Chiral vinylphosphonate and phosphonate analogues of the immunosuppressive agent FTY720

Article abstract of DOI:10.1021/jo900023u

The first enantioselective synthesis of chiral isosteric phosphonate analogues of FTY720 is described. One of these analogues, FTY720-(E)- vinylphosphonate (S)-5, but not its R enantiomer, elicited a potent antiapoptotic effect in intestinal epithelial ce

Full text of DOI:10.1021/jo900023u

Thus, FTY720 has therapeutic potential and, in fact, is the first
S1P receptor modulator that has entered the stage of a phase-
III clinical study.4
Chiral Vinylphosphonate and Phosphonate
Analogues of the Immunosuppressive Agent
FTY720
Several syntheses of 15 and of phosphate 3 have been
accomplished.6 In contrast to phosphates such as 3, phosphonate
analogues are resistant to the action of lipid phosphate phos-
phatases and may offer improved cellular stability. A racemic
mixture of the nonhydrolyzable phosphonate analogue of
FTY720 (4) was reported in which the C-O-P bond is replaced
with a C-C-P bond;2b rac-4 was found to be a high-affinity
agonist of the S1P-type 1 receptor (S1P1), with a similar potency
as (S)-3.7 We report here the first asymmetric syntheses of the
chiral phosphonate analogues of FTY720, (R)-4 and (S)-4.
Oxazoline intermediate (S)-14 (Scheme 1), prepared by a
modification of our previous route,6c was further elaborated to
give the corresponding (E)-vinylphosphonate analogue (S)-5.
We have included a preliminary pharmacological characteriza-
tion of the effects of these analogues on the nontransformed rat
intestinal epithelial cell line IEC-6. This study revealed that (S)-
5, but not its (R) enantiomer, exerts a potent antiapoptotic effect
in a camptothecin (CPT)-induced apoptosis model.8 Unlike
phosphate (S)-3, (S)-5 did not activate the S1P1 receptor of the
Endothelial Differentiation Gene (EDG) family of G protein-
coupled receptors, making it a novel enantioselective probe
activating a cytoprotective mechanism against apoptosis induced
by DNA damage.
Xuequan Lu,† Chaode Sun,† William J. Valentine,‡
Shuyu E,‡ Jianxiong Liu,‡ Gabor Tigyi,‡ and
Robert Bittman†,*
Department of Chemistry and Biochemistry, Queens College
of The City UniVersity of New York, Flushing, New York
11367-1597, and Department of Physiology, UniVersity of
Tennessee Health Science Center, Memphis, Tennessee
38163
robert.bittman@qc.cuny.edu
ReceiVed January 7, 2009
Wittig reaction of 4-bromobenzaldehyde with the ylide of
n-heptyltriphenylphosphonium bromide gave arylalkene 6 as an
E,Z (1:3) mixture (Scheme 1). Sonogashira coupling between
6 and 4-(phenylmethoxy)-1-butyne delivered enyne 7 as a 1:3
E:Z mixture in 92% yield. Alcohol 8 was obtained on reduction
of the unsaturated bonds and hydrogenolysis of the O-benzyl
group in the presence of Pearlman’s catalyst. After Swern
oxidation of 8 provided aldehyde 9, use of a Mannich reagent,
The first enantioselective synthesis of chiral isosteric phos-
phonate analogues of FTY720 is described. One of these
analogues, FTY720-(E)-vinylphosphonate (S)-5, but not its R
enantiomer, elicited a potent antiapoptotic effect in intestinal
epithelial cells, suggesting that it exerts its action via the
enantioselective activation of a receptor. (S)-5 failed to activate
the sphingosine 1-phosphate type 1 (S1P1) receptor.
(3) (a) Gonzalez-Cabrera, P. J.; Hla, T.; Rosen, H. J. Biol. Chem. 2007, 282,
7254–7264. (b) Oo, M. L.; Thangada, S.; Wu, M. T.; Liu, C. H.; Macdonald,
T. L.; Lynch, K. R.; Lin, C. Y.; Hla, T. J. Biol. Chem. 2007, 282, 9082–9089.
(4) FTY720 appears to be efficacious against autoimmune diseases such as
multiple sclerosis: (a) Kappos, L.; Antel, J.; Comi, G.; Montalban, X.; O’Connor,
P.; Polman, C. H.; Haas, T.; Korn, A. A.; Karlsson, G.; Radue, E. W. N. Engl.
