Synthesis of 6-Hydroxysphingosine and α-Hydroxy Ceramide Using a Cross-Metathesis Strategy

Article abstract of DOI:10.1021/acs.joc.5b00823

(Chemical Equation Presented) In this paper, a new synthetic route toward 6-hydroxysphingosine and α-hydroxy ceramide is described. The synthesis employs a cross-metathesis to unite a sphingosine head allylic alcohol with a long-chain fatty acid alkene that also bears an allylic alcohol group. To allow for a productive CM coupling, the sphingosine head allylic alcohol was protected with a cyclic carbonate moiety and a reactive CM catalyst system, consisting of Grubbs II catalyst and CuI, was employed.

Full text of DOI:10.1021/acs.joc.5b00823

Note
pubs.acs.org/joc
Synthesis of 6‑Hydroxysphingosine and α‑Hydroxy Ceramide Using a
Cross-Metathesis Strategy
Patrick Wisse, Mark A. R. de Geus, Gen Cross, Adrianus M. C. H. van den Nieuwendijk,
Eva J. van Rooden, Richard J. B. H. N. van den Berg, Johannes M. F. G. Aerts, Gijsbert A. van der Marel,
Jeroen D. C. Codee,* and Herman S. Overkleeft*
́
Gorleaus Laboratories, Leiden Institute of Chemistry, Einsteinweg 55, 2300 RA Leiden, The Netherlands
S
* Supporting Information
ABSTRACT: In this paper, a new synthetic route toward 6-hydroxysphingosine and α-hydroxy ceramide is described. The
synthesis employs a cross-metathesis to unite a sphingosine head allylic alcohol with a long-chain fatty acid alkene that also bears
an allylic alcohol group. To allow for a productive CM coupling, the sphingosine head allylic alcohol was protected with a cyclic
carbonate moiety and a reactive CM catalyst system, consisting of Grubbs II catalyst and CuI, was employed.
(Glyco)sphingolipids are a family of complex lipids found in all
mammalian cells. Besides playing important structural roles as
membrane components, they are involved in a multitude of
intra- and intercellular signaling events and play a role in many
(patho)physiological processes.1 This structurally diverse class
of lipids is composed of a sphingosine base (a 2-amino-1,3-
dihydroxy long chain alkyl lipid) which can be acylated at the
nitrogen with a variety of acyl chains.2 Further structural
variation comes from differences in substitution at the primary
alcohol group, at which position a large variety of glycans and
phosphate groups can be attached. Structural modifications in
the sphingosine base are also found. The most recently
reported members of the human sphingolipid family, the 6-
hydroxyceramides (e.g., 2, Figure 1), were discovered in 1989,3
and their structure, based on a 6-hydroxysphingosine base (1,
See Figure 1), was fully established in 1994.4 These
sphingolipids are important constituents of the human skin,
especially the stratum corneum (SC), where they play a role in
skin barrier pathologies.5 Authentic samples of these
sphingolipids are valuable to study their role in skin physiology
processes. Because they are not commercially available and
cannot be obtained from natural sources in pure form and
sufficient quantity, the development of synthetic routes to
access these molecules is important.6 To date, three reports
describing the synthesis of the 6-hydroxysphingosine base have
appeared.7−9 These three syntheses all hinge on the
diastereoselective nucleophilic attack of an appropriately
protected alkyne lipid to (S)-Garner aldehyde10 (3, See Figure
1) using strongly basic conditions and necessitating a
subsequent reduction step. We and others have previously
described the assembly of (glyco)sphingolipids using a cross-
metathesis (CM) strategy.11−14 In this approach, an allylic
sphingosine head is coupled with a long-chain alkene (varying
in length and carrying different functionalities12 or 13C labels13)
through the formation of the E-double bond. The mild
conditions required for this transformation and the broad
functional group tolerance make this an attractive strategy, and
we therefore reasoned that it could be an effective approach to
access 6-hydroxysphingosines. To make this strategy successful,
we realized that difficulties associated with the cross-metathesis
of two similar allylic alcohols (type II or III CM coupling
partners)15 had to be overcome. We here describe a strategy for
the CM of two similar allylic alcohols and present the synthesis
of 6-hydroxysphingosine 1 (see Figure 1) as well as the
synthesis of ceramide 2.
The synthesis of the required cross-metathesis partners 6 and
7 bearing different protecting group patterns is depicted in
Scheme 1. The sphingosine head 6a was accessed in six steps
from L-serine as previously described by Yamamoto et al.14 The
long-chain allylic alcohol 7 was assembled using a “tellurium
transposition” strategy, in which a primary allylic alcohol (12) is
transformed into the regioisomeric secondary allylic alcohol
(7a) following a Sharpless asymmetric epoxidation (SAE)−
tellurium-mediated reductive elimination sequence.16 To this
end, we first generated the required primary allylic alcohol 12
from tridecanal 10. Because we found that commercial grade
tridecanal did not perform well in the ensuing olefination
reaction, we generated this aldehyde from tridecanoic acid.
Thus, this acid was first transformed via the acid chloride into
the Weinreb amide (99% over two steps), which was reduced
to give tridecanal 10. The aldehyde was immediately used in
the ensuing olefination event. We found that the best E/Z-
selectivity for trans-olefin 11 (≥98% E) was achieved using a
Horner−Wadsworth−Emmons (HWE) reaction with diiso-
propyl (ethoxycarbonylmethyl)phosphonate.7 The Horner−
Wittig reaction of tridecanal with (ethoxycarbonylmethyl)-
triphenylphosphonium bromide, as well as the HWE reaction
with diethyl (ethoxycarbonylmethyl)phosphonate, proceeded
Received: April 14, 2015
© XXXX American Chemical Society
A
DOI: 10.1021/acs.joc.5b00823
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The Journal of Organic Chemistry
Note
Figure 1. Literature strategy and this work.
Scheme 1. Synthesis of Cross-Metathesis Partners 8 and 9
with less selectivity (E/Z = 9:1 to 95:5). The α,β-unsaturated
ester 11 was then reduced to the allylic alcohol 12 with
diisobutylaluminum hydride (DIBAL-H) to set the stage for
Sharpless asymmetric epoxidation reaction, which was used to
introduce the chirality in the molecule. After substantial
optimization of this reaction, optimal conditions were found
in the use of 13.5 mol % of Ti(O-i-Pr)4, 17.5 mol % of D-
(−)-diethyl tartrate (D-(−)-DET), 2.2 equiv of tert-butyl
hydroperoxide (TBHP), and molecular sieves 4 Å (1 g/mol)
in dichloromethane at −19 °C. This delivered the chiral
epoxide 13 in 79% yield and 89% ee (determined from tosylate
14). Installation of a tosylate function at the primary alcohol
allowed for the tellurium-mediated reductive elimination
reaction. To this end, an aqueous solution of Na2Te was
generated from tellurium and Rongalite (HOCH2SO2Na) in
NaOH (aq).16 Addition of 14 to this solution led to the
nucleophilic displacement of the primary tosylate by tellurium
ion, after which the ensuing epoxide ring opening generates an
epitelluride ring that collapses upon exposure to air to give the
“transposed” secondary allylic alcohol 7a. With both allylic
alcohols in hand, the stage was set for the crucial CM reaction.
Generally, for a productive CM event, two reaction partners of
differing reactivity are required. Grubbs and co-workers14 have
divided alkenes in four categories based on their ability to form
homodimers in CM reactions. Type I alkenes undergo rapid
homodimerization, and these can participate in an ensuing CM
event. Type II alkenes undergo slow homodimerization leading
to homodimers that can participate in CM to a limited extent.
