Novel method for preparation of monoesters of symmetric diphenolic compounds like curcumin (1,7-bis(4-hydroxy-3-methoxy phenyl)-1,6-heptadiene-3,5- dione) via solid-phase synthesis

Article abstract of DOI:10.1080/00397910701575863

Synthesis of a monoester of symmetrical diphenolic compound curcumin (1,7-bis(4-hydroxy-3-methoxy phenyl)-1,6-heptadiene-3,5-dione) with glycine has been carried out by anchoring one of its free phenolic groups to an insoluble polymeric solid-support resin controlled pore glass-long chain alkylamine (CPG-LCAA) via a 2-carbon linker by solid-phase synthesis. The other free phenolic was esterified selectively with N-protected glycinoyl chloride to give the monoester exclusively. Subsequent deprotection of the amino group and deblocking of the monoester from polymer support by treatment with hydriodic acid (HI) gave the desired product. We earlier reported synthesis of a large number of diesters of curcumin, but selective esterification of one phenolic has been accomplished by this novel method, which can be used for preparing monoesters of any symmetric diphenol in quantitative yields. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/00397910701575863

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Novel Method for Preparation of Monoesters
of Symmetric Diphenolic Compounds like
Curcumin (1,7‐Bis(4‐hydroxy‐3‐methoxy
phenyl)‐1,6‐heptadiene‐3,5‐dione) via
Solid‐Phase Synthesis
Shiv Kumar Dubey a , Vishnu Dwivedi b & Krishna Misra b
a Centre for Biotechnology, University of Allahabad, Allahabad, India
b Chemistry Department, Science Faculty, University of Allahabad,
University Road, Allahabad, India
Available online: 10 Dec 2007
To cite this article: Shiv Kumar Dubey, Vishnu Dwivedi & Krishna Misra (2007): Novel Method for
Preparation of Monoesters of Symmetric Diphenolic Compounds like Curcumin (1,7‐Bis(4‐hydroxy‐3‐methoxy
phenyl)‐1,6‐heptadiene‐3,5‐dione) via Solid‐Phase Synthesis, Synthetic Communications: An International
Journal for Rapid Communication of Synthetic Organic Chemistry, 37:23, 4265-4271
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Synthetic Communicationsw, 37: 4265–4271, 2007
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910701575863
Novel Method for Preparation of
Monoesters of Symmetric Diphenolic
Compounds like Curcumin (1,7-Bis(4-
hydroxy-3-methoxy phenyl)-1,6-heptadiene-
3,5-dione) via Solid-Phase Synthesis
Shiv Kumar Dubey
Centre for Biotechnology, University of Allahabad, Allahabad, India
Vishnu Dwivedi and Krishna Misra
Chemistry Department, Science Faculty, University Road, University of
Allahabad, Allahabad, India
Abstract: Synthesis of a monoester of symmetrical diphenolic compoundcurcumin (1,7-
bis(4-hydroxy-3-methoxy phenyl)-1,6-heptadiene-3,5-dione) with glycine has been
carried out by anchoring one of its free phenolic groups to an insoluble polymeric
solid-support resin controlled pore glass-long chain alkylamine (CPG-LCAA) via a
2-carbon linker by solid-phase synthesis. The other free phenolic was esterified selec-
tively with N-protected glycinoyl chloride to give the monoester exclusively. Subsequent
deprotection of the amino group and deblocking of the monoester from polymer support
by treatment with hydriodic acid (HI) gave the desired product. We earlier reported
synthesis of a large number of diesters of curcumin, but selective esterification of one
phenolic has been accomplished by this novel method, which can be used for preparing
monoesters of any symmetric diphenol in quantitative yields.
Keywords: CPG-LCAA, curcumin, monoglycinoyl curcumin, solid phase
INTRODUCTION
The principle of solid-phase synthesis was developed by Bruce Merrifield in
the 1960s while synthesizing peptides.[1] Indeed, the impact and importance
Received in India May 11, 2007
Address correspondence to Krishna Misra, Chemistry Department, Science
Faculty, University Road, University of Allahabad, Allahabad 211002, India.
E-mail: krishnamisra@hotmail.com or kkmisra@yahoo.com
4265

