Synthesis and antitussive activity of obtucarbamate A derivatives

Article abstract of DOI:10.1080/00397911.2020.1762093

Obtucarbamate A was purified from Disporum cantoniense with good antitussive property. In present work, a series of obtucarbamate A derivatives were designed and synthesized from obtucarbamate A by microwave method, and their antitussive activity were evaluated. The results showed that the toluene diisocyanate was obtained with a yield of 95.1percent using a simple method, 1-methyl-2-pyrrolidinone as solvent, temperature of 190 °C, microwave irradiation at 60 W power for 30 min. All compounds have good antitussive activity, and small steric hindrance unsaturated groups of ester chains and amino groups favor activity. It is the first reported of obtucarbamate A derivatives used as antitussive, and the results provide a basis for the application of obtucarbamate derivatives as new antitussive.

Full text of DOI:10.1080/00397911.2020.1762093

Synthetic Communications
An International Journal for Rapid Communication of Synthetic Organic
Chemistry
ISSN: 0039-7911 (Print) 1532-2432 (Online) Journal homepage: https://www.tandfonline.com/loi/lsyc20
Synthesis and antitussive activity of
obtucarbamate A derivatives
Xiaoyun Ma, Zhiyuan Liang, Xiuhai Gan, Gang Wei & Qingdi Zhou
To cite this article: Xiaoyun Ma, Zhiyuan Liang, Xiuhai Gan, Gang Wei & Qingdi Zhou (2020):
Synthesis and antitussive activity of obtucarbamate A derivatives, Synthetic Communications, DOI:
10.1080/00397911.2020.1762093
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SYNTHETIC COMMUNICATIONSV
https://doi.org/10.1080/00397911.2020.1762093
Synthesis and antitussive activity of obtucarbamate A
derivatives
Xiaoyun Maa, Zhiyuan Lianga, Xiuhai Gana, Gang Weib, and Qingdi Zhouc
b
aSchool of Chemistry and Materials Science, Guizhou Education University, Guiyang, P. R. China; CSIRO
c
Mineral Resources, Lindfield, NSW, Australia; School of Chemistry, The University of Sydney, Sydney,
NSW, Australia
ABSTRACT
ARTICLE HISTORY
Received 8 January 2020
Obtucarbamate A was purified from Disporum cantoniense with good
antitussive property. In present work, a series of obtucarbamate A
derivatives were designed and synthesized from obtucarbamate A
by microwave method, and their antitussive activity were evaluated.
The results showed that the toluene diisocyanate was obtained with
a yield of 95.1% using a simple method, 1-methyl-2-pyrrolidinone as
solvent, temperature of 190ꢀC, microwave irradiation at 60 W power
for 30 min. All compounds have good antitussive activity, and small
steric hindrance unsaturated groups of ester chains and amino
groups favor activity. It is the first reported of obtucarbamate A
derivatives used as antitussive, and the results provide a basis for
the application of obtucarbamate derivatives as new antitussive.
KEYWORDS
Antitussive action;
microwave reaction;
obtucarbamate A; structural
modification; toluene
diisocyanate
GRAPHICAL ABSTRACT
Introduction
As we known, cough follows our lives and significantly impacts our quality of life,
including physical activity and psychosocial domain.[1] As the most common reason for
sick patients visit physicians, cough belongs to the most frequent symptoms of respira-
tory system diseases,[2] which can be caused by a variety of factors, such as pulmonary
infection, amygdalitis, upper respiratory infection, and so on. So, cough follows our lives
and remains a worldwide problem.[3] In the United State alone in 2006, the sales of
CONTACT Xiuhai Gan
gxh200719@163.com
School of Chemistry and Materials Science, Guizhou Education
University, Guiyang, P. R. China.
Supplemental data for this article can be accessed on the publisher’s website.
ß 2020 Taylor & Francis Group, LLC