Type III alkenes do not form homodimers, but they are able to
react with type I and II homodimers in a CM. Type IV alkenes
are essentially “spectators to cross-metathesis” as they do not
display any activity toward the catalyst. For a selective CM, the
reaction partners are preferably from different types. The two
allylic alcohols at hand are classified as type II CM partners,
making the desired CM reaction a challenging process. To
discriminate between the reactivity of the alkenes, we first
decided to protect the long chain alcohol 7a (generating a type
III CM partner), and we masked the hydroxyl group as a
benzoyl ester (7b), a tert-butyldimethylsilyl ether (7c), a p-
methoxybenzyl (PMB) ether (7d), or methoxymethyl (MOM)
ether (7e). The results of the CM reactions are summarized in
Table 1. The first attempt, involving diol 6a and alcohol 7a,
provided the desired CM 8a product in 23% yield (entry 1).
Raising the temperature of this reaction did not lead to an
B
DOI: 10.1021/acs.joc.5b00823
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Note
Table 1. Optimization of Cross-Metathesis
a
b
entry
6/7
catalyst
solvent
temp (°C)
time (h)
product (yield, %)
1
6a/7a
6a/7a
6a/7b
6a/7c
6b/7a
6b/7b
6b/7c
6b/7d
6b/7e
6b/7a
6b/7a
6b/7a
6b/7a
Grubbs II
Grubbs II
Grubbs II
Grubbs II
Grubbs II
Grubbs II
Grubbs II
Grubbs II
Grubbs II
Grubbs II
DCM
DCE
DCM
DCM
DCM
DCM
DCM
DCM
DCM
DCE
DCM
tol
40
80
40
40
40
40
40
40
40
80
40
40
48
48
48
48
48
48
48
48
66
48
70
48
48
8a (23%)
8a (−)
8b (−)
2
3
4
8c (−)
5
8d (48%)
c
6
8e (−)
8f (−)
c
7
c
8
8g (37%)
8h (43%)
8d (−)
8d (48%)
8d (78%)
8d (83%)
c
9
10
11
12
13
Hoveyda-Grubbs
Grubbs II + CuI
Grubbs II + CuI
Et2O
r.t.
a
b
Reaction conditions: molar ratio 6:7 (3:1), 20 mol % catalyst, 30 mol % (CuI). Yields denote isolated yields after column chromatography.
c
Unreacted cyclic carbonate 6b as well the protected allylic olefin (7b−e) could be recovered.
Scheme 2. Synthesis of 6-Hydroxysphingosine 1 and α-Hydroxy Ceramide 2
improved reaction (entry 2). Next, a CM was attempted with
the more electron-poor benzoylated allylic alcohol 7b in
combination with diol 6a, but this CM was unproductive (entry
3). Similarly, the use of silylated CM partner 7c was to no avail
(entry 4). Because modulation of the reactivity of the long-
chain allylic alcohol proved unsuccessful, we decided to protect
diol 6 and generated the cyclic carbonate 6b. The cycic
carbonate group is strongly electron withdrawing, changing the
electronic properties of the alkene, and ties back the
functionalities of the groups attached to the alkene, making it
more accessible. When the allylic carbonate 6b and alcohol 7a
were combined in a CM event, the desired E-alkene 8d was
obtained in an increased yield (48%, entry 5). The use of
benzoylated and silylated CM partners 7b and 7c again led to
unproductive CM reactions (entries 6 and 7). The use of PMB-
and MOM-protected allylic alcohols 7d and 7e did deliver the
desired CM products 8g and 8h, respectively, but in a lower
yield than obtained for 8d (entries 8 and 9). Having established
that the most productive CM reaction occurred between
carbonate 6b and alcohol 7a, this reaction was further
optimized. Raising the temperature led to decomposition of
the cyclic carbonate, and therefore, no product was obtained
(entry 10). We then explored different catalyst systems. The
use of the Grubbs−Hoveyda catalyst led to an identical result as
compared to the Grubbs II catalyzed CM reaction (entry 11),
and we therefore moved to the use of additives to improve the
reactivity of the catalyst. As described by Voigtritter et al.,17
copper iodide (CuI) can be used to generate a more stable
catalyst (due to the iodide) while making the system more
reactive because the copper sequesters the phosphine ligands.
As shown in entries 12 and 13, the use of this additive proved
very successful, and the cyclic carbonate protected alkene diol
6b and allylic alcohol 7a could be fused to provide the desired
E-alkene 8d in good yield. Having successfully constructed the
C
DOI: 10.1021/acs.joc.5b00823
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Note
tert-Butyl ((4R,5S)-2-Oxo-4-vinyl-1,3-dioxan-5-yl)carbamate
(6b). Allylic alcohol 6a (3.03 g, 13.95 mmol, 1 equiv) was dissolved
in anhydrous THF (400 mL) under an argon atmosphere. N,N′-
Disuccinimidyl carbonate (8.93 g, 34.88 mmol, 2.5 equiv) and DMAP
(4.26 g, 34.88 mmol, 2.5 equiv) were added, and the mixture was
allowed to stir for 20 h at room temperature. The reaction mixture was
concentrated in vacuo and purified by silica gel chromatography (30%
EtOAc in pentane) to give cyclic carbonate 6b (2.57 g, 10.56 mmol,
76%) as a thick, colorless oil: Rf = 0.6 (50% EtOAc in pentane); [α]D
= +46.0 (c = 1.0, CHCl3); 1H NMR (400 MHz, CDCl3) δ: 5.92 (ddd,
1 H, J = 16.8, 10.8, 4.4 Hz), 5.58 (d, 1 H, J = 7.2 Hz), 5.50 (dd, 1 H, J
= 16.8, 1.6 Hz), 5.47 (dd, 1 H, J = 10.8, 1.6 Hz), 5.02 (br s, 1 H), 4.54
(dd, 1 H, J = 11.2, 2.4 Hz), 4.31 (d, 1 H, J = 11.2 Hz), 3.97 (m, 1 H),
1.46 (s, 9 H); 13C NMR (101 MHz, CDCl3) δ 155.3, 147.7, 132.5,
119.7, 81.9, 80.9, 68.2, 45.8, 28.3; IR (neat) 3329, 2978, 2932,
1751,1701, 1165 cm−1; HRMS (ESI) [M + H+] calcd for C11H18NO5
244.1180, found 244.1184
6-hydroxysphingosine backbone, the base was globally
deprotected by saponification of the carbonate group and the
ensuing debocylation using dilute acid at low temperature (0
°C) to give 6-hydroxysphingosine 1, as depicted in Scheme 2.
The use of more forceful acidic conditions led to complex
reaction mixtures, presumably as a result of acid-catalyzed allylic
substitution reactions. The synthesis of the 6-hydroxysphingo-
sine-based ceramide 2 featuring an α-hydroxyl side chain was
finally accomplished. First, α-hydroxy fatty acid 16a was
generated from optically pure cyanohydrin 15, obtained from
crotonaldehyde by the action of almond hydroxynitrilase.18 The
cyanohydrin was transformed into the corresponding methyl
ester using a Pinner reaction.19 Next, a CM reaction of the
alkene with 1-tetradecene gave the unsaturated long-chain lipid
that was reduced and saponified to give the fatty acid 16b. To
condense the α-hydroxy fatty acid with the 6-hydroxy-
sphingosine, the α-hydroxy group was first masked with an
acetyl group. Activation of acid 16c first with 2-ethoxy-1-
(ethoxycarbonyl)-1,2-dihydroquinoline (EEDQ)20 and the
ensuing condensation then gave acetylated ceramide 17. Final
saponification of the acetyl ester completed the synthesis of the
target 6-hydroxyceramide 2.
