Design, Synthesis, and Activity Study of Water-Soluble, Rapid-Release Propofol Prodrugs

Article abstract of DOI:10.1021/acs.jmedchem.0c00698

In this work, a series of water-soluble propofol prodrugs were synthesized, and their propofol release rate and pharmacodynamic characteristics were measured. We found that inserting glycolic acid as a linker between propofol and the cyclic amino acid accelerated the release of propofol from prodrugs into the plasma while preserving its safety. In animal experiments, prodrugs (3e, 3g, and 3j) were significantly better than fospropofol (the only water-soluble propofol prodrug that has been used clinically) in terms of safety, onset, and duration time of anesthesia. Their molar dose, onset time, and anesthesia duration time were comparable to those of propofol, helping to maintain the clinical benefits of propofol. The experimental results showed the potential of such compounds as water-soluble prodrugs of propofol.

Full text of DOI:10.1021/acs.jmedchem.0c00698

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Article
Design, Synthesis and Activity Study of a
Water-soluble, Rapid-release Propofol Prodrug
Liangquan Liu, Peixi Hong, Xinghai Song, Changcui Zhou, Rui Ling, Yi Kang, Qingrong Qi, and Jun Yang
J. Med. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jmedchem.0c00698 • Publication Date (Web): 26 Jun 2020
Downloaded from pubs.acs.org on June 27, 2020
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Design, Synthesis and Activity Study of a Water-soluble, Rapid-release
Propofol Prodrug
Liang-Quan Liu#，1，2, Pei-Xi Hong#，1, Xing-Hai Song1, Chang-cui Zhou1, Rui Ling1, Yi Kang1, Qing-
Rong Qi*，2, Jun Yang*，1
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1 Laboratory of Anesthesia and Critical Care Medicine, Translational Neuroscience Center, Department of
Anesthesiology, Sichuan University West China Hospital, Sichuan University, Chengdu, 610041, China
2 Key Laboratory of Drug-Targeting and Drug Delivery System of the Education Ministry, Sichuan Engineering
Laboratory for Plant-Sourced Drug and Sichuan Research Center for Drug Industrial Technology, Sichuan Research
Center of Precision Engineering Technology for Small Molecule Drugs, West China School of Pharmacy Sichuan
University, Chengdu, 610041, China
#: Contributed equally to this work.
*: Corresponding authors. Jun Yang, E-mail address: yang215jun@163.com; Qing-Rong Qi, E-mail address:
qiqinrong@scu.edu.cn;
O
X
X=CH2 or O
O
N
O
O
OH
HCl
plasma
1 min
Therapeutic index >4
Propofol intake: 22~25 mg/kg
Duration of anesthesia: 5.5~7.3 min
~100% decomposition
in mice
O
P
ONa
ONa
O
plasma
OH
O
Therapeutic index <3
Propofol intake:112 mg/kg
Duration of anesthesia: 44.8 min
2 hours
~40% decomposition
In vitro
In vivo (2XED50
)
ABSTRACT: In this work, a series of water-soluble propofol prodrugs were synthesized, and their propofol release rate and
pharmacodynamic characteristics were measured. We found that inserting glycolic acid as a linker between propofol and
the cyclic amino acid accelerated the release of propofol from prodrugs into plasma while preserving safety. In animal
experiments, prodrugs (3e, 3g, 3j) were significantly better than fospropofol (the only water-soluble propofol prodrug that
has been used clinically) in terms of safety, onset and duration time of anesthesia. Their molar dose, onset time and
anesthesia duration time were comparable to those of propofol, helping to maintain the clinical benefits of propofol. The
experimental results showed the potential of such compounds as water-soluble prodrugs of propofol.
INTRODUCTION
Propofol is a mainstream intravenous general anesthesia
drug in clinical practice; its most popular clinical
pharmacological characteristics are fast onset and rapid
recovery after withdrawal.1 However, propofol is difficult to
dissolve in water. To meet the requirements of intravenous
administration, a variety of formulations have been used to
increase the solubility of propofol,2-5 and fat emulsion is
widely used in clinical practice today.6 Some emulsion-
related disadvantages do arise, such as pain at injection,7
bacterial contamination,8 propofol infusion syndrome,9 and
fat overload syndrome.10 Therefore, how to improve the
water solubility of propofol has been a hot spot in drug
development, and water-soluble prodrugs are the most
promising approach. The goal of propofol prodrug was not
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only to increase the water solubility but also to maximize
the advantages of rapid onset and rapid recovery after
withdrawal, which has increased the difficulty in
development. It takes a certain amount of time for propofol
prodrug to release the prototype drug in the body,11 and this
process can lead to a slower onset of propofol prodrug;12 the
continuous release of the remaining prodrug may cause the
drug to fade slowly after withdrawal.
12.85,15 165.4 and 82.1515 mg/kg, and the amounts of
propofol released from prodrugs at 2×ED50 were 25.7, 195.1
and 88.1 mg/kg, respectively. The anesthesia duration
times for these three drugs at 2×ED50 were 5.6±1.314,
86.3±32.414 and 39.5±9.615 min, respectively. Obviously, PP
and fospropofol ‘carry’ too much propofol. Propofol
prodrug remaining in the body continues to release
propofol, resulting in delayed wake-up and slow recovery.
In our previous reports,18 we emphasized that the
decomposition rate of propofol prodrugs and the molecular
utilization of propofol were the keys to the development of
propofol prodrugs. For developing more advantageous
propofol prodrug, four series of prodrugs (C-series, X-
series, N-series and O-series) were synthesized and
tested in this research. (Figure 1)
9
A large number of water-soluble structural fragments
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have been introduced into the design of propofol prodrugs,
15
such as amino acids,13 phosphates,14,
sugars,16 and
polyethylene glycols17. However, due to the huge steric
hindrance of the isopropyl group of propofol, most of these
prodrugs cannot release propofol quickly and completely in
vivo. For instance, the ED50 values of propofol, propofol
phosphate (PP) and fospropofol in mice for anesthesia were
ONa
O
O
O
O
O
O
O
ONa
ONa
O
ONa
O
ONa
O
O
O
O
ONa
O
O
O
C-series compounds
O
O
1a
1b
1
c
1d
O
O
O
O
O
O
O
O
H
O
O
S
N
O
O
ONa
ONa
O
ONa
O
OH
O
ONa
HCl
X-series compounds
-O
HX0921
2a
2b
2c
O
O
O
O
O
O
O
O
O
N
H
O
NH2
HCl
O
N
O
NH2
HCl
HCl
O
O
O
O
HCl
N-series compounds
3c
3d
3a
3b
O
HN
O
O
O
HCl
HCl
HCl
N
O
O
O
O
O
O
O
N
O
N
O
HCl
O
O
O
N
O
O
3f
3g
3h
3e
O
O
HCl
N
O
O
O
O
N
H
HCl
O
O
3j
3i
O
O
O
O
O
O
O
OH
N
O
ONa
O
O
O
O
ONa
O-series compounds
O
O
O
GP
4a
4b
Ref-21
Figure 1. Chemical structures of prodrugs and important intermediate GP.
RESULTS AND DISCUSSION
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hydroxypropionate, reacted with compound 1 to yield 4-7,
which were treated with 10% Pd/C in an H2 atmosphere at
room temperature to obtain 8-11. These intermediates
were treated with a saturated aqueous solution of NaHCO3
to generate the target products 1a-1d.
