Synthesis of a nitrogen analogue of sphingomyelin as a sphingomyelinase inhibitor

Article abstract of DOI:10.1021/ol034771u

Matrix presented Sphingomyelin nitrogen analogue 1 was designed and synthesized as a sphingomyelinase inhibitor. The synthesis was established by continuous Hofmann rearrangement and Crutius rearrangement as key steps in constructing the 3-hydroxy-1,2-dia

Full text of DOI:10.1021/ol034771u

ORGANIC
LETTERS
2003
Vol. 5, No. 16
2801-2804
Synthesis of a Nitrogen Analogue of
Sphingomyelin as a Sphingomyelinase
Inhibitor
Toshikazu Hakogi, Misako Taichi, and Shigeo Katsumura*
School of Science and Technology, Kwansei Gakuin UniVersity, 2-1 Gakuen Sanda,
Hyogo 669-1337, Japan
katsumura@ksc.kwansei.ac.jp
Received May 7, 2003
ABSTRACT
Sphingomyelin nitrogen analogue 1 was designed and synthesized as a sphingomyelinase inhibitor. The synthesis was established by continuous
Hofmann rearrangement and Crutius rearrangement as key steps in constructing the 3-hydroxy-1,2-diamine structure in the backbone of 1.
This analogue showed moderate inhibitory activity toward SMase isolated from B. cereus.
Sphingolipids are known as secondary lipid messengers in
mammalian cells and cell membranes, and a great deal of
attention has been devoted to studies of the biological
processes regulated by sphingolipids.1 It is now well accepted
that the sphingolipids play key roles in the cellular signal
transmission pathway. Ceramide, the primary sphingomyelin
metabolite, is generated through the action of sphingomy-
elinase (SMase) and is believed to be an essential signal
transduction factor in cell differentiation and in programmed
cell death (apoptosis) derivation.2 Sphingosine, the secondary
metabolite of sphingomyelin, strongly inhibits protein kinase
C (Figure 1).3 Although the significance of the sphingomyelin
pathway, which is initiated by hydrolysis of sphingomyelin
by SMase, has been well recognized, none of the three-
dimensional structures of these important enzymes have been
determined and their hydrolytic mechanism has not been well
defined. Revealing the mechanism of the catalytic action of
this important enzyme is, therefore, a very attractive chal-
lenge. Strong and selective sphingomyelinase inhibitors
would contribute to a better understanding of both the roles
of these enzymes and ceramide in signal transduction.4 To
elucidate the detailed catalytic mechanism of SMase, supple-
ments of sphingomyelin analogues, which act competitively
at the catalytic site and strongly inhibit the hydrolytic ability
of the enzyme, are desired.
We have reported the synthesis of sphingomyelin carbon
analogues, and these analogues actually showed moderate
inhibitory activities toward the SMase from B. cereus.5 The
sphingomyelin nitrogen analogue 1 was then designed to
(4) (a) Yokomatsu, T.; Murao, T.; Akiyama, T.; Koizumi, J.; Shibuya,
S.; Tsuji, Y.; Soeda, S.; Shimeno, H. Bioorg. Med. Chem. Lett. 2003, 13,
229. (b) Arenz, C.; Giannis, A. Angew. Chem., Int. Ed. 2000, 39, 1440. (c)
Nara, F.; Tanaka, M.; Hosoya, T.; Suzuki-Konagai, K.; Ogita, T. J. Antibiot.
1999, 52, 525. (d) Uchida, R.; Tomoda, H.; Dong, Y.; Omura, S. J. Antibiot.
1999, 52, 572. (e) Tanaka, M.; Nara, F.; Yamasato, Y.; Masuda-Inoue, S.;
Doi-Yoshioka, H.; Kumakura, S.; Enokita, R.; Ogita, T. J. Antibiot. 1999,
52, 670. (f) Tanaka, M.; Nara, F.; Yamasato, Y.; Ono, Y.; Ogita, T. J.
Antibiot. 1999, 52, 827. (g) Lister, M. D.; Ruan, Z.-s.; Bittman, R. Biochim.
Biophys. Acta 1995, 1256, 25.
(1) For recent reviews on signal transduction mediated by sphingolipids,
see; (a) Hannun, Y. A.; Luberto, C.; Argraves, K. M. Biochemistry 2001,
40, 4893. (b) Kolter, T.; Sandhoff, K. Angew. Chem., Int. Ed. 1999, 38,
1532 and references therein.
(2) (a) Sawai, H.; Hannun, Y. A. Chem. Phys. Lipids 1999, 102, 141.
(b) Tilly, J. L.; Kolesnick, R. N. Chem. Phys. Lipids 1999, 102, 149. (c)
Kronke, M. Chem. Phys. Lipids 1999, 102, 157. (d) Hannun, Y. A. Science
1996, 274, 1855 and references therein.
(5) (a) Hakogi, T.; Monden, Y.; Taichi, M.; Iwama, S.; Fujii, S.; Ikeda,
K.; Katsumura, S. J. Org. Chem. 2002, 67, 4839. (b) Hakogi, T.; Monden,
Y.; Iwama, S.; Katsumura, S. Org. Lett. 2000, 2, 2627.
(3) Vankar, Y. D.; Schmidt, R. R. Chem. Soc. ReV. 2000, 29, 201.
10.1021/ol034771u CCC: $25.00 © 2003 American Chemical Society
Published on Web 07/09/2003