In conclusion, we have described a new synthetic route for 6-
hydroxysphingosine and its α-hydroxyceramide counterpart,
employing a cross-metathesis (CM) strategy. The crucial CM
reaction on which the synthesis hinges unites two similar allylic
alcohol alkenes. We have used a cyclic carbonate group to
protect the diol system, present in the sphingosine head CM
partner, with a cyclic carbonate functionality to serve two
purposes. First, it makes the double bond less electron rich,
discriminating it from its designated CM partner, the long-
chain allylic alcohol. Second, it ties back the functional groups
on the olefin, making the alkene sterically most accessible for
the catalyst and the CM event. In combination with an
activated catalyst system (the Grubbs II−CuI reagent pair), this
led to an efficient CM connection of the sphingosine head and
tail alkenes. The mild conditions required for this connection in
conjunction with the straightforward deprotection scheme
(mild base followed by mild acid) make the approach versatile
and amenable to the use of a variety of CM coupling partners
to generate labeled and tagged 6-hydroxysphingosine derived
probes for future biochemical studies.13,21
Tridecanal (10). Tridecanoic acid 9 (7.50 g, 35.0 mmol, 1 equiv)
was dissolved in anhydrous DCM (110 mL) under an argon
atmosphere. The solution was cooled to 0 °C before addition of
oxalyl chloride (2 M in DCM, 35 mL, 70 mmol, 2 equiv) and DMF (3
drops, cat.). The mixture was stirred for 4−5 h at room temperature.
Once gas formation subsided, the reaction mixture was concentrated in
vacuo, and the crude acyl chloride was immediately dissolved in
anhydrous DCM (110 mL) under an argon atmosphere. The solution
was cooled to −78 °C before slow addition of distilled N,O-
dimethylhydroxylamine (6.42 mL, 87.5 mmol, 2.5 equiv). After 30
min, the reaction mixture was allowed to reach room temperature and
stirred for 20 h. The reaction mixture was filtered, concentrated in
vacuo, and purified by silica gel chromatography (5% → 10% EtOAc in
pentane) to give N-methoxy-N-methyltridecanamide (8.94 g, 34.74
1
mmol, 99%) as an oil: Rf = 0.3 (10% EtOAc in pentane); H NMR
(400 MHz, CDCl3) δ 3.68 (s, 3 H), 3.18 (s, 3 H), 2.41 (t, 2 H, J = 7.6
Hz), 1.67−1.571 (m 2 H), 1.31−1.26 (m, 18 H), 0.88 (t, 3 H, J = 6.8
Hz); 13C NMR (101 MHz, CDCl3) δ 175.0, 61.3, 32.3, 32.0 (×2),
29.8, 29.76 (×2), 29.64, 29.59, 29.56, 29.5, 24.8, 22.8, 14.3; IR (neat)
2922, 2853, 1668 cm−1; HRMS (ESI) [M + H+] calcd for C15H32NO2
258.2428, found 258.2426.
N-Methoxy-N-methyltridecanamide (2.59 g, 10.05 mmol, 1 equiv)
was dissolved in anhydrous THF (25 mL) under an argon atmosphere.
The solution was cooled to −60 °C followed by addition of
diisobutylaluminum hydride (1 M in THF, 12 mL, 12 mmol, 1.2
equiv). The reaction mixture was stirred for 3 h at −60 °C. The
reaction was quenched by addition of Rochelle salt solution (satd, 20
mL) at −60 °C. The mixture was then allowed to reach room
temperature before extraction with EtOAc (2 × 150 mL). The
combined organic layers were washed with brine, dried over MgSO4,
filtrated, and concentrated in vacuo. The crude tridecanal 10 was
collected as an oil, which was used for the next reaction without
EXPERIMENTAL SECTION
1
■
further purification: Rf = 0.7 (5% EtOAc in pentane); H NMR (400
General Methods. Commercially available reagents and solvents
were used as received. DCM and THF were dried and distilled by
standard procedures. All moisture-sensitive reactions were carried out
under an argon atmosphere. Molecular sieves (3 Å) were flame-dried
before use. Column chromatography was carried out with silica gel 60
(40−63 μm mesh). IR spectra are reported in cm−1. Optical rotations
were measured with an automatic polarimeter (sodium D line, λ = 589
nm). The enantiomeric purity was determined by HPLC analysis using
an OD column (hexane/isopropyl alchohol (98:2), 1 mL/min, UV
254 nm). NMR spectra were recorded on a 400 or 850 MHz
spectrometer. Chemical shifts are reported as δ values (ppm) and were
referenced to tetramethylsilane (δ = 0.00 ppm) directly in CDCl3 or
using the residual solvent peak (D2O). High-resolution mass spectra
were recorded on an LTQ-Orbitrap mass spectrometer equipped with
an electrospray ion source in positive mode with a 355 nm laser.
Samples (1 μL, 100 mM in CHCl3) were spotted on the MALDI plate,
followed by addition of aqueous silver benzoate (0.5 μL, 10 mM),
drying, and application of the matrix (2,5-dihydroxybenzoic acid, 0.5
μL, 0.5 M in methanol). A laser frequency of 1000 Hz (power set at
60%) was used.
MHz, CDCl3) δ 9.76 (t, 1 H, J = 1.6 Hz), 2.42 (dt, 2 H, J = 7.2, 1.6
Hz), 1.67−1.57 (m, 2 H), 1.30−1.26 (m, 18 H), 0.88 (t, 3 H, J = 6.8
Hz); 13C NMR (101 MHz, CDCl3) δ 202.9, 44.0, 32.3, 29.76, 29.74,
29.70, 29.55, 29.48, 29.47, 29.28, 22.8, 22.2, 14.2; IR (neat) 3024,
2984, 2941, 1732, 1236 cm−1.
Ethyl (E)-Pentadec-2-enoate (11). Diisopropyl (ethoxycarbonyl-
methyl)phosphonate (3.53 g, 14 mmol, 1.4 equiv) was dissolved in
anhydrous THF (40 mL) under an argon atmosphere. n-Butyllithium
(2.5 M in hexanes, 5 mL, 12.5 mmol, 1.25 equiv) was added and the
mixture stirred for 15 min at room temperature followed by addition
of a solution of crude tridecanal 10 in anhydrous THF (15 mL). The
reaction mixture was stirred for 20 h. The reaction mixture was diluted
with H2O (100 mL) and extracted with Et2O (3 × 100 mL). The
combined organic layers were washed with brine, dried over MgSO4,
filtrated, and concentrated in vacuo. The crude product was purified by
silica gel chromatography (0% → 1% → 2% EtOAc in pentane). The
α,β-unsaturated ester 11 (2.08 g, 7.73 mmol, 77% over two steps,
≥98% E) was collected as a light yellow oil: Rf = 0.5 (2% EtOAc in
1
pentane); H NMR (400 MHz, CDCl3) δ 6.97 (dt, 1 H, J = 15.6, 6.8
Hz), 5.81 (dt, 1 H, J = 15.6, 1.6 Hz), 4.18 (q, 2 H, J = 7.2 Hz), 2.23−
D
DOI: 10.1021/acs.joc.5b00823
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Note
2.15 (m, 2 H), 1.48−1.40 (m, 2 H), 1.32−1.26 (m, 21 H), 0.88 (t, 3
H, J = 6.8 Hz); 13C NMR (101 MHz, CDCl3) δ 166.9, 149.6, 121.3,
60.2, 32.3, 32.4, 29.78, 29.76 (×2), 29.65, 29.52, 29.48, 29.28, 28.1,
22.8, 14.4, 14.2; IR (neat) 2922, 2853, 1722, 1655, 1179 cm−1; ESI
HRMS (ESI) [M + H+] calcd for C17H33O2 269.2475, found 269.2475.
