Syntheses of sulfur and selenium analogues of pachastrissamine via double displacements of cyclic sulfate

Article abstract of DOI:10.1039/c1ob05920c

Bioisosteric analogues of pachastrissamine that contain sulfur and selenium atoms replacing the oxygen in the ring system, were efficiently prepared from a cyclic sulfate intermediate by sequential intermolecular and intramolecular S_N2 displace

Full text of DOI:10.1039/c1ob05920c

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PAPER
Syntheses of sulfur and selenium analogues of pachastrissamine via double
displacements of cyclic sulfate†
Hongjun Jeon,a Hoon Bae,a Dong Jae Baek,a Young-Shin Kwak,b Deukjoon Kima and Sanghee Kim*a
Received 8th June 2011, Accepted 19th July 2011
DOI: 10.1039/c1ob05920c
Bioisosteric analogues of pachastrissamine that contain sulfur and selenium atoms replacing the
oxygen in the ring system, were efficiently prepared from a cyclic sulfate intermediate by sequential
intermolecular and intramolecular SN2 displacement reactions of the dianions. The analogues exhibited
cytotoxicities comparable to that of pachastrissamine.
Until now, studies on the structure–activity relationship (SAR)
of pachastrissamine have mainly focused on the substituents on the
Introduction
Pachastrissamine (also called jaspine B, 1, Fig. 1)1 is a marine
natural product with a tetrahydrofuran ring possessing three con-
tiguous stereogenic centers. It can be considered as an anhydrous
derivative of the typical sphingoid base D-ribo-phytosphingosine
(2). This natural product and its analogues have drawn much
attention from synthetic and medicinal chemists2,3 owing to both
unusual structural features relative to the other sphingolipids
and potent anticancer activity. In a recent report, the anticancer
activity of pachastrissamine was ascribed to its ability to inhibit
the activity of sphingomyelin synthase.4 It was also postulated
in a different report that an autophagy-related process might be
responsible for the pachastrissamine’s cytotoxic activity as the
major mechanism of programmed cell death.3k
tetrahydrofuran ring.3b,3g–3i,3k There is only one report concerning
modification of the tetrahydrofuran core: Ge´nisson et al. recently
reported the synthesis and biological evaluation of aza analogues
of pachastrissamine 3.3j To elucidate the SAR of this promising
natural product requires further exploration of its tetrahydrofuran
core, for instance, by replacing it with a different ring system
or size. With this in mind, the core ring-modified analogues of
pachastrissamine 4 and 5 were designed.
The most common bioisosteric substitution is the replacement
of C with N in an aromatic ring, and the second most common
is the exchange of O and S.5 Thus, the ring oxygen atom of
pachastrissamine (1) was replaced with a sulfur atom to yield
tetrahydrothiophene 4 (Fig. 1). The ring oxygen atom was also
replaced by a selenium atom to create tetrahydroselenophene 5
because much attention has recently been given to selenium as a
bioisostere of oxygen and sulfur.6 Described herein is an efficient
synthesis and a preliminary biological evaluation of the sulfur and
selenium analogues of pachastrissamine, 4 and 5.
Results and discussion
It was envisioned that the desired heterocyclic compounds 4 and 5
could be accessible from D-ribo-phytosphingosine 2 because three
substituents on the heterocyclic rings of 4 and 5 are identical to
those of 2. The opposite absolute configuration at C-4 suggested
that intermolecular substitution of the primary hydroxyl group of
2 by sulfur or selenium followed by subsequent intramolecular
alkylation at C-4 with inversion of the stereochemistry would
be a reasonable synthetic pathway towards 4 and 5. For this
synthetic strategy, the prior protection of the 2,3-amino alcohol
functionality in 2 was required. To this end, the oxazolidinone
ring was selected as a protecting group because the conforma-
tional restriction imposed by this cyclic group would facilitate
intramolecular cyclization.
Fig. 1 Chemical structures of compounds 1–5.
aCollege of Pharmacy, Seoul National University, San 56-1, Shilim, Kwanak,
Seoul 151-742, Korea. E-mail: pennkim@snu.ac.kr; Fax: +82-2-888-0649;
Tel: +82-2-880-2487
bKorea Research Institute of Bioscience & Biotechnology (KRIBB), Chung-
buk 363-883, Korea. E-mail: yskwak@kribb.re.kr; Fax: +82-43-240-6009;
Tel: +82-43-240-6108
† Electronic supplementary information (ESI) available: Copies of 1H
NMR and 13C NMR spectra of compounds 4–5, 7–12 and 15–18. See
DOI: 10.1039/c1ob05920c
The starting material was the known N-Boc-protected D-ribo-
phytosphingosine 6 (Scheme 1). The primary hydroxyl group of 6
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Scheme 1 (a) TrCl, DMAP, CH2Cl2–pyridine, 24 h; (b) NaH, DMF,
30 min; (c) BF3·Et2O, toluene–MeOH, 24 h.
was selectively protected as its trityl ether to afford compound 7
in 95% yield. After several trials, it was found that treatment of 7
with sodium hydride in DMF gave the desired oxazolidinone 8 in
95% yield.7 This reaction proceeded in an exclusively regioselective
manner. No trace of 6-membered oxazinanone was detected in the
1
crude H NMR spectra.8 Removal of the trityl group on 8 was
achieved with boron trifluoride to afford diol 9 in 93% yield.
