Efficient synthesis of the immunosuppressive agent FTY720

Article abstract of DOI:10.1055/s-2006-926342

The concise and practical synthesis of the biologically important FTY720 was achieved employing the palladium-catalyzed Sonogashira coupling reaction as a key step. The commercial tris(hydroxymethyl)aminomethane was converted to alkyne 2 via a three-step synthesis. The coupling reactions of alkyne 2 with aryl iodide 3, followed by subsequent hydrogenation of the internal alkyne and removal of the protecting groups provided FTY720 in high overall yield. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2006-926342

SHORT PAPER
753
Efficient Synthesis of the Immunosuppressive Agent FTY720
Synthesis of Im
a
munosupp
n
ressive
A
ge
g
Y
720 hee Kim,*a,b Hyeseung Lee,a,b Minhee Lee,a,b Taeho Leeb
a
College of Pharmacy, Seoul National University, San 56-1, Shilim Kwanak, Seoul 151-742, Korea
Natural Products Research Institute, College of Pharmacy, Seoul National University, 28 Yungun, Jongro, Seoul 110-460, Korea
Fax +82(2)7628322; E-mail: pennkim@snu.ac.kr
b
Received 1 September 2005; revised 12 October 2005
FTY720 (1) is amphipathic with a hydrophilic head group
(2-aminopropane-1,3-diol) and a lipophilic hydrocarbon
chain containing a phenyl ring. A variety of syntheses of
FTY720 and other related structures were reported.6,7
Abstract: The concise and practical synthesis of the biologically
important FTY720 was achieved employing the palladium-cata-
lyzed Sonogashira coupling reaction as a key step. The commercial
tris(hydroxymethyl)aminomethane was converted to alkyne 2 via a
three-step synthesis. The coupling reactions of alkyne 2 with aryl Many synthetic approaches for FTY720 employed the use
iodide 3, followed by subsequent hydrogenation of the internal
alkyne and removal of the protecting groups provided FTY720 in
high overall yield.
of acetaminomalonate to introduce the hydrophilic head
group. In some experiments, the alkylation of the sodium
salt of acetaminomalonate with the appropriate alkyl io-
dide failed to provide the desired product, due to compet-
itive elimination. These difficulties were circumvented by
the use of a-haloketone as the alkylating agent6a or proper
reaction medium.6c As part of our efforts to investigate the
biochemical and pharmaceutical effects of G-protein-cou-
pled receptor ligands, we needed to synthesize FTY720
and its analogues in large quantities. Herein, we report a
new concise and flexible synthetic route to FTY720 from
tris(hydroxymethyl)aminomethane (TRIS, 4) which is
commercially available at low cost.
Key words: cross-coupling, synthesis, FTY720, immunosuppres-
sants, alkynes
FTY720 (1, Scheme 1) is a synthetic analogue of the
sphingosine ISP-I (myriocin, Figure 1), a fungal metabolite
of the Chinese herb Iscaria sinclarii.1 It is a novel immu-
nosuppressant that is currently in Phase III clinical trials
for the prevention of allograft rejection.2,3 The molecular
mechanism of this new class of immunosuppressant is not
entirely clear. Recently, it was revealed that one of the hy-
droxyl groups of FTY720 is phosphorylated in vivo by
sphingosine kinase to form FTY720-phosphate, which
then acts as a potent agonist at the specific G-protein-cou-
pled receptors (S1P).4 This agonistic effect on T and B
lymphocytes seems to result in defective egress of these
cells from spleen, lymph nodes, and Peyer’s patch rather
than directing the onset of sequestration.3,5
The synthetic strategy for FTY720 was designed with the
aim of preparing the analogues containing various aro-
matic groups as well as introducing the functional groups
at C-3 and C-4. This led us to consider the coupling reac-
tions of alkyne 2 with aryl iodide 3 (Scheme 1). With this
strategy in mind, synthetic efforts towards 1 were com-
menced as shown in Scheme 2.