Spectroscopic data was identical to literature values.7
The crude product was purified by silica gel chromatography (2 → 3
→ 5% EtOAc in pentane). Tosylate 14 (1.12 g, 2.82 mmol, 96%) was
collected as a colorless oil that slowly crystallized into a white solid: Rf
1
= 0.3 (5% EtOAc in pentane); [α]D = +24.0 (c = 1.0, CHCl3); H
NMR (400 MHz, CDCl3) δ 8.00 (d, 2 H, J = 8.4 Hz), 7.35 (d, 2 H, J =
8.0 Hz), 4.18 (dd, 1 H, J = 11.2, 4.0 Hz), 3.97 (dd, 1 H, J = 11.2, 6.0
Hz), 2.95 (ddd, 1 H, J = 6.0, 4.0, 2.0 Hz), 2.78 (m, 1 H), 2.45 (s, 3 H),
1.55−1.47 (m, 2 H), 1.43−1.33 (m, 2 H), 1.32−1.25 (m, 18 H), 0.88
(t, 3 H, J = 6.8 Hz); 13C NMR (101 MHz, CDCl3) δ 145.2, 132.9,
130.0, 128.1, 70.3, 57.0, 54.7, 32.0, 31.4, 29.79, 29.77, 29.76, 29.65,
29.61, 29.5, 29.4, 25.9, 22.8, 21.8, 14.3; IR (neat) 2953, 2916, 2870,
2849, 1599, 1364, 1177, 829, 808 cm−1; HRMS (ESI) [M + H+] calcd
for C22H37O4S 397.2407, found 397.2404.
(E)-Pentadec-2-en-1-ol (12). Ethyl (E)-pentadec-2-enoate (11)
(2.39 g, 8.89 mmol, 1 equiv) was dissolved in anhydrous THF (45
mL) under an argon atmosphere. The solution was cooled to −78 °C
followed by addition of diisobutylaluminum hydride (1 M in THF,
26.7 mL, 26.7 mmol, 3 equiv). The reaction mixture was stirred for 3
h, slowly warming to −60 °C. The reaction was quenched with NH4Cl
solution (satd) at −60 °C. The mixture was then allowed to warm to
room temperature before addition of HCl (5%, 100 mL). The mixture
was extracted with Et2O (3 × 100 mL). The combined organic layers
were washed with brine, dried over MgSO4, filtrated, and concentrated
in vacuo. The crude product was purified by silica gel chromatography
(2.5% → 5% EtOAc in pentane). Allylic alcohol 12 (1.89 g, 8.34
mmol, 94%) was collected as a colorless oil which slowly crystallized
(R)-Pentadec-1-en-3-ol (7a). Sodium hydroxymethanesulfinate
hydrate (6.50 g, 55.0 mmol, 7.3 equiv) was dissolved in NaOH (1 M,
150 mL). Argon was purged through the solution before addition of
tellurium (powder, −200 mesh, 1.92 g, 15.1 mmol, 2 equiv). The
reaction mixture was stirred for 2 h at 50 °C. The purple solution of
tellurides was cooled to 0 °C followed by slow addition of a solution of
tosylate 14 (2.99 g, 7.53 mmol, 1 equiv) in THF (75 mL). The
reaction was stirred for 20 h at room temperature. The reaction was
quenched by bubbling air through the solution. The crude reaction
mixture was then filtrated over a pad of Celite and concentrated in
vacuo. The aqueous layer was extracted with Et2O (2 × 150 mL). The
combined organic layers were washed with H2O2 (3%, 75 mL),
sodium thiosulfate (10%), and brine before being dried over MgSO4,
filtrated, and concentrated in vacuo. The crude product was purified by
silica gel chromatography (5% → 10% Et2O in pentane). Allylic
alcohol 7a (1.54 g, 6.78 mmol, 90%) was collected as a white solid: Rf
= 0.4 (20% Et2O in pentane); [α]D = −7.0 (c = 1.0, CHCl3); 1H NMR
(400 MHz, CDCl3) δ 5.87 (ddd, 1 H, J = 16.8, 10.4, 6.4 Hz), 5.22 (dt,
1 H, J = 17.2, 1.2 Hz), 5.10 (dt, 1 H, J = 10.4, 1.2 Hz), 4.13−4.08 (m,
1 H), 1.69 (br s, 1 H), 1.59−1.48 (m, 2 H), 1.43−1.26 (m, 20 H), 0.88
(t, 3 H, J = 6.8 Hz); 13C NMR (101 MHz, CDCl3) δ 141.5, 114.7,
73.5, 37.2, 32.1, 29.82, 29.80 (×2), 29.74 (×2), 29.70, 29.51, 25.48,
1
into a white solid: Rf = 0.3 (5% EtOAc in pentane); H NMR (400
MHz, CDCl3) δ 5.73−5.59 (m, 2 H), 4.08 (d, 2 H, J = 6.0 Hz), 2.04
(q, 2 H, J = 7.4 Hz), 1.50 (br s, 1 H), 1.42−1.33 (m, 2 H), 1.32−1.26
(m, 18 H), 0.88 (t, 3 H, J = 6.8 Hz); 13C NMR (101 MHz, CDCl3) δ
133.8, 128.9, 64.0, 32.4, 32.1, 29.83, 29.81, 29.79, 29.76, 29.65, 29.5,
29.3, 29.28, 22.8, 14.3; IR (neat) 3292, 2955, 2918, 2849, 1672, 1462
cm−1. Spectroscopic data was identical to literature values.7
((2R,3R)-3-Dodecyloxiran-2-yl)methanol (13). Activated, pow-
dered molecular sieves (∼5 g, 4 Å) were added to a flame-dried flask
with freshly distilled, anhydrous DCM (15 mL) under an argon
atmosphere. The suspension was stirred for 10 min at room
temperature, completely drying DCM in the process. (−)-Diethyl D-
tartrate (0.15 mL, 0.86 mmol, 0.17 equiv) and titanium(IV)
isopropoxide (0.2 mL, 0.69 mmol, 0.14 equiv) were added to this
solution at −19 °C. Allylic alcohol 12 (1.13 g, 5.00 mmol, 1 equiv) was
coevaporated with toluene (2×) and dissolved in freshly distilled,
anhydrous DCM (10 mL). After the titanium tartrate solution was
stirred for 30 min, the solution of allylic alcohol 12 was added followed
by addition of tert-butyl hydroperoxide (∼5.5 M in decane, 2 mL, 11.0
mmol, 2.2 equiv). The reaction mixture was stirred for 5 h at −19 °C.
The reaction was quenched by addition of H2O (20 mL) at −19 °C.
After the mixture was warmed to room temperature, NaOH (30% in
brine, 2.5 mL) was added to aid in the hydrolysis of (−)-diethyl D-
tartrate. The mixture was stirred for 15 min, followed by extraction
with DCM (3 × 30 mL). The combined organic layers were dried over
MgSO4, filtrated, and concentrated in vacuo. The remaining tert-butyl
hydroperoxide was removed by coevaporation with toluene. The crude
product was purified by silica gel chromatography (10 → 15% EtOAc
in pentane). Epoxide 13 (0.92 g, 3.80 mmol, 76%, ee = 89%
determined from tosylate 14) was collected as a white solid. The
analytical sample was recrystallized from petroleum ether (60%): Rf =
22.8, 14.3; IR (neat) 3348, 2918, 2853, 1643, 1466 cm−1
Spectroscopic data was identical to literature values.22
.
