An efficient total synthesis of trilepisiumic acid

Article abstract of DOI:10.1080/14786419.2014.918126

Total synthesis of trilepisiumic acid (4-((3-(3,4-dihydroxyphenyl)acryloyl) oxy)-3-hydroxybenzoic acid) isolated from Trilepisium madagascariense was carried out. Doebner condensation of 3,4-dimethoxybenzaldehyde with malonic acid yielded 3,4-dimethoxycinnamic acid (2). Esterification of the latter with vanillin afforded 4-formyl-2-methoxyphenyl-3-(3,4-dimethoxy phenyl)acrylate (3) followed by permanganate oxidation in acidic medium provided the corresponding acid 4. Finally, demethylation of 4 was achieved by refluxing in hydrobromic acid to unveil the trilepisiumic acid (1).

Full text of DOI:10.1080/14786419.2014.918126

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An efficient total synthesis of
trilepisiumic acid
Aamer Saeeda & Muhammad Qasima
a Department of Chemistry, Quaid-I-Azam University, Islamabad
45320, Pakistan
Published online: 20 May 2014.
To cite this article: Aamer Saeed & Muhammad Qasim (2014) An efficient total synthesis of
trilepisiumic acid, Natural Product Research: Formerly Natural Product Letters, 28:14, 1121-1126,
DOI: 10.1080/14786419.2014.918126
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Natural Product Research, 2014
Vol. 28, No. 14, 1121–1126, http://dx.doi.org/10.1080/14786419.2014.918126
SHORT COMMUNICATION
An efficient total synthesis of trilepisiumic acid
Aamer Saeed* and Muhammad Qasim
Department of Chemistry, Quaid-I-Azam University, Islamabad 45320, Pakistan
(Received 19 March 2014; final version received 22 April 2014)
Total synthesis of trilepisiumic acid (4-((3-(3,4-dihydroxyphenyl)acryloyl)oxy)-3-
hydroxybenzoic acid) isolated from Trilepisium madagascariense was carried out.
Doebner condensation of 3,4-dimethoxybenzaldehyde with malonic acid yielded 3,4-
dimethoxycinnamic acid (2). Esterification of the latter with vanillin afforded
4-formyl-2-methoxyphenyl-3-(3,4-dimethoxy phenyl)acrylate (3) followed by per-
manganate oxidation in acidic medium provided the corresponding acid 4. Finally,
demethylation of 4 was achieved by refluxing in hydrobromic acid to unveil the
trilepisiumic acid (1).
Keywords: trilepisiumic acid; cinnamic acid; Trilepisium madagascariense
1. Introduction
Polyhydroxyaromatic acids are important secondary metabolites due to the presence of free
phenolic hydroxy functions capable of exhibiting high free radical-scavenging activity.
In addition, cinnamic acids and derivatives have a valuable place due to their pharmacological
and industrial applications (Miliovsky et al. 2013). In nature, cinnamic acids display vast
structural diversity due to different substitution patterns on the aromatic ring as well as various
derivatives of the acid moiety. Cinnamic acids and derivatives exhibit a broad spectrum of
biological activities such as anti-tuberculosis, antidiabetic, antimicrobial, antimalarial, cytotoxic
and antifungal (Lee et al. 2000; Zhu et al. 2000; Narasimhan et al. 2004; Adisakwattana et al.
2008; Rao et al. 2011; Sharma 2011). Trilepisium madagascariense is a deciduous tree, found in
Cameroon, Congo and Madagascar. The leaves of T. madagascariense are used as a vegetable;
other parts of the plant exhibit antihyperglycaemic, antidiabetic, antimicrobial, antioxidant and
pain killer activities. Moreover, it is used to treat venereal diseases, arthritis, diarrhoea,
rheumatism, dysentery, stomach troubles, debility, malnutrition, and cutaneous and
subcutaneous parasitic infections (Teke et al. 2010; Ampa et al. 2013).
Ango et al. (2012), during the phytochemical investigation of T. madagascariense, isolated
two new compounds named as trilepisflavan and trilepisiumic acid (Figure 1), besides the ten
known compounds, from the ethyl acetate extract of the stem bark and the leaves. The structure
1
of trilepisiumic acid was established unambiguously by H, 13C, COSY, HMQC and HMBC
data as (E)-4-((3-(3,4-dihydroxyphenyl)acryloyl)oxy)-3-hydroxy benzoic acid. Hydroxycin-
namic acids are a class of phenylpropanoids having a C6–C3 skeleton. These compounds are
hydroxy derivatives of cinnamic acid. The compound displayed potent antimicrobial activity
against eight microorganisms: reference strains of Providencia smartii, Pseudomonas
aeruginosa, Klebsiella pneumoniae, Staphylococcus aureus, Salmonella typhi, Escherichia
coli and Candida albicans. Trilepisiumic acid possesses some very important functionalities
*Corresponding author. Email: aamersaeed@yahoo.com
q 2014 Taylor & Francis