HO
HO
H
O
O
OH
a, b
c
OH
HO2C
HO
O
O
O
(ref. 8)
NH2
NHBoc
NHBoc
4
5
2
NH2 OH
O
d
Figure 1 Structure of ISP-I (myriocin)
5
e
O
HO
3
4
O
HO
FTY720 (1)
6
NHBoc
NH2⋅HCl
O
5
f, g
FTY720 (1)
O
O
7
+
NHBoc
O
I
3
2
Scheme 2 Reagents and conditions: (a) Boc2O, (MeO)2CMe2, cat.
TsOH, DMF, r.t., 3 h; (b) (COCl)2, DMSO, Et3N, CH2Cl2,, –78 °C to
r.t., 5 h, 85% (two steps); (c) MeCOCH2P(O)(OMe)2, TsN3, K2CO3,
MeCN–MeOH (1:1), r.t., 5 h, 84%; (d) 3, Pd(PPh3)4, CuI, DMF–Et3N
(4:1), r.t., 3 h, 94%; (e) H2, 10% Pd/C, benzene, r.t., 5 h, 99%; (f)
TFA–CH2Cl2–H2O (2:2:1), r.t., 12 h, 96%; (g) anhyd HCl, THF, r.t.,
3 h, 100%.
NHBoc
Scheme 1
SYNTHESIS 2006, No. 5, pp 0753–0755
x
x
.
x
x
.2
0
0
6
Advanced online publication: 08.02.2006
DOI: 10.1055/s-2006-926342; Art ID: F14705SS
© Georg Thieme Verlag Stuttgart · New York

754
S. Kim et al.
SHORT PAPER
tert-Butyl 2,2-Dimethyl-5-[(4-octylphenyl)ethynyl]-1,3-dioxan-
5-ylcarbamate (6)
The known aldehyde 5 was conveniently prepared from
TRIS in two steps with high overall yield, according to the
established synthetic procedure.8 The alkyne 2, which was
previously synthesized from aldehyde 5 by a three-step
alkynylation procedure,9 was successfully obtained in a
single step (84%) by employing Roth’s recent one-pot
protocol.10 The other coupling partner, aryl iodide 3, was
prepared by a one-pot sequence involving diazotization–
iodination of the commercially available 4-octylaniline,
as reported previously.11
To a solution of alkyne 2 (1.00 g, 3.92 mmol) and 1-iodo-4-octyl-
benzene (3) (1.50 g, 4.74 mmol) in degassed DMF–Et3N (4:1, 15
mL) were added Pd(PPh3)4 (226 mg, 0.200 mmol, 5 mol%) and CuI
(74 mg, 0.39 mmol, 10 mol%). The reaction mixture was stirred at
r.t. for 3 h and then quenched with 10% KF soln (20 mL). After be-
ing stirred for additional 10 min, it was then diluted with EtOAc
(150 mL), washed with brine (150 mL), dried over Na2SO4, filtered,
and concentrated in vacuo. The resulting residue was purified by
flash silica gel column chromatography (hexane–EtOAc, 10:1) to
give 6 (1.63 g, 94%) as a white solid. Mp 56–57 °C; Rf = 0.3 (hex-
ane–EtOAc, 10:1).
With multigram quantities of 2 and 3 in hand, we explored
the possibility of the palladium-catalyzed Sonogashira
coupling reaction.12 The optimal conditions for coupling
1H NMR (300 MHz, CDCl3): d = 0.88 (t, J = 6.9 Hz, 3 H), 1.27 (m,
12 H), 1.47 (d, J = 13.2 Hz, 3 H), 1.48 (s, 9 H), 1.52 (d, J = 13.2 Hz,
between 2 and 3 comprised 5 mol% of Pd(PPh3)4 and 10 3 H), 2.58 (t, J = 7.5 Hz, 2 H), 4.02 (d, J = 11.7 Hz, 2 H), 4.10 (d,
J = 11.7 Hz, 2 H), 5.19 (br s, 1 H), 7.09 (d, J = 8.4 Hz, 2 H), 7.33
(d, J = 8.4 Hz, 2 H).