(R)-Pentadec-1-en-3-yl Benzoate (7b). Allylic alcohol 7a (325
mg, 1.44 mmol, 1 equiv) was dissolved in anhydrous DCM (17 mL)
under an argon atmosphere. Benzoic anhydride (974 mg, 4.31 mmol, 3
equiv), triethylamine (0.80 mL, 5.74 mmol, 4 equiv), and DMAP (17
mg, 0.14 mmol, cat.) were added, and the reaction mixture was stirred
under reflux for 20 h. The reaction was quenched by addition of
NH4Cl (satd, 25 mL). The aqueous layer was extracted with Et2O (3
× 30 mL). The combined organic layers were washed with brine, dried
over MgSO4, filtrated, and concentrated in vacuo. The crude product
was purified by silica gel chromatography (0 → 2% EtOAc in
pentane). The benzoylated product 7b (424 mg, 1.28 mmol, 89%) was
1
collected as an oil: Rf = 0.8 (10% EtOAc in pentane); H NMR (400
MHz, CDCl3) δ 8.07 (m, 2 H), 7.55 (m, 1 H), 7.44 (m, 2 H), 5.89
(ddd, 1 H, J = 17.2, 10.4, 6.4 Hz), 5.49 (m, 1 H), 5.32 (dt, 1 H, J =
17.2, 1.2 Hz), 5.20 (dt, 1 H, J = 10.4, 1.2 Hz), 1.84−1.68 (m, 2 H),
1.46−1.25 (m, 20 H), 0.88 (t, 3 H, J = 6.8 Hz); 13C NMR (101 MHz,
CDCl3) δ 166.0, 136.8, 133.0, 130.7, 129.7, 128.4, 166.7, 75.5, 34.5,
32.1, 29.80, 29.77 (×2), 29.70, 29.64, 29.54, 29.49, 25.2, 22.8, 14.3; IR
(neat) 3088, 3030, 2922, 2853, 1719, 1267 cm−1. HRMS (MALDI-
TOF) [M + Ag]+ calcd for C22H34O2Ag [M + Ag]+ 437.1610, found
437.1602.
(R)-tert-Butyldimethyl(pentadec-1-en-3-yloxy)silane (7c). Al-
lylic alcohol 7a (259 mg, 1.14 mmol, 1 equiv) was dissolved in
anhydrous DMF (5 mL) under an argon atmosphere. DMAP (6 mg,
0.05 mmol, cat.) was added, and the solution was cooled to 0 °C
followed by addition of tert-butyldimethylsilyl chloride (175 mg, 1.16
mmol, 1.02 equiv) and triethylamine (0.18 mL, 1.29 mmol, 1.1 equiv).
The reaction mixture was stirred for 20 h at room temperature. The
reaction was quenched with H2O (>50 mL) and extracted with Et2O
(3 × 50 mL). The combined organic layers were washed with brine,
dried over MgSO4, filtrated, and concentrated in vacuo. The crude
product was purified by silica gel chromatography (0% → 2% EtOAc
in pentane). The silylated product 7c was collected as a colorless oil
1
0.3 (20% EtOAc in pentane); [α]D = +23.4 (c = 1.0, CHCl3); H
NMR (400 MHz, CDCl3) δ 3.92 (ddd, 1 H, J = 12.4, 5.2, 2.4 Hz), 3.63
(ddd, 1 H, J = 12.0, 7.2, 4.4 Hz), 2.96 (m, 1 H), 2.99−2.90 (m, 1 H),
1.69−1.63 (m, 1 H), 1.59−1.54 (m, 2 H), 1.49−1.39 (m, 2 H), 1.35−
1.26 (m, 18 H), 0.88 (t, 3 H, J = 6.8 Hz); 13C NMR (101 MHz,
CDCl3) δ 61.8, 58.5, 56.1, 32.1, 31.7, 29.81, 29.78 (×2), 29.70, 29.68,
29.55, 29.5, 26.1, 22.8, 14.3; IR (neat) 3252, 2953, 2916, 2870, 2847,
1458, 1248, 868 cm−1; HRMS (ESI) [M + H+] calcd for C15H31O2
243.2319, found 243.2321. Spectroscopic data was identical to
literature values.8,22
((2R,3R)-3-Dodecyloxiran-2-yl)methyl 4-Methylbenzenesul-
fonate (14). Epoxide 13 (716 mg, 2.95 mmol, 1 equiv) was dissolved
in anhydrous DCM (30 mL) under an argon atmosphere. The
solution was cooled to 0 °C followed by addition of p-toluenesulfonyl
chloride (1.13 g, 5.91 mmol, 2 equiv), DMAP (25 mg, 0.2 mmol, cat.),
and triethylamine (1.24 mL, 8.86 mmol, 3 equiv). The reaction
mixture was stirred for 20 h at room temperature. The reaction was
quenched with H2O (30 mL). The aqueous layer was extracted with
DCM (3 × 30 mL). The combined organic layers were washed with
H2O (2×), dried over MgSO4, filtrated, and concentrated in vacuo.
E
DOI: 10.1021/acs.joc.5b00823
J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Note
(265 mg, 0.78 mmol, 68%): Rf = 0.4 (pentane); 1H NMR (400 MHz,
CDCl3) δ 5.79 (ddd, 1 H, J = 16.8, 10.4, 6.0 Hz), 5.12 (dt, 1 H, J =
17.2, 1.6 Hz), 5.01 (dt, 1 H, J = 10.4, 1.6 Hz), 4.07 (q, 1 H, J = 6.2
Hz), 1.58−1.40 (m, 2 H), 1.37−1.26 (m, 20 H), 0.90 (s, 9 H), 0.88 (t,
3 H, J = 6.8 Hz), 0.05 (s, 3 H), 0.03 (s, 3 H); 13C NMR (101 MHz,
CDCl3) δ 142.1, 113.5, 74.1, 38.3, 32.1, 29.85, 29.83, 29.82, 29.80,
29.79 (×2), 29.5, 26.1, 25.4, 22.9, 18.4, 14.3, −4.2, −4.7; IR (neat)
2955, 2924, 2853, 1252, 1080, 814 cm−1; HRMS (MALDI-TOF) [M
+ Ag]+ calcd for C21H44OSiAg 447.2212, found 447.2229.
(R)-1-Methoxy-4-((pentadec-1-en-3-yloxy)methyl)benzene
(7d). Allylic alcohol 7a (232 mg, 1.02 mmol, 1 equiv) was dissolved in
anhydrous DMF (5 mL) under an argon atmosphere. The solution
was cooled to 0 °C, followed by addition of sodium hydride (60% in
mineral oil, 48 mg, 2.0 mmol, 2 equiv). After the mixture was stirred
for 15 min, 4-methoxybenzyl chloride (0.27 mL, 2.0 mmol, 2 equiv)
was slowly added to the reaction mixture. The solution was stirred for
20 h at room temperature. The reaction was quenched by adding
dropwise of NH4Cl (satd, 20 mL). After quenching, H2O (>50 mL)
was added and extracted with Et2O (2 × 100 mL). The combined
organic layers were washed with brine, dried over MgSO4, filtrated,
and concentrated in vacuo. The crude product was purified by silica gel
chromatography (0% → 1% Et2O in pentane). The PMB-protected
product 7d (309 mg, 0.89 mmol, 87%) was collected as a light yellow
oil: Rf = 0.2 (1% Et2O in pentane); [α]D = +19.0 (c = 1.0, CHCl3); 1H
NMR (400 MHz, CDCl3) δ 7.25 (d, 2 H, J = 8.8 Hz), 6.87 (d, 2 H, J =
8.8 Hz), 5.72 (ddd, 1 H, J = 18.4, 10.4, 8.0 Hz), 5.22−5.18 (m, 1 H),
5.17−5.14 (m, 1 H), 4.52 (d, 1 H, J = 11.6 Hz), 4.28 (d, 1 H, J = 11.6
Hz), 3.80 (s, 3 H), 3.69 (q, 1 H, J = 6.8 Hz), 1.68−1.56 (m, 1 H),
1.53−1.45 (m, 1 H), 1.40−1.25 (m, 20 H), 0.88 (t, 3 H, J = 6.8 Hz);
13C NMR (101 MHz, CDCl3) δ 159.1, 139.5, 131.1, 129.5, 117.0,
NMR (400 MHz, CDCl3) δ 5.96 (dd, 1 H, J = 15.6, 4.8 Hz), 5.78 (dd,
1 H, J = 15.2, 4.8 Hz), 5.53 (d, 1 H, J = 7.2 Hz), 5.03−4.96 (m, 1 H),
4.55 (br d, 1 H, J = 9.6 Hz), 4.30 (br d, 1 H, J = 10.4 Hz), 4.22−4.15
(m, 1 H), 3.94 (br s, 1 H), 2.41 (br s, 1 H), 1.56−1.46 (m, 2 H), 1.46
(s, 9 H), 1.32−1.26 (m, 20 H), 0.88 (t, 3 H, J = 6.8 Hz); 13C NMR
(101 MHz, CDCl3) δ 155.3, 147.8, 139.2, 123.8, 81.7, 80.9, 71.3, 68.4,
46.2, 37.2, 32.0, 29.76, 29.74 (×2), 29.71, 29.66, 29.61, 29.4, 28.4, 25.4,
22.8, 14.2; IR (neat) 3464, 3352, 2951, 2917, 2850, 1759, 1695, 1190,
1165 cm−1; HRMS (ESI) [M − Boc + H+] calcd for C19H36NO4
342.2639, found 342.2641.
