Synthesis of enantiomerically pure (Z)-(2′R)-1-O-(2′- methoxyhexadec-4′-enyl)-sn-glycerol present in the liver oil of cartilaginous fish

Article abstract of DOI:10.1016/j.tetasy.2010.10.033

Synthesis of enantiopure (Z)-(2′R)-1-O-(2′-methoxyhexadec- 4′-enyl)-sn-glycerol 1, the principal methoxylated glyceryl ether found in Nature, is described by a highly convergent five-step process taking place in 27% overall yield. The synthesis is based on an ether bond formation between the chiral synthon (R)-2,3-O-isopropylidene-sn-glycerol and (Z)-(R)-1- chlorohexadec-4-en-2-ol employing ground potassium hydroxide and tetra-n-butylammonium bromide as a catalyst under solvent free conditions.

Full text of DOI:10.1016/j.tetasy.2010.10.033

Tetrahedron: Asymmetry 21 (2010) 2841–2847
Contents lists available at ScienceDirect
Tetrahedron: Asymmetry
journal homepage: www.elsevier.com/locate/tetasy
Synthesis of enantiomerically pure (Z)-(20R)-1-O-(20-methoxyhexadec-
40-enyl)-sn-glycerol present in the liver oil of cartilaginous fish
Carlos D. Magnusson a, Gudmundur G. Haraldsson a,
a Science Institute, University of Iceland, Dunhaga 3, 107 Reykjavik, Iceland
⇑
a r t i c l e i n f o
a b s t r a c t
Synthesis of enantiopure (Z)-(20R)-1-O-(20-methoxyhexadec-40-enyl)-sn-glycerol 1, the principal meth-
oxylated glyceryl ether found in Nature, is described by a highly convergent five-step process taking place
in 27% overall yield. The synthesis is based on an ether bond formation between the chiral synthon (R)-
2,3-O-isopropylidene-sn-glycerol and (Z)-(R)-1-chlorohexadec-4-en-2-ol employing ground potassium
hydroxide and tetra-n-butylammonium bromide as a catalyst under solvent free conditions.
Ó 2010 Elsevier Ltd. All rights reserved.
Article history:
Received 20 October 2010
Accepted 28 October 2010
Available online 23 December 2010
1. Introduction
rated ranging from C14 to C22. The monounsaturated analogs are
characterized by constituting a
D A
4 Z-configured double bond.9,13
Methoxylated lipids have gained considerable attention from the
medical science point of view due to their antibacterial, antifungal,
antiviral, and antitumor properties.1 The naturally occurring meth-
oxylated lipids bearing a methoxyl group at the alkyl chain can be di-
vided into two groups of compounds, that is, the methoxylated fatty
acids and the methoxyl substituted alkylglycerols. Hitherto, the only
methoxylated alkylglycerols known are those of the 1-O-(20-meth-
oxyalkyl)-sn-glycerol type. They are a particular category of 1-O-al-
kyl-sn-glycerols, characterizedbybearingamethoxylgroupatthe2-
position of their 1-O-alkyl moiety.
The 1-O-alkyl-sn-glycerols, also known as glyceryl ethers, are
widely found in Nature, but in especially high amounts in the liver
oilofvariouscartilaginous fishincludingsharkspecies.2,3 Inhumans,
they are widely found in various tissues, usually as minor lipid com-
ponents.4 Theglycerylethersare biologically activecompoundscon-
sidered to have high therapeutic potential.5,6 These properties are
mutually related to their chemical structure, serving as essential
precursors of platelet activating factors (PAF) and plasmalogens.7–9
In the crude liver oil of some cartilaginous fish they are present in
their diacylated form and commonly constitute about 25% of the
oil.3,10,11 The methoxylated alkylglycerols have been found to make
up 2–4% of the glyceryl ether content of such oils.12,13 Their occur-
rence in mammals and especially in humans has also been demon-
strated but only in trace quantities.14
peculiar polyunsaturated derivative, an all cis-(20R)-1-O-(20-meth-
oxydocosa-40,70,100,130,160,190-hexaenyl)-sn-glycerol, first discov-
ered by Hallgren et al.,16 is present in appreciable amounts in the
liver oil of cartilaginous fish.13
The principal 1-O-(20-methoxyalkyl)-sn-glycerols found in Nat
ure are the monounsaturated (Z)-(20R)-1-O-(20-methoxyhexadec-
40-enyl)-sn-glycerol 1, its bis-homo (Z)-(20R)-1-O-(20-methoxyocta-
dec-40-enyl)-sn-glycerol congener, and the saturated (20R)-1-O-(20-
methoxyhexadecyl)-sn-glycerol 2. The first one is by far the most
abundant methoxylated alkylglycerol derivative found in the liver
oil of cartilaginous fish. These derivatives are the same as those
first reported in the pioneering work of Hallgren and Stallberg.9
Methoxyl substituted glyceryl ethers have been shown to pos-
sess antibacterial17 and antifungal18 activities, and to inhibit some
cancer cell lines19,20 and metastasis formation in mice.17,18
OH
OH
O
4´
OMe
1
OH
Structurally, 1-O-(20-methoxyalkyl)-sn-glycerols contain a long
alkyl chain situated at the sn-1 position of the glycerol moiety via
an O-ether linkage, implying an (S)-configuration for the stereogenic
center at the glycerol backbone. The second chiral center located at
the 2-position of the O-alkyl chain possessing the methoxyl group
displays an (R)-absolute configuration.15 In general, the alkyl chain
components may be saturated, monounsaturated, or polyunsatu-
OH
O
OMe
2
Furthermore, several studies have demonstrated their immune
stimulating properties in mice.21 A deeper look into these studies
shows that in most cases, mixtures of methoxylated alkylglycerols,
⇑
Corresponding author. Tel.: +354 525 4818; fax: +354 552 8911.