1122
A. Saeed and M. Qasim
O
O
OH
O
OH
HO
OH
(1)
Figure 1. (E)-4-((3-(3,4-dihydroxyphenyl)acryloyl)oxy)-3-hydroxybenzoic acid.
such as an a,b-unsaturated carbonyl moiety, three free phenolic groups and one free carboxylic
function, with an extensive potential of derivatisation into a diversity of interesting homo- and
heterocyclic compounds. Unsaturated fatty acids, such as linoleic acid, palmitoleic acid, oleic
acid and arachidonic acid, inhibit bacterial enoyl-acyl carrier protein reductase (FabI), an
essential component of bacterial fatty acid synthesis, whereas the saturated analogues such as
stearic acid do not (Zheng et al. 2005). Chalcones containing an a,b-unsaturated carbonyl
system display a wide spectrum of biological activities. Similarly, benzofurancarboxylic acid
derivatives are known to exhibit antimicrobial activity (Kossakowski et al. 2010). Antimicrobial
activity, structure–activity relationship analysis and docking studies of phenolic compounds in
wild mushrooms have been reported (Alves et al. 2010).
The presence of two important pharmacophoric fragments namely phenolic groups and a,b-
unsaturated carbonyl system in one molecule suggests synergistic effect making this compound
an attractive target for synthesis (Figure 1).
2. Results and discussion
We now divulge an efficient synthesis of (E)-4-((3-(3,4-dihydroxyphenyl)acryloyl)oxy)-3-
hydroxybenzoic acid. The synthesis started with Doebner modification of Knoevenagel
condensation of 3,4-dimethoxybenzaldehyde with malonic acid in refluxing pyridine using
tetrahydropyrrole as an organocatalyst to afford directly the 3,4-dimethoxycinnamic acid
(2). In Doebner modification instead of diethylmalonate, the malonic acid is used and its
coupling product with benzaldehyde undergoes concerted decarboxylation and elimination
to cinnamic acid (Stacey et al. 2013). In the 1H NMR spectrum of 2, the signal at d
12.2 ppm confirmed the presence of acidic proton besides the doublets at d 6.4 ppm with
J ¼ 15.9 Hz and 7.52 ppm J ¼ 15.9 Hz assigned to a and b protons, respectively, the
coupling constants also establish the E-configuration around the double bond at the very
first step.
The acid (2) was converted into corresponding acid chloride on refluxing with thionyl
chloride in the presence of 1 or 2 drops of DMF which act as a catalyst. Esterification of the latter
with 4-hydroxy-3-methoxy benzaldehyde (vanillin) was carried out in dry THF in the presence
of triethyl amine to afford the (E)-4-formyl-2-methoxyphenyl-3-(3,4-dimethoxyphenyl)acrylate
(3) as a white crystalline solid. In the FTIR spectrum, the stretching frequency of ester carbonyl
group was found at 1708 cm21 which is lesser than the normal range due to the presence of
1
extended conjugation. The H NMR spectrum confirmed the presence of aldehydic proton at
9.98 ppm and the absence of acidic proton besides doublets at 7.86 for b-H, 6.80 for a-H, nine
proton singlet 3.9 for OMe protons, while in 13C NMR carbonyl carbons of aldehyde and ester
functions appeared at d 191 and 164 ppm, respectively, in addition to signals at 152.14 (b-C),
109.62 (a-C) and 55.91–56.14 (ZOMe), respectively.
The oxidation of formyl group in 3 into (E)-4-((3-(3,4-dimethoxyphenyl)acryloyl)
oxy)-3-methoxybenzoic acid (4) was achieved by treating with one equivalent of KMnO4

