In vitro evaluation of caffeoyl and cinnamoyl derivatives as potential prolyl oligopeptidase inhibitors

Article abstract of DOI:10.1055/s-0033-1350897

A screening of the natural product chlorogenic acid, isolated from the Brazilian medicinal plant Hypericum brasiliense, caffeic acid, cinnamic acid, and p-methoxycinnamic acid, and derivatives of caffeoylquinic, caffeoyl, and cinnamoyl against the enzymes prolyl oligopeptidase and dipeptidyl peptidase IV was carried out. Caffeoylquinic, caffeoyl, and cinnamoyl derivatives were prepared using simple derivatization procedures and through coupling reactions with the amino acid proline. The dipeptidyl peptidase IV assay showed inhibitory activity of the tested compounds at a high concentration (500 μM) in the range of 81.5-7.2%. In contrast, the derivatives methyl ester and 1,7-acetonide obtained from chlorogenic acid, and caffeic acid and its methyl ester derivative showed selectivity and activity as prolyl oligopeptidase inhibitors, with IC₅₀ values of 3 to 14 mM.

Full text of DOI:10.1055/s-0033-1350897

Letters 1531
Supporting information available online at
http://www.thieme-connect.de/ejournals/toc/plantamedica
In Vitro Evaluation of Caffeoyl and
Cinnamoyl Derivatives as Potential
Prolyl Oligopeptidase Inhibitors
Prolyl oligopeptidase (POP, prolyl endopeptidase or post-proline
cleaving enzyme, EC 3.4.21.26) is a large intracellular serine pro-
tease (80 kDa) found in over 20 human tissue types. This enzyme
cleaves short peptides (up to 30 amino acid residues) at the car-
boxyl side of an internal proline (-Pro-Xaa-; where Xaa is differ-
ent from Pro) [1,2]. Previous studies indicate that POP activity is
involved in key physiological functions, such as learning and
memory, cell division and differentiation, signal transduction, as
well as in some psychiatric disorders [3–5]. This activity is di-
rectly related to the fact that several neuropeptides, such as an-
giotensin I and II, vasopressin, bradykinin, thyroid-releasing hor-
mone, and substance P, are potential substrates for POP [6,7].
Thus, the activity of this enzyme in the central nervous system
(CNS) can decrease the concentrations of neuropeptides related
to psychiatric and neurodegenerative disorders, such as schizo-
phrenia and bipolar disorder [8].
The specificity of an inhibitor against POP can be examined by as-
saying, in parallel, the inhibitory capacity of candidate molecules
against the enzyme dipeptidyl peptidase IV (DPP IV; EC 3.4.14.5)
[9,10]. This serine protease cleaves peptides and proteins that
hold a proline or alanine in the penultimate position of the N-ter-
minus, these being relevant targets in the treatment of type 2 dia-
betes mellitus (T2DM) [11]. Although POP and DPP IV are related
to a number of pathologies and present low amino acid sequence
homology, the similarity of their three-dimensional structures
causes many compounds to indiscriminately inhibit both en-
zymes.
Luciana O. Adolpho1, Daniele Marin1, Albert Puigpinos2, Laura
Mendieta2, Teresa Tarragó2, Ademir F. Morel1, Ernest Giralt2,
Ionara I. Dalcol1
1
Núcleo de Pesquisa de Produtos Naturais (NPPN), Chemistry De-
partment, Universidade Federal de Santa Maria, Santa Maria – RS,
Brazil
2
Institute for Research in Biomedicine, Barcelona Science Park,
Barcelona, Spain
Abstract
!
A screening of the natural product chlorogenic acid, isolated from
the Brazilian medicinal plant Hypericum brasiliense, caffeic acid,
cinnamic acid, and p-methoxycinnamic acid, and derivatives of
caffeoylquinic, caffeoyl, and cinnamoyl against the enzymes prol-
yl oligopeptidase and dipeptidyl peptidase IV was carried out.
Caffeoylquinic, caffeoyl, and cinnamoyl derivatives were pre-
pared using simple derivatization procedures and through cou-
pling reactions with the amino acid proline. The dipeptidyl pep-
tidase IV assay showed inhibitory activity of the tested com-
pounds at a high concentration (500 µM) in the range of 81.5–
7.2%. In contrast, the derivatives methyl ester and 1,7-acetonide
obtained from chlorogenic acid, and caffeic acid and its methyl
ester derivative showed selectivity and activity as prolyl oligo-
peptidase inhibitors, with IC50 values of 3 to 14 mM.
