Synthesis and characterization of potential pharmacopeial impurities of oseltamivir: An antiviral drug

Article abstract of DOI:10.14233/ajchem.2018.21376

Impurities of oseltamivir phosphate were synthesized from chiral epoxide (1) in a simpler and much feasible synthetic approach in seven steps accounting to 8.2 % overall yield. The nucleophilic addition of N3 (highly regioselective and stereoselective) in

Full text of DOI:10.14233/ajchem.2018.21376

Asian Journal of Chemistry; Vol. 30, No. 9 (2018), 2003-2007
A
SIAN
J
OURNAL OF HEMISTRY
C
https://doi.org/10.14233/ajchem.2018.21376
Synthesis and Characterization of Potential Pharmacopeial
Impurities of Oseltamivir: An Antiviral Drug
2
1
1
1
RAJASEKHAR PONDURI1,2,*, PRAMOD KUMAR , LAKSHMANA RAO VADALI , KOMARAIAH AELUGU and KISHORE MATCHA
1Mylan Laboratories Limited, Bollaram, Jinnaram (Mandal), Medak-502 325, India
2Jawaharlal Nehru Technological University-Hyderabad, College of Engineering, Centre for Chemical Sciences & Technology, Institute of
Science and Technology, Kukatpally, Hyderabad-500 085, India
*Corresponding author: E-mail: rajasekharponduri123@gmail.com
Received: 9 April 2018;
Accepted: 6 June 2018;
Published online: 31 July 2018;
AJC-19010
Impurities of oseltamivir phosphate were synthesized from chiral epoxide (1) in a simpler and much feasible synthetic approach in seven
steps accounting to 8.2 % overall yield. The nucleophilic addition of N3 (highly regioselective and stereoselective) in the first and third
stage of the synthesis has been tailored and the reaction conditions were optimized.
Keywords: Oseltamivir, Impurities, Antiviral, Aziridine.
INTRODUCTION
O
The spreading of avian flu in winged animals increased
O
OEt
the chance of undeviating contamination in people. Till now,
transmission through individual to individual has been only
from time to time and aligned with close human contact [1].
At present, hostile to flu medicines comprise of two classes of
medications: M2 protein inhibitors (amantadine and riman-
tadine) and neuraminidase inhibitors (oseltamivir and zanamivir)
[2-4].As a class, neuraminidase inhibitors are successful against
all neuraminidase subtypes and, hence, against all strains of
flu. This is a key point in pestilence and pandemic readiness
and an imperative favourable position over the M2 protein
inhibitors which are successful just against touchy strains of
flu A2. Among every single antiviral medication, oseltamivir
is the prescribed antiviral to treat patients tainted with avian
flu (H5N1) incorporating chemoprophylaxis in high-hazard
populaces [5]. To protect people from the attack of pandemic
human influenza or H5N1 Avian flu, it is recommended that
oseltamivir phosphate (Tamiflu, Fig. 1) should be manufac-
tured and stocked in every country all over the world [6,7]. As
a continuous requirement of this drug in bulk stock, in recent
years, many researchers have reported many synthetic seque-
nces towards the preparation of oseltamivir phosphate [8-18].
Furthermore, in order to improve the efficacy oseltamivir drug,
HN
NH2
O
Fig. 1. Structure of tamiflu
continuous efforts has been put into action for the development
of new derivatives of oseltamivir [19-21].
The existence of impurities in an active pharmaceutical
ingredient can have a substantial influence on the quality and
safety of the drug pr oducts. Therefore, it is essential to unders-
tand the impurity profile of theAPI to be castoff in the manufa-
cturing of the drug product. A level of impurity profile ≥ 0.1
% [22]. Guidelines was endorsed by International Conference
on Harmonization (ICH) for the identification and characteri-
zation of all impurities.In this perspective, we have been taken
to synthesize and characterization of the two potential WHO
impurities: 5-acetylamino-4-amino-3-(1-ethyl propoxy)cyclo-
hex-1-enecarboxylic acid ethylester (9, WHO Impurity-F) and
5-acetylamino-4-amino-3-(1-ethyl propoxy)cyclohex-1-enecar-
boxylic acid (10, WHO impurity-A) (Fig. 2).