4266
S. K. Dubey, V. Dwivedi, and K. Misra
of Merrifield’s work was such that he was awarded the Nobel Prize for
chemistry in 1984. Soon after the solid-phase method had been shown to be
valuable for peptide synthesis, the technique was applied to synthesis of oligo-
nucleotides and other compounds of commercial value. In the past two
decades, there have been several important developments,[2,3] and solid-
phase synthesis is now a widely used technique.
Curcumin (1,7-bis(4-hydroxy-3-methoxy phenyl)-1,6-heptadiene-3,5-
dione), a common Indian dietary pigment and spice, has been shown to
posses a wide range of therapeutic utilities in traditional Indian medicine
for wound healing, liver ailments, blood purification, and rheumatoid
arthritis.[3–5] The free phenolic groups in curcumin have been shown to be
responsible for many of its reported activities.[6,7] On the other hand, unsatura-
tion and active methylene do not seem to play any significant role.
However, it is well known that curcumin has very poor bioavailability, its
cellular uptake is low, and it gets metabolized fast once inside the cell,
requiring repetitive oral doses to achieve a significant concentration inside
the cell for therapeutic activity. We have earlier reported that covalent
linking of glycine, glycyl-glycine, and a number of other ligands with the
phenolic hydroxyls enhances antibacterial and antifungal activities multiple
[8–10]
`
times vis-a-vis curcumin.
Further, we have found that diesters of
curcumin with other ligands (viz., a number of amino acids and piperic
acid) also show better antimicrobial as well as anticancerous[11] and antipro-
liferative (apoptotic)[12] properties in vitro.
The enhancement in antipathogenic activity of these curcumin bioconju-
gates may be due to (1) an increase in hydrophilicity of the molecule and (2)
better cellular uptake as a result of the transportation of the conjugate via the
amino acid carrier protein. However, our studies further show that some
diesters of curcumin in which both the phenolic groups are covalently
protected by ligands other than amino acids (e.g., piperic acid) show much
`
less anticancer activity vis-a-vis curcumin.
Because monoesters enjoy both advantages (i.e., have one free phenolic
for anchoring and giving free radicals (ROS) and another phenolic esterified
with amino acids enhancing their bioavailability), the monoesters are
expected to have enhanced antimicrobial activity. It is with purpose that we
have prepared the monoglycine ester of curcumin by applying a solid-phase
approach. The method is of wide applicability for preparing monoesters of
any other symmetric phenol.
MATERIALS AND METHODS
All solvents used were purified and distilled prior to use. Long-chain alkyl
amine on controlled pore glass (CPG) resin was purchased from Sigma, and
curcumin and glycine were purchased from Merck-Schuchardt, Germany.
UV-visible spectra were recorded on
a Hitachi 220S UV-visible

