Synthesis of a novel plant growth promoter from gallic acid

Article abstract of DOI:10.1016/j.bmcl.2004.11.079

Gallic acid has been modified to naphthophenone derivatives with esterified fatty acid side chain. Compound 12, an ethyl crotonate ester of naphthophenone derivative has shown potent auxin like growth promoter activity. This is the first example of naphthophenone derivatives with plant growth promoting activity.

Full text of DOI:10.1016/j.bmcl.2004.11.079

Bioorganic & Medicinal Chemistry Letters 15 (2005) 1243–1247
Synthesis of a novel plant growth promoter from gallic acidq
Arvind Singh Negi,* Mahinder P. Darokar, Sunil K. Chattopadhyay, Ankur Garg,
Asish K. Bhattacharya, Vandana Srivastava and Suman P. S. Khanuja
Central Institute of Medicinal and Aromatic Plants (CIMAP), PO CIMAP, Kukrail Road, Lucknow 226015, India
Received 15 October 2004; accepted 24 November 2004
Available online 18 January 2005
Abstract—Gallic acid has been modified to naphthophenone derivatives with esterified fatty acid side chain. Compound 12, an ethyl
crotonate ester of naphthophenone derivative has shown potent auxin like growth promoter activity. This is the first example of
naphthophenone derivatives with plant growth promoting activity.
ꢀ 2005 Elsevier Ltd. All rights reserved.
1. Introduction
naphthol in the presence of DCC/DMAP in dry dichlo-
romethane under refluxing condition to give 3,4,5-tri-
methoxybenzoic acid naphthalene-2-yl ester (3) in
77% yields. Compound 3 then subjected to Fries rear-
rangement using anhydrous AlCl3 at 120–130 ꢁC under
neat conditions gave the desired naphthophenone
derivative (4) with a yield of 31% along with two
byproducts 4-demethylated and 3,4-didemethylated
derivatives of starting ester 3. It is worth mentioning
here that the Friedel Crafts reaction of trimethoxy ben-
zoic acid (2) with b-naphthol in the presence of various
Lewis acids (AlCl3–DCM, AlCl3–CS2, AlCl3 neat,
ZnCl2, BF3–etherate and SnCl4) was unsuccessful.
However, it was successful when PPA was used, but
the yield was very poor (less than 5%). Finally, the
condensation of naphthophenone derivative 4 with dif-
ferent ethyl bromo ester was affected in the presence of
potassium carbonate and dry acetone at room tempera-
ture for preparations of compounds 5, 6, 10, 11 and 12
and under refluxing conditions for rest of the com-
pounds (7, 8, 9 and 13). The desired compounds 5–
13 were obtained in variable yields, 58–89%.
Gallic acid (1) and its related compounds are widely dis-
tributed in plants.2,3 It has been reported to possess anti-
carcinogenic, antioxidative, antimutagenic, anti-allergic
and anti-inflammatory activities.4 Gallic acid has been
a building block of choice for different pharmaceutical
leads due to the presence of this moiety in several bioac-
tive natural products.5 Hence, numerous derivatisations
have been done and are reported as anticancer agents,6
HIV-1 Integrase7 and HIV-1RT inhibitors,8 antioxi-
dants,9 antimalarials,10 etc.
While working on structural modification of phytomole-
cules,11,12 we report a novel plant growth promoter
having potent auxin like growth promoting activity
derived from gallic acid.
2. Chemistry
The methodology adopted for the synthesis of above
molecules is presented in Scheme 1. Gallic acid was
first methylated13 with dimethyl sulfate in aqueous
alkali to give trimethoxy benzoic acid (2) in 76% yield.