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2004 Ponduri et al.
Asian J. Chem.
8
8
10
10
heated to 65-70 ºC for 16 h. The solvents were stripped from
the reaction mixture under vacuum up to 4 vol. Water (130
mL) was added to the reaction mixture and the product was
extracted with ethyl acetate (2 × 100 mL). The organic layer
was evaporated under vacuum and the residue was purified by
column chromatography to obtain amine 4. Pale-yellow syrupy
liquid; Yield:70 %; Anal. calcd (%) for C14H24N4O3: C, 56.74;
H, 8.16; N, 18.90. Found: C, 56.71; H, 8.12; N, 18.95. 1H NMR
(CDCl3, 300 MHz): δ 0.98 (t, J = 6.4 Hz, 6H), 1.30 (t, J = 7.2
Hz, 3H), 1.45-1.67 (m, 4H), 2.25-2.36 (m, 1H), 2.84-2.96 (m,
2H), 3.37-3.51 (m, 2H), 3.86-3.90 (m, 1H), 4.26 (q, J = 7.2
Hz, 2H) ,6.80 (brs, 1H); ESI-MS: m/z 297.2 (M+H).
11
11
9
9
O
O
7
7
13
2
2
12
OH
12
O
O
O
1
1
14
3
3
6
6
4
4
H2N
H2N
5
5
HN
10, WHO Imp-A
13
O
HN 15
14
16
9, WHO Imp-F
O
Fig. 2. Structures of WHO impurity-F and WHO impurity-A
EXPERIMENTAL
tert-Butyl (1R,2R,6S)-4-(ethoxycarbonyl)-6-azido-2-
(pentan-3-yloxy)cyclohex-3-enylcarbamate (5): Boc anhy-
dride (5.12 g, 50.61 mmol) was added dropwise to a solution
of compound 4 (10 g, 33.78 mmol) in dichloromethane (100
mL) and triethylamine (8.1 g, 37.11 mmol) at 0 ºC. The reaction
mixture was allowed to stir at room temperature for 16 h. After
completion of the reaction, checked byTLC, water (100 mL) was
added to the reaction mixture and stirred for 15 min. The organic
layer was separated and evaporated under vacuum, the residue
was purified by column chromatography to obtain N-protected
Boc compound 5. White solid; Yield: 65 %; Anal. calcd (%)
for C19H32N2O5: C, 57.56; H, 8.14; N, 14.13. Found: C, 57.60; H,
8.16; N, 14.00. 1H NMR (CDCl3, 300 MHz): δ 0.92 (t, J = 6.6
Hz, 6H), 1.30 (t, J = 7.2 Hz, 3H), 1.43 (s, 9H), 1.45-1.57 (m, 4H),
2.15-2.36 (m, 1H), 2.74-2.87 (m, 1H), 3.07-3.18 (m, 1H), 3.31-
3.40 (m, 1H), 4.21(q, J = 7.2 Hz, 2H), 4.4-4.5 (brs, 1H), 4.8-
4.9 (brs, 1H), 6.75 (brs, 1H); 13C NMR (300 MHz, DMSO-d6):
δ 9.3, 9.5, 14.1, 25.6, 26.2, 28.3 (3C), 30.7, 57.4, 58.3, 60.9,
73.4, 79.8, 82.2, 128.0, 138.1, 155.2, 165.8; ESI-MS m/z for
[M+H]-calculated (found) for C19H32N4O5: (397.6) 397.3
Ethyl-(3R,4R,5S)-5-amino-4-[(tert-butoxycarbonyl)-
amino]-3-(pentan-3-yloxy)cyclohex-1-ene-1-carboxylate
(6): To a solution Boc-compound 5 (7 g, 17.67 mmol) in THF
(70 mL) was added triphenyl phosphine (5.5 g, 21.21 mmol)
in portions at 25-30 ºC. The reaction mixture was stirred at
25-30 ºC for 16 h. The reaction mixture was diluted with water
(70 mL) and extracted with ethyl acetate (2 × 50 mL) and
evaporated under vacuum to obtain the crude compound 6.
