Phenolic esters of O-desmethylvenlafaxine with improved Oral bioavailability and brain uptake

Article abstract of DOI:10.3390/molecules181214920

O-Desmethylvenlafaxine (desvenlafaxine, ODV) is a recently approved antidepressant which in some clinical studies failed to meet a satisfactory end-point. The aim of this study was to prepare a series of phenolic esters of ODV and evaluate their potential as ODV prodrugs with improved brain uptake. Fifteen phenolic esters (compounds 1a-o) were synthesized and their pharmacokinetic profiles evaluated in rat. The four compounds producing the highest relative bioavailability of ODV in rat (compounds 1c, 1e, 1n, 1o) were then studied to evaluate their brain uptake. Of these four compounds, compound 1n (the piperonylic acid ester of ODV) demonstrated the highest Cmax of ODV both in the rat hypothalamus and total brain. Finally the pharmacokinetics of 1n were evaluated in beagle dog where the increase in relative bioavailability of ODV was found to be as great as in rat. This high relative bioavailability of ODV coupled with its good brain penetration make 1n the most promising candidate for development as an ODV prodrug.

Full text of DOI:10.3390/molecules181214920

Molecules 2013, 18, 14920-14934; doi:10.3390/molecules181214920
OPEN ACCESS
molecules
ISSN 1420-3049
www.mdpi.com/journal/molecules
Article
Phenolic Esters of O-Desmethylvenlafaxine with Improved Oral
Bioavailability and Brain Uptake
Yang Zhang 1,2,3, Yan Yang 2, Sen Zhao 2, Zhichao Yang 2, Hong Yang 2, J. Paul Fawcett 4,
Youxin Li 2, Jingkai Gu 2,* and Tiemin Sun 1,*
1
Key Laboratory of Structure-Based Drug Design and Discovery, Shenyang Pharmaceutical
University, Ministry of Education, Shenyang 110016, China
2
Research Center for Drug Metabolism, College of Life Sciences, Jilin University,
Changchun 130021, China
3
School of Chemical and Pharmaceutical Engineering, Jilin Institute of Chemical Technology,
Jilin 132022, China
4
School of Pharmacy, University of Otago, PO Box 56, Dunedin 9054, New Zealand
* Authors to whom correspondence should be addressed; E-Mails: suntiemin@syphu.edu.cn (T.S.);
gujk@jlu.edu.cn (J.G.); Tel.: +86-24-2398-6398 (T.S.); +86-431-8515-5380 (J.G.).
Received: 30 October 2013; in revised form: 2 December 2013 / Accepted: 2 December 2013 /
Published: 4 December 2013
Abstract: O-Desmethylvenlafaxine (desvenlafaxine, ODV) is a recently approved
antidepressant which in some clinical studies failed to meet a satisfactory end-point.
The aim of this study was to prepare a series of phenolic esters of ODV and evaluate their
potential as ODV prodrugs with improved brain uptake. Fifteen phenolic esters
(compounds 1a–o) were synthesized and their pharmacokinetic profiles evaluated in rat.
The four compounds producing the highest relative bioavailability of ODV in rat
(compounds 1c, 1e, 1n, 1o) were then studied to evaluate their brain uptake. Of these
four compounds, compound 1n (the piperonylic acid ester of ODV) demonstrated the
highest Cmax of ODV both in the rat hypothalamus and total brain. Finally the
pharmacokinetics of 1n were evaluated in beagle dog where the increase in relative
bioavailability of ODV was found to be as great as in rat. This high relative bioavailability
of ODV coupled with its good brain penetration make 1n the most promising candidate for
development as an ODV prodrug.

Molecules 2013, 18
14921
Keywords: O-desmethylvenlafaxine; phenolic ester; prodrug; pharmacokinetics; brain
uptake; rat; dog
1. Introduction
Depression is a common mental disease estimated to affect some 350 million people worldwide [1].
In fact, a World Mental Health Survey conducted in 17 countries in 2012 found that about 5% of
people reported having an episode of depression in the previous year [2]. The condition displays a high
rate of lifetime incidence, early age onset, high chronicity and significant role impairment. Despite a
wide range of pharmacotherapeutic options, response to antidepressant medication is subject to
delayed onset and is highly variable. It is also not without significant adverse effects. Thus the search
for improved antidepressant drugs remains an ongoing concern.
Venlafaxine (VEN) is a bicyclic phenylethylamine-based antidepressant which selectively blocks
presynaptic reuptake of norepinephrine (NE) and serotonin (5-HT) without blocking histaminergic,
muscarinic or 1-adrenergic receptors [3,4]. Because of this action as a selective 5-HT-NE reuptake
inhibitor (SNRI), VEN has a wide therapeutic index and improved tolerability profile when compared
with tricyclic antidepressants (TCAs) [5]. Apart from depression, VEN is also used to treat generalized
anxiety, obsessive-compulsive and panic disorder as well as social phobia [6]. Its most common side
effects are nausea, somnolence, dizziness, dry mouth, and sweating [7].
In humans, VEN is well absorbed and subject to extensive first-pass metabolism in the liver by
cytochrome P450 2D6 (CYP2D6). This makes it susceptible to CYP2D6 polymorphism and the associated
variability in pharmacokinetics, efficacy and/or tolerability [8–10]. O-Desmethylvenlafaxine (ODV, also
known as desvenlafaxine) is the major (56%) metabolite of VEN (Scheme 1) with antidepressant
activity similar to that of VEN but with a much longer half-life [11–13]. ODV is mainly metabolized
by UDP-glucuronosyltransferase enzymes [14], making it less prone to polymorphic pharmacokinetic
and pharmacodynamic variability than VEN [10].
Scheme 1. The conversion of venlafaxine to its principal metabolite O-desmethylvenlafaxine by CYP2D6.
These favorable properties led to ODV being approved by the United States Food and Drug
Administration in 2008 for the treatment of major depressive disorder but, interestingly, it was not