J. Med. 2006, 355, 1124–1140. (b) Baumruker, T.; Billich, A.; Brinkmann, V.
Expert Opin. InVestig. Drugs 2007, 16, 283–289.
FTY720 (2-amino-[2-(4-n-octylphenyl)ethyl]-1,3-propanediol,
Fingolimod, 1, Chart 1) is a synthetic analogue of the chiral
sphingolipid myriocin (2).1 As an analogue of sphingosine,
FTY720 is phosphorylated in vivo by sphingosine kinases,
affording (S)-FTY720-phosphate (3), which activates four of
the five known sphingosine 1-phosphate (S1P, 2a) G protein-
coupled receptors.2
Internalization and subsequent polyubiquitination of the S1P
receptors leads to their proteasomal degradation and renders
the cells unresponsive to S1P; therefore, lymphocytes are not
capable of recirculation to peripheral inflammatory tissues.3
(5) See: Matsumoto, N.; Hirose, R.; Sasaki, S.; Fujita, T. Chem. Pharm. Bull.
2008, 56, 595–597, and references cited therein.
(6) (a) Hinterding, K.; Cottens, S.; Albert, R.; Ze´cri, F.; Buehlmayer, P. B.;
Spanka, C.; Brinkmann, V.; Nussbaumer, P.; Ettmayer, P.; Hoegenauer, K.; Gray,
N.; Pan, S. F. Synthesis 2003, 1667–1670. (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, 4803–4807. (c) Lu, X.; Bittman, R. Tetrahedron Lett. 2006, 47, 825–
827. (d) 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.
(e) Takeda, S.; Chino, M.; Kiuchi, M.; Adachi, K. Tetrahedron Lett. 2005, 46,
5169–5172.
† CUNY.
‡ University of Tennessee Health Science Center.
(1) For recent reviews, see: (a) Zhang, Z.; Schluesener, H. J. Mini ReV. Med.
Chem. 2007, 7, 845–850. (b) Martini, S.; Peters, H.; Bohler, T.; Budde, K. Expert
Opin. InVestig. Drugs 2007, 16, 505–518. (c) Kihara, A.; Igarashi, Y. Biochim.
Biophys. Acta 2008, 1781, 496–502.
(2) (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.
(7) (a) Forrest, M.; Sun, S. Y.; Hajdu, R.; Bergstrom, J.; Card, D.; Doherty,
G.; Hale, J.; Keohane, C.; Meyers, C.; Milligan, J.; Mills, S.; Nomura, N.; Rosen,
H.; Rosenbach, M.; Shei, G. J.; Singer, I. I.; Tian, M.; West, S.; White, V.; Xie,
J.; Proia, R. L.; Mandala, S. J. Pharmacol. Exp. Ther. 2004, 309, 758–768. For
the activity of FTY720 R-hydroxyphosphonates, see: (b) Hale, J. J.; Neway,
W.; Mills, S. G.; Hajdu, R.; Keohane, C.; 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, 3351–3355.