With the 2,3-amino alcohol-protected phytosphingosine 9 in
hand, we examined the activation of both of its two hydroxyl
groups as the mesylates (Scheme 2). Treatments of diol 9 under
typical mesylation conditions furnished the desired bis-mesylate
10, but in unacceptably low yield (31%). The major product was
tetrahydrofuran 11 which resulted from the initial mesylation of
the primary hydroxyl group of 9 and subsequent intramolecular
cyclization involving the C-4 hydroxyl group. To circumvent this
problem, a cyclic sulfate9 was used as a diol-activating group
instead. The formation of the 7-membered cyclic sulfate 12
proceeded smoothly when diol 9 was treated with thionyl chloride
followed by oxidation with RuCl3–NaIO4 (74% overall yield).
Scheme 3 (a) Na2S·9H2O, DMF (see text); (b) (i) KSAc, DMF, 3 h, (ii)
NaOMe, MeOH, 1 h; (c) LiOH, EtOH–THF–H2O (3 : 2 : 1), 60 ◦C, 12 h.
formation of dimeric sulfide 16 could be attributed to the fact
that the anionic sulfate group of intermediate 13 is a less reactive
leaving group than a cyclic sulfate. To suppress the dimerization,
the same reaction was performed under high dilution conditions
(0.005 M), but still only dimeric sulfide 16 was obtained (71%). The
desired tetrahydrothiophene 15 was obtained when the reaction
was carried out with an excess of Na2S (3.0 equiv) under high
dilution conditions (DMF, 0.005 M), but with a low yield (31%)
due to the formation of dimeric sulfide 16 (35%). Under the
same conditions, the use of other solvent systems, such as MeOH,
MeOH–DMF, THF, and MeOH–THF, did not improve the yield,
but rather resulted in a lower yield of 15. Finally, the competing
dimerization could be minimized and the yield was improved to
79% when a diluted solution of cyclic sulfate 12 in DMF was slowly
added via syringe pump over 0.5 h to a heated solution (60 ◦C) of
Na2S in DMF followed by additional stirring for 5 h.
As an alternative sulfide source, potassium thioacetate was
employed.12 Thioacetate can be regarded as a mono-protected
form of S2-. Thus, we anticipated that the use of this sulfide source
would eliminate the possibility of dimerization and enable us to
avoid high dilution conditions. The reaction of 12 with potassium
thioacetate in DMF (0.1 M) gave the d-acetylthio sulfate ester
intermediate 14 by regiospecific attack at the less hindered
primary position.13 Treatment of the resulting intermediate 14 with
NaOMe–MeOH gave tetrahydrothiophene 15 (69%), possibly via
intramolecular substitution of sulfate ester group by thiolate.
After successfully achieving the transformation of the 7-
membered cyclic sulfate to tetrahydrothiophene, the transfor-
mation of cyclic sulfate 12 into the tetrahydroselenophene was
examined. As in the case of tetrahydrothiophenes, there is no
precedent for such a transformation. With the information from
the above studies with sulfide, reaction conditions were established
for the synthesis of tetrahydroselenophene 17 from 12. In this
transformation, the selenium dianion provided the cyclized prod-
uct with good yield. The desired tetrahydroselenophene 17 was
obtained in 84% yield when a solution of cyclic sulfate 12 in THF
Scheme 2 (a) MsCl, CH2Cl2–pyridine, 0 ◦C, 12 h; (b) (i) SOCl2, CHCl3,
reflux, 1 h, (ii) RuCl3·3H2O, NaIO4, CCl4–CH3CN–H2O (1 : 1 : 2), 1.5 h.