E-mail address: gghar@hi.is (G.G. Haraldsson).
0957-4166/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2010.10.033

2842
C. D. Magnusson, G. G. Haraldsson / Tetrahedron: Asymmetry 21 (2010) 2841–2847
isolated from shark liver oil, or synthetic stereoisomeric mixtures
of 1-O-(20-methoxyhexadecyl)glycerol, or (Z)-1-O-(20-methoxy-
hexadec-4-enyl)glycerol were utilized.17–21 At the same time only
few studies have been carried out on pure individual compounds
possessing the natural configuration. Presumably, this is due to
the low concentrations of methoxylated alkylglycerols present in
shark liver oil and the tedious isolation methods needed for their
separation into singular compounds. Therefore, the development
of new routes to synthesize enantiomerically pure methoxylated
alkylglycerols in the laboratory setting is a tempting option to sup-
ply such valuable natural compounds.
preparation is via an ether synthesis between a chiral 2,3-O-isopro-
pylidene-sn-glycerol, (R)-solketal, and the corresponding long-
chain primary alkyl halides or sulfonates.25,26
Hallgren and Stallberg13 reported the first synthesis of the
methoxylated alkylglycerol 1-O-(20-methoxyhexadecyl)glycerol 2
as a racemic mixture of diastereomers. The key step of their syn-
thetic route involved a coupling of the potassium salt of racemic
solketal with racemic tosylate of 2-methoxyhexadecan-1-ol in
45% yield. Following a similar methodology, Stallberg27 synthe-
sized the monounsaturated 20-methoxylated alkylglycerol (Z)-1-
O-(20-methoxyhexadec-40-enyl)glycerol 1 also obtained as a mix-
ture of four stereoisomers. More recently, Stallberg15 performed
the first synthesis of the naturally occurring (20R)-1-O-(20-meth-
oxyhexadecyl)-sn-glycerol 2 enantiomerically pure. The key step,
taking place in 60% yield, involved an ether formation between
(R)-solketal and (R)-2-methoxyhexadecyl p-toluenesulfonate in
the presence of powdered potassium hydroxide and solvent.
The task of the current synthesis of enantiopure (Z)-1-O-(20-
methoxyhexadec-40-enyl)-sn-glycerol 1 involves preparing a target
molecule possessing two stereogenic centers and a Z-configured
carbon–carbon double bond. To address that goal and searching
for a new efficient synthetic plan the retrosynthetic analysis shown
in Scheme 1 was proposed.
Stallberg reported on the synthesis of enantiopure (20R)-1-O-
(methoxyhexadecyl)-sn-glycerol 2 in 1990.15 Herein, we report
the first synthesis of enantiomerically pure (Z)-(20R)-1-O-(20-meth-
oxyhexadec-40-enyl)-sn-glycerol 1 by a highly convergent five step
synthesis, that is, based on ether bond formation between the chi-
ral synthon (R)-2,3-O-isopropylidene-sn-glycerol and (Z)-(R)-1-
chlorohexadec-4-en-2-ol 5.
2. Results and discussion
Although the structure of the principal unsubstituted 1-O-alkyl-
sn-glycerols has been known since the early 1920s, it was not until
the late 1960s that the first methoxylated alkylglycerols were iso-
lated and their structures elucidated by Hallgren and Stallberg13
when working with 1-O-alkyl-sn-glycerols from the unsaponifiable
matter of Greenland shark (Somniousus microcephalus) liver oil.
They found that the mixture of methoxylated alkylglycerols made
up to 4% of the glyceryl ether content. Likewise, Hayashi and Tak-
agi12 have reported the methoxyl substituted alkylglycerol content
in three shark species and three ratfish species where they ac-
counted for 0.1% to 0.3% of the total liver lipid content. Similar per-
centages have been reported in several other aquatic animals,
ranging from 0.01% to 0.17% in the non-polar lipids and from
0.06% to 0.47% in the phospholipids.22 More recently, methoxylat-
ed alkylglycerols have been isolated from the brachiopod Gryphus
vitreus23 and from the marine sponge Spirastrella abata.24
The retrosynthetic approach was started with a disconnection of
the methyl group from the methoxyl ether moiety of the acetonide
protected target molecule 3. This implies a late-stage incorporation
of the methoxyl group by methylation of the hydroxyl group in alco-
hol adduct 4. Then, considering previous strategies in the synthesis
of regular and substituted glyceryl ethers, the proposed synthetic
strategy involves the disconnection of the main ether function at
the O-alkyl site of 4. This indicates a coupling between 2,3-O-isopro-
pylidene-sn-glycerolandthefunctionalized compound5. TheZ-con-
figured double bond in 5 is easily obtained by partial hydrogenation
of the corresponding triple bond in 6 with a Lindlar catalyst. Com-
pound 6 contains three functional groups closely situated and may
be constructed by a highly regioselective oxirane ring-opening of
(R)-epichlorohydrinwiththelithiumsaltof1-tridecyne. Inthisman-
ner, the target molecule 1 is disconnected down to three commer-
cially available compounds, including two enantiopure C3-
synthons, offering a synthesis composed of five steps.