The methylated gallic acid was next esterified with b-
2.1. Synthesis of 3,4,5-trimethoxy benzoic acid naphtha-
lene-2-yl ester (3)
In a 25 mL round bottom flask a mixture of 3,4,5-tri-
methoxy benzoic acid (2, 4.0 g, 18.87 mmol), DCC
(4.0 g, 19.42 mmol), dry dichloromethane (100 mL)
was refluxed for 30 min. To this reaction mixture b-
naphthol (2.2 g, 15.28 mmol) was added and refluxing
was continued for 3 h. After completion of the reaction,
solvent was evaporated off. The residue thus obtained
Keywords: Gallic acid; Plant growth promoters; Naphthophenone
derivatives; Synthesis; Bacopa test.
q See Ref. 1.
*
Corresponding author. Tel.: +91 522 2717529x212; fax: +91 522
2342666; e-mail: arvindcimap@rediffmail.com
0960-894X/$ - see front matter ꢀ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2004.11.079

1244
A. S. Negi et al. / Bioorg. Med. Chem. Lett. 15 (2005) 1243–1247
OCH3
OCH3
OCH3
O
O C
COOH
COOH
(i)
(ii)
OH
HO
OCH3
OCH3
H3CO
3
OH
1
2
(iii)
OCH3
OCH3
H3CO
H3CO
H3CO
H3CO
O
O
(iv)
OX
OH
5-13
4
5, X = -CH2COOC2H5; 6, X = -CH2.CH2COOC2H5;
7, X = -CH2.CH2.CH2COOC2H5; 8, X = -CH2.CH2.CH2.CH2COOC2H5;
9, X = -CH2.CH2.CH2.CH2.CH2COOC2H5; 10, X = -CHFCOOC2H5;
11, X = -CF2COOC2H5; 12, X = -CH2.CH=CH.COOC2H5;
13, X = -CH2.CO.COOC2H5.
Scheme 1. Reagents and conditions: (i) Me2SO4/KOH, 10–20 ꢁC for 30 min, then reflux for 3 h, 76%; (ii) DCC/DMAP, DCM, 4 h, 71%; (iii) AlCl3
neat, 120–130 ꢁC, 31%; (iv) different ethyl bromo esters, dry acetone, K2CO3, 58–89%.
was purified through silica gel column by eluting with
hexane–ethyl acetate to get 3 as a white crystalline solid,
yield 77%.
ica gel column using hexane–ethyl acetate as eluent to
get 12 as oil,17 yield 83%.
In order to establish structure–activity relationship
(SAR) for the derivatives of 12, several chemical modi-
fications were tried on it as described in Scheme 2.
Reduction of the keto group of 12 into corresponding
alcohol 14 resulted in complete loss of activity. When
the ester group of 12 was hydrolysed with aqueous
methanolic alkali it yielded an inactive acid 15. Demeth-
ylation14 of the methoxy group para to keto group of
compound 12 gave inactive product 16. Replacement
of the unsaturated butyrate side chain by saturated
chain, for example, compound 17 and 18 resulted in
inactive compounds. Thus, it may be concluded that
for the expression of activity of 12, 3,4,5-trimethoxy
benzoyl moiety as well as double bond in the side chain
are essential.
2.2. Synthesis of (2-hydroxy-naphthalen-1-yl)-(3,4,5-tri-
methoxyphenyl)methanone (4)
A mixture of compound 3 (500 mg, 1.48 mmol) and an-
hyd AlCl3 (1.0 g, 7.49 mmol) was heated at 120–130 ꢁC
in an oil bath for 40 min. Then the reaction mixture
was cooled and 10 mL dil HCl (1 N) was added to it
drop wise. The reaction mixture was extracted with ethyl
acetate (3 · 50 mL) and the combined organic layer was
washed with water, dried over anhyd sodium sulfate and
distilled off the solvent to get a yellowish crude oil. It
was purified through a silica gel column with a mixture
of hexane–ethyl acetate (43:7) as eluent. The pure com-
pound 4 was recrystallised from CHCl3–hexane to get a
creamish white crystalline solid, yield 31%.