Molecules 2013, 18
14922
approved in the European Union because of an unfavorable risk-benefit balance in both hot flushes and
depression [15]. More recent studies have shown that the minimum effective dose of ODV (as the
succinate salt) is 50 mg/day which may explain the lack of efficacy found in some studies [16,17].
ODV has been shown to have high bioavailability in humans (ca. 80%), raising the question of
whether its somewhat unconvincing antidepressant efficacy is the result of low brain exposure after
oral dosing. On this basis, we decided to compare the relative bioavailability and brain uptake of ODV
with some of its phenolic esters as potential prodrugs of ODV.
Prodrugs are usually designed to improve passive and/or transporter-mediated intestinal
absorption [18,19] to increase oral bioavailability [20–22] and/or tissue-selective delivery [23]. In some
cases they are also used to reduce the side effects of a drug, particularly if it is to be used chronically
or for chemotherapy [24,25]. In our previous work [26], a preclinical pharmacological evaluation of
the p-methoxybenzoic acid ester of ODV (TP1) in rat was reported. It was shown that after oral
administration, TP1 rapidly penetrates the rat brain and hypothalamus, is converted into ODV and
demonstrates higher relative bioavailability than ODV. This proof-of-concept that lipophilic phenolic
esters of ODV improve the oral bioavailability and brain uptake of ODV led us to synthesize a series
of lipophilic phenolic esters of ODV (including TP1, compound 1k) and examine their bioavailability
and, in some cases, brain uptake in rat.
2. Results and Discussion
2.1. Chemistry
Acyl chlorides a–o were synthesized from the corresponding carboxylic acids by reaction with SOCl2 in
pyridine at 90 °C for 3 h [27]. Compounds 1a–o were synthesized by treatment of ODV with the
corresponding acyl chloride in the presence of anhydrous pyridine and THF at 0–25 C for 6 h (Scheme 2).
The target compounds were obtained in low to moderate yield [28].
2.2. Pharmacokinetic (PK) Studies in Rat
Compounds 1a–o and ODV were administered orally to Wistar rats at a dose of 0.02 mmol/kg.
Plasma samples were collected over 24 h and analyzed for ODV by liquid chromatography-tandem
mass spectrometry (LC-MS/MS) [8,29,30]. Calculated log P (Clog P) values of compounds 1a–o and
ODV were predicted by Molinspiration. PK parameters including area under the plasma
concentration-time curve (AUC), mean residence time (MRT), elimination half life (t1/2), peak
concentration (Cmax) and time to reach Cmax (Tmax) were calculated by non-compartmental analysis
using DAS Version 3.0. The relative bioavailability of ODV (F) of compounds 1a–o compared to ODV
(as 100) was calculated as F = AUC0-t(1a–o)/AUC0-t(ODV) × 100%. Clog P values of the esters along
with PK parameters of ODV produced from them are shown in Table 1.

Molecules 2013, 18
14923
Scheme 2. Formation of phenolic esters of ODV 1a–o by reaction with RCOCl in
anhydrous pyridine/THF at 0 C for 1 h, followed by room temperature for 5 h.
Table 1. Clog P of the esters and PK parameters of ODV after oral administration of 1a–o
and ODV to rats at a dose of 0.02 mmol/kg (data are means ± SD, n = 4).
Cmax
Tmax
h
t1/2
h
AUC0-t
μg/L × h
219 ± 56
AUC0-∞
μg/L × h
222 ± 59
MRT
h
F
Compd. Clog P
μg/L
%
ODV
1a
1b
1c
1d
1e
1f
3.3
4.8
5.4
5.2
6.7
5.9
5.6
4.2
4.9
4.0
6.1
5.7
5.4
5.4
5.5
5.1
66.6 ± 14.6 1.25 ± 1.06 4.14 ± 1.21
6.03 ± 2.82 100
7.67 ± 1.21 1.50 ± 0.71 2.13 ± 0.83 41.1 ± 3.8
41.1 ± 3.7 4.70 ± 0.47 18.7
156 ± 20 6.99 ± 1.40 69.5
18.2 ± 3.4 1.50 ± 0.24 3.95 ± 1.84
98.8 ± 14.5 0.50 ± 0.12 5.47 ± 1.50
152 ± 15
278 ± 86
293 ± 103 4.81 ± 2.06 127
246 ± 148 6.31 ± 0.44 101
33.3 ± 18.0 0.92 ± 0.83 6.40 ± 5.30 222 ± 114
118 ± 16
0.33 ± 0.04 2.39 ± 0.15
321 ± 83
216 ± 89
321 ± 93
220 ± 87
4.37 ± 1.39 146
4.53 ± 1.96 98.4
47.0 ± 13.4 2.00 ± 1.41 4.61 ± 2.28
1g
1h
1i
9.36 ± 3.60 0.58 ± 0.59 1.65 ± 0.11 29.4 ± 0.2
15.7 ± 4.6 0.50 ± 0.07 2.53 ± 1.65 58.7 ± 23.9 58.9 ± 23.6 4.92 ± 1.14 26.8
10.5 ± 2.7 0.50 ± 0.12 1.19 ± 0.80 21.3 ± 2.8 21.3 ± 2.8 2.35 ± 0.40 9.73
29.4 ± 0.2 4.14 ± 0.10 13.4
1j
101 ± 31
0.42 ± 0.09 2.49 ± 0.44
241 ± 61
228 ± 38
251 ± 80
231 ± 47
2.77 ± 0.80 110
4.95 ± 1.85 104
1k
1l
96.3 ± 24.7 1.75 ± 0.35 4.32 ± 0.82
12.4 ± 13.5 1.50 ± 0.71 8.61 ± 3.09 27.8 ± 23.6 33.9 ± 23.7 9.29 ± 3.43 12.7
30.4 ± 5.9 1.25 ± 0.35 6.35 ± 4.09 178 ± 60 197 ± 84 6.75 ± 1.60 81.3
141 ± 48 1.00 ± 0.58 8.29 ± 5.12 421 ± 146 456 ± 153 4.42 ± 0.74 192
87.7 ± 13.3 0.44 ± 0.10 9.02 ± 1.74 278 ± 85 318 ± 84 6.83 ± 0.73 127
1m
1n
1o

Molecules 2013, 18
14924
The results show that the Clog P values of all ODV esters are higher than that of ODV and span the
range 4.0–6.7. They also show that the t1/2 values of ODV vary considerably and are approximately
proportional to F, indicating that F is controlled by absorption of the esters. A plot of Clog P vs. F
supports this in that it gives a reasonably linear correlation (r2 = 0.3599, Figure 1) with four
compounds lying above the linear regression line and one below it. The presence of these outliers
suggests that the rate of hydrolysis of the esters may also contribute to the F value. This is supported
by the fact that the ester with R = –C(CH3)3 (compound 1a) has a much lower F than ODV.
Figure 1. Relationship between F and Clog P values for compounds 1a–o showing the
linear regression line of best fit.
250
R² = 0.3599
200
150
Compd 1a‐o
ODV
100
50
0
3
4
5
6
7
Clog P
Considering the F values in relation to the structures of the esters, those containing an alicyclic
ring (compounds 1b–e) have F values that do not follow the trend of their respective Clog P values in
that 1c and 1e are higher than ODV, whereas 1b is lower. The compound with a phenyl group
(compound 1f) has a similar F to ODV but, for compounds with aromatic bioisosteres
(compounds 1g–i), F is much lower, consistent with their lower lipophilicity. Compounds with
substituted phenyl groups (compounds 1j, 1k, 1n, 1o) have higher F values than ODV, especially
compound 1n. However, compounds with aralkyl groups (compounds 1l, 1m) have lower F values,
particularly 1l. On the basis of these results, the four compounds with the highest F values
(ie., compounds 1c, 1e, 1n, and 1o) were selected for evaluation of their brain penetration. The mean
plasma concentration-time curves of ODV after oral administration of these selected compounds and
ODV are shown in Figure 2.

