A facile and convenient synthesis of (±)-biotin via MgCl2/Et3N-mediated C-C coupling and Mitsunobu reaction

Article abstract of DOI:10.1055/s-0034-1379365

A synthesis of (±)-biotin is described starting from simple starting materials viz. cyclohexanone and amino malonic acid ester. The key steps involved are MgCl₂/Et₃N coupling of amino malonic acid ester derivative and acid chloride,

Full text of DOI:10.1055/s-0034-1379365

LETTER
▌2879
lAetteFr acile and Convenient Synthesis of (±)-Biotin via MgCl2/Et3N-Mediated
C–C Coupling and Mitsunobu Reaction
Synthesis of (±)-Biotin
Subhash P. Chavan,* Prakash N. Chavan, Pradeep B. Lasonkar, Lalit B. Khairnar, Appasaheb L. Kadam
Organic Chemistry Division, CSIR-NCL (National Chemical Laboratory), Dr. Homi Bhabha Road, Pune-411008, Maharashtra, India
Fax +91(20)25902629; E-mail: sp.chavan@ncl.res.in
Received: 08.07.2014; Accepted after revision: 29.09.2014
Our longstanding interest in the synthesis of biologically
Abstract: A synthesis of (±)-biotin is described starting from sim-
important molecule led us to explore a practical route for
ple starting materials viz. cyclohexanone and amino malonic acid
biotin. Earlier we have reported the syntheses of D-(+)-bi-
otin involving features of acyliminium chemistry, stereo-
ester. The key steps involved are MgCl2/Et3N coupling of amino
malonic acid ester derivative and acid chloride, Mitsunobu reaction,
ozonolysis, Staudinger reduction, novel urea formation, and subse- selective amido alkylation, intramolecular radical
quent dibenzylation. This approach is economical and involves
high-yielding steps and simple reaction conditions.
cyclization, and Sharpless asymmetric dihydroxylation as
the key steps.6 Considering key requirements and needful
Key words: biotin, ozonolysis, Appel reaction, Mitsunobu reac-
tion, Staudinger reduction
objectives in mind, this communication describes our ef-
forts towards a facile and convenient strategy for the total
synthesis of biotin (1), which involves notable features
like MgCl2/Et3N-mediated C–C coupling reaction, Mitsu-
Biotin is the water-soluble vitamin H that was isolated by nobu inversion, ozonolysis, Staudinger reduction, novel
Kogl et al. in 1936 from egg yolk and later on from pig liv- urea formation, and subsequent dibenzylation as the key
er and milk concentrate.1 It is present as a key constituent organic reactions.
of animal and human tissues. The structure of vitamin H
was elucidated in 1942, and the presence of bicyclic
It was envisaged that biotin (1) can be synthesized from
ketone 2 which could be derived from crucial intermediate
3 using proper chemical transformations. Intermediate 3
would be simply obtained from β-keto ester 4, which in
framework was confirmed by the first total synthesis in
1945.2 (+)-Biotin acts as a cofactor in CO2 fixation, decar-
boxylation, and transcarboxylation in some key physio-
turn can be easily prepared from cyclohexanone and ami-
logical processes, that is, gluconeogenesis and fatty acid
no malonic acid ester derivative (Scheme 1).
synthesis. It also has significant importance in human nu-
trition and plays a key role in animal-growth promotion.
O
S
O
Biotin deficiency is found in humans and birds, and ani-
mals are treated by providing biotin as a feed additive es-
pecially in poultry and swine. In addition, biotin is used in
pharmaceutical formulations as an additive, and its avidin
complex is used in the area of drug delivery, immunoas-
say, isolation, and localization.3
EtOOC
HN
NH
N
O
NH
MeOOC
OH
COOH
O
biotin (1)
2
EtOOC
Cl
Given the fundamental and commercial importance of vi-
tamin H in the poultry (biochemistry and pharmaceutical
formulations) interest in this molecule was revived. As a
result, numerous efforts have been directed by synthetic
community to develop new and efficient approaches for
biotin.4,5 Although several elegant syntheses have been re-
ported in the literature, many of them possess drawbacks
like tedious reaction conditions and use of expensive cat-
alysts and reagents, with low overall yields. Biotin is man-
ufactured and supplied on an industrial scale by using
Hoffmann La Roche’s method from fumaric acid. Al-
though a variety of methods are known for the synthesis
of biotin, there still exists a need to develop an efficient
and practical strategy which involves simple starting ma-
terials, inexpensive reagents, and high-yielding steps.