mol% of CuI in Et3N and DMF at room temperature. Un-
der these conditions we were able to obtain the desired
13C NMR (75 MHz, CDCl3): d = 14.0, 18.5, 22.5, 28.26, 28.31 (3
product 6 in 94% yield without formation of a detectable
C), 29.09, 29.12, 29.3, 31.1, 31.8, 35.8, 47.8, 66.4 (2 C), 79.8, 84.8,
amount of the homocoupling product. Hydrogenation of
85.0, 98.3, 119.4, 128.2 (2 C), 131.7 (2 C), 143.5, 154.3.
the internal alkyne of 6 was achieved by using Pd/C in
benzene to give 7 in nearly quantitative yield. Removal of
the acetonide and Boc protecting groups was accom-
MS (EI, 70 eV): m/z (%) = 443 (1) [M+], 387 (5), 299 (100), 281
(13), 57 (30).
plished in a single step by treatment with TFA–CH2Cl2– HRMS–FAB: m/z [M + H]+ calcd for C27H42NO4: 444.3114; found:
444.3108.
H2O (2:2:1) at room temperature to give the free base of 1
in 96% yield after purification. Finally, the obtained free
base was converted to its HCl salt by treatment with dry
HCl–Et2O in THF in quantitative yield. The spectroscopic
data of our synthetic FTY720 (1) were in good agreement
tert-Butyl 2,2-Dimethyl-5-(4-octylphenethyl)-1,3-dioxan-5-yl-
carbamate (7)
To a solution of 6 (1.71 g, 3.85 mmol) in benzene (15 mL) was add-
ed 10% Pd/C (850 mg, 50 wt%). The reaction mixture was hydro-
genated (1 atm) while being stirred vigorously at r.t. for 5 h. It was
then filtered through celite, washed with benzene (15 mL), and con-
centrated. The residue was purified by flash silica gel column chro-
matography (hexane–EtOAc, 5:1) to give 7 (1.70 g, 99%) as a white
solid. Mp 63 °C; Rf = 0.25 (hexane–EtOAc, 10:1).
1H NMR (300 MHz, CDCl3): d = 0.88 (t, J = 6.9 Hz, 3 H), 1.28 (m,
10 H), 1.41 (s, 3 H), 1.43 (s, 3 H), 1.47 (s, 9 H), 1.58 (m, 2 H), 1.97
(m, 2 H), 2.50–2.58 (m, 4 H), 3.67 (d, J = 12.0 Hz, 2 H), 3.90 (d,
J = 12.0 Hz, 2 H), 4.97 (br s, 1 H), 7.08 (s, 4 H).
with those reported in the literature.
In conclusion, these studies provided a practical prepara-
tive route to FTY720 (1) from the commercially available
TRIS in seven steps and high overall yield (64%). We be-
lieve this sequence allows efficient and flexible synthesis
of 1 as well as other modified analogues in large quantities
for biochemical and pharmaceutical studies.
13C NMR (75 MHz, CDCl3): d = 13.9, 19.7, 22.5, 27.1, 28.2 (3 C),
28.5, 29.1, 29.2, 29.3, 31.4, 31.7, 33.6, 35.4, 51.5, 66.1 (2 C), 78.9,
98.1, 128.0 (2 C), 128.2 (2 C), 138.9, 140.2, 154.7.
MS (EI, 70 eV): m/z (%) = 447 (2) [M+], 376 (7), 342 (11), 258 (37),
216 (100), 190 (46), 105 (41), 57 (79).
HRMS–FAB: m/z [M + H]+ calcd for C27H46NO4: 448.3427; found:
448.3416.
All chemicals were reagent grade and used as purchased. All reac-
tions were performed under an inert atmosphere of dry argon or ni-
trogen using distilled anhydrous solvents. Reactions were
monitored by TLC analysis using Merck silica gel 60 F-254 thin
layer plates. Flash column chromatography was carried out on
Merck silica gel 60 (230–400 mesh). Melting points are uncorrect-
ed. Mass spectra (MS) were recorded at 70 eV using electron impact
(EI). High resolution mass spectra (HRMS) were recorded using
fast atom bombardment (FAB).