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1123
in acidic medium at room temperature to furnish the product as a white crystalline solid.
The acidic medium was used to augment the electrophilic character of the formyl group to
carry out the oxidation under mild conditions. 1H NMR spectrum of 4 confirmed the
presence of acidic proton at 12.95 ppm and acid carbonyl acid signal at 170.1 ppm
(Scheme 1).
Complete demethylation of the dimethoxy acid (3) was achieved in refluxing hydrobromic
acid in glacial acetic acid (Zou et al. 2008) to unveil the trilepisiumic acid. Although BBr3 is
the mild reagent of choice for the complete cleavage of O-methyl ethers of natural products,
HBr was to be used for demethylation due to its unavailability. In the IR spectrum, the
presence of strong band at 3450 cm21 confirms the presence of hydroxyl groups. The target
compound obtained as a silvery solid with m.p. at 1808C was characterised by the complete
absence of all MeO singlets, both in the 1H NMR and 13C NMR spectra, and other
characteristic changes.
Thus, the present synthesis constitutes a simple route to a natural product trilepisiumic acid
possessing biological activities. It involves three linear steps and proceeds with good overall
yield, which makes it available for biological evaluation. Trilepisiumic acid is being tested for
antioxidant and cytotoxic activities.
O
O
OH
O
O
pyridine, pyrollidine
24 h, reflux
H3CO
HO
OH
H3CO
OCH3
(2)
OCH3
i) SOCl2, THF, 12 h, reflux
ii) Vanillin
O
O
O
OH
O
KMnO4 , H+, H2O
Stirring , RT
O
O
OCH3
OCH3
H3CO
H3CO
OCH3
OCH3
(4)
(3)
33 % HBr
Glacial acetic acid
Reflux
2 h
O
O
OH
O
OH
HO
OH
(1)
Scheme 1. Synthetic pathway to trilepisiumic acid.

1124
A. Saeed and M. Qasim
3. Experimental
3.1. General methods
All the chemicals used in the synthesis were purchased from Sigma-Aldrich Chemie Gmbh
(Munich, Germany) and were used without any further purification. Thin-layer chromatography
was used to monitor the progress of the reactions. All the compounds were purified over silica
gel column. Solvents were distilled before using for purification purposes. Melting points were
recorded using a digital Gallenkamp (SANYO, Lough borough, UK) model MPD BM 3.5
apparatus and are uncorrected. The 1H NMR and 13C NMR spectra were recorded using Bruker
AM-300 spectrophotometer (Billerica, Middlesex, MA, USA) at 300 and 75.5 MHz,
respectively, using TMS as an internal standard. The chemical shift values are recorded on d
scale and the coupling constants (J) are in Hz. The FTIR spectra were recorded using Bio Rad
Excalibur FTS 3000 MX spectrophotometer (Madison, WI, USA). Rf values reported using
solvent system: petroleum ether and ethyl acetate (2:1).
3.1.1. 3,4-Dimethoxycinnamic acid (2)
3,4-Dimethoxybenzaldehyde (5.0 g, 0.02 mol) was refluxed with malonic acid (8.0 g, 0.06 mol)
in pyridine (50 mL) and few drops of tetrahydropyrrole as a catalyst for 20 h. The reaction
mixture was acidified with dilute hydrochloric acid to attain pH 7. The precipitates of product
obtained were settled down, filtered, washed with cold water and dried to afford 3,4-
dimethoxycinnamic acid (2) as a light yellow solid. Yield: 85%, Rf: 0.22, m.p.: 130–1338C, IR
(neat) y (cm21): 1650 (CvO acid). 1H NMR (DMSO, d ppm): 12.2 (1H, s, acid), 7.52 (1H, d,
´
J ¼ 15.9 Hz, b-H), 7.32 (1H, d, J ¼ 1.8 Hz, HC-20), 7.20 (1H, m, HC-60), 6.96 (1H, d,
J ¼ 8.4 Hz, HC-50), 6.4 (1H, d, J ¼ 15.9 Hz, a-H), 3.7–3.8 (6H, s, ZOMe). 13C NMR (DMSO, d
ppm): 168.3 (CvO acid), 151.2 (b-C), 111.9–151.2 (ArZC), 110.66 (a-C), 55.97–56.01
(ZOMe); elemental analysis: found: C, 63.49, H, 5.81%; calcd for C11H12O4: C, 63.45; H,
5.81%.
3.1.2. (E)-4-Formyl-2-methoxyphenyl 3-(3,4-dimethoxyphenyl)acrylate (3)
3,4-Dimethoxycinnamic acid (2) (4.5 g, 0.012 mol) was refluxed with SOCl2 (8 mL) in dry THF
for 12 h. The solvent was rotary evaporated to afford viscous yellow oil of 3,4-
dimethoxycinnamoyl chloride. Then, this acid chloride was treated with vanillin (3.5 g,
0.012 mol) using triethyl amine (5 mL) in dry THF at room temperature for 12 h. Then, the
reaction mixture was poured into ice-cold water and precipitates that appeared after 30 min were
filtered out. These precipitates were washed with 5% HCl and then with ice-cold water to afford
(E)-4-formyl-2-methoxyphenyl 3-(3,4-dimethoxyphenyl)acrylate as a white solid. Yield: 75%,
Rf: 0.89, m.p.: 130–1338C, IR (neat) y (cm21): 1710 (CvO ester), 1725 (CvO acid). 1H NMR
´
(DMSO, d ppm): 9.98 (1H, s, ZCHO), 7.86 (1H, d, J ¼ 15.9 Hz, b-H), 7.52 (2H, m, HC-600, HC-
200), 7.31 (1H, d, J ¼ 7.8 Hz, HC-500), 7.18 (2H, m, HC-60, HC-20), 6.92 (1H, d, J ¼ 8.4 Hz, HC-
50), 6.5 (1H, d, J ¼ 15.9 Hz, a-H), 3.90 (9H, s, ZOMe). 13C NMR (DMSO, d ppm): 191 (CvO
aldehyde), 164 (CvO ester), 152.14 (b-C), 109.76–151.95 (ArZC), 109.62 (a-C), 55.91–56.14
(ZOMe); elemental analysis: found: C, 66.63; H, 5.29%; calcd for C19H18O6: C, 66.66; H,
5.30%.
3.1.3. (E)-4-((3-(3,4-Dimethoxyphenyl)acryloyl)oxy)-3-methoxybenzoic acid (4)
(E)-4-formyl-2-methoxyphenyl 3-(3,4-dimethoxyphenyl)acrylate (3) was dissolved in acetone
(3 g, 0.054 mol) and stirred with KMnO4 acidified with dilute H2SO4, at 08C for 30 min. The
reaction mixture was then stirred overnight at room temperature. Then was extracted with ethyl