Cl
O
N
NHCbz
COOEt
NCbz
COOEt
3
4
O
NHCbz
COOEt
+
HOOC
5
6
Scheme 1 Retrosynthetic analysis for biotin (1)
Accordingly, the synthesis of biotin (1) commenced with
coupling of the acid 6 and acid choride 8 (which was read-
ily prepared from cyclohexanone as shown in Scheme 2)7
in the presence of MgCl2 and Et3N and furnished β-keto
ester 4 in 65% yield.8 The chemoselective reduction of
β-keto ester 49 was carried out using NaBH4 in MeOH to
SYNLETT 2014, 25, 2879–2882
Advanced online publication: 05.11.2014
0
9
3
6
-
5
2
1
4
1
4
3
7
-
2
0
9
6
DOI: 10.1055/s-0034-1379365; Art ID: st-2014-b0573-l
© Georg Thieme Verlag Stuttgart · New York

2880
S. P. Chavan et al.
LETTER
afford β-hydroxy ester 9 in 90% yield as a mixture of dia- to be cis and was in accordance with the data of similar
stereomers in the ratio of 9:1.
compounds reported in the literature.10,12
Next task was the introduction of second nitrogen atom,
which was done by treating 9 under optimized Mitsunobu
reaction conditions, involving Bu3P, N3H, and DEAD in
toluene, to give azide 10 in 82% yield.13 The azide 10 was
subjected to Staudinger reaction conditions14 using Ph3P
in Et2O to afford an amine, which without further purifi-
cation was subjected to chemical masking with ethyl chlo-
roformate and Et3N as the base to obtain cyclic urea 315 as
the sole product in excellent yield. After successfully
forming the urea ring, the task remaining for biotin (1)
synthesis was the construction of the tetrahydrothiophene
ring and unmasking of the valeric acid side chain. Further,
urea 3 was reduced with NaBH4 in MeOH to furnish alco-
hol 11 in 95% yield (Scheme 3). It is interesting to note
that two reactions occur in one pot viz. reduction of the es-
ter to an alcohol group and removal of the N-Cbz group.
i) NaH2PO4
NaClO2
H2O2, MeCN
r.t.
Cl
O
Cl
O
O
POCl3, DMF
Cl
H
CH2Cl2, 0 °C to r.t.
6 h, quant.
ii) (COCl)2, r.t.
95% ( 2 steps)
5
7
8
Scheme 2 Synthesis of acid chloride 8
The stereochemistry of the major isomer of 9 was expect-
ed to be syn based on literature reports,10 and it was further
established by carrying out acetonide protection of hy-
droxy amine 9 using 2,2-dimethoxypropane in acetone in
the presence of a catalytic amount of BF3·OEt211 and was
confirmed by 1H NMR spectroscopy (coupling constant, J
= 6.84 Hz), which clearly established its stereochemistry
The resultant alcohol 11 was subjected to ozonolysis us-
ing O3 and NaHCO3 in CH2Cl2–MeOH, but unfortunately
did not furnish the desired product.
Cl
O
Cl
O
NHCbz
COOEt
NHCbz
COOEt
MgCl2, Et3N
Cl
However, when the hydroxy group was protected as its
TBS ether 12, using TBSCl, imidazole, and catalytic
DMAP, it underwent smooth ozonolysis to afford ketone
13 in 96% yield. The TBS deprotection of ketone 13 was
carried out with CSA and MeOH to afford alcohol 2 in
92% yield.16 As per structural demand for biotin (1) motif,
further plan was to introduce a sulfur atom by converting
hydroxy group into a good leaving group.