Molecules 2013, 18
14925
Figure 2. Plasma concentration-time profiles of ODV after administration of single oral
doses (0.02 mmol/kg) of the four phenolic esters of ODV producing the highest relative
bioavailability of ODV in rat (data are means, n = 4).
120
ODV
Ic
Ie
In
Io
100
80
60
40
20
0
0
5
10
15
20
25
Time(h)
Time (h)
2.3. Brain Uptake Studies in Rat
For brain uptake studies, the selected compounds were administered to groups of Wistar rats at a
dose of 0.06 mmol/kg [10,26]. Since the density of receptors for 5-HT and NE reuptake is high in the
hypothalamus [31], the concentrations of ODV were determined in both hypothalamus and total brain
where total brain represents the brain tissue after removal of the hypothalamus. The results, shown in
Figure 3, indicate that the piperonylic acid ester of ODV (compound 1n) produced the highest level of
ODV in the hypothalamus at 0.25 h (514 ng/g) and the highest level in total brain at 1 h (180 ng/g). At
4 h, concentrations of ODV produced by all esters were higher than those produced by ODV itself.
Figure 3. Concentrations of ODV in the hypothalamus and total brain produced after
single oral doses of (a) ODV, (b) compound 1c, (c) compound 1e, (d) compound 1n and
(e) compound 1o. (f) shows the concentrations of ODV in the hypothalamus after
administration of ODV, 1c, 1e, 1n and 1o to rats at a dose of 0.06 mmol/kg (data are means
+ SD, n = 6).
600
500
400
300
200
100
0
300
250
200
150
100
50
Hypothalamus
Total brain
Hypothalamus
Total brain
0
0.25h
0.5h
1h
2h
4h
0.25h
0.5h
1h
2h
4h
Time(h)
Time(h)
(a)
(b)

Molecules 2013, 18
14926
Figure 3. Cont.
Hypothalamus
Total brain
700
600
500
400
300
200
100
800
700
600
500
400
300
200
100
0
Hypothalamus
Total brain
0
0.25h
0.5h
1h
2h
4h
0.25h
0.5h
1h
2h
4h
Time(h)
Time(h)
(c)
(d)
Hypothalamus
Total brain
ODV
Ic
Ie
In
Io
800
600
400
200
800
600
400
200
0
0
0.25h
0.5h
1h
2h
4h
0.25h
0.5h
1h
2h
4h
Time(h)
Time(h)
(e)
2.4. PK Studies of 1n and ODV in Beagle Dog
(f)
A group of beagle dogs was administered single oral doses (0.007 mmol/kg) of compound 1n and
ODV in a cross-over study with a washout period of one week. As shown in Table 2 and Figure 4, 1n
was rapidly absorbed and metabolized to ODV in beagle dogs. Thus the Tmax of ODV after
administration of 1n was much shorter than after administration of ODV (1.21 vs. 2.67 h), the Cmax
was much higher (20.8 vs. 7.55 µg/L) and the F value was nearly doubled, consistent with the results
observed in rat.
Table 2. PK parameters of ODV in a cross-over study involving oral administration of
compound 1n and ODV at a dose of 0.007 mmol/kg to a group of beagle dogs (data are
means ± SD, n = 6).
Cmax
Tmax
h
t1/2
h
AUC0–t
AUC0–∞
MRT
h
F
Compd.
μg/L
μg/L × h
μg/L × h
%
ODV
7.55 ± 4.34 2.67 ± 0.58 1.55 ± 0.29 27.7 ± 12.1 27.8 ± 12.6 4.10 ± 0.70 100
20.8 ± 6.6 1.21 ± 0.61 3.41 ± 1.54 55.1 ± 17.2 55.5 ± 16.9 3.91 ± 0.76 199
1n

Molecules 2013, 18
14927
Figure 4. Mean plasma concentration-time profiles of ODV in a cross-over study
involving oral administration of compound 1n and ODV at a dose of 0.007 mmol/kg to a
group of beagle dogs (data are means, n = 6).
14
ODV
In
12
10
8
6
4
2
0
0
5
10
15
20
25
Time(h)
Time (h)
3. Experimental
3.1. General
ODV was purchased from Dingjin Chemical Co., Ltd (Zibo City, China). Other commercial
reagents and solvents were used without further purification. Melting points were determined on a
Walden Precision Apparatus Electrothermal 9300 apparatus and are uncorrected. 1H-NMR (400 MHz)
and 13C-NMR (100 MHz) spectra were recorded on a Bruker Advance 400 nuclear magnetic resonance
spectrometer. High resolution mass spectroscopy (HRMS) was carried out using a Triple-TOF 5600
mass spectrometer equipped with an electrospray ionization (ESI) source. Compound purity was assessed
by HPLC analysis on an Agilent 1200 HPLC system and shown to be >95% in all cases. Animal
experiments were carried out in compliance with the Guidelines for the Care and Use of Laboratory
Animals of the National Research Council of USA, 1996 and related ethical regulations of Jilin University.
Drug concentrations in the PK studies were determined by LC-MS/MS using an Agilent 1100 Series
HPLC system and a QTRAP 2000TM mass spectrometer.
3.2. General Procedure for Synthesis of Compounds a–o
Compounds a–o were prepared from the corresponding carboxylic acids (9.2 mmol) and thionyl
chloride (2 mL) with heating under reflux for 3 h. After removal of the thionyl chloride in vacuo, the
resulting acyl chlorides were used without further purification.
3.3. General Procedure for Synthesis of Compounds 1a–o
ODV (2.0 g, 7.6 mmol) was dissolved in anhydrous pyridine (40 mL) at ambient temperature. The
appropriate acyl chloride in anhydrous THF (5 mL) was slowly added dropwise at 0 C and the