6-Hydroxysphingosine (1). Protected 6-hydroxysphingosine 8d
(35 mg, 0.080 mmol) was dissolved in THF/H2O (3:1, 1.5 mL) at
room temperature. The solution was cooled to 0 °C before addition of
lithium hydroxide monohydrate (9 mg, 0.21 mmol, 2.7 equiv). The
reaction mixture was stirred for 3 h at 0 °C. The reaction mixture was
acidified by addition of Amberlyst. The reaction mixture was filtrated,
washed with MeOH/EtOAc, and concentrated in vacuo. The crude
tert-butyl ((2S,3R,6R,E)-1,3,6-trihydroxyoctadec-4-en-2-yl)carbamate
was collected as a solid which was used for the next reaction without
further purification: Rf = 0.4 (80% EtOAc in pentane); 1H NMR (400
MHz, CDCl3) δ 5.82 (dd, 1 H, J = 15.6, 5.2 Hz), 5.74 (dd, 1 H, J =
15.6, 5.2 Hz), 5.46 (d, 1 H, J = 8.4 Hz,), 4.33 (t, 1 H, J = 4.6 Hz), 4.11
(q, 1 H, J = 6.0 Hz), 3.88 (dd, 1 H, J = 11.2, 3.6 Hz), 3.67 (dd, 1 H, J =
11.2, 3.6 Hz), 3.63−3.56 (m, 1 H), 1.55−1.45 (m, 2 H), 1.44 (s, 9 H),
1.28−1.26 (m, 20 H), 0.88 (t, 3 H, J = 6.8 Hz); 13C NMR (101 MHz,
CDCl3) δ 156.6, 135.7, 129.6, 80.1, 73.6, 72.0, 62.3, 55.4, 37.4, 32.1,
29.83 (×3), 29.80 (×2), 29.76, 29.5, 28.6, 25.7, 22.8, 14.3; HRMS
(ESI) [M + Na]+ calcd for C23H45NO5Na 438.3190, found 438.3187.
The crude tert-butyl ((2S,3R,6R,E)-1,3,6-trihydroxyoctadec-4-en-2-
yl)carbamate previously described was dissolved in DCM (2.7 mL).
The solution was cooled to 0 °C before slow addition of TFA (0.3
mL). The solution was stirred for 90 min at 0 °C. The reaction
mixture was diluted with toluene (∼20 mL) followed by concentration
in vacuo. Before complete evaporation of all solvents, the reaction
mixture was diluted with toluene 2 more times (2 × 20 mL). The
crude product was purified by silica gel chromatography (neutralized
silica, 5% → 7.5% MeOH in CHCl3). 6-Hydroxysphingosine (1) was
collected as a waxy solid (20 mg, 0.063 mmol, 80% over two steps): Rf
113.9, 80.4, 69.8, 55.4, 35.7, 32.1, 29.83, 29.81 (×2), 29.78, 29.75,
29.70, 29.5, 25.5, 22.9, 14.3; IR (neat) 2922, 2853, 1612, 1246, 1038
cm−1. HRMS (MALDI-TOF) [M + Ag]+ calcd for C17H34O2Ag
377.1610, found 377.1598.
(R)-3-(Methoxymethoxy)pentadec-1-ene (7e). Allylic alcohol
7a (229 mg, 1.01 mmol, 1 equiv) was dissolved in anhydrous DCM (6
mL) under an argon atmosphere. DMAP (16 mg, 0.13 mmol, cat.) was
added, and the solution was cooled to 0 °C. DIPEA (0.87 mL, 5.0
mmol, 5 equiv) and chloromethyl methyl ether (0.34 mL, 4.5 mmol,
4.5 equiv) were added. The reaction was stirred for 20 h at room
temperature. The reaction was quenched by addition of NH4Cl (satd,
20 mL). The reaction mixture was diluted with H2O and extracted
with DCM (3 × 50 mL). The combined organic layers were dried over
MgSO4, filtrated, and concentrated in vacuo. The crude product was
purified by silica gel chromatography (1% → 10% → 20% toluene in
pentane). The MOM-protected product 7e (256 mg, 0.95 mmol,
94%) was collected as a light yellow oil: Rf = 0.2 (20% Toluene in
pentane); [α]D = +50.0 (c = 1.0, CHCl3); 1H NMR (400 MHz,
CDCl3) δ 5.66 (ddd, 1 H, J = 17.6, 10.4, 7.6 Hz), 5.23−5.20 (m, 1 H),
5.19−5.15 (m, 1 H), 4.70 (d, 1 H, J = 6.8 Hz), 4.53 (d, 1 H, J = 6.8
Hz), 3.98 (q, 1 H, J = 6.8 Hz), 3.37 (s, 3 H), 1.68−1.58 (m, 1 H),
1.52−1.42 (m, 1 H), 1.42−1.26 (m, 20 H), 0.88 (t, 3 H, J = 6.8 Hz);
13C NMR (101 MHz, CDCl3) δ 138.7, 117.1, 93.8, 77.5, 55.5, 35.6,
1
= 0.3 (30% MeOH in CHCl3); [α]D = −9.6 (c = 0.5, MeOH); H
NMR (400 MHz, MeOD) δ 5.86 (dd, 1 H, J = 15.6, 6.0 Hz), 5.67 (dd,
1 H, J = 15.6, 6.4 Hz), 4.37 (t, 1 H, J = 5.2 Hz,), 4.09 (q, 1 H, J = 6.0
Hz), 3.80 (dd, 1 H, J = 11.6, 4.0 Hz), 3.70 (dd, 1 H, J = 11.6, 8.0 Hz),
3.28−3.21 (m, 1 H), 1.58−1.48 (m, 2 H), 1.46−1.29 (m, 20 H), 0.90
(t, 3 H, J = 6.8 Hz); 13C NMR (101 MHz, MeOD) δ 138.3, 128.7,
72.5, 70.4, 59.3, 58.3, 38.3, 33.1, 30.77 (×2), 30.74 (×4), 30.5, 26.5,
23.7, 14.4; IR (neat) 3329, 3096, 2953, 2922, 2853, 1668, 1464, 1456,
1435, 1200, 1186, 1136 cm−1; HRMS (ESI) [M + H]+ calcd for
C18H37NO3 316.2846, found 316.2847. Spectroscopic data was
identical to literature.8
Methyl (R)-2-Hydroxyhexadecanoate (16a). (R,E)-2-Hydrox-
ypent-3-enenitrile 15 (1.95 g, 20.10 mmol, 1 eq, ee >99%) was
dissolved in anhydrous Et2O (25.0 mL) in a flame-dried, three-necked,
round-bottom flask under an argon atmosphere. Anhydrous MeOH
(1.66 mL, 20.98 mmol, 2.0 equiv) was added. This solution was
purged with dry HCl gas (1.47 g, 40.19 mmol, 2 equiv). The acidified
reaction mixture was stored at −20 °C for 20 h under an argon
atmosphere. H2O (10 mL) was added and the mixture stirred for 40
min. The aqueous layer was extracted with EtOAc (3 × 40 mL). The
combined organic layers were washed with NaHCO3 (satd, 40 mL)
and brine, dried over MgSO4, filtrated, and concentrated in vacuo. The
crude product was purified by silica gel chromatography (10% DCM,
10% Et2O in pentane, isocratic) to give methyl (R,E)-2-hydroxypent-3-
enoate as a yellow oil (1.26 g, 9.66 mmol, 48%): Rf = 0.2 (10% DCM,
10% Et2O in pentane); 1H NMR (400 MHz, CDCl3) δ 5.95−5.85 (m,
1 H), 5.58−5.50 (m, 1 H), 4.61 (d, 1 H, J = 6.4 Hz), 3.80 (s, 3 H),
3.20 (br s, 1 H), 1.74 (d, 3 H, J = 6.8 Hz); 13C NMR (101 MHz,
CDCl3) δ 174.3, 129.9, 127.3, 71.5, 52.8, 17.7; IR (neat) 3439, 2922,
2855, 1732, 1445, 1198 cm−1. Spectroscopic data was identical to
literature values.18
32.1, 29.82, 29.80 (×2), 29.76, 29.75, 29.70, 29.5, 25.5, 22.8, 14.3; IR
(neat) 2924, 2853, 1036 cm−1.HRMS (MALDI-TOF) [M + Ag]+
calcd for C22H34O2Ag 437.1610, found 437.1602.
