Design, Prins-cyclization reaction promoting diastereoselective synthesis of 10 new tetrahydropyran derivatives and in vivo antinociceptive evaluations

Article abstract of DOI:10.1016/j.ejmech.2012.09.046

We described in this article the very efficient 2,6-cis ou 2,4,6-cis diastereoselective synthesis (2 or 3 steps, 62-65% global yields) from Prins-cyclization reaction as synthetic key-step to tetrahydropyran rings construction of 10 new congeners compounds (3-12) designed from Naproxen structure. These tetrahydropyran derivatives were in vivo bioevaluated on antinociceptive effect in the acetic acid-induced abdominal writhing test, the tail-flick test, the rota-rod performance and open field tests. All new compounds showed greater antinociceptive activity compared to compound 1a, an analgesic tetrahydropyran derivative previously described by us. We can detach the high activity of tetrahydropyran derivative 10 which presented 87.5% inhibition (14% inhibition was presented by 1a) in the acetic acid-induced abdominal writhing test. Besides that the tail-flick tests indicate compounds 7 and 10 as the most actives. All these new compounds showed no toxicity in mice in all biologically studied models.

Full text of DOI:10.1016/j.ejmech.2012.09.046

European Journal of Medicinal Chemistry 58 (2012) 1e11
Contents lists available at SciVerse ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Original article
Design, Prins-cyclization reaction promoting diastereoselective synthesis of 10
new tetrahydropyran derivatives and in vivo antinociceptive evaluations
Saulo L. Capim a, Paulo H.P. Carneiro b, Paloma C. Castro b, Maithê R.M. Barros b, Bruno G. Marinho b,
,
Mário L.A.A. Vasconcellos a
*
a Laboratório de Síntese Orgânica Medicinal da Paraíba (LASOM-PB), Departamento de Química, Universidade Federal da Paraíba, Campus I, João Pessoa, PB 58059-900, Brazil
b Departamento de Ciências Fisiológicas, Instituto de Biologia, Universidade Federal Rural do Rio de Janeiro, BR465, Km07, Seropédica, RJ 23890-000, Brazil
a r t i c l e i n f o
a b s t r a c t
Article history:
We described in this article the very efficient 2,6-cis ou 2,4,6-cis diastereoselective synthesis (2 or 3 steps,
62e65% global yields) from Prins-cyclization reaction as synthetic key-step to tetrahydropyran rings
construction of 10 new congeners compounds (3e12) designed from Naproxen structure. These tetra-
hydropyran derivatives were in vivo bioevaluated on antinociceptive effect in the acetic acid-induced
abdominal writhing test, the tail-flick test, the rota-rod performance and open field tests. All new
compounds showed greater antinociceptive activity compared to compound 1a, an analgesic tetrahy-
dropyran derivative previously described by us. We can detach the high activity of tetrahydropyran
derivative 10 which presented 87.5% inhibition (14% inhibition was presented by 1a) in the acetic acid-
induced abdominal writhing test. Besides that the tail-flick tests indicate compounds 7 and 10 as the
most actives. All these new compounds showed no toxicity in mice in all biologically studied models.
Ó 2012 Elsevier Masson SAS. All rights reserved.
Received 19 May 2012
Received in revised form
24 September 2012
Accepted 27 September 2012
Available online 5 October 2012
Keywords:
Prins-cyclization reaction
Tetrahydropyrane derivatives
In vivo
Antinociceptive
Cytotoxicity
1. Introduction
bioactivity of the isolated Vitex cymosa sp extract [7]. However,
when spectroscopic data of synthetic 1a were compared with the
Substituted tetrahydropyranyl moieties are extensively distrib-
uted in the natural product structures that present a large phar-
macological profile [1,2]. Many methodologies are being developed
aiming to prepare these structures, e.g. the hetero-DielseAlder,
natural product we have found that lactone 2 [8] was the actual
natural product responsible for the analgesic activity of V. cymosa
sp (Fig. 1). Fortunately, this mistake [7] was very convenient for us,
considering that unpublished 1a and 1b compounds showed higher
antinociceptive activities than V. cymosa sp extract, and so
compound 1aeb could be presented as a new promising non-
steroidal prototype to antinociceptive class of drugs.
The antinociceptive activity of 1a was evaluated in mice on
acetic acid-induced abdominal writhing, on tail-flick test, on hot-
plate test, on formalin test, on reduction of spontaneous activity
[5,9]. It described that the opioid receptor antagonist Naloxone
totally reverted effects on 1a in all models. In fact, the pharmaco-
logical profile described for 1a indicating that it substance can
mediate antinociception at peripheral and central sites even when
orally administered through activation of opioid receptors [9].
Although, 1a induced less tolerance when compared to morphine.
Recently, our research group described pharmacological profile to
pure enantiomer 1b [10] indicating that 1b also develops signifi-
cant antinociceptive activity and, at least part of its effects seems to
be mediated by the opioid system.
intramolecular Michael, the cyclization of diols and
d-hydrox-
yketones, the iodolactonization, the unsaturated alcohols undergo
seleno-etherification, the epoxide opening, the Prins-cyclization
reaction and others [3]. The Prins-cyclization reaction is a rela-
tively new and very efficient reaction that has significantly
advanced in the last years demonstrated by a number of applica-
tions described in the literature [4].
In the previous articles we described the first diastereoselective
synthesis of (ꢀ)-cis-(6-ethyl-tetrahydropyran-2-yl) formic acid (1a)
[5], and for the (-)e(S,S)e1b acid [6] (Fig. 1) both of them using
Prins-cyclization reactions as key-step on synthetic strategy to
construct the tetrahydropyran skeletons. Compound 1a presented
important antinociceptive (analgesic and anti-inflammatory)
properties. This compound was proposed as responsible for the
It is well established that there are multiple pain states and that
these states differ not only in the reported sensation of pain, but
* Corresponding author. Tel.: þ55 83 3248 2352; fax: þ55 83 3216 7433.
E-mail address: mlaav@quimica.ufpb.br (M.L.A.A. Vasconcellos).
0223-5234/$ e see front matter Ó 2012 Elsevier Masson SAS. All rights reserved.
http://dx.doi.org/10.1016/j.ejmech.2012.09.046

2
S.L. Capim et al. / European Journal of Medicinal Chemistry 58 (2012) 1e11
Molinspiration cheminformaticsÒ program (Table 1) [22,23]. It is
OH
important to detach that compounds 1a, 3e12 (Fig. 2 and Table 1)
are in agreements to the Lipinski’s Rule of Five [24], also calculated
by the Molinspiration cheminformaticsÒ program. Recently, several
publications in Medicinal Chemistry have been described using
Molinspiration cheminformaticÒ program assisting the design of
new drugs [25].
HO
HO
O
O
O
O
O
O
cis
(-)-(S,S)
1b
2
1a
2. Results and discussion
Fig. 1. (ꢀ)-Cis-(6-ethyl-tetrahydropyran-2-yl) formic acid (1a), (e)e(S,S)-1b acid and
(ꢀ)-lactone 2 structures.
2.1. Chemistry
also in the pharmacology of therapeutic agents and in the sites of
the nervous system where the pain is generated and can be altered
[11]. Current pharmacological therapy for pain comes primarily
from two classes of compounds: non-steroidal anti-inflammatory
drugs and opioids. Up to now there is a continuous search for new
pharmacologically active analgesic agents with minor adverse
effects.
In our continuing search for bioactive substances [12e18] we
present in this article the designed, diastereoselective synthesis,
in vivo antinociceptive and toxicological evaluation to a new
congener series of tetrahydropyranyl derivatives: the acids 3 and 4,
its synthetic precursors 5e8 and also the derivatives 9e12 (Fig. 2).
Even compound 1a has already been extensively investigated in the
previous work, it was also bioevaluated in vivo in this article as
reference compound.
We realized the design these new compounds inspirited on
(ꢀ)-naproxen structure 13 (Fig. 3), a PGHS1/PGHS2 enzymes
inhibitor [19] which present the carboxylic acid and the naphthyl
moieties. In our design we included a spacer group [20] from
(ꢀ)-Naproxen structure (13), producing the virtual structure 14
(Scheme 1), followed by the conformational restriction strategy
[21], producing the virtual structure 15. The use of the bio-
2.1.1. Improved synthesis of (ꢀ)-cis-(6-ethyl-tetrahydropyran-2-yl)
formic acid (1a)
We began our experimental work optimizing of the previous
diastereoselective synthesis of compound 1a [5].