Figure 1. Sphingomyelin catabolism.
provide a desired stronger inhibitor of SMase. In this
analogue 1, one of the oxygen atoms, at which the sphin-
gomyelin was hydrolyzed by SMase, was replaced with a
nitrogen atom (Figure 2).
polarity compared with that of the compound with the acetyl
group, was introduced to the nitrogen to afford amide 9 under
the Shotten-Baumann condition followed by removal of the
tetrahydropyranyl group to give alcohol 11. Jones oxidation
gave the desired carboxylic acid 12 in good yield.
The Crutius rearrangement of compound 12 with diphenyl
phosphoryl azide (DPPA)7 in the presence of triethylamine
in toluene proceeded smoothly at 60 °C, and gave the
corresponding imidazolidinone 13 almost quantitatively. In
this reaction, the intermediary isocyanate was successfully
trapped with the vicinal amide nitrogen to afford the
corresponding cyclic imidazolidinone. In the literature, few
examples can be found that use this intramolecular imida-
zolidinone formation method in natural product synthesis.8
Obviously, these reactions are very useful for the construction
of the protected 1,2-diamine moiety (Scheme 2).
Since the method for stereoselective construction of the
desired 1,2-diamino moiety was established by utilizing
continuous rearrangements, the next objective was the
completion of the synthesis of the nitrogen analogue 1. When
monocyclic imidazolidinone 13 was used for the synthesis
of 1, it was necessary to hydrolyze the imidazolidinone ring
accompanied by differentiation of the resulting two nitrogen
atoms by introduction of different kinds of protecting groups.
Hydrolysis of imidazolidinone has usually needed vigorous
Figure 2. Designed SMase inhibitor.
The backbone skeleton of 1 possesses a characteristic
structure, which consists of continuous vicinal amino alcohol
and vicinal diamine as illustrated in Figure 2. A 1,2-diamino
moiety can be found in various natural products possessing
valuable biological properties.6 We planned to utilize an
amino alcohol 6, which had been used as an intermediate
for the synthesis of carbon analogues, as a precursor of the
desired 1,2-diamine moiety. Diamine construction utilizing
continuous rearrangement reactions, such as the Hofmann
and the Crutius rearrangements, was very attractive. To
examine the latter rearrangement, oxazolidinone 6 was first
synthesized via Hofmann rearrangement by following the
previously reported procedure (Scheme 1).5
Scheme 1. Synthesis of Oxazolidinonea
The carboxylic acid derivative for the Crutius rearrange-
ment was synthesized from compound 6. Thus, after protec-
tion of the primary hydroxyl group of 6, hydrolysis of the
oxazolidinone ring of 7 by treatment with potassium
hydroxide in ethanol under reflux provided amino alcohol 8
in good yield. A long-chain acyl group, which decreased the
a Reagents and conditions: (i) H2, cat. (R)-BINAP-RuCl2, 60
°C, 100 atm, 10 days, 99%, 98% de; (ii) conc NH3, DME; (Iiii)
AgOAc, NBS, DMF, 77% for 2 steps.
(6) Lucet, D.; Gall, T. L.; Mioskowski, C. Angew. Chem., Int. Ed. 1998,
37, 2580 and references therein.
2802
Org. Lett., Vol. 5, No. 16, 2003

