Design and synthesis of piperidine-containing sphingoid base analogues

Article abstract of DOI:10.1021/jo900378h

(Chemical Equation Presented) We report an approach that allows the efficient synthesis of the designed sphingoid base analogues in which the conformational restriction is introduced by incorporation of a cyclic moiety between the 2-amino group and the C-

Full text of DOI:10.1021/jo900378h

Design and Synthesis of Piperidine-Containing Sphingoid Base
Analogues
Jihee Cho, Yun Mi Lee, Deukjoon Kim, and Sanghee Kim*
College of Pharmacy, Seoul National UniVersity, San 56-1, Shilim, Kwanak, Seoul 151-742, Korea
pennkim@snu.ac.kr
ReceiVed February 19, 2009
We report an approach that allows the efficient synthesis of the designed sphingoid base analogues in
which the conformational restriction is introduced by incorporation of a cyclic moiety between the 2-amino
group and the C-4 carbon atom of the sphingoid base. Our synthesis features a tandem enyne/diene-ene
metathesis reaction that provides access to the designed framework. The diene moiety of the metathesis
product is stereoselectively elaborated for the synthesis of the designed analogues. The preliminary
biological evaluation indicates that the designed constrained analogues are much more effective than
prototype natural sphingoid bases at inhibiting cancer cell growth.
Introduction
Conformationally restricted analogues of bioactive molecules
are valuable tools for the understanding of structure-bioactivity
relationships and the development of novel compounds with
beneficial biological and physical properties.1 The concept of
conformational restriction has been used extensively in the field
of peptides. It has also been widely applied to various other
biomolecules and natural products. However, there are relatively
few examples where this concept was applied to sphingolipids.2
FIGURE 1. Chemical structures of compounds 1-4.
Sphingoid bases are the fundamental backbone of all sphin-
golipids and the primary subject of structural modification in
sphingolipid research. They are long-chain aliphatic compounds
typically possessing a 2-amino-1,3-diol functionality. The most
common natural sphingoid bases are D-ribo-phytosphingosine
(1, Figure 1) and D-erythro-sphingosine (2).3 The amino and
hydroxyl groups of sphingoid bases can be engaged in several
inter-/intramolecular hydrogen bonds.4 Therefore, sphingoid
bases are able to adopt multiple conformations depending on
the environment as well as the degree of hydrogen bonding
interactions.
As part of our ongoing research focused on the preparation
of sphingolipid analogues, we were particularly interested in
the design and synthesis of conformationally restricted analogues
of sphingoid bases since these analogues could be useful in the
investigation of the biological functions of sphingolipids and
provide opportunities for modulating cellular processes.
Interestingly, there are a couple of naturally occurring
conformationally restricted sphingoid bases, such as pachas-
trissamine5 and penaresidine6 (Figure 2), which can be consid-
* To whom correspondence should be addressed. Tel.: 82-2-880-2487. Fax:
82-2-888-0649.
(1) (a) Wermuth, C. G., Ed. The Practice of Medicinal Chemistry, 3rd ed.;
Academic Press: San Diego, 2008. (b) Silverman, R. B. The Organic Chemistry
of Drug Design and Drug Action, 2nd ed.; Academic Press: San Diego, 2004.
(2) Kolter, T. In Highlights in Bioorganic Chemistry: Methods and Applica-
tions; Schmuck, C., Wennemers, H., Ed.; Wiley-VCH: Weinheim, 2004; Chapter
1.4, p 48.
(4) (a) Li, L.; Tang, X.; Taylor, K. G.; DuPre´, D. B.; Yappert, M. C. Biophys.
J. 2002, 82, 2067. (b) DuPre´, D. B.; Yappert, M. C. J. Mol. Struct. THEOCHEM
1999, 467, 115, and references therein.
(3) Howell, A. R.; Ndakala, A. J. Curr. Org. Chem. 2002, 6, 365.
3900 J. Org. Chem. 2009, 74, 3900–3904
10.1021/jo900378h CCC: $40.75 2009 American Chemical Society
Published on Web 04/09/2009

Synthesis of Piperidine-Containing Sphingoid Base
SCHEME 1. Retrosynthetic Analysis of Compounds 3 and 4
Results and Discussion
We envisioned that the designed cyclic analogues 3 and 4
could be accessible from diene 5 (Scheme 1). The requisite diene
5 would, in turn, arise from the ring-closing metathesis (RCM)
of enyne 6 and subsequent cross metathesis (CM)8 between the
resulting diene and an appropriate olefin. Since the enyne RCM
and CM can be performed in a tandem fashion,8,9 the synthesis
of 5 would be achieved in a single step from enyne 6. Further
analysis indicated the known epoxyalkyne 7 to be a suitable
synthetic precursor for metathesis substrate 6.