+
HOOC
Cl
THF, 0 °C, 4 h
65%
8
6
4
OH
Cl
N3
Bu3P, DEAD
NaBH4, MeOH
NHCbz
NHCbz
COOEt
N3H, 0 °C
15 min
82%
0 °C, 10 min
90%
COOEt
9
10
O
O
Attempts to convert alcohol 2 into its mesylate and to-
sylate derivatives under standard conditions met with fail-
ure. So the alcohol 2 was subjected to Appel reaction
conditions using Ph3P and CBr4 to furnish bromide 14 in
87% yield.17
i) Ph3P, Et2O
r.t., 1 h
EtOOC
Cl
EtOOC
Cl
NaBH4, MeOH
N
N
NCbz
NH
0 °C to r.t., 2 h
95%
ii) ClCOOEt, Et3N
0 °C to r.t., 1.5 h
93%
COOEt
OH
3
11
Although the bromide 14 appeared to be an ideal substrate
for thiol substitution, various conditions were utilized to
Scheme 3 Synthesis of alcohol 11
O
EtOOC
Cl
TBSCl, imidazole
N
O3, NaHCO3
DMAP, CH2Cl2
CH2Cl2 MeOH (5:1)
NH
11
0 °C– r.t., 2 h
88%
–78 °C, 1 h
96%
OTBS
12
O
O
EtOOC
N
NH
EtOOC
O
N
NH
CSA, MeOH
MeO
MeOOC
r.t., 3 h
92%
OTBS
HO
O
O
13
2
O
O
i) NaSH, DMF
r.t.
CBr4, Ph3P
EtOOC
EtOOC
N
NH
N
NH
Br
O
O
CH2Cl2, 0 °C to
r.t., 2 h
ii) thiourea
NaOH, EtOH
MeO
MeO
87%
HS
O
O
14
15
Scheme 4 Synthetic attempt towards thiol 15
Synlett 2014, 25, 2879–2882
© Georg Thieme Verlag Stuttgart · New York

LETTER
Synthesis of (±)-Biotin
2881
introduce the sulfur functionality such as NaSH/DMF,
thiourea/NaOH/EtOH, KSAc/DMF, etc., proved to be in-
effective (Scheme 4). Notably, the reactions failed to pro-
vide the desired thiol 15. These observations forced us to
slightly modify our strategy for biotin (1).
Acknowledgment
P.N.C., P.B.L., L.B.K., and A.L.K. thanks CSIR, New Delhi for Re-
search fellowship. We thank Dr. U. R. Kalkote, Dr. H. B. Borate,
and Dinesh Kalbhor for useful discussion. The authors thank CSIR,
New Delhi for financial support as of XII year plan programme un-
der title ORIGIN (CSC-0108) and ACT (CSC-0301).
It was decided to protect the NH group of urea 12 as its N-
benzyl ether. Accordingly, the urea 12 was treated with
benzyl bromide and NaH as the base, and, interestingly,
the formation of dibenzyl urea 1618 was observed in excel-
lent yield. It is interesting to note that this transformation
involves unusual decaboxylation followed by protection
of the NH functionality of urea as its bisbenzyl deriva-
tive.19 The dibenzyl urea 16 thus obtained was subjected
to ozonolysis to provide ester 17 in good yield. The TBS
deprotection of ester 17 was carried out in MeOH using
CSA to afford alcohol 18 in 92% yield.
Supporting Information for this article is available online
at
http://www.thieme-connect.com/products/ejournals/journal/
10.1055/s-00000083.SunogIpimrfiantoSuIpg
n
fonirtat
ori
References and Notes
(1) (a) Kogl, F.; Tonnis, B.; Sey, H. Z. Physiol. Chem. 1936,
242, 443. (b) du Vigneoud, V.; Hofmann, K.; Melville, D.
B.; Gyorgy, P. J. Biol. Chem. 1941, 140, 643. (c) Melville,
D. B.; Hofmann, K.; Hague, E. R.; du Vigneaud, V. J. Biol.
Chem. 1942, 142, 615.