Although there are several examples of the formation of
tetrahydrothiophenes from bis-sulfonates,10 to the best of our
knowledge no study has been reported of a 7-membered cyclic
sulfate. Bis-sulfonates and cyclic sulfates could be regarded as
synthetic equivalents. Thus, our initial synthetic attempts to pre-
pare tetrahydrothiophene from cyclic sulfate 12 were made using
the general reaction conditions employed for the transformation
of bis-sulfonates to tetrahydrothiophenes. The reaction of 12 with
a slight excess of Na2S in DMF (0.1 M) at room temperature
failed to give the desired tetrahydrothiophene 15 due to undesired
dimerization (Scheme 3). The dimeric sulfide 16 was obtained in
91% yield after hydrolysis of the resulting reaction mixture.11 The
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(0.005 M) wa◦s slowly added via syringe pump over 0.5 h to a heated
solution (60 C) of freshly prepared Na2Se14 (5.0 equiv) in EtOH
followed by additional stirring for 3 h (Scheme 4). Under more
concentrated conditions (0.1 M), the reaction gave diselenide 18
as the main product (73%).
employed as a common intermediate. Double displacements of
the cyclic sulfate 12 with the dianions of sulfur and selenium
atoms allowed the efficient synthesis of the desired heterocycles.
The natural product pachastrissamine and its sulfur and selenium
analogues exhibited comparable cytotoxicity, yielding similar IC50
values. We believe that these analogues could be of value in the
investigation of the biological functions of pachastrissamine and
in the development of novel therapeutics as a lead scaffold because
such bioisosteric replacement would systematically alter the
physicochemical and biological properties of pachastrissamine.
Experimental section
A: Preparation of the compounds
General. All chemicals were of reagent grade and used as
purchased. All reactions were performed under an inert atmo-
sphere of dry argon or nitrogen using dry solvents. Reactions were
monitored with TLC analysis using Merck silica gel 60 F-254
thin layer plates. Flash column chromatography was performed
Scheme 4 (a) Se, NaBH4, EtOH–THF, 60 ◦C (see text); (b) LiOH,
1
on silica gel (230–400 mesh). H NMR and 13C NMR spectra
EtOH–THF–H2O (3 : 2 : 1), 60 ◦C, 12 h.
were recorded in d units relative to the deuterated solvent as
internal reference at 300/400/500 and 75/100 MHz, respectively.
IR spectra were measured on a Fourier Transform Infrared
spectrometer. Mass spectra (MS) were recorded using fast atom
bombardment (FAB). High resolution mass spectra (HRMS) were
also recorded using FAB.
The syntheses of the desired sulfur and selenium analogues
of pachastrissamine, 4 and 5, were completed by the cleavage
of the oxazolidinone protecting groups of 15 and 17 with LiOH
(Schemes 3 and 4).
Because pachastrissamine shows potent cytotoxicity against
several cancer cell lines,3i,3k the cytotoxic activities of analogues
4 and 5 were examined as part of their preliminary evaluation
(Table 1). Pachastrissamine 1 and D-ribo-phytosphingosine 2 were
also tested to provide a direct comparison. As shown in Table
1, the sulfur and selenium analogues of pachastrissamine, 4 and
5, were found to be much more effective in inducing cytotoxicity
than the prototype sphingoid base 2. They exhibited comparable
potency to the natural product pachastrissamine against various
cell lines. The sulfur analogue 4 was slightly more effective than
the selenium analogue 5 at inhibiting cancer cell growth. The
observed biological results indicate that the ring oxygen atom
of pachastrissamine is amenable to bioisosteric replacement with
sulfur and selenium atoms.
tert-Butyl (2S,3S,4R)-3,4-dihydroxy-1-(trityloxy)octadecan-2-
ylcarbamate (7). To a solution of 6 (2.4 g, 5.80 mmol) in CH2Cl2
(19.3 mL) and pyridine (11.6 mL) were added trityl chloride
(1.94 g, 6.95 mmol) and 4-dimethylaminopyridine (142 mg, 1.16
mmol) at room temperature. After stirring for 24 h, the reaction
mixture was poured into water and extracted twice with EtOAc.
The combined organic layer was washed with brine, dried over
MgSO4, filtered and concentrated in vacuo. The residue was
purified by silica gel column chromatography (hexane–EtOAc
4 : 1) to give 7 (3.64 g, 95%) as a colorless oil. [a]2D4 +21.0 (c 0.5,
CHCl3); 1H NMR (300 MHz, CDCl3) d 0.83 (t, J = 6.8 Hz, 3H),
1.16–1.37 (m, 24H), 1.40 (s, 9H), 1.56–1.72 (m, 2H), 2.14 (d, J = 7.2
Hz, 1–OH), 2.84 (d, J = 7.8 Hz, 1–OH), 3.27–3.38 (m, 3H), 3.49–
3.58 (m, 1H), 3.84–3.93 (m, 1H), 5.15 (d, J = 9.9 Hz, 1H), 7.15–7.28
(m, 9H), 7.34–7.39 (m, 6H); 13C NMR (75 MHz, CDCl3) d 14.1,
22.7, 25.8, 28.4, 29.3, 29.5, 29.6, 29.7, 31.9, 33.0, 51.1, 63.2, 73.1,
75.8, 79.7, 87.5, 127.3, 128.0, 128.5, 143.3, 155.7; IR (CHCl3) umax
3443, 2924, 2853, 1694, 1493, 1449, 1366, 1247, 1171, 1060 (cm-1);
HRMS (FAB) calcd for C42H61NO5Na 682.4447 ([M+Na]+), found
682.4442.