We identified the natural 3-caffeoylquinic acid (chlorogenic acid,
1), isolated from the Brazilian medicinal plant Hypericum brasi-
liense (Hypericaceae) and used as an excitant and antispasmodic,
as a new POP inhibitor [12]. Using the commercial chlorogenic
acid 1, caffeic acid 6, trans-cinnamic acid 12, and p-methoxycin-
namic acid 13 as starting materials, we synthesized the deriva-
Key words
prolyl oligopeptidase · dipeptidyl peptidase IV · chlorogenic
acid · caffeoyl and cinnamoyl derivatives · Hypericum brasi-
liense · Hypericaceae
"
tives series 2–5, 7–11, and 16–19 as depicted in l Figs. 1–3.
Fig. 1 Synthesis of the caffeoylquinic derivatives.
Reagents and conditions: (a) MeOH, Amberlite IRA
120 H; (b) Ac2O, DMAP, pyridine; (c) acetone,
H2SO4; (d) Pro-OMe. HCl, HATU, DIEA in DMF.
Adolpho LO et al. In Vitro Evaluation… Planta Med 2013; 79: 1531–1535

1532 Letters
Fig. 2 Synthesis of the caffeoyl derivatives.
Reagents and conditions: (a) Me2SO4, NaOH;
(b) MeOH, H2SO4; (c) Pro-OMe. HCl, HATU, DIEA in
DMF; (d) Ac2O, DMAP, pyridine.
Fig. 3 Structures of the cinnamoyl derivatives.
"
Briefly, compound 1 was esterified following the procedure de-
as inhibitors of POP and DPP IV (l Table 1). From these results,
scribed by Lopez Giraldo et al. [13] to yield the methyl chlorogen-
ate 2, while the methyl esters 8, 14, and 15 were prepared by the
Fischer method. Acetylation of 1 and 6 with acetic anhydride and
pyridine/4-(dimethylamino)pyridine [14,15] yielded the deriva-
tives pentaacetylchlorogenic acid 3 and diacetylcaffeic acid 10,
respectively. To obtain 1,7-acetonide 4, chlorogenic acid 1 was al-
lowed to react with anhydrous acetone and concentrated H2SO4
[16]. Dimethylcaffeic acid 7 was prepared from 6 in reaction to
Me2SO4 in NaOH [17]. The structures of these derivatives were
confirmed by NMR and mass spectroscopy and compared with
spectral data in the literature [14–19]. Compounds 5, 9, 11, 16,
and 17 were synthesized by reacting the appropriate natural acid
with proline methyl ester hydrochloride, using either O-(7-aza-
we selected the active compounds to be tested in an IC50 assay.
At 500 µM, all the derivatives of the cinnamoyl and p-methoxy-
cinnamoyl series (compounds 12–19) showed inhibitory activity
below 50% against POP and DPP IV. Also, the DPP IV inhibition
preliminary assay at 500 µM displayed only moderate inhibitory
activity for caffeoylquinic derivatives 1–5, caffeic acid 6, and its
methyl ester 8, in the range of 57–73%, while 7, 9, 10, and 11 reg-
istered low activity (< 50%), so the IC50 for these compounds was
not determined. In contrast, all derivatives from the caffeoyl-
quinic and caffeoyl series, except 5 and 7, showed interesting re-
sults regarding POP inhibition, so we proceeded to determine
"
their IC50 values against this enzyme (l Table 1). Among the caf-
feoylquinic series, 2 and 4 showed POP inhibition with IC50 values
of 3.0 and 14.3 µM, respectively, while from the caffeoyl series,
ester 8 (IC50 5 µM) and caffeic acid 6 (IC50 12.5 µM) showed the
highest inhibitory capacity. Liposoluble compounds are of inter-
est for biological applications because they can easily pass
through biological barriers such as the blood-brain barrier. Un-
fortunately, the results obtained for derivatives 3 (IC50 99 µM)
and 10 (IC50 28 µM) indicated that, in comparison with the start-
ing natural products, derivatization with acetyl groups did not
improve inhibitory capacity against the enzymes.
benzotriazol-1-yl)-N,N,N′,N′-tetramethyluronium
hexafluoro-
phosphate (HATU)/diisopropylethylamine (DIEA) in dimethylfor-
mamide or isobutyl chloroformate/N-methylmorpholine in tet-
rahydrofuran [20,21]. Alkaline hydrolysis of 16 and 17 yielded
the corresponding derivatives 18 and 19, respectively. The struc-
tures of the synthesized derivatives were confirmed by MS, opti-
cal rotation, and NMR spectra (see Supporting Information).