78% yield as reported,11 we were unwilling to proceed with
scaling up of this reaction because of the extremely unpleas-
ant odor of the thiophenol. Odorless decanethiol12 was
therefore used for the removal of the nosyl group. Thus,
treatment of nosylamide 16 with decanethiol and sodium
hydride in DMF successfully afforded amine 17 in quantita-
tive yield (Scheme 3).
Scheme 2. Synthesis of Imidazolidinonea
Scheme 3. Synthesis of Primary Aminea
a Reagents and conditions: (i) DHP, PPTS, CH2Cl2, quant; (ii)
KOH, EtOH, reflux, 87%; (iii) C5H11COCl, K2CO3, THF, H2O, 0
°C, quant; (iv) BnBr, NaH, DMF, rt, 87%; (v) TsOH, MeOH, 99%;
(vi) Jones oxid., acetone, 0 °C, 98%; (vii) DPPA, Et3N, toluene,
60 °C, 96%.
reaction conditions such as treatment with concentrated
hydrochloric acid or saturated barium hydroxide under reflux
for long periods.9 If imidazolidinone could be easily hydro-
lyzed under mild conditions, this heterocycle could be used
as a more useful synthetic intermediate. In the case of the
hydrolysis of an oxazolidinone ring, introduction of a tert-
butoxycarbonyl group at the nitrogen has been very effective,
and cesium carbonate treatment of oxazolidinone derivatives
in methanol at room temperature has produced the desired
hydrolyzed product in good yield.10 In the case of the imida-
zolidinone ring, however, introduction of a tert-butoxycar-
bonyl group was not effective, and that group was easily
removed under the same reaction conditions. When the nosyl
group (4-nitrobenzenesulfonate), which is hydrolytically
stable and easily removed by a treatment with thiophenol in
the presence of potassium carbonate,11 was introduced to the
imidazolidinone nitrogen, the imidazolidinone ring was easily
cleaved with potassium hydroxide in ethanol to produce
primary amine 15 at room temperature. In this reaction, the
N-acyl group was first removed and then subsequent hy-
drolysis of the imidazolidinone ring proceeded to give the
amine 15. The acyl group was introduced again into the
resulting primary amine to produce the desired amide 16.
Although the removal of the nosyl group of 16 was
realized by treatment with thiophenol and DBU in DMF in
a Reagents and conditions: (i) NsCl, LDA, THF, 0 °C, 87%;
(ii) KOH, EtOH, H2O; (iii) C5H11COCl, K2CO3, THF, H2O, 70%
for 2 steps.
For the synthesis of nitrogen analogue 1, the remaining
objectives were introduction of the phosphoryl choline
moiety to primary amine 17 and the removal of the benzyl
group. Introduction of a phosphoryl group was examined.
Unfortunately, treatment of amine 17 with 2-bromoethyl-
chloromethyl phosphite in THF followed by oxidation of the
resulting phosphite to the corresponding phosphate with
hydrogen peroxide according to literature13 gave a complex
mixture. After various trials, phosphorylation of 17 with
the reagent A,14 which was easily prepared in situ by the
reaction of methyl phosphorodichloridate with lithium 2-
bromoethoxide, readily proceeded in the presence of diiso-
propylethylamine in THF to produce 18. Compound 18 thus
obtained was treated with anhydrous trimethylamine in
toluene in a sealed tube13 to give O-protected nitrogen
analogue 19 in 25% yield after purification by reverse-phase
HPLC, and the starting primary amine 17, which would be
generated by hydrolysis, was also recovered in 20% yield
after flash chromatography. Finally, removal of the benzyl
group of 19 was achieved by hydrogenolysis with a catalytic
amount of Pd-black and one portion of formic acid, and the
nitrogen analogue 1 was successfully produced. Purification
by reverse-phase HPLC afforded pure nitrogen analogue 1.
Thus, the convenient synthesis of the nitrogen analogue 1
was achieved (Scheme 4).15
(7) Ninomiya, K.; Shioiri, T.; Yamada, S. Tetrahedron 1974, 30, 2151.
(8) (a) Dunn, P. J.; Haner, R.; Rapoport, H. J. Org. Chem. 1990, 55,
5017. (b) Olsen, R. K.; Hennen, W. J.; Wardle, R. B. J. Org. Chem. 1982,
47, 4605.
(9) (a) Kitahira, T.; Ishizuka, T.; Matsunaga, H.; Kunieda, T. Tetrahedron
Lett. 2001, 42, 6319. (b) Abdel-Aziz, A. A.-M.; Matsunaga, H.; Kunieda,
T. Tetrahedron Lett. 2001, 42, 6565. (c) Katritzky, A. R.; Luo, Z.; Fang,
Y.; Steel, P. J. J. Org. Chem. 2001, 66, 2858. (d) Park, Y. S.; Boys, M. L.;
Beak, P. J. Am. Chem. Soc. 1996, 118, 3757. (e) Cardillo, G.; Orena, M.;
Penna, M.; Sandri, S.; Tomasini, C. Tetrahedron Lett. 1991, 47, 2263.
(10) Ishizuka, T.; Kunieda, T. Tetrahedron Lett. 1987, 28, 4185.
(11) Fukuyama, T.; Jow, C. K.; Cheung, M. Tetrahedron Lett. 1995,
36, 6373.
(12) Node, M.; Kumar, K.; Nishide, K.; Ohsugi, S.; Miyamoto, T.
Tetrahedron Lett. 2001, 42, 9207.
(13) Martin, S. F.; Josey, J. A. Tetrahedron Lett. 1988, 29, 3631.
(14) Chabrier, P.; Nguyen-Thanh-Thuong; Le Maitre, D.; Perat, M. Patent
FR 1551060, 1968.
Org. Lett., Vol. 5, No. 16, 2003
2803

