A new facile chemoenzymatic synthesis of levamisole

Article abstract of DOI:10.1016/j.bmcl.2004.11.054

An efficient and facile chemoenzymatic synthesis of levamisole by employing lipase-mediated resolution of 3-hydroxy-3-phenylpropanenitrile followed by its conversion to β-amino alcohol as the key intermediate is described.

Full text of DOI:10.1016/j.bmcl.2004.11.054

Bioorganic & Medicinal Chemistry Letters 15 (2005) 613–615
A new facile chemoenzymatic synthesis of levamisole
Ahmed Kamal,* G. B. Ramesh Khanna, T. Krishnaji and R. Ramu
Biotransformation Laboratory, Division of Organic Chemistry, Indian Institute of Chemical Technology, Hyderabad 500 007, India
Received 29 October 2004; accepted 16 November 2004
Available online 15 December 2004
Abstract—An efficient and facile chemoenzymatic synthesis of levamisole by employing lipase-mediated resolution of 3-hydroxy-3-
phenylpropanenitrile followed by its conversion to b-amino alcohol as the key intermediate is described.
Ó 2004 Elsevier Ltd. All rights reserved.
Levamisole (lee-VAM-i-sole) the levo isomer of tetrami-
sole is a broad spectrum anthelmintic.1 It is a synthetic
imidazothiazole derivative belonging to a general class
of agents called biologic response modifiers and has
been originally designed for anthelmintic properties,
has immunomodulating and immuno-stimulating prop-
erties and also has been later used in cancer adjuvant
therapy and in the treatment of other ailments. It has
found wide application in the treatment of worm infest-
ations and eliminating intestinal parasites in both
humans2 and animals.1b,2a Levamisole is one of the non-
specific immunomodulating agents used in clinical prac-
tice. It helps restore the function of certain cells of the
bodyÕs defense system when they have been impaired.
It is currently indicated in combination with 5-fluroura-
cil (5-FU) as adjuvant treatment after surgical resection
of stage TNM 3 or DukeÕs C colon cancer over a dura-
tion of one year postoperatively, and is also combined
with radiation therapy for DukeÕs stage B2 and TNM
stage 4 cancer.3
potential building block for the synthesis of levamisole.
History reveals that b-hydroxy nitriles are important
both as technical products and as reagents in organic
chemistry.6 They have been extensively investigated
and employed in the preparation of various intermedi-
ates for naturally occurring bioactive compounds.7–12
In view of their enormous potential for the construction
of chiral organic frameworks they have been exploited
in the present investigation. In continuation of our inter-
est13 in the preparation of optically pure b-hydroxynitr-
iles and their applications towards the preparation of
biologically important compounds or their intermedi-
ates by employing lipase catalyzed resolution processes
we herein wish to report a practical synthesis of levam-
isole employing (R)-3-hydroxy-3-phenylpropanenitrile
and (R)-3-acetyloxy-3-phenylpropanenitrile. Moreover,
this is the first report on the chemoenzymatic synthesis
of levamisole.
The transesterification of 3-hydroxy-3-phenylpropane-
nitrile by vinyl acetate has been carried out as reported
earlier by us in good yields with high enantioselectivity
(>99% ee).13b We herein have also investigated the
lipase-mediated hydrolysis of 3-acetoxy-3-phenylpro-
In spite of the biological importance of this compound
there are not many reports of its preparation. The race-
mic form of this compound has been prepared by
Raeymaekers et al.1b employing phenacyl bromide.
They have also prepared the optically pure form starting
from optically pure phenylethylenediamine.4 Achiwa
and co-workers5 employed rhodium catalyst in the
asymmetric synthesis of levamisole.
panenitrile in phosphate buffer to afford required
30
(R)-3-hydroxy-3-phenylpropanenitrile (1R) ½aꢀ ¼ þ59:9
D
(c 1.0, CHCl3) in good yields and high enantioselectivity
(Scheme 1 and Table 1).
Enantiomerically pure (R)-3-hydroxy-3-phenylpropane-
nitrile (1R) and (R)-3-acetoxy-3-phenyl propanenitrile
(2R) obtained after lipase-catalyzed resolution have
been effectively employed in the preparation of levami-
sole in a simple reaction sequence as shown in Scheme
2. 1R and 2R on treatment with H2O2 in aqueous
ammonia have been efficiently transformed into
Based on the retrosynthetic strategy optically pure 3-hydr-
oxy-3-phenylpropanenitrile has been considered as a
*
Corresponding author. Tel.: +91 40 27193157; fax: +91 40
27193189; e-mail: ahmedkamal@iict.res.in
0960-894X/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2004.11.054

614
A. Kamal et al. / Bioorg. Med. Chem. Lett. 15 (2005) 613–615
OH
OH
N
N
N
N
OH
OAc
N
N
1S
1R
OAc
i
ii
OAc
1
2
2R
2S
Scheme 1. Reagents and conditions: (i) immobilized Pseudomonas cepacia (PS-C) lipase, vinyl acetate, diisopropyl ether; (ii) immobilized P. cepacia
lipase, phosphate buffer (pH = 7.2).