The crude compound was utilized in the next step without any
purification.Anal. calcd (%) for C19H34N4O5: C, 61.60; H, 9.25;
N, 7.56. Found: C, 61.57; H, 9.20; N, 7.52.
Ethyl-(3R,4R,5S)-5-(acetylamino)-4-[(tert-butoxy-
carbonyl)amino]-3-(pentan-3-yloxy)cyclohex-1-ene-1-
carboxylate (7): A mixture of amine 6 (7 g, 18.89 mmol),
potassium carbonate (3.91 g, 28.33 mmol) and acetic anhydride
(2.14 mL, 22.67 mmol) in THF (70 mL) was stirred at room
temperature for 4 h. Water (56 mL) was added to the reaction
mixture and extracted with ethyl acetate twice (2 × 42 mL) and
evaporated under vacuum, the residue was purified by column
chromatography to obtain acetyl compound 7. Pale-yellow
syrupy liquid;Yield: 60 %; Anal. calcd (%) for C21H36N2O6: C,
61.14; H, 8.80; N, 6.79. Found: C, 61.19; H, 8.76; N, 6.82. 1H
NMR (CDCl3, 300 MHz): δ 0.94 (t, J = 6.6 Hz, 6H), 1.28 (t, J
= 7.2 Hz, 3H), 1.43 (s, 9H), 1.46-1.58 (m, 4H), 1.94 (s, 3H),
2.25-2.31 (m, 1H), 2.72-2.79 (m, 1H), 3.38-3.42 (m, 1H), 3.72-
3.78 (m, 1H), 3.93-3.9 6 (m, 1H), 4.23 (q, J = 7.2 Hz, 2H), 4.69
Thin-layer chromatography (TLC) were run on silica gel
60 F254 precoated plates (0.25 mm, Merck) and spots were visu-
alized inside an UV cabinet under short UV. 1H NMR spectra
were recorded on Bruker 300 MHz Advance NMR spectro-
meter at 300 MHz TMS as an internal standard. Mass spectra
were obtained using an Agilent 1100 Series LC-MSD-TRAP-
SL system.
Ethyl-(3R,4S,5R)-5-azido-4-hydroxy-3-(pentan-3-
yloxy)cyclohex-1-ene-1-carboxylate (2): To a stirred solution
of epoxide 1 (30 g, 118.1 mmol) in a mixture of methanol
(920 mL) and water (120 mL) was added sodium azide (38.3
g, 50.05 mmol) followed by ammonium chloride (13.64 g,
259.8 mmol). The reaction mixture was heated to 65-70 ºC
for 16 h. After completion of the reaction, the solvents were
stripped from the reaction mixture under vacuum up to 4.0
volumes. Water (120 mL) was added to the reaction mixture
and the product was extracted with ethyl acetate (2 × 200 mL).
The organic layer was evaporated under vacuum and the residue
was purified by column chromatography to obtain azide 2.
Light brown liquid;Yield: 70 %;Anal. calcd (%) for C14H23N3O4:
C, 56.55; H, 7.80; N, 14.13. Found: C, 56.58; H, 7.85; N, 14.01.
1H NMR (CDCl3, 300 MHz): δ 0.98 (t, J = 6.6 Hz, 6H), 1.30
(t, J = 7.2 Hz, 3H), 1.49-1.63 (m, 4H), 2.21-2.30 (m, 1H), 2.72
(d, J = 6.6 Hz, 1H ), 2.80-2.87 (m, 1H), 3.40-3.48 (m, 1H), 3.71-
3.80 (m, 1H), 3.84-3.91 (m, 1H), 4.11-4.14 (m, 1H), 4.25 (q,
J = 6.6 Hz, 2H); 6.83-6.85 (m, 1H); ESI-MS: m/z 298.2 (M+H).