We initially planned to prepare the chiral epoxyalkyne 7 from
(E)-2-penten-4-yn-1-ol (8) by Sharpless asymmetric epoxidation.
However, the previously reported chemical yield (47%) of this
reaction was low,10 and the chemical purity of commercial 8 is
not sufficient to warrant the best stereochemical outcome in the
asymmetric epoxidation. Therefore, we utilized silyl-protected
enyne 11 (Scheme 2) as an alternative substrate for the Sharpless
epoxidation. The requisite enyne 11 was easily prepared in high
overall yield as shown in Scheme 2. The palladium-catalyzed
cross-coupling of 3-bromopropargyl alcohol 9 with TIPS-
acetylene provided the known TIPS-diyne 1011 in 85% yield,
and subsequent selective reduction of the ∆2,3-triple bond to
the trans double bond with LiAlH4 afforded (E)-allylic alcohol
11 in 92% yield. With this substrate, Sharpless asymmetric
epoxidation with (-)-diethyl tartrate as a ligand afforded
(2R,3R)-epoxy alcohol 12 in 73% yield and 92% ee.12
The obtained epoxy alcohol 12 was treated with allyl
isocyanate/Et3N in a sealed tube to provide allyl carbamate 13
in 87% yield. The intramolecular ring opening of 13 using
NaHMDS in THF proceeded very smoothly and regioselectively
in excellent yield (97%) to give the desired oxazolidinone 14.13
Removal of the silyl-protecting group of 14 with TBAF gave
the terminal acetylene 15 (94%).
FIGURE 2. Chemical structures of conformationally restricted repre-
sentative natural and non-natural sphingoids. Pachastrissamine and
penaresidines are naturally occurring sphingoids, and the others are
non-natural products.
ered as cyclized derivatives of sphingoid bases. A number of
cyclic derivatives of sphingolipids have been recently designed
and synthesized to provide conformational restriction of the polar
part of the sphingoid base.7 The structures of some representative
compounds are shown in Figure 2.
In this regard, we designed different types of cyclic analogues
(3 and 4, Figure 1), wherein the conformational restriction is
introduced by incorporation of a cyclic moiety between the
2-amino group and the C-4 carbon atom of the sphingoid base.
Piperidine compound 3 could be considered a rigid structural
analogue of phytosphingosine 1 that mimics the hydrogen
bonding between the 2-NH2 and 4-OH groups of phytosphin-
gosine. Piperidinylidene analogue 4 could be regarded as a rigid
analogue of sphingosine 2 since the incorporated ethylene bridge
restricts the rotations of C2-C3 and C3-C4 single bonds, thus
fixing the conformation of the polar part of sphingosine.
Herein, we wish to report a novel approach that allows the
efficient synthesis of the designed sphingoid base analogues 3
and 4, in which the alkyl chain lengths are 18 carbon atoms,
which is identical to those in sphingoid bases 1 and 2. In
addition, preliminary activity studies of these new sphingoid
base analogues are reported.
With multigram quantities of enyne 15, we first tested the
feasibility of the tandem enyne/diene-ene metathesis reaction
with 1-tetradecene to give diene 16. Unfortunately, all of our
attempts using the first- and second-generation Grubbs catalyst
in various solvents resulted in the recovery of unreacted starting
(8) For reviews of enyne metathesis, see: (a) Villar, H.; Frings, M.; Bolm,
C. Chem. Soc. ReV. 2007, 36, 55. (b) Diver, S. T.; Giessert, A. J. Chem. ReV.
2004, 104, 1317. For reviews of cross metathesis, see: (c) Grubbs, R. H.
Tetrahedron 2004, 60, 7117. (d) Connon, S. J.; Blechert, S. Angew. Chem., Int.
Ed. 2003, 42, 1900.
(9) For representative examples, see: (a) Kummer, D. A.; Brenneman, J. B.;
Martin, S. F. Org. Lett. 2005, 7, 4621. (b) Royer, F.; Vilain, C.; Elka¨ım, L.;
Grimaud, L. Org. Lett. 2003, 5, 2007. (c) Lee, H.-Y.; Kim, H. Y.; Tae, H.;
Kim, B. G.; Lee, J. Org. Lett. 2003, 5, 3439.
(10) (a) McDonald, F. E.; Gleason, M. M. J. Am. Chem. Soc. 1996, 118,
6648. (b) Oehlschlager, A. C.; Czyzewska, E. Tetrahedron Lett. 1983, 24, 5587.