Molecules 2013, 18
14928
reaction mixture left with stirring at 0 C for 1 h under nitrogen, followed by 5 h at room temperature.
The reaction mixture was then added to water (100 mL) with vigorous stirring over 5 min, after which
the pH of the reaction mixture was adjusted to 9.0 using 1N NaOH solution to precipitate the crude
product. After standing overnight, the precipitate was filtered, washed with water and purified by
column chromatography (silica gel, methanol-dichloromethane 1:15 v/v then 1:10 v/v) to give the
desired products 1a–o.
4-(2-(Dimethylamino)-1-(1-hydroxycyclohexyl)ethyl)phenyl pivalate (1a). ODV was treated with
1
pivaloyl chloride (a, 0.9 g) to give 1a (1.3 g, 48.1%) as a white powder; mp 131–133 C; H-NMR
(DMSO-d6) δ 0.91–1.57 (m, 10H, cyclohexane-CH2-), 1.29 (s, 9H, -C(CH3)3), 2.11 (s, 6H, -N(CH3)2),
2.84 (m, 2H, -CH2-N), 3.30 (m, 1H, Ar-CH), 6.95 (d, J = 8.4 Hz, 2H, Ar-H), 7.23 (d, J = 8.4 Hz, 2H,
Ar-H); 13C-NMR (DMSO-d6) δ 21.22, 21.28, 25.55, 26.71 (3C), 33.43, 36.82, 38.45, 45.27 (2C),
51.95, 59.95, 71.99, 120.40 (2C), 130.14 (2C), 139.24, 148.85, 176.28; HRMS(ESI): m/z calcd. for
[M+H]+: 348.2494; found: 348.2535.
4-(2-(Dimethylamino)-1-(1-hydroxycyclohexyl)ethyl)phenyl cyclohexanecarboxylate (1b). ODV was
treated with cyclohexanecarbonyl chloride (b, 1.1 g) to give 1b (1.5 g, 52.0%) as a white powder; mp
1
122–124 C; H-NMR (DMSO-d6) δ 1.08–1.74 (m, 20H, 2 × cyclohexane-CH2-), 1.96 (m, 1H,
CHCOO-), 2.11 (s, 6H, -N(CH3)2), 2.56 (m, 1H, -CH2-N), 2.84 (m, 1H, -CH2-N), 3.30 (m, 1H,
13
Ar-CH), 4.99 (br, 1H, -OH), 6.95 (d, J = 8.2 Hz, Ar-H), 7.22 (d, J = 8.2 Hz, 2H, Ar-H); C-NMR
(DMSO-d6) δ 21.23, 21.29, 24.67 (2C), 25.26, 25.55, 28.46 (2C), 33.51, 36.81, 42.03, 45.29 (2C),
51.96, 59.96, 71.98, 120.49 (2C), 130.15 (2C), 139.26, 148.67, 173.77; HRMS (ESI): m/z calcd. for
[M+H]+: 374.2650; found: 374.2691.
4-(2-(Dimethylamino)-1-(1-hydroxycyclohexyl)ethyl)phenyl 4-methylcyclohexanecarboxylate (1c).
ODV was treated with 4-methylcyclohexane carbonyl chloride (c, 1.2 g) to give 1c (1.1 g, 36.4%) as a
1
white powder; mp 157–159 C; H-NMR (DMSO-d6) δ 0.88 (m, 3H, 4-methylcyclohexane-CH3),
0.94–1.75 (m, 19H, 4-methylcyclohexane-CH2-, cyclohexane-CH2-, 4-methylcyclohexane-CH), 2.04
(m, 1H, CHCOO-), 2.11 (s, 6H, -N(CH3)2), 2.43–2.90 (m, 3H, -CH2-N, Ar-CH), 5.04 (br, 1H,
-OH), 6.95 (d, J = 8.0 Hz, Ar-H), 7.22 (d, J = 8.0 Hz, 2H, Ar-H); 13C-NMR (DMSO-d6)
δ 21.10, 21.16, 22.08, 25.40, 28.40 (2C), 31.28, 33.45 (3C), 36.68, 42.13, 45.11 (2C), 51.92, 59.91,
71.87, 120.28 (2C), 129.99 (2C), 139.11, 148.60, 173.70; HRMS (ESI): m/z calcd. for [M+H]+:
388.2807; found: 388.2850.
4-(2-(Dimethylamino)-1-(1-hydroxycyclohexyl)ethyl)phenyl 4-isopropylcyclohexanecarboxylate (1d).
ODV was treated with 4-isopropylcyclohexane carbonyl chloride (d, 1.4 g) to give 1d (0.7 g, 22.5%)
as a white powder; mp 149–152 C; 1H-NMR (DMSO-d6) δ 0.86 (m, 6H, isopropyl-(CH3)2), 1.06–2.11
(m, 20H, cyclohexyl-(CH2)5-, isopropyl-(CH2)4-, isopropyl-CH, -CH), 2.11 (s, 6H, -N(CH3)2), 2.45 (m,
1H, CHCOO-), 2.53 (m, 1H, -CH2-N), 2.82 (m, 1H, -CH2-N), 2.88 (m,1H, Ar-CH), 5.01 (br, 1H, -OH),
13
6.95 (d, J = 8.4 Hz, 2H, Ar-H), 7.22 (d, J = 8.4 Hz, 2H, Ar-H); C-NMR (DMSO-d6) δ 19.42 (2C),
21.10, 21.17, 25.40, 28.08 (2C), 28.60 (2C), 32.03, 33.50, 36.69, 42.53, 42.60, 45.14 (2C), 51.94,
59.92, 71.88, 120.28 (2C), 129.99 (2C), 139.16, 148.58, 173.69; HRMS (ESI): m/z calcd. for [M+H]+:
416.3120; found: 416.3147.