(8) For a recent review of CPT and its derivatives, see: Verma, R. P.; Hansch,
C. Chem. ReV. 2009, 109, 213–235.
3192 J. Org. Chem. 2009, 74, 3192–3195
10.1021/jo900023u CCC: $40.75 2009 American Chemical Society
Published on Web 03/18/2009

SCHEME 1. Synthesis of (S)-14 from 4-Bromobenzaldehyde
CHART 1. Structures of FTY720 (1); Myriocin (2); S1P
(2a); and FTY720 Phosphate, Phosphonate, and
(E)-Vinylphosphonate Analogues (3-5)
Eschenmoser’s salt,9 afforded R-methylene aldehyde 10. Reduc-
tion of 10 with NaBH4 in the presence of CeCl3 (to suppress
conjugate reduction) gave allyl alcohol 11.10 CeCl3, which is a
mild Lewis acid, is not required, since CsCl also provided 11
as the only product. Asymmetric Sharpless epoxidation11 of 11
with cumene hydroperoxide (CHP) in the presence of L-(+)-
DIPT, Ti(OPr-i)4, and molecular sieves gave epoxide (S)-12.12
The synthesis of (S)-12 was accomplished in 7 steps from
p-bromobenzaldehyde and in 46% overall yield. Reaction of
alcohol (S)-12 with trichloroacetonitrile in the presence of DBU
gave 2,3-epoxy-1-trichloroacetimidate (R)-13. The tetrasubsti-
tuted carbon in oxazoline 14 was set up bearing the desired
nitrogen substituent by opening of epoxide (R)-13 with catalytic
Et2AlCl,13 affording (S)-14 in 74% yield for the two steps.
Swern oxidation of oxazoline (S)-14 gave oxazoline aldehyde
15 (Scheme 2), which on Horner-Wadsworth-Emmons reaction
with tetramethyl methylenediphosphonate afforded ester (S)-
16 in 87% yield and with an E/Z ratio of ∼10:1. Simultaneous
demethylation and release of the hydroxy and amino groups by
treatment with trimethylsilyl bromide (TMSBr) provided (S)-
5, but the yield was low. Therefore, the hydroxy and amino
groups were first released by treatment with 1 M HCl. After
the amine hydrochloride was neutralized (saturated aq Na2CO3),
amino alcohol 17 was converted to (S)-5 with TMSBr followed
by 95% methanol; 84% yield for the two steps. Reduction of
(S)-5 using Pearlman’s catalyst gave (S)-4.
Asymmetric epoxidation of 11 with D-(-)-DIPT gave epoxide
(R)-12, which was converted via (R)-14 to (R)-5 in six steps
(Scheme 3). Catalytic hydrogenation of (R)-5 afforded (R)-4.
S1P promotes the survival of many cell types.14 Both 2a and
(S)-3 protect oligodendrocyte progenitor cells from apoptotic
cell death in response to growth factor withdrawal, and (S)-3
was also shown to be cytoprotective in response to pro-apoptotic
(9) Schreiber, J.; Maag, H.; Hashimoto, N.; Eschenmoser, A. Angew. Chem.,
Int. Ed. Engl. 1971, 10, 330–331.
(10) Luche, J. L. J. Am. Chem. Soc. 1978, 100, 2226–2227.
(11) Katsuki, T.; Martin, V. S. Org. React. 1995, 48, 1–299.
(12) Sharpless epoxidation of an analogue of 11 with L-diethyl tartrate gave
the corresponding (S)-2,3-epoxy alcohol in 95% ee: Li, X.; Borhan, B. J. Am.
Chem. Soc. 2008, 130, 16126–16127 (Table 1, entry 20).
(13) Hatakeyama, S.; Matsumoto, H.; Fukuyama, H.; Mukugi, Y.; Irie, H.
J. Org. Chem. 1997, 62, 2275–2279.
(14) Cuvillier, O.; Pirianov, G.; Kleuser, B.; Vanek, P. G.; Coso, O. A.;
Gutkind, S.; Spiegel, S. Nature 1996, 381, 800–803.
(15) (a) Saini, H. S.; Coelho, R. P.; Goparaju, S. K.; Jolly, P. S.; Maceyka,
M.; Spiegel, S.; Sato-Bigbee, C. J. Neurochem. 2005, 95, 1298–1310. (b) Coelho,
R. P.; Payne, S. G.; Bittman, R.; Spiegel, S.; Sato-Bigbee, C. J. Pharmacol.
Exp. Ther. 2007, 323, 626–635.
J. Org. Chem. Vol. 74, No. 8, 2009 3193

SCHEME 2. Synthesis of (S)-4 from (S)-14
FIGURE 1. Ca2+ mobilization dose-response relationships for S1P
(2a), (S)-3, and FTY720 analogues 4 and 5 in HTC4 cells expressing
the S1P1 receptor.
activity of (S)-5 is not mediated by S1P1. Experiments are
underway to characterize the cellular effects of these analogues.