tert-Butyl ((4R,5S)-4-((R,E)-3-Hydroxypentadec-1-en-1-yl)-2-
oxo-1,3-dioxan-5-yl)carbamate (8d). Allylic alcohol 7a (24 mg,
0.11 mmol, 1 equiv) and cyclic carbonate 6b (73 mg, 0.30 mmol, 3
equiv) were combined and coevaporated with toluene in a 50 mL
round-bottom flask. The mixture was dissolved in anhydrous Et2O (0.5
mL) under an argon atmosphere. The solution was stirred briefly
before addition of second-generation Grubbs catalyst (17 mg, 0.02
mmol, 0.2 equiv) and copper(I) iodide (6 mg, 0.03 mmol, 0.3 equiv).
The reaction mixture was stirred at room temperature for 48 h. The
reaction mixture was concentrated in vacuo. The crude product was
purified by silica gel chromatography (20% EtOAc → 25% EtOAc →
30% EtOAc in pentane). The metathesized product 8d was collected
as a brown oil that slowly crystallized (39 mg, 0.088 mmol, 83%): Rf =
1
0.4 (40% EtOAc in pentane); [α]D = +24.4 (c = 1.0, CHCl3); H
F
DOI: 10.1021/acs.joc.5b00823
J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Note
Methyl (R,E)-2-hydroxypent-3-enoate (1.42 g, 10.94 mmol, 1
equiv) was dissolved in anhydrous DCM (6 mL) under an argon
atmosphere in a 250 mL round-bottom flask. 1-Tetradecene (5.55 mL,
21.88 mmol, 2 equiv), acetic acid (63 μL, 1.09 mmol, 0.5 equiv), and
second-generation Grubbs catalyst (93 mg, 0.11 mmol, 0.05 equiv)
were added to the reaction mixture. The reaction mixture was stirred
for 60 h at 50 °C. Afterward, the reaction mixture was concentrated in
vacuo. The crude product was purified by silica gel chromatography
(5% Et2O, 10% DCM → 7.5% Et2O, 10% DCM → 10% Et2O, 10%
DCM in pentane). The metathesized product methyl (R,E)-2-
hydroxyhexadec-3-enoate was collected as a brown oil (2.27 g, 7.99
(MALDI-TOF) [M + Ag]+ calcd for C18H34O4Ag 421.1508, found
421.1516. Spectroscopic data was identical to literature values.23
(R)-1-Oxo-1-(((2S,3R,6R,E)-1,3,6-trihydroxyoctadec-4-en-2-
yl)amino)hexadecan-2-yl Acetate (17). 6-Hydroxysphingosine (1)
(11 mg, 0.035 mmol, 1 equiv) and carboxylic acid 16c (14 mg, 0.045
mmol, 1.3 equiv) were dissolved in anhydrous EtOH (1.5 mL) under
an argon atmosphere. 2-Ethoxy-1-(ethoxycarbonyl)-1,2-dihydroquino-
line (17 mg, 0.069 mmol, 2 equiv) was added, and the reaction mixture
was stirred for 20 h at 50 °C. The reaction mixture was concentrated
in vacuo and purified by silica gel chromatography (0% → 1% → 3%
MeOH in CHCl3). Acetylated ceramide 17 was collected as a waxy
white solid (14 mg, 0.023 mmol, 66%): Rf = 0.3 (5% MeOH in
1
mmol, 73%): Rf = 0.2 (10% Et2O, 10% DCM in pentane); H NMR
1
CHCl3); H NMR (400 MHz, CDCl3) δ 6.76 (d, 1 H, J = 8.0 Hz,),
(400 MHz, CDCl3) δ 5.88 (dt, 1 H, J = 14.4, 6.8 Hz), 5.50 (dd, 1 H, J
= 15.2, 6.0 Hz), 4.61 (t, 1 H, J = 4.4 Hz), 3.80 (s, 3 H), 2.80 (br s, 1
H), 2.06 (q, 2 H, J = 6.8 Hz), 1.45−1.35 (m, 2 H), 1.35−1.26 (m, 18
H), 0.88 (t, 3 H, J = 6.8 Hz); 13C NMR (101 MHz, CDCl3) δ 174.4,
135.3, 126.0, 71.6, 52.9, 32.3, 32.1, 29.82, 29.80, 29.79, 29.75, 29.6,
29.5, 29.3, 29.0, 22.8, 14.3; IR (neat) 3458, 2922, 2853, 1713, 1466
cm−1.
5.84 (dd, 1 H, J = 15.6, 6.4 Hz), 5.73 (dd, 1 H, J = 15.6, 5.6 Hz), 4.99
(t, 1 H, J = 6.4 Hz), 4.37 (t, 1 H, J = 4.8 Hz), 4.13 (q, 1 H, J = 6.4 Hz),
3.97 (dd, 1 H, J = 11.2, 3.2 Hz), 3.92−3.86 (m, 1 H), 3.69 (dd, 1 H, J
= 11.2, 3.6 Hz), 3.24 (br s, 1 H), 2.86 (br s, 1 H), 2.16 (s, 3 H), 1.88−
1.78 (m, 2 H), 1.56−1.47 (m, 2 H), 1.37−1.26 (m, 44 H), 0.88 (t, 6
H, J = 6.8 Hz); 13C NMR (101 MHz, CDCl3) δ 170.9, 170.8, 136.3,
129.5, 74.8, 73.6, 72.2, 61.9, 54.2, 37.3, 32.1, 32.0, 29.85−29.81 (m,
×12), 29.73 (×2), 29.6, 29.5 (×2), 29.4, 25.6, 25.2, 22.8, 21.1, 14.3;
HRMS (ESI) [M + Na]+ calcd for C36H69NO6Na 634.5017, found
634.5011.