(2) (a) Harris, S. A.; Wolf, D. E.; Mozingo, R.; Anderson, R. C.;
Arth, G. E.; Easton, N. R.; Heyl, D.; Wilson, A. N.; Folkers,
K. J. Am. Chem. Soc. 1944, 66, 1756. (b) Harris, S. A.; Wolf,
D. E.; Mozingo, R.; Anderson, R. C.; Arth, G. E.; Easton, N.
R.; Heyl, D.; Wilson, A. N.; Folkers, K. J. Am. Chem. Soc.
1945, 67, 2098.
Next task was to introduce the thiol group. Accordingly,
alcohol 18 was converted into tosylate 19 using tosyl cho-
ride, Et3N, and catalytic DMAP to furnish tosylate 19. To-
sylate 19 was then subjected to nucleophilic displacement
using potassium thioacetate in DMF–THF to afford thio-
acetate 20 in 90% yield.20 The conversion of thioacetate
20 into biotin (1) has been recently reported by us
(Scheme 5).6a
(3) Wilcheck, M.; Bayer, E. A. Anal. Biochem. 1988, 171, 1.
(4) For the synthesis of biotin, see: (a) De Clercq, P. J. Chem.
Rev. 1997, 97, 1755. (b) Seki, M. Med. Res. Rev. 2006, 26,
434; and references cited therein.
In conclusion, we have demonstrated a novel and efficient
total synthesis of (±)-biotin (1) using cyclohexanone and
amino malonic acid ester derivative as commercially
readily available inexpensive starting materials. The note-
worthy features of this synthesis are the MgCl2/Et3N-me-
diated coupling, Mitsunobu reaction, ozonolysis, and
Staudinger reduction as the key synthetic protocols. The
synthesis of biotin has been accomplished in 13 purifica-
tion steps with 13.68% overall yield. This method could
be of great value in terms of its simplicity in the construc-
tion of urea, the tetrahydrothiophene ring, and also elabo-
ration of the pentanoic acid side chain of the biotin
skeleton. Investigation of the enzymatic and catalytic
asymmetric reduction procedures to accomplish the
asymmetric total synthesis of (+)-biotin is currently under
way, and the results will be reported in due course.
(5) (a) Chen, F. E.; Zhao, J. F.; Xiong, F. J.; Xie, B.; Zhang, P.
Carbohydr. Res. 2007, 342, 2461. (b) Kale, A. S.; Puranik,
V. G.; Deshmukh, A. R. A. S. Synthesis 2007, 1159.
(c) Goldberg, M. W.; Strenbach, L. H. US 2, 489235, 1949;
Chem. Abstr. 1951, 45, 186g (d) Harris, S. A.; Wolf, D. E.;
Mozinco, R.; Anderson, R. C.; Arth, G. E.; Easton, N. R.;
Hely, D.; Wilson, A. N.; Folkers, K. J. Am. Chem. Soc. 1944,
60, 1756. (e) Bory, S.; Luche, M. J.; Moreau, B.; Lavielle,
S.; Marquet, A. Tetrahedron Lett. 1975, 827. (f) Lavielle, S.;
Bory, S.; Moreau, B.; Luche, J.; Marquet, A. J. Am. Chem.
Soc. 1978, 100, 1558. (g) Ohrui, H.; Emoto, S. Tetrahedron
Lett. 1975, 16, 2765. (h) Wilson, S. R.; Mao, D. T. J. Am.
Chem. Soc. 1978, 100, 6291. (i) Ravindranathan, T.;
Hiremath, S. V.; Reddy, D. R.; Rama Rao, A. V. Carbohydr.
Res. 1984, 134, 332. (j) Poetsch, E.; Casutt, M. Chimia 1987,
41, 148. (k) Turos, E.; Parvez, M.; Garigipati, R. S.;
Weinreb, S. M. J. Org. Chem. 1988, 53, 1116. (l) Matsuki,
K.; Inoue, H.; Takeda, M. Tetrahedron Lett. 1993, 34, 1167.