Natural Product Research
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acetate and the precipitates appeared were filtered out. The organic layer was dried over
anhydrous sodium sulphate and evaporated to yield (E)-4-((3-(3,4-dimethoxyphenyl)acryloyl)
oxy)-3-methoxybenzoic acid (4) as a white solid. Yield: 75%, Rf: 0.42, m.p.: 130–1338C, IR
(neat) y (cm21): 1710 (CvO ester), 1720 (CvO acid). 1H NMR (DMSO, d ppm): 12.95 (1H, s,
´
ZCOOH), 7.76 (1H, d, J ¼ 15.9 Hz, b-H), 7.61 (2H, m, HC-600, HC-200), 7.47 (1H, d, J ¼ 1.8 Hz,
HC-500), 7.31 (2H, m, HC-60, HC-20), 7.02 (1H, d, J ¼ 8.4 Hz, HC-50), 6.80 (1H, d, J ¼ 15.90Hz,
a-H), 3.90 (9H, s, ZOMe). 13C NMR (DMSO, d ppm): 170.1 (CvO acid), 164 (CvO ester),
152.14 (b-C), 109.76–151.95 (ArZC), 109.62 (a-C), 55.91–56.14 (ZOMe); elemental
analysis: found: C, 66.59, H, 5.11%; calcd for C19H18O7: C, 63.68; H, 5.06%.
3.1.4. Trilepisumic acid ((E)-4-((3-(3,4-dihydroxyphenyl)acryloyl)oxy)-3-hydroxybenzoic acid)
(1)
(E)-4-((3-(3,4-dimethoxyphenyl)acryloyl)oxy)-3-methoxybenzoic acid (4) (1.2 g, 0.000034 mol)
was refluxed with 33% HBr in glacial acetic acid (6 mL) for 2 h. The reaction mixture was poured
into ice (50 g) and then solid sodium carbonate was added to attain pH 6. The compound was
extracted with ethyl acetate and the solvent was evaporated to afford (E)-4-((3-(3,4-
dihydroxyphenyl)acryloyl)oxy)-3-hydroxybenzoic acid as a silvery crystalline solid. Yield:
75%, Rf: 0.22, m.p.: 130–1338C, IR (neat) y (cm21): 1712 (CvO ester), 1725 (CvO acid), 3450
´
(ZOH). 1H NMR (DMSO, d ppm): 12.95 (1H, s, ZCOOH), 7.78 (1H, d, J ¼ 15.9 Hz, b-H), 7.63
(2H, m, HC-600, HC-200), 7.47 (1H, d, J ¼ 1.8 Hz, HC-500), 7.32 (2H, m, HC-60, HC-20), 7.04 (1H, d,
J ¼ 8.4 Hz, HC-50), 6.82 (1H, d, J ¼ 15.9 Hz, a-H), 5.35 (3H, s, b, ZOH). 13C NMR (DMSO,
d ppm): 170.1 (CvO acid), 164 (CvO ester), 152.14 (b-C), 109.76–151.95 (ArZC), 109.62
(a-C), 55.91–56.14 (ZOMe); MS (70 eV) m/z (%): 296 [M]þz, 251 (34), 177 (16), 147 (100%), 91
(28); elemental analysis: found: C, 60.73, H, 5.26%; calcd for C16H12O7: C, 60.76; H, 4.82%.
4. Conclusions
The first total synthesis of natural antimicrobial metabolite trilepisiumic acid was achieved. The
pivotal steps include the esterification of vanillin with 3,4-dimethoxycinnamic acid followed by
the oxidation of the aldehyde function.
Supplementary material
Supplementary relating to this article is available online, alongside Figures S1–S5.
References
Adisakwattana S, Moonsan P, Anun SY. 2008. Insulin-releasing properties of a series of cinnamic acid derivatives
in vitro and in vivo. J Agric Food Chem. 56:7838–7844.
Ampa R, Ahombo G, Nguimbi E, Diatewa M, Dimo T, Ouamba JM, Abena A. 2013. Evaluation of hypoglycemic,
antihyperglycemic and antidiabetics properties of Trilepisium madagascariense D.C. Leeuwenberg (Moraceae).
J Biotechnol Pharm Res. 4:48–53.
Ango PY, Kapche D, Kuete V, Ngadjui BT, Bezabih M, Abegaz M. 2012. Chemical constituents of Trilepisium
madagascariense (Moraceae) and their antimicrobial activity. Phytochem Lett. 5:524–528.
Alves MJ, Ferreira ICFR, Froufe HJC, Abreu RMV, Martins A, Pintado M. 2013. Antimicrobial activity of phenolic
compounds identified in wild mushrooms, SAR analysis and docking studies. J Appl Microb. 2013. doi:10.1111/
jam12196.
´
Kossakowski J, Krawiecka M, Kuran B, Stefanska J, Wolska I. 2010. Synthesis and preliminary evaluation of the
antimicrobial activity of selected 3-benzofurancarboxylic acid derivatives. Molecules. 15:4737–4749.
Lee SU, Shin CG, Lee CK, Lee YS. 2000. Caffeoylglycolic and caffeoylamino acid derivatives, halfmers of l-chicoric
acid, as a new HIV-1 integrase inhibitors. Eur J Med Chem. 42:1309–1315.