Previous studies on the synthesis of unsubstituted 1-O-alkyl-sn-
glycerols have established that the most suitable route for their
OH
O
O
O
O
OH
C11H23
C
11H23
C
11H23
O
O
O
OH
OMe
OMe
3
1
4
O
C
11H23
O
Cl
(R)
OH
+
OH
5
(R)
Cl
Cl
+
H
C11H23
O
OH
C11H23
6
Scheme 1.

C. D. Magnusson, G. G. Haraldsson / Tetrahedron: Asymmetry 21 (2010) 2841–2847
2843
Cl
BF3.ET2O,
C11H23
O
Cl
Cl
n-ButLi
Lindlar catalyst
H2, 1 atm, 25°C
+
OH
OH
C11H23
-78°C, THF
H
C11H23
5
6
50%
O
O
O
Ag2O, MeI
TBAB, KOH
25°C
O
25°C, toluene
C11H23
C11H23
O
O
O
O
OMe
OH
4
3
OH
Amberlyst 15,
EtOH (96%),
reflux
OH
OH
O
C
11H23
OMe
1
Scheme 2.
The execution of the proposed synthetic plan is shown in
Scheme 2 and was started with the regioselective opening of the
epoxide ring in (R)-epichlorohydrin with tridec-1-ynyllithium in
the presence of boron trifluoride etherate according to a method
developed by Yamaguchi and Hirao.28 This afforded (R)-1-chloro-
hexadec-4-yn-2-ol 6 in 50% yields and 98% ee as was established
by 1H NMR analysis of its Mosher ester derivative. In this step
BF3 plays a crucial role by activating the epoxide ring thus directing
the nucleophilic attack of the organolithium adduct exclusively to
the less substituted carbon in the oxirane ring rather than the
methylene group possessing the chloride group. That would result
in an inversion of the desired configuration of the initial
epichlorohydrin.
Such regioselective control is thought to be induced by boron
trifluoride coordination to the oxirane oxygen resulting in the for-
mation of an alkoxyboron trifluoride salt following the nucleo-
philic attack29 (Scheme 3). In the absence of such coordination,
the liberated alkoxide anion could substitute the chlorine atom,
hence forming a new epoxide that in turn may undergo a second
attack of the organolithium nucleophile.
thought to be caused by a low cation–anion interaction energy in-
duced by the large TBA cation rendering the alkoxide anion with
higher nucleophilicity.30 There is evidence from the 1H NMR investi-
gations that 8 was produced slowly as an intermediate and con-
verted to 4 during the 52 h reaction time at room temperature.
Under these reaction conditions, however, formation of the elimina-
tion side-product, hexadec-2,4-dien-1-ol 9, was greatly diminished
compared to what occurred with other attempted approaches and is
described in the discussion below.
Three other compounds closely related to 5 were screened for
the ether synthesis coupling reaction with (R)-solketal under vari-
ous reaction conditions (Scheme 5). For instance, employment of
the methoxylated chloroalkyne, 1-chloro-2-methoxyhexadec-4-
yne 10, gave no reaction product when reacted with the solketal.
All attempts to couple the protected glycerol with adduct 10 were
unsuccessful, although a variety of conditions were screened,
including sodium or sodium hydride in THF or DMSO and pulver-
ized potassium hydroxide with TBAB under solvent free conditions.
The closer proximity of the methoxyl group to the chloride was
thought to induce some steric effects on nucleophilic attack of the
alkoxide. On the other hand, the coupling of (R)-solketal with chlo-
roalkynol 6 and its corresponding epoxide derivative, 1,2-epoxy-
hexadec-4-yne 11, in the presence of ground potassium hydroxide
and TBAB at 30–40 °C furnished the desired coupling adduct, but in
low yields, mainly due to the production of high amounts of the
elimination side-product hexadec-2-en-4-yn-1-ol 7 as a 1:1 mix-
ture of E- and Z-isomers. The presence of 7 strongly indicates its
formation via 11, the epoxide form of 6, although it was not de-
tected during the progress of the reaction involving chloroalkynol
6, unlike that which was observed during the coupling reaction
of chlorohydrin 5.
Alternatively, such an epoxide may undergo a base promoted
elimination to form hexadec-2-en-4-yn-1-ol 7. Subsequent hydro-
genation of 6 over a Lindlar catalyst afforded the chloroalkenol 5 in
96% yield.
