 63%)
1-Mesyloxy-8-trityloxy-3,6-dioxaoctane (3). Using a
Modification of the procedure reported by Harris
et al.19 compound 2 was dissolved in pyridine (25 mL)
and cooled to 0 ꢁC under nitrogen gas. A solution of me-
syl chloride (1.97 mL, 0.018 mol) was added slowly, and
the reaction was allowed to proceed overnight at 4 ꢁC.
The resultant dark liquid was added to ice-cold water
(200 mL) and partitioned between water and CH2Cl2
(4 · 20 mL). The organic layer was dried over anhy-
drous MgSO4 and the solvent was removed azeotropi-
cally at low pressure on a rotary evaporator. The
resulting syrup was eluted through a silica gel column
with 2% MeOH in CHCl3, to afford pale yellow crystals
of compound 3 with a yield of 1.8 g (60%).
1-Azido-8-trityloxy-3,6-dioxaoctane (4). In an adapta-
tion of the method employed by Reynolds et al.,20
compound 3 (1.77 g, 0.0037 mol) was stirred into
dimethylformamide (DMF) under nitrogen gas. Lithium
azide (0.91 g, 0.019 mol) was added, and the resultant
mixture was heated to 45ꢁC for 24 h, after which time
the reaction was essentially complete. The DMF was re-
moved in vacuo and the resulting syrup was added to
water (15 mL) and partitioned between water and
CH2Cl2 (4 · 20 mL). The organic layer was dried over
MgSO4 and evaporated to yield an oily liquid. The
crude product 4 was used for the next synthetic reaction
without further purification with a yield of 1.46 g (93%).
Scheme 2. Activation of indomethacin by reaction with carbonyl
diimidazole (CDI), and its use in the synthesis of indomethacin–TEG
ester (10) and indomethacin–TEG amide (12) prodrugs.
1-Amino-8-trityloxy-3,6-dioxaoctane (5). Compound 4
(0.300 g, 0.000718 mol) was added to lithium aluminum
hydride (LAH) (0.120 g, 0.0032 mol) that had been dis-
solved in dry tetrahydrofuran (THF) (10 mL). The reac-
tion mixture was cooled to 0 ꢁC and allowed to stir for
45 min. The reaction was quenched by addition of a
water–THF mixture (0.5 mL water in 10 mL THF)
and filtered through a Celite filter pad using petroleum
ether. The ethereal solution was evaporated to dryness
and compound 5 was obtained as a syrup with a yield
of 0.098 g (35%).
The indomethacin–TEG amide prodrug 12 was synthe-
sized utilizing a strategy similar to that employed in
the preparation of 10 (Scheme 2), starting from the O-
trityl protected precursor 5, which was synthesized from
TEG via the four-step procedure illustrated in Scheme 1.
This procedure involved initial monotritylation of TEG
followed by O-mesylation to give 3, displacement of the
O-mesyl group with azide ion to give 4. Azide reduction
was carried out using lithium aluminum hydride in
anhydrous THF, affording compound 5 in 35% yield.
Coupling of 5 with 8 afforded the protected conjugate
11 in 61% yield. Finally, O-detritylation with TFA affor-
ded a good yield (74%) of the indomethacin–TEG amide
prodrug 12.
1-{3-[1-(p-Chlorobenzoyl)-5-methoxy-2-methyl)-indolace-
tyl]}-imidazole (8). Carbonyl diimidazole (CDI) (0.038 g,
0.000234 mol) was added to a solution of indomethacin 6
(0.077 g, 0.000215 mol) in dry THF (0.5 mL) and the solu-
tion was allowed to stir over 3 h. After this time, the reac-
tion was found to be essentially complete, as indicated by
TLC monitoring. The product from this reaction was
immediately used for the next synthetic step without fur-
ther manipulation.
10,10,10-Triphenyl-3,6,9-trioxadecan-1-ol (2). Using a
modification of the procedure reported by Blickenstaf,18
triethylene glycol (TEG) 1 (1.5 g, 0.01 mol) was stirred
into pyridine containing trityl chloride (2.7 g,
0.0096 mol). The resultant mixture was heated to
45 ꢁC and allowed to stir overnight under nitrogen
gas. The mixture was added to ice-cold water (200 mL)
and partitioned between water and CH2Cl2
(4 · 20 mL). The organic layer was separated and dried
over MgSO4, and the solvent was removed azeotropical-
ly with toluene under vacuum on a rotary evaporator.