FTY720 (1)
A solution of 7 (1.40 g, 3.13 mmol) in CH2Cl2 (6 mL), TFA (6 mL),
and H2O (3 mL) was stirred at r.t. for 12 h. The reaction mixture was
quenched with sat. aq NaHCO3 soln (10 mL) and then extracted
with EtOAc (50 mL). The organic layer was washed with brine (40
mL), dried over Na2SO4, filtered, and concentrated in vacuo. The
residue was purified by flash silica gel column chromatography
(CH2Cl2–MeOH, 7:1, with 1% NH4OH) to give the free base of 1
(905 mg, 96%) as a white solid. Mp 121–124 °C; Rf = 0.4 (CH2Cl2–
MeOH, 7:1).
1H NMR (300 MHz, CD3OD): d = 0.88 (t, J = 6.9 Hz, 3 H), 1.29
(m, 10 H), 1.57 (m, 2 H), 1.63–1.68 (m, 2 H), 2.54 (t, J = 7.8 Hz, 2
H), 2.57–2.63 (m, 2 H), 3.45 (d, J = 10.8 Hz, 2 H), 3.51 (d, J = 10.8
Hz, 2 H), 7.05 (d, J = 8.1 Hz, 2 H), 7.11 (d, J = 8.1 Hz, 2 H).
tert-Butyl 5-Ethynyl-2,2-dimethyl-1,3-dioxan-5-ylcarbamate
(2)
To a solution of dimethyl-2-oxopropylphosphonate (1.65 mL, 11.12
mmol) in MeCN (20 mL) were added K2CO3 (373 mg, 3.72 mmol)
and p-toluenesulfonylazide (3.89 mL, 28.14 mmol). After the sus-
pension had been stirred at r.t. for 2 h, aldehyde 58 (2.42 g, 9.33
mmol) in MeOH (10 mL) was added. The resulting solution was
stirred at r.t. for an additional 8 h. It was concentrated in vacuo and
dissolved in EtOAc (100 mL). It was washed with H2O (100 mL),
dried over Na2SO4, filtered, and concentrated. The resulting residue
was purified by flash silica gel column chromatography (hexane–
EtOAc, 5:1) to give alkyne 2 (1.99 g, 84%) as a white solid. The ob-
tained NMR spectral data were virtually identical to those reported.9
1H NMR (300 MHz, CDCl3): d = 1.42 (s, 3 H), 1.47 (s, 12 H), 2.42
(s, 1 H), 3.97 (d, J = 11.6 Hz, 2 H), 4.04 (d, J = 11.6 Hz, 2 H), 5.15
(br s, 1 H).
Synthesis 2006, No. 5, 753–755 © Thieme Stuttgart · New York

SHORT PAPER
Synthesis of Immunosuppressive Agent FTY720
755
13C NMR (75 MHz, CD3OD): d = 14.4, 23.7, 30.0, 30.3, 30.4, 30.6,
32.8, 33.0, 36.5, 37.7, 56.9, 66.5 (2 C), 129.2 (2 C), 129.4 (2 C),
141.2, 141.3.
MS (EI, 70 eV): m/z (%) = 307 (2) [M+], 276 (100), 258 (15), 203
(10), 117 (8), 105 (20), 91 (10).
HRMS–FAB: m/z [M + H]+ calcd for C19H34NO2: 308.2590; found:
308.2589.
(4) (a) Mandala, S.; Hajdu, R.; Bergstrom, J.; Quackenbush, E.;
Xie, J.; Milligan, J.; Thornton, R.; Shei, G.-J.; Card, D.;
Keohane, C.; Rosenbach, M.; Hale, J.; Lynch, C. L.;
Rupprecht, K.; Parsons, W.; Rosen, H. Science 2002, 296,
346. (b) Brinkmann, V.; Davis, M. D.; Heise, C. E.; Albert,
R.; Cottens, S.; Hof, R.; Bruns, C.; Prieschl, E.; Baumruker,
T.; Hiestand, P.; Foster, C. A.; Zollinger, M.; Lynch, K. R.
Biol. Chem. 2002, 227, 21453.