Conclusion
In summary, we report the design and synthesis of the sulfur and
selenium analogues of pachastrissamine in which the tetrahydro-
furan core of pachastrissamine was bioisosterically replaced with
tetrahydrothiophene and tetrahydroselenophene. For the synthesis
of the designed analogues, the 7-membered cyclic sulfate 12 was
(4S,5S)-5-((R)-1-Hydroxypentadecyl)-4-(trityloxymethyl)oxa-
zolidin-2-one (8). To a solution of 7 (2.16 g, 3.27 mmol) in DMF
(32.7 mL) was added sodium hydride (60% dispersion in mineral
oil, 196 mg, 4.91 mmol) at room temperature. The reaction mixture
was stirred for 30 min, quenched with a saturated aqueous NH4Cl
solution and extracted twice with EtOAc. The combined organic
layer was washed with brine, dried over MgSO4, filtered and
concentrated in vacuo. The residue was purified bysilicagel column
chromatography (hexane–EtOAc 3 : 1) to give 8 (3.64 g, 95%) as
Table 1 Cytotoxic activities for analogues of pachastrissamine
d
IC50 (mM)
Cell lines
1
2
4
5
HCT 116a
A549b
0.22
0.18
0.17
6.64
5.09
5.29
0.14
0.14
0.06
0.69
0.28
0.10
PC-3c
a Human colon carcinoma. b Human lung carcinoma. c Human prostate
adenocarcinoma. d 50% inhibition concentration.
1
a colorless oil. [a]2D4 +11.5 (c 0.5, CHCl3); H NMR (300 MHz,
CDCl3) d 0.88 (t, J = 6.5 Hz, 3H), 1.18–1.45 (m, 24H), 1.58–1.79
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(m, 2H), 3.03 (d, J = 3.9 Hz, 1–OH), 3.21–3.32 (m, 2H), 3.40–
3.51 (m, 1H), 3.98–4.09 (m, 1H), 4.32 (dd, J = 6.9, 9.0 Hz, 1H),
6.21 (br s, 1–NH), 7.18–7.32 (m, 9H), 7.35–7.40 (m, 6H); 13C NMR
(75 MHz, CDCl3) d 14.1, 22.6, 24.7, 29.3, 29.4, 29.57, 29.61, 29.64,
31.9, 33.6, 54.3, 61.7, 68.0, 80.9, 88.0, 127.5, 128.2, 142.6, 159.0;
IR (CHCl3) umax 3278, 2923, 2853, 1753, 1490, 1449, 1220, 1064
(cm-1); HRMS (FAB) calcd for C38H52NO4 586.3896 ([M+H]+),
found 586.3910.
(cm-1); HRMS (FAB) calcd for C19H36NO3 326.2695 ([M+H]+),
found 326.2674.
(3aS,8R,8aS)-8-Tetradecyltetrahydro-[1,3,2]dioxathiepino[5,6-
d]oxazol-2(3H)-one dioxide (12). To a solution of diol 9 (445
mg, 1.30 mmol) in CHCl3 (25 mL) was added SOCl2 (140 mL, 1.95
mmol) at room temperature. The reaction mixture was refluxed
for 1 h, cooled to room temperature, poured into brine and
extracted twice with EtOAc. The combined organic layer was dried
over MgSO4, filtered and concentrated in vacuo. After removal of
solvent in the evaporator, the crude cyclic sulfite was dried in vacuo
for 3 h using a vacuum pump, then dissolved in CCl4–MeCN–H2O
(1 : 1 : 2, 25 mL) at room temperature. To the solution of crude
cyclic sulfite, were added RuCl3·3H2O (15.0 mg, 0.06 mmol) and
NaIO4 (790 mg, 3.70 mmol). The reaction mixture was stirred
at room temperature for 1.5 h, diluted with EtOAc and washed
with a saturated aqueous NaHSO3 solution. The organic layer
was dried over MgSO4, filtered and concentrated in vacuo. The
residue was purified by silica gel (hexane–EtOAc 1.3 : 1) to give
the cyclic sulfate 12 (390 mg, 74%) as a white solid. [a]2D4 +42.6
(4S,5S)-4-(Hydroxymethyl)-5-((R)-1-hydroxypentadecyl)oxa-