Molecules 2013, 18
14929
4-(2-(Dimethylamino)-1-(1-hydroxycyclohexyl)ethyl)phenyl cycloheptanecarboxylate (1e). ODV was
treated with cycloheptanecarbonyl chloride (e, 1.2 g) to give 1e (1.5 g, 51.8%) as a light yellow
powder; mp 110–112 C; 1H-NMR (CDCl3) δ 0.95–2.08 (m, 22H, cyclohexane-CH2- and
cycloheptane-CH2-), 2.30 (m, 1H, -CH2-N), 2.98 (m, 1H, -CH2-N), 2.32 (s, 6H, -N(CH3)2), 2.73 (m,
1H, CHCOO-), 3.29 (m, 1H, Ar-CH), 6.98 (d, J = 8.4 Hz, 2H, Ar-H), 7.13 (d, J = 8.4 Hz, 2H, Ar-H);
13C-NMR (CDCl3) δ 21.30, 21.59, 25.94, 26.32 (2C), 28.31 (2C), 30.75 (2C), 31.20, 38.13, 44.95,
45.47 (2C), 52.00, 61.04, 74.15, 120.93 (2C), 130.06 (2C), 138.00, 149.62, 175.45; HRMS (ESI): m/z
calcd. for [M+H]+: 388.2807; found: 388.2835.
4-(2-(Dimethylamino)-1-(1-hydroxycyclohexyl)ethyl)phenyl benzoate (1f). ODV was treated with
1
benzoyl chloride (f, 1.1 g) to give 1f (1.4 g, 50.7%) as a white powder; mp 175–178 C; H-NMR
(DMSO-d6) δ 0.91–1.61 (m, 10H, cyclohexane-CH2-), 2.13 (s, 6H, -N(CH3)2), 2.88 (m, 2H,
-CH2-N), 3.29 (m, 1H, Ar-CH), 7.15 (d, J = 8.4, 2H, Ar-H), 7.30 (d, J = 8.4, 2H, Ar-H), 7.61 (t,
13
J = 7.4, 2H, Ar-H), 7.75 (t, J = 7.4, 1H, Ar-H), 8.13 (d, J =7.4, 2H, Ar-H); C-NMR (DMSO-d6) δ
21.23, 21.30, 25.55, 33.62, 36.78, 45.29 (2C), 51.97, 59.92, 71.97, 120.65 (2C), 128.92 (2C), 129.67
(2C), 130.29 (2C), 131.45, 128.61, 139.60, 148.71, 164.56; HRMS (ESI): m/z calcd. for [M+H]+:
368.2181; found: 368.2224.
4-(2-(Dimethylamino)-1-(1-hydroxycyclohexyl)ethyl)phenyl furan-3-carboxylate (1g). ODV was
treated with furan-3-carbonyl chloride (g, 1.0 g) to give 1g (1.2 g, 42.6%) as a white powder; mp
1
159–162 C; H-NMR (DMSO-d6) δ 0.97–1.61 (m, 10H, cyclohexane-CH2-), 2.12 (s, 6H, -N(CH3)2),
2.58 (m, 1H, -CH2-N), 2.86 (m, 1H, -CH2-N), 3.32 (m, 1H, Ar-CH), 4.99 (br, 1H, -OH), 6.80 (m, 1H,
furan-H), 7.12 (d, J = 8.0, 2H, Ar-H), 7.29 (d, J = 8.0, 2H, Ar-H), 7.54 (m, 1H, furan-H), 8.09 (m, 1H,
13
furan-H). C-NMR (DMSO-d6) δ 21.11, 21.19, 25.40, 33.68, 36.65, 45.14 (2C), 51.95, 59.87, 71.84,
112.45, 119.74, 120.35 (2C), 130.20 (2C), 139.67, 143.03, 147.92, 148.28, 156.20. HRMS (ESI): m/z
calcd. for [M+H]+: 358.1974; found: 358.1997.
4-(2-(Dimethylamino)-1-(1-hydroxycyclohexyl)ethyl)phenyl thiophene-3-carboxylate (1h). ODV was
treated with thiophene-3-carbonyl chloride (h, 1.1 g) to give 1h (1.5 g, 53.7%) as a white powder; mp
1
168–172 C; H-NMR (DMSO-d6) δ 1.05–1.64 (m, 10H, cyclohexane-CH2-), 2.15 (s, 6H, -N(CH3)2),
2.57 (m, 1H, -CH2-N), 2.87 (m, 1H, -CH2-N), 2.94 (m, 1H, Ar-CH), 4.62 (br, 1H, -OH), 7.13 (d,
J = 8.2, 2H, Ar-H), 7.30 (d, J = 8.2, 2H, Ar-H), 7.60 (d, J = 4.8, 1H, thiophene-H), 7.69 (m, 1H,
13
thiophene-H), 8.50 (s, 1H, thiophene-H); C-NMR (DMSO-d6) δ 20.73, 20.80, 24.92, 33.60, 36.30,
44.61 (2C), 52.01, 59.78, 71.62, 119.73 (2C), 126.98 (2C), 129.63 (2C), 131.91, 133.85, 139.12,
148.27, 159.87; HRMS (ESI): m/z calcd. for [M+H]+: 374.1745; found: 374.1777.
4-(2-(Dimethylamino)-1-(1-hydroxycyclohexyl)ethyl)phenyl nicotinate (1i). ODV was treated with
1
nicotinoyl chloride (i, 1.1 g) to give 1i (1.1 g, 38.6%) as a white powder; mp 180–182 C; H-NMR
(DMSO-d6) δ 1.04–1.69 (m, 10H, cyclohexane-CH2-), 2.68 (s, 6H, -N(CH3)2), 3.17 (m, 1H, -CH2-N),
3.46 (m, 1H, -CH2-N), 3.62 (m, 1H, Ar-CH), 5.47 (br, 1H, -OH), 7.33 (d, J = 8.3, 2H, Ar-H), 7.48 (d,
J = 8.3, 2H, Ar-H), 7.71 (m,1H, pyridine-H), 8.51 (m, 1H, pyridine-H), 8.93 (m, 1H, pyridine-H), 9.28
13
(s, 1H, pyridine-H); C-NMR (DMSO-d6) δ 20.95, 21.35, 25.22, 33.54, 36.05, 42.66, 43.30, 50.01,