We conducted our experiment by following well-
established methods for propofol prodrugs 15, 18. First, we
tested the stability of prodrugs in water before the
hydrolysis studies in plasma. The results suggested that 1a-
1d were relative stable in water (Supporting Information,
Table S1).
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13
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Subsequently, the hydrolysis studies in plasma showed
that 1c and 1d did not decompose, and the release rate of
propofol from 1a and 1b only reached 9.79±1.33% and
15.75±1.31%, respectively (Figure 2 and Supporting
Information, Table S2). The results suggested that the
propofol release rate of C-series prodrugs was not rapid.
Eventually, the safety and efficacy of prodrugs in mice were
determined, and the in vivo data are shown in Table 1. Even
if C-series prodrugs were administered at ten times the
effective molar amount of propofol per animal, they were
not able to produce anesthesia; no higher doses were given
for testing. The hydrolysis studies in plasma and the
pharmacodynamic studies in mice were mutually
confirmed. The invalidation of C-series compounds may be
caused by steric hindrance, which blocks the hydrolysis of
carbonates by hydrolase.
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Figure 2. Percentages of propofol released from C-series
compounds into mouse plasma.
C-series compounds design and evaluation. To obtain
a fast-release water-soluble prodrug in vivo, we introduced
a carbonate group that is theoretically easily attacked by
hydrolase19 into the propofol derivative and then coupled it
with hydroxy carboxylic acid to obtain the C-series of
compounds (1a-1d).
The synthetic route of the C-series compounds is
illustrated in Scheme 1. Compound 1 was prepared by
reaction of propofol and triphosgene in dichloromethane.
Then, compounds 2 and 3, benzyl glycolate and benzyl 3-
Scheme 1. Synthetic Route to C-series Compounds
O
O
O
ONa
OH
OBn
c
d
O
O
n1
O
O
n1
O
O
n1
O
O
O
O
O
4 (n1=1)
5 (n1=2)
8
9
1a
1b
(n1=1)
(n1=2)
(n1=1)
(n1=2)
O
Cl
b
OH
a
O
O
n1
n1
OH
ONa
O
n1
OBn
O
O
O
d
c
O
O
O
O
O
OH
O
ONa
1
O
Propofol
O
O
O
OBn
BnO
BnO
OBn
OH
2
6 (n1=0)
7 (n1=1)
10 (n1=0)
11 (n1=1)
1c (n1=0)
1d (n1=1)
O
OBn
OH
O
3
Conditions and reagents: (a) triphosgene, Et3N, dichloromethane, -5°C and rt, overnight; (b) 2 or 3 or benzyl glycolate or benzyl 3-
hydroxypropionate, pyridine, dichloromethane, -5°C and rt, overnight; (c) 10%Pd/C, H2, CH3OH, rt, 4 h; (d) NaHCO3, H2O, rt.
Scheme 2. Synthetic Route to 2a
O
O
O
O
O
O
O
O
O
O
c
a
b
O
O
BnO
O
BnO
OH
BnO
O
OBn
BnO
OBn
N2
OBn
13
OBn
14
12
O
O
O
O
O
e
O
O
O
O
O
f
d
O
OBn
O
OH
O
ONa
ONa
OBn
OH
O
15
16
2a
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Conditions and reagents: (a) TsN3, Et3N, MeCN, 0 to 25°C, 1 h; (b) tert-butyl 2-hydroxyacetate, Rh2(OAc)4, toluene, 85°C, 3 h; (c) TFA,
20°C, 1 h; (d) propofol, Et3N, HATU, dichloromethane, 20 °C, 12 h; (e) Pd/C, H2, ethyl acetate, 25°C, 2 h; (f) Na2CO3, H2O, 0~20°C.
Scheme 3. Synthetic Route to 2b
O
O
O
O
S
S
O
O
S
O
a
OH
O
OH
O
ONa
b
+
8
17
2b
9
Conditions and reagents: (a) Et3N, DMAP, dichloromethane, rt, 8 h; (b) NaHCO3, H2O, 0 to 20°C.
significantly shorter than that of fospropofol. In this study,
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we designed the X-series of compounds with O (2a), S (2b),
and N (2c) at the α-positions of the esters, with the hope of
obtaining prodrugs with high molecular utilization and
short anesthesia duration time. Among them, disodium salt
was introduced in 2a to improve the solubility of HX0921,
and α-O was replaced by S (2b) and N (2c) to investigate the
influence of heteroatoms. The synthetic route of 2a is
illustrated in Scheme 2. TsN3 was used to replace the active
hydrogen of dibenzyl malonate to obtain compound 12.
Then, tert-butyl 2-hydroxyacetate and compound 12
underwent nucleophilic substitution to obtain compound
13. The Boc group of compound 13 was cleaved in the
presence of TFA to yield compound 14. Compound 14 was
condensed with propofol to obtain compound 15, and
compound 15 was then transformed to compound 16 by
catalyzed hydrogenation. Eventually, compound 16 reacted
with Na2CO3 to obtain 2a. The synthetic route of 2b is
illustrated in Scheme 3. Propofol reacted with
thiodiglycolic anhydride to form 17, and compound 17
reacted with NaHCO3 to obtain 2b. The synthetic route of 2c
is illustrated in Scheme 4. Propofol was condensed with N-
boc-iminodiacetic acid to obtain compound 18, and this
intermediate was then treated with HCl gas in ethyl acetate
to yield 2c.
Figure 3. Percentages of propofol released from X-series
compounds in mouse plasma.
Figure 3 and Table 1 showed that 2a did not decompose
in plasma in 2 h or produce anesthesia in mice. This result
may be caused by the large steric hindrance of the isopropyl
group and sodium carboxylates. Compound 2b did not
completely breakdown in plasma within the 2 h test time,
and the ED50 of 2b was 189.8 mg/kg. The dose of propofol
carried by 2b was 203.64 mg/kg at 2×ED50, which was much
higher than that of propofol at 2×ED50 (23.4 mg/kg). The
result suggested that the release of propofol from 2b in vivo
was extremely slow. In addition, the TI of 2b was only 1.17,
and the testing of 2×ED50 caused death in all mice due to
acute respiratory depression. Only 2c completely broke
down in plasma within the 2-h test time, and the release rate
of propofol was slightly slower than that of HX0921.
However, due to the insufficient water-solubility of 2c (<10
mg/ml), we have not conducted any animal experiments on
it.
Figure 4. Percentages of propofol released from N-series
compounds, O-series compounds and fospropofol in mouse
plasma.
X-series compounds design and evaluation. X-series
compounds are modified on the basis of the structure of
HX0921 (Figure 1). HX0921 is a propofol ester derivative
with α-O from our previous research.18
In an in vitro experiment, HX0921 decomposed
significantly faster in mouse plasma than fospropofol
(Supporting Information, Table S2), which suggested that
the introduction of heteroatoms in the α position of the
ester might accelerate the decomposition in vivo. In the in
vivo experiments, the propofol dose released from HX0921
at 2×ED50 was 74.0 mg/kg, which was lower than that from
fospropofol (112.7 mg/kg). The result suggested that the
propofol molecular utilization of HX0921 was higher than
that of fospropofol, but the LD50 of HX0921 was not tested
due to the insufficient water solubility, as shown in Table 1.
In addition, the anesthesia duration time of HX0921 was
Design and evaluation of N- and O-series compounds.