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X. MA ET AL.
Figure 1. The structure of obtucarbamate A and B from Disporum cantoniense.
only over-the-counter cough and cold remedies were more than $3.6 billion.[4] The pre-
sent therapies are often limited for the lack of effective medications and most of the
antitussive drugs have grave side effects.[5] So, it is quite necessary to discover new
compounds with strong antitussive activity, few or no side effects and favorable
pharmacological and clinical properties.[6]
Disporum cantoniense is one of the Chinese medicinal herbs, widely used as a folk
medicine for the treatment of cough,[7] which is an important part of Kesuting syrup
made by Guizhou Bailing Co. Ltd. However, there are few reported on antitussive con-
stituents and structural derivation. In our previous work, compounds obtucarbamate A
and obtucarbamate B (Figure 1) with excellent antitussive was isolated from D. canto-
niense.[8] It provided the lead compounds for the discovery of new antitussive.
Disporum cantoniense is widely distributed in southern China and an abundance of
obtucarbamate A and obtucarbamate B can be extracted and isolated from it. According
to our previous work, D. cantoniense has a higher content of obtucarbamate A as com-
pared to obtucarbamate B, the extraction and isolation of obtucarbamate A from D.
cantoniense is relatively easy.
In the present work, we aim to diversify the structure of obtucarbamate A and obtain
some compounds with higher cough activity and to pave the way for the discovery of
new antitussive. As shown in Scheme 1, Obtucarbamate A derivatives were prepared
from Obtucarbamate A and intermediates B, and 15 Obtucarbamate A derivatives were
divided into three series.
Results and discussion
Chemistry
For our derivatization of structural diversity, the structure of obtucarbamate A was
derived from toluene diisocyanate (intermediate B). Isocyanate derivatives were usually
obtained with thermal decomposition reactions carried out in harsh reaction conditions,
like high temperature, pressure, and catalyst.[9] Furthermore, significant amounts of
byproducts are formed under these reaction conditions. Fernandez et al.[10] have
reported that isocyanates can be synthesized from carbamates with montmorillonite as
catalyst and this reported method is very effective for synthesizing monoisocyanates
from monocarbamates. However, synthesizing diisocyanates from dicarbamates is rela-
tively difficult. These conversions would take long reaction time (24 h) with moderate
yield. In this paper, diisocyanate was synthesized under microwave radiation, the yield

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Scheme 1. The synthetic route of obtucarbamate A derivatives.
Table 1. Optimization of the reaction conditions for synthesis toluene diisocyanatea.
Entry
Solvent
Temperature
Time (min)
Yieldb/%
1
2
3
4
5
6
7
8
9
DMF
100
100
100
100
100
190
100
190
190
30
30
30
30
30
30
30
30
45
5.8
10.1
8.2
14.6
45.8
89.3
51.2
95.1
94.3
DMSO
Pyridine
Toluene
Decaline
Decaline
NMPc
NMP
NMP
aReaction conditions: substrate/montmorillonite K-10 is 4/1(m/m); microwave 60 watt power.
bThe yield was analyzed by GC.
cNMP is 1-methyl-2-pyrrolidinone.
was improved and the reaction time was reduced to 30 min. Under microwave irradi-
ation, the reaction conditions including solvent, reaction temperature, and reaction time
were studied and optimized. As shown in Table 1, the choice of solvent proved crucial
factor to the reaction outcome, the yields of DMF, DMSO, pyridine, and toluene as sol-
vents are all below 15.0% (entries 1–4). At the same conditions, the yield was increased
with decaline or 1-methyl-2-pyrrolidinone (NMP) as solvent (entries 5 and 7). The yield
was significantly increased to more than 89.3% (entries 6, 8, and 9) when the reaction
system was heated to 190 ꢀC. It is worth noting that the high yield was observed in
NMP with 95.1% (entry 8). In addition, when the reaction time prolonged from 30 to
45 minutes, the yield was relatively low (entry 9). Hence, it is better for the reaction to
be proceeded at 190 ꢀC, 30 minutes, NMP as solvent under microwave irradiation at 60
watt power. Then, the intermediate B was reacted with corresponding alcohol[11] and
amine[12] to obtain compound C and D by the reported methods, respectively. In add-
ition, the obtucarbamate A was oxidized to compound E by potassium permanganate in
the presence of hexadecyl trimethyl ammonium bromide. Fifteen obtucarbamate A
derivatives were obtained by structural diversity.