O
O
O3, NaHCO3
O
CH2Cl2–MeOH
Cl
BnN
BnN
NBn
BnN
NBn
TsCl, Et3N
(5:1)
NaH, BnBr, THF
CSA, MeOH
NBn
12
4
1.5 h
–78 °C
96%
MeOOC
4
CH2Cl2, 0 °C to r.t.
0 °C, 3 h
94%
MeOOC
r.t., 5–6 h
92%
3 h
90%
TBSO
O
HO
O
OTBS
16
17
18
O
BnN
4
O
NBn
KSAc
CH2Cl2–THF
BnN
NBn
ref. 6a
MeOOC
( )-biotin (1)
4
r.t., 3 h
90%
MeOOC
TsO
O
AcS
O
20
19
Scheme 5 Synthesis of (±)-biotin (1)
© Georg Thieme Verlag Stuttgart · New York
Synlett 2014, 25, 2879–2882

2882
S. P. Chavan et al.
LETTER
(m) Kurimoto, I.; Mizuno, M.; Hirata, N.; Minami, M. JP 06
263752, 1994; Chem. Abstr. 1995, 122, 81011s (n) Chen, F.
E.; Huang, Y. D.; Fu, H.; Cheng, Y.; Zhang, D. M.; Li, Y.
Y.; Peng, Z. Z. Synthesis 2000, 2004. (o) Xiong, F.; Chen,
X.-X.; Liu, Z.-Q.; Chen, F.-E. Tetrahedron Lett. 2010, 51,
3670.
(13) Green, J. E.; Bender, D. M.; Jackson, S.; O’Donnell, M. J.;
McCarthy, J. R. Org. Lett. 2009, 11, 807.
(14) Staudinger, H.; Meyer, J. Helv. Chim. Acta 1919, 2, 635.
(15) Data for Compound 3
Rf = 0.7 (PE–EtOAc = 75:25). 1H NMR (400MHz, CDCl3 +
CCl4): δ = 7.43–7.28 (m, 5 H), 5.39–5.23 (m, 3 H), 4.40–
4.14 (m, 5 H), 2.48–2.36 (m, 2 H), 1.98 (br s, 2 H), 2.06–1.91
(m, 2 H), 1.79–1.60 (m, 4 H), 1.34 (t, J = 7.2 Hz, 3 H), 1.25
(t, J = 7.2 Hz, 3 H). 13C NMR (100 MHz, CDCl3 + CCl4): δ
= 168.5, 150.9, 150.5, 147.3, 134.7, 131.6, 129.4, 128.5,
128.4, 127.9, 68.8, 63.2, 62.4, 57.9, 55.4, 33.9, 24.1, 23.3,
21.7, 14.2, 14.0. IR (CHCl3): νmax = 2983, 2938, 1817, 1750,
1728, 1661, 1370, 1024 cm–1. ESI-HRMS: m/z calcd for
C23H27ClN2O7Na: 510.1399 [M + Na]+; found: 501.1400.
(16) Narina, S. V.; Kumar, T. V.; Gorge, S.; Sudalai, A.
Tetrahedron Lett. 2007, 48, 65.
(6) (a) Chavan, S. P.; Lasonkar, P. B.; Chavan, P. N.
Tetrahedron: Asymmetry 2013, 24, 1473. (b) Chavan, S. P.;
Chittiboyina, A. G.; Ravindranathan, T.; Kamat, S. K.;
Kalkote, U. R. J. Org. Chem. 2005, 70, 1901. (c) Chavan, S.
P.; Chittiboyina, A. G.; Ramakrishna, G.; Tejwani, R. B.;
Ravindranathan, T.; Kamat, S. K.; Rai, B.; Sivadasan, L.;
Balakrishnan, K.; Ramalingam, S.; Deshpande, V. H.
Tetrahedron 2005, 61, 9273. (d) Chavan, S. P.;
Ramakrishna, G.; Gonnade, R. G. Bhadbhade M. M.
Tetrahedron Lett. 2004, 45, 7307. (e) Chavan, S. P.;
Tejwani, R. B.; Ravindranathan, T. J. Org. Chem. 2001, 66,
6197.
(17) Appel, R. Angew. Chem., Int. Ed. Engl. 1975, 14, 801.