Due to the effects of electron deficiency, the hydroxyl group
at the alpha position of the carboxyl group was theoretically
easy to hydrolyze after forming an ester. There is evidence
that compounds with glycolic acid ester hydrolyzed at a
faster rate.20 Therefore, glycolic acid was also selected as a
linker between propofol and the water-soluble group. We
first confirmed that the glycolate derivative of propofol
(GP) was able to release all of the propofol in plasma in 1
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min; however, GP could not be used in the in vivo
obtained by coupling GP with an amino acid, and the sodium
2
experiment due to poor water solubility. Therefore, it is
feasible to use GP as a lead compound of a water-soluble
propofol prodrug. The synthetic route of GP is illustrated in
Scheme 5. Propofol reacted with benzyloxyacetyl chloride
to form ester 19. Then, 19 was treated with Pd/C in the
atmosphere of H2 to obtain compound GP. Two types of
water-soluble derivative of GP were prepared: the
hydrochloride derivative (N-series compounds) was
salt derivative (O-series prodrugs) was obtained by
coupling GP with a polybasic acid ester. The synthetic route
of N-series compounds is illustrated in Scheme 6.
Compound 20 was prepared by reaction of propofol and
chloroacetic chloride in dichloromethane. Then, a series of
amino acetic acids (21-30) were reacted with compound 20
to yield 31-40, which were then treated with HCl in ethyl
acetate to yield 3a-3j.
3
4
5
6
7
8
9
10
11
12
13
14
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16
17
18
19
20
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Scheme 4. Synthetic Route to 2c
O
Boc
N
O
O
O
H
N
OH
a
b
HO
OH
O
OH
O
O
+
N
H
HCl
O
Boc O
2c
18
Conditions and reagents: (a) DIC, DMAP, DMF, rt, 12 h; (b) HCl, ethyl acetate, rt, 8 h.
Scheme 5. Synthetic Route to Compound GP
O
O
OH
O
O
O
a
OH
b
O
O
+
Cl
19
GP
Conditions and reagents: (a) pyridine, dichloromethane, -10°C to rt, 12 h; (b) Pd/C, H2, ethyl acetate, rt, 72 h.
Scheme 6. Synthetic Route to N-series Compounds
O
O
O
O
O
R2
HO
R1
O
O
R1
Cl
O
c
21~30
O
O
OH
a
O
b
3a~3j
31~40
20
Propofol
R1
R2
HCl
N
N
N
NH
Boc
Boc
2 HCl 3f
N
3a
3b
N
N
N
H
N
H
21
22
26
31
36
37
N
N
N
N
27
28
N
N
32
33
3g
HCl
HCl
HCl
H
N
Boc
Boc
N
Boc
Boc
Boc
Boc
N
N
23
24
N
N
3h
3c
38
39
HCl
H
O
O
O
H
N
Boc
Boc
34
35
29
30
N
N
3i
3j
HCl
HCl
3d
3e
HCl
O
N
N
NH2
N
H
H
N
N
25
40
N
N
N
O
O
HCl
Conditions and reagents: (a) chloroacetyl chloride, pyridine, dichloromethane, -5°C and rt, overnight; (b) 21-30, K2CO3, NaI, DMF,
70°C, 4 h; (c) HCl, ethyl acetate, rt, 4-12 h.
Scheme 7. Synthetic Route to O-series Compounds
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3
O
Cl
O
O
O
O
O
R2
O
R3
O
O
O
R1
4
5
6
a
O
b
c
O
O
O
20
O
7
8
9
HO
R1
43, 44
45, 46
R2
4a, 4b
41, 42
R1
R1
R3
10
11
12
13
14
15
16
17
18
19
20
21
22
23
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OH
ONa
OBn
45
46
4a
OBn
43
44
41
42
O
O
O
O
O
O
O
O
4b
OH
OBn
ONa
OBn
Conditions and reagents: (a) 40 or 41, K2CO3, NaI, DMF, 70°C, 4 h; (b) 10% Pd/C, H2, ethyl acetate, rt, 4 h; (c) Na2CO3, H2O, 0°C to rt.
Table 1. Pharmacodynamic Characteristics in Mice.
a
One bolus
Propofol
Dose
from
Drug
ED50(mg/kg)
LD50(mg/kg)
TI
Survival
rate
Duration time
c
Onset time (s)
b
d
(min)
Prodrug
e
(mg/kg)
ND
1a
1b
1c
1d
2a
2b
3a
3b
3c
3d
3e
3f
3g
3h
3i
3j
4a
*
*
*
*
ND
ND
ND
ND
ND
ND
ND
ND
ND
1.2
2.6
2.3
2.0
2.5
4.7
2.3
3.6
2.3
2.6
4.1
2.8
3.2
ND
2.8
4.5
2.1
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
*
ND
ND
189.8±19.9
34.3±5.3
40.2±3.6
29.6±5.5
20.5±3.1
28.1±2.7
40.3±4.0
25.2±2.5
30.4±3.2
20.8±2.2
22.3±2.0
73.1±7.6
75.9±7.9
65.7±8.5
105.0±10.5
11.7±1.2
36.6±3.8
222.0±35.3
89.2±8.9
93.8±8.9
60.8±6.4
51.9±8.8
131.7±26.0
91.6±26.5
92.1±11.8
69.6±6.3
54.4±6.2
91.4±9.5
205.1±19.4
243.8±25.2
NT
20.2±7.1
9.1±1.6
4.6±1.0
8.0±1.7
18.2±5.7
3.1±1.8
2.4±0.5
4.0±0.8
6.7±1.9
10.6±3.0
3.0±0.8
25.5±8.0
72.2±6.1
82.3±8.0
46.4±6.0
1.0±0.7
12.0±1.8
0%
-
-
203.6
37.1
40.1
30.7
21.2
25.1
34.8
23.4
28.1
19.3
22.0
75.7
76.0
74.0
112.7
23.4
42.7
10%
40%
60%
50%
100%
70%
100%
60%
20%
100%
80%
100%
100%
100%
100%
30%
13.9±18.6
13.5±14.6
7.1±3.8
5.5±0.9
10.6±4.3
7.3±4.6
12.5±3.2
-
6.4±1.7
39.6±13.0
42.6±10.5
19.7±8.7
44.8±7.6
4.6±0.7
9.0±6.5
4b
HX0921
Fospropofol
Propofol
Ref-21
288.5±26.7
52.2±4.7
75.0±7.1
(a) The dose for one bolus was 2×ED50 of each drug; (b) survival rate of mice at 2×ED50 (10 mice); (c) time from the end of injection
to the appearance of LORR; (d) time from the appearance of LORR to the recovery of LORR; (e) propofol released from prodrugs at
2×ED50; Propofol Dose from Prodrugs = (Molecular Weight Propofol/Molecular Weight Prodrug)×(2×ED50) mg/kg.
*: prodrugs did not produce anesthesia at ten times the effective molar dose of propofol; -: no statistics; ND means not detected; NT
means that the LD50 could not be tested in mice due to the inadequate water-solubility of HX0921 (<20 mg/mL).
The synthetic route of O-series compounds is illustrated
in Scheme 7. A series of monobenzyl-protected carboxylic
acids (41 and 42) reacted with compound 20 to yield 43
and 44, which were then treated with 10% Pd/C in the
presence of H2 at room temperature to obtain 45 and 46.
These intermediates were treated with a saturated aqueous
solution of Na2CO3 to produce the target products 4a and
4b.
plasma was much faster than from C, X-series prodrugs and
fospropofol, while O-series compounds were not able to
release propofol rapidly (Figure
Information, Table S2). These results suggested that N-
series compounds might rapidly release propofol in vivo.