zolidin-2-one (9). To a solution of 8 (1.61 g, 2.44 mmol) in
toluene (6 mL) and methanol (6 mL) was added BF3·OEt2
(905 mL, 7.33 mmol) at room temperature. After stirring for
24 h, reaction mixture was quenched with a saturated aqueous
NaHCO3 solution. The quenched reaction mixture was poured
into water and extracted twice with EtOAc. The combined organic
layer was washed with brine, dried over MgSO4, filtered and
concentrated in vacuo. The residuewas purifiedbysilicagel column
chromatography (hexane–EtOAc 1 : 1) to give 9 (779 mg, 93%) as
a white solid. [a]2D4 -39.9 (c 0.5, CHCl3); 1H NMR (CDCl3–MeOD
1 : 3, 400 MHz) d 0.87 (t, J = 6.2 Hz, 3H), 1.26–1.48 (m, 24H), 1.49–
1.62 (m, 1H), 1.65–1.78 (m, 1H), 3.66 (dd, J = 5.1, 11.4 Hz, 1H),
3.77 (dd, J = 5.6, 11.4 Hz, 1H), 3.83–3.92 (m, 2H), 4.32–4.40 (m,
1H); 13C NMR (CDCl3–MeOD 1 : 3, 75 MHz) d 15.2, 24.3, 26.5,
31.0, 31.29, 31.32, 31.34, 33.6, 35.9, 58.0, 62.0, 69.9, 82.9, 162.1;
IR (CHCl3) umax 3340, 2917, 2850, 1717, 1691, 1054, 941, 705
(cm-1); HRMS (FAB) calcd for C19H37NO4 344.2801 ([M+H]+),
found 344.2815.
1
(c 0.5, CHCl3); H NMR (CDCl3, 400 MHz) d 0.86 (t, J = 6.2
Hz, 3H), 1.15–1.62 (m, 24H), 1.63–1.74 (m, 1H), 1.89–1.99 (m,
1H), 4.32–4.38 (m, 1H), 4.42 (d, J = 13.7 Hz, 1H), 4.52 (dd, J =
6.4, 13.8 Hz, 1H), 4.67 (t, J = 8.0 Hz, 1H), 4.79 (t, J = 9.3 Hz,
1H), 6.31 (br s, 1–NH); 13C NMR (CDCl3, 75 MHz) d 14.1, 22.7,
24.3, 29.0, 29.29, 29.34, 29.5, 29.57, 29.6, 29.7, 31.9, 32.2, 53.6,
66.3, 77.2, 80.5, 157.3; IR (CHCl3) umax 3276, 2922, 2851, 1793,
1468, 1411, 1382, 1311, 1204, 1044 (cm-1); HRMS (FAB) calcd for
C19H36NO6S 406.2263 ([M+H]+), found 406.2263.
Mesylation of compound 9. To a solution of diol 9 (55 mg, 0.16
mmol) in CH2Cl2 (1.6 mL) were added MsCl (125 mL, 1.60 mmol)
(3aR,6S,6aS)-6-Tetradecyltetrahydrothieno[3,4-d]oxazol-
2(3H)-one (15).
◦
and pyridine (130 mL, 1.60 mmol) at 0 C. The reaction mixture
Method A. To an unclear solution of Na2S (89 mg, 0.37 mmol)
in DMF (10 mL) at 60 ◦C was added the solution of cyclic sulfate
12 (30 mg, 0.07 mmol) in DMF (5 mL) using a syringe pump
over a 30 min period. After being stirred for an additional 5 h,
the reaction mixture was cooled, poured into water and extracted
twice with EtOAc. The organic layer was washed with brine, dried
over MgSO4, filtered, and concentrated in vacuo. The residue was
purified by silica gel column chromatography (CH2Cl2–MeOH
20 : 1) to give 15 (20 mg, 79%) as a white solid.
Method B. To a solution of 12 (67 mg, 0.17 mmol) in DMF
(1.6 mL) was added potassium thioacetate (38 mg, 0.33 mmol)
at room temperature. After stirring for 3 h, the reaction mixture
was concentrated in vacuo. The crude product was dissolved in
methanol (1.6 mL). To the methanol solution was added a sodium
methoxide solution (25 wt.% in methanol, 113 mL, 0.50 mmol).
After stirring for 1 h, the reaction mixture was quenched with
a saturated aqueous NH4Cl solution. The quenched reaction
mixture was poured into water and extracted twice with EtOAc.