(11) Marino, J. P.; Nguyen, H. N. J. Org. Chem. 2002, 67, 6841.
(12) The enantiopurity was determined by chiral HPLC analysis of its
benzoate derivative.
(13) For a similar transformation, see: (a) Mart´ın, R.; Murruzzu, C.; Perica`s,
M. A.; Riera, A. J. Org. Chem. 2005, 70, 2325. (b) Torssell, S.; Somfai, P. Org.
Biomol. Chem. 2004, 2, 1643. (c) Roush, W. R.; Adam, M. A. J. Org. Chem.
1985, 50, 3752.
(5) Kuroda, I.; Musman, M.; Ohtani, I. I.; Ichiba, T.; Tanaka, J.; Gravalos,
D. G.; Higa, T. J. Nat. Prod. 2002, 65, 1505.
(6) Kobayashi, J.; Cheng, J.-F.; Ishibashi, M.; Wa¨lchli, M. R.; Yamamura,
S.; Ohizumi, Y. J. Chem. Soc., Perkin Trans. I 1991, 1135.
(7) For representative examples, see: (a) Fuhshuku, K.; Hongo, N.; Tashiro,
T.; Masuda, Y.; Nakagawa, R.; Seino, K.; Taniguchi, M.; Mori, K. Bioorg. Med.
Chem. 2008, 16, 950. (b) Zhu, R.; Snyder, A. H.; Kharel, Y.; Schaffter, L.; Sun,
Q.; Kennedy, P. C.; Lynch, K. R.; Macdonald, T. L. J. Med. Chem. 2007, 50,
6428. (c) Hanessian, S.; Charron, G.; Billich, A.; Guerini, D. Bioorg. Med. Chem.
Lett. 2007, 17, 491. (d) Wascholowski, V.; Giannis, A. Angew. Chem., Int. Ed.
2006, 45, 827. (e) Dougherty, A. M.; McDonald, F. E.; Liotta, D. C.; Moody,
S. J.; Pallas, D. C.; Pack, C. D.; Merrill, A. H. Org. Lett. 2006, 8, 649. (f) Ha,
H.-J.; Hong, M. C.; Ko, S. W.; Kim, Y. W.; Lee, W. K.; Park, J. Bioorg. Med.
Chem. Lett. 2006, 16, 1880. (g) Macchia, M.; Barontini, S.; Bertini, S.; Bussolo,
V. D.; Fogli, S.; Giovannetti, E.; Grossi, E.; Minutolo, F.; Danesi, R. J. Med.
Chem. 2001, 44, 3994.
J. Org. Chem. Vol. 74, No. 10, 2009 3901

Cho et al.
SCHEME 4. Synthesis of Piperidinylidene Analogue 4
SCHEME 2. Synthesis of Diene 18 Using the Tandem
Enyne/Diene-ene Metathesis Reaction
in methanol provided the desired analogue 3 in nearly quantita-
tive yield in each case.
After achieving the synthesis of the designed piperidine
analogue 3, we then investigated the synthesis of the piperidi-
nylidene analogue 4, in which the stereochemistry of the
exocyclic ∆4,5-double bond is E, identical to that in sphingosine
2. Conceivably, the 1,4-hydrogenation of conjugated diene 18
would provide a quick way to generate the desired exocyclic
olefin of 4. Thus, we investigated the feasibility of this
transformation by using transition metal catalysts such as
Ar·Cr(CO)3 and Pd/C, which are known to catalyze 1,4-
hydrogenation reactions.15 Unfortunately, all attempts to bring
about this reduction failed.
SCHEME 3. Synthesis of Piperidine Analogue 3
An alternative approach was therefore devised in which a
SN2′ reduction of a vinyloxirane was utilized for migration of
the double bond to the desired position (Scheme 4). To this
end, we first studied the monoepoxidation of conjugated diene
18. Attempted epoxidations of 18 with various reagents such
as m-CPBA and dioxiranes were not successful and gave a
complex mixture of products arising from nonselective epoxi-
dation. To increase the selectivity of the reaction by using the
directing effect of a hydroxyl group, the acetate protecting group
was removed by NaOMe/MeOH to give hydroxy diene 22
(90%). After some trials, it was found that epoxidation of 22
using the VO(acac)2/t-BuOOH system16 proceeded cleanly and
gave monoepoxide 23 in excellent yield (99%) as the only
detectable product. The result of this superb regioselective
reaction was somewhat surprising, since the vanadium-catalyzed
epoxidation of hydroxy dienes generally occurs at the allylic
double bond rather than the homoallylic double bond.17
Although the origins responsible for this unusual regioselectivity
remain to be explored, we speculated that this hydroxy-directed
material. The attempted enyne RCM of 15 was also not
successful. These results could be attributed to the presence of
the propargylic hydroxyl group in 15, which has the potential
to inhibit the Grubbs catalyst by coordinating to the ruthenium
center.14 Thus, it was necessary to protect the free hydroxyl
group of 15 to overcome the chelate trap. This was accomplished
by treating compound 15 with Ac2O to furnish 17 in 99% yield.