The 2,2-dimethoxyethyl isobutyrate (19) is
a
strategic
compound that has been used in several nucleosides synthesis and
other applications [26]. For example 19 was used for the synthesis
of mescarine [27], oxetanocin [28], kallolide A [29], (ꢀ)-kumau-
sallene and (þ)-epi-kumausalene [30]. The synthesis of 2,2-
dimethoxyethyl isobutyrate (19) could be performed in high yield
by reaction between potassium isobutyrate (16) and 2-chloro-
1,1dimethoxyethane (17) in N,N-dimethyl formamide (DMF),
through a nucleophilic substitution leading to an 2-chloro-1,1-
dimethoxyethane (18) in high yield [31], followed by hydrolysis
with aqueous formic acid resulting 2,2-dimethoxyethyl isobutyrate
(19) [32]. Using these protocols we could easily prepare 19 on scales
of 60 g in two steps on high yield (Scheme 1).
The synthesis of (ꢀ)-homoallylic alcohol (20), was performed
through a Barbier reaction between allyl bromide and aldehyde 19
(1.0 Equiv.) in water in the presence of tin chloride (dihydrate)
(1.5 Equiv.), potassium iodide (3.0 Equiv.) and solution of saturated
ammonium chloride at room temperature for 2 h, resulting in 20 on
80% of yield (Scheme 2) [33].
The (ꢀ)-homoallylic alcohol 20 was employed as the substrate
for the Prins cyclization reaction with propanal, mediated by AlCl3
as the Lewis acid [34], dissolved in dried CH2Cl2 for 6 h, resulting
tetrahydropyran derivative 21 in 85e90 % yield (Scheme 2). An only
diastereoisomer was obtained by CG-MS analysis (see experimental
section).
Based on the most commonly accepted reaction mechanism
explaining the 2,4,6-cis preferential geometry for this reaction,
proposed by Li and Yang et al. [35], we propose the mechanism
shown in Fig. 4. The mechanism begins with the nucleophilic attack
of alcohol 20 on the complexed aldehyde with AlCl3 (step a) leading
to formation of intermediate 22. Step b is a proton exchange fol-
lowed by elimination (step c) with the formation of intermediate
24. The step d (slow step) subsequently occurs by synchronously
nucleophilic attack of chloride ion through the transition state 25,
which produces 21. It should be noted that the attack of chloride ion
occurs preferentially on equatorial position which is a more stable
transition state (Fig. 4).
isosterism concept [22] led to the
a and b naphthyl tetrahy-
dropyranyl acids 3 and 4. These new compounds can be prepared at
diastereoselective form from the Prins-cyclization as strategy to
construction of its tetrahydropyran skeletons like the 1a and 1b
prototype [3].
Even knowledge that (ꢀ)-Naproxen (13) does not present an
opioid-type action [19] like our prototypes 1a and 1b we also
choose 13 as starting structure for design of the tetrahydropyranyl
acids 3 and 4 (Fig. 2) due to the presence of the pharmacophoric
and auxoforic groups like 1a and 1b and also because 13 present
a strong antinociceptive activity, being an PGHS1 and PGHS2
enzyme inhibitor [19]. In addition, compounds 3 and 4 and these
derivatives presented, respectively, a good in silico calculated
enzyme inhibitor and GPCR ligand scores from the on line
Cl
HO
HO
O
O
R
O
R
O
R
O
O
5;R= β-naphthyl
6;R= α-naphthyl
3;R= β-naphthyl
Another proposal explaining the stereoselectivity on C4 (Chlo-
rine) of tetrahydropyran derivatives was based on the theoretical
studies by Alder et al. [36]. They proposed that the favoring equa-
torial C4 selectivity obtained on this reaction originates from the
geometry of the cationic intermediate (e.g. 26, Fig. 4) involved in
the reaction.
7;R= β-naphthyl
4;R= α-naphthyl
8;R= α-naphthyl
Cl
Cl
HO
HO
O
O
R
HO
O
R
O
According to the Alder interpretation, the interaction between
O
one of the n electrons pair of oxygen with two
in each of the CeC bonds of the ring cyclic
s
electrons pairs (one
) and the empty p-
cis-(+/-)
9;R= β-naphthyl
10;R= α-naphthyl
11;R= β-naphthyl
12;R= α-naphthyl
s
1a
orbital of carbocation makes particular stability on the system. This
particular geometry favors the nucleophilic attack of chloride ion
on exo-face of 26 (Fig. 5) leading the C4-equatorial product 21.
Fig. 2. Designed, synthesized and bioevaluated new compounds (3e12) and 1a as
biological reference compound.

S.L. Capim et al. / European Journal of Medicinal Chemistry 58 (2012) 1e11
conformational restriction
spacer strategy
3
strategy
HO
HO
HO
O
O
O
O
O
O
O
O
14
15
13
bioisosterism
strategy
HO
HO
O
O
O
O
3
4
Fig. 3. Designed to acids 3 and 4 from (ꢀ)-Naproxen structure (13).
Comparison of 21 prepared here with spectroscopic data of this
same compound previously described by us [9] corroborated its
relative geometry.
2.1.3. Geometries determinations of new tetrahydropyranyl
derivatives
In accordance of the results described here to preparation of 1a
an only diastereoisomer was obtained for new compounds (3e12)
evaluated by GCeMS analysis. As previously discussed here the
geometries 2,6-cis (to compounds 3e6) and 2,4,6-cis (to
compounds 7e12) are expected based on the Prins-cyclization
reaction proposed mechanism [3,4].
The scalar constant coupling values obtained on 3e12 were not
sufficient to establish accurately the relative 2,4,6 cis geometries to
these new compounds. However, the 2D-NOESY spectrum, e.g. on
compound 10 (Fig. 6) presented significant signals of correlation
between HaeHb, HaeHc and HbeHc that determine unequivocally
the 2,4,6-cis geometry, confirming the mechanistic prediction.
Besides that, computational studies on 10 and 10a (10a is a C4-
epimer of 10, Fig. 6) at M06-2X/6-311þþG(d,p) as level of calcu-
lations, were able to determinate the theoretical distances between
Ha, Hb and Hc (see data in Table 2).
These theoretical results corroborate the 2D-NOESY spectrum. If
the structure 10a was a correct structure would not be expecting
correlation signals between HaeHb and HbeHc due to the large
distance between these atoms (see Table 2). We have shown in
Fig. 7 two different visions for each of the calculated structures 10
and 10a. So, 2D-NOESY and theoretical results corroborated the
correct relative geometry for this compound as 10.
The reduction of esters was carried out by reaction with sodium
borohydride in anhydrous ethanol under reflux where it was
successful resulting in yields of 90e100% [37]. The subsequent
chlorine atom removing could be performed one pot from reduction
of ester 21 producing the alcohol 22 in quantitative yield (step iii,
Scheme 2) by using lithium aluminum hydride on refluxing dried
THF for 12 h [38]. The alcohol 22 were efficiently oxidized by nitric
acid, furnishing the carboxylic acids 1a in 100% yield [39]. In our
previous article [5] this synthetic step was performed by Jones
reagent on 91% yield. This protocol presented here is cheaper and
avoids the utilization of chromium (VI) compounds which are
highly toxic for both acute and chronic exposures and can cause
cancer and care must be taken when handling chromium (VI)
reagents [40]. It should be noted that in previous article [9] we
prepare 1a in four steps from 19 in 33% yield and here 1a is
prepared in four steps from 19 in 72%.
2.1.2. Synthesis of new tetrahydropyranyl derivatives
The preparation of the new acids 3 and 4 (Scheme 3) was ob-
tained in accordance with the experimental procedures developed
to acid 1a in this article. Curiously, the Prins reaction between
alcohol 18 and b-naphtaldehyde to prepare 7 and a-naphtaldehyde
to prepare 8 was more efficient on chloroform as solvent than
dichloromethane (steps i/ii, Scheme 3). Moreover, when these
reactions were made in different reaction times we obtained
increases in yields (85% of 7 and 100% of 8). The subsequent
reduction of compounds 7 and 8 may be chemoselectively per-
formed depending on chosen reduction reagent. Only the ester
group in 7 and 8 was reduced using sodium borohydride preparing
compounds 9 and 10 in quantitative yields (steps iii/iv, Scheme 3).
Differently using lithium aluminum hydride both, dechlorination
reaction of C4 of 7 and 8 and transformations of esters moieties on
corresponding alcohols could be made in one pot reactions (steps
vii/viii) producing alcohols 5 and 6 respectively. Finally, oxidations
of 9 and 10 to 11 and 12 (steps v/vi) and oxidation of 5 and 6 to 3
and 4, respectively (steps ix/x) were quantitatively performed using
HNO3 (Scheme 3).
It should be noted that it was possible to observe one intra-
molecular hydrogen bond (IHB) between the alcoholic hydrogen
and oxygen in the tetrahydropyran ring in 10 (OeH/O ¼ 2.36 Å)
(Fig. 7). The presence of this IHB on 10 must have an important role
in the conformational stability as well as the interaction with the
biological receptor.