Fluorimetric assays were used to estimate POP and DPP IV inhibi-
tion [4,10,22]. POP was obtained by expression in E. coli follow-
ing a procedure described in the literature [22]. Porcine DPP IV
was from a commercial source. Initially, we screened 500 µM of
all the derivatives obtained and the natural acids 1, 6, 12, and 13
Given that POP and DPP IV have a high affinity for substrates con-
taining proline, it was expected that the presence of a proline res-
idue in the derivatives (compounds 5, 9, 11, and 16–19) would
Adolpho LO et al. In Vitro Evaluation… Planta Med 2013; 79: 1531–1535

Letters 1533
Compound
DPP IV Inhibition (%)*
POP Inhibition (%)**
POP IC50 (µM)
Table 1 POP and DPP IV inhibi-
tion of caffeoylquinic, caffeoyl, and
cinnamoyl derivatives.
Caffeoylquinic derivatives
(500 µM)
81.5 3.9
64.3 2.6
53.8 6.0
62.7 4.1
66.5 3.3
(500 µM)
88.0 2.9
92.6 2.6
81.9 0.8
88.3 1.7
75.5 1.6
ꢀ1
23.0
3.0
1
1
ꢀ2
ꢀ3
98.9 1
ꢀ4
14.3
1
4
ꢀ5
210.0
Caffeoyl derivatives
ꢀ6
50.1 1.2
45.0 1.2
69.4 3.8
48.8 5.6
28.6 5.0
43.9 1.4
93.8 1.1
29.4 1.2
90.5 1.2
96.3 2.9
72.9 0.4
98.3 1.1
12.5
198.0
5.0
5
2
2
1
1
1
ꢀ7
ꢀ8
ꢀ9
105.7
28.0
10
11
120.0
Cinnamoyl derivatives
12
4.4 1.6
11.5 4.3
7.2 4.2
16.1 2.8
–
–
–
–
–
–
–
–
13
< 10.0
14
20.0 3.6
22.0 4.0
15
20.5 3.4
16
< 10.0
< 10.0
17
17.0 1.4
35.5 5.5
14.5 1.3
42.8 4.0
14.6 3.9
18
19
< 10.0
Control
Verbascoside
Isoleucine thiazolide
Z-prolyl-prolinal
–
–
–
3.4 0.2
0.52§
–
4.9 × 10−3
Data are represented as mean SEM. * Percentages of DPP IV inhibition calculated using GP‑AMC as the substrate. ** Percentages of POP
inhibition calculated using ZGP‑AMC as the substrate. § DPP IV IC50 (µM)
enhance their performance as inhibitors. However, none of these
derivatives displayed a relevant inhibitory capacity. Compounds
5 and 11 showed IC50 values of 210 and 120 µM, respectively.
The DPP IV inhibitory capacity of all derivatives and natural acids
1–11 at a high concentration (500 µM) was not exceptional
(81.5–7.2%). We therefore determined the IC50 values of only nat-
ural compounds 1 and 6, which were found to be 128 µM and
> 200 µM, respectively.
These general results are significant and demonstrate simple
structural modifications of natural products improving their per-
formance as enzymatic inhibitors, making them potential candi-
dates for the development of new drugs. None of the compounds
tested were DPP IV inhibitors; however, methyl ester 2 and 1,7-
acetonide 4 derived from natural products chlorogenic acid,
methyl ester 8, and caffeic acid 6 proved to be interesting and se-
lective POP inhibitors. These observations indicate the influence
of the free 4,5-dihydroxyl groups in the caffeoyl moiety for the
activity of these compounds.