The resultant syrupy mass was purified by column chro-
matography on silica gel, eluting with 2% methanol in
1-{3-[1-(p-Chlorobenzoyl)-5-methoxy-2-methylindol-acet-
oxy]}-8-trityloxy-3,6-dioxaoctane. [1-Indomethacin-8-tri-
tyl TEG (ester) conjugate] (9). Compound 2 (0.2 g,
0.000509 mol) was dissolved in dry THF (1 mL) and
the solution was added to the indomethacin–CDI inter-
mediate 8. The reaction was allowed to proceed over
24 h. The solvent was evaporated in vacuo, the residue
was dissolved in chloroform, and silica gel column

S. Chandrasekaran et al. / Bioorg. Med. Chem. Lett. 16 (2006) 1874–1879
1877
1
chromatography was performed with 95:5 CHCl3/MeOH
as eluting solvent. The fractions were combined and evap-
orated to yield compound 9 as an oily liquid with a yield
of 0.035 g (9%).
0.5
0
0
2
4
6
8
10
12
-0.5
1-{1-3-[(p-Chlorobenzoyl)-5-methoxy-2-methylindol-acet-
oxy]}-3,6-dioxaoctane. [Indomethacin–TEG ester conju-
gate] (10). Using the synthetic method reported by
Hanessian et al.21 compound 9 was dissolved in CH2Cl2
(1 mL) and a 5:1 CH2Cl2/trifluoroacetic acid mixture
was slowly added to the solution under a nitrogen atmo-
sphere. After 30 min, the reaction was found to be essen-
tially complete and was quenched by addition of MeOH.
Purification of the product was carried out by elution
through a silica gel pad with CHCl3, followed by 95:5
CHCl3/MeOH. After evaporation of solvent, a yield of
compound 10 was obtained (0.015 g, 64%).
-1
-1.5
-2
-2.5
pH
Figure 1. pH rate profile of indomethacin–TEG ester prodrug.
1
0.5
0
8-Trityloxy-1-{1-3-[(p-chlorobenzoyl)-5-methoxy-2-meth-
ylindol-acetamido]}-3,6-dioxaoctane (11). Compound 5
(0.08 g, 0.002 mol) was dissolved in THF (1 mL) and
the resulting solution was added to a prepared mixture
of the indomethacin–CDI intermediate (0.00027 mol).
The mixture was warmed to 40ꢁC and left to stand for
24 h. The solvent was evaporated in vacuo, the residue
was dissolved in chloroform and silica gel column chro-
matography was performed with 95:5 CHCl3/MeOH as
eluting solvent. The fractions were combined and evapo-
rated to yield compound 11 (0.1 g, 61%).
0
2
4
6
8
10
12
-0.5
-1
-1.5
-2
-2.5
-3
pH
Figure 2. pH rate profile of indomethacin–TEG amide prodrug.
are most stable at pH 4.7. The sharp decline in the
half-life value as the pH exceeds 7 indicates that the pro-
drug is more susceptible to hydrolysis by hydroxyl ion.
1-{1-3-[(p-Chlorobenzoyl)-5-methoxy-2-methylindol-acet-
amido]}-3,6-dioxaoctane. [Indomethacin–TEG amide con-
jugate] (12). Compound 11 (0.08 g, 0.000106 mol) was
dissolved in CH2Cl2 (1.5 mL) and a mixture of 5:1
CH2Cl2/trifluoroacetic acid (2 mL) was added to the solu-
tion. The mixture was stirred for 30 min, and the reaction
was quenched by addition of MeOH, after confirming the
completion of the reaction by TLC analysis (9:1 chloro-
form/methanol). The crude product was purified by pre-
parative silica gel TLC (9:1 CHCl3/MeOH) to obtain
compound 12 as a crystalline, pale yellow solid with a
yield of 0.04 g (74%).
Earlier experiments have shown that amide prodrugs of
indomethacin do not normally hydrolyze to yield the
parent drug during the course of the experiment. The
major hydrolytic product produced is from cleavage of
the indole N-4-chlorobenzoyl group of indomethacin.22
Degradation of the indomethacin–TEG amide prodrug
12 followed first-order kinetics. The t1/2 values are fairly
stable over the pH range tested and are most stable at
pH 5. At this pH, a half-life of almost 15 days was ob-
served. As the pH is increased, however, the stability of
the prodrug drops, and the prodrug appears to be more
susceptible to hydrolysis.