2.3. General procedure for the synthesis of [(3,4,5-
trimethoxy-benzoyl)naphthalene-2-yloxy]-alkanoic/alke-
noic acid ethyl esters (5–13)
3. Biological evaluation and discussions
3.1. Growth promoting activity of compound 12 using
Bacopa sensor system
2.3.1. 4-[1-(3,4,5-Trimethoxy-benzoyl)-naphthalen-2-yl-
oxy]-but-2-enoic acid ethyl ester (12). A mixture of (2-hy-
droxy-naphthalen-1-yl)-(3,4,5-trimethoxyphenyl)metha-
none (4, 200 mg, 0.59 mmol) and potassium carbonate
(1.0 g, 7.24 mmol) was taken in dry acetone (10 mL)
and stirred at room temperature for 2 h. On completion
of the reaction the colour of the reaction mixture chan-
ged from light yellow to creamish white. The reaction
mixture was filtered through sintered funnel, washed
with acetone. The solvent was evaporated and the resi-
due was dissolved in ethyl acetate, washed with water
(20 mL · 3). The organic layer was dried over anhyd so-
dium sulfate and distilled off. It was purified through sil-
For testing the growth promoting effect, all these com-
pounds were dissolved in DMSO and added into the
medium at 1.0 lg/mL. Only solvent was used as a con-
trol in the experiment for comparison. A fast propagat-
ing strain of Bacopa monnieri developed15 as a biosensor
system through tissue culture at CIMAP was used in the
tests. The MS basal supplemented16 with test compound
was used in the assays. Measured 0.5–1.0 mL medium
was poured into 1.5 mL graduated microcentrifuge
tubes. Twig cuttings of 2.5 cm were inoculated in 10 rep-
licates for each treatment. These inoculated tubes were
put into a half transparent desiccator allowing air

A. S. Negi et al. / Bioorg. Med. Chem. Lett. 15 (2005) 1243–1247
1245
OCH3
H3CO
OH
H
H3CO
O.CH2.CH=CHCOOC2H5
14
OCH3
a
H3CO
H3CO
OCH3
O
H3CO
H3CO
O.CH2.CH=CHCOOC2H5
b
O
O.CH2.CH=CHCOOH
12
c
15
OCH3
HO
O
H3CO
O.CH2.CH=CHCOOC2H5
16
OH
OCH2.CH=CH.COOC2H5
K2CO3, Acetone
Ethyl bromo crotonate
b
17
OCH2.CH=CH.COOH
18
Scheme 2. Reagents and conditions: (a) NaBH4/MeOH, 40–50 ꢁC, 89%; (b) 10% KOH in 10 mL MeOH–H2O = 3:1, 60 ꢁC, 1 h, 82%; (c) AlCl3–
DCM, rt, 62%.
passage through sterile cotton plugs fixed on opening
vent. The tubes were placed such that the medium-con-
taining portion of the tubes where roots would be initi-
ating is inserted in to the holes of the stand made from a
thermocol sheet. These desiccators were incubated at
normal ambient temperature of 25–28 ꢁC with 14 h light
and 10 h dark cycle. The root initiation, shoot elonga-
tion, callus induction, shoot proliferation and wilting
was recorded from day 2 to 14 every 24 h.
and cytokine. Different concentrations of 1-naphthalene
acetic acid (NAA) (0.0, 0.2, 2.0 lg/mL) were used in
combination with different concentrations of 6-benzyl
amino purine (BAP) (0, 5 and 10 lg/mL). On each kind
of media 10 replicates of the explants were inoculated
into three Petri plates with each plate containing four
explants. The compound 12 was serially replaced with
each concentration of NAA and BAP individually to
observe its growth promoting activity. The experiment
was arranged in the form of a completely randomised
design (CRD). Cultures were maintained at 25 2 ꢁC
and 400–600 lx light intensity with 16 h photoperiod.
The response of explants was recorded every 24 h over
a four weeks period. Each explant was observed at
two week intervals and subcultured on the same fresh
medium. The proportional increase in biomass was re-
corded by taking the fresh weight of the growing tissue
during subculturing and dividing the increase with the
initial weight. At the end of 12 weeks from inoculation
the shoots were separated and individually transferred
to MS basal media containing vitamins for rooting.
