First asymmetric synthesis of chiral analogues of the novel immunosuppressant FTY720

Article abstract of DOI:10.1016/S0040-4039(02)01925-1

FTY720 is an immunosuppressant with a novel mode of action and is highly effective in animal models of transplantation and autoimmunity. Herein we describe the first asymmetric synthesis of chiral FTY720 analogues using the Sch?llkopf-protocol. We also describe a practical synthesis of the corresponding phosphates, which are essential tools for elucidation of FTY720's mechanism of action.

Full text of DOI:10.1016/S0040-4039(02)01925-1

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 43 (2002) 8095–8097
First asymmetric synthesis of chiral analogues of the novel
immunosuppressant FTY720
Klaus Hinterding,* Rainer Albert and Sylvain Cottens
Transplantation Research, Novartis Pharma AG, CH-4002 Basel, Switzerland
Received 7 August 2002; accepted 9 September 2002
Abstract—FTY720 is an immunosuppressant with a novel mode of action and is highly effective in animal models of
transplantation and autoimmunity. Herein we describe the first asymmetric synthesis of chiral FTY720 analogues using the
Scho¨llkopf-protocol. We also describe a practical synthesis of the corresponding phosphates, which are essential tools for
elucidation of FTY720’s mechanism of action. © 2002 Elsevier Science Ltd. All rights reserved.
FTY720 1 (Fig. 1) is a novel immunosuppressant which
is highly effective in animal models of transplantation
and autoimmunity.1 Additionally, in a recently com-
pleted Phase II trial, the drug has proven efficacious in
preventing kidney allograft rejection in humans.2
Unlike any other immunosuppressant currently on the
market, FTY720 does not inhibit T- and B-cell prolifer-
ation and activation at therapeutically relevant concen-
trations in vitro; instead it leads to a sequestration of
lymphocytes from the periphery into secondary
lymphoid organs.3 According to our current under-
standing, the phosphorylated molecule FTY720-phos-
phate 2 (Fig. 1), which is generated in vivo via a
sphingosine-kinase, signals as an agonist through four
of five sphingosine-1-phosphate (S1P) receptors (for-
merly known as EDG-receptors).4
revealed that only R-enantiomer (R)-3 is biologically
active in vivo and only phosphate (R)-4 has low
nanomolar affinities on S1P-receptors.4 Chiral ana-
logues and phosphates are therefore invaluable tools to
differentiate biological effects and to further elucidate
FTY720’s mechanism of action.
We herein describe a practical and versatile stereoselec-
tive synthesis of chiral FTY720 analogues 3 and their
corresponding phosphates 4. This synthetic protocol is
also amenable to the preparation of additional struc-
tural analogues.
The Scho¨llkopf-protocol5 is the centerpiece of our syn-
thesis. It was chosen because both Gly- and Ala-derived
auxiliaries are commercially available in either enan-
tiomeric form.6 In addition, the protocol allows for
broad structural variations at the quaternary center,
which was considered to be advantageous for the gener-
Using chiral FTY720 analogues (R)-3 and (S)-3 and
their corresponding phosphates (R)-4 and (S)-4 (Fig. 1)
Figure 1. Structures of immunosuppressant FTY720 and chiral analogues.
Keywords: immunosuppressant; FTY720; Schoellkopf-auxiliary; phosphates.
* Corresponding author. Tel.: +41613243724; fax: +41613246735; e-mail: klaus.hinterding@pharma.novartis.com
0040-4039/02/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(02)01925-1

8096
K. Hinterding et al. / Tetrahedron Letters 43 (2002) 8095–8097
Boc-protected aminoalcohols 814 were phosphorylated
with tri-valent phosphorylating agent 915 and oxidized
in situ using H2O2. This sequence produced fully pro-
tected phosphates 10 in 85% yield. At this stage, the
compounds were purified by chromatography and then
subjected to two deprotection steps without any further
purification. This protocol delivered phosphates 416
from Boc-protected aminoalcohols with an overall yield
of 75%. Again as described earlier, only phosphate
(R)-4 had low nanomolar affinities to S1P-receptors.4
ation of a larger collection of chiral FTY720 analogues.
As shown in Scheme 1 for the synthesis of the biologi-
cally active R-enantiomer,
D
-cyclo-Val-Gly-OEt 57 was
lithiated and treated with iodide 68 to generate the
monoalkylated Scho¨llkopf adduct as pure diastereomer
in 71% yield.9 This intermediate was subsequently lithi-
ated and methylated to generate the quaternary center
in 7 stereoselectively with 65% yield.10 Hydrolysis of the
bislactimether proceeded uneventfully to produce the
aminoacid ester (58% yield), which was reduced to
(R)-3 in 95% yield.11
In summary, we described a highly practical asymmet-
ric synthesis of chiral FTY720 analogues and an
efficient procedure to generate the corresponding phos-
phates. These compounds as well as additional struc-
tural analogues accessible via the synthetic procedures
described here will be essential tools to further elucidate
the mechanism of action of the novel immunosuppres-
sant FTY720.
The (S)-enantiomer was synthesized in an analogous
manner starting from L
-cyclo-Val-Gly-OEt.12 The enan-
tiomeric purity of (R)-3 and (S)-3 was confirmed by
HPLC analysis of the corresponding dinitrobenzamide
derivatives.13 As described earlier, only the R-enan-
tiomer was biologically active and induced lymphocyte
depletion after oral dosing in rats.4
Due to the difficult physicochemical properties of phos-
phates 4, in particular their low solubility, and due to
lack of availability of sphingosine kinases, biochemical
synthesis and isolation is tedious. We therefore describe
here a straightforward chemical approach for the
preparation of phosphates (R)- and (S)-4 (Scheme 2).
Acknowledgements
We wish to thank E. Francotte for chiral HPLC separa-
tions and K. Christ, H. Jundt, H. Knecht, C. Simeon
and B. Thai for technical assistance.
Scheme 1. (a) BuLi, THF, −78°C to 0°C; then 6, −78°C to 0°C, 71%; (b) BuLi, THF, −78°C to 0°C, then MeI, −78°C to 0°C,
65%; (c) 0.5N HCl, dioxane, rt, 16 h, 58%; (d) LiAlH4, THF, 65°C, 2 h, 95%.
Scheme 2. (a) (1,5-Dihydro-benzo[e][1,3,2]dioxaphosphepin-3-yl)-diethylamine 9, tetrazole, THF, rt, 2 h; then 30% H2O2, rt, 1 h,
85%; (b) 1 bar H2, Pd/C, MeOH, rt, 1 h, 88%; (c) conc. HCl, HOAc, rt, 16 h, quant.

K. Hinterding et al. / Tetrahedron Letters 43 (2002) 8095–8097
8097
References
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1
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