The non-enzymatic kinetics of the two prodrugs 10 and
12 were studied in 0.1 M buffer solutions (hydrochloric
acid, acetate, phosphate, and alkaline borate buffers),
at pH 1–11 (1, 3, 5, 6, 7.4, 8.5, 9.5, 10, and 11),
37 2 ꢁC; pH rate profiles were obtained by plotting
the logarithm of the observed first-order rate constant
(k) versus pH (Figs. 1 and 2). The hydrolysis of the pro-
drugs followed apparent first-order kinetics, and the rate
constants (k) were obtained as slopes from the semi-log-
arithmic plots of the unchanged prodrug concentration
versus time.
Hydroxyl ion is hypothesized to increase the susceptibil-
ity of the indomethacin–TEG amide bond to cleavage.
However, under these conditions the indole N-amide
bond may also be equally susceptible to cleavage, and
4-chloro-benzoic acid and the N-debenzylated indo-
methacin–TEG amid prodrug may be the major hydro-
lytic product. Thus, the prodrug could decompose either
by hydrolysis of the indomethacin–TEG amide bond or
by cleavage of the indole N-amide bond. The half-life of
indomethacin in buffer and plasma is about 135 h at
physiological pH and 37 ꢁC, while the half-life of the
amide prodrug 12 is about 35 h under the same condi-
tions. This indicates that the prodrug is most likely
being lost by indole N-amide bond cleavage, while it is
still attached to the TEG chain, since no indomethacin
was observed to be released from the amide prodrug).
Chemical stability was assessed by determining the
decomposition half-life and the pH rate profile curve
of indomethacin–TEG ester prodrug 10, which indicates
that this prodrug is subject to specific acid- and base-cat-
alyzed hydrolysis. The calculated half-life (t1/2) values
indicate that the prodrug is most stable between pH 3
and 6. This is in agreement with earlier reports by Kahns
et al.22 who reported that indomethacin ester prodrugs

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S. Chandrasekaran et al. / Bioorg. Med. Chem. Lett. 16 (2006) 1874–1879
Enzymatic hydrolysis of the above-mentioned prodrugs
10 and 12 in fresh buffered human plasma followed first
order kinetics with some variation in the rate of hydro-
lysis among the different prodrugs (Figs. 3 and 4).
linked to the TEG backbone, rather than by cleavage
of the indomethacin–TEG amide linkage.
The values of octanol–water partition coefficient (logP)
were calculated using Daylight Toolkit from Daylight
Chemical Information system (Mission Viejo, CA,
USA). The logP values for the indomethacin ester and
amide prodrugs were 3.8 and 3.1, respectively. These
values are slightly higher than the logP value of 3.0
for indomethacin. The enhancement in partition coeffi-
cient of the ester prodrug compared to that of indometh-
acin is due to the non-ionic nature of this prodrug
moiety compared to the ionic nature of the surface ac-
tive indomethacin molecule. Ester prodrugs of this type
should improve drug delivery of indomethacin and also
render formulations of the indomethacin prodrug less
damaging to biological membranes.
The average half-life of the ester prodrug 10 was 5.24 h,
which is in accordance with the reported half lives of
various indomethacin–PEG esters.22 The amide prodrug
12 exhibited a half-life of about 74 h, indicating that it is
fairly stable but not completely resistant to enzymatic
hydrolysis. The prodrug 12 can theoretically be cleaved
at the indomethacin–TEG amide bond to release indo-
methacin, which is subsequently degraded to the
N-debenzoylated form, or the indomethacin moiety
could be degraded via N-de-4-chlorobenzylation while
it is still attached to the TEG backbone.
HPLC analysis of the product resulting from the amide
prodrug hydrolysis did not show significant release of
indomethacin, which suggests that the prodrug is bro-
ken down primarily by cleavage of the indole N-amide
bond, affording N-debenzoylated indomethacin still
In conclusion, we have synthesized indomethacin pro-
drugs 10 and 12, consisting of indomethacin conjugated
to a TEG moiety via an ester and amide linkage, respec-
tively.23 As can be seen from the data, the esterase-sen-
sitive prodrug 10 can be converted to indomethacin
through a fairly rapid hydrolytic cleavage. However,
this cleavage in buffered solutions at pH 3–6 is relatively
slow, demonstrating that it may be possible to design
and formulate stable and effective ester prodrugs of
indomethacin in aqueous solution formulations.
20
18
16
14
12
10
8
References and notes
6
1. Bruckner, F. E.; Randle, A. P. Ann. Phys. Med. 1965, 13,
100.