Ethyl-(1R,5R,6R)-5-(pentan-3-yloxy)-7-azabicyclo-
[4.1.0]hept-3-ene-3-carboxylate (3): To a solution of Azide 2
(25 g, 84.17 mmol) in acetonitrile (200 mL), triphenyl phosphine
(27.56 g, 105.21 mmol) was added portion wise (exothermic)
over a period of 15 min at room temperature. The reaction mixture
was heated to 80 ºC for 3 h. The solvent was evaporated and the
residue was purified by column chromatography to obtain aziridine
[3]. Pale yellow syrupy liquid;Yield: 63 %; Anal. calcd (%) for
C14H23NO3: C, 66.37; H, 9.15; N, 5.53. Found: C, 66.34; H, 9.17;
N, 5.58. 1H NMR (DMSO-d6, 300 MHz): δ 0.90 (t, J = 6.4 Hz,
6H), 1.20 (t, 3H, J = 7.4Hz), 1.36-1.59 (m, 4H), 2.17 (brs, 1H),
2.32 (brs, 1H), 2.40 (brs, 1H), 3.38 (t, J = 7.2 Hz, 1H), 4.15 (q, J
= 7.2 Hz, 2H), 4.18 (brs, 1H), 6.61 (d, J = 7.2 Hz, 1H); ESI-MS:
m/z 254.1 (M+H).
Ethyl-(3R,4R,5S)-4-amino-5-azido-3-(pentan-3-
yloxy)cyclohex-1-ene-1-carboxylate (4): To a stirred solution
of aziridine 3 (13 g, 51.38 mmol) in DMF (150 mL) was added
sodium azide (16.69 g, 102.76 mmol) followed by ammonium
chloride (13.64 g, 259.8 mmol). The reaction mixture was

Vol. 30, No. 9 (2018)
Synthesis and Characterization of Potential Pharmacopeial Impurities of Oseltamivir 2005
(brs, 1H), 6.58 (brs, 1H), 6.78 (brs, 1H);13C NMR (300 MHz,
DMSO-d6): δ 9.2, 9.5, 14.0, 23.0, 25.8, 26.2, 28.2 (3C), 30.4,
48.5, 55.8, 60.7, 75.6, 79.4, 82.5, 129.2, 137.3, 156.7, 165.6,
170.3; ESI-MS m/z for [M+H]-calculated (found) for C21H36N2O6:
413 (413.3).
(KBr, νmax, cm-1): 1316 (-C-N), 1651 (C=O), 3085 (alkene -C-H),
3434, 3277 (-NH/-OH); 1H NMR (CDCl3, 300 MHz): δ 0.84-
0.89 (t, J = 6.6 Hz, 6H), 1.35-1.62 (m, 4H), 1.83 (s, 3H), 1.91-
2.02 (m, 1H), 2.50-2.51 (m, 1H), 2.69-2.75 (m, 1H), 3.41 (t, J
= 7.2 Hz, 1H), 3.68-3.75 (m, 1H), 3.88-3.90 (m, 1H), 6.60 (s,
1H), 7.88 (d, J = 7.2 Hz, 1H); 13C NMR (300 MHz, DMSO-d6):
δ 9.3, 9.6, 22.8, 25.7, 25.8, 31.3, 48.0, 54.8, 76.9, 79.5, 133.2,
133.5, 168.5, 169.3; ESI-MS m/z for [M+H]-calculated for
C14H24N2O4: 285, found: 307 (M+Na).