Many natural products are known POP inhibitors in the micro-
molar range, such as the flavonoids oroxylin [23] and baicalin
[9], the alkaloid berberin [24], and 6-(8′Z-pentadecenyl)salicylic
acid [25]. In addition, some naturally occurring compounds con-
taining one or more caffeoyl groups have also been reported to
exert POP inhibitory activity: the phenylpropanoid verbascoside
[10], isolated as the main constituent of the crude extract of
Buddleja brasiliensis Jacq.; rosmarinic acid [26], a polyphenol
found in various species of the Boraginaceae; the pentacyclic tri-
terpenoid 3a-(3′′,4′′-dehydroxy-trans-cinnamoyloxy)-D-friedo-
olean-14-en-28-oic acid present in leaves Tamarix hispida Willd
[27]; and also chlorogenic acid, isolated by our group from Hyper-
icum brasiliense [12]. From the three series of caffeoyl and cinna-
moyl derivatives obtained in this study, we observed that the de-
rivatives presenting the 4,5-dihydroxyl groups in the free caffeoyl
moiety, such as the methyl ester 2 and 1,7-acetonide 4 derived
from chlorogenic acid, the methyl ester 8, and the caffeic acid 6,
were the good POP inhibitors, showing selective inhibition in a
dose-dependent manner, with IC50 values in the low micromolar
range (3.0–14.3 µM). Although the mechanism of the POP inhibi-
tion by these derivatives has not been elucidated, the findings of
this study indicate the potential of the molecules as POP inhib-
itors. Thus, these compounds are of interest since they can be
used as leads in the development of new potent therapeutic
drugs to treat neuropsychiatric disorders.
Materials and Methods
!
Provenance, purity of substances, and equipment used is given in
Supporting Information.
(E)-methyl 1-(3-(3-(3,4-dihydroxyphenyl)acryloyloxy)-1,4,5-trihy-
droxycyclohexanecarbonyl)pyrrolidine-2-carboxylate (5): This de-
rivative was synthesized using the coupling method described by
Salmi et al. [20] with slight modifications. Chlorogenic acid 1
(1.10 mmol) and L-proline methyl ester hydrochloride
(1.10 mmol) were dissolved in DMF (3 mL). Next, DIEA
(1.10 mmol) was added to the mixed solution at 0°C. After
15 min, the coupling reagent HATU (1.10 mmol) was added at
0°C and the resulting mixture was stirred for 72 h at room tem-
perature. The reaction mixture was then poured into chloroform
and extracted with HCl 1 N, a saturated solution of NaHCO3, and
water. The organic phase was dried with MgSO4 and evaporated
to dryness, resulting in an oil, which was purified by recrystalli-
zation with CHCl3. Yield 40%. [α]D − 34 (c 0.05, CH3OH). 1H NMR
(CD3COD, δ [ppm], J [Hz]): 7.64 (d, J = 15.9, H-7), 7.41 (s, H-2),
7.21 (d, J = 8.3, H-5), 7.01 (d, J = 8.3, H-6), 6.35 (d, J = 15.9, H-8),
Adolpho LO et al. In Vitro Evaluation… Planta Med 2013; 79: 1531–1535

1534 Letters
5.44 (s, OHs), 4.52 (m, H-8′), 4.37 (m, H-2′), 4.12 (m, H-1′), 3.83 (s,
and C-9), 160.9 (C-4), 142.5 (C-7), 129.4 (C-2 and C-6), 127.8 (C-
8), 115.4 (C-1′), 114.1 (C-3 and C-5), 58.9 (C-1′), 55.3 and 52.2 (2-
OCH3), 46.8 (C-4′), 29.1 (C-2′), 24.8 (C-3′).
OCH3), 3.44 (m, H-11′), 3.12 (m, H-3′), 2.3–1.9 (m, H-9′, H-6′, H-4′,
and H-10′). 13C NMR (CD3COD, δ [ppm]): 169.7, 169.0, and 168.9
(C-7′, C-9, and C-12′), 147.0 (C-4), 146.8 (C-3), 141.0 (C-7), 129.9
(C-1), 122.9 (C-6), 122.1 (C-8), 116.5 (C-5), 115.2 (C-2), 86.5 (C-
5′), 74.0 (C-2′), 71.0 (C-1′), 70.5 (C-3′), 58.8 (C-8′), 49.5 (-OCH3),
47.0 (C-11′), 37.3 (C-4′), 37.0 (C-6′), 30.4 (C-9′), 23.2 (C-10′).
(E)-methyl 1-(3-(3,4-dihydroxyphenyl)acryloyl)pyrrolidine-2-car-
boxylate (9): Compound 9 was prepared as described for 5 using
caffeic acid 6 and L-proline methyl ester hydrochloride. The oily
product obtained was purified by chromatography on silica gel,
eluting with dichloromethane. Yield: 40%. [α]D − 64 (c 0.05,
CH3OH). 1H NMR (DMSO-d6, δ [ppm], J [Hz]): 7.31 (d, J = 15.4, H-
7), 7.06 (s, H-2), 6.97 (d, J = 8.6, H-5), 6.76 (d, J = 8.6, H-6), 6.66 (d,
J = 15.4, H-8), 4.40 (m, H-1′), 3.72 (m, H-4a’), 3.68 (s, -OCH3), 3.50
(m, H-4b’), 2.19–1.86 (m, H-2′, and H-3′). 13C NMR (DMSO-d6, δ
[ppm]): 172.4 and 164.1 (C-5′ and C-9), 147.4 (C-4), 145.3 (C-3),
141.7 (C-7), 126.3 (C-1), 120.6, 115.5, and 115.2 (C-6, C-8, and C-
5), 114.6 (C-2), 58.4 (C-1′), 51.4 (-OCH3), 46.3 (C-4′), 28.5 (C-2′),
24.2 (C-3′).