2.2. Biology
2.2.1. Effect of tetrahydropyranyl derivatives on acetic acid-induced
writhing
Intraperitoneal injection of acetic acid (1.2%) induced a total of
51 ꢀ8.1 writhes in a period of 30 min. The mice were pre-treated
orally with tetrahydropyranyl derivatives at a dose of 30 mg/kg,
control and vehicle (Table 3).
O
O
O
i
ii
O
O
OK
O
+
Cl
O
O
O
O
16
18
19
17
Scheme 1. (i) 1.5 Equiv. 16, 1 Equiv. 17, DMF, 80 ꢁC, 4 h, 90e95%. (ii) Dimethylacetal 18, HCO2H/H2O (8:2), r.t., 12 h, 80e85%.

4
S.L. Capim et al. / European Journal of Medicinal Chemistry 58 (2012) 1e11
Table 1
for each timeeeffect curve. The dose of compounds was 30 mg/kg
(p.o.). The results are presented as percentage increase over the
baseline or area under the curve (AUC); n ¼ 6 per group. Statistical
significance was calculated by the analysis of variance followed by
Bonferroni’s test. *P < 0.05 relative to the control group. Where no
error bars are shown, it is because they are smaller than the symbol.
Enzyme inhibitor, GPCR ligand scores and number of Lipinski’s rule violations
calculated by Molinspiration cheminformaticÒ program.
Compound
Enzyme inhibitor
GPCR ligand
LRVa
1a
3
4
5
6
7
8
9
ꢂ0.06
þ0.54
þ0.47
þ0.48
þ0.40
þ0.16
þ0.10
þ0.37
þ0.30
þ0.43
þ0.36
ꢂ0.55
þ0.48
þ0.51
þ0.38
þ0.42
þ0.21
þ0.24
þ0.31
þ0.35
þ0.40
þ0.44
0
0
0
0
2.2.3. Effect of tetrahydropyran derivatives in the rota-rod
performance and open field tests
0
1b
1c
0
The rota-rod performance (forced motor activity) and open-field
(spontaneous motor activity) tests were used to exclude the
possibility that the antinociceptive action of tetrahydropyran
derivatives could be related to nonspecific disturbances in the
locomotors activity of the animals. We observed that at dose that
has antinociceptive action (30 mg/kg, p.o.), tetrahydropyran
derivatives did not alter the motor performance of mice in both
tests (Fig. 9).
10
11
12
0
0
0
a
Number of Lipinski’s rule violations.
log P ¼ 5.029.
b
c
log P ¼ 5.005. A molecule contradicts Lipinski’s rule when two or more viola-
tions of this rule are calculated.
The acetic acid-induced writhing method is able to determine
antinociceptive effects of compounds and dose levels that might
seem to be inactive in other methods [41]. The results showed that
all the new tetrahydropyranyl derivatives had a significant reduc-
tion in the number of abdominal writhes compared to the control
group, showing an antinociceptive effect. The compounds 5, 10 and
12 were the most effective (55.7%, 87.5% and 54.4%, respectively)
(Table 3).
2.2.4. Toxicological evaluation in vivo of tetrahydropyran
derivatives
All tetrahydropyran derivatives described in this paper were
evaluated for their acute toxicity in mice. No symptom of intoxi-
cation was observed in animals (disorientation, hyperactivity,
piloerection and hyperventilation). Investigated compounds were
not toxic after oral administration (LD50 >2000 mg/kg).
According to previous results [9], the compound 1a showed
antinociceptive activity in a dose of 50 mg/kg (approximately 15%
inhibition in the number of abdominal writhes), from there we
decided to evaluate and compare this compound with the new
tetrahydropyranyl derivatives in a lower dosage (30 mg/kg). Table 3
shows that all new compounds showed greater antinociceptive
activity than compound 1a.
3. Conclusion
In this article we presented firstly a high improvement on the
analgesic tetrahydropyran 1a preparation (from 33% in previous
article to 72% presented here). After, we described the design and
total synthesis for 10 novel tetrahydropyranyl derivatives
(compounds 3e12), using the Prins-cyclization reactions as key-
step to construction on diastereoselective form the 2,4-cis and
2,4,6-cis tetrahydropyranyl rings. This non-toxic congener series of
compounds presented high analgesic activity observed in animal
models (mice). All new compounds showed greater antinociceptive
effect in the acetic acid-induced abdominal writhing test,
compared to compound 1a previously described by us. We can
detach the high activity of tetrahydropyranyl derivative 10 which
presented 87.5% inhibition (1a presented only 14% inhibition). The
tail-flick test demonstrated compounds 7 and 10 as the most
actives. The new compounds showed central antinociceptive
activity (except compound 12) without producing motor impair-
ment. Compound 7 could be prepared in 65% yield (2 steps from
aldehyde 19) and compound 10 could be prepared in 65% yield (3
steps from aldehyde 19). Finally, considering a significant increase
between the antinociceptive values of 1a and compounds 3e12 we
concluded that the strategy shown in Fig. 3 was very satisfactory.
We also can notice that 1a score values is negative (Table 1) and
differently all new compounds 3e12 showed positive values of
scores for both enzymatic inhibition and ligands GPCR. These
results are in according of obtained antinociceptive values. We
believe that these new class of compounds discovered here are
candidates for analgesics. Our complementary studies on related
new compounds are now in progress.
2.2.2. Effect of tetrahydropyran derivatives in the tail-flick test
The tail-flick test was used to assess the central activity of the
compounds, since this test is predominantly a spinal reflex, and is
considered to be selective for centrally acting analgesic substances,
whereas peripherally acting analgesics are known to be inactive
against thermal stimuli [42,43].
Fig. 8(AeD) shows that all the compounds presented a result
significantly greater than the control group, except compound 12,
in the tail-flick test throughout the experiment, confirming the
central antinociceptive effect of these compounds, however
compounds 4 and 7 (Fig. 8A and B), and 8, 10 and 11 (Fig. 8C and D)
produced greater effect than the compound 1a.
In Fig. 8A and C, graphs represent timeeeffect curve. In Fig. 8B
and D, graphs represent the area under the curve (AUC) calculated
Cl
OH
O
i
ii
O
O
O
O
O
O
19
O
20
21
iii
iv
4. Experimental procedures
HO
HO
O
O
O
4.1. Chemistry
1a
22
4.1.1. General methods
Scheme 2. Improved synthesis of 1a. (i) Aldehyde 19 (1 Equiv.), H2O, SnCl2 (1.5 Equiv.),
KI (3.0 Equiv.), allyl bromide, NH4Cl, r.t., 2 h, 80 %; (ii) 20 (1 Equiv.), propanal, AlCl3,
CH2Cl2, 0 ꢁC, 6 h, 85e90%; (iii) 21, LiAlH4, THF, 100 ꢁC, 12 h, 100%; and (iv)
22,concentrated nitric acid, r.t, 4 h, 100%.
All commercially available reagents and solvent were obtained
from commercial providers and used without further purification.
Reactions were monitored by TLC using Silica gel 60 UV254

S.L. Capim et al. / European Journal of Medicinal Chemistry 58 (2012) 1e11
5
AlCl3
O
AlCl2
O
O
+
O
OH
+ Cl
O
O
O
H
a
20
22
b
24
AlCl2
-
HO
AlCl2
O
HO
O
O
O
O
c
O
23
d
Cl
δ−
Cl
δ+
O
O
O
O
O
O
δ+
δ+
21
25
Fig. 4. Proposal mechanism to the 21 preparation based on the Li and Yang studies.
MachereyeNagel pre-coated silica gel plates; detection was by
means of a UV lamp and revelation to vanillin. Flash column
chromatography was performed on 300e400 mesh silica gel.
Organic layers were dried over anhydrous MgSO4 or Na2SO4 prior to
evaporation on a rotary evaporator. 1H NMR and 13C NMR spectra
were recorded using Varian Mercury Spectra AC 20 spectrometer
(400 MHz and 200 MHz for 1H, 101 MHz and 50 MHz for 13C) in
CDCl3. Chemical shifts were reported relative to internal tetrame-
16 (110.6 mmol, 13.95 g) was charged to the reactions mixture
portion wise while refluxing. The reflux was continued for 13 h and
mixture was allowed to room temperature. Water (300 mL) was
added, and the resulting mixture was extracted with EtOAc
(3 ꢃ100 mL). The organic phase was dried with sodium sulfate
anhydrous and concentrated under reduced pressure where 18 was
obtained a 80% yield; IR (KBr, cmꢂ1): 1130, 1195 (CeO), 1739 (CO2),
2974 (CeH sp3); 1H NMR (CDCl3, 200 MHz):
2.67 (m, 1H), 3.41 (s, 6H), 4.12 (d, 2H, J 5.22 Hz), 4.54 (m, 1H); 13C
d 1.19 (d, 6H, J 6.84 Hz),
thylsilane (d d
0.00 ppm) for 1H, and CDCl3 ( 77.0 ppm) for 13C. FTIR
spectra were recorded on a Shimadzu spectrophotometer model
IRPrestige-21 in KBr pellets. MS data were measured with a Shi-
madzu GCMS e QP2010 mass spectrometer. High-resolution mass
spectra were determined using a Shimadzu spectrophotometer LC-
MS-IT-TOF.