Ceramide (2). Acetylated ceramide 17 (11 mg, 0.018 mmol, 1
equiv) was dissolved in DCM/MeOH (4:1, 0.2 mL) under an argon
atmosphere. Potassium carbonate (catalytic amount) was added, and
the reaction mixture was stirred for 2 h at room temperature. The
reaction mixture was acidified by addition of Amberlyst IR120,
followed by filtration and concentration in vacuo. The crude product
was purified by silica gel chromatography (0% → 1% → 5% MeOH in
CHCl3) giving ceramide (2) as a white solid (9 mg, 0.016 mmol,
88%): Rf = 0.5 (10% MeOH in CHCl3); 1H NMR (850 MHz, CDCl3/
MeOD, 9:1) δ 7.42 (d, 1 H, J = 8.5 Hz), 5.77 (dd, 1 H, J = 15.3, 6.0
Hz), 5.66 (dd, 1 H, J = 15.3, 6.0 Hz), 4.23 (t, 1 H, J = 5.1 Hz), 4.08−
4.05 (m, 1 H), 4.03 (dd, 1 H, J = 8.5, 3.4 Hz), 3.87−3.83 (m, 1 H),
3.81 (dd, 1 H, J = 12.0, 4.3 Hz), 3.69 (dd, 1 H, J = 11.9, 2.6 Hz), 2.35−
2.28 (m, 1 H), 2.09−2.04 (m, 1H), 2.03−1.98 (m, 1 H), 1.80 (m, 1
H), 1.58−1.44 (m, 4 H), 1.41−1.26 (m, 44 H), 0.88 (t, 6 H, J = 6.8
Hz); 13C NMR (214 MHz, CDCl3/MeOD, 9:1) δ 176.2, 135.8, 129.2,
72.6, 72.2, 71.8, 61.5, 54.6, 37.1, 34.4, 32.0, 29.75, 29.73 (×2), 29.72
(×2), 29.71 (×2), 29.70 (×2), 29.68 (×2), 29.66, 29.63, 29.5, 29.4
(×2), 25.6, 22.7, 14.1; IR (neat) 3377, 3264, 2953, 2916, 2849, 1738,
1715, 1651, 1620, 1470, 1074, 1043 cm−1; HRMS (ESI) [M + H]+
calcd for C34H68NO5 570.5092, found 570.5087.
Methyl (R,E)-2-hydroxyhexadec-3-enoate (1.16 g, 4.08 mmol, 1
equiv) was dissolved in EtOAc (40 mL) under an argon atmosphere.
The solution was purged with argon followed by addition of palladium
on carbon (10% loading, 22 mg, 0.2 mmol, 0.05 equiv). The mixture
was then stirred for 30 min under a flow of hydrogen gas and was then
left for 60 h under a hydrogen atmosphere. The mixture was filtered
over a pad of Celite and concentrated in vacuo to give the crude
product 16a as a solid (1.07 g, 3.72 mmol, 91%): Rf = 0.2 (10% Et2O,
10% DCM in pentane); 1H NMR (400 MHz, CDCl3) δ 4.19 (dd, 1 H,
J = 7.2, 4.4 Hz), 3.79 (s, 3 H), 2.69 (br s, 1 H), 1.85−1.76 (m, 1 H),
1.68−1.58 (m, 1 H), 1.54−1.25 (m, 24 H), 0.88 (t, 3 H, J = 6.8 Hz);
13C NMR (101 MHz, CDCl3) δ 176.0, 70.6, 52.6, 34.6, 32.1, 29.84,
29.83, 29.81 (×2), 29.78, 29.70, 29.6, 29.51, 29.45, 24.9, 22.9, 14.3; IR
(neat) 3462, 2920, 2853, 1736, 1460, 1215 cm−1; HRMS (MALDI-
TOF) [M + Ag]+ calcd for C17H34O3Ag 393.1559, found 393.1572.
α-Hydroxy Fatty Acid (16b). Methyl ester 16a (926 mg, 3.23
mmol, 1 equiv) was dissolved in THF/MeOH/H2O (2:2:1, 30 mL) at
room temperature. Lithium hydroxide monohydrate (420 mg, 10.0
mmol, 3.1 equiv) was added, and the reaction mixture was stirred for
20 h at room temperature. The reaction mixture was quenched by HCl
(1 M, 15 mL). The aqueous mixture was extracted with EtOAc (3 ×
75 mL). The combined organic layers were washed with H2O (100
mL) and brine, dried over MgSO4, filtrated, and concentrated in
vacuo. The crude α-hydroxy fatty acid 16b was collected as a solid
(873 mg, 3.20 mmol, 99%) and was used for the next step without
further purification: Rf = 0.1 (30% EtOAc in pentane); 1H NMR (400
MHz, CDCl3) δ 4.28 (dd, 1 H, J = 7.6, 4.4 Hz), 1.91−1.81 (m, 1 H),
1.75−1.65 (m, 1 H), 1.52−1.42 (m, 2 H), 1.38−1.26 (m, 22 H), 0.88
(t, 3 H, J = 6.8 Hz); 13C NMR (101 MHz, CDCl3) δ 179.4, 70.4, 34.4,
32.1, 29.84 (×2), 29.81 (×2), 29.79, 29.71, 29.6, 29.5, 29.4, 24.9, 22.9,
14.3; IR (neat) 3445, 2920, 2851, 1732, 1466 cm−1. Spectroscopic data
was identical to literature values.23
ASSOCIATED CONTENT
■
S
* Supporting Information
1H NMR and 13C NMR spectra of all new compounds. The
Supporting Information is available free of charge on the ACS
Publications website at DOI: 10.1021/acs.joc.5b00823.
(R)-2-Acetoxyhexadecanoic Acid (16c). The crude α-hydroxy
fatty acid 16b (808 mg, 2.97 mmol, 1 equiv) was dissolved in
anhydrous DCM (30 mL) under an argon atmosphere at room
temperature. Acetic anhydride (4.49 mL, 47.45 mmol, 16 equiv) and
pyridine (7.45 mL, 92.15 mmol, 31 equiv) were added, and the
reaction mixture was stirred for 20 h. The reaction was quenched by
addition of NaHCO3 (satd, 50 mL). The aqueous layer was extracted
with CHCl3 (2 × 50 mL). The combined organic layers were washed
with KHSO4 (0.5 M, 75 mL), dried over MgSO4, filtrated, and
concentrated in vacuo. The acetylated product 16c was collected as a
yellow solid (905 mg, 2.88 mmol, 97%) which was used for the next
step without further purification: Rf = 0.2 (30% EtOAc in pentane);
AUTHOR INFORMATION
■
Corresponding Authors
*E-mail: jcodee@chem.leidenuniv.nl.
*E-mail: h.s.overkleeft@chem.leidenuniv.nl.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The Netherlands Organization for Scientific Research (NWO-
CW, Top grant to H.S.O. and J.M.F.G.A.) and the European
Research Council (ERC AdG, to H.S.O.) are acknowledged for
financial support.
1
[α]D = +9.0 (c = 1.0, CHCl3); H NMR (400 MHz, CDCl3) δ 10.61
(br s, 1 H), 5.00 (t, 1 H, J = 6.4 Hz), 2.14 (s, 3 H), 1.91−1.82 (m, 2
H), 1.46−1.38 (m, 2 H), 1.37−1.26 (m, 22 H), 0.88 (t, 3 H, J = 6.8
Hz); 13C NMR (101 MHz, CDCl3) δ 176.0, 170.8, 72.0, 32.1, 31.1,
29.83 (×2), 29.80 (×2), 29.76, 29.68, 29.51, 29.49, 29.3, 25.3, 22.9,
20.7, 14.3; IR (neat) 2955, 2916, 2849, 1742, 1722, 1228 cm−1. HRMS
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DOI: 10.1021/acs.joc.5b00823
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