4 and Supporting
As expected, all the N-series compounds had an improved
ED50 compared to C, X, O-series prodrugs and fospropofol
with rapid onset in animals, and the doses of propofol
carried by some prodrugs were close to that of propofol at
2×ED50. However, the safety of N- series compounds varied
The result of the plasma decomposition test showed that
the release rate of propofol from N-series prodrugs in
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greatly depending on the amino acid selected. When some
improved. Meanwhile, the pH values of the prodrugs (3e, 3g,
2
simple natural amino acids or N-alkylated natural amino
acids were selected as water-soluble fragments, the
compounds often showed great toxicity (TI <3), and some
of the animals had already died at 2×ED50. For 3a, 3b, 3c,
3d, 3f, 3h, and 3i, the TI was less than 3. High percentages
of animals injected with them died due to respiratory
depression at 2×ED50, with obvious respiratory slowing or
apnea accompanied by cyanosis of the limbs and lips;
however, no autopsy was performed to analyze other
possible causes of death. When some unnatural amino acids
such as cyclic morpholine acetic acid and piperidine acetic
acid were introduced into the molecules as water-soluble
fragments, the safety of propofol prodrug molecules was
significantly improved. The therapeutic index of these
compounds was similar to propofol (TI was close to or
greater than 4). As shown in Table 1, the TI values of
propofol, 3e, 3g, 3j and fospropofol were 4.5, 4.7, 3.6, 4.1
and 2.8, respectively. The survival rates of animals in the 3e,
3g and 3j groups at 2×ED50 were all 100%.
3j) were close to the pH values of common intravenous
anesthesia medicines, such as midazolam (2.9 ~ 3.7),
cistracurium (3.25 ~ 3.65) and naloxone (3.0 ~ 4.0), etc.,
which can be used for intravenous infusion.22 Hence,
prodrugs (3e, 3g, 3j) were considered to be acceptable for
intravenous injection or infusion.
3
4
5
6
7
8
9
Table 2. The pH and Solubility of 3e, 3g, 3j
Solubility
(g/100 mL in water)
pH
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18
19
20
21
22
23
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59
60
Compound
10 mg/mL in Saline
3e
3g
3j
76.33
83.96
85.86
3.00~3.06
4.24~4.26
4.11~4.15
CONCLUSION
General anesthetics suppress most of the body's
protective reflexes (such as breathing, circulation), and
general anesthesia is a very dangerous medical activity that
requires the responsibility of professional anesthesiologist.
The status of general anesthesia should be as short as
possible in nonessential medical procedures. Therefore, the
decrease in the safety of propofol prodrugs or the extension
of the duration of anesthesia cannot be accepted clinically.
To retain the clinical advantages of propofol, prodrugs
should be as safe and as effective as propofol. Molar dose,
onset time, anesthesia duration time and safety should be
comparable. We present some newly synthesized water-
soluble prodrugs of propofol in this research. Among them,
N and O series compounds were designed based on GP,
which was found to be very sensitive to plasma. Due to the
poor water solubility of GP, we introduced the most
common amino acid and poly-acid fragments into the
structure of GP to render the molecule water-soluble. It was
found that GP's polycarboxylic acid derivatives (4a, 4b) did
not retain the sensitivity to plasma, and the introduction of
some amino acid fragments increased the toxicity of GP
derivatives (3a, 3b, 3c, 3d, 3f, 3h, 3i), interestingly, the
introduction of certain unnatural cyclic amino acids into GP
derivatives not only retained the plasma sensitivity but also
had good safety (3e, 3g, 3j); these three compounds could
release almost all propofol that they carried into the plasma
within tens of seconds. Further, the onset time and
anesthesia duration time of 3e, 3g and 3j were similar to
those of propofol, while minimizing the intake of propofol
and preserving drug safety. The in vivo investigations
demonstrated that 3e, 3g and 3j may maximize the clinical
benefits of propofol. C series, X series and O series
compounds were not able to produce rapid and short-acting
anesthesia due to their slow release rate of propofol.
In pharmacodynamic studies, we confirmed that the
onset times of 3e, 3g and 3j were very close to that of
propofol. These prodrugs produced anesthesia immediately
after administration. The molecular weights of 3e, 3g, 3j
and fospropofol were 399.91, 383.91, 397.94 and 332.24
g/mol, respectively; therefore, the propofol doses carried
by the four prodrugs at 2×ED50 were 25.1, 23.4, 22.0 and
112.7 mg/kg, respectively. The propofol doses carried by
3e, 3g, 3j were similar to that of propofol (23.4 mg/kg at
2×ED50), and much smaller than that of fospropofol. These
results suggested that the utilization of propofol carried by
these prodrugs was close to 100%. Because there was no
excess propofol ingested, no significant differences in the
duration time of anesthesia between 3e, 3g, 3j and the
propofol group were observed (P>0.05).
If an unnatural amino acid was directly coupled to
propofol without inserting glycolic acid, such as compound
Ref-21 (Figure 1),21 the safety of propofol prodrug
decreased. Ref-21 could completely release propofol in
plasma within 10 min, and the onset time was 12.00±1.80 s
after injection. These results indicated that Ref-21 retained
plasma sensitivity and rapid decomposition ability, but its
toxicity was unacceptable, and the therapeutic index was
low (TI =2.0), the animal mortality was 70% at 2×ED50.
Finally, we found that the position of the carboxyl group of
the cyclic amino acid also had a large impact on the safety of
propofol prodrug. As shown in Table 1, the conjugate of
morpholine-3-carboxylic acid and GP (3h) was unsafe, but
the conjugate of 2-morpholinoacetic acid and GP (3e) had
relatively low toxicity. Compound 3i, the conjugate of 2-
piperidylacetic acid and GP, was not safe since the survival
rate in the 3i group was only 20% at 2×ED50. However, 3j,
the conjugate of 3-piperidineacetic acid and GP, showed
relatively good safety, with a TI=4.1 and a survival rate of
100% at 2×ED50.
In summary, propofol + glycolic acid + cyclic amino acids
might generate a key structural feature to aid in the
development of a safe, water-soluble, fast-release propofol
prodrug with high utilization of propofol molecules. Such a
compound may help to overcome the bottleneck in the
development of water-soluble prodrugs of propofol. The
performance of the compounds with the above structural
characteristics needs further study in large animals or
humans. In addition, which type of hydrolase promoted the
In addition, we tested the solubility in water and the pH
in saline solution of the preferred prodrugs (3e, 3g, 3j),
with the results shown in Table 2. Compared with the
solubility of propofol (1.53×10-2 g/100 mL),13 the
solubilities of the prodrugs (3e, 3g, 3j) were greatly
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2
3
rapid decomposition of the above prodrugs was not
confirmed, which was a limitation of this study.
during the daytime, and mice were allocated randomly into
each group.
4
5
6
7
8
9
Pharmacodynamic characteristics in mice. Ten drug-
naïve healthy KM mice (male, 20-30 g) were prepared for
pharmacodynamic testing for each drug. Equivalent doses
(2×ED50) for each drug were injected through the tail vein,
and the onset and duration times of anesthesia and survival
rate were recorded.