O
O
OR
OH O
N
NH
ii
iii
i
NH2
1R : R = H
4S
3R
2R : R = Ac
TBDMS
OTBDMS
NH2
OH
O
H
N
vi
NH2
iv
v
Cl
N
7S
5S
6S
HN
OH
S
OH
H
N
S
N
viii
vii
Cl
N
8S
Levamisole (9S)
Scheme 2. Reagents and conditions: (i) H2O2, aq NH3; (ii) Pb(OAc)4, pyridine; (iii) NaOH, EtOH–H2O, reflux; (iv) TBDMS–Cl, imidazole; (v) 1,2-
dichloroethane, K2CO3, 18-crown-6; (vi) TBAF, THF; (vii) KSCN, EtOH–H2O; (viii) SOCl2, CH2Cl2.
30
D
27
amine (7S)14 ½aꢀ ¼ þ47:1 (c 1.0, CHCl3) in 60% yield
(R)-3-phenyl-3-hydroxypropanamide (3R)14 ½aꢀ
¼
D
(two steps). Deprotection of the protecting group re-
þ32:1 (c 1.0, EtOH) without any loss in optical purity
in almost quantitative yield. The resulting amide has
been subjected to Hoffmann-like rearrangement in the
presence of Pb(OAc)4 in pyridine to afford (S)-5-phen-
yl-1,3-oxazolidine-2-one (4S)14 ½aꢀ ¼ þ51:4 (c 1.1,
sulted in the formation of N-(2-chloroethylamino)-1-
27
D
phenyl-1-ethanol (8S) ½aꢀ ¼ þ31:0 (c 1.1, MeOH),
which on coupling with KSCN in refluxing ethanol
afforded 2-imino-3-(2S-hydroxy-2-phenylethyl)thiazo-
lidine a precursor for levamisole as described by Achiwa
and co-workers.5 This precursor without purification
has been transformed into the target molecule (9S)
29
D
CHCl3) in about 80% yield without any racemization
or inversion at the chiral center. In principle, in Hoff-
mann rearrangement the isocyanate formed is hydro-
lyzed with external nucleophile like water to yield
amine after the rearrangement. Here, in this process
the vicinal hydroxyl group acts as a nucleophile on the
isocyanate resulting in the cyclization to form an oxazo-
lidinone ring system. N-Alkylation at this stage (4S)
using various reagents under different conditions has
not been successful. Hence, 4S has been hydrolyzed in
aqueous-alcoholic NaOH to provide (S)-2-amino-1-
phenyl-1-ethanol (5S)14 in 79% yield. Alkylation of the
amino alcohol (5S) resulted in the formation of both
N-alkylation and O-alkylated product. To overcome this
problem, alcohol function has been protected with
TBDMSCl (6S) and then refluxed in 1,2-dichloroethane
in the presence of K2CO3 and 18-crown-6 to afford N-(2-
chloroethyl)-2-tert-butyldimethylsilyloxy-2-phenylethan-
29
D
27
D
½aꢀ ¼ ꢁ51:2 (c 1.1, CHCl3) lit.5 ½aꢀ ¼ ꢁ49:0 (c 1.0,
Table 1. Enzymatic hydrolysis of 3-acetyloxy-3-phenylpropanenitrile
in phosphate buffer
Entry Lipasesa Time (h)
Alcohol
Acetate
Yieldb% eec% Yieldb% eec%
1
2
PS-C
PS-D
14
80
41
40
>99
>99
40
41
>99
>99
a Pseudomonas cepacia lipase immobilized on modified ceramic parti-
cles (PS-C), P. cepacia lipase immobilized on diatomite (PS-D).
b Isolated yields.
c Determined by chiral HPLC (chiral OJ-H column; Diacel) employing
hexane–isopropanol (90:10) as mobile phase at 0.5 mL/min and
monitored by UV (254 nm).

A. Kamal et al. / Bioorg. Med. Chem. Lett. 15 (2005) 613–615
615
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CHCl3) on treating with SOCl2 in CH2Cl2 with double
inversion at the chiral center in about 50% yield.
