A photoreactive analogue of the immunosuppressant FTY720

Article abstract of DOI:10.1021/jo0526237

An azido group was incorporated into the immunomodulatory agent FTY720, accomplishing the first synthesis of a photoactivatable analogue of this ligand (2) in 9 steps from 2-(4-hydroxyphenyl)ethanol and in 34% overall yield. The key steps are formation of

Full text of DOI:10.1021/jo0526237

A Photoreactive Analogue of the
Immunosuppressant FTY720
Chaode Sun and Robert Bittman*
Department of Chemistry and Biochemistry,
Queens College of The City UniVersity of New York,
Flushing, New York 11367-1597
FIGURE 1. Structures of FTY720 (1) and its azido analogue 2.
The potent biological activity of 1 has led to the development
of efficient routes to its chemical synthesis. These methods
include the Petasis reaction of vinylboronic acid with hydroxy-
acetone in the presence of an amine,6 alkylation of diethyl
2-acetamidomalonate with iodo or bromo compounds,7-9 and
bis-formylation of 1-nitro-2-(4-octylphenyl)ethane with aqueous
formaldehyde.10 However, photoreactive analogues of 1 have
not yet been synthesized. Aryl azides are highly photoreactive,11
producing a nitrene intermediate on photolysis. Since the small
size of the azido group is desirable for ligand binding to target
proteins with minimal perturbation of ligand structure, we syn-
thesized aryl azido analogue 2 (Figure 1) for use in identifying
binding sites between this ligand and its receptors.12
robert.bittman@qc.cuny.edu
ReceiVed December 21, 2005
The synthesis of 2 began with commercially available 2-(4-
hydroxyphenyl)ethanol, which was converted to monoacetate
3 in almost quantitative yield in the presence of immobilized
NaHSO4/SiO2.7 After nitration of 313 and reaction with triflic
anhydride afforded triflate 4 in 80% overall yield, we attempted
an Fe(acac)3-catalyzed cross-coupling reaction with n-octyl-
magnesium bromide. This step was used with an aryl triflate in
the preparation of 1;7 however, we found that application of
this procedure to nitro compound 4 did not result in cross-
coupling in the expected position (C-1). Instead, the n-octyl
group underwent net substitution (presumably via an anionic
nitronate adduct)14 into the benzene ring at C(5) in the presence
An azido group was incorporated into the immunomodulatory
agent FTY720, accomplishing the first synthesis of a
photoactivatable analogue of this ligand (2) in 9 steps from
2-(4-hydroxyphenyl)ethanol and in 34% overall yield. The
key steps are formation of a primary amine at a quaternary
center of aniline derivative 13 followed by selective diazo-
tization of the arylamine.
FTY720 (2-amino-[2-(4-octylphenyl)ethyl]-1,3-propanediol,
Figure 1, 1) is a potent immunosuppressive agent that causes
lymphocytes to be sequestered in secondary lymphoid organs,
without decreasing host immune defense responses to most
infections.1 FTY720 may be approved by the U.S. FDA for
treatment of multiple sclerosis, and is in phase III clinical studies
to evaluate its effects with respect to kidney graft rejection in
humans.2 In addition, 1 is efficacious against other autoimmune
diseases.1,3 As an analogue of sphingosine, FTY720 is phos-
phorylated in vivo by sphingosine kinases, converting 1 to a
chiral FTY720-phosphate, which is a high affinity agonist of
four of the five known sphingosine 1-phosphate (S1P) G protein-
coupled receptors in thymocytes and lymphocytes.4 Internaliza-
tion of the receptor renders the cells unresponsive to S1P; thus,
lymphocytes are not capable of recirculation to peripheral
inflammatory tissues and sites of the transplant. Unphosphor-
ylated FTY720 (1) also causes internalization of some S1P
receptors, but this action is independent of agonism and affects
a different spectrum of S1P receptors than the phosphorylated
derivative.5
(4) (a) 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. J. Biol. Chem. 2002, 277, 21453-21457.