The coupling of (R)-solketal with 5 was performed using freshly
ground potassium hydroxide in the presence of a catalytic amount
of tetra-n-butylammonium bromide (TBAB) under solvent free con-
dition at room temperature, affording the highly functionalized key
adduct 4 in 62% yield. Scheme4 shows a plausiblemechanismfor the
reaction where TBAB plays a dual function, as a phase-transfer agent
and as a catalyst. TBAB exchanges its bromide anion for the hydrox-
ide anion, which is transferred from the solid phase to the organic
phase. Then, the hydroxide ion deprotonates the hydroxyl groups
of 5 and the solketal, forming epoxide 8, and presumably, a tetra-
n-butylammonium (TBA) isopropylideneglyceroxide salt, respec-
tively. The high reactivity of the ammonium-alkoxide ion-pair is
The hydroxyl group in 4 was smoothly methylated by taking
advantage of silver oxide and methyl iodide in a toluene suspen-
sion containing molecular sieves at room temperature. The mild
reaction conditions employed triggered complete methylation
without any deterioration of the closely situated Z-configured

2844
C. D. Magnusson, G. G. Haraldsson / Tetrahedron: Asymmetry 21 (2010) 2841–2847
cation was needed and 3 was afforded in excellent yields (93%) and
Cl
high purity as indicated by 1H and 13C NMR analysis.
O
Finally, the isopropylidene moiety in 3 was cleaved under mild
reaction condition employing AmberlystÒ 15, an ion exchanger, in
96% ethanol at gentle reflux.31 Again, under these conditions, the Z-
configured double bond in 1 remained stable as was confirmed by
1H NMR spectroscopy. Isolation of the final product 1 was accom-
plished by simple filtration of the ion exchanger, followed by re-
moval of the solvents, affording 1 in 99% yield and 27% overall
yield from (R)-epichlorohydrin. The structure of 1 was confirmed
by 1H and 13C NMR analysis and two dimensional 1H–1H COSY
and HETCOR correlation analysis.
+
H
C11H23
BF3.ET2O,
n-ButLi, -78°C, THF
Cl
Cl
Li
O
C11H23
O
BF3Li
BF3
Table 1
1H NMR data of compound 1
C11H23
Position
Compound 1a
Compound 1b
1H (ppm)
1H (ppm)
H2O
sn-3
3.71 (dd, 1H, J = 11.4, 3.9)
3.65 (dd, 1H, J = 11.4, 5.2)
3.86 (m, 1H)
3.62 (dd, 1H, J = 10.1, 3.6)
3.55 (dd, 1H, J = 10.1, 6.2)
3.57 (dd, 1H, J = 10.5, 3.6)
3.48 (dd, 1H, J = 10.5, 6.0)
3.33 (m, 1H)
1.47 (m, 2H)
1.26 (m, 24H)
0.88 (t, 3H)
3.40 (s, 3H)
3.69 (dd, J = 11.5, 3.9)
3.63 (dd, J = 11.5, 5.2)
3.85 (m, 1H)
3.61 (dd, 1H, J = 10.0, 3.8)
3.53 (dd, 1H, J = 9.9, 6.2)
3.56 (dd, 1H, J = 10.3, 3.6)
3.47 (dd, 1H, J = 10.5, 6.0)
3.32 (m, 1H)
1.47 (m, 2H)
1.25 (m, 24H)
0.87 (t, 3H, J = 6.9)
3.39 (s, 3H)
sn-2
sn-1
6
Scheme 3.
10
20
30
40 to 150
O
160
C11H23
OCH3
O
Cl
a
From the literature;15 measured at 125 MHz in CDCl3; J = Hz.
Prepared by hydrogenation of 2; measured at 400 MHz in CDCl3–D2O (7:0.1);
OH
+
b
OH
5
J = Hz.
TBAB, KOH
25°C
The fact that no loss of chirality was observed for adduct 6 (98%
ee) nor any degradation of the isopropylidene protective moiety
was detected throughout the total synthesis, strongly implies a
high enantiopurity of the final product 1. Examination of the 1H
NMR spectrum (400 MHz) of the saturated 2 that was prepared
from 1 by hydrogenation revealed its excellent agreement with
that of 2 found in the literature (125 MHz)15 as may be seen from
Table 1, which shows the details of the comparison.
O
O
C11H23
O
O
N
8
Table 2
Comparison of optical activity data for 1 and 2
Compound
1a
1b
2c
2d
[a
]
D
ꢀ3.0
ꢀ3.0
ꢀ12.5
ꢀ12.0
4
a
b
c
c 0.89, CHCl3, 20 °C; obtained from the hydrogenation of 2.
c 1.3, CHCl3, 20 °C; from the literature.15
Scheme 4.
c 0.84, CHCl3, 20 °C; prepared by the presented approach.
d
c 1.3, CHCl3, 25 °C; from the literature.27
Although some minor differences can be noticed in Table 1, they
C
11H23
are presumably due to the solvent and the concentration differ-
ences under which the measurements were performed. Further-
more, comparison of specific rotation data of 1 and 2 with the
corresponding data from the literature, firmly establishes the abso-
lute configuration of the stereogenic centers in compound 1 as can
be noticed from Table 2.
HO
Cl
HO
C
11H23
7
9
O
OMe
10
C11H23
C11H23
3. Conclusion
11
The most abundant methoxylated alkylglycerol present in the
liver oil of cartilaginous fish, (Z)-(20R)-1-O-(20-methoxyhexadec-
40-enyl)-sn-glycerol 1, has been synthesized in enantiomerically
pure form by a highly convergent chemical route. It is anticipated
that the facile and efficient synthetic approach described herein
will prompt scientists to investigate further on the biological prop-
erties of this intriguing compound.