The tandem metathesis reaction of enyne 17 and 1-tetradecene
(5 equiv), in the presence of second-generation Grubbs catalyst
19 (10 mol %) in refluxing CH2Cl2, proceeded cleanly to provide
18 with exclusively (E)-stereochemistry in 76% yield. No cis-
1
olefin was detected in the crude H NMR spectrum.
With a facile route to the key intermediate 18, our study then
focused on the synthesis of the designed analogues 3 and 4
through modification of the diene moiety in 18. First, we
investigated the full reduction of the conjugated diene moiety
of 18 to give piperidine analogue 3 (Scheme 3). Initial attempts
at this reduction utilizing either Pt2O or Pd/C as hydrogenation
catalysts resulted in the formation of the desired piperidine 20
in a 4:1 ratio with its C-4 diastereomer in 98% combined yield.
On the other hand, hydrogenation of 18 over Raney nickel in
methanol proceeded with complete facial selectivity to give 20
and its deprotected form 21 in a 3:1 ratio and 88% combined
yield. The stereochemistry of 20 was established by NOE
difference experiments (see Supporting Information). Basic
hydrolysis of 20, 21, or a crude mixture of 20 and 21 with NaOH
(15) (a) Tong, R.; Valentine, J. C.; McDonald, F. E.; Cao, R.; Fang, X.;
Hardcastle, K. I. J. Am. Chem. Soc. 2007, 129, 1050. (b) Chandiran, T.;
Vancheesan, S. J. Mol. Catal. 1994, 88, 31. (c) Takahashi, A.; Kirio, Y.; Sodeoka,
M.; Sasai, H.; Shibasaki, M. J. Am. Chem. Soc. 1989, 111, 643. (d) Shibasaki,
M.; Sodeoka, M.; Ogawa, Y. J. Org. Chem. 1984, 49, 4096.
(16) (a) Rossiter, B. E.; Verhoeven, T. R.; Sharpless, K. B. Tetrahedron Lett.
1979, 20, 4733. (b) Itoh, T.; Jitsukawa, K.; Kaneda, K.; Teranishi, S. J. Am.
Chem. Soc. 1979, 101, 159. (c) Tanaka, S.; Yamamoto, H.; Nozaki, H.; Sharpless,
K. B.; Michaelson, R. C.; Cutting, J. D. J. Am. Chem. Soc. 1974, 96, 5254.
(17) (a) Jogireddy, R.; Maier, M. E. J. Org. Chem. 2006, 71, 6999. (b)
Hatakeyama, S.; Yoshida, M.; Esumi, T.; Iwabuchl, Y.; lrle, H.; Kawmoto, T.;
Yamada, H.; Nishizawa, M. Tetrahedron Lett. 1997, 38, 7887. (c) Hatakeyama,
S.; Sugawara, K.; Takano, S. Tetrahedron Lett. 1991, 32, 4513.
(14) Smulik, J. A.; Diver, S. T. Org. Lett. 2000, 2, 2271.
3902 J. Org. Chem. Vol. 74, No. 10, 2009

Synthesis of Piperidine-Containing Sphingoid Base
epoxidation reaction might proceed via the s-trans conformation,
where the homoallylic double bond moiety is spatially close to
the hydroxyl group. In fact, the NOESY correlations indicated
that the preferred conformation of 22 in solution was s-trans.
On the basis of this assumption, the stereochemistry of the
epoxide moiety was tentatively assigned as shown and was
ultimately established by its conversion to 25.
Conclusions
In summary, we have presented a novel approach that allows
the efficient synthesis of conformationally constrained sphingoid
base analogues, in which a cyclic moiety was incorporated
between the 2-amino group and the C-4 carbon atom. Our
methodology features a tandem enyne/diene-ene metathesis
reaction that provides access to the designed framework. The
diene moiety of the metathesis product was stereoselectively
elaborated for the synthesis of the designed analogues. We
believe that the presented constrained analogues, as well as the
synthetic method, could be of value in the development of novel
sphingoid base analogues for sphingolipid research. The above
and other constrained analogues are currently being biologically
evaluated, and the details will be reported in due course.