4
2. Ogawa, T.; Ohara, K.; Shimizu, H.; Terai, T.; Watanabo,
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3. Durrani, O. M.; Tehrani, N. N.; Marr, J. E.; Moradi, P.;
Stavrou, P.; Murray, P. I. Br. J. Ophthalmol. 2004, 88,
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2
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Time (hours)
4. Lobes, L. A., Jr.; Grand, M. G. Arch. Ophthalmol. 1980,
98, 1230.
5. Ferris, F. L., 3rd; Patz, A. Surv. Ophthalmol. 1984, 28,
452.
6. Klein, R. M.; Katzin, H. M.; Yannuzzi, L. A. Am. J.
Ophthalmol. 1979, 87, 487.
Figure 3. The stability of indomethacin–TEG ester prodrug 10 in 80%
buffered human plasma. The data show the time course for the
disappearance of the prodrug 10 (Ç) and the appearance of the
indomethacin parent drug (j).
7. Yannuzzi, L. A.; Klein, R. M.; Wallyn, R. H.; Cohen, N.;
Katz, I. Am. J. Ophthalmol. 1977, 84, 517.
8. Sholiton, D. B.; Reinhart, W. J.; Frank, K. E. J. Am.
Intra-Ocular Implant Soc. 1979, 5, 137.
9. Peyman, G. A.; Schulman, J. A. Jap. J. Ophthalmol. 1989,
33, 392.
10. Katz, I. M. Ophthalmology 1987, 88, 455.
11. Ashton, P.; Walters, K.; Brian, K. R.; Hadgraft, J. Int. J.
Pharm. 1992, 87, 256.
12. Tang-Liu, D. D.; Liu, S. J. Pharm. Biopharm. 1987, 15,
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13. Riegelman, S.; Crowell, W. J. Am. Pharm. Assoc. 1958, 47,
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60
50
40
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14. Walters, K. A.; Dugart, P. H.; Florence, A. T. J. Pharm.
Pharmacol. 1981, 33, 207.
0
2
4
20
27
30
15. Nishiyama, T.; Iwata, Y.; Nakajima, K.; Mitsui, T. J. Soc.
Cosmet. Chem. 1973, 34, 263.
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enterology 1977, 73, 247.
Figure 4. The stability of indomethacin–TEG amide prodrug 12 in
80% buffered human plasma. The data show the time course for the
disappearance of the prodrug 12 (j). No significant release of
indomethacin was observed.

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1879
18. Blickenstaff, R. T. J. Am. Chem. Soc. 1960, 82, 3673.
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Compound 9: 1H NMR: d 2.46 (3H, s, 20-CH3); 3.64–3.77
(12H, m, 1,2,4,5,7,8-CH2’s); 3.85 (3H, s, 50-OCH3); 6.64
(1H, m, 60-CH); 6.87 (1H, d, 70-CH); 6.98 (1H, d, 40-CH)
7.20–7.41 [15H, 2· m at 7.20–7.35 (meta and para
aromatic protons, 9H) and 7.38–7.41 (ortho aromatic
protons, 6H)]; 7.44–7.52 (2H, apparent d, 200, 600-CH’s);
7.66–7.69 (2H, apparent d, 300, 500-CH’s). Compound 10:
1H NMR; d 1.26–1.34 (1H, br s, OH); 2.40 (3H, s, 20-
CH3); 3.62–3.74 (12H, m, 1,2,4,5,7,8-CH2’s); 7.42–7.50
(2H, apparent d, 200, 600-CH’s); 7,64–7.68 (2H, apparent d,
300, 500-CH’s). Elemental analysis: theoretical C, 61.29: H,
5.76; N, 2.86; found: C, 61.86; H, 5.94; N, 2.93%.