EXPERIMENTAL SECTION
General. All chemicals and Diprivan (Propofol injection)
were commercially obtained and used without further
purification unless otherwise specified. Column
chromatography was carried out using silica gel (200−300
mesh). The purities of all the tested prodrugs in vivo are
>95% as determined by HPLC (Supporting Information,
Table S3 and Figure S1 to Figure S20).
Statistical analyses. Data were analyzed by the Dixon–
Mood method to derive the median effective dose with a 95%
confidence interval (CIs). Data for the stability of
metabolites in prodrugs and fospropofol in vitro are given
as the mean ± SD, and n denotes the number of experiments
in each group. The significant difference was applied for
comparison of the duration time of anesthesia for in vivo
tests. P < 0.05 was considered significant. Analyses were
carried out using SPSS v21 (IBM, Armonk, NY, USA). Figure
preparation and curve fits were undertaken using Origin 9.0
(Origin Laboratories, Northampton, MA, USA).
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11
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20
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41
42
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44
45
46
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50
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60
In vitro and in vivo experiments. The study protocol
was approved by the Scientific Research Committee and
Animal Experimental Ethics Committee of West China
Hospital (Sichuan University, Chengdu, China). The animals
were cared for in accordance with the Guide for the Care
and Use of Laboratory Animals. Adult Kunming (KM) mice
were purchased from Chengdu Dassy Biological Technology
Co., Ltd. (Chengdu, China). They were housed in the Animal
Experimental Center of West China Hospital, Sichuan
University, at an ambient temperature of 25 ± 1 °C, with
controlled humidity of 60% and a 12-h light–dark cycle (7
am to 7 pm). All mice had access to water and food ad
General procedure for the synthesis of C-series
compounds. Triphosgene (15 mmol) was dissolved in dry
dichloromethane (50 mL) and stirred at -10°C, followed by
addition of the mixture of propofol (30 mmol) and Et3N (40
mmol) drop by drop (reaction temperature not exceeding 5
°C). After dropping, the mixture was allowed to slowly
warm to room temperature and was then stirred for 8 h to
libitum. Mice were acclimatized for
experimentation.
1 week before
obtain compound 1.
A dichloromethane solution of
Plasma decomposition experiment in vitro. Solutions
of prodrugs (10 mg/ml) and fospropofol (10 mg/ml) in
water were prepared. The stability of prodrugs and
fospropofol in water was respectively determined at 30 °C
for 4 h before the hydrolysis studies in plasma (n=3). The
results are shown in the Supporting Information.
compound 1 (3 mmol) and alcohol compounds (3 mmol)
was stirred at -10°C, followed by dropwise addition of
pyridine (7.5 mmol) to obtain 4-7. Then, compounds 4-7
were treated with 10% Pd/C at room temperature and
atmospheric pressure (H2 balloon) for 4 h to obtain 8-11.
Last, the intermediates 8-11 (1 mmol) were reacted with a
saturated aqueous solution of NaHCO3 (1 mmol) in an ice
bath, and the reaction solution was lyophilized to dryness,
yielding a white solid.
Plasma was sampled from drug-naïve healthy Kunming
(KM) mice (15 mice for each drug, 20-30 g, male) for each
drug. The blood samples were mixed with heparin
immediately after sampling. Then, the whole blood was
centrifuged at 3500×g for 5 min at 4 °C to obtain plasma.
Subsequently, 10 μl of prodrugs (10 mg/ml) or fospropofol
(10 mg/ml) was added to mouse plasma (990 μl), and the
mixture (1 ml, 100 μg/ml) was shaken at 37°C for 2 h. The
samples (50 μl) withdrawn from the mixture were added to
150 μl of acetonitrile to deproteinize the plasma at 0.25, 0.5,
1, 2, 5, 10, 15, 20, 30, 40, 60, and 120 min. Propofol was
detected by isocratic elution chromatography using thymol
as the internal standard. The hydrolysis data are provided
in Supporting Information Table S2.
Sodium2-(((2,6-diisopropylphenoxy)carbonyl)oxy)acetate
(1a). The title compound was synthesized according to the
general procedure with compound 1 (3 mmol) and benzyl
1
glycolate (3 mmol). H NMR (400 MHz, D2O) δ 7.29 –
7.21 (m, 3H), 4.51 (s, 2H), 3.05 – 2.96 (m, 2H), 1.10
(d, J = 6.8 Hz 12H) ppm. 13C NMR (150 MHz, D2O) δ
174.02, 154.95, 144.92, 140.89, 127.53, 124.39, 66.38,
+
26.79, 22.49 ppm. HRMS calcd for C15H19Na2O5 (M+Na) ,
325.1028; found, 325.1029.
Sodium
3-(((2,6-
diisopropylphenoxy)carbonyl)oxy)propanoate (1b). The title
compound was synthesized according to the general
procedure with compound 1 (3 mmol) and benzyl 3-
hydroxypropionate (3 mmol).1H NMR (400 MHz, DMSO-
d6) δ 7.26 – 7.18 (m, 3H), 4.34 (t, J = 7.2 Hz, 2H), 2.
97 – 2.87 (m, 2H), 2.29 (t, J = 7.2 Hz, 2H), 1.14 (d, J
= 6.8 Hz, 12H) ppm. 13C NMR (100 MHz, D2O) δ 178.38,
Animal experiments
Determination of ED50 and LD50 in mice. Experiments
were performed to determine the median effective doses
(ED50), lethal doses (LD50) and therapeutic index (TI) of
propofol prodrugs, fospropofol and Diprivan. Before
injection, the animals were weighed and placed in a
restraint. Drugs were given via tail vein injection. The
injection took ~10 s, and ED50 and LD50 were measured by
the up and down method.23 At least 20 drug-naïve healthy
KM mice (male, 20-30 g) were prepared for the test of ED50
or LD50 for each drug. Water and food were provided ad
libitum. All experimental procedures were undertaken
154.88, 145.10, 140.85, 127.49, 124.48, 66.89, 36.47, 27.09,
+
22.59 ppm. HRMS calcd for C16H21Na2O5 (M+Na)
339.1184; found, 339.1180.
,
Sodium
2-(((2,6-
diisopropylphenoxy)carbonyl)oxy)malonate (1c). The title
compound was synthesized according to the general
procedure with compound 1 (3 mmol) and compound 2 (3
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Journal of Medicinal Chemistry
mmol). 1H NMR (400 MHz, D2O) δ 7.30 – 7.09 (m, 3H),
7.28 – 7.21 (m, 3H), 5.31 (s, 2H), 4.17 (s, 2H), 2.97 –
2
3
4
5
6
7
5.30 (s, 1H), 3.03 – 2.94 (m, J = 6.8 Hz, 2H), 1.10 (
d, J = 6.8 Hz, 12H) ppm. 13C NMR (100 MHz, D2O) δ
169.51, 153.99, 144.80, 140.93, 127.84, 124.60, 76.93,
26.81, 22.46 ppm. HRMS calcd for C16H18Na3O7 (M+Na) ,
391.0746; found, 391.0748.
2.87 (m, 2H), 2.59 (s, 3H), 1.13 (d, J = 6.8 Hz, 12H)
ppm. 13C NMR (100 MHz, D2O) δ 169.01, 166.72, 143.93,
140.73, 127.92, 124.67, 61.79, 48.35, 32.84, 27.06, 22.88,
+
+
21.93 ppm. HRMS calcd for C17H26NO4 (M+H) , 308.1862;
found, 308.1860.