(E)-4-(3-(2-(methoxycarbonyl)pyrrolidin-1-yl)-3-oxoprop-1-en-
yl)-1,2-phenylene-diacetate (11): Diacetylcaffeic acid 10 and L-
proline methyl ester hydrochloride were coupled as described
for 5 and 9. Yield 49%. [α]D − 48 (c 0.05, CHCl3). 1H NMR (CDCl3, δ
[ppm], J [Hz]): 7.64 (d, J = 15.4, H-7), 7.38, 7.34, and 7.19 (H-6, H-
2, and H-5), 6.67 (d, J = 15.4, H-8), 4.59 (m, H-1′), 3.83 (m, H-4′a),
3.74 (s, -OCH3), 2.29 (2 -OCOCH3), 2.16–1.75 (H-4b’, H-2′, and H-
3′). 13C NMR (CDCl3, δ [ppm]): 172.6, 168.0, 167.9, 164.4 (C-5′, C-
9, and 2 -OCOCH3), 143.0 (C-4), 142.3 (C-3), 141.0 (C-7), 134.0 (C-
1), 126.3, 123.7, and 122.3 (C-6, C-8, and C-5), 119.1(C-2), 59.0 (C-
1′), 52.2 (-OCH3), 46.9 (C-4′), 29.1 (C-2′), 22.6 (C-3′), 20.5 (2-
OCOCH3).
1-cinnamoylpyrrolidine-2-carboxylic acid (18): 1 mL of 1 M NaOH
was added to a methanol solution (1 mL) of compound 16
(0.4 mmol). The mixture was stirred at r.t. for 2 h, neutralized
with 1 M HCl, and the methanol was evaporated under reduced
pressure. The aqueous solution was cooled in an ice bath and ac-
idified at pH 2 with 1 M HCl. The solid obtained was separated by
filtration and washed with water. Yield: 87%. RMN 1H (CD3OD, d
[ppm], J [Hz]): 7.55 (d, J = 15.4, H-7), 7.53–6.93 (5 Har), 6.89 (d,
J = 15.4, H-8), 4.46 (m, H-1′), 3.76 (m, H-4′), 2.22–1.96 (m, H2′,
and H3′). 13C NMR (CD3OD, d [ppm]): 173.0 and 165.7 (C-5′ and
C-9), 142.8 (C-7), 134.8 (C-1), 129.7, 128.5, 127.8, 117.8 (5 C‑ar),
117.6 (C-8), 59.2 (C-1′), 30.6 (C-2′), 24.3 (C-3′).
(E)-1-(3-(4-methoxyphenyl)acryloyl)pyrrolidine-2-carboxylic acid
(19): This derivative was obtained as described for 18, by alkaline
hydrolysis with methanol and 1 M NaOH. Yield: 87%. 1H‑NMR
(CD3OD, δ [ppm], J [Hz]): 7.65 (d, J = 15.6, H-7), 7.68–7.11 (4
Har), 6.95 (d, J = 15.6, H-8), 4.72 (m, H-1′) 4,00 (s, -OCH3), 3.97
(m, H-4′), 2.50–2.22 (m, H2′, and H3′). 13C NMR (CD3OD, δ
[ppm]): 175.7 and 167.7 (C-5′ and C-9), 162.9 (C-4), 143.9 (C-7),
130.8 (C-2 and C-6), 129.7 (C-8), 116.8 (C-1), 115.5 (C-3 and C-5),
60.7 (C-1′), 55.9 (-OCH3), 48.6 (C-4′), 30.3 (C-2′), 25.7 (C-3′).
In vitro measurement of enzyme inhibition: POP and DPP IV ac-
tivities were determined as described previously [10,,23,28].