The combined organic layer was washed with brine, dried over
MgSO4, filtered and concentrated in vacuo. The residue was
purified by silica gel column chromatography (CH2Cl2–MeOH
20 : 1) to give 15 (39 mg, 69%) as a white solid. [a]2D4 +57.8 (c 0.5,
CHCl3); 1H NMR (CDCl3, 400 MHz) d 0.86 (t, J = 6.4 Hz, 3H),
1.15–1.48 (m, 24H), 1.69–1.90 (m, 2H), 2.75 (d, J = 13.1 Hz, 1H),
2.88 (dd, J = 4.7, 13.1 Hz, 1H), 3.17 (m, 1H), 4.49 (m, 1H), 4.99
(dd, J = 4.0, 6.8 Hz, 1H), 5.45 (br s, 1–NH); 13C NMR (CDCl3,
75 MHz) d 14.1, 22.7, 27.9, 28.8, 29.34, 29.4, 29.48, 29.55, 29.61,
29.64, 29.7, 31.9, 39.8, 55.5, 59.5, 83.4, 159.4; IR (CHCl3) umax
was stirred at 0 ◦C for 12 h, poured into water and extracted twice
with EtOAc. The combined organic layer was washed with brine,
dried over MgSO4, filtered and concentrated in vacuo. The residue
was purified by silica gel column chromatography (CH2Cl2–
MeOH 20 : 1) to provide bis-mesylate 10 and tetrahydrofuran 11.
(R)-1-((4S,5S)-4-(Methylsulfonyloxymethyl)-2-oxooxazolidin-
5-yl)pentadecyl methanesulfonate (10). As a colorless oil (25 mg,
31%). [a]2D4 -29.8 (c 1.0, CHCl3); 1H NMR (400 MHz, CDCl3) d
0.85 (t, J = 6.3 Hz, 3H), 1.15–1.53 (m, 24H), 1.76–1.89 (m, 2H),
3.08 (s, 3H), 3.09 (s, 3H), 4.15–4.22 (m, 1H), 4.36 (dd, J = 6.9, 10.8
Hz, 1H), 4.49 (dd, J = 3.3, 10.9 Hz, 1H), 4.72 (m, 1H), 4.99 (dd,
J = 5.7, 11.4 Hz, 1H), 6.54 (br s, 1–NH); 13C NMR (100 MHz,
CDCl3) d 14.1, 22.6, 24.3, 29.2, 29.31, 29.33, 29.5, 29.56, 29.60,
29.63, 29.64, 31.2, 31.9, 37.6, 39.1, 53.7, 67.5, 76.8, 77.2, 78.1,
157.6; IR (CHCl3) umax 3364, 3028, 2924, 2853, 1769, 1467, 1352,
1262, 1223, 1175 (cm-1); HRMS (FAB) calcd for C21H42NO8S2
500.2352 ([M+H]+), found 500.2342.
(3aS,6R,6aS)-6-Tetradecyltetrahydrofuro[3,4-d]oxazol-2(3H)-
one (11). As a white solid (26 mg, 50%). [a]2D4 +8.2 (c 0.5, CHCl3);
1H NMR (400 MHz, CDCl3) d 0.86 (t, J = 6.8 Hz, 3H), 1.19–1.55
(m, 26H), 3.75 (dd, J = 2.5, 10.2 Hz, 1H), 3.92 (dd, J = 4.9, 10.2
Hz, 1H), 4.01–4.06 (m, 1H), 4.30–4.34 (m, 1H), 4.69 (dd, J =
2.3, 8.1 Hz, 1H), 5.63 (br s, 1–NH); 13C NMR (75 MHz, CDCl3)
d 14.1, 22.7, 25.4, 29.27, 29.35, 29.45, 29.51, 29.61, 29.64, 29.7,
30.6, 31.9, 56.3, 63.0, 72.6, 77.2, 84.0, 84.2, 158.7; IR (CHCl3)
umax 3249, 2954, 2920, 2850, 1758, 1728, 1703, 1469, 1408, 1250
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3329, 2920, 2849, 1745, 1714, 1467, 1413, 1251, 1070, 1046 (cm-1);
HRMS (FAB) calcd for C19H36NO2S, 342.2497 ([M+H]+), found
342.2456.
solution and brine. The organic layer was dried over MgSO4,
filtered and concentrated in vacuo to provide a crude mixture. The
crude mixture was purified by silica gel column chromatography
(CH2Cl2–MeOH 20 : 1) to give only the dimer 18 (37 mg, 73%) as a
white solid. [a]2D4 -75.8 (c 0.2, CHCl3); 1H NMR (CDCl3, 400 MHz)
d 0.86 (t, J = 6.1 Hz, 6H), 1.18–1.40 (m, 48H), 1.41–1.52 (m, 2H),
1.74–1.86 (m, 2H), 2.86 (t, J = 12.1 Hz, 2H), 2.94 (d, J = 4.5 Hz
2–OH), 3.67 (d, J = 12.5 Hz 2H), 3.75–3.87 (m, 2H), 3.95–4.08 (m,
2H), 4.38 (t, J = 8.3 Hz, 2H), 5.84 (br s, 2–NH); 13C NMR (CDCl3,
75 MHz) d 14.1, 22.7, 24.5, 29.36, 29.45, 29.56, 29.66, 29.69, 31.9,
32.7, 34.6, 55.0, 68.5, 77.2, 80.8, 158.6; IR (CHCl3) umax 3301,
2922, 2852, 1744, 1468, 1379, 1241, 1066 (cm-1); HRMS (FAB)
calcd for C38H73N2O6Se2 813.3808 ([M+H]+), found 813.3797.