(b) 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, 346-349. (c) Albert, R.; Hinterding, K.; Brinkmann, V.; Guerini,
D.; Mu¨ller-Hartwieg, C.; Knecht, H.; Simeon, C.; Streiff, M.; Wagner, T.;
Welzenbach, K.; Ze´cri, F.; Zollinger, M.; Cooke, N.; Francotte, E. J. Med.
Chem. 2005, 48, 5373-5377.
(5) Wang, W.; Graeler, M. H.; Goetzl, E. J. FASEB J. 2004, 18, 1043-
1045.
(6) Sugiyama, S.; Arai, S.; Kiriyama, M.; Ishii, K. Chem. Pharm. Bull.
2005, 53, 100-102.
(7) Seidel, G.; Laurich, D.; Fu¨rstner, A. J. Org. Chem. 2004, 69, 3950-
3952.
(8) Kiuchi, M.; Adachi, K.; Kohara, T.; Minoguchi, M.; Hanano, T.;
Aoki, Y.; Mishina, T.; Arita, M.; Nakao, N.; Ohtsuki, M.; Hoshino, Y.;
Teshima, K.; Chiba, K.; Sasaki, S.; Fujita, T. J. Med. Chem. 2000, 43,
2946-2961.
(9) Adachi, K.; Kohara, T.; Nakao, N.; Arita, M.; Chiba, K.; Mishina,
T.; Sasaki, S.; Fujita, T. Bioorg. Med. Chem. Lett. 1995, 5, 853-856.
(10) Kalita, B.; Barua, N. C.; Bezbarua, M.; Bez, G. Synlett 2001, 9,
1411-1414.
(11) Bayley, H. In Photogenerated Reagents in Biochemistry and
Molecular Biology; Work, T. S., Burdon, R. H., Eds.; Elsevier: Amsterdam,
The Netherlands, 1983; pp 29 and 31.
(12) Compound 2 is phosphorylated in an analogous manner as 1 in
primary mouse lymphocytes, demonstrating the utility of 2 as a potential
photoaffinity probe.
(13) Yamane, T.; Kondo, H.; Fuse, Y.; Hashizume, T.; Kano, F.;
Yamashita, K.; Hosoe, K.; Watanabe, K. Japanese Patent 63045282 A2,
1988; Chem. Abstr. 1989, 110, 57408.
* Corresponding author. Phone: (718) 997-3279. Fax: (718) 997-3349.
(1) For a recent review, see: Chiba, K. Pharmacol. Ther. 2005, 108,
308-319.
(2) Brinkmann, V.; Cyster, J. G.; Hla, T. Am. J. Transplant. 2004, 4,
1019-1025.
(3) Kohno, T.; Tsuji, T.; Hirayama, K.; Iwatsuki, R.; Hirose, M.; Watabe,
K.; Yoshikawa, H.; Kohno, T.; Matsumoto, A.; Fujita, T.; Hayashi, M. Biol.
Pharm. Bull. 2005, 28, 736-739.
10.1021/jo0526237 CCC: $33.50 © 2006 American Chemical Society
Published on Web 02/09/2006
2200
J. Org. Chem. 2006, 71, 2200-2202

SCHEME 1. Synthesis of Iodide 8a
SCHEME 2. Electrophilic Amination of 9
SCHEME 3. Completion of the Synthesis of Photoprobe 2a
a Reagents and conditions: (a) HOAc, HNO3, 10-15 °C; (b) Tf2O, Py,
CH2Cl2, 0 °C-rt; (c) (E)-(HO)2BCHdCHC6H13-n, Pd(dppf)2Cl2‚CH2Cl2,
K2CO3, THF/H2O (10:1), reflux, overnight; (d) NaOMe, MeOH, rt; (e)
MeSO2Cl, Et3N, CH2Cl2, 0 °C; (f) LiI, n-Bu4NI, THF, rt, 1 h.
of Fe(III) with retention of the triflate group, which was
hydrolyzed during workup, giving compound 5a15 in 50% yield.