Scheme 5.
double bond as was evidenced from the 1H NMR spectrum of 3. The
simple separation of 3 from the reaction mixture consisted of a
rapid flush of the reaction suspension through silica gel packed in-
side a Pasteur pipette eluting with diethyl ether. No further purifi-

C. D. Magnusson, G. G. Haraldsson / Tetrahedron: Asymmetry 21 (2010) 2841–2847
2845
(C„C), 74.30 (C„C), 69.98, 48.31, 31.90, 29.61 (2), 29.52, 29.33,
29.11, 28.88, 28.86, 24.70, 22.67, 18.69, 14.10 ppm.
4. Experimental
4.1. General
4.1.2. Synthesis of (Z)-(R)-1-chlorohexadec-4-en-2-ol 5
1H and 13C nuclear magnetic resonance spectra were recorded on
a Bruker Avance 400 spectrometer in deuterated chloroform as a
solvent, unless otherwise stated, at 400.12 and 100.61 MHz, respec-
tively. Chemical shifts (d) are quoted in parts per million (ppm) and
the coupling constants (J) in hertz (Hz). The following abbreviations
are used to describe the multiplicity: s, singlet; d, doublet; t, triplet;
dd, doublet of doublets; ddt, doublet of doublets of triplets; m, mul-
tiplet. The number of carbon nuclei behind each 13C signal is indi-
cated in parentheses after each chemical shift value, when there is
more than one carbon responsible for the peak. All Infrared spectra
were conducted on a Nicolet Avatar 360 FT-IR (E.S.P.) Spectropho-
tometer on a ZnSe plate. The optical activities were measured on
an Autopol V from Rudolph Research Analytical, New Jersey USA.
Melting points were determined on a Büchi 520 melting point appa-
ratus and are uncorrected. The high-resolution mass spectra (HRMS)
To
a solution of (R)-1-chlorohexadec-4-yn-2-ol 6 (1.6 g,
5.87 mmol) and quinoline (59 mg, 0.458 mmol) in dry petroleum
ether (100 ml), Lindlar catalyst (169 mg) was added. The resulting
suspension was placed in a PARR reactor under hydrogen pressure
(1 atm) and stirred for 50 min at room temperature. The reaction
mixture was filtered over a pad of Celite, flushed with dichloro-
methane, and concentrated. Further purification was accomplished
by silica gel column chromatography with gradient elution, diethyl
ether/petroleum ether (10:90), and pure diethyl ether, affording
the product 5 as a clear oil (1.56 g, 96% yield). ½a D20
¼ þ2:0 (c
ꢂ
1.00, ethanol); IR(ZnSe) 3372 (O–H), 3010 (@C–H cis), 2922 (C–
H), 1656 (C@C) cmꢀ1; HRMS (ESI): m/z calcd for C16H31OCl + Li:
281.2218; found 281.2205 amu. 1H NMR (400 MHz, CDCl3): d
5.58 (m, 1H, @CH), 5.37 (m, 1H, @CH), 3.85 (ddd, J = 13.5, 6.5,
3.7 Hz, 1H, CH2CHCH2), 3.64 (dd, J = 11.1, 3.7 Hz, 1H, CH2Cl), 3.51
(dd, J = 11.1, 6.6 Hz, 1H, CH2Cl), 2.35 (t, J = 7.2 Hz, 2H, CHCH2C@),
2.19–1.90 (br s, 1H, CHOH), 2.05 (quartet (br), J = 6.8 Hz, 2H,
@CCH2), 1.39–1.32 (m, 2H, @CCH2CH2), 1.32–1.19 (m, 16H, CH2),
0.88 (br t, J = 6.9 Hz, 3H, CH3) ppm; 13C NMR (100 MHz, CDCl3) d
134.13 (C@C), 123.36 (C@C), 71.20 (CH2CHCH2), 49.60 (CH2Cl),
32.23 (CHCH2CH@), 31.91, 29.65, 29.63, 29.61, 29.55, 29.51,
29.34, 29.30, 27.42 (@CCH2), 22.68, 14.11 (CH3) ppm.
were acquired on
a Bruker micrOTOF-Q mass spectrometer
equipped with an atmospheric pressure chemical ionization cham-
ber (APCI) or an E-spray atmospheric pressure ionization chamber
(ESI). All data analysis was done on Bruker software.
All chemicals and solvents were used without further purifica-
tion unless otherwise stated. (R)-2,3-O-Isopropylidene-sn-glycerol
(98%, 99% ee), (R)-epichlorohydrin (99%, 98% ee), (S)-epichlorohy-
drin (98%, 97% ee), n-butyllithium solution (2.0 M in cyclohexane),
quinoline (98%), and all the solvents (HPLC grade) were purchased
from Sigma-Aldrich (Steinheim, Germany). Tetra-n-butylammo-
4.1.3. Synthesis of (Z)-(20R)-1-O-(20-hydroxyhexadec-40-enyl)-
2,3-O-isopropylidene-sn-glycerol 4
To a mixture of (Z)-(R)-1-chlorohexadec-4-en-2-ol 5 (1.0 g,
3.64 mmol), (R)-2,3-O-isopropylidene-sn-glycerol (480 mg, 3.64
mmol) and tetra-n-butylammonium bromide (242 mg, 0.728
mmol), freshly pulverized potassium hydroxide (408 mg, 7.28
mmol) was added and the resulting slurry mixture stirred at room
temperature for 52 h. Then, water and diethyl ether were added to
the reaction mixture, after which the organic phase was separated,
washed three times with water, and once with a brine solution.