Next, we turned our attention to the conversion of the
vinyloxirane group of 23 into the allylic alcohol group by SN2′
reduction.18 To this end, the C2-hydroxyl group of 23 was
protected again with Ac2O prior to the SN2′ reduction to give
acetate 24 (99%). BH3 ·THF reduction of vinyloxirane 24
proceeded effectively to give the desired SN2′ product 25 in
high yield (87%). The stereochemistry of the newly generated
∆4,5-double bond was established to be (E) by NOE measure-
ments. The absolute stereochemistry at C-6 of 25 was assigned
to be (R) using a modified Mosher ester analysis.19
Experimental Section
(8R,8aS)-3-Oxo-7-((E)-tetradec-1-enyl)-3,5,8,8a-tetrahydro-
1H-oxazolo[3,4-a]pyridin-8-yl Acetate (18). To a solution of 17
(540 mg, 2.42 mmol) and 1-tetradecene (3.40 mL, 12.3 mmol) in
CH2Cl2 (48 mL) was added Grubbs second-generation catalyst 19
(205 mg, 0.240 mmol) at room temperature. The resulting mixture
was refluxed for 3 h. After the mixture was cooled to room
temperature, the solvent was removed under reduced pressure. The
residue was purified by column chromatography on silica gel
Deoxygenation of the C6-hydroxyl group of 25 was ac-
complished with a two-step sequence. Bromination of the
hydroxyl group of 25 with CBr4/PPh3 followed by reduction of
the resulting allylic bromide with ZnCl2/NaBH3CN20 led to the
formation of the desired alkene 26 in 64% overall yield. Finally,
removal of the protecting groups of 26 by basic hydrolysis gave
the target 4 in nearly quantitative yield.
(hexane/EtOAc, 4:1) to give diene 18 (720 mg, 76%) as a white
solid: mp 75.0-77.4 °C; [R]24 +23.6 (c 1.0, CHCl3); H NMR
1
D
Although many synthetic steps are required for the transfor-
mation of diene 18 to the final product 4, the sequence is
efficient and preparatively simple. In addition, this sequence
provides selective access to the additional hydroxyl group at
C-6. Since 6-(R)-hydroxy-4E-sphingosine is naturally occur-
ring,21 the deprotected form of 25, compound 27, could also be
regarded as a conformationally restricted analogue of the natural
sphingoid bases.
(CDCl3, 300 MHz) δ 0.88 (t, J ) 6.3 Hz, 3H), 1.18-1.40 (m, 20H),
2.03-2.08 (m, 2H), 2.10 (s, 3H), 3.70-3.78 (m, 2H), 4.16-4.23
(m, 1H), 4.43 (dd, J ) 5.7, 9.3 Hz, 1H), 4.52 (dd, J ) 8.1, 9.3 Hz,
1H), 5.46-5.48 (m, 1H), 5.58 (td, J) 7.2, 15.9 Hz, 1H), 5.85 (d,
J ) 16.8, 1H), 5.88-5.92 (m, 1H); 13C NMR (CDCl3, 75 MHz) δ
14.0, 20.7, 22.6, 29.0, 29.2, 29.3, 29.4, 29.52, 29.55, 29.6 (2C),
31.8, 33.0, 40.3, 55.7, 68.1, 69.4, 123.3, 126.6, 132.4, 133.6, 156.6,
170.8; IR (CHCl3) υmax 2918, 2849, 1757, 1420, 1230 (cm-1); MS
(FAB) m/z 392 ([M + 1]+, 100), 332 (23); HRMS (FAB) calcd for
C23H38O4N 392.2801 ([M + H]+), found 392.2797.
Among various biological functions of the sphingoid bases,
it is known that they can induce apoptotic cell death.22 Thus,
as a preliminary evaluation of constrained analogues 3 and 4,
the cytotoxic activity in various cancer cells was determined
using the SRB assay (see Supporting Information). In our
experiments, analogues 3 and 4 turned out to be much more
effective than prototype sphingoid bases 1 and 2 at inhibiting
cancer cell growth. For example, while the IC50 values of the
natural sphingoid bases 1 and 2 against A549 human lung
carcinoma cells are 9.6 and 13.6 µM, those of the constrained
analogues 3 and 4 are 1.5 and 1.7 µM, respectively. Although
the reason for these higher cytotoxic activities is not clear
presently, the observed results indicate that the polar part of
the sphingoid bases is amenable to conformational restriction
by incorporation into a piperidine ring, providing a basis for
further investigation.