Fortunately, we found that the Suzuki cross-coupling of triflate
4 with (E)-1-octen-1-ylboronic acid in the presence of catalytic
Pd(dppf)Cl2 proceeded as expected to provide 5. The yield of
5 increased from 53% to 89% when the boronic acid concentra-
tion was increased from 0.77 to 1.5 equiv. Hydrolysis of 5 with
NaOMe in MeOH, followed by treatment of alcohol 6 with
methanesulfonyl chloride and displacement of mesylate 7 with
iodide ion afforded 8 in 95% overall yield.
a Reagents and conditions: (a) DMF, rt, 20 h; (b) H2, 10% Pd/C, EtOH,
36 °C, 6 h; (c) 2 M HCl, NaNO2, H2O, 0 °C; (d) (i) NaN3, H2O, 0 °C, (ii)
NaHCO3.
Initially, we tried to establish the quaternary center by means
of an electrophilic amination reaction16 (Scheme 2). After
alkylation of 8 with diethyl malonate afforded 9, the amino
group was installed with O-(di-p-methoxyphenyl)phosphinyl-
hydroxylamine.17 Unfortunately, this method was inefficient,
providing amine 10 in 31% yield; the corresponding tertiary
alcohol byproduct was obtained in 15% yield according to NMR
analysis, with recovery of 26% of compound 9.
An alternative route to an intermediate bearing a primary
amine at a quaternary carbon involves the use of the lithium
salt of 2-nitropropane-1,3-diol acetonide (11),18 followed by
reduction (Scheme 3). This salt, which was prepared in situ by
deformylation of tris(hydroxymethyl)nitromethane acetonide
with lithium hydroxide,19 reacted with iodide 8 in DMF to form
dinitro compound 12 in 60% yield. The elimination byproduct,
styryl derivative 12a, was formed in 14% yield. Dinitro
compound 12 was reduced to diamine 13 under hydrogen
atmosphere with Pd/C as the catalyst, with concomitant reduc-
tion of the double bond. Chemoselective installation of an azido
group in the aromatic ring was accomplished by diazotization
of the aryl amino group in 13 and treatment of the resulting
intermediate diazonium chloride with sodium azide to give 2
in 90% overall yield.20
In summary, the first photoreactive analogue of 1, a new im-
munosuppressant that traps T cells in lymph nodes, was syn-
thesized in 9 steps and 34% overall yield. The key steps were
the generation of a quaternary center via alkylation of iodide 8
with the lithium salt of 2-nitropropane-1,3-diol acetonide (11)
and the selective diazotization of diamine 13.
(14) For the reaction of Grignard reagents with nitroarenes, followed by
reaction with an oxidant (DDQ, KMnO4, or Pb(OAc)4) see: (a) Bartoli,
G.; Bosco, M.; Dalpozzo, R. Tetrahedron Lett. 1985, 26, 115-118. (b)
Bartoli, G. Acc. Chem. Res. 1984, 17, 109-115.
(15) The structure of compound 5a was assigned on the basis of mass
spectral and NMR data (see the Supporting Information).
Experimental Section
3-Nitro-4-((E)-oct-1-enyl)phenethyl Methanesulfonate (7) and
4-(2-Iodoethyl)-2-nitro-1-((E)-oct-1-enyl)benzene (8). To a solu-
tion of alcohol 6 (280 mg, 1.0 mmol) in 10 mL of CH2Cl2 and
(19) Archibald, T. G.; Taran, C.; Baum, K. J. Fluorine Chem. 1989, 43,
243-248.
(20) The lower basicity of the aromatic amino group may permit reaction
with nitrous acid. For a report on the selective deamination of an aromatic
amino group in the presence of an aliphatic amino group by diazotization
and reaction with H3PO2, see: Kornblum, N.; Iffland, D. C. J. Am. Chem.
Soc. 1949, 71, 2137-2143.
(16) (a) Erdik, E.; Ay, M. Chem. ReV. 1989, 89, 1947-1980. (b) Erdik,
E. Tetrahedron 2004, 60, 8747-8782.
(17) Smulik, J. A.; Vedejs, E. Org. Lett. 2003, 5, 4187-4190.
(18) Umemoto, T.; Kuriu, Y. Tetrahedron Lett. 1981, 22, 5197-
5200.