Sodium
2-(((2,6-
(S)-2-(2,6-Diisopropylphenoxy)-2-oxoethyl 2-aminopropa-
noate hydrochloride (3d). The title compound was
synthesized according to the general procedure with
compound 20 (5 mmol) and N-(tert-butoxycarbonyl)-L-
8
9
diisopropylphenoxy)carbonyl)oxy)succinate (1d). The title
compound was synthesized according to the general
procedure with compound 1 (3 mmol) and compound 3 (3
mmol). 1H NMR (400 MHz, D2O) δ 7.28 – 7.20 (m, 3H),
5.05 (dd, J = 11.4, 2.6 Hz, 1H), 3.03 – 2.99 (m, 2H),
2.72 (dd, J = 15.8, 2.6 Hz, 1H), 2.54 (dd, J = 15.8, 11.4
Hz, 1H), 1.09 (t, J = 6.8 Hz, 12H) ppm. 13C NMR (100
MHz, D2O) δ 177.88, 176.12, 154.68, 145.07, 141.22, 127.73,
124.60, 77.77, 39.74, 22.65 ppm. HRMS calcd for
C17H20Na3O7 (M+Na) +, 405.0902; found, 405.0903.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
1
alanine (5 mmol). H NMR (400 MHz, DMSO-d6) δ 8.66
(s, 3H), 7.28 – 7.21 (m, 3H), 5.34 – 5.25 (m, 2H), 4.2
6 (q, J = 7.1 Hz, 1H), 2.97 – 2.90 (m, 2H), 1.48 (d, J
= 7.1 Hz, 3H), 1.13 (d, J = 6.8 Hz, 12H) ppm. 13C NMR
(100 MHz, D2O) δ 170.20, 168.56, 144.09, 140.62, 127.60,
124.43, 61.69, 48.55, 27.06, 22.94, 22.07, 15.24 ppm. HRMS
calcd for C17H26NO4 (M+H) +, 308.1862; found, 308.1865.
General procedure for synthesis of N-series
compounds. Propofol (50 mmol) and chloroacetyl chloride
(55 mmol) were dissolved in dry dichloromethane (90 mL)
and stirred at -10°C, followed by addition of pyridine (125
mmol) drop by drop (reaction temperature not exceeding 5
°C). After dropping, the mixture was allowed to slowly
warm to room temperature and was then stirred for 6 h to
obtain compound 20. Compound 20 (5 mmol), amino acetic
acid (21 to 30) (5 mmol) and NaI (5 mmol) were added to
5 mL of anhydrous dimethylformamide (DMF) at room
temperature for 30 min, followed by addition of K2CO3 (5
mmol) to obtain N-series intermediates (31 to 40) at 70 °C
for 4 h. The N-series intermediates were reacted with HCl in
ethyl acetate at 30 °C for 4~12 h to obtain N-series
compounds (3a-3j) as white solids. Eventually, the crude
products were recrystallized by cyclohexane/ethyl acetate
or ethyl acetate/ethanol.
2-(2,6-Diisopropylphenoxy)-2-oxoethyl
2-
morpholinoacetate hydrochloride (3e). The title compound
was synthesized according to the general procedure with
compound 20 (5 mmol) and 4-morpholineacetic acid (5
1
mmol). H NMR (400 MHz, D2O) δ 7.31 – 7.23 (m, 3H),
5.25 (s, 2H), 4.31 (s, 2H), 3.95 – 3.92 (br, 4H), 3.42
(br, 4H), 2.88 – 2.81 (m, 2H), 1.08 (d, J = 6.9 Hz, 12
H) ppm. 13C NMR (150 MHz, D2O) δ 169.00, 165.74, 144.35,
140.99, 128.09, 124.89, 62.19, 62.17, 56.11, 52.80, 27.38,
23.28, 22.83, 21.94 ppm. HRMS calcd for C20H30NO5 (M+H)
+, 364.2129; found, 364.2124.
2-(2,6-Diisopropylphenoxy)-2-oxoethyl
2-(4-
methylpiperazin-1-yl)acetate hydrochloride (3f). The title
compound was synthesized according to the general
procedure with compound 20 (5 mmol) and (4-methyl-
1
piperazin-1-YL)-acetic acid (5 mmol). H NMR (400 MHz,
D2O) δ 7.33 – 7.20 (m, 3H), 5.16 (s, 2H), 3.82 (s, 2H),
3.56 – 3.54 (br, 1H), 3.28 (br, 6H), 2.97 (br, 1H), 2.
87 – 2.80 (m, 5H), 1.07 (d, J = 6.9 Hz, 12H) ppm. 13C
NMR (100 MHz, D2O) δ 169.14, 167.68, 143.96, 140.70,
127.88, 124.64, 61.59, 55.94, 51.24, 49.22, 42.76, 27.05,
22.44 ppm. HRMS calcd for C21H33N2O4 (M+H) +, 377.2440;
found, 377.2447.
2-(2,6-Diisopropylphenoxy)-2-oxoethyl 2-aminoacetate
hydrochloride (3a). The title compound was synthesized
according to the general procedure with compound 20 (5
mmol) and boc-glycine (5 mmol). 1H NMR (400 MHz, D
MSO-d6) δ 8.52 (s, 3H), 7.28 – 7.21 (m, 3H), 5.29 (s,
2H), 4.00 (s, 2H), 2.97 – 2.90 (m, 2H), 1.13 (d, J = 6.
8
Hz, 12H) ppm. 13C NMR (100 MHz, Methanol-d4) δ
2-(2,6-Diisopropylphenoxy)-2-oxoethyl
2-(pyrrolidin-1-
168.67, 165.93, 144.03, 140.65, 127.73, 124.54, 61.82,
56.72, 43.71, 27.06, 22.25 ppm. HRMS calcd for C16H24NO4
(M+H) +, 294.1705; found, 294.1701.
yl)acetate hydrochloride (3g). The title compound was
synthesized according to the general procedure with
compound 20 (5 mmol) and 2-(1-pyrrolidyl) acetic acid (5
2-(2,6-Diisopropylphenoxy)-2-oxoethyl
2-
1
mmol). H NMR (400 MHz, D2O) δ 7.31 – 7.23 (m, 3H),
(dimethylamino)acetate hydrochloride (3b). The title
compound was synthesized according to the general
procedure with compound 20 (5 mmol) and N, N-
5.23 (s, 2H), 4.33 (s, 2H), 3.41 (br, 4H), 2.88 – 2.81
(m, 2H), 2.04 – 2.00 (m, 4H), 1.08 (d, J = 6.9 Hz, 12
H) ppm. 13C NMR (100 MHz, D2O) δ 168.70, 166.36, 144.04,
140.66, 127.74, 124.54, 61.80, 55.17, 54.41, 27.05, 22.86,
22.08 ppm. HRMS calcd for C20H30NO4 (M+H) , 348.2175;
found, 348.2176.
1
dimethylglycine (5 mmol). H NMR (400 MHz, DMSO-d6)
δ 10.78 (s, 1H), 7.28 – 7.18 (m, 3H), 5.32 (s, 2H), 4.
42 (s, 2H), 2.97 – 2.90 (m, 2H), 2.85 (s, 6H), 1.13 (d,
J = 6.8 Hz, 12H) ppm. 13C NMR (100 MHz, D2O) δ 168.67,
165.93, 144.03, 140.65, 127.73, 124.54, 61.82, 56.72, 43.71,
27.06, 22.93, 22.07 ppm. HRMS calcd for C18H28N2O4 (M+H)
+, 322.2018; found, 322.2013.