In summary, a simple, practical and highly enantioselec-
tive synthesis of levamisole has been accomplished by
employing (R)-3-acetoxy-3-phenylpropanenitrile and
(R)-3-hydroxy-3-phenylpropanenitrile obtained by both
enzymatic transesterification and hydrolysis processes.
Acknowledgements
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The authors G.B.R.K., T.K. and R.R. are thankful to
CSIR, New Delhi for the award of research fellowship.
References and notes
13. (a) Kamal, A.; Khanna, G. B. R. Tetrahedron: Asymmetry
2001, 12, 405; (b) Kamal, A.; Khanna, G. B. R.; Ramu, R.
Tetrahedron: Asymmetry 2002, 13, 2039; (c) Kamal, A.;
Khanna, G. B. R.; Ramu, R.; Krishnaji, T. Tetrahedron
Lett. 2003, 44, 4783.
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Vandenberk, J.; Demoen, P. J. A.; Van Offenwert, T. T.
T.; Janssen, P. A. J. J. Med. Chem. 1966, 9, 545.
14. 1R: IR (Neat) 3438, 3046, 3015, 2954, 2923, 2892, 2238,
1
1115, 1092 cmꢁ1; H NMR (200 MHz, CDCl3) d 2.67 (d,
2. (a) Janssen, P. A. J. Prog. Drug Res. 1976, 20, 347; (b)
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2H, J = 7.23 Hz), 3.15 (br s, 1H), 4.94 (t, 1H, J = 5.78),
7.35 (s, 5H); Mass (EI) 147 (M+), 121, 107, 105, 91, 79, 77.
2R: mp 121–124 °C; IR (KBr) 3054, 3008, 2961, 2923,
1
2254, 1738, 1238, 1200, 1046 cmꢁ1; H NMR (200 MHz,
3. (a) Moertal, G. G.; Fleming, T. R.; Macdonald, J. S. Anal.
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J. Tetrahedron Lett. 1967, 1467.
5. (a) Sakuraba, S.; Takahashi, H.; Takeda, H.; Achiwa, K.
Chem. Pharm. Bull. 1995, 43, 738; (b) Takeda, H.;
Tachinami, T.; Aburatani, M.; Takahashi, H.; Morimoto,
T.; Achiwa, K. Tetrahedron Lett. 1988, 30, 363.
6. (a) Dittus, G. In Methoden Der Organishen Chemie
(Huben-Weyl); Muller, E., Ed.; Georg Thieme: Stutgart,
1965; Vol. 6/3, p 451; (b) Henecka, H., Erwin, O. In
Methoden der Organishen Chemie (Huben-Weyl), 4th ed.;
Muller, E., Ed.; Georg Thieme: Stutgart, 1952; Vol. 8, pp
427–661.
7. (a) Seidel, W.; Seebach, D. Tetrahedron Lett. 1982, 23,
159; (b) Meyers, A. I.; Amos, R. A. J. Am. Chem. Soc.
1980, 102, 870; (c) Ha, D. C.; Hart, D. J. Tetrahedron Lett.
1987, 28, 4489; (d) Kramer, A.; Pfander, H. Helv. Chim.
Acta 1982, 65, 293; (e) Amstutz, R.; Hungerbuhler, E.;
Seebach, D. Helv. Chim. Acta 1981, 64, 1796.
8. (a) Challis, B. C.; Challis, J. A. In Comprehensive Organic
Chem.; Pergamon: Oxford, 1979; Vol. 2, p 957; (b)
Simons, S. S., Jr. J. Org. Chem. 1973, 38, 414; (c) Quiros,
M.; Rebolledo, F.; Liz, R.; Gotor, V. Tetrahedron: Asym-
metry 1997, 8, 3035; (d) Garcia, M. J.; Rebolledo, F.;
Gotor, V. Tetrahedron: Asymmetry 1992, 3, 1519; (e)
Garcia, M. J.; Rebolledo, F.; Gotor, V. Tetrahedron:
Asymmetry 1993, 4, 2199; (f) Kumar, A.; Ner, D. H.; Dike,
S. Y. Tetrahedron Lett. 1991, 32, 1901.
9. (a) Muller, H. M.; Seebach, D. Angew. Chem., Int. Ed.