(7S,8R,8aS)-3-Oxo-7-tetradecyl-hexahydro-1H-oxazolo[3,4-
a]pyridin-8-yl Acetate (20) and (7S,8R,8aS)-8-Hydroxy-7-tet-
radecyl-tetrahydro-1H-oxazolo[3,4-a]pyridin-3(5H)-one (21). To
a solution of diene 18 (100 mg, 0.260 mmol) in MeOH (6 mL)
was added Raney Ni (slurry in H2O, ca. 50 mg). The resulting
mixture was stirred for 10 min at room temperature under a
hydrogen atmosphere. The catalyst was removed by filtration, and
the filtrate was concentrated in vacuo. The crude mixture was
purified by column chromatography on silica gel (hexane/EtOAc,
2:1) to give 20 (68 mg, 66%) and 21 (20 mg, 22%).
20. As a white solid: mp 76.5-78.0 °C; [R]24 +10.0 (c 1.0,
D
1
CHCl3); H NMR (CDCl3, 300 MHz) δ 0.88 (t, J ) 6.6 Hz, 3H),
1.02-1.35 (m, 26H), 1.35-1.54 (m, 2H), 1.86-1.91 (m, 1H), 2.10
(s, 3H), 2.82 (dt, J ) 3.3, 13.2 Hz, 1H), 3.51-3.58 (m, 1H), 3.86
(ddd, J ) 1.5, 4.8, 13.2 Hz, 1H), 4.14 (dd, J ) 6.0, 9.0 Hz, 1H),
4.33 (dd, J ) 8.1, 9.0 Hz, 1H), 4.56 (dd, J ) 9.3, 10.2 Hz, 1H);
13C NMR (CDCl3, 75 MHz) δ 14.1, 20.8, 22.7, 26.1, 28.6, 29.3,
29.48, 29.50, 29.6 (3C), 29.7 (3C), 30.9, 31.9, 40.1, 40.5, 57.8,
66.2, 75.0, 156.7, 170.6; IR (CHCl3) υmax 2919, 2850, 1747, 1235
(cm-1); MS (CI) m/z 396 ([M + 1]+, 100), 336 (27); HRMS (CI)
calcd for C23H42O4N 396.3115 ([M + H]+), found 396.3114.
(18) For SN2′ reduction of vinyloxirane, see: (a) Ueki, H.; Chiba, T.;
Kitazume, T. J. Org. Chem. 2006, 71, 3506. (b) Werner, F.; Parmentier, G.;
Luu, B. Tetrahedron 1996, 52, 5525. (c) Molander, G. A.; Belle, B. E. L.; Hahn,
G. J. Org. Chem. 1986, 51, 5259. (d) Lenox, R. S.; Katzenellenbogen, J. A.
J. Am. Chem. Soc. 1973, 95, 957.
(19) Ohtani, I.; Kusumi, T.; Kashman, Y.; Kakisawa, H. J. Am. Chem. Soc.
1991, 113, 4092. See Supporting Information.
(20) Kim, S.; Kim, Y. J.; Ahn, K. H. Tetrahedron Lett. 1983, 24, 3369.
(21) (a) Yadav, J. S.; Geetha, V.; Raju, A. K.; Gnaneshwar, D.; Chan-
drasekhar, S. Tetrahedron Lett. 2003, 44, 2983. (b) Wakita, H.; Nishimura, K.;
Takigawa, M. J. InVest. Dermatol. 1992, 99, 617.
(22) (a) Nagahara, Y.; Shinomiya, T.; Kuroda, S.; Kaneko, N.; Nishio, R.;
Ikekita, M. Cancer Sci. 2005, 96, 83. (b) Ahn, E. H.; Schroeder, J. J. Exp. Biol.
Med. 2002, 227, 345.
21. As a white solid: mp 65.0-66.5 °C; [R]24 -7.8 (c 1.0,
D
1
CHCl3); H NMR (CDCl3, 300 MHz) δ 0.88 (t, J ) 6.6 Hz, 3H),
1.12-1.34 (m, 26H), 1.36-1.48 (m, 1H), 1.69-1.77 (m, 1H),
1.80-1.85 (m, 1H), 2.84 (dt, J ) 3.3, 12.9 Hz, 1H), 3.12 (t, J )
9.3 Hz, 1H), 3.38-3.45 (m, 1H), 3.85 (ddd, J ) 1.2, 4.8, 12.9 Hz,
1H), 4.21 (dd, J ) 4.8, 9.0 Hz, 1H), 4.45 (dd, J ) 8.1, 9.0 Hz,
1H); 13C NMR (CDCl3, 75 MHz) δ 14.1, 22.6, 26.2, 28.6, 29.3,
29.6, 29.61 (3C), 29.65 (3C), 29.9, 30.8, 31.9, 40.7, 42.3, 59.4,
66.6, 74.6, 157.2; IR (CHCl3) υmax 3347, 2922, 2850, 1720 (cm-1);
J. Org. Chem. Vol. 74, No. 10, 2009 3903

Cho et al.