After evaporation of the solvent, the resulting crude residue was
applied to a silica gel column with gradient elution, diethyl
ether/petroleum ether (60:40 and 40:60), affording the product 4
nium bromide (P99.0%), (R)-a-methoxy-a-(trifluoromethyl)phen-
ylacetyl chloride (P99.0%, enantiomeric ratio: P99.5:0.5),
Amberlyst 15, and Lindlar catalyst were obtained from Fluka (Buc-
hs, Switzerland) and silver(I) oxide from Fischer Scientific UK. Bor-
on trifluoride etherate (ꢁ50%), methyl iodide (99%), activated
palladium (10% Pd), and potassium hydroxide were purchased
from Merck (München or Darmstad, Germany). Molecular sieves
4 Å were obtained from Acros Organics (Geel, Belgium), 1-tride-
cyne (>99.0%) from GFS Chemicals (Ohio, USA) and preparative
TLC plates (250 lm, F-254) from Silicycle (Quebec, Canada).
as a clear oil (1.34 g, 62% yield). ½a D20
¼ ꢀ5:7 (c 0.86, ethanol);
ꢂ
4.1.1. Synthesis of (R)-1-chlorohexadec-4-yn-2-ol 6
IR(ZnSe) 3461 (O–H), 2923 (C–H), 1656 (C@C), 1123 and 1054
To a solution of 1-tridecyne (2.16 g, 11.98 mmol) in freshly dis-
tilled tetrahydrofuran (60 ml) under a nitrogen atmosphere, n-
butyllithium (2.0 M) in cyclohexane (6 ml, 12 mmol) was added
at ꢀ78 °C and the resulting solution stirred for 20 min. Subse-
quently, boron trifluoride etherate (1.6 ml, 12.7 mmol) was added
to the solution and stirred vigorously for 15 min at ꢀ78 °C. Then,
(R)-epichlorohydrin (1.11 g, 12.0 mmol) was added, after which
the solution was stirred for 3 h at ꢀ78 °C, and finally left to reach
room temperature. The reaction was quenched with water, treated
with saturated ammonium chloride solution, and extracted with
diethyl ether. After drying over magnesium sulphate and evapora-
tion of the solvents, the concentrate was applied to silica gel col-
umn chromatography using diethyl ether/n-hexane (10:90 and
20:80) as eluents affording the product 6 as a clear oil (1.63 g,
(C–O–C) cmꢀ1
; HRMS (APCI): m/z calcd for C22H42O4 + NH4:
388.3408; found 388.3417 amu. 1H NMR (400 MHz, CDCl3): d
5.56–5.48 (m, 1H, C@CHCH2CH2), 5.42–5.35 (m, 1H, CHCH2CH@C),
4.30–4.25 (m, 1H, CHOC(CH3)2), 4.05 (dd, J = 8.3, 6.5 Hz, 1H,
(CH3)2COCH2), 3.85–3.78 (m, 1H, CHOH), 3.74 (dd, J = 8.3, 6.4 Hz,
1H, (CH3)2COCH2), 3.57 (dd, J = 10.2, 5.5 Hz, 1H, (CH3)2COCHCH2O),
3.54 (dd, J = 9.6, 3.1 Hz, 1H, OCH2CHOH), 3.53 (dd, J = 10.0, 2.6 Hz,
1H, (CH3)2COCHCH2O), 3.38 (dd, J = 9.8, 7.6 Hz, 1H, OCH2CHOH),
2.41 (d, J = 3.4 Hz, 1H, OH), 2.30–2.18 (m, 2H, CHOHCH2C@), 2.02
(quartet (br), J = 6.8 Hz, 2H, @CCH2CH2), 1.42 (s, 3H, (CH3)2CO),
1.36 (s, 3H, (CH3)2CO), 1.33–1.20 (m, 18H, CH2), 0.88 (br t, 3H,
J = 6.9 Hz, CH3) ppm; 13C NMR (100 MHz, CDCl3)
d 134.12
(C@CHCH2CH2), 124.24 (CHCH2CH@C), 109.46 ((CH3)2C), 75.44
(OCH2CHOH), 74.68 (CHOC(CH3)2), 72.29 ((CH3)2COCHCH2O),
70.21 (CHOH), 66.58 ((CH3)2COCH2), 31.91, 31.20 (CHOHCH2C@),
29.66, 29.63 (2), 29.59, 29.54, 29.33 (2), 27.38 (@CCH2CH2), 26.72
((CH3)2CO), 25.37 ((CH3)2CO), 22.68 (CH2CH3), 14.11 (CH3) ppm.