Acknowledgment. We thank Professor K. Ikeda and Dr.
S. Fujii at Osaka University of Pharmaceutical Sciences for
conducting the SMase assay. We also thank Professor M.
Node at Kyoto Pharmaceutical University for kindly provid-
ing some odorless thiols. This research is partly supported
by a Grant-in-Aid for Scientific Research from the Ministry
of Education, Science and Culture, Japan. T.H. is grateful
to the JSPS for a Research Fellowship for Young Scientists.
Scheme 4. Synthesis of Sphingomyelin Nitrogen Analogue 1a
Supporting Information Available: 1H and 13C NMR
spectra of compounds 13, 17, and 1. This material is available
free of charge via the Internet at http://pubs.acs.org.
OL034771U
a Reagents and conditions: (i) 2-bromoethanol, nBuLi, MeO-
P(O)Cl2, iPr2NEt, THF, 64%; (ii) Me3N, DMF, 60 °C, 25%; (iii)
H2, HCO2H, Pd-black, MeOH, 27%.
(15) Data for 1: [R]25.0 23.3 (c 0.29, CH3OH); IR (NaCl neat) 3331,
D
2924, 1638, 1202, 1055 cm-1; 1H NMR (CD3OD, 400 MHz) δ 4.14-4.21
(m, 2H), 3.67-3.73 (m, 1H), 3.58-3.64 (m, 3H), 3.22 (s, 9H), 3.02-3.16
(m, 2H), 2.22 (dt, J ) 3.7, 8.6 Hz, 2H), 1.23-1.70 (m, 18H), 0.91 (t, J )
7.1 Hz, 3H), 0.89 (t, J ) 7.1 Hz, 3H); 13C NMR (CD3OD, 100 MHz) δ
176.2, 72.0, 67.7 (m), 59.5 (d, JC-P ) 5.0 Hz), 56.7 (d, JC-P ) 3.3 Hz),
54.7 (m), 42.8, 37.4, 34.7, 33.0, 32.6, 30.8, 30.4, 27.0, 26.9, 23.7, 23.5,
14.4, 14.3.
The synthesized substrate analogue 1 showed moderate
inhibitory activity toward SMase isolated from B. cereus.
2804
Org. Lett., Vol. 5, No. 16, 2003