Cl
O
Cl
O
Cl
O
iii or iv
v or vi
HO
HO
R
R
O
R
O
4.1.2. Synthesis of 2,2-dimethoxyethyl isobutyrate (18) [31]
O
naphthyl
naphthyl
naphthyl
naphthyl
9= β−
naphthyl
naphthyl
7 = β−
8 = α−
11 = β−
12 = α−
The reaction was performed using
a solution of chlor-
10= α−
oacetaldehyde dimethyl acetal (17, 201 mmol, 24.92 g, 22.70 mL) in
DMF (300 mL) was added potassium isobutyrate (16, 110.6 mmol,
13.95 g) and the mixture was refluxed at 150 ꢁC for 2 h. Additional
vii or viii
i
or
ii
ix or x
HO
HO
O
R
O
O
R
OH
nucleophilic attack
O
O
O
by exo face
O
naphthyl
naphthyl
5 = β−
6 = α−
naphthyl
naphthyl
3 = β−
O
Cl
6 coplanar and
4 = α−
18
O
.
.
conjugated electrons
.. O
.
.
O
Cl
Scheme 3. Synthesis of new tetrahydropyranyl derivatives. (i) 18 (1 Equiv.),
b-naph-
In accordance with
H
..
taldehyde, AlCl3 (1.3 Equiv.), CHCl3, 0 ꢁC, 6 he85%/6dayse85%; (ii) 18 (1 Equiv.),
a-
Huckel'srule
all groups in
equatorial conformation
naphtaldehyde, AlCl3 (1.3 Equiv.), CHCl3, 0 ꢁC, 6 he85%/6days-100%; (iii) 7, NaBH4
(1 Equiv.), EtOH, 100 ꢁC, 3 h, 85e90 %; (iv) 8, NaBH4 (1 Equiv.), EtOH, 100 ꢁC, 3 h, 85e90
%; (v) 9, concentrated nitric acid, r.t, 4 h, 100%; (vi) 10, concentrated nitric acid, r.t, 4 h,
100%; (vii) 7, LiAlH4, THF, 100 ꢁC, 12 h, 100%; (viii) 8, LiAlH4, THF, 100 ꢁC, 12 h, 100%; (ix)
5, concentrated nitric acid, r.t, 4 h, 100%; and (x) 6, concentrated nitric acid, r.t, 4 h,
100%.
cation
homoaromatic
26
21
Fig. 5. The Alder’s model to the equatorial diastereoselectivity on C4 of the Prins
cyclization reactions.

6
S.L. Capim et al. / European Journal of Medicinal Chemistry 58 (2012) 1e11
into this flask at 0 ꢁC. The mixture reaction is stirring at this
temperature for 6 h. After this time, 5 mL of a saturated sodium
bicarbonate solution NaHCO3 is added. The organic phase into
reaction mixture was separated and washed with brine, dried with
Na2SO4 and the evaporated under reduced pressure. This crude
product is then submitted to flash column chromatography,
yielding a colorless oil in 85% yield. We have also observed that the
addition of CHCl3 in place of CH2Cl2 occurs an improvement in the
yield of the reaction between 85 and 100%.
OH
OH
O
O
Cl
Hb
Hb
Hc
Ha
Hc
Ha
Cl
NOESY
10
10a
Fig. 6. Compounds 10 and 10a representation (see data in Table 2).
4.1.5.1. (4-Chloro-6-(naphthalen-2-yl)-tetrahydro-2H-pyran-2-yl)
methyl isobutyrate (7). This product was obtained using (1.0 mmol,
0.156 g) of b-naphthaldehyde, resulting in 85% yield in both CH2Cl2
NMR (CDCl3, 50 MHz): d 18.7, 34.1, 53.5, 53.7, 62.6, 101.4, 171.8; GC:
RT ¼ 6.94 min (100%); Mass calculated: 176.1, C8H16O4.
or CHCl3 solvents. The product was purified by silica gel column
chromatography using EtOAc/hexane (1:10, v/v) as eluent. IR (KBr,
cmꢂ1): 821 and 748 (CeH aromatic), 1249 and 1157 (CeO ester),
1627 and 1462 (C]C aromatic), 1735 (C]O ester), 2970 (CeH sp3),
4.1.3. Synthesis of 2-oxoethyl isobutyrate (19) [32]
A solution of 2,2-dimethoxyethyl isobutyrate (18, 12.4 mmol,
2.19 g) in formic acid aqueous solution (HCO2H/H2O ¼ 8:2 v/v, 30
mL) was stirred at room temperature for 12 h. After the end of
reaction (verified by TLC), the mixture where extracted (3 ꢃ 50 mL
of CH2Cl2) and the organic phase was washed with a saturated
solution of NaHCO3. The organic phase was dried with sodium
sulfate anhydrous and concentrated under reduced pressure
producing 80% yield; IR (KBr, cmꢂ1): 1654, 1724 (CO2), 2704 (-CHO),
3055 (¼CeH aromatic) cmꢂ1; 1H NMR (CDCl3, 200 MHz):
d 1.21 (dd,
6H, J ¼ 4 Hz),1.86 (m, 2H), 2.5 (m,1H), 2.62 (m,1H), 3.85 (m,1H), 4.3
(m, 3H), 4.57 (d, J ¼ 12 Hz), 7.48 (m, 3H), 7.83 (m, 4H); 13C NMR
(CDCl3 50 MHz): 18.96, 33.88, 38.54, 43.96, 55.05, 65.99, 74.83,
78.62, 123.85, 124.50, 125.93, 126.12, 127.61, 127.97, 128.17, 132.98,
133.19, 138.25, 176.86; GC: RT ¼ 27.17 min (100%); Mass calculated:
2931(CeH sp3); 1H NMR (CDCl3, 400 MHz):
1.23 (d, 3H, J ¼ 8 Hz), 2.63 (m, 1H), 4.21 (s, 1H), 4.65 (d, 1H), 9.61 (s,
1H); 13C NMR (CDCl3, 50 MHz):
18.87, 18.70, 33.64, 68.44, 176.52,
d
1.19 (d, 3H, J ¼ 4 Hz),
346.1,
C
C
20H23ClO3;
HRMS
e
mass
calculated
for
20H23ClO3[(M þ Na)þ] 369,0979; Found 369,0979.
d
195.85; GC: RT ¼ 13.73 min (100%); Mass calculated: 130.06,
4.1.5.2. (4-Chloro-6-(naphthalen-1-yl)-tetrahydro-2H-pyran-2-yl)
methyl isobutyrate (8). This product was obtained using (1.0 mmol,
C6H10O3.
0.156 g) of a-naphthaldehyde, resulting in 85% yield when CH2Cl2
4.1.4. Synthesis of 2-hydroxypent-4-enyl isobutyrate (20) [33]
The 2-oxoethyl isobutyrate aldehyde (19, 25 mmol, 3.25 g) was
added to water (120 mL) containing potassium iodide (75 mmol,
12.45 g), stannous chloride dehydrate (37.55 mmol, 8.45 g) and
allyl bromide (3 mmol). The orange solution turns white by addi-
tion of saturated ammonium chloride (80 mL). The stirring was
continued for 2 h at room temperature. After the end of reaction,
the reaction mixture was extracted with CH2Cl2 (3 ꢃ 50 ml) gave an
organic phase, washed with water, dried with sodium sulfate
anhydrous, concentrated under reduced pressure and purified by
flash chromatography on silica gel (AcOEt:hexane 3:7 as eluent.)
The products were concentrated under reduced pressure yielding
a pale oil in 75% yield; IR (KBr, cmꢂ1): 1157,1199 (CeO),1392 (CeOe
H), 1732 (C]O), 2939, 2978 (CeH sp3), 3456 (OeH) cmꢂ1; 1H NMR
was used and 100% yield when CHCl3 was used. The product was
purified by silica gel column chromatography using EtOAc/hexane
(1:10, v/v) as eluent. IR (KBr, cmꢂ1): 779 and 732 (CeH aromatic),
1246 and 1157 (CeO ester), 1597 and 1465 (C]C aromatic), 1735
(C]O ester), 2873 (CeH sp3), 3051 (]CeH aromatic) cmꢂ1
;
1H
NMR (CDCl3, 200 MHz):
d
1.19 (dd, 6H, J ¼ 8 Hz), 1.83 (q, 1H,
J ¼ 12 Hz), 2.07 (q,1H, J ¼ 12 Hz), 2.31 (m,1H), 2.60 (m, 2H), 3.95 (m,
1H), 4.27 (m, 1H), 5.09 (d, 1H, J ¼ 12 Hz), 7.7 (m, 7H); 13C NMR
(CDCl3 50 MHz): 18.97, 33.89, 38.60, 42.72, 55.20, 66.08, 75.16,
75.81, 123.02, 123.29, 125.42, 125.52, 126.09, 128.49, 128.90, 130.31,
133.77, 136.06, 176.85; GC: RT ¼ 24.42 min (100%); Mass calculated:
346.1,
C
C
20H23ClO3;
HRMS
e
mass
calculated
for
20H23ClO3[(M þ Na)þ] 369,0979; Found 369,0979.