Ethyl-(3R,4R,5S)-5-(acetylamino)-4-amino-3-(pentan-
3-yloxy)cyclohex-1-ene-1-carboxylate (WHO-Imp-F, 9): To
a solution of acetyl compound 7 (6 g, 14.56 mmol) and dichloro-
methane (60 mL), cooled to 0-5 ºC, was slowly added trifluoro-
acetic acid (1.67 mL, 21.8 mmol). The reaction mixture was stirred
at 25-30 ºC for 16 h. After completion of reaction, checked by
TLC, the reaction mixture cooled to 0-5 ºC and basified with
saturated NaHCO3 solution and extracted with dichloromethane
(2 × 42 mL) and evaporated under vacuum, the residue was
purified by column chromatography to obtain WHO-Imp-F,
9. White solid;Yield: 70 %;Anal. calcd (%) for C16H28N2O4: C,
61.51; H, 9.03; N, 8.97. Found: C, 61.55; H, 9.06; N, 8.95. IR
(νmax, KBr, cm-1): 1281 (-C-N), 1714,1703 (C=O), 3071 (alkene,
RESULTS AND DISCUSSION
The synthesis of two potential WHO impurities of oselta-
mivir phosphate, (i) ethyl-(3R,4R,5S)-5-(acetylamino)-4-amino-
3-(pentan-3-yloxy)cyclohex-1-ene-1-carboxylate (WHO-
IMP-F, 9) and (ii) (3R,4R,5S)-5-(acetylamino)-4-amino-3-
(pentan-3-yloxy)cyclohex-1-ene-1-carboxylic acid (WHO-
IMP-A, 10) is illustrated in Scheme-I. These two impurities
were prepared starting from epoxide compound 1 [6,7].
The ring opening of epoxide 1 was carried out in presence
of sodium azide, ammonium chloride in methanol:THF at 65-
70 ºC for 16 h produced azide-hydroxy 2. Reduction of azide
2 followed by cyclization in presence of triphenyl phosphine
in acetonitrile at 80 ºC for 3 h produced aziridine 3 [23-25].
Ring opening of aziridine 3 [26] in presence of NaN3, NH4Cl
in methanol:THF, DMF at 65-70 ºC for 16 h yielded azide-
amine 4. Bocylation of azide-amine 4 in presence of Boc anhy-
dride, triethyl amine in dichloromethane at room temperature
for 16 h yielded N-Boc-azidecompound 5. Reduction of N-
Boc-azide 5 was carried out in presence of triphenyl phosphine
in THF at 25-30 ºC for 16 h produced N-Boc-amine 6. Acety-
lation of N-Boc-amine 6 was done in the presence of acetic
anhydride, potassium carbonate in THF at room temperature
for 4 h gave compound 7. De-bocylation of compound 7 in
presence of trifluoroacetic acid in dichloromethane, at 25-30
ºC for 16 h resulted in the formation of impurity WHO-Imp-F, 9
[27]. Initial attempts to prepare WHO Imp-A, 10 by LiOH
hydrolysis of WHO-Imp-F, 9 was unsuccessful mainly due to
its high soluble property in water and difficulty in isolating the
product. Therefore, as an alternative approach, Boc-protected
ethyl ester compound 7 was hydrolyzed in presence of LiOH
and isolated compound 8. After purification, it was directly
used in the next step. Boc de-protection of compound 8, in presence
of IPA·HCl resultant in the formation of desired compound
WHO-Imp-A, 10.
The structural determination of newly synthesized WHO-
Imp-F, 9 and WHO-Imp-A, 10 was established by 1H NMR,
13C NMR, mass and IR techniques. Characterization of ethyl
(3R,4R,5S)-5-(acetylamino)-4-amino-3-(pentan-3-yloxy)-
cyclohex-1-ene-1-carboxylate (WHO-Imp-F, 9): 1H NMR descri-
ption: The protons resonating at 1.21 ppm as triplet (3H) and
4.16 ppm as quartet (2H) is assigned to the ethyl ester group.