(4S,5R)-5-((S)-1-Hydroxypentadecyl)-4-((((4R,5S)-5-((R)-1-
hydroxypentadecyl)-2-oxooxazolidin-4-yl)methylthio)methyl)oxa-
zolidin-2-one (16). To a solution of 12 (30 mg, 0.07 mmol) in
DMF (0.74 mL, 0.1 M) was added Na2S·9H2O (21 mg, 0.09
mmol) at room temperature. After stirring for 30 min, the reaction
mixture was concentrated in vacuo to remove DMF, and the
concentrated residue was dissolved in THF (1 mL), H2O (30 mL)
and conc. H2SO4 (20 mL). The mixture was stirred for 1 h at
room temperature, diluted with EtOAc and then washed with
a saturated aqueous NaHCO3 solution and brine. The organic
layer was dried over MgSO4, filtered and concentrated in vacuo
to provide a crude mixture. Purification of the crude material
by column chromatography on silica gel (CH2Cl2–MeOH 20 : 1)
afforded only dimer 16 (23 mg, 91%) as a white solid. [a]2D4 -44.9 (c
0.5, CHCl3); 1H NMR (CDCl3–MeOD 3 : 1, 400 MHz) d 0.68 (t,
J = 6.0 Hz, 6H), 1.10–1.29 (m, 48H), 1.29–1.40 (m, 2H), 1.51–1.62
(m, 2H), 2.39–2.48 (m, 2H), 2.82–2.90 (m, 2H), 3.52–3.60 (m, 2H),
3.70–3.78 (m, 2H), 4.10–4.17 (m, 2H); 13C NMR (CDCl3–MeOD
3 : 1, 100 MHz) d 13.6, 22.3, 24.3, 29.0, 29.27, 29.29, 29.3, 31.6,
32.6, 34.3, 53.9, 67.7, 77.2, 80.6, 159.2; IR (CHCl3) umax 3381, 2922,
2852, 1738, 1468, 1437, 1380, 1250, 1071 (cm-1); HRMS (FAB)
calcd for C38H73N2O6S 685.5189 ([M+H]+), found 685.5204.
General procedure for the cleavage of the oxazolidinone protecting
groups of 15 and 17. To a solution of 15 or 17 (19 mg or 22 mg,
0.06 mmol) in EtOH–THF–H2O (3 : 2 : 1, 3 mL) was added lithium
hydroxide (14 mg, 0.60 mmol) at room temperature. The reaction
mixture was stirred at 60 ◦C for 12 h, cooled to room temperature,
poured into a saturated aqueous NaHCO3 solution and extracted
three times with EtOAc. The combined organic layer was washed
with brine, dried over MgSO4, filtered and concentrated in vacuo.
The residue was purified by silica gel column chromatography
(CH2Cl2–MeOH–NH4OH 100 : 10 : 0.5) to give 4 or 5.
(2S,3S,4R)-4-Amino-2-tetradecyltetrahydrothiophen-3-ol (4).
1
As a white solid (14 mg, 82%). [a]2D4 -10.3 (c 0.5, CHCl3); H
(3aR,6S,6aS)-6-Tetradecyltetrahydroselenopheno[3,4-d]oxazol-
2(3H)-one (17). To a suspension of selenium powder (47 mg,
0.60 mmol) in ethanol (500 mL) was added sodium borohydride
(46 mg, 1.20 mmol) at room temperature. The mixture was heated
to 60 ◦C and the cyclic sulfate 12 (48 mg, 0.12 mmol) in THF
(24 mL, 0.005 M) was added to the mixture using a syringe pump
over a 30 min period. After being stirred for an additional 3 h,
the reaction mixture was cooled, poured into water and extracted
twice with EtOAc. The organic layer was washed with brine, dried
over MgSO4, filtered, and concentrated in vacuo. The residue was
purified by silica gel column chromatography (CH2Cl2–MeOH
20 : 1) to give 17 (39 mg, 84%) as a white solid. [a]2D4 +65.5 (c 0.5,
CHCl3); 1H NMR (CDCl3, 400 MHz) d 0.86 (t, J = 6.2 Hz, 3H),
1.13–1.46 (m, 24H), 1.75–1.95 (m, 2H), 1.75–1.95 (m, 1H), 2.84
(d, J = 12.2 Hz, 1H), 3.00 (dd, J = 4.8, 12.4 Hz, 1H), 3.47 (m,
1H), 4.50–4.57 (m, 1H), 4.98–5.03 (m, 1H), 6.21 (br s, 1–NH);
13C NMR (CDCl3, 100 MHz) d 14.1, 22.7, 29.0, 29.3, 29.4, 29.55,
29.61, 29.64, 29.7, 30.0, 31.9, 32.3, 51.3, 60.9, 77.2, 85.1, 159.6; IR
(CHCl3) umax 3285, 2920, 2850, 1737, 1709, 1469, 1412, 1252, 1047
(cm-1); HRMS (FAB) calcd for C19H36NO2Se 390.1912 ([M+H]+),
found 390.1901.