(CDCl3, 400 MHz):
J ¼ 8 Hz), 3.68 (m, 1H), 3.96 (m, 1H), 4.12 (m, 1H), 4.93e5.17 (m, 2H),
5.78 (m, 1H); 13C NMR (CDCl3, 101 MHz):
18.74,18.94, 33.92, 38.01,
d
1.17 (d, 6H, J ¼ 8 Hz), 2.31(m, 2H), 2.6 (sp, 1H,
4.1.5.3. (4-Chloro-6-ethyl-tetrahydro-2H-pyran-2-yl)methyl
iso-
butyrate (21). This product was obtained using (1.0 mmol, 0.156 g)
of propionaldehyde, resulting in 88% yield when used in CH2Cl2 and
90% yield when used in CHCl3. The product was purified by silica gel
column chromatography using EtOAc/hexane (1:10, v/v) as eluent.
IR (KBr, cmꢂ1): 757 (C-Cl), 1150 and 1193 (CeO ester), 1737 (C]O
ester), 2972 and 2878 (CeH sp3), cmꢂ1; 1H NMR (CDCl3, 200 MHz):
d
67.69, 69.17, 118.47, 133.46, 177.33; GC: RT ¼ 7.92 min (100%);
Found: C9H16O3 172.1.
4.1.5. Procedure general for Prins-cyclization: a typical procedure
for synthesis of derivates tetrahydropyrans
d
0.93 (t, 3H, J ¼ 4 Hz), 1.18 (d, 6H, J ¼ 7 Hz), 1.55 (m, 5H), 2.10 (m,
1H), 2.60 (sp, 1H, J ¼ 7.1 Hz), 3.20 (m, 1H), 3.60 (m, 1H), 3.90e4.10
(m, 3H); 13C NMR (CDCl3 50 MHz):
9.76, 18.93, 28.61, 33.87,
A typical procedure for the Prins cyclization reaction [5],
aluminum chloride (AlCl3,1.5 mmol, 0.2 g) was place in a dried flask
under magnetic stirrer followed by addition of 3 mL dichloro-
methane (dried under calcium hydride). After, a solution of
homoallylic alcohol (20, 1.0 mmol, 0.172 g), the corresponding
aldehyde (1.0 mmol), in 3 mL of dichloromethane was slowly place
d
38.76, 41.87, 55.32, 66.08, 74.32, 78.16, 176,83; GC: RT ¼ 10.25 min
(100%); Mass calculated: 248.1, C12H21ClO3.
4.1.6. General procedure for the reduction of esters in alcohols using
sodium borohydride [37]
Table 2
In a dried Argon atmosphere flask under magnetic stirrer was
placed NaBH4 (6 mmol) dissolved in 10 mL of anhydrous ethanol
following by addition of the product corresponding of Prins-
cyclization dissolved in 10 mL of anhydrous ethanol to this flask
at 0 ꢁC. The reaction mixture was refluxed for 3 h at temperature
100 ꢁC. After the end of reaction, a saturated aqueous ammonium
chloride (10 mL) was placed at 0 ꢁC and the reaction mixture was
Calculated distances (Å) between Ha/Hb/Hc in 10 and 10a at M06-2X/6-311þþG(d,p)
as level of calculations.
Compound 10
Compound 10a
HaeHb
HaeHc
HbeHc
2.56609
2.35396
2.64134
HaeHb
HaeHc
HbeHc
3.78258
2.32529
3.84439

S.L. Capim et al. / European Journal of Medicinal Chemistry 58 (2012) 1e11
7
Fig. 7. Two different visions for each of the calculated structures 10 and 10a at M06-2X/6-311þþG(d,p) as level of calculation. See distances data between HaeHbeHc in Table 2.
extracted with CH2Cl2 (3 ꢃ 20 ml) gave an organic phase, dried with
sodium sulfate anhydrous, concentrated under reduced pressure
providing the tetrahydropirans derivatives in high yields.
product corresponding of Prins cyclization dissolved in 5 mL dried
THF. The mixture was refluxed for 12 h at temperature 100 ꢁC. After
the end of reaction, a saturated aqueous ammonium chloride
(10 mL) and excess of THF was removed in vacuo. The crude reac-
tion mixture was extracted with CH2Cl2 (3 ꢃ 20 ml) gave an organic
phase, dried with sodium sulfate anhydrous, concentrated under
reduced pressure providing the tetrahydropirans derivatives in
high yields (90e100%).
4.1.6.1. (4-Chloro-6-(naphthalen-2-yl)-tetrahydro-2H-pyran-2-yl)
methanol (9). Reaction of 1.0 mmol (0.346 g) of 7 produces 100%
yield of 9 as a yellow oil IR (KBr, cmꢂ1): 817 and 748 (CeH
aromatic), 1053 (CeO), 1600 and 1442 (C]C aromatic), 2862 (Ce
H sp3), 3383 (OeH) cmꢂ1; RMN 1H (400 MHz; CDCl3)
d: 1.77 (m,
1H), 1.95 (q, 1H J ¼ 12), 2.10 (s, 1H), 2.16 (dd, 1H), 2.45 (dt, 1H), 3.69
4.1.7.1. (6-(Naphthalen-2-yl)-tetrahydro-2H-pyran-2-yl) methanol
(5). Reaction of 1.0 mmol (0.346 g) of 7 produced 100% yield of 5 as
a yellow liquid. IR (KBr, cmꢂ1): 867 and 879 (CeH aromatic), 1041
(m, 2H), 4.21 (m, 1H), 4.56 (dd, 1H), 4.83 (s. 1H), 7.47 (m, 3H), 7.83
(m, 4H), RMN 13C (101 MHz; CDCl3)
d: 38,06; 42,80; 55,45; 65,62;
75,80; 78,01; 123,71; 124,45; 125,85; 125,71; 126,29; 128,63;
(CeO), 1458 (C]C aromatic), 2862 (CeH sp3), 3417 (OeH) cmꢂ1
;
128,97; 130,45; 133,85; 136,29; GC: RT ¼ 25.30 min (100%); Mass
RMN 1H (400 MHz; CDCl3)
d: 1.58 (m, 6H), 3.58 (m, 1H), 4.73 (t, 1H,
calculated
C
16H17ClO2 346.1; HRMS
e
Mass calculated for
J ¼ 8 Hz); 7.55 (m, 7H); RMN 13C (101 MHz; CDCl3)
d: 23.50, 26.86,
C
16H17ClO2[(M þ Na)] 299.0612; Found 299.0612.
33.63, 66.34, 78.74, 79.86, 124.34, 125.11, 126.12, 127.60, 127.66,
127.83, 127.92, 128.26, 132.89, 133.33; RT ¼ 23.20 min (100%); Mass
4.1.6.2. (4-Chloro-6-(naphthalen-1-yl)-tetrahydro-2H-pyran-2-yl)
methanol (10). Reaction of 1.0 mmol (0.346 g) of 8 produces 90%
yield of 10 as a yellow oil. IR (KBr, cmꢂ1): 779 and 860 (CeH
aromatic), 1068 (CeO), 1396 and 1597 (C]C aromatic), 2862 (Ce
Table 3
Antinociceptive activity of tetrahydropyranyl derivatives on acetic acid-induced
abdominal writhes in mice (30 mg/kg, p.o.).
H sp3), 3390 (OeH) cmꢂ1; RMN 1H (400 MHz; CDCl3)
d: 1.24 (m,
Compound
Number of writhes ꢀ SD
Inhibition (%)
1H),1.78 (q, 1H, J ¼ 12 Hz), 2.10 (dd, 1H, J ¼ 12 Hz), 2.19 (m, 2H), 2.57
Control
Vehicle
1a
3
4
5
6
7
8
51 ꢀ 8.1
e
(dt,1H), 3.68 (m,1H), 3.77 (m, 1H), 4.28 (m, 1H), 5.10 (t,1H), 7.76 (m,
7H); RMN 13C (101 MHz; CDCl3)
d: 38.01, 42.74, 55.32, 65.55, 75.60,
47 ꢀ 7.1
7.8
43.8 ꢀ 6.2
29 ꢀ 3.5*
26 ꢀ 3.4*
22.6 ꢀ 3.6*
31 ꢀ 6.0*
28.3 ꢀ 2.5*
31.4 ꢀ 5.2*
27.3 ꢀ 4.1*
6.4 ꢀ 1.3*
36.7 ꢀ 4.5*
23.3 ꢀ 4.8*
14.1
43.1
49
77.93, 122.88, 123.24, 125.34, 125.61, 126.25, 128.57, 128.93, 130.32,
133.72, 136.09; GC: RT ¼ 22.50 min (100%); Mass calculated:
C
C
16H17ClO2
346.1;
HRMS
e
mass
calculated
for
55.7
39.2
44.4
38.4
46.6
87.5
28.1
54.4
16H17ClO2[(M þ Na)] 299.0616; Found 299.0616.