4
X. MA ET AL.
Table 2. Effect of compounds against ammonia induced mice cough (ꢀx s, n ¼ 10).
Compd.
R1/R2
Dosage (mgꢁkgꢂ1
)
Latent period of cough (s)
No. of coughs
ꢃ
ꢃ
C1
C2
C3
C4
C5
C6
C7
C8
C9
D1
D2
D3
D4
D5
E
Ethyl
Propyl
Isopropyl
Butyl
Isopentyl
600.0
600.0
600.0
600.0
600.0
600.0
600.0
600.0
600.0
600.0
600.0
600.0
600.0
600.0
600.0
–
81.56 3.28
89.23 3.89
102.62 5.12
96.75 5.89
116.06 6.02
114.52 5.67
110.65 4.68
92.56 3.69
86.60 3.57
78.93 3.25
75.01 2.56
65.28 3.90
51.80 3.12
75.26 4.18
65.25 2.81
27.53 3.26
10.88 0.58
10.45 2.01
8.95 1.26
7.98 1.54
7.13 1.16
8.05 1.21
9.21 1.59
10.24 2.14
11.60 2.01
10.67 1.65
12.53 2.12
16.86 2.24
22.27 2.58
18.43 1.89
17.22 3.01
21.73 4.21
ꢃ
ꢃ
ꢃꢃꢃ
ꢃꢃꢃ
ꢃꢃꢃ
ꢃꢃꢃ
ꢃꢃꢃ
ꢃꢃꢃ
ꢃꢃꢃ
ꢃꢃꢃ
Methylallyl
3-Methylbut-2-en-1-yl
(E)-hex-2-en-1-yl
(Z)-hex-3-en-1-yl
Methyl
ꢃꢃꢃ
ꢃꢃꢃ
ꢃꢃ
ꢃꢃ
ꢃ
ꢃ
ꢃꢃ
ꢃꢃ
ꢃꢃ
ꢃꢃ
Ethyl
Isopropyl
Phenyl
Benzyl
ꢃ
ꢃ
ꢃꢃ
ꢃꢃ
ꢃꢃꢃ
ꢃꢃꢃ
ꢃꢃ
ꢃꢃ
Control group
Obtucarbamate A
ꢃ
ꢃꢃꢃ
ꢃꢃꢃ
600.0
70.41 4.55
15.27 2.18
ꢃꢃ
ꢃꢃꢃ
p < 0.05, p < 0.01,
p < 0.001, compared with data of negative control after drug administration.
Antitussive activity
Antitussive activity of the synthesized compounds was tested on the basis of reported
methods,[3,8,13] and the results were listed in Table 2. As shown in Table 2, most of the
compounds showed good antitussive activity against ammonia induced mice cough at
dosages of 600 mg/kg, of which, compound C3, C4, C5, C6, and C7 would obviously
prolong the latent period of cough with the value of 102.62, 96.75, 116.06, 114.52, and
110.65 seconds, respectively, better than the leading compound obtucarbamate A
(70.41 seconds). Meanwhile, compound C3, C4, C5, C6, and C7 treatment at dosages of
600 mg/kg had strongly decreased the frequency of cough of mice, the cough of 8.95,
7.98, 7.13, 8.05, and 9.21 times in 5 min, respectively, superior to the leading compound
obtucarbamate A (15.27 times). However, the urea derivatives D and benzoic acid
derivative only has similar antitussive activity to the leading compound obtucarbamate
A against ammonia induced mice cough at dosages of 600 mg/kg.
Conclusions
In summary, seventeen obtucarbamate A derivatives were synthesized with a simple
method based on leading compound obtucarbamate A. All of the compounds have
good antitussive activity at dosages of 600 mg/kg, of which C3, C4, C5, C6, and C7
showed excellent antitussive activity, superior to leading compound obtucarbamate A.
This work indicated that obtucarbamate A derivatives of carbamates can be used to
develop new antitussive.
Experimental
Instruments and chemicals
Melting points were determined on a Thomas Hoover capillary apparatus and were
uncorrected. NMR spectra were obtained on a Bruker DPX-500 or a DPX-400 spec-
trometer (1H NMR at 500 or 400 MHz, 13C NMR at 125 or 100 MHz) in CDCl3 or