50% yield). ½a 2D0
¼ ꢀ12:2 (c 2.50, ethanol); IR(ZnSe) 3375 (O–H),
ꢂ
2922 (C–H) cmꢀ1; HRMS (APCI): m/z calcd for C16H29OCl + H:
273.1980; found 273.1981 amu. 1H NMR (400 MHz, CDCl3): d
3.93 (quintet, J = 5.7 Hz, 1H, CH2CHCH2), 3.70 (dd, J = 11.1, 4.6 Hz,
1H, CH2Cl), 3.61 (dd, J = 11.1, 6.1 Hz, 1H, CH2Cl), 2.48 (ddt,
J = 17.6, 7.3, 2.3 Hz, 1H, CHCH2C„), 2.54 (ddt, J = 16.4, 5.4, 2.5 Hz,
1H, „CCH2), 2.31–2.17 (br s, 1H, CHOH), 2.15 (tt, J = 7.1, 2.4 Hz,
2H, „CCH2), 1.48 (quintet, J = 7.2, 2H, „CCH2CH2), 1.39–1.32 (m,
2H, „CCH2CH2CH2), 1.32–1.18 (m, 14H, CH2), 0.88 (br t,
J = 6.8 Hz, 3H, CH3) ppm; 13C NMR (100 MHz, CDCl3) d 83.96
4.1.4. Synthesis of (Z)-(20R)-1-O-(20-methoxyhexadec-40-enyl)-
2,3-O-isopropylidene-sn-glycerol 3
To a mixture of (Z)-(20R)-1-O-(20-hydroxyhexadec-40-enyl)-2,3-
O-isopropylidene-sn-glycerol 4 (500 mg, 1.349 mmol), silver oxide
(937 mg, 4.047 mmol) and 4 Å molecular sieves (9.37 g) in freshly

2846
C. D. Magnusson, G. G. Haraldsson / Tetrahedron: Asymmetry 21 (2010) 2841–2847
distilled toluene (15 ml), methyl iodide (843
l
l, 13.49 mmol) was
CH2OH), 3.63 (dd, J = 11.5, 5.2 Hz, 1H, CH2OH), 3.61 (dd, J = 10.0,
3.8 Hz, 1H, HOCHCH2OCH2), 3.56 (dd, J = 10.3, 3.6 Hz, 1H, OCH2-
CHOCH3), 3.53 (dd, J = 9.9, 6.2 Hz, 1H, HOCHCH2OCH2), 3.47 (dd,
J = 10.5, 6.0 Hz, 1H, OCH2CHOCH3), 3.39 (s, 3H, OCH3), 3.35–3.30
(m, 1H, CHOCH3), 1.54–1.41 (m, 2H, CH3OCHCH2C), 1.37–1.18 (m,
24H, CH2), 0.87 (br t, 3H, J = 6.9 Hz, CH3) ppm; 13C NMR
(100 MHz, CDCl3–D2O, 7:0.1): d 80.37 (CHOCH3), 73.51 (OCH2-
CHOCH3), 73.34 (HOCHCH2OCH2), 70.45 (CHOH), 63.86 (CH2OH),
57.26 (OCH3), 31.91, 30.80 (CH3OCHCH2C), 29.77, 29.68 (2),
29.66, 29.64 (2), 29,58, 29.56, 29.34, 25,33, 22.68 (CH2CH3), 14.10
(CH3) ppm.
added, and the resulting mixture stirred for 17 h at room temper-
ature under an argon atmosphere. The reaction mixture was fil-
tered over a small cake of silica gel and eluted with diethyl
ether. Removal of volatile constituents in vacuo afforded the pure
compound 3 as a slightly yellowish oil (480 mg, 93% yield).
½
a 2D0
ꢂ
¼ ꢀ13:1 (c 0.83, ethanol); IR(ZnSe) 2922 (C–H), 1657 (C@C),
1102 and 1055 (C–O–C) cmꢀ1; HRMS (APCI): m/z calcd for
23H44O4 + NH4: 402.3578; found 402.3576 amu. 1H NMR
C
(400 MHz, CDCl3): d 5.51–5.44 (m, 1H, C@CHCH2CH2), 5.40–5.33
(m, 1H, CHCH2CH@C), 4.26 (quintet, J = 5.9 Hz, 1H, CHOC(CH3)2),
4.05 (dd, J = 8.3, 6.4 Hz, 1H, (CH3)2COCH2), 3.76 (dd, J = 8.3,
6.3 Hz, 1H, (CH3)2COCH2), 3.57 (dd, J = 10.0, 5.3 Hz, 1H,
(CH3)2COCHCH2O), 3.50 (d, J = 5.0 Hz, 2H, OCH2CHOCH3), 3.48
(dd, J = 10.0, 5.8 Hz, 1H, (CH3)2COCHCH2O), 3.41 (s, 3H, OCH3),
3.37 (quintet, J = 5.4 Hz, 1H, CHOCH3), 2.27 (t, J = 6.4 Hz, 2H,
CH3OCHCH2C@), 2.02 (quartet (br), J = 6.8 Hz, 2H, @CCH2CH2),
1.41 (s, 3H, (CH3)2CO), 1.36 (s, 3H, (CH3)2CO), 1.33–1.20 (m, 18H,
CH2), 0.88 (br t, 3H, J = 6.9 Hz, CH3) ppm; 13C NMR (100 MHz,
CDCl3) d 132.43 (C@CHCH2CH2), 124.55 (CHCH2CH@C), 109.30
((CH3)2C), 80.08 (CHOCH3), 74.65 (CHOC(CH3)2), 73.25 (OCH2-
CHOCH3), 72.37 ((CH3)2COCHCH2O), 66.90 ((CH3)2COCH2), 57.46
(OCH3), 31.91, 29.67 (CHOHCH2C@), 29.64 (2), 29.59, 29.56,
29.36, 29.34, 28.85 (CH3OCHCH2C@), 27.38 (@CCH2CH2), 26.76
((CH3)2CO), 25.42 ((CH3)2CO), 22.68 (CH2CH3), 14.11 (CH3) ppm.