J. Org. Chem, Vol. 71, No. 5, 2006 2201

0.28 mL (2.0 mmol) of Et3N was added methanesulfonyl chloride
(0.21 mL, 1.5 mmol) at 0 °C. The reaction mixture was stirred for
1 h. The reaction was quenched with saturated aqueous NaHCO3
solution (10 mL), and the aqueous layer was extracted with
CH2Cl2 (2 × 20 mL), dried (Na2SO4), and evaporated to yield crude
mesylate 7 (391 mg, ∼109%), which was used without further
purification (Rf 0.38, EtOAc/hexane 1:2). To a solution of 7 (391
mg, 1.0 mmol) in 10 mL of THF were added LiI (406 mg, 3.0
mmol) and n-Bu4NI (110 mg, 0.30 mmol). The reaction was
completed within 1 h of stirring at room temperature. After
evaporation of the volatile components, the residue was purified
by flash chromatography (EtOAc/hexane 1:10) to give 370 mg
(95%) of iodide 8 as a pale yellow solid: Rf 0.51 (EtOAc/hexane
5-(3-Amino-4-octylphenethyl)-2,2-dimethyl-1,3-dioxan-5-
amine (13). A suspension of 12 (70 mg, 0.17 mmol) and 10% Pd/C
(36 mg) in 20 mL of EtOH was stirred under 1 atm of H2 at 36 °C
for 6 h. The mixture was filtered through a short pad of Celite,
and the pad was washed with EtOH (20 mL). The filtrate was
concentrated to give 58 mg (95%) of 13 as a pale yellow oil: 1H
NMR (CDCl3) δ 0.89 (t, 3H, J ) 6.8 Hz), 1.27-1.44 (m, 8H),
1.41 (s, 3H), 1.46 (s, 3H), 1.59 (m, 2H), 1.66 (m, 2H), 2.42 (dt,
2H, J ) 6.8, 6.8 Hz), 2.57 (m, 2H), 3.49 (br s, 4H), 3.56 (d, 2H,
J ) 11.6 Hz), 3.78 (d, 2H, J ) 11.6 Hz), 6.53-6.55 (m, 2H), 6.92
(d, 1H, J ) 7.6 Hz); 13C NMR (CDCl3) δ 14.0, 19.5, 22.5, 27.4,
28.2, 28.7, 29.2, 29.4, 29.6, 30.8, 31.8, 36.7, 49.7, 49.4, 69.0, 98.3,
115.3, 118.4, 124.5, 129.3, 140.2, 144.0; HR-MS (ESI, MH+) m/z
calcd for C22H39N2O2 385.3006, found 363.3016.
1
1:10); mp 34-35 °C; H NMR (CDCl3) δ 0.89 (t, 3H, J ) 6.8
Hz), 1.31-1.37 (m, 6H), 1.48 (m, 2H), 2.25 (dt, 2H, J ) 6.8, 6.8
Hz), 3.22 (t, 2H, J ) 7.2 Hz), 3.36 (t, 2H, J ) 7.2 Hz), 6.24 (dt,
1H, J ) 15.6, 6.8 Hz), 6.80 (d, 1H, J ) 15.6 Hz), 7.35 (d, 1H, J
) 8.0 Hz), 7.54 (d, 1H, J ) 8.0 Hz), 7.71 (s, 1H); 13C NMR
(CDCl3) δ 4.2, 14.1, 22.6, 28.8, 28.9, 31.7, 33.2, 38.9, 124.0, 124.6,
128.6, 132.0, 132.8, 136.9, 140.1, 147.6; LR-MS (APPI, MH+) m/z
calcd for C16H23NIO2 388.1, found 388.2; (2M + Na)+ calcd m/z
797.1, found 797.3.