The IC50 value was defined as the concentration of fraction re-
quired to inhibit 50% of enzyme activity. Data were analyzed us-
ing GraphPad Prism 6 software. The assays were performed in
triplicate and with a blank for each sample without enzyme, and
the percentage of inhibition was calculated by comparing the ab-
sorbance of the sample to the blank. POP activity was evaluated
using verbascoside [10] and Z-prolyl-prolinal as positive con-
trols, while in the DPP IV assay, the standard inhibitor isoleucine
thiazolide (P32/98) was used as the control.
Methyl 1-cinnamoylpyrrolidine-2-carboxylate (16): Isobutyl
chloroformate (2.7 mmol) was added to a cooled (− 15°C) solu-
tion of cinnamic acid 12 (2.7 mmol) and NMM (2.7 mmol) in THF
(14 mL) and stirred at − 15°C for 15 min. A solution of L-proline
methyl ester hydrochloride (2.7 mmol) and NMM (2.7 mmol) in
DMF (5 mL) was then added and the reaction mixture was stirred
for 24 h, allowing it to warm up to r.t. slowly [21]. The reaction
mixture was evaporated, then poured into chloroform and ex-
tracted with a saturated solution of HCl 1 N, NaHCO3, and water.
The organic phase was dried with MgSO4 and evaporated to dry-
ness, resulting in an oil which was purified by recrystallization
Supporting information
Details regarding the synthesis of the known derivatives 2–4, 7–
8, 10, and 14–15, NMR spectra of compounds as well as
provenance, purity of substances, and equipment are available
as Supporting Information.
Acknowledgments
!
using hexane/ethyl acetate to give 16 as
a
white solid
1
(m.p. 85.3–88.3°C). Yield 81%. [α]D − 68 (c 0.05, CHCl3). H NMR
(CDCl3, δ [ppm], J [Hz]): 7.61 (d, J = 15.5, H-7), 7.39–7.24 (5 Har),
6.63 (d, J = 15.5, H-8), 4.49 (m, H1′), 3.75 (m, H-4′a), 3.64 (s,
-OCH3), 3.59 (m, H-4′b), 1.97 (m, H-2′, and H-3′). 13C NMR (CDCl3,
δ [ppm]): 172.7 and 164.8 (C-5′ and C-9), 142.8 (C-7), 142.6,
135.0, 129.6, 128.7, and 127.8, 117.8, (6 C‑ar and C-8), 58.9 (C-
1′), 52.1(-OCH3), 46.8 (C-4′), 29.0 (C-2′), 24.7 (C-3′).
The study was supported by CAPES-Coordenação de Aperfeiçoa-
mento de Pessoal de Nível Superior (Ministério da Educação-Bra-
zil), the MECD (Ministerio de Educación, Cultura y Deporte de
España), MCI-FEDER (BIO2008-00799), the Fundació la Marató
de TV3, and the Generalitat de Catalunya (CeRBa and
2005SGR‑00663).
(E)-methyl 1-(3-(4-methoxyphenyl)acryloyl)pyrrolidine-2-carbox-
ylate (17): This derivative was prepared as described for 16 using
p-methoxycinnamic acid 13 and L-proline methyl ester hydro-
chloride. The oily product obtained was purified by chromatogra-
phy on silica gel, eluting with chloroform. Yield: 50%. [α]D − 56 (c
0.05, CHCl3).1H NMR (CDCl3, δ [ppm], J [Hz]): 7.67 (d, J = 15.4, H-
7), 7.44–6.88 (4 Har), 6.60 (d, J = 15.4, H-8), 4.61 (m, H1′), 3.85 (m,
H-4′a), 3.82 (s, -OCH3), 3.74 (s, -OCH3), 3.69 (m, H-4′b), 2.11 (m,
H-2′, and H-3′). 13C NMR (CDCl3, δ [ppm]): 172.9 and 165.2 (C-5′
Conflict of Interest
!
The authors declare no conflict of interest.
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DOI http://dx.doi.org/10.1055/s-0033-1350897
Published online October 1, 2013
Planta Med 2013; 79: 1531–1535
© Georg Thieme Verlag KG Stuttgart · New York ·
ISSN 0032‑0943
Correspondence
Profa Dra Ionara I. Dalcol
Núcleo de Pesquisa de Produtos Naturais (NPPN)
Chemistry Department
Universidade Federal de Santa Maria
Campus Camobi
97105–900 Santa Maria – RS
Brazil
Phone: + 55553208798
Fax: + 555532208031
iidalcol@gmail.com
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of esters of caffeic and dihydrocaffeic acids. Bioorg Med Chem 2001; 9:
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cient peptide coupling method. Lett Org Chem 2005; 2: 628–633
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