1126
A. Saeed and M. Qasim
Miliovsky M, Svinyarov I, Mitrev Y, Evstatieva Y, Nikolovac D, Chochkova M, Bogdanova MG. 2013. A novel one-pot
synthesis and preliminary biological activity evaluation of cis-restricted polyhydroxy stilbenes incorporating
protocatechuic acid and cinnamic acid fragments. Eur J Med Chem. 66:185–192.
Narasimhan B, Belsare D, Pharande D, Mourya V, Dhake A. 2004. Esters, amides and substituted derivatives of cinnamic
acid. Eur J Med Chem. 39:827–834.
Rao BV, Ramanjaneyulu K, Rao TB. 2011. Synthesis and bioactivity evaluation of cinnamic acid esters from Oxalis
pescaprace. J Chem Pharm. 3:589–594.
Sharma P. 2011. A new chapter of various pharmacological activities. J Chem Pharm Res. 3:403–423.
Stacey JM, Dicks AP, Goodwin AA, Rush BM, Nigam M. 2013. Green carbonyl condensation reactions demonstrating
solvent and organocatalyst recyclability. J Chem Edu. 90:1067–1070.
´
Teke GN, Kuiate JR, Kuete V, Teponno RB, Tapondjou LA, Tane P, Giacinti G, Vilarem G, Afr S. 2010. Antidiarrheal
activity of extracts and compound from Trilepisium madagascariense stem bark. J Antarct Res. 77:319–327.
Zheng CJ, Yoo JS, Lee TG, Cho HY, Kim YH, Kim WG. 2005. Fatty acid synthesis is a target for antibacterial activity of
unsaturated fatty acids. FEBS Lett. 579:5157–5162.
Zhu J, Zhu H, Kobamoto N, Yasuda M, Tawata S. 2000. Fungitoxic and phytotoxic activities of cinnamic acid esters and
amide. J Pest Sci. 25:263–266.
Zou CL, Ji H, Xie GB, Chen DL, Wang FP. 2008. An effective O-demethylation of some C19-diterpenoid alkaloids with
HBr-glacial acetic acid. J Asian Nat Prod Res. 10:1063–1067.