MS (FAB) m/z 354 ([M + 1]+, 100); HRMS (FAB) calcd for
C21H40O3N 354.3008 ([M + H]+), found 354.3011.
The residue was purified by column chromatography on silica gel
(hexane/EtOAc, 1:2) to give alcohol 25 (410 mg, 87%) as a white
1
(2S,3R,4S)-2-(Hydroxymethyl)-4-tetradecylpiperidin-3-ol (3).
To a solution of 20 and 21 (0.160 mmol) in MeOH (3 mL) was
added 1 N NaOH (3 mL), and the resulting solution was heated at
80 °C (oil bath) for 5 h. After the mixture was cooled to room
temperature, it was diluted with EtOAc and extracted with 1 N
NaOH. The aqueous layer was then extracted with EtOAc. The
combined organic layers were dried over MgSO4 and concentrated
in vacuo. The residue was purified by column chromatography on
silica gel (CH2Cl2/MeOH, 7:1, 1% NH4OH) to give 3 (52 mg,
solid: mp 109-111 °C; [R]24 -42.0 (c 1.0, CHCl3); H NMR
D
(CDCl3, 300 MHz) δ 0.88 (t, J ) 6.3 Hz, 3H), 1.14-1.50 (m, 22H),
2.04-2.16 (m, 1H), 2.18 (s, 3H), 2.70-2.77 (m, 2H), 3.53-3.60
(m, 1H), 4.01 (dd, J ) 5.7, 12.9 Hz, 1H), 4.16 (dd, J ) 4.2, 8.7
Hz, 1H), 4.34-4.45 (m, 2H), 5.06 (d, J ) 8.7 Hz, 1H), 5.37 (d, J
) 9.0 Hz, 1H); 13C NMR (CDCl3, 75 MHz) δ 14.0, 20.7, 22.6,
25.5, 27.5, 29.3, 29.5, 29.54 (2C), 29.57 (2C), 29.6, 31.8, 37.5,
41.7, 59.1, 65.6, 67.5, 72.9, 126.6, 133.0, 156.7, 169.5; IR (CHCl3)
υmax 3465, 2919, 2850, 1720, 1439, 1236 (cm-1); MS (FAB) m/z
432 ([M + 23]+, 27), 392 (19), 350 (100); HRMS (FAB) calcd for
C23H39O5NNa 432.2726 ([M + Na]+), found 432.2727.
100%) as a white solid: mp 72.8-74.5 °C; [R]24 +12.6 (c 1.0,
D
MeOH); 1H NMR (CD3OD, 300 MHz) δ 0.89 (t, J ) 6.6 Hz, 3H),
1.06-1.42 (m, 26H), 1.80-1.89 (m, 3H), 2.51-2.58 (m, 1H), 2.67
(dt, J ) 2.7, 12.3 Hz, 1H), 3.00-3.11 (m, 2H), 3.61 (dd, J ) 6.9,
11.1 Hz, 1H), 3.89 (dd, J ) 3.3, 10.8 Hz, 1H); 13C NMR (CD3OD,
75 MHz) δ 14.4, 23.7, 27.4, 30.5, 30.76 (4C), 30.78 (4C), 31.1,
32.9, 33.1, 44.3, 46.0, 62.8, 64.4, 72.7; IR (MeOH) υmax 3365, 2917,
2849 (cm-1); MS (FAB) m/z 328 ([M + 1]+, 100), 296 (19), 154
(25), 136 (20); HRMS (FAB) calcd for C20H42O2N 328.3216 ([M
+ H]+), found 328.3224.