+
2-(2,6-diisopropylphenoxy)-2-oxoethyl
carboxylate hydrochloride (3h). The title compound was
synthesized according to the general procedure with
morpholine-3-
compound
20
(5
mmol)
and
4-N-boc-3-
2-(2,6-Diisopropylphenoxy)-2-oxoethyl
2-
1
morpholinecarboxylic acid (5 mmol). H NMR (400 MHz,
DMSO-d6) δ 10.10 (br, 2H), 7.28 – 7.21 (m, 3H), 5.34
(s, 2H), 4.62 (dd, J = 7.4, 3.8 Hz, 1H), 4.15 – 4.11 (m,
1H), 3.95 – 3.86 (m, 2H), 3.79 – 3.68 (m, 1H), 3.29 –
3.11 (m, 2H), 2.98 – 2.88 (m, 2H), 1.13 (d, J = 6.8 H
(methylamino)acetate hydrochloride (3c). The title
compound was synthesized according to the general
procedure with compound 20 (5 mmol) and boc-sarcosine
1
(5 mmol). H NMR (400 MHz, DMSO-d6) δ 9.46 (s, 2H),
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z, 12H) ppm. 13C NMR (100 MHz, D2O) δ 168.47, 166.30,
143.99, 140.67, 127.82, 124.59, 64.89, 63.45, 62.04, 54.21,
41.85, 27.05, 22.92, 21.97 ppm. HRMS calcd for C19H28NO5
(M+H) +, 350.1967; found, 350.1962.
D2O) δ 7.32 – 7.25 (m, 3H), 5.09 (s, 2H), 3.40 (s, 2H),
2.91 – 2.82 (m, 2H), 1.10 (d, J = 6.8 Hz, 12H) ppm.
13C NMR (100 MHz, D2O) δ 173.15, 170.34, 169.64, 1
44.05, 140.74, 127.71, 124.52, 61.25, 43.93, 27.02, 22.
+
93, 21.93 ppm. HRMS calcd for C17H21Na2O6 (M+Na)
367.1134; found, 367.1129.
,
2-(2,6-diisopropylphenoxy)-2-oxoethyl
piperidine-2-
carboxylate hydrochloride (3i). The title compound was
synthesized according to the general procedure with
compound 20 (5 mmol) and 1-(tert-butoxycarbonyl)
Sodium 2-(2-(2,6-diisopropylphenoxy)-2-oxoethoxy)malo
nate (2a). 1H NMR (400 MHz, D2O) δ 7.29 – 7.22 (m,
3H), 4.52 (s, 2H), 4.31 (s, 1H), 2.88 – 2.78 (m, 2H),
1.08 (d, J = 6.9 Hz, 12H) ppm. 13C NMR (150 MHz, D2O)
δ 174.46, 172.41, 144.41, 141.20, 127.98, 124.86, 83.79, 66.
05, 27.45, 23.27, 22.26 ppm. HRMS calcd for C17H20Na3O7 (
M+Na) +, 405.0902; found, 405.0898.
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piperidine-2-carboxylic acid (5 mmol). H NMR (400 MH
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z, D2O) δ7.31 – 7.23 (m, 3H), 5.22 (q, J = 16.8 Hz, 2
H), 4.21 – 4.17 (br, 1H), 3.43 – 3.38 (br, 1H), 3.06 –
3.00 (br, 1H), 2.87 – 2.80 (m, 2H), 2.28 – 2.25 (br, 1
H), 1.82 – 1.75 (br, 3H), 1.63 – 1.55 (br, 2H), 1.08 (
d, J = 6.9 Hz, 12H) ppm. 13C NMR (100 MHz, D2O) δ
169.01, 168.59, 144.04, 140.67, 127.74, 124.54, 61.75,
56.19, 43.89, 27.05, 25.62, 22.53, 22.03, 21.22, 20.83 ppm.
HRMS calcd for C20H30NO4 (M+H) +, 348.2175; found,
348.2177.
Sodium 2-((2-(2,6-diisopropylphenoxy)-2-oxoethyl)thio)a
cetate (2b). 1H NMR (400 MHz, DMSO-d6) δ 7.24 – 7.
15 (m, 3H), 3.69 (s, 2H), 3.17 (s, 2H), 3.01 – 2.94 (m,
2H), 1.12 (d, J = 6.9 Hz, 12H) ppm. 13C NMR (100 MHz,
DMSO-d6) δ 171.71, 170.09, 145.45, 140.60, 126.93, 124.3
2, 38.89, 33.06, 27.09, 23.95, 23.41 ppm. HRMS calcd for C16
H21Na2O6S (M+Na) +, 355.0956; found, 355.0965.
2-(2,6-diisopropylphenoxy)-2-oxoethyl
2-(piperidin-1-
yl)acetate hydrochloride (3j). The title compound was
synthesized according to the general procedure with
compound 20 (5 mmol) and 1-piperidineacetic acid (5
2-((2-(2,6-diisopropylphenoxy)-2-oxoethyl)amino)acetic
acid hydrochloride (2c).1H NMR (400 MHz, DMSO-d6) δ
10.85 (br, 3H), 7.30 – 7.23 (m, 3H), 4.48 (s, 2H), 3.96
(s, 2H), 2.97 – 2.90 (m, 2H), 1.14 (d, J = 6.8 Hz, 12H)
ppm. 13C NMR (100 MHz, DMSO-d6) δ 168.19, 166.31, 144.
70, 140.43, 127.61, 124.65, 47.03, 46.50, 27.13, 23.97, 23.3
1
mmol). H NMR (400 MHz, DMSO-d6) δ 10.54 (m, 1H),
7.28 – 7.21 (m, 3H), 5.33 (s, 2H), 4.40 (s, 2H), 3.48 –
3.45 (br, 2H), 3.04 (br, 2H), 2.97 – 2.88 (m, 2H), 1.82
– 1.78 (br, 4H), 1.70 – 1.67 (br, 1H), 1.35 (br, 1H), 1.1
3 (d, J = 6.9 Hz, 12H) ppm. 13C NMR (100 MHz, D2O) δ
168.89, 165.79, 143.95, 140.70, 127.89, 124.65, 61.86,
55.69, 54.28, 27.05, 22.88, 22.42, 21.96, 20.66 ppm. HRMS
calcd for C21H31NO4 (M+H) +, 362.2231; found, 362.2235.
+
7 ppm. HRMS calcd for C16H24NO4 (M+H) , 294.1705; foun
d, 294.1698.
2,6-diisopropylphenyl 2-morpholinoacetate (Ref-21). 1H
NMR (400 MHz, DMSO-d6) δ 11.65 (br, 1H), 7.31 – 7.
23 (m, 3H), 4.78 (s, 2H), 3.91 (br, 4H), 3.59 (br, 4H),
2.97 – 2.87 (m, 2H), 1.14 (d, J = 6.8 Hz, 12H) ppm. 13
C NMR (100 MHz, D2O) δ 166.08, 143.85, 140.50, 128.18, 1
24.79, 63.50, 55.64, 52.48, 27.29, 22.80, 21.93 ppm. HRMS c
alcd for C18H27NNaO3 (M+H) +, 328.1889; found, 328.1896.