3.2. Growth promoting activity of compound 12 using
aromatic plant species Mentha arvensis
To confirm the growth promoting activity, compound
12 was tested with a medicinal and aromatic plant spe-
cies M. arvensis. The explants used were 0.5 cm long
pieces of the second and third internodes of the shoots
formed from auxiliary buds and culture. The internode
segments were inoculated in MS basal media16 contain-
ing vitamins 100 lg/mL, myo-inositol 3%, w/v, sucrose
1.5% w/v, Agar and different concentrations of auxins

1246
A. S. Negi et al. / Bioorg. Med. Chem. Lett. 15 (2005) 1243–1247
Table 1. Growth promoting activity of compound 12 using Bacopa sensor system
Test compound 12
Shoot elongation
(cm)
Branching
(nos.)
Root elongation
(cm)
No. of leaves
(nos.)
No. of roots
(nos.)
Browning yellowing
death
Control
Compound 12
1.0
1.6
2.0
2.0
0.8
0.8
5.0
11.0
2+2
2+2
Nil
Nil
Table 2. Growth promoting activity of compound 12 with M. arvensis
Medium
Concentration of growth regulators in
MS basal medium
Observations after number of days
IAAa
BAPb
Compd 12
8
14
22
A3
A2
2.0
—
10.0
10.0
—
—
Callusing
Callusing
No growth
Shooting
Shooting
No growth
Shooting
Shooting (single root in one replication)
No growth
2.0
10.0
2.0
0.2
—
5.0
5.0
—
—
Callusing
Callusing
Less growth
Shooting
Shooting
Browning
Shooting (no roots)
Shooting (no root in any)
Death
0.2
5.0
0.2
a Indole acetic acid.
b 6-Benzyl amino purine.
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The growth promoting activity data of compound 12
using Bacopa sensor system is given in Table 1. Only
the compound 12 was found to possess potent growth
promoting activity, rest of the compounds were found
to be inactive. The growth promoting activity of com-
pound 12 was further confirmed to be auxin like, by an-
other experiment using an aromatic plant M. arvensis,
given in Table 2.
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4. Conclusion
All the compounds except compound 12 were found to
be inactive as plant growth promoters. However, com-
pound 12, possessed potent auxin like growth promot-
ing activity. Compound 12 on modifications to some
of its derivatives as described above led to inactive mole-
cules. Thus, it was concluded that the complete naphtho-
phenone moiety is required along with the crotonate
ester chain for the activity. Inactivity of compound 5
(acetic acid ester) suggests a possible difference in the
SAR of these compounds with that of naphthalene ace-
tic acid. This study suggests that properly functionalised
gallic acid derived molecules can also act as plant
growth promoters.
Acknowledgements
12. Chattaopadhyay, S. K.; Shantakumar, T. R.; Maulik, P.
R.; Srivastava, S.; Garg, A.; Sheron, A.; Negi, A. S.;
Khanuja, S. P. S. Bioorg. Med. Chem. 2003, 11(23), 4945–
4948.
13. Gilman, H.; Blat, A. H. In Organic Syntheses; John Wiley
& Sons, 1932; Vol. I, pp 537–538.
The financial assistance from the Department of Science
and Technology (DST), Govt. of India under FAST-
TRACK scheme is duly acknowledged.
14. Negi, A. S.; Chattopadhyay, S. K.; Srivastava, S.; Bhat-
tacharya, A. K. Synth. Commun. 2004, 35, 15–21.
15. Khanuja, S. P. S.; Darokar, M. P.; Misra, S.; Gangwar,
A.; Shasany, A. K.; Shantakumar, T. R.; Saikia, D.;
Kumar, A. S. J. Env. Pathol. Toxicol. Oncol. (JEPTO)
2001, 20, 15–22.