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DMSO-d6 using TMS as internal standard. Elemental analyses were performed on an
Elementar Vario-III CHN analyzer. Chemical shifts (d) are given in ppm and coupling
constants (J) are given in hertz (Hz). Analytical thin layer chromatography (TLC) was
performed on precoated silica GF254 plates. Yields refer to isolated yields of the products
after purification by silica-gel column chromatography (200–300 meshes). Reagent grade
chemicals were purchased from Aladdin Reagent (Shanghai, China) and were used with-
out further purification.
Procedure for the preparation of intermediate toluene diisocynate (B)
To a 100 mL round-bottom flask equipped with magnetic stirrer were added obtucarba-
mate A (9.52 g, 40 mmol), montmorillonite K-10 (2.38 g) and NMP (50 mL). The mix-
ture was heated to 190 ꢀC under microwave irradiation for 30 min and filtered. The
filtrate was isolated by vacuum distillation under N2 atmosphere to give corresponding
compound B, which was used in the next step without any purification.
General procedure for the preparation of compounds C1–C9 and D1–D5
Intermediate B (0.348 g, 2 mmol) was added dropwise into corresponding alcohol or
amine at 0 ꢀC and then the mixture was stirred to room temperature. The precipitate
was gathered by filtration and purified with recrystallization in ethyl acetate.
Procedure for the preparation of compound E
To a solution of obtucarbamate A (1.19 g, 5 mmol), hexadecyl trimethyl ammonium
bromide (0.36 g, 1 mmol) in water (20 mL), heated to reflux for 30 min. Then, the solu-
tion of KMnO4 (1.58 g, 10 mmol) in hot water (10 mL) was added dropwise. The result-
ant mixture was stirred for 4 h and filtered. The filtrate was acidified and purified with
recrystallization to give compound E.
The above obtucarbamate A derivative was confirmed on the basis of NMR and
elemental analysis.
Animals and drug administration
Kunming mice, half male and half female (body weight 18–22 g) for ammonia induced
mice cough study were purchased from Tianqin Biotechnology Co. Ltd. in
Changsha, China. All animals were housed at 25 2 ꢀC and 40–70% humidity under a
half light–dark cycle. According to the international rules considering animal experi-
ments and the internationally accepted ethical principles for laboratory animal use and
care, the animal studies were performed.
Compounds were suspended with 0.5% carboxylmethyl cellulose (CMC-Na) solution
to obtain doses agents of 600 mg/kg, 0.5% CMC-Na solution was taken as control.
Treatments were carried out orally.

6
X. MA ET AL.
Antitussive activity
Antitussive activity of compounds was performed with the ammonia liquor induced
mice cough method.[3,8,13] One hundred seventy mice were randomly divided into 17
groups, 10 mice in each group, giving the doses once a day and successive administra-
tion for 6 days with 600 mg/kg doses agents. One hour after the last dose, the mice was
placed into a 500 ml special glass chamber which was placed upside down and exposed
to 25% NH4OH evenly atomized by superbirth atomizer for 5 seconds and the latent
period and the cough in 5 min were recorded on the basis of obvious contraction of the
abdominal cavity.
Statistical analysis
All the data were expressed as mean standard error. The differences between results of
before drug administration and that of after drug administration in the same groups
were evaluated with a t test. One-way analysis of variance was used to assess statistical
significance of differences between different groups. The statistical analysis was per-
formed in the SPSS 17.0. A level of p < 0.05, p < 0.01, and p < 0.001 was taken as statis-
tically significant compared with data of negative control after drug administration.
Funding
This work was supported by the Chunhui project of Ministry of Education [Grant No.
(2013)2213] and the Construction Project of Key Laboratories from the Education Department of
Guizhou Province [Grant No. QJHKY(2018)001].
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