4.1.7. General procedure for the reduction of esters in alcohols using
lithium aluminum hydride [38]
In dried Argon atmosphere flask under magnetic stirrer was
place lithium aluminum hydride (LiAlH4, 2.5 mmol) and 5 mL THF
(dried under sodium/benzophenone), was slowly added at 0 ꢁC the
9
10
11
12
SD e standard deviation; *P < 0,05 against control group.

8
S.L. Capim et al. / European Journal of Medicinal Chemistry 58 (2012) 1e11
Fig. 8. Effects of tetrahydropyran derivatives in the tail-flick. In (A), ( ) Control, ( ) Vehicle, ( ) Compound 1a, ( )Compound 3, ( )Compound 4, ( ) Compound 5, (
Compound 6, ( ) Compound 7. In (C), ( ) Control, ( ) Vehicle, ( ) Compound 1a, ( ) Compound 8, ( ) Compound 9, ( ) Compound 10, ( ) Compound 11, and (
Compound 12.
)
)
calculated C16H18O2 242.1; HRMS
e
mass calculated for
maintained for 3e4 h at 30 ꢁC until discoloration, then it was
C
16H17ClO2[(M þ Na)] 265.0610; Found 265.0610.
poured into 50 ml of cold water, extracted with chloroform
(3 ꢃ 50 mL), the extract was dried with Na2SO4. The chloroform was
distilled off and the carboxylic acid obtained on 100% yield.
4.1.7.2. (6-(Naphthalen-1-yl)-tetrahydro-2H-pyran-2-yl) methanol
(6). Reaction of 1.0 mmol (0.346 g) of 8 produces 100% yield of 6 as
a pale oil IR (KBr, cmꢂ1): 867 and 879 (CeH aromatic), 1041 (CeO),
1458 (C]C aromatic), 2862 (CeH sp3), 3417 (OeH) cmꢂ1; RMN 1H
(400 MHz; CDCl3)
1H), 2.69 (m, 1H), 4.19 (m, 2H), 4.68 (t, 1H, J ¼ 12 Hz), 8.03 (m, 7H);
RMN 13C (400 MHz; CDCl3)
: 23.65, 27.00, 32.20, 66.34, 76.67,
79.16, 122.88, 123.58, 125.79, 125.93, 126.25, 128.01, 128.46, 128.59,
128.79, 133.72; RT ¼ 23.20 min (100%); Mass calculated C16H18O2
242.1; HRMS e mass calculated for C16H17ClO2[(M þ Na)] 265.1029;
Found 265.1029.
4.1.8.1. 6-Ethyl-tetrahydro-2H-pyran-2-carboxylic
acid
(1a).
Reaction of 1.0 mmol (0.144 g) of 21 produces 100% yield of 1a as
a yellow solid. IR (KBr, cmꢂ1): 1280(CeO), 1730 (C]O), 2877,
2931 and 2966 (CeH sp3), 3140 (OeH) cmꢂ1; 1H NMR (CDCl3, 40):
d: 0.91 (m,1H),1.20 (m, 2H),1.99 (m, 2H), 2.51 (m,
d
d
0.97 (t, 3H, J ¼ 8 Hz), 1.68 (m, 5H), 2.19 (m, 1H), 2.56 (m, 1H),
3.36 (m, 1H), 4.05 (t, 2H, J ¼ 12 Hz), 8.81 (s, 1H); 0 MHz 13C NMR
(CDCl3 101 MHz):
d 9.67, 28.32, 38.56, 41.07, 54.21, 74.67, 78.62,
173.53; GC: RT ¼ 10.20 min (100%); Mass calculated: 158.10,
C8H14O3.
4.1.7.3. (6-Ethyl-tetrahydro-2H-pyran-2-yl) methanol (22) [5].
Reaction of 1.0 mmol (0.144 g) of 21 produce 100% yield of 22 as
a pale oil IR (KBr, cmꢂ1): 1178, 1227 (CeO),1375 (CeOH), 2877, 2931
and 2962 (CeH sp3), 3383 (OeH) cmꢂ1; 1H NMR (CDCl3, 200 MHz):
4.1.8.2. 6-(naphthalen-2-yl)-tetrahydro-2H-pyran-2-carboxylic acid
(3). reaction of 1.0 mmol (0.242 g) of 5 producing 100% yield of 3
after purifications by silica gel flash chromatography (EtOAc/
hexane ,1:10 as eluent).as a dark colored solid. IR (KBr, cmꢂ1): 763,
825 (CeH aromatic), 1280, 1338 (CeO), 1523 (C]C aromatic), 1720
(C]O), 2927 (CeH sp3), 3429 (OeH) cmꢂ1; RMN 1H (400 MHz;
d
0.94 (t, 3H, J ¼ 8 Hz), 1.15e1.25 (m, 1H), 1.48e1.64 (m, 4H), 1.95 (s,
1H), 2.04 (m,1H), 2.15 (m,1H), 3.28 (m,1H), 3.44e3.64 (m, 3H), 4.04
(m, 1H); 13C NMR (CDCl3 50 MHz):
9.75, 28.66, 38.21, 41.92, 55.50,
d
CDCl3)
d
: 1.62 (m, 4H), 3.49(m, 2H), 4.17 (m, 1H), 4.73 (m, 1H), 8.08
65.60, 76.88, 78.04; GC: RT ¼ 8.81 min (100%); Mass calculated:
(m, 7H), 10.20 (s, 1H); RMN 13C (101 MHz; CDCl3)
d
: 19.15, 24.29,
144.1, C8H16O2.
33.21, 76.25, 76.42, 125.30, 126.42, 126.76, 127.78, 128.29, 128.47,
128.67, 129.52, 132.36, 135.91, 172.37; HRMS - Mass calculated for
4.1.8. General procedure for the synthesis oxidation of alcohols [39]
The appropriate alcohol (1.0 mmol) was added in a stirring flask
following by slow addition of HNO3 at 80% of concentration
(5.0 mmol, 0,315 g). The reaction occurred with evolution of heat
and nitrogen oxides that caused the brown color of the reaction
mixture. After the end of heat evolution the reaction mixture was
C16H16O3: 256.1099; Found 256.7039.
4.1.8.3. 6-(Naphthalen-1-yl)-tetrahydro-2H-pyran-2-carboxylic acid
(4). Reaction of 1.0 mmol (0.242 g) of 6 producing 100% yield of 4
after purifications by silica gel flash chromatography (EtOAc/
hexane, 1:10 as eluent).as a dark colored solid. IR (KBr, cmꢂ1): 763,

S.L. Capim et al. / European Journal of Medicinal Chemistry 58 (2012) 1e11
9
Fig. 9. Effects of tetrahydropyran derivatives in the Rota-rod Performance and open-field tests. In (A) and (C), graphs represent number of fallings of mice. In (B) and (D), graphs
represent the number of walked squares by mice. The dose of compounds was 30 mg/kg (p.o.); n ¼ 6 per group. Statistical significance was calculated by the analysis of variance
followed by Bonferroni’s test. *P < 0.05 relative to the control group.
825 (CeH aromatic), 1280, 1338 (CeO), 1523 (C]C aromatic), 1720
(C]O), 2927 (CeH sp3), 3429 (OeH) cmꢂ1; RMN 1H (400 MHz;
125.68, 126.40, 128.75, 129.02, 130.00, 133.66, 135.28, 173.66; HRMS
e mass calculated for C16H15ClO3: 290.7415; Found 289.0301.
CDCl3)
(m, 1H), 7.83 (m, 7H), 10.39 (s, 1H); RMN 13C (101 MHz; CDCl3)
RMN 13C (101 MHz; CDCl3) : 29,70; 38,44; 42,48; 75,23; 75,87;
d: 1.97 (m, 2H), 2.45(m, 2H), 3.05 (m, 2H), 3.98 (m, 1H), 4.89
d:
4.2. Computational details
d
122,62; 123,59; 125,55; 125,68; 126,40; 128,75; 129,02; 130,00;
133,66; 135,28; 173,66; HRMS e mass calculated for C16H16O3:
256.1099; Found 255.0735.