References and notes
1. CIMAP Communication No. 2004-50J.
2. (a) Niehaus, J. U.; Gross, G. G. Phytochemistry 1997, 45,
1555–1560; (b) Kandi, F. E.; Sayed El, N. H.; Michael, H.

A. S. Negi et al. / Bioorg. Med. Chem. Lett. 15 (2005) 1243–1247
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16. Murashige, T.; Skoog, F. Physiol. Planta 1962, 15, 473–
497.
17. Selected physical data: compound 3: yield: 77%, mp = 99–
(CDCl3): 3.74 (s, 6H, 30 and 50-OCH3), 3.89 (s, 3H, 40-
OCH3), 4.08 (s, 1H, CHOH), 4.21 (s, 2H, OCH2), 4.76 (s,
2H, OCH2), 7.26–7.89 (m, 8H, all aromatic protons);
electrospray mass: 475 [M+Na]+, elemental analysis for
C26H28O7 calcd: C, 69.01; H, 6.24; obsd: C, 68.86; H, 6.48.
Compound 15: yield: 69%, mp = 132–35 ꢁC, 1H NMR
(CDCl3): 3.87 (s, 6H, 30 and 50-OCH3), 4.08 (s, 3H, 40-
OCH3), 6.60–6.65 (d, 1H, @CHÆCOOH, J = 15.6 Hz), 6.72
(s, 2H, OCH2), 7.53–7.58 (d, 1H, CH@, J = 15.6 Hz),
7.26–7.96 (m, 8H, all aromatic protons); electrospray
mass: 445 [M+Na]+, elemental analysis for C24H22O7
calcd: C, 68.24; H, 5.25; obsd: C, 68.46; H, 5.48.
Compound 16: yield: 42%, oil, 1H NMR (CDCl3): 1.25
(t, 3H, CH3, 6.5 Hz), 3.82 (s, 6H, 30 and 50-OCH3), 4.15 (q,
br s, 2H, OCH2ÆCH3, J = 6.5 Hz), 4.74 (br s, 2H,
OCH2ÆCH@), 5.80 (d, 1H, @CHCO, J = 15.7 Hz), 6.92
(d, 1H, CH2ÆCH@, J = 15.7 Hz), 7.14–7.94 (m, 8H, all
aromatic protons), FAB mass: 459 [M+Na]+, elemental
analysis for C25H24O7, calcd: C, 68.80; H, 5.54; obsd: C,
68.62; H, 5.37.
1
102 ꢁC, H NMR (CDCl3): 3.97 (s, 9H, OCH3), 7.35–7.94
(m, 9H, all aromatic protons), electrospray mass: 360.9
[M+Na]+, 338.9 [M+H]+. Compound 4: yield: 31%,
1
mp = 138–40 ꢁC, H NMR (CDCl3): 3.70 (s, 6H, 30 and
50-OCH3), 3.92 (s, 3H, 40-OCH3), 6.90–7.93 (m, 8H, all
aromatic protons), 10.85 (s, 1H, phenolic OH); electro-
spray mass: 360.9 [M+Na]+, 338.9 [M+H]+; elemental
analysis for C20H18O5 calcd: C, 70.99; H, 5.36; obsd: C,
1
71.46; H, 5.18. Compound 12: yield: 83%, oil, H NMR
(CDCl3): 1.28 (t, 3H, CH3, J = 6.58 Hz), 3.78 (s, 6H, 30
and 50-OCH3), 3.92 (s, 3H, 40-OCH3), 4.16 (q, 2H,
OCH2ÆCH3, J = 6.7 Hz), 4.76 (br s, 2H, OCH2ÆCH@),
5.76–5.82 (d, 1H, @CHCO, J = 15.8 Hz), 6.89–6.95 (d,
1H, CH2ÆCH@, J = 15.7 Hz), 7.14–7.96 (m, 8H, all
aromatic protons), FAB mass: 451 [M+H]+; elemental
analysis for C26H26O7 calcd: C, 69.32; H, 5.82; obsd: C,
1
68.48; H, 5.34. Compound 14: yield: 74%, oil, H NMR