NMR (CDCl3, 500 MHz) d 0.86 (t, J = 6.6 Hz, 3H), 1.18–1.36 (m,
24H), 1.52–1.62 (m, 1H), 1.76–1.85 (m, 1H), 2.66 (t, J = 10.1 Hz,
1H), 2.91 (dd, J = 7.4, 10.1 Hz, 1H), 3.39–3.46 (m, 1H), 3.46–3.54
(m, 1H), 3.89–3.93 (m, 1H); 13C NMR (CDCl3, 100 MHz) d 14.1,
22.7, 28.6, 29.3, 29.5, 29.57, 29.65, 29.7, 30.9, 31.9, 34.3, 51.2,
59.5, 76.4, 77.2; IR (CHCl3) umax 2918, 2850, 1739, 1376, 1217
(cm-1); HRMS (FAB) calcd for C18H38NOS 316.2674 ([M+H]+),
found 316.2668.
(2S,3S,4R)-4-Amino-2-tetradecyltetrahydroselenophen-3-ol (5).
1
As a white solid (16 mg, 80%). [a]2D4 -15.2 (c 0.5, CHCl3); H
NMR (CDCl3, 400 MHz) d 0.86 (t, J = 6.3 Hz, 3H), 1.15–1.35
(m, 24H), 1.62–1.96 (m, 3H), 2.70 (t, J = 9.8 Hz, 1H), 3.0 (t, J =
8.6 Hz, 1H), 3.35–3.48 (m, 1H), 3.59–3.69 (m, 1H), 4.0 (m, 1H);
13C NMR (CDCl3, 75 MHz) d 14.1, 22.7, 25.9, 29.3, 29.4, 29.49,
29.54, 29.61, 29.63, 29.7, 31.5, 31.9, 46.3, 61.0, 78.1; IR (CHCl3)
u
max 2919, 2849, 1743, 1468, 1374, 1011 (cm-1); HRMS (FAB) calcd
for C18H38NOSe 364.2119 ([M+H]+), found 364.2112.
B: Bioassay
Measurements of cell viability. The cytotoxicity of individual
compounds screened was determined by the SRB assay. Briefly,
cells were plated in 96-well plates at a density of 5 ¥ 104 cells well-1
(HCT 116 and PC-3) or 2.5 ¥ 104 cells well-1 (A549) and incubated
for 24 h. Test compounds (dissolved in pure DMSO) were diluted
in the medium and the cells were treated for 48 h. The tested cells
were then fixed with 10% trichloroacetic acid for 60 min at 4 ◦C.
The fixed cells were stained with 0.4% sulforhodamine B (SRB) for
60 min at room temperature. The stained cells were then dissolved
in 10 mM Tris (pH 10.0). The absorbance was measured at 515 nm.
The cell survival (%) of each tested group was determined by
comparison with solvent-treated control cells. The IC50 value, the
(4R,5R)-4-((R)-1-Hydroxypentadecyl)-5-(((((4R,5S)-5-((R)-1-
hydroxypentadecyl) - 2 - oxooxazolidin - 4 -yl)methyl)diselanyl)-
methyl)oxazolidin-2-one (18). To a suspension of selenium pow-
der (20 mg, 0.25 mmol) in ethanol (200 mL) was added sodium
borohydride (19 mg, 0.50 mmol) at room temperature. The cyclic
sulfate 12 (51 mg, 0.13 mmol) in THF (1.3 mL, 0.1 M) was added
to the mixture. After stirring for 30 min, the reaction mixture was
concentrated in vacuo, and the concentrated residue was dissolved
in THF (2 mL), H2O (60 mL) and conc. H2SO4 (40 mL). The
mixture was stirred for 1 h at room temperature, diluted with
EtOAc and then washed with a saturated aqueous NaHCO3
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This work was supported by the SRC/ERC program (R-11-2007-
107-02001-0) and the WCU program (R32-2008-000-10098-0) of
the National Research Foundation of Korea (NRF) grant founded
by Korea government (MEST).
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