Monoesters of Symmetric Diphenolic Compounds
4267
spectrophotometer. Synthetic-grade solvents were purchased from Qualigens
1
and were dried and purified prior to use. H NMR data were recorded on a
DRX300 instrument.
EXPERIMENTAL
N-Phthaloyl Glycine
Glycine (3.09 g; 0.04 M) and phthalic anhydride (8.88 g; 0.06 M) were taken
in a round-bottom flask and fused at 180–1858C with stirring for 10 min and
left undisturbed for 10 min. After 10 min, the solid mass was crystallized from
ethanolic water. Yield 86% (7.301 g).
N-Phthaloyl Glycinoyl Chloride
Phthaloyl glycine (2.051 g; 0.01 M) was heated on a water bath, and redistilled
thionyl chloride was added to it slowly for half an hour with proper shaking for
mixing. It was refluxed for 1 h on a water bath, and the thionyl chloride
was distilled at reduced pressure to get the product. Yield 72% (1.610 g),
mp 144–1488C.
Sodium Derivative of Curcumin
Curcumin (736 mg; 2 mM) was taken in EtOH, and the NaOEt (containing
115 mg of metallic sodium; 5 mmol) was added dropwise for 10 min. The
reaction mixture was stirred at rt for 30 min. The completion of reaction
was indicated by thin-layer chromatography (TLC). The resulting sodium
salt was concentrated in vacuo to remove ethanol.
p-Nitrophenyl Ester of Chloroacetic Acid
To chloroacetic acid (190 mg; 2 mM) dissolved in dry dioxane (8 ml), p-nitro
phenol (280 mg; 2 mM) was added dropwise. The reaction mixture was made
basic by addition of 0.5 ml of pyridine and 0.5 ml of TEA (triethyl amine).
After stirring for 10 min, dicyclohexyl carbodiimide (DCC) (1030 mg;
5 mM) was added. The reaction mixture was stirred for 2 h under a nitrogen
atmosphere (caution: protection from moisture) and monitored with TLC.
The completion of reaction was assessed by total consumption of the
starting reagent. Rf ¼ 0.88 (DCM–MeOH: 9.5:0.5).

4268
S. K. Dubey, V. Dwivedi, and K. Misra
Steps in Synthesis of Monoester of Curcumin
1. We suspended dried long-chain alkyl amine on CPG resin (LCAA-
CPG) (200 mg; loading 60 mM/100 mg; 120 mM of NH2 gp; pore
˚
size 500 A) in dry dimethylformamide (DMF) (2 ml) and loaded it
on a column.
2. We dissolved chloroacetic acid (190 mg; 2 mM) in dry dioxane (8 ml)
containing dry pyridine (0.5 ml) and p-nitrophenol (280 mg; 2 mM)
and stirred it for 20 min in a round-bottom flask.
3. To it, dicyclohexyl carbodiimide (DCC) (1030 mg; 5 mM) was added.
After few minutes, dicyclohexylurea began to precipitate. The reaction
mixture was stirred for 2.5 h under a nitrogen atmosphere (caution: pro-
tection from moisture) and monitored with TLC. The completion of
reaction was assessed by total consumption of starting reagent.
Rf ¼ 0.88 (DCM–MeOH: 9.5:0.5).
4. We removed dicyclohexylurea by filteration and added the supernatant
to LCAA-CPG (200 mg) suspended in DMF on column.
5. To it, 0.5 ml of triethylamine (TEA) was added; a bright yellow color
due to release of p-nitrophenol developed immediately. The reaction
mixture was kept for 8 h.
6. The supernatant was removed, and chloroacetic acid derivatized LCAA-
CPG was washed with dry DMF and methanol followed by ether
(2 ꢀ 3 ml). The derivatization of chloroacetic acid as linker to LCAA-
CPG was confirmed by ninhydrin test of the solid support, which was
negative, indicating no free amino group, and it was ready for further
synthesis.
7. Sodium salt of curcumin (2 mM) dissolved in dry pyridine (10 ml) was
passed through the column repeatedly and was kept overnight.
8. The column was washed with pyridine and methanol followed by water
(2 ꢀ 5 ml). It was again washed with methanol and ether (2 ꢀ 2 ml).
9. Phthaloyl glycinoyl chloride (2 mM) dissolved in pyridine (5 ml) was
passed through the column with little addition (5 mg) of DMAP as
catalyst, and it was kept overnight.
10. Column was washed with water (2 ꢀ 2 ml) followed by methanol
(2 ꢀ 2 ml).
11. To the column, 5 ml of solution of ammonia and pyridine (ammonia–
pyridine: 9:1) were added, and it was kept for 5–10 min.
12. Column was again washed with water (2 ꢀ 2 ml) followed by methanol
(2 ꢀ 2 ml).
13. Hydriodic acid (HI; 2 ml) was added to the column and kept for 12 h.
14. The monoester was eluted from solid support with methanol along with
HI, and methanol was distilled off.
15. The remaining solution DCM was added, and it was washed with aqueous
KI (10%) and DCM repeatedly until all the color was removed from the
DCM layer to remove any I2. Compound was extracted with DCM.