2-(3-Azido-4-octylphenethyl)-2-aminopropane-1,3-diol (2). To
a solution of 13 (22 mg, 0.060 mmol) in 0.10 mL of 2 M HCl and
0.05 mL of H2O was added NaNO2 (4.3 mg, 0.060 mmol)
portionwise at 0 °C. After the suspension was stirred for 15 min,
NaN3 (3.9 mg, 0.060 mmol) was added in one portion. The mixture
was stirred at 0 °C for 30 min. The reaction was quenched with
saturated aqueous NaHCO3 solution (10 mL) and the aqueous layer
was extracted with EtOAc (3 × 50 mL). The organic layer was
dried (MgSO4) and concentrated. The crude product was purified
by flash chromatography (EtOAc/hexane 4:1) to give 20 mg (90%)
of 2 as a pale yellow solid: Rf 0.20 (EtOAc/hexane 4:1); mp
63-65 °C; 1H NMR (CDCl3/CD3OD 10:1) δ 0.82 (t, 3H, J ) 6.8
Hz), 1.21-1.24 (m, 10H), 1.47 (m, 2H), 1.68 (m, 2H), 2.44 (t, 2H,
J ) 7.6 Hz), 2.57 (m, 2H), 3.47 (d, 2H, J ) 10.8 Hz), 3.56 (d, 2H,
J ) 10.8 Hz), 6.83 (d, 1H, J ) 7.6 Hz), 6.90 (s, 1H), 7.00 (d, 1H,
J ) 7.6 Hz); 13C NMR (CDCl3/CD3OD 10:1) δ 13.9, 22.5, 28.8,
29.1, 29.31, 29.32, 30.3, 30.7, 31.8, 35.9, 56.7, 65.3, 117.7, 124.5,
130.3, 131.9, 137.6, 140.8; HR-MS (ESI, MH+) m/z calcd for
C19H33N4O2 349.2598, found 349.2598.
5-(3-Nitro-4-((E)-oct-1-enyl)phenethyl)-2,2-dimethyl-5-nitro-
1,3-dioxane (12). To a solution of the lithium salt of 2-nitropropane-
1,3-diol acetonide (11, prepared by the reaction of 494 mg (2.58
mmol) of 2-hydroxymethyl-2-nitropropane-1,3-diol monoacetonide
with 111 mg (2.58 mmol) of LiOH‚H2O, using a Dean-Stark trap
to remove water) in 4 mL of DMF was added 200 mg (0.52 mmol)
of 8. After the reaction mixture was stirred at room temperature
for 20 h, H2O was added (10 mL), and the aqueous layer was
extracted with EtOAc (3 × 50 mL). The organic layer was dried
(MgSO4) and evaporated. The residue was purified by flash
chromatography (EtOAc/hexane 1:2) to give 76 mg (60%) of 12
as an off-white solid: Rf 0.60 (EtOAc/hexane 1:2); mp 80-82 °C;
1H NMR (CDCl3) δ 0.89 (t, 3H, J ) 6.8 Hz), 1.31-1.50 (m, 8H),
1.41 (s, 3H), 1.45 (s, 3H), 2.14 (m, 2H), 2.25 (m, 2H), 2.60 (m,
2H), 3.97 (d, 2H, J ) 12.8 Hz), 4.52 (d, 2H, J ) 12.8 Hz), 6.22
(dt, 1H, J ) 15.6, 6.8 Hz), 6.79 (d, 1H, J ) 15.6 Hz), 7.30 (d, 1H,
J ) 8.0 Hz), 7.51 (d, 1H, J ) 18.0 Hz), 7.66 (s, 1H); 13C NMR
(CDCl3) δ 14.1, 21.1, 22.6, 25.4, 28.4, 28.8, 29.9, 31.7, 33.2, 35.2,
63.9, 85.8, 99.3, 123.8, 124.4, 128.8, 131.9, 132.8, 137.0, 139.1,
147.6; HR-MS (ESI, MNa+) m/z calcd for C22H32N2O6Na 443.2153,
found 443.2146.
Supporting Information Available: We thank Dr. Markis
Gra¨ler for conducting the cell-based phosphorylation experi-
ments. Financial support from NIH Grant HL083187 is gratefully
acknowledged.
Supporting Information Available: Experimental procedures
for compounds 3-6, 9, and 10 and spectroscopic data. This material
is available free of charge via the Internet at http://pubs.acs.org.
JO0526237
2202 J. Org. Chem., Vol. 71, No. 5, 2006