The protons resonating at 0.84-0.89 as multiplet (6H), 1.38-
1.58 as multiplet (4H) and 3.67-3.72 ppm is assigned to the
pental group. The protons resonating at 6.66 ppm (1H), 1.84
ppm (3H) as singlets corresponds to olefinic proton and acetyl
group, respectively. The D2O exchangeable protons of -NH2
and -NH groups resonated at 1.63 and 7.79 ppm. The protons
associated with the cyclohexene ring resonated at 1.95-2.04
1
-HC=C-), 3383(-N-H); H-NMR (CDCl3, 300 MHz): δ 0.89
(t, J = 6.6 Hz, 6H), 1.21 (t, J = 7.2 Hz, 3H), 1.38-1.58 (m, 4H),
1.63 (brs, 2H), 1.84 (s, 3H), 1.95-2.04 (m, 1H), 2.49-2.57 (m,
1H), 2.66-2.72 (m, 1H), 3.33-3.44 (m, 1H), 3.67-3.72 (m, 1H),
3.85 (d, J = 7.2 Hz, 1H), 4.16 (q, J = 7.2 Hz, 2H), 6.66 (s, 1H),
7.79 (d, J = 7.5 Hz, 1H); 13C NMR (300 MHz, DMSO-d6): δ
9.2, 9.5, 14.0, 22.8, 25.3, 25.7, 30.3, 48.8, 54.8, 78.2, 80.0,
128.3,137.8,165.6, 169.1; ESI-MS m/z for [M+H]-calculated
(found) for C16H28N2O4: 313 (313.2).
(3R,4R,5S)-5-(Acetylamino)-4-[(tert-butoxycarbonyl)-
amino]-3-(pentan-3-yloxy)cyclohex-1-ene-1-carboxylic acid
(8):To a stirred solution of acetyl compound 7(15.0 g, 36.3 mmol)
in a mixture of methanol (15 mL) and THF (60 mL) was slowly
added a pre-mixed solution of lithium hydroxide monohydride
(15.25 g, 363.3 mmol) in water (45 mL). The reaction mixture
was stirred at room temperature 7 h.After the completion of the
reaction, checked by TLC, the solvents were stripped from the
reaction mixture under vacuum. The aqueous layer was acidified
with citric acid solution and the product was extracted with
ethylacetate (2 × 25 mL). The organic layer was evaporated under
vacuum and isolated compound 8. Off white solid;Yield: 70 %;
Anal. calcd (%) for C19H32N2O6: C, 59.36; H, 8.39; N, 7.29.
Found: C, 59.33; H, 8.42; N, 7.25.1H NMR (CDCl3, 300 MHz):
δ 0.85 (t, J = 6.6 Hz, 6H), 1.29-1.50 (m, 4H), 138 (s, 9H), 1.76
(s, 3H), 2.06-2.16 (m, 1H), 2.38 -2.50 (m, 1H), 3.33-3.42 (m,
2H), 3.83-3.88 (m, 1H), 4.08-4.10 (m, 1H), 6.56 (brs, 1H), 6.67
(d, J = 6.2 Hz, 1H), 7.70 (d, J = 7.4 Hz, 1H); 13C NMR (300
MHz, DMSO-d6): δ 9.1, 9.2, 22.7, 25.4, 25.7, 25.9, 28.2 (3C),
30.5, 47.7, 55.9, 75.1, 77.2, 81.3, 129.3,137.8, 155.8, 167.2,
168.6; ESI-MS m/z for [M+H]-calculated for C16H28N2O4: 407.2
(M+Na) found: 407.2.
(3R,4R,5S)-5-(acetylamino)-4-amino-3-(pentan-3-yl-
oxy)cyclohex-1-ene-1-carboxylic acid (WHO-Imp-A, 10):
To a mixture of compound 8 (3.5 g, 9.103 mmol) in dichloro-
methane (35 mL) was added IPA·HCl (15 mL), dropwise at 0-5
ºC. The reaction mixture was stirred for 5 h at 25-30 ºC. The
solvent was evaporated and the residue was purified by ethyl
acetate and IPE and isolated compound WHO-Imp-A, 10. Off
white solid; Yield: 80 %; Anal. calcd (%) for C14H24N2O4: C,
59.13; H, 8.51; N, 9.85. Found: C, 59.17; H, 8.53; N, 9.90. IR

2006 Ponduri et al.
Asian J. Chem.