(5) Matloubian, M.; Lo, C. G.; Cinamon, G.; Lesneski, M. J.;
Xu, Y.; Brinkmann, V.; Allende, M. L.; Proia, R. L.; Cyster,
J. G. Nature 2004, 427, 355.
(6) For previous syntheses of FTY720, see: (a) Durand, P.;
Peralba, P.; Sierra, F.; Renaut, P. Synthesis 2000, 505.
(b) Kalita, B.; Barua, N. C.; Bezbarua, M.; Bez, G. Synlett
2001, 1411. (c) Seidel, G.; Laurich, D.; Fürstner, A. J. Org.
Chem. 2004, 69, 3950. (d) Sugiyama, S.; Arai, S.; Kiriyama,
M.; Ishii, K. Chem. Pharm. Bull. 2005, 53, 100; see also
references 1a and 1b.
(7) For recent syntheses of FTY720-related compounds, see:
(a) Kiuchi M., Adachi K., Tomatsu A., Chino M., Takeda S.,
Tanaka Y., Maeda Y., Sato N., Mitsutomi N., Sugahara K.,
Chiba K.; Bioorg. Med. Chem.; 2005, 13: 425. (b) Hale, J.
J.; Yan, L.; Neway, W. E.; Hajdu, R.; Bergstrom, J. D.;
Milligan, J. A.; Shei, G.-J.; Chrebet, G. L.; Thornton, R. A.;
Card, D.; Rosenbach, M.; Rosen, H.; Mandala, S. Bioorg.
Med. Chem. 2004, 12, 4803. (c) Hale, J. J.; Neway, W.;
Mills, S. G.; Hajdu, R.; Keohane, C. A.; Rosenbach, M.;
Milligan, J.; Shei, G.-J.; Chrebet, G.; Bergstrom, J.; Card,
D.; Koo, G. C.; Koprak, S. L.; Jackson, J. J.; Rosen, H.;
Mandala, S. Bioorg. Med. Chem. Lett. 2004, 14, 3351.
(d) Hinterding, K.; Albert, R.; Cottens, S. Tetrahedron Lett.
2002, 43, 8095. (e) Hinterding, K.; Cottens, S.; Albert, R.;
Zecri, F.; Buehlmayer, P.; Spanka, C.; Brinkmann, V.;
Nussbaumer, P.; Ettmayer, P.; Hoegenauer, K.; Gray, N.;
Pan, S. Synthesis 2003, 1667.
To a solution of the free base of 1 (569 mg, 1.85 mmol) in THF (10
mL) was added anhyd HCl (1.85 mL, 1.0 M soln in Et2O) at 0 °C.
The resulting mixture was warmed to r.t. and stirred for 3 h, and
then it was concentrated under reduced pressure to give FTY720 (1)
(636 mg, 100%) as a white solid. Mp 105 °C.
1H NMR (300 MHz, DMSO-d6): d = 0.85 (t, J = 6.0 Hz, 3 H), 1.24
(br s, 10 H), 1.53 (m, 2 H), 1.81 (m, 2 H), 2.51 (m, 2 H), 2.61 (m, 2
H), 3.55 (d, J = 4.2 Hz, 4 H), 5.42 (br s, 2 H), 7.08 (d, J = 8.1 Hz, 2
H), 7.12 (d, J = 8.1 Hz, 2 H), 8.02 (br s, 3 H).
13C NMR (75 MHz, DMSO-d6): d = 14.1, 22.2, 28.1, 28.81, 28.83,
29.0, 31.2, 31.4, 33.4, 34.9, 60.5 (2 C), 61.1, 128.2 (2 C), 128.3 (2
C), 139.1, 139.8.
MS (EI, 70 eV): m/z (%) = 308 (1) [M – Cl]+, 276 (100), 258 (8),
203 (9), 117 (31), 105 (67).
Acknowledgment
This study was supported by a grant of the Korea Health 21 R & D
Project, Ministry of Health & Welfare, Republic of Korea (Project
No.: A040004).
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Synthesis 2006, No. 5, 753–755 © Thieme Stuttgart · New York