2,6-diisopropylphenyl 2-hydroxyacetate (GP). 1H NMR (
400 MHz, DMSO-d6) δ 7.27 – 7.16 (m, 3H), 5.66 (t, J
= 6.7 Hz, 1H), 4.39 (d, J = 6.7 Hz, 2H), 2.91 – 2.82 (
m, 2H), 1.12 (d, J = 6.9 Hz, 12H) ppm. 13C NMR (100
MHz, DMSO-d6) δ 172.32, 145.24, 140.53, 126.92, 124.39,
59.88, 27.30, 23.60 ppm. HRMS calcd for C14H20NaO3
(M+Na) +, 259.1310; found, 259.1308.
General procedure for synthesis of O-series
compounds. Compound 20 (5 mmol), benzyl ester polyacid
(41 and 42) (5 mmol) and NaI (5 mmol) were added to 5
mL of anhydrous dimethylformamide (DMF) at room
temperature for 30 min, followed by the addition of K2CO3
(5 mmol) to obtain Bn-series intermediates (43 and 44) at
70 °C for 4 h. The Bn-series intermediates were treated with
Pd/C and H2 in ethyl acetate at room temperature for 4 h to
obtain O-series intermediates (45 and 46). Eventually, O-
series intermediates were treated with an overdose of
saturated aqueous Na2CO3, and the reaction solution was
lyophilized to obtain crude products. Then, crude products
were dissolved in ethyl acetate to eliminate the existing
Na2CO3. Ethyl acetate was then removed by evaporation
under reduced pressure to obtain the products 4a and 4b
as white solids.
AUTHOR INFORMATION
Corresponding Author
*For Jun Yang: E-mail: yang215jun@163.com. Phone: (86)
028-85164040.
Sodium
4-(2-(2,6-diisopropylphenoxy)-2-oxoethoxy)-4-
oxobutanoate (4a). The title compound was synthesized
according to the general procedure with compound 20 (5
mmol) and compound 41 (5 mmol). 1H NMR (400 MHz, D
MSO-d6) δ 7.26 – 7.19 (m, 3H), 5.00 (s, 2H), 2.95 – 2.8
6 (m, 2H), 2.51 (t, J = 7.2 Hz, 2H), 2.16 (t, J = 7.2 H
z, 2H), 1.12 (d, J = 6.9 Hz, 12H) ppm. 13C NMR (150
MHz, D2O) δ 180.81, 175.31, 170.08, 144.40, 141.01, 127.97,
124.80, 61.22, 32.09, 30.38, 27.36, 22.96, 22.23 ppm. HRMS
calcd for C18H24NaO6 (M+H) +, 359.1471; found, 359.1467.
*For Qing-Rong Qi: E-mail: qiqinrong@scu.edu.cn. Phone: (86)
028-85502157
Author Contributions
Liang-Quan Liu helped design and conduct the study and
wrote the manuscript.
Pei-Xi Hong assisted in animal experiments, conducted the
study, and analyzed the data.
Rui Ling helped conduct the synthesis study.
Xing-Hai Song helped conduct the animal study.
Chang-cui Zhou helped conduct the animal study.
Yi Kang helped conduct the analytical study.
Sodium
3-(2-(2,6-diisopropylphenoxy)-2-oxoethoxy)-3-
oxopropanoate (4b). The title compound was synthesized
according to the general procedure with compound 20 (5
mmol) and compound 42 (5 mmol). 1H NMR (400 MHz,
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Qing-Rong Qi designed the study, analyzed the data, and
Lange, R.; Langemeijer, H. J.; Danhof, M.
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wrote the manuscript.
Jun Yang designed and conducted the study, analyzed the data,
and wrote the manuscript.
Pharmacokinetics, induction of anaesthesia and safety
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clinical anesthesia outcomes are both common and
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M. J.; Villarino, M. E.; Perrotta, D. M.; Burwen, D. R.;
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infections traced to contamination of an intravenous
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Propofol infusion syndrome: a structured review of
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Critical Care. 2015, 19, 398.
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Notes
The authors declare no competing financial interests.
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ACKNOWLEDGMENT
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This study was supported by grant 2019YFS0093 (to Dr. Jun
Yang) from the Key Research & Development Projects of the
Department of Science & Technology of Sichuan Province.
ABBREVIATIONS
ED50, the dose at which 50% of animals displayed anesthesia;
LD50, the dose at which 50% of animals died; TI, therapeutic
index was calculated as TI = LD50/ED50; LORR, loss of righting
reflex; TsN3, p-toluenesulfonyl azide; HATU, 2-(7-aza-1H-
benzotriazole-1-yl)-1,1,3,3-tetramethyluronium
hexafluorophosphate; Et3N, triethylamine; TFA, trifluoroacetic
acid; DMF, dimethylformamide;
(10) MB, H.; S, S.; E, A. M. The fat overload syndrome.
Report of a case and literature review. American Journal
of Diseases of Children. 1981, 135, 628-630.
(11) Stella, V. J.; Charman, W.; Naringrekar, V. Prodrugs.
Drugs. 1985, 29, 455-473.
SUPPORTING INFORMATION
1 Synthesis of the Title Compounds
2 Stability of Prodrugs and Fospropofol in Water
3 In vitro study: metabolic stability in mice plasma
4 In vivo studies: pharmacodynamic evaluation
5 Determination of the pH and Solubility of 3e, 3g, 3j
6 Purity Study of Tested Compounds in vivo
7 NMR spectra
(12) Sneyd, J. Recent advances in intravenous
anaesthesia. Br. J. Anaesth. 2004, 93, 725-736.
(13) Altomare, C.; Trapani, G.; Latrofa, A.; Serra, M.;
Sanna, E.; Biggio, G.; Liso, G. Highly water-soluble
derivatives of the anesthetic agent propofol: in vitro and
in vivo evaluation of cyclic amino acid esters. Eur. J.
Pharm. Sci. 2003, 20, 17-26.
8 Molecular formula strings
(14) Banaszczyk, M. G.; Carlo, A. T.; Millan, V.; Lindsey, A.;
Moss, R.; Carlo, D. J.; Hendler, S. S. Propofol phosphate, a
water-soluble propofol prodrug: in vivo evaluation.
Anesthesia & Analgesia. 2002, 95, 1285-1292.
(15) Zhou, Y.; Yang, J.; Liu, J.; Wang, Y.; Zhang, W. Efficacy
comparison of the novel water-soluble propofol prodrug
HX0969w and fospropofol in mice and rats. Br. J. Anaesth.
2013, 111, 825-832.
(16) Brian, S.; John, B.; Gopalaswamy, R.; Zishan, H.
Synthesis and Use of Glycoside Prodrug Analogs.
WO2012142141, 2012.
(17) Deng, T.; Mao, X.; Li, Y.; Bo, S.; Yang, Z.; Jiang, Z.-X.
Monodisperse oligoethylene glycols modified Propofol
prodrugs. Bioorg. Med. Chem. Lett. 2018, 28, 3502-3505.
(18) Zhang, W.; Yang, J.; Fan, J.; Wang, B.; Kang, Y.; Liu, J.;
Zhang, W.; Zhu, T. An improved water-soluble prodrug of
propofol with high molecular utilization and rapid onset
of action. Eur. J. Pharm. Sci. 2019, 127, 9-13.
(19) Wang, Y.; He, X.; Zhong, B. Design, synthesis and
biological activity of prodrugs of alamifovir analogs. Chin.
J. Med. Chem. 2010, 20, 484-489.
(20) Allcock, H. R.; Pucher, S. R.; Scopelianos, A. G.
Synthesis of poly (organophosphazenes) with glycolic
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