O
O
O
O
O
O
O
O
a
c
b
OEt
OEt
OEt
OEt
H2N
HO
HN
O
N3
4
N3
3
1
2
d
O
O
O
O
O
OEt
O
O
O
HN
f
g
OEt
OEt
OEt
e
HN
HN
H2 N
HN
Boc N3
RT, 16h
BocHN
Boc NH2
5
O
O
6
7
9, WHO Imp-F
LiOH
O
h
LiOH
O
O
i
O
OH
OH
HN
H2N
HN
BocHN
O
O
8
10, WHO Imp-A
Scheme-I: Synthesis of oseltamivir impurities WHO-Imp-A and WHO-Imp-F
and 2.49-2.57 ppm (-CH2 adjacent to ethyl ester group), 2.66-
2.72 ppm (-CH flanked to acetyl group), 3.33-3.44 ppm (-CH
flanked to -NH2 group) and 3.85 ppm (-CH flanked to -O-pent-
anal group). Thus, above 1H NMR description is in agreement
with the desired number of protons in the structure.
ation of WHO Imp-A, 10 was established as per the above
description.
Conclusion
The synthesis and characterization of two potential WHO
listed impurities of oseltamivir phosphate viz., (i) ethyl-(3R,
4R,5S)-5-(acetylamino)-4-amino-3-(pentan-3-yloxy)cyclo-
hex-1-ene-1-carboxylate (WHO-IMP-F, 9) and (ii) (3R,4R,5S)-
5-(acetylamino)-4-amino-3-(pentan-3-yloxy)cyclohex-1-ene-
1-carboxylic acid (WHO-IMP-A, 10) are demonstrated. These
impurities were characterized by IR, mass and NMR spectro-
scopic techniques. Synthesis of these impurities helps in obtaining
a good-quality output of API and formulation, also helps in
establishing the impurity profile of API by understanding the
cause of its origin and control.
13C NMR: The carbon signals resonating at 169.1 ppm,
165.6 ppm is assigned to the characteristic carbonyl groups
viz., ethylester carbonyl (C-12) and acetyl carbonyl group (C-15),
respectively. The carbon signals resonating at 128.3 and 137.8
ppm is assigned to oelfin carbons (C-2 and C-1), respectively.
The methylene carbons signals (-CH2, C-6, C-8, C-10 and C-13)
resonated in the region 25.3 ppm, 25.7 ppm, 30.3 ppm and
60.2 ppm, respectively and were confirmed by carbon DEPT
experiment. The methyl carbons viz., C-9, C-11, C-14 and C-
16 resonated at 9.2, 9.5, 14.0 and 22.8 ppm, respectively while
tertiary carbon signals of cyclohexene ring such as C-5, C-4,
C-3 and C-7 resonated at 48.8, 54.8, 78.2 and 80.0 ppm, respec-
tively. Thus, above 13 C NMR description is in agreement with
the desired number of carbons in the structure.
ACKNOWLEDGEMENTS
The authors express their thanks to Analytical Division
of Mylan Laboratories Ltd., India for providing analytical and
spectral facilites.
IR: IR data suggest that strong characteristic bands appe-
ared at 3383, 1714, 1634 and 1281 cm-1 are due to the following
characteristic groups -NH, -C=O, -C=C-, -C-N associated with
the desired compound.
CONFLICT OF INTEREST
Mass spectra: Mass spectrum of WHO Imp-F, 9 showed
M+1 peaks at m/z 313 in positive mode and is in agreement
with its molecular formula. Similarly, the structural determin-
The authors declare that there is no conflict of interests
regarding the publication of this article.

Vol. 30, No. 9 (2018)
Synthesis and Characterization of Potential Pharmacopeial Impurities of Oseltamivir 2007
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