Experimental Section
(2S)-2-(2′-(Trichloromethyl)-4′,5′-dihydrooxazol-5-yl)-4-(4′′-oc-
tylphenyl)-butan-1-ol [(S)-(+)-14]. To a solution of 435 mg (1.5
mmol) of epoxy alcohol (S)-12 in 25 mL of CH2Cl2 at 0 °C were
added Cl3CCN (0.17 mL, 1.65 mmol) and DBU (0.023 mL, 0.15
mmol). After being stirred at 0 °C for 1.5 h, the reaction mixture
was diluted with Et2O (20 mL) and water (20 mL). The organic
layer was separated, washed with brine (20 mL), dried (MgSO4),
and concentrated. The residue was purified by chromatography
(hexane/EtOAc 20:1) to give 565 mg (87%) of (R)-13; Rf 0.58
(EtOAc/hexane 1:3). To an ice-cold solution of 565 mg (1.31 mmol)
of (R)-13 in 20 mL of CH2Cl2 was added Et2AlCl (0.75 mL, 0.75
mmol, a 1.0 M solution in hexane). After the mixture was stirred
at 0 °C for 20 min and then at rt for 3 h, the reaction was quenched
with saturated aq NaHCO3 solution (20 mL). The organic layer
was washed with brine (20 mL), dried (MgSO4), and concentrated.
The residue was purified by chromatography (hexane/EtOAc 3:1)
to give 480 mg (85%) of (S)-14 as a white solid; mp 56.7-57.5
°C; Rf 0.29 (EtOAc/hexane 1:3); [R]25D +24.9 (c 1.60, CHCl3); 1H
NMR (CDCl3) δ 0.88 (t, 3H, J ) 6.8 Hz), 1.26-1.38 (m, 10H),
1.58 (m, 2H), 1.84 (m, 1H), 2.01 (m, 1H), 2.57 (m, 4H), 3.30 (s,
1H), 3.55 (dd, 1H, J ) 11.6, 8.4 Hz), 3.85 (dd, 1H, J ) 11.6, 4.8
Hz), 4.45 (d, 1H, J ) 8.4 Hz), 4.65 (d, 1H, J ) 8.4 Hz), 7.08 (s,
4H); 13C NMR (CDCl3) 14.2, 22.7, 29.3, 29.4, 29.5, 29.8, 31.6,
32.0, 35.6, 37.6, 66.8, 76.0, 86.5, 128.2, 128.9, 138.2, 140.8, 163.2.
HRMS (MNa+) m/z calcd for C21H30Cl3NO2Na 456.1234, found
456.1241. Data for (R)-(14): [R]25D -25.0 (c 2.75, CHCl3); 1H NMR
(CDCl3) δ 0.88 (t, 3H, J ) 6.8 Hz), 1.26-1.38 (m, 10H), 1.58 (m,
2H), 1.85 (m, 1H), 2.01 (m, 1H), 2.14 (s, 1H), 2.60 (m, 4H), 3.54
(d, 1H, J ) 11.6 Hz), 3.83 (d, 1H, J ) 11.6 Hz), 4.45 (d, 1H, J )
8.4 Hz), 4.63 (d, 1H, J ) 8.4 Hz), 7.09 (s, 4H); 13C NMR (CDCl3)
δ 14.1, 22.7, 29.0, 29.3, 29.5, 29.7, 31.6, 31.9, 35.5, 37.5, 67.0,
75.9, 86.4, 128.1, 128.6, 138.1, 140.9, 163.3.
SCHEME 3. Outline of the Synthesis of (R)-5 and (R)-4
cytokines and microglial activation.15 The ability of 2a, (S)-3,
and phosphonate analogues 4 and 5 to protect IEC-6 cells from
apoptotic cell death in response to the topoisomerase inhibitor
CPT was assessed by DNA fragmentation. Pretreatment with
2a, (S)-3, (R)-4, or (R)-5 did not result in a significant reduction
in DNA fragmentation in response to a 4-h treatment with 20
µM CPT. However, we found that the cytoprotective effect was
enantioselective, since pretreatment with 1 µM of (S)-4 or (S)-5
showed a significant reduction (21 and 50%, respectively) in
DNA fragmentation in response to CPT.