Monoesters of Symmetric Diphenolic Compounds
4269
16. The DCM solution was washed with cold 5% aq. sodium bicarbonate
(10 ml) solution followed by water (10 ml) to remove any HI.
17. It crystallized from DCM. Yield 50% (25 mg), lmax 360, and 295 nm:
Rf ¼ 0.6, (DCM–methanol: 9.5:0.5). The pure product was character-
1
ized by H NMR (CDCl3) d ppm ¼ 3.70 (s, 6H, -OCH3), 4.13 (s, 2H,
C4-H), 4.49–4.61 (m, 4H, CH2-NH2), 5.03 (s, 1H, -OH), 6.53 (d, 2H,
C2-H & C6-H), 6.85–7.08 (M, 6H, Ar-H), 7.53 (d, 2H, C1-H & C7-H).
RESULTS AND DISCUSSION
Curcumin has an interesting structure with two phenolic groups and one active
methylene function, which can act as potential active sites for chemical modi-
fication and covalent linking with biomolecules. There is not much scope for
structural variation in curcumin molecule to enhance its activity, because it is
reported that blocking of phenolic groups decreases its antioxidant activity
and therefore phenolic groups appear to be the sites involved in enzymatic
activity at the receptor site.[6,7] The double bonds are essential for proper con-
formational flexibility of the molecule.
We earlier reported the synthesis of large number of diesters of curcumin
by solution-phase chemistry.[8–12] Because curcumin is a symmetrical diphe-
nolic compound, preparing a monoester of such a compound was rather pro-
blematic. This has now been achieved using solid-phase synthesis coordinated
with solution-phase synthesis. One of the phenolic groups of curcumin was
attached to solid polymer support LCAA-CPG (long chain alkyl amine–
controlled pore glass) via chloroacetic acid as a linker, and the other
phenolic was esterified with amino acid on resin and later delinked to get
the monoester in solution (Scheme 1).
During the synthesis, the carboxy function of chloroacetic acid was ester-
ified (activated) by reaction with p-nitrophenol by addition of dicyclohexyl
carbodiimide (DCC) in the presence of pyridine and triethyl amine to make
the solution basic to get the corresponding activated ester. The activated
ester of chloroacetic acid was reacted with the amino function of LCAA-
CPG using DCC/DMAP to get the amide bond, a well-established strategy
in peptide synthesis.
To this, sodium salt of curcumin, a symmetrical diphenolic compound,
was added which reacts with chloroacetic-acid-derivatized LCAA-CPG,
such that one phenolic forms the bond while the other remains free for
further synthesis.
During the synthesis, the amino function of glycine was protected with
phthalic anhydride as N-phthaloyl glycine and the carboxy function was
activated with thionyl chloride to get the corresponding acid chloride.
This N-protected and carboxy-activated amino acid was reacted with
sodium salt of curcumin on a solid support to give the ester of glycine
with curcumin.

4270
S. K. Dubey, V. Dwivedi, and K. Misra
Scheme 1. Synthesis of monoglycinoyl curcumin on CPG-LCAA.
The phthaloyl group of protected amino acid was removed using
ammonia. HI was used to deblock the monoester from the solid support by
cleaving the etheral bond, and thus selective esterification of curcumin with
glycine was accomplished.
In summary, we have developed a novel strategy for the selective esterfi-
cation of symmetrical diphenolic compounds like curcumin, using solid as
well as solution-phase synthesis. This strategy can be used further for
selective synthesis of monoesters of any symmetrical diphenolic compound.
Another advantage of the procedure is that after deblocking, the resin is left
activated (i.e., with a -CO-CH2I group attached to its terminal NH2 group)
and can be used as such for another cycle.
Since the transporter proteins for many amino acids as well as peptides
are known, the monoesters of curcumin with these amino acids or peptides