(18) Data for Compound 16
(7) (a) Hartung, W. H.; Beaujon, J. H. R.; Cocolas, G. Org.
Synth. 1960, 40, 24; Org. Synth. Coll. Vol. V 1973, 5, 376.
(b) Vilsmeier, A.; Haack, A. Ber. Dtsch. Chem. Ges. 1927,
60, 119. (c) Bal, B. S.; Childers, W. E.; Pinnick, H. W.
Tetrahedron 1981, 37, 2091.
Rf = 0.5 (PE–EtOAc = 60:40); mp 87–89 °C. 1H NMR (400
MHz, CDCl3 + CCl4): δ = 7.34–7.21 (m, 10 H), 4.59 (d, J =
6.0 Hz, 1 H), 4.52 (d, J = 14.7 Hz, 1 H), 4.12–3.97 (m, 1 H),
4.10–4.00 (m, 2 H), 3.52–3.45 (m, 1 H), 3.14–3.07 (m, 1 H),
2.22 (t, J = 6.2 Hz, 2 H), 1.77–1.68 (m, 1 H), 1.58–1.49 (m,
3 H), 1.42–1.33 (m, 1 H), 1.20 (dd, J = 6.4, 13.3 Hz, 1 H),
0.84 (s, 9 H), –0.01 (s, 3 H), –0.03 (s, 3 H). 13C NMR (100
MHz, CDCl3 + CCl4): δ = 160.3, 137.3, 131.1, 130.1, 128.8,
128.4, 128.3, 127.3, 127.2, 62.5, 57.6, 56.5, 46.8, 46.1, 34.2,
25.8, 23.6, 21.6, 18.2., –5.4, –5.5. IR (CHCl3): νmax = 3030,
2930, 1698, 1657, 1448, 1357, 1119 cm–1. ESI-HRMS: m/z
calcd for C30H41ClN2O2SiNa: 547.2518 [M + Na]+; found:
547.2523.
(8) Krysan, D. J. Tetrahedron Lett. 1996, 37, 3303.
(9) Data for Compound 4
Rf = 0.6 (PE–EtOAc = 70:30). 1H NMR (200 MHz, CDCl3 +
CCl4): δ = 7.40–7.26 (m, 5 H), 5.99 (d, J = 7.7 Hz, 1 H), 5.66
(d, J = 7.8 Hz, 1 H), 5.12 (s, 2 H), 4.23 (q, J = 7.1 Hz, 2 H),
2.59–2.21 (m, 4 H), 1.83–1.52 (m, 4 H), 1.28 (t, J = 7.1 Hz,
3 H). 13C NMR (50 MHz, CDCl3 + CCl4): δ = 195.2, 165.9,
155.3, 134.5, 133.2, 128.5, 128.0, 127.8, 67.1, 62.6, 62.3,
34.0, 28.2, 23.0, 21.2, 14.0. IR (CHCl3): νmax = 2937, 2866,
1728, 1716, 1699, 1653, 1502, 1330 cm–1. ESI-HRMS: m/z
calcd for C19H22ClNO5Na: 402.1079 [M + Na]+; found:
402.1074.
(19) The urea 16 is the same intermediate which we recently
reported in enantiopure form, by following an entirely
different strategy for the synthesis of D-(+)-biotin.6a Based
on this, the stereochemistry of other major compounds have
been deduced and depicted.
(20) (a) Baxter, R. L.; Camp, D. J.; Coutts, A.; Shaw, N. J. Chem.
Soc., Perkin Trans. 1 1992, 255. (b) Effenberger, F.; Gaupp,
S. Tetrahedron: Asymmetry 1999, 10, 1765.
(10) Karjalainen, O. K.; Koskinen, A. M. P. Org. Biomol. Chem.
2012, 10, 4311; and references cited therein.
(11) Marshall, J. A.; Beaudoin, S. J. Org. Chem. 1996, 61, 581.
(12) Harris, B. D.; Joullie, M. M. Tetrahedron 1988, 44, 3489.
Synlett 2014, 25, 2879–2882
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