5810
D. Brégeon et al. / Bioorg. Med. Chem. Lett. 22 (2012) 5807–5810
yield, vs 7 steps/37% for the analogous mesylate via the previously
reported route.6
1/3, see Supplementary information). Worthy of note is that our
many attempts to dry and purify N-HDMAPP precursor 14 failed
to give the pure compound, which seems rather elusive except in
basic solution that is required to ensure stability of the N–P bond
towards hydrolysis. For the same reason, our trials to transform
14 into N-HDMAPP 2 were unsuccessful.18
In conclusion, we describe two complementary routes for han-
dy and scalable access to the enantiomers of BrHPP. Both of them
are rapid, robust and reliable, allowing the synthesis of multigram
samples. Biological evaluation is under progress and will be pub-
lished elsewhere. Our studies on N-HDMAPP synthesis consisted
in the development of a handy and rapid access to the organic
backbone, the phosphorylation of which was examined under var-
ious conditions.
Removal of the PMP protecting group in compound PMP-3 re-
quires the use of ceric ammonium nitrate, and therefore cannot
be conducted in the presence of an unprotected primary alcohol.
In order to minimize the use of removable protecting groups, we
first converted PMP-3 into the corresponding tosylate, before
applying the standard deprotection conditions to give compound
9. Tosylation of the remaining primary hydroxyl of 9 using DABCO
or catalytic DMAP/DIEA gave the bis-tosylate 7 in satisfying yields
(Scheme 3). Poulter showed that tris-(tetra-n-butylammonium)
hydrogen pyrophosphate (TTAPP) is an excellent nucleophilic
source of inorganic pyrophosphate for displacements on a wide
variety of appropriately activated primary alcohols.12 However,
the treatment of unprotected 10 with TTAPP failed to give the ex-
pected phosphorylated bromohydrin, in contrast to the results re-
ported by Oldfield for the mesylated bromohydrin.6,13 Protection of
10 as tetrahydropyranyl ether proceeded smoothly using DHP and
a catalytic amount of pyridinium p-toluenesulfonate, provided that
the DHP is slowly added to the reaction mixture (Scheme 4).
The crude protected bromohydrin tosylate THP-10 was then re-
acted with TTAPP to give BrHPP 1 as the tetrabutylammonium salt,
which was converted to the ammonium or benzathin salt by a ser-
ies of ions exchange: in these conditions, the temporary THP pro-
tection was also cleanly removed. The benzathin salts of both
enantiomers of BrHPP 1 are crystalline, non-hygroscopic and air-
stable compounds, which could be thoroughly purified by crystal-
lization (Scheme 4).14
Supplementary data
Supplementary data associated with this article can be found, in
References and notes
1. (a) Espinosa, E.; Belmant, C.; Pont, F.; Luciani, B.; Poupot, R.; Romagne, F.;
Brailly, H.; Bonneville, M.; Fournie, J. J. J. Biol. Chem. 2001, 276, 18337; (b)
Espinosa, E.; Belmant, C.; Sicard, H.; Poupot, R.; Bonneville, M.; Fournie, J. J.
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Rolland, F.; Bruzzoni-Giovanelli, H.; Rimbert, M.; Galéa, C.; Tiollier, J.; Calvo, F. J.
Immunol. Immunother. 2010, 59, 1521; Information on IPH 1101 clinical studies
4. Hintz, M.; Reichenberg, A.; Altincicek, B.; Bahr, U.; Gschwind, R. M.; Kollas, A.
K.; Beck, E.; Wiesner, J.; Eberl, M.; Jomaa, H. FEBS Lett. 2001, 509, 317.
5. Belmant, C.; Nury, P. PCT Int. Appl. WO 2005/054258 A, 2005.
6. Song, Y.; Zhang, Y.; Wang, H.; Raker, A. M.; Sanders, J. M.; Broderick, E.; Clark,
A.; Morita, C. T.; Oldfield, E. Bioorg. Med. Chem. 2004, 14, 4471.
7. The cyclic phosphates that constitute two of the main metabolites of BrHPP
have been synthesized starting from precursor 3, and are under current
biological evaluation. Full details will be published elsewhere.