Molecules 2013, 18
14930
58.09, 72.04, 121.38 (2C), 124.84, 125.91, 130.74 (2C), 136.94, 139.20, 148.98, 149.33, 152.49,
162.93; HRMS (ESI): m/z calcd. for [M+H]+: 369.2133; found: 369.2159.
4-(2-(Dimethylamino)-1-(1-hydroxycyclohexyl)ethyl)phenyl 4-methylbenzoate (1j). ODV was treated
with 4-methylbenzoyl chloride (j, 1.2 g) to give 1j (0.8g, 28.2%) as a white powder; mp 159–162 C;
1H-NMR (DMSO-d6) δ 1.06-1.69 (m, 10H, cyclohexane-CH2-), 2.44 (s, 3H, Ar-CH3), 2.68 (s,
6H, -N(CH3)2), 3.17 (m, 1H, -CH2-N), 3.59 (m, 1H, -CH2-N), 3.64 (m, 1H, Ar-CH), 4.66
(br, 1H, -OH), 7.27 (d, J = 8.0 Hz, 2H, Ar-H), 7.42-7.47 (dd, J1=13.2, J2=8.0, 4H, Ar-H), 8.0 (d,
J = 8.0 Hz, 2H, Ar-H); 13C-NMR (DMSO-d6) δ 20.95, 21.25, 21.34, 25.22, 33.44, 36.04, 42.71, 43.23,
50.06, 58.10, 72.05, 115.11, 121.49 (2C), 126.18, 129.53 (2C), 129.78 (2C), 130.65, 136.57, 144.53,
149.66, 164.42; HRMS (ESI): m/z calcd. for [M+H]+: 382.2337; found: 382.2305.
4-(2-(Dimethylamino)-1-(1-hydroxycyclohexyl)ethyl)phenyl 4-methoxybenzoate (1k). ODV was treated
with 4-methoxybenzoyl chloride (k, 1.3 g) to give 1k (0.7 g, 24.3%) as a white powder; mp 133–137 C;
1H-NMR (CDCl3) δ 0.90-1.74 (m, 10H, cyclohexane-CH2-), 2.57 (m, 1H, -CH2-N), 2.72 (s, 6H,
-N(CH3)2), 3.16 (m, 1H, -CH2-N), 3.37 (m, 1H, Ar-CH), 3.88 (s, 1H, -OCH3), 6.98 (d, J = 8.8 Hz, 2H,
13
Ar-H), 7.19 (m, 4H, Ar-H), 8.12 (d, J = 8.8 Hz, 2H, Ar-H); C-NMR (CDCl3) δ 21.11, 21.43, 25.24,
31.33, 36.62, 44.05 (2C), 52.69, 55.48, 60.14, 73.59, 113.86 (2C), 121.41, 121.96 (2C), 130.18, 132.22
(2C), 136.67, 150.28, 163.99, 164.77, 165.34; HRMS (ESI): m/z calcd. for [M+H]+: 398.2287;
found: 398.2237.
4-(2-(Dimethylamino)-1-(1-hydroxycyclohexyl)ethyl)phenyl 3-phenylpropanoate (1l) ODV was treated
with 3-phenylpropanoyl chloride (l, 1.3 g) to give 1l (0.6 g, 19.1%) as a white powder; mp 124–127 C;
1H-NMR (DMSO-d6) δ 0.95–2.07 (m, 10H, m, 10H, cyclohexane-CH2-), 1.96 (s, 6H, -N(CH3)2), 2.63
(m, 2H, -CH2-N), 2.57 (m, 2H, -OCOCH2-), 2.70 (m, Ar-CH), 2.82 (m, 2H, Ar-CH2-), 6.64 (d,
13
J = 8.0, 2H, Ar-H), 6.93 (d, J = 8.0, 2H, Ar-H), 7.18-7.29 (m, 5H, Ar-H). C-NMR (DMSO-d6) δ
20.84 (2C), 24.63, 30.11, 30.77, 31.00, 35.90, 45.03 (2C), 47.47, 58.84, 85.67, 114.35 (2C), 125.76,
128.00 (2C), 128.05 (2C), 130.19 (3C), 140.47, 155.60, 171.22; HRMS (ESI): m/z calcd for [M+H]+:
396.2494; found: 396.2509.
4-(2-(Dimethylamino)-1-(1-hydroxycyclohexyl)ethyl)phenyl cinnamate (1m). ODV was treated with
cinnamoyl chloride (m, 1.3 g) to give 1m (0.7 g, 23.8%) as a white powder; mp 118–122 C; 1H-NMR
(CDCl3) δ 0.87–1.73 (m, 10H, cyclohexane-CH2-), 2.38 (s, 6H, -N(CH3)2), 2.47 (m, 1H, -CH2-N), 3.07
(m, 1H, -CH2-N), 3.40 (m, 1H, Ar-CH), 5.06 (br, 1H, -OH), 6.88 (d, J = 16.0, 1H, -COHC=CH-),
7.09–7.59 (m, 8H, Ar-H), 7.85 (d, J = 16.0, 1H, -COHC=CH-); 13C-NMR (DMSO-d6) δ 20.96, 21.35,
25.23, 33.42, 36.05, 42.81, 43.11, 50.09, 58.14, 72.07, 117.23, 121.36 (2C), 128.65 (2C), 128.90,
129.00, 130.43, 130.62, 130.90, 133.80, 136.59, 146.40, 149.49, 164.77; HRMS (ESI): m/z calcd. for
[M+H]+: 394.2337; found: 394.2346.
4-(2-(Dimethylamino)-1-(1-hydroxycyclohexyl)ethyl)phenyl benzo[d][1,3]dioxole-5-carboxylate (1n).
ODV was treated with benzo[d][1,3]dioxole-5-carbonyl chloride (n, 1.4 g) to give 1n (1.5 g, 48.6%) as a
1
white powder; mp 154–157 C; H-NMR (DMSO-d6) δ 0.90-1.66 (m, 10H, cyclohexane-CH2-), 2.13
(s, 6H, -N(CH3)2), 2.54 (m, 1H, -CH2-N), 2.87 (m, 1H, -CH2-N), 3.32 (m, 1H, Ar-CH), 5.00 (1H, br,