Engl. 1993, 32, 477, and references cited therein; (b) Zhou,
B. N.; Gopalan, A. S.; VanMiddlesworth, F.; Shieh, W.
R.; Sih, C. J. J. Am. Chem. Soc. 1983, 105, 5925; (c) Boaz,
N. W. J. Org. Chem. 1992, 57, 4289.
CDCl3) d 2.15 (s, 3H), 2.86 (d, 2H, J = 5.52 Hz), 5.94 (t,
1H, J = 5.52 Hz), 7.35 (s, 5H); Mass (EI) 189, 162, 149,
130, 120, 107, 77. 3R: mp 101–103 °C; IR (KBr) 3377,
3300, 3177, 2961, 2900, 2761, 1623, 1431, 1392, 1331,
1046 cmꢁ1; 1H NMR (200 MHz, CD3OD) d 2.41–2.70 (m,
2H), 4.93–5.11 (m, 1H), 7.20–7.40 (m, 5H); Mass (EI) 165,
141, 120, 105, 91, 77, 59. 4S: mp 92–94 °C; IR (Neat) 3262,
2933, 2902, 2839, 1718, 1239, 1082, 972 cmꢁ1
;
1H
NMR (200 MHz, CDCl3) d 3.55 (t, 1H, J = 8.2 Hz), 3.99
(t, 1H, J = 8.2 Hz), 5.60 (t, 1H, J = 7.3 Hz), 6.67 (br
s, 1H), 7.28–7.40 (m, 5H); Mass (EI) 163 (M+), 118, 107,
29
105, 91, 79, 77. 5S: mp 57–59 °C; lit.15 ½aꢀD ¼ þ45:5 (c
23
1.5, EtOH); ½aꢀD ¼ þ47:9 (c 1.5, EtOH); IR (Neat) 3412,
3349, 3318, 2941, 2902, 2862, 1082, 1004 cmꢁ1
;
1H
NMR (300 MHz, CDCl3) d 2.78 (dd, 1H, J1 = 7.7 Hz,
J2 = 12.6 Hz), 2.98 (dd, 1H, J1 = 3.8 Hz, J2 = 12.6 Hz),
4.58 (dd, 1H, J1 = 3.8 Hz, J2 = 7.7 Hz), 7.21–7.30 (m, 5H);
28
Mass (EI) 106, 90, 78, 77, 51. 6S: ½aꢀD ¼ þ67:4 (c 1.1,
CHCl3); IR (Neat) 3373, 3059, 3027, 2957, 2925, 2886,
2855, 1247, 1098, 1058 cmꢁ1; 1H NMR (300 MHz, CDCl3)
d ꢁ0.16 (s, 3H), 0.00 (s, 3H), 0.86 (s, 12H), 2.74 (d, 2H,
J = 5.6 Hz), 4.57 (t, 1H, J = 5.6 Hz), 7.15–7.27 (m, 5H);
Mass (EI) 251 (M+), 236, 222, 194, 155, 141, 102, 91, 77,
73. 7S: IR (Neat) 2941, 2910, 2870, 2847, 1741, 1247,
1105, 1059, 1035 cmꢁ1 1H NMR (300 MHz, CDCl3) d
;
ꢁ0.19 (s, 3H), 0.00 (s, 3H), 0.84 (s, 12H), 3.23–3.31 (m,
3H), 3.57–3.65 (m, 1H), 4.13–4.20 (m, 2H), 4.88 (t, 1H,
J = 6.2 Hz), 7.19–7.30 (m, 5H); Mass (EI) 264
(M+ꢁCH2Cl), 222, 155, 141, 102, 77, 73, 44. 8S:
mp 135–137 °C; IR (Neat) 3357, 3027, 2988, 2925, 2847,
1
1710, 1451, 1255, 1082, 1051 cmꢁ1; H NMR (200 MHz,
DMSO (D6)) d 3.22–3.42 (m, 2H), 3.46–3.58 (m, 1H),
3.70–3.82 (m, 1H), 4.21–4.30 (m, 2H), 4.76–4.85 (m, 1H),
5.30 (br s, 1H), 7.22–7.39 (m, 5H); Mass (EI) 200, 107,
101, 79, 77, 56, 51. 9S: 1H NMR (300 MHz, CDCl3) d
3.26–3.60 (m, 3H), 3.65–3.80 (m, 2H), 4.04 (t, 1H,
J = 8.75 Hz), 5.48 (t, 1H, J = 8.23 Hz), 7.24–7.33 (m,
5H); Mass (EI) 178 (M+ꢁC2H4), 132, 105, 91, 77, 42.
15. Meyers, A. I.; Slade, J. J. Org. Chem. 1980, 45, 2785.
10. (a) Servi, S. Synthesis 1990, 1, and references cited therein;
(b) North, M. Tetrahedron Lett. 1996, 37, 1699, and