23. Compound 2: 1H NMR; d 2.36 (1H, m, OH); 3.25 (2H, m,
8-CH2); 3.61 (2H, m, 7-CH2); 3.64–3.78 (8H, m, 1,2,3,4,5-
CH2’s); 7.22–7.49 [15H, 2· m at 7.21–7.34 (meta and para
aromatic protons, 9H) and 7.42–7.49 (ortho aromatic
protons, 6H)]. Elemental analysis: theoretical C, 76.50; H,
7.19; found: C, 76.35; H 7.25%. Compound 3: 1H NMR: d
2.92 (3H, s, CH3SO2); 3.22 (2H, t, 8-CH2); 3.62 (2H, t, 7-
CH2); 3.70 (4H, s, 4,5 CH2’s); 3.80 (2H, t, 2-CH2); 4.38
(2H, t, 1-CH2); 7.22–7.49 [15H, 2· m at 7.21–7.34 (meta
and para aromatic protons, 9H) and 7.42–7.49 (ortho
aromatic protons, 6H]. Elemental analysis: theoretical C,
66.36; H, 6.43; found: C, 66.27; H, 6.40%. Compound 4:
1H NMR: d 3.41 (2H, m, 8-CH2); 3.56–3.61 (2H, m, 7-
CH2); 3.82 (8H, m, 1,2,4,5-CH2’s); 7.39–7.72 [15H, 2· m
at 7.39–7.56 (meta and para aromatic protons, 9H) and
7.64–7.72 (ortho aromatic protons, 6H)]; 13C NMR: 50.62
(1-CH2); 63.25 (2-CH2); 70.01 (4-CH2); 70.69–70.79 (5,7,8-
CH2’s); 86.45 [(Ph)3C-O]; 126.85–128.62 (meta and para
carbons, trityl C’s); 144.01 (ortho carbons, trityl C’s);
Elemental analysis: theoretical C, 71.92; H, 6.52; N, 10.06;
found: C, 72.00; H, 6.53, N, 10.00%. Compound 5: 1H
NMR: d 1.82–2.21 (2H, br s, NH2) 2.86–2.94 (2H, t, 1-
CH2); 3.51–3.59 (2H, t, 7-CH2); 3.62–3.78 (6H, m, 2,4,5-
CH2’s); 7.22–7.48 [15H, 2· m at 7.22–7.36 (meta and para
aromatic protons, 9H) and 7.41–7.48 (ortho aromatic
protons, 6H)]. Elemental analysis: theoretical C, 76.69;
H, 7.47; N, 3.58; found: C, 76.69; H, 7.53; N, 3.49%.
1
Compound 11: H NMR: d 2.32 (3H, s, 20-CH3); 3.18–
3.21 (2H, m, 8-CH2); 3.4–3.42 (2H, m, 7-CH2);3.51–3.56
(2H, s, 1-CH2); 3.58–3.62 (8H, m, 1,2,4,5-CH2s); 3.8(3H, s,
5-OCH3); 6.12 (1H, t, NH); 6.62–6.68 (1H, m, 6-CH);
6.81–6.83 (1H, apparent d, 7-CH); 6.86–6.91 (1H, appar-
ent d, 4-CH); 7.19–7.42 [15H, 2· m at 7.19–7.34 (meta and
para aromatic protons, 9H) and 7.40–7.42 (ortho aromatic
protons, 6H)]; 7.42–7.46 (2H, apparent d, 200, 600-CH’s);
7.62–7.64 (2H, apparent d, 300, 500-CH’s). 13C NMR: d
11.80 (20-CH2); 32.50 (8-CH2); 38.00 (7-CH2); 56.00 (50-
OCH3); 62.00 (CH2-CONH); 69.80–70.50 (2,4,5-CH2’s);
72.20 (1-CH2); 101.00 (40-CH); 112.0 (60-CH); 113.20 (400-
CCl); 115.00 (70-CH) ; 129.50 (200, 600-CH’s); 130.50 (100-
CH); 131.00 (20-CH); 131.50 (300, 500-CH’s); 133.80 (30a-
CH); 136.20 (70a-CH); 139.60 (30-CH); 156.00 (50-CH);
168.80 (10-NC@O); 170.00 (CONH). Compound 12: 1H
NMR: d 1.24 (1H, s, OH); 2.40 (3H, s, 20-CH3); 3.38–3.44
(2H, m, 1-CH2); 3.45–3.51 (8H, m, 2,4,5,7-CH2’s); 3.61–
3.62 (2H, m, 8-CH2); 3.62–3.66 (2H, s, 1-CH2); 3.80 (3H, s,
50-OCH3); 6.18 (1H, t, NH); 6.64–6.68 (1H, m, 60-CH);
6.82–6.85 (1H, apparent d, 70-CH); 6.86–6.88 (1H, appar-
ent d, 40-CH); 7.42–7.51 (2H, apparent d, 200, 600-CH’s);
7.62–7.64 (2H, apparent d, 30, 50-CH’s). Elemental anal-
ysis: theoretical C, 61.41; H, 5.98; N, 5.73; found: C, 61.66;
H, 6.04; N, 5.66 %.