Monoesters of Symmetric Diphenolic Compounds
4271
can act as substrates for the carrier proteins. ABTOþ is one such example,
which is a known substrate for monovalinoyl curcumin and can be used for
characterizing the ester by transporter expression system. However, these
transport proteins for amino acids and peptides are known to be very pro-
miscuous and can transport amino acid esters of many other compounds also.
ACKNOWLEDGMENT
One of the authors (S. K. D.) wish to thank University Grants Commission
(UGC), India, for providing financial assistance in the form of a scholarship
during the course of this study.
REFERENCES
1. Merrifield, R. B. Solid phase peptide synthesis. I. The synthesis of a tetra peptide.
J. Am. Chem. Soc. 1963, 85 (14), 2149–2154.
2. Uhlman, E.; Peyman, A. Antisense oligonucleotides: a new therapeutic. Chem.
Rev. 1990, 90 (4), 543–584.
3. Engels, J. W.; Uhlman, E. Gene synthesis. Angew. Chem. Int. Ed. Engl. 1989, 28,
716–724.
4. Srimal, R. C.; Dhawan, B. N. Pharmacology of diferuloyl methane (Curcumin), a
non-steroidal anti-inflammatory agent. J. Pharm. Pharmacol. 1973, 25, 447–454.
5. Satoskar, R. R.; Shah, S. J.; Shenoy, S. G. Evaluation of anti-inflammatory
property of curcumin (diferuloyl methane) in patients with postoperative inflam-
mation. Int. J. Clin. Pharmacol. Ther. Toxicol. 1986, 24, 651–654.
6. Venkatesan, P.; Unnikrishnan, M. K.; Kumar, S. M.; Rao, M. N. A. Effect of
curcumin analogues on oxidation of haemoglobin and lysis of erythrocytes.
Curr. Sci. 2003, 84, 74–78.
7. Priyadarsini, K. I.; Maity, D. K.; Naik, G. H.; Kumar, M. S.; Unnikrishnan, M. K.;
Satav, J. G.; Mohan, H. Role of phenolic O-H and methylene hydrogen on the free
radical reactions and antioxidant activity of curcumin. FRBM 2003, 35, 474–484.
8. Mishra, S.; Narain, U.; Mishra, R.; Misra, K. Design, development and synthesis of
mixed bioconjugates of piperic acid–glycine, curcumin–glycine/alanine and
curcumin–glycine–piperic acid and their antibacterial and antifungal properties.
Bioorg. Med. Chem. 2005, 13, 1477–1486.
9. Kumar, S.; Narain, U.; Tripathi, S.; Misra, K. Syntheses of curcumin bioconjugates
and study of their antibacterial activities against ?-lactamase-producing microor-
ganisms. Bioconjugate Chem. 2001, 12, 464–469.
10. Kumar, S.; Dubey, K. K.; Tripathi, S.; Fujii, M.; Misra, K. Design and synthesis of
curcumin-bioconjugates to improve systemic delivery. Nucleic Acids Symp. Ser.
2000, 44, 75–76.
11. Misra, S.; Tripathi, S.; Misra, R.; Misra, K. Design, synthesis and characterisation
of a novel anticancer prodrughaving antiproliferative activity against prostrate
tumour. Ind. J. Chem. 2005, 44B (12), 2582–2588.
12. Mishra, S.; Kapoor, N.; Ali, A. M.; Pardhasarathi, B. V.; Kumari, A. L.; Khar, A.;
Misra, K. Differential apoptotic and redox regulatory activities of curcumin and its
derivatives. FRBM 2005, 38, 1353–1360.