Initially, Relaxed Potential Energy Surface Scan (RPESS) was
performed using GAUSSIAN 09WÒ package [44], at semi-empirical
AM1 level, considering important rotational degrees of freedoms
for MBHA’s (sigma bonds). For this purpose, dihedral angles were
frozen in steps of 10ꢁ and the remainder portion of molecule was
optimized. From potential energy curves for each molecule, the
lowest energy conformation was selected and submitted to a full
optimization at M06-2X/6-311þþg(d,p) as level of calculations. All
real frequencies have confirmed the presence of the local
minimum. No imaginary frequency was observed. The structures
were visualized by GaussView 5Ò program.
4.1.8.4. 4-Chloro-6-(naphthalen-2-yl)-tetrahydro-2H-pyran-2-
carboxylic acid (11). Reaction of 1.0 mmol (0.276 g) of 9 producing
100% yield of 11 after purifications by silica gel flash chromatog-
raphy (EtOAc/hexane, 1:10 as eluent).as a dark colored solid. IR
(KBr, cmꢂ1): 794, 837 (CeH aromatic), 1257, 1338 (CeO), 1523 (C]C
aromatic), 1724 (C]O), 2924 (CeH sp3), 3429 (OeH) cmꢂ1; RMN 1H
(400 MHz; CDCl3)
1H), 5.20 (m, 1H), 8.07 (m, 7H), 10.12 (s, 1H); RMN 13C (101 MHz;
CDCl3) : 38.19, 43.33, 54.14, 74.91, 75.14, 125.31, 126.79, 127.80,
d: 2.00(m, 3H), 2.67(m, 1H), 4.12 (m, 1H), 4.36 (m,
d
4.3. Pharmacology
128.33, 129.54, 132.20, 132.37, 133.15, 135.95, 137.08, 172.34; HRMS
e mass calculated for C16H15ClO3: 290.7415; Found 293.1571.
4.3.1. Animals
The experiments were carried out on male Albino-Swiss mice
(body weight 20e24 g). The animals were housed in wire mesh
cages in a room at 20 ꢀ 2 ꢁC and exposed to a 12 h light:12 h dark
cycle. The animals had free access to standard pellet diet, tap water
was given ad libitum. The protocol for this study was approved by
the ethics committee for Animal Research of the Federal Rural
University of Rio de Janeiro (COMEP e UFRRJ) under number 002/
2009.
4.1.8.5. 4-Chloro-6-(naphthalen-1-yl)-tetrahydro-2H-pyran-2-
carboxylic acid (12). Reaction of 1.0 mmol (0.276 g) of 10 producing
100% yield of 12 after purifications by silica gel flash chromatog-
raphy (EtOAc/hexane,1:10 as eluent) as a dark colored solid. IR (KBr,
cmꢂ1): 794, 837 (CeH aromatic), 1257, 1338 (CeO), 1523 (C]C
aromatic), 1724 (C]C]O), 2924 (CeH sp3), 3429 (OeH) cmꢂ1
;
RMN 1H (400 MHz; CDCl3)
2H), 4.65 (m, 1H), 8.12 (m, 7H), 10.14 (s, 1H); RMN 13C (101 MHz;
CDCl3) : 21.72, 29.70, 38.44, 75.23, 75.87, 122.62, 123.59, 125.55,
d: 1.94 (m, 2H), 2.53(m, 2H), 4.13 (m,
Control and experimental groups consisted of 6 animals each.
The investigated compounds were administered orally (p.o.) as the
d

10
S.L. Capim et al. / European Journal of Medicinal Chemistry 58 (2012) 1e11
suspension in 5% ethyl acetate (vehicle) in constant volume of
5 mL/kg.
were counted. The spontaneous activity was quantified as either
number of squares walked within 5 min after compound
administration.
4.3.2. Statistical analysis
All experimental groups were composed of 6 animals. The
results are presented as the mean ꢀ SD in the acetic acid-induced
writhing, rota-rod and open field tests, and percentage increase
over the baseline or area under the curve (AUC) in the tail-flick test.
Statistical significance between groups was performed by the
application of one way analyses of variance (ANOVA) followed by
Bonferroni’s test. P < 0.05 was considered as statistically significant.
The estimated LD50 was obtained by fitting the data points rep-
resenting the percentage of deaths with increasing doses of the
compounds up to 2000 mg/kg calculated by nonlinear regression
method using the Graph Pad Prism software version 3.0 (San Diego,
CA, USA).
4.3.5. In vivo toxicological evaluation of tetrahydropyran
derivatives
Acute toxicity test was performed according to the World Health
Organization (WHO) guideline [49] and the Organization of
Economic Co-operation and Development (OECD) guideline for
testing of chemicals [50]. The investigated compounds were
administered orally in increasing doses up to 2000 mg/kg. The
animal behavior was observed from 5 h after a single administra-
tion of the compounds and subsequently monitored daily until the
14th day. Acute toxicity was expressed by the required dose in g/kg
body weight to cause death in 50% of animals tested (LD 50).
Acknowledgments
4.3.3. Antinociceptive evaluations
4.3.3.1. Acetic acid-induced abdominal writhing. Mice were used as
described previously [45]. In brief, the total number of writhes after
the i.p. administration of 1.2% (v/v) acetic acid was recorded over
a period of 30 min, starting immediately after acetic acid injection.
The pattern of abdominal writhes is the appearance of strong
abdominal contractions, stretching the body of the animal, fol-
lowed by elongation of hind limbs and abdomen contact with the
floor of the counting chamber.
CNPq, CAPES, FAPESQ (PB) and FAPERJ (RJ) by financial support.
Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.ejmech.2012.09.046.
References
4.3.3.2. Tail-flick test. The test was performed as previously
described [46]. The mice were kept in an acrylic tube and then
placed on equipment to perform tail-flick test. A light beam is
focused to approximately 4 cm from the tip of the tail and the tail
withdrawal latency is automatically registered. The light intensity
was adjusted for baseline values between 4 and 6 s;this intensity
has not changed and the animals that had baseline values outside
these limits were excluded from the experiment. Measures of
latency time were made at intervals of 20 min between each one.
The first two measures were made before drug administration. The
average of these measures is called “baseline”. After drug admin-
istration six measures of the latency time was performed. Anti-
nociception was quantified as either the (IBL) percentage increase
over the baseline at each measurement time, or the area under the
curve (AUC) of responses from 20 to 120 min after drug adminis-
tration, calculated according to the following formula based on the
[1] L. Liu, P.E. Floreancig, Angew. Chem. Int. Ed. 49 (2010) 3069e3072.
[2] I. Larrosa, P. Rome, F. Urpí, Tetrahedron 64 (2008) 2683e2723.
[3] M.L.A.A. Vasconcellos, L.S.M. Miranda, Quím. Nova 29 (2006) 834e839.
[4] C. Olier, M. Kaafarani, S. Gastaldi, M.P. Bertrand, Tetrahedron 66 (2010)
413e445.
[5] L.S.M. Miranda, B.G. Marinho, S.G. Leitão, M.E. Matheus, P.D. Fernandes,
M.L.A.A. Vasconcellos, Bioorg. Med. Chem. Lett. 14 (2004) 1573e1575.
[6] L.S.M. Miranda, B.A. Meireles, J.S. Costa, V.L.P. Pereira, M.L.A.A. Vasconcellos,
Synlett (2005) 869e871.
[7] Santos T.C., Delle Monache Leitão, S.G.F. 22nd IUPAC international symposium
on the chemistry of natural products; Setembro São Carlos, Brazil, 2000.
[8] L.S.M. Miranda, B.G. Marinho, J.S. Costa, S.G. Leitão, T.C. Santos, F.D. Monache,
P.D. Fernandes, M.L.A.A. Vasconcellos, V.L.P. Pereira, Bioorg. Chem. 38 (2010)
181e185.
[9] B.G. Marinho, L.S.M. Miranda, N.M. Gomes, M.E. Matheus, S.G. Leitão,
M.L.A.A. Vasconcellos, P.D. Fernandes, Eur. J. Pharmacol. 550 (2006) 47e53.
[10] B.G. Marinho, L.S.M. Miranda, B.G. Marinho, M.L.A.A. Vasconcellos,
M.E. Matheus, V.L.P. Pereira, P.D. Fernandes, Behav. Pharmacol. 22 (2011)
564e572.
[11] L.E. Rueter, K.L. Kohlhaas, P. Curzon, C.S. Surowy, M.D. Meyer, Pain 103 (2003)
269e276.
[12] A.L. Coelho, M.L.A.A. Vasconcellos, A.B.C. Simas, J.A. Rabi, P.R.R. Costa,
Synthesis (1992) 914e916.
[13] L.M. Cabral, P.R.R. Costa, M.L.A.A. Vasconcellos, E.J. Barreiro, R.N. Castro, Synth.
Commun. 26 (1996) 3671e3676.