(2S,3R,E)-2-(Hydroxymethyl)-4-tetradecylidenepiperidin-3-
ol (4). To a solution of carbamate 26 (140 mg, 0.360 mmol) in
MeOH (6 mL) was added 1 N NaOH (6 mL), and the resulting
solution was heated at 80 °C (oil bath) for 5 h. After the mixture
was cooled to room temperature, it was diluted with EtOAc and
extracted with 1 N NaOH. The aqueous layer was then extracted
with EtOAc. The combined organic layers were dried over MgSO4
and concentrated in vacuo. The residue was purified by column
chromatography on silica gel (CH2Cl2/MeOH, 7:1, 1% NH4OH)
(8R,8aS)-7-(3-Dodecyloxiran-2-yl)-8-hydroxy-8,8a-dihydro-
1H-oxazolo[3,4-a]pyridin-3(5H)-one (23). To a solution of hy-
droxy diene 22 (460 mg, 1.32 mmol) in CH2Cl2 (13 mL) was added
VO(acac)2 (18 mg, 0.06 mmol) and t-BuOOH (1.0 mL, 5.0-6.0
M solution in decane) at 0 °C. After being stirred at room
temperature for 10 min, the reaction mixture was poured into
saturated NH4Cl solution and extracted with CH2Cl2. The organic
layer was washed with brine, dried with MgSO4, and concentrated
in vacuo. The residue was purified by column chromatography on
silica gel (hexane/EtOAc, 1:1) to give epoxide 23 (479 mg, 99%)
to give 4 (117 mg, 100%) as a white solid: mp 72.5-74.0 °C; [R]24
D
-8.2 (c 0.14, CHCl3); 1H NMR (CD3OD, 300 MHz) δ 0.89 (t, J )
6.3 Hz, 3H), 1.18-1.44 (m, 22H), 1.89-2.10 (m, 3H), 2.44-2.51
(m, 1H), 2.56 (dd, J ) 3.3, 11.7 Hz, 1H), 2.66 (td, J ) 3.0, 14.1
Hz, 1H), 3.02-3.09 (m, 1H), 3.67 (dd, J ) 6.6, 11.1 Hz, 1H),
3.79-3.84 (m, 2H), 5.56 (t, J ) 7.2 Hz, 1H); 13C NMR (CD3OD,
75 MHz) δ 14.4, 23.7, 27.8, 28.5, 30.3, 30.5, 30.7, 30.8 (5C), 31.1,
33.1, 46.5, 63.0, 65.4, 72.1, 122.2, 138.4; IR (CHCl3) υmax 3303,
2919, 2850, 1737, 1243 (cm-1); MS (FAB) m/z 326 ([M + 1]+,
100), 308 (76), 294 (35); HRMS (FAB) calcd for C20H40O2N
326.3059 ([M + H]+), found 326.3064.
as a white solid: mp 70.0-71.4 °C; [R]24 +39.3 (c 1.0, CHCl3);
D
1H NMR (CDCl3, 300 MHz) δ 0.87 (t, J ) 6.3 Hz, 3H), 1.14-1.50
(m, 20H), 1.57-1.64 (m, 2H), 3.19 (dt, J ) 2.4, 5.7 Hz, 1H), 3.37
(d, J ) 2.1 Hz, 1H), 3.59 (dt, J ) 4.2, 7.5 Hz, 1H), 3.69-3.77 (m,
1H), 4.09-4.20 (m, 2H), 4.33 (dd, J ) 3.9, 8.7 Hz, 1H), 4.54 (dd,
J ) 8.1, 9.0 Hz, 1H), 5.89-5.90 (m, 1H); 13C NMR (CDCl3, 75
MHz) δ 14.1, 22.6, 25.6, 29.3, 29.33, 29.4, 29.5, 29.58 (2C), 29.6,
31.7, 31.9, 41.0, 56.6, 59.1, 61.0, 67.4, 67.8, 124.0, 133.8, 157.1;
IR (CHCl3) υmax 3348, 2922, 2851, 1721, 1705, 1435 (cm-1); MS
(FAB) m/z 366 ([M + 1]+, 100), 348 (52), 154 (39); HRMS (FAB)
calcd for C21H36O4N 366.2644 ([M + H]+), found 366.2655.
(8R,8aS,E)-7-(2-Hydroxytetradecylidene)-3-oxohexahydro-
1H-oxazolo[3,4-a]pyridin-8-yl Acetate (25). To a solution of
vinyloxirane 24 (470 mg, 1.15 mmol) in THF (29 mL) was added
BH3 ·THF (2.30 mL, 2.30 mmol, 1.0 M solution in THF) at room
temperature. After being stirred at room temperature for 1 h, the
reaction was quenched with 2 N NaOH, and the organic layer was
extracted with EtOAc twice. The combined organic layers were
washed with brine, dried over MgSO4, and concentrated in vacuo.
Acknowledgment. This work was supported by the Korea
Science and Engineering Foundation (KOSEF) through the
National Research Laboratory Program funded by the Ministry
of Science and Technology (M10500000055-06J0000-05510).
Supporting Information Available: Experimental proce-
dures for the synthesis of 10-15, 17, 22, 24, 26, 27, and the
benzoate derivative of epoxide 12; HPLC data of the benzoate
derivative of compound 12; assignment of the absolute config-
uration of 25 by Mosher ester analysis; sulforhodamine B (SRB)
assay; copies of 1H NMR and 13C NMR spectra of new
compounds. This material is available free of charge via the
Internet at http://pubs.acs.org.
JO900378H
3904 J. Org. Chem. Vol. 74, No. 10, 2009