Molecules 2013, 18
14931
-OH), 6.19 (s, 2H, -O-CH2-O-), 7.12 (d, J = 8.0 Hz, 2H, Ar-H), 7.28 (d, J = 8.0 Hz, 2H, Ar-H), 7.55
(s, 1H, Ar-H), 7.75(d, J = 1.6 Hz, 1H, Ar-H),7.73 (d, J = 1.6Hz, 1H, Ar-H); 13C-NMR (CDCl3) δ 21.22,
21.49, 25.83, 31.14, 38.04, 45.36 (2C), 51.94, 60.94, 74.05, 101.89, 108.06, 109.79, 121.04 (2C),
123.32, 126.07, 130.06 (2C), 138.12, 147.83. 149.57, 152.12, 164.37; HRMS (ESI): m/z calcd. for
[M+H]+: 412.2079; found: 412.2113.
4-(2-(Dimethylamino)-1-(1-hydroxycyclohexyl)ethyl)phenyl
2,3-dihydrobenzo[b][1,4]dioxine-6-
carboxylate (1o). ODV was treated with 2,3-dihydrobenzo[b][1,4]dioxine-6-carbonyl chloride (o, 0.8 g)
to give 1o (1.5 g, 27.5%) as a white powder; mp 159–162 C; 1H-NMR (CDCl3) δ 1.02–1.72 (m, 10H,
cyclohexane-CH2-), 2.37 (s, 6H, -N(CH3)2), 2.42(m, 1H, -CH2-N), 3.06(m, 1H, -CH2-N), 3.37(m, 1H,
Ar-CH), 4.31(m, 2H, -O-(CH2)2-O-), 4.33 (m, 2H, -O-(CH2)2-O-), 7.18(d, J = 8.0 Hz, 2H, Ar-H),
7.11(d, J = 8.0 Hz, 2H, Ar-H), 6.95 (d, J = 8.8 Hz, 1H, Ar-H), 7.71(d, J = 8.8 Hz, 1H, Ar-H), 7.72 (s,
13
1H, Ar-H); C-NMR (CDCl3) δ 21.29, 21.51, 25.83, 31.19, 37.98, 45.31 (2C), 52.06, 60.98, 64.06,
64.66, 74.08, 117.31, 119.53, 121.18 (2C), 122.60, 124.06, 130.09 (2C), 138.01, 143.28, 148.37,
149.71, 164.58; HRMS (ESI): m/z calcd. for [M+H]+: 426.2236; found: 426.2269.
3.4. PK Studies in Rat
Mature normal class Wistar rats (aged 4–6 weeks, weight 200 ± 20 g) were obtained from the
Animal Research Institute, Jilin University. Animals were housed under controlled temperature and
humidity conditions and allowed free access to food and water. After a 12 h fast, rats were
administered a single dose of 0.02 mmol/kg drug by oral gavage. Blood samples (250 μL) were
collected into heparinized. Eppendorf tubes before dosing and at 0.167, 0.33, 0.5, 1, 1.5, 2.0, 3.0, 4.0,
6.0, 8.0, 12.0 and 24.0 h after dosing. After centrifugation at 3500 rpm for 5 min, 100 μL plasma was
removed and stored at −80 °C until analysis by LC-MS/MS. The system consisted of an Agilent 1100
Series HPLC (Agilent Technologies, Palo Alto, CA, USA) connected to a QTRAP 2000TM mass
spectrometer (Applied Biosystems Sciex, Concord, ON, Canada), equipped with an ESI source
operated in the positive ion mode. HPLC separation was performed on an Agilent SB-AQ column
(150 × 4.6 mm, 5 μm, Agilent Technologies) maintained at 40 C using a mobile phase of methanol:10
mM ammonium acetate (85:15, v:v). Applied Biosystems/MDS SCIEX Analyst software (Version 1.3.2)
was used for data acquisition and processing. PK parameters were estimated by a non-compartmental
method using DAS 3.0 software package (Mathematical Pharmacology Professional Committee of China,
Shanghai, China).
3.5. Brain Uptake Studies in Rat
After a 12 h fast, rats were administered a single dose of 0.06 mmol/kg by oral gavage. At 0.25, 0.5,
1, 2, and 4 h after dosing, rats were sacrificed and perfused with 40 mL PBS through the left ventricle.
The brain was removed and the hypothalamus was dissected out. The hypothalamus and total brain
were then placed in 1 mL and 2 mL respectively of ice-cold methanol:water (1:1, v:v) and maintained
on ice until homogenization using a Tempest Virtishear tissue homogenizer (Virtis, Apache Junction,
AZ, USA) for about 45 s followed by sonication using a Heat Systems Ultrasonic sonicator for 1 min.

Molecules 2013, 18
14932
After centrifugation at 3,500 rpm for 5 min, the supernatant was separated and stored at −80 °C
until analysis.
3.6. PK Studies in Beagle Dog
Beagle dogs (10 ± 2 kg, n = 6) were obtained from the Chengdu Dashuo Biological Technology
Co., Ltd (Sichuan, China). After a 12 h fast, dogs were administered a single dose of 0.007 mmol/kg of
either compound 1n or ODV by oral gavage on two occasions separated by a one week washout
period. Blood samples (1 mL) were collected into heparinized Eppendorf tubes before dosing and at
0.083, 0.167, 0.33, 0.5, 0.75, 1.0, 1.5, 2.0, 3.0, 5.0, 7.0, 11.0 and 24.0 h after dosing. After centrifugation at
3500 rpm for 5 min, plasma was collected and 100 µL aliquots stored at −80 °C until analysis.
4. Conclusions
In this study, a series of 15 phenolic esters of ODV 1a–o were synthesized and their PK evaluated
in rat in comparison with ODV itself. The four compounds with the highest relative bioavailabilities
(compounds 1c, 1e, 1n, and 1o) were selected for brain uptake studies in rat in which compound 1n
exhibited the highest levels in both hypothalamus and total brain. Finally the PK of 1n was compared
with ODV in beagle dogs where it again demonstrated a relative bioavailability increase similar to that
in rat. On the basis of these results, the newly synthesized ODV piperonylic acid ester 1n is the most
promising candidate for development as an ODV prodrug.
Acknowledgments
This work was supported by the National Natural Science Foundation of China (Grant No.
30973587 and No. 81102383), the Science and Technology Major Specialized Projects for “Significant
New Drugs Creation” of the 12th five-year plan (2012ZX09303-015), the National Key Technology
R&D Program of the Ministry of Science and Technology (2012BAI30B00), and the Science and
Technology Program of Jilin Institute of Chemical Technology (Grant No. 201350).
Conflicts of Interest
The authors declare no conflict of interest.
References
1.
2.
Richards, D. Prevalence and clinical course of depression: A review. Clin. Psychol. Rev. 2011,
31, 1117–1125.
World Health Organization (WHO). Depression: A global public health concern; WHO: Geneva,
Switzerland, 2012; Available online: http://www.who.int/mental_health/management/depression/
who_paper_depression_wfmh_2012. pdf (accessed on 5 October 2012).
Andrews, J.M.; Ninan, P.T.; Nemeroff, C.B. Venlafaxine: A novel antidepressant that has a dual
mechanism of action. Depression 1996, 4, 48–56.
3.
4.
Makhija, S.N.; Vavia, P.R. Stability indicating LC method for the estimation of venlafaxine in
pharmaceutical formulations. J. Pharm. Biomed. Anal. 2002, 28, 1055–1059.