Finally we focused on N-HDMAPP synthesis. Unlike other
known bioisosters of the natural phosphoantigen HDMAPP (pyro-
phosphonate and thiopyrophosphate analogues15,16) N-HDMAPP
was reported5 to achieve a greater activating effect in vitro than
HDMAPP (3–4 times greater potency when assessed in a relative
screening test using the TNF-a release assay). Although stable un-
der physiological and basic pH conditions, pyrophosphoramidate
esters are however very prone to acidic hydrolysis which may rep-
resent a strong limitation for the design of robust chemical routes.
For further investigations on N-HDMAPP biological properties, we
have explored a multigram scale synthesis route, the results of
which are summarized below.
In order to get N-HDMAPP backbone, the commercially avail-
able racemic oxirane 11 was opened by sodium azide at rt,17 and
the resulting mixture of azides was submitted to Staudinger reduc-
tion (Scheme 5), to afford only the (E)-isomer of the allylic amine
13. Both for storage and easy removal of triphenylphosphine oxide,
we directly protected it as hydrochloride salt, with 52% overall
yield starting from 11. We assume that the only production of
the (E)-stereoisomer results from allylic transposition of the
branched isomer of 12 during the reduction process.
We further examined the phosphorylation step in order to ac-
cess to N-HDMAPP, which is the more challenging issue in this syn-
thesis mainly because of the lability of the P–N bond. Among many
attempts including variants of the Staudinger reaction, we only
succeeded to connect a triphosphate moiety by using Tsuhako re-
agent,18 by reacting 13.HCl with an excess of sodium cyclotriphos-
phate hexahydrate (Scheme 6).
8. Corey, E. J.; Guzman-Perez, A.; Noe, M. C. J. Am. Chem. Soc. 1995, 117, 10805.
9. Tietze, L. F.; Görlitzer, J. Synthesis 1998, 873.
10. Freedman, H. H.; Dubois, R. A. Tetrahedron Lett. 1975, 3251.
11. It must be noted that these conditions lead to the formation of a substantial
amount of TMS-protected bromohydrin, requiring an extensive acidic aqueous
work-up to obtain a good yield of compound 10.
12. Davisson, V. J.; Woodside, A. B.; Neal, T. R.; Stremler, K. E.; Muehlbacher, M.;
Poulter, C. D. J. Org. Chem. 1986, 51, 4768.
13. Under these basic conditions, only phosphorylated and unphosphorylated
epoxides were observed. Careful examination of Oldfield publication suggests
that the actual intermediate might be the O-TMS protected bromohydrin
instead of the free OH compound, as no purification nor special treatment is
done after epoxide opening with TMSBr.3
14. (a) Coquerel, G.; Aubin, E. PCT Int. Appl., WO 2007039635 A2 20070412, 2007.
For our further studies on benzathin derivatives, see:.; (b) Mahieux, J.; Gonella,
S.; Sanselme, M.; Coquerel, G. CrystEngComm 2012, 14, 103; (c) Zgonnik, V.;
Gonella, S.; Mazières, M.-R.; Guillen, F.; Coquerel, G.; Saffon, N.; Plaquevent, J.-
C. Org. Process Res. Dev. 2012, 16, 277.
15. Boëdec, A.; Sicard, H.; Dessolin, J.; Herbette, G.; Ingoure, S.; Raymond, C.;
Belmant, C.; Kraus, J.-L. J. Med. Chem. 2008, 51, 1747.
16. Breccia, P.; Angeli, F.; Cerbara, I.; Topai, A.; Auricchio, G.; Martino, A.; Colizzi,
V.; Poccia, F. J. Med. Chem. 2009, 52, 3716.
17. Tenaglia, A.; Waegell, B. Tetrahedron Lett. 1988, 29, 4851.
18. Tsuhako, M.; Kunitomi, R.; Baba, Y.; Miyajima, T. Bull. Chem. Soc. Jpn. 1991, 64,
490.
NMR analysis of the resulting aqueous solution showed obten-
tion of the target 14, along with linear sodium triphosphate (ratio