In a preliminary study of the activity of the FTY720-
phosphonate analogues on S1P receptors, we performed Ca2+
mobilization assays with HTC4 cells that were stably transfected
with S1P1. As shown in Figure 1, the S1P1 transfectants were
activated by (S)-3 to 76% of the maximal S1P-induced activa-
tion, and displayed a similar potency as S1P (13 ( 2 nM for
S1P vs 9 ( 1 nM for (S)-3). (R)-5 and (R)-4 both showed a
modest activity against S1P1 with Emax values that ranged from
73 to 93% of the maximal S1P-induced responses, and EC50
values that were increased by ∼2- to 3-fold. (S)-4 activated S1P1
to 36% of the maximal S1P-induced response, and the EC50
value was increased by ∼5-fold to 75 ( 21 nM. Since (S)-5
did not elicit a Ca2+ response from cells transfected with the
S1P1 receptor, we conclude that the potent cytoprotective effect
of (S)-5 is not mediated by S1P1.
In conclusion, we have described the synthesis of the
enantiomers of FTY720 phosphonate analogues 4 and 5. (S)-4
and (S)-5, but not 2a or (S)-3, all at 1 µM, protected IEC-6
cells from apoptosis. The extent of CPT-induced DNA frag-
mentation was reduced by 50% and 21% in the presence of 1
µM of (S)-5 and (S)-4, respectively. The potent cytoprotective
(3S)-3-(Amino)-3-(hydroxymethyl)-5-(4′-octylphenyl)-pent-
(1E)-enyl-phosphonic acid [(S)-(+)-5]. To a solution of 269 mg
(0.50 mmol) of (S)-16 in 10 mL of THF at rt was added 3 mL of
1 M HCl. After the reaction mixture was stirred overnight, the
solvent was evaporated and the residue was extracted with a mixture
of CHCl3 and saturated Na2CO3 aq solution. The organic phase
was dried (MgSO4) and concentrated. The residue was purified by
chromatography (CHCl3/MeOH/NH4OH 135:25:4) to give 185 mg
(90%) of (S)-17 as a pale yellow oil after filtration through a Teflon
syringe filter. Rf 0.37 (CHCl3/MeOH/NH4OH 135:25:4); [R]25
D
1
+18.8 (c 1.52, CHCl3); H NMR (CDCl3) δ 0.88 (t, 3H, J ) 6.4
Hz), 1.26-1.29 (m, 10H), 1.58 (m, 2H), 1.48-1.86 (m, 5H), 2.49-
2.58 (m, 4H), 3.50 (dd, J ) 21.2, 10.6 Hz), 3.73 (s, 3H), 3.75 (s,
3194 J. Org. Chem. Vol. 74, No. 8, 2009

3H), 5.93 (dd, 1H, J ) 20.0, 17.6 Hz), 6.85 (dd, 1H, J ) 22.8,
17.6 Hz), 7.05-7.10 (m, 4H); 13C NMR (CDCl3) δ 14.1, 22.7, 29.3,
29.36, 29.44, 29.5, 31.6, 31.9, 35.5, 39.4, 52.4 (d, J ) 6.0 Hz),
59.4 (d, J ) 19.1 Hz), 69.2, 115.0 (d, J ) 188.1 Hz), 128.1, 128.3,
6.99 (d, 2H, J ) 8.0 Hz), 7.07 (d, 2H, J ) 8.0 Hz); 13C NMR
(CDCl3/CD3OD 9:1) δ 14.1, 22.9, 29.1, 29.5, 29.6, 31.8, 32.3, 35.8,
36.5, 62.2 (d, J ) 20.1 Hz), 64.4, 123.3, 125.2, 128.3, 128.9, 137.6,
141.4, 144.2; 31P NMR (CDCl3/CD3OD 9:1) δ 13.1. HRMS (MNa+)
128.6, 138.6, 140.8, 157.9 (d, J ) 6.0 Hz); 31P NMR (CDCl3) δ
m/z calcd for C20H34NO4PNa 406.2118, found 406.2106.