Molecules 2013, 18
14933
5.
6.
Preskorn, S. Pharmacotherapeutic profile of venlafaxine. Eur. Psychiatr. 1997, 12, 285s–294s.
Gutierrez, M.A.; Stimmel, G.L.; Aiso, J.Y. Venlafaxine: A 2003 update. Clin. Ther. 2003, 25,
2138–2154.
7.
8.
Ellingrod, V.L.; Perry, P.J. Venlafaxine: A heterocyclic antidepressant. Am. J. Hosp. Pharm.
1994, 51, 3033–3046.
Klamerus, K.J.; Maloney, K.; Rudolph, R.L.; Sisenwine, S.F.; Jusko, W.J.; Chiang, S.T.
Introduction of a composite parameter to the pharmacokinetics of venlafaxine and its active
O-desmethyl metabolite. J. Clin. Pharmacol. 1992, 32, 716–724.
Schweizer, E.; Thielen, R.J.; Frazer, A. Venlafaxine: A novel antidepressant compound. Expert
Opin. Investig. Drugs 1997, 6, 65–78.
9.
10. Perry, R.; Cassagnol, M. Desvenlafaxine: A new serotonin-norepinephrine reuptake inhibitor for
the treatment of adults with major depressive disorder. Clin. Ther. 2009, 31, 1374–1404.
11. Muth, E.A.; Haskins, J.T.; Moyer, J.A.; Husbands, G.E.; Nielsen, S.T.; Sigg, E.B. Antidepressant
biochemical profile of the novel bicyclic compound Wy-45030, an ethyl cyclohexanol
derivative. Biochem. Pharmacol. 1986, 35, 4493–4497.
12. Rudorfer, M.V.; Potter, W.Z. The role of metabolites of antidepressants in the treatment of
depression. CNS Drugs 1997, 7, 273–312.
13. Ereshefsky, L.; Dugan, D. Review of the pharmacokinetics, pharmacogenetics, and drug
interaction potential of antidepressants: Focus on venlafaxine. Depress. Anxiety 2000, 12, 30–44.
14. De Ruiter, J.; Holston, P.L. New Drug Review 2008. US Pharm. 2008, 33, 30–44.
15. Desvenlafaxine: Application withdrawal. Desvenlafaxine: Withdrawal of marketing application
for depression also. Prescrire Int. 2009, 18, 197.
16. Liebowitz, M.R.; Tourian, K.A.; Hwang, E.; Mele, L. A double-blind, randomized,
placebo-controlled study assessing the efficacy and tolerability of desvenlafaxine 10 and 50
mg/day in adult outpatients with major depressive disorder. BMC Psychiatry 2013, 13, 94–102.
17. Iwata, N.T.K.; Hwang, E.; Mele, L.; Vialet, C. Efficacy and safety of desvenlafaxine 25 and 50
mg/day in a randomized, placebo-controlled study of depressed outpatients. J. Psychiatr. Pract.
2013, 19, 5–14.
18. Kubo, S.H.; Cody, R.J. Clinical pharmacokinetics of the angiotensin converting enzyme
inhibitors. A review. Clin. Pharmacokinet. 1985, 10, 377–391.
19. Mizuno, N.; Niwa, T.; Yotsumoto, Y.; Sugiyama, Y. Impact of drug transporter studies on drug
discovery and development. Pharmacol. Rev. 2003, 55, 425–461.
20. Baudy, R.B.; Butera, J.A.; Abou-Gharbia, M.A.; Chen, H.; Harrison, B.; Jain, U.; Magolda, R.;
Sze, J.Y.; Brandt, M.R.; Cummons, T.A.; et al. Prodrugs of perzinfotel with improved oral
bioavailability. J. Med. Chem. 2009, 52, 771–778.
21. Xie, Q.; Wang, X.; Jiang, Z.; Qiu, Z. Design, synthesis, and bioavailability evaluation of
coumarin-based prodrug of meptazinol. Bioorg. Med. Chem. Lett. 2005, 15, 4953–4956.
22. Kahns, A.H.; Møss, J.; Bundgaard, H. Improved oral bioavailability of salicylamide in rabbits by
a 1,3-benzoxazine-2,4-dione prodrug. Int. J. Pharm.1992, 78, 199–202.
23. Horn, A.S.; Kelly, P.; Westerink, B.H.; Dijkstra, D. A prodrug of ADTN: Selectivity of
dopaminergic action and brain levels of ADTN. Eur. J. Pharmacol. 1979, 60, 95–99.

Molecules 2013, 18
14934
24. Bandgar, B.P.; Sarangdhar, R.J.; Viswakarma, S.; Ahamed, F.A. Synthesis and biological
evaluation of orally active prodrugs of indomethacin. J. Med. Chem. 2011, 54, 1191–1201.
25. De Graaf, M.; Nevalainen, T.J.; Scheeren, H.W.; Pinedo, H.M.; Haisma, H.J.; Boven, E. A
methylester of the glucuronide prodrug DOX-GA3 for improvement of tumor-selective
chemotherapy. Biochem. Pharmacol. 2004, 68, 2273–2281.
26. Tian, J.W.; Jiang, W.L.; Zhong, Y.; Meng, Q.; Gai, Y.; Zhu, H.B.; Hou, J.; Xing, Y.; Li, Y.X.
Preclinical pharmacology of TP1, a novel potent triple reuptake inhibitor with antidepressant
properties. Neuroscience 2011, 196, 124–130.
27. Ibáñez, E.; Plano, D.; Font, M.; Calvo, A.; Prior, C.; Palop, J.A.; Sanmartín , C. Synthesis and
antiproliferative activity of novel symmetrical alkylthio- and alkylseleno-imidocarbamates.
Eur. J .Med. Chem. 2011, 46, 265–274.
28. Zhang, L.P. Compounds, preparation process, and uses thereof used for interrupting reuptake of
5-hydroxytryptamine and norepinephrine or treating diseases such as depression et al. WO
Patent 2006133652, 21 December 2006.
29. Bhatt, J.; Jangid, A.; Venkatesh, G.; Subbaiah, G.; Singh, S. Liquid chromatography-tandem
mass spectrometry (LC-MS-MS) method for simultaneous determination of venlafaxine and its
active metabolite O-desmethyl venlafaxine in human plasma. J. Chromatogr. B Analyt. Technol.
Biomed. Life Sci. 2005, 829, 75–81.
30. Liu, W.; Cai, H.L.; Li, H.D. High performance liquid chromatography-electrospray ionization
mass spectrometry (HPLC-MS/ESI) method for simultaneous determination of venlafaxine and
its three metabolites in human plasma. J. Chromatogr. B Analyt. Technol. Biomed. Life Sci.
2007, 850, 405–411.
31. Rosendorff, C.; Cranston, W.I. Effects of intrahypothalamic and intraventricular norepinephrine
and 5-hydroxytryptamine on hypothalamic blood flow in the conscious rabbit. Circ. Res. 1971,
28, 492–502.
Sample Availability: Samples of the compounds 1a–o are available from the authors.
© 2013 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access article
distributed under the terms and conditions of the Creative Commons Attribution license
(http://creativecommons.org/licenses/by/3.0/).