[14] H.C.A. Filho, U.F.L. Filho, S. Pinheiro, M.L.A.A. Vasconcellos, P.R.R. Costa,
Tetrahedron: Asymmetry 5 (1994) 1219e1220.
[15] C.G.L. Junior, P.A.C. de Assis, F.P.L. Silva, S.C.O. Sousa, N.G. de Andrade,
T.P. Barbosa, P.L.N. Nerís, L.V.G. Segundo, I.C. Anjos, G.A.U. Carvalho,
G.B. Rocha, M.R. Oliveira, M.L.A.A. Vasconcellos, Bioorg. Chem. 38 (2010)
279e284.
[16] T.C. Barbosa, C.G.L. Junior, F.P.L. Silva, H.M. Lopes, L.R.F. Figueiredo,
S.C.O. Souza, G.N. Batista, T.G. Silva, T.M. Silva, M.R. Oliveira,
M.L.A.A. Vasconcellos, Eur. J. Med. Chem. 44 (2009) 1726e1730.
[17] M.L.A.A. Vasconcellos, D. Desmaële, P.R.R. Costa, J. d’Angelo, Tetrahedron Lett.
33 (1992) 4921e4922.
[18] E.B.A. Filho, E. Ventura, S.A. do Monte, B.G. Oliveira, C.G.L. Junior, G.B. Rocha,
M.L.A.A. Vasconcellos, Chem. Phys. Lett. 449 (2007) 336e340.
[19] M.B. Sevigny, K. Graham, E. Ponce, M.C. Louie, K. Mitchell, Pharmacol. Res. 65
(2012) 445e450.
trapezoid
þ . þ (120 min)/2].
rule:
[AUC ¼ 20 ꢃ IBL
[(20 min) þ (40
min) -
4.3.4. Locomotor activity
4.3.4.1. Rota-rod performance test. The rota-rod performance test is
an established method for evaluating motor impairment and ataxia
[47]. The day before the test the animals were trained twice to
maintain the equilibrium for 5 min on a roller apparatus (‘Rotarod
for mice’, U. Basile, Italy). The speed selector was set to 10 rev/min.
Twenty-four hours later, mice were treated orally with tetrahy-
dropyran derivatives (30 mg/kg, p.o.) and vehicle; and 60 min after
administration were placed on the roller for 5 min. Neurological
deficit was evaluated by the inability of the animal to remain on the
roller for the test period and reported as number of falling of
animals.
[20] A.M.A. Abdel-Aziz, A.S. El-Aza, H.I. El-Subbagh, A.M. Al-Obaid, A.M. Alanazi,
M.A. Al-Omar, Bioorg. Med. Chem. Lett. 22 (2012) 2008e2014.
[21] S. Chang, L. Zhang, S. Xu, J. Luo, X. Lu, Z. Zhang, T. Xu, Y. Liu, Z. Tu, Y. Xu, X. Ren,
M. Geng, J. Ding, D. Pei, K. Ding, J. Med. Chem. 55 (2012) 2711e2723.
[22] D. Forge, D. Cappoen, J. Laurent, D. Stanicki, A. Mayence, T.L. Huang,
L. Verschaeve, K. Huygen, J.J.V. Eynde, Eur. J. Med. Chem. 49 (2012) 95e101.
[23] http://www.molinspiration.com/cgi-bin/properties, [accessed 11.05.12].
[24] C.A. Lipinski, F. Lombardo, B.W. Dominy, P.J. Feeney, Adv. Drug Deliv. Rev. 23
(1997) 3e25.
4.3.4.2. Open-field test. The procedure was similar to the method
described by [48]. Mice received tetrahydropyran derivatives
(30 mg/kg, p.o.) and vehicle by oral administration and were placed
individually in an observation chamber (60 min after oral admin-
istration) whose floor was divided into 50 squares (5 cm ꢃ 5 cm).
Total numbers of squares by which mouse walked during 5 min

S.L. Capim et al. / European Journal of Medicinal Chemistry 58 (2012) 1e11
11
[25] http://www.molinspiration.com/papers/index.html, [accessed 11.05.12].
[26] R. Rothermel, M. Hanack, Liebigs Ann. Chem. (1991) 1013e1020.
[27] M.H. Hopkins, L.E. Overman, G.M. Rishton, J. Am. Chem. Soc. 113 (1991)
5354e5365.
[28] R. Hambeck, G. Just, Tetrahedron Lett. 31 (1990) 5445e5448.
[29] A.D. Rodrigruez, J.G. Shi, Y.P. Shi, J. Org. Chem. 65 (2000) 3192e3199.
[30] T.A. Grese, K.D. Hutchinson, L.E. Overman, J. Org. Chem. 58 (1993) 2468e2477.
[31] A.G. Popp, A. Mersier, A.L. Petersen, H. Mechlem, J.R. Stohrer, J, Adv. Synth.
Catal. 346 (2004) 682e690.
[32] J. Du, K.A. Watanabe, Synth. Commun. 34 (2004) 1925e1930.
[33] D. Houllemare, F. Outurquin, C. Paulmier, J. Chem. Soc., Perkin Trans. 1 (1997)
1629e1632.
[34] S.V. Pansare, A. Bhattacharyya, Tetrahedron 59 (2003) 3275.
[35] X.-F. Yang, J.T. Mangue, C.-J. Li, J. Org. Chem. 66 (2001) 739e747.
[36] R.W. Alder, J.N. Harvey, M.T. Oabley, J. Am. Chem. Soc. 124 (2002) 4960e4961.
[37] E.R. Burkhardt, K. Matos, Chem. Rev. 106 (2006) 2617e2650.
[38] M.P.J. Donners, M.C. Hersmis, J.P.A. Custers, J. Meuldijk, J.A.J.M. Vekemans,
L.A. Hulshof, Org. Process. Res. Dev. 6 (2002) 606e610.
[43] K. Ramabadran, M. Bansinath, H. Turndorf, M.M. Puig, J Pharmacol. Methods
21 (1989) 21e31.
[44] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman,
G. Scalmani, V. Barone, B. Mennucci, G.A. Petersson, H. Nakatsuji, M. Caricato,
X. Li, H.P. Hratchian, A.F. Izmaylov, J. Bloino, G. Zheng, J.L. Sonnenberg,
M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima,
Y. Honda, O. Kitao, H. Nakai, T. Vreven, J.A. Montgomery Jr., J.E. Peralta,
F. Ogliaro, M. Bearpark, J.J. Heyd, E. Brothers, K.N. Kudin, V.N. Staroverov,
R. Kobayashi, J. Normand, K. Raghavachari, A. Rendell, J.C. Burant, S.S. Iyengar,
J. Tomasi, M. Cossi, N. Rega, J.M. Millam, M. Klene, J.E. Knox, J.B. Cross,
V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R.E. Stratmann, O. Yazyev,
A.J. Austin, R. Cammi, C. Pomelli, J.W. Ochterski, R.L. Martin, K. Morokuma,
V.G. Zakrzewski, G.A. Voth, P. Salvador, J.J. Dannenberg, S. Dapprich,
A.D. Daniels, Ö Farkas, J.B. Foresman, J.V. Ortiz, J. Cioslowski, D.J. Fox, Gaussian
09, Revision A.1, Gaussian, Inc, Wallingford CT, 2009.
[45] R. Koster, M. Anderson, E.J. de Beer, Federation Proc. 18 (1959) 412.
[46] L.I. Robles, M. Barrios, E. Del Pozo, A. Dordal, J.M. Baeyens, Eur. J. Pharmacol.
295 (1996) 181e188.
[39] K.S. Svetlakov, V.G. Nikitin, E.A. Nikolaeva, Russian J. Org. Chem. 43 (2007)
773e774.
[40] F. Freeman, "Chromic Acid" Encyclopedia of Reagents for Organic Synthesis,
John Wiley & Sons, 2001. http://dx.doi.org/10.1002/047084289X.rc164.
[41] R.M. Gene, L. Segura, T. Adzet, E. Marin, J. Inglesias, J Ethnopharmacol. 60
(1998) 157e162.
[47] B.J. Jones, D.J. Roberts, J. Pharm. Pharmacol. 20 (1968) 302e304.
[48] H.M. Barros, M.A. Tannhauser, S.L. Tannhauser, M. Tannhauser, J. Pharmacol.
Methods 26 (4) (1991) 269e275.
[49] World Health Organization (WHO), General Guidelines for Methodologies on
Research and Evaluation of Traditional Medicine, WHO, Switzerland, 2000.
[50] The Organization of Economic Co-operation and Development (OECD), The
OECD Guideline for Testing of Chemical: 420 Acute Oral Toxicity, OECD,
France, 2001.
[42] K. Srinivasan, S. Muruganandan, J. Lal, S. Chandra, S.K. Tandan, V. Raviprakash,
Phytother. Res. 17 (2003) 259e264.