1
1
21.8. Data for (R)-(17): [R]25 -17.1 (c 1.51, CHCl3); H NMR
Data for (R)-5. [R]25 -13.0 (c 1.05, CHCl3/MeOH 9:1); H
D
D
(CDCl3) δ 0.88 (t, 3H, J ) 6.4 Hz), 1.26-1.29 (m, 10H), 1.58 (m,
2H), 1.79-1.82 (m, 5H), 2.53-2.57 (m, 4H), 3.50 (dd, J ) 21.2,
10.6 Hz), 3.73 (s, 3H), 3.75 (s, 3H), 5.93 (dd, 1H, J ) 20.0, 17.6
Hz), 6.85 (dd, 1H, J ) 22.8, 17.6 Hz), 7.07-7.10 (m, 4H); 13C
NMR (CDCl3) δ 14.1, 22.7, 29.3, 29.4, 29.42, 29.5, 29.7, 31.6,
31.9, 35.5, 39.4, 52.4 (d, J ) 2.0 Hz), 52.5 (d, J ) 2.0 Hz), 59.4
(d, J ) 19.1 Hz), 69.1, 115.0 (d, J ) 188.1 Hz), 128.1, 128.4,
128.5, 138.7, 140.7, 157.9 (d, J ) 6.0 Hz); 31P NMR (CDCl3) δ
21.8. To a solution of (S)-17 in 10 mL of dry CH2Cl2 at rt was
added 0.66 mL (5.0 mmol) of TMSBr. After the reaction mixture
was stirred for 4 h, the solvent was removed, and the residue was
dried and dissolved in 2 mL of 95% MeOH with stirring for 1 h.
Removal of the solvent afforded 224 mg (93%) of (S)-5 as a white
solid: mp 159.2-161.1 °C; Rf 0.14 (CHCl3/MeOH/H2O/AcOH 65:
25:4:1); [R]25D +12.2 (c 1.04, CHCl3/MeOH 9:1); 1H NMR (CDCl3/
CD3OD 9:1) δ 0.87 (t, 3H, J ) 6.8 Hz), 1.26 (br s, 10H), 1.51 (s,
2H), 1.95-2.10 (m, 2H), 2.47 (t, 2H, J ) 7.6 Hz), 2.55-2.68 (m,
2H), 3.83 (br s, 2H), 4.08 (br s, 4H), 6.30 (m, 1H), 6.60 (m, 1H),
NMR (CDCl3/CD3OD 9:1) δ 0.88 (t, 3H, J ) 6.8 Hz), 1.26-1.27
(m, 10H), 1.52-1.55 (m, 2H), 2.01-2.11 (m, 2H), 2.52 (t, 2H, J
) 7.6 Hz), 2.55-2.68 (m, 2H), 3.26 (br s, 4H), 3.82 (br s, 2H),
6.30 (m, 1H), 6.59 (dd, 1H, J ) 23.2, 18.0 Hz), 7.03 (d, 2H, J )
8.0 Hz), 7.08 (d, 2H, J ) 8.0 Hz), 8.34 (br s, 1H); 13C NMR (CDCl3/
CD3OD 9:1) δ 14.2, 22.9, 29.0, 29.5, 29.6, 29.7, 29.9, 31.8, 32.3,
35.8, 36.5, 62.2 (d, J ) 20.1 Hz), 64.4, 123.4, 125.2, 128.3, 128.9,
137.6, 141.4, 144.2; 31P NMR (CDCl3/CD3OD 9:1) δ 13.1.
Acknowledgment. This work was supported by NIH Grants
HL083187 and CA92160.
Supporting Information Available: Experimental details for
the synthesis of compounds 6-8, 10, 11, 12, 16, and 4, and
NMR spectra of all new compounds. This material is available
free of charge via the Internet at http://pubs.acs.org.
JO900023U
J. Org. Chem. Vol. 74, No. 8, 2009 3195