4.1.7. Preparation of (R,R)-MTPA ester of (R)-6
The (R)-MTPA ester of 6, obtained from (R)-epichlorohydrin was
prepared according to the reported method32 and purified by pre-
parative TLC with ethyl acetate/petroleum ether (2.5:97.5) as an
eluent affording the Mosher ester product as a clear liquid. 1H
NMR (400 MHz, CDCl3): d 7.60–7.55 (m, 2H, @C–H), 7.43–7.37
(m, 3H, @C–H), 5.34–5.28 (m, 1H, CH2CHCH2), 3.76 (dd, J = 11.9,
4.7 Hz, 1H, CH2Cl), 3.69 (dd, J = 11.9, 5.9 Hz, 1H, CH2Cl), 3.59 (m,
3H, OCH3), 2.72 (ddt, J = 17.1, 6.3, 2.4 Hz, 1H, CHCH2C„), 2.65
(ddt, J = 16.7, 5.8, 2.4 Hz, 1H, „CCH2), 2.13 (tt, J = 7.1, 2.4 Hz, 2H,
„CCH2), 1.45 (quintet, J = 7.2, 2H, „CCH2CH2), 1.38–1.19 (m,
16H, CH2), 0.88 (br t, J = 6.9 Hz, 3H, CH3) ppm.
4.1.8. Preparation of (R,S)-MTPA ester of (S)-6
4.1.5. Synthesis of (Z)-(20R)-1-O-(20-methoxyhexadec-40-enyl)-
sn-glycerol 1
A procedure identical to the one described for the preparation of
the (R,R,)-MTPA ester of 6 was followed in detail using (S)-6. Ad-
duct (S)-6 was obtained from (S)-epichlorohydrin by the same
methodology previously described for 6. 1H NMR (400 MHz,
CDCl3): d 7.61–7.54 (m, 2H, @C–H), 7.43–7.37 (m, 3H, @C–H),
5.31–5.26 (m, 1H, CH2CHCH2), 3.88 (dd, J = 12.0, 3.8 Hz, 1H, CH2Cl),
3.77 (dd, J = 12.0, 6.4 Hz, 1H, CH2Cl), 3.60 (m, 3H, OCH3), 2.58 (m,
2H, CHCH2C„), 2.07 (tt, J = 7.0, 2.4 Hz, 2H, „CCH2), 1.44 (quintet,
J = 7.0, 2H, „CCH2CH2), 1.37–1.17 (m, 16H, CH2), 0.88 (br t,
J = 6.9 Hz, 3H, CH3) ppm.
To a solution of (Z)-(20R)-1-O-(2’methoxyhexadec-40-enyl)-2,3-
O-isopropylidene-sn-glycerol 3 (359 mg; 0.933 mmol) in 96% etha-
nol (3 ml), wet Amberlyst 15 (63 mg) was added and refluxed for
5 h and 30 min. After filtration of Amberlyst the solution was con-
centrated in vacuo, affording the pure compound as slightly yel-
lowish oil (317 mg, 99% yield). ½a D20
¼ ꢀ12:5 (c 0.84, chloroform);
ꢂ
IR(ZnSe) 3402 (O–H), 3010 (@C–H cis), 2921 (C–H), 1655 (C@C),
1082 and 1046 (C–O–C) cmꢀ1; HRMS (APCI): m/z calcd for
C
20H40O4 + H: 345.2999; found 345.2999 amu. 1H NMR (400 MHz,
CDCl3–D2O, 7:0.1) d 5.52–5.45 (m, 1H, C@CHCH2CH2), 5.38–5.31
(m, 1H, CHCH2CH@C), 3.88–3.83 (m, 1H, CHOH), 3.69 (dd,
J = 11.5, 4.0 Hz, 1H, CH2OH), 3.63 (dd, J = 11.5, 5.2 Hz, 1H, CH2OH),
3.61 (dd, J = 10.0, 3.7 Hz, 1H, HOCHCH2OCH2), 3.57 (dd, J = 10.4,
3.2 Hz, 1H, OCH2CHOCH3), 3.53 (dd, J = 10.0, 6.3 Hz, 1H, HOCH-
CH2OCH2), 3.46 (dd, J = 10.5, 6.2 Hz, 1H, OCH2CHOCH3), 3.42 (s,
3H, OCH3), 3.40–3.35 (m, 1H, CHOCH3), 2.35–2.21 (m, 2H,
CH3OCHCH2C@), 2.02 (quartet (br), J = 6.8 Hz, 2H, @CCH2CH2),
1.35–1.20 (m, 18H, CH2), 0.88 (br t, 3H, J = 6.9 Hz, CH3) ppm; 13C
Acknowledgements
Lysi ehf in Iceland and the Icelandic Research Fund are acknowl-
edged for the financial support. Dr. Sigridur Jonsdottir and Dr.
Sigurdur V. Smarason at University of Iceland are acknowledged
for high-resolution 2D NMR and accurate MS measurements.
References
1. Carballeira, N. M. Prog. Lipid Res. 2002, 41, 437–456.
2. Karnovsky, M. L.; Rapson, W. S.; Black, M. S. J. Soc. Chem. Ind. 1946, 65, 425–428.
3. Wetherbee, B. M.; Nichols, P. D. Compd. Biochem. Physiol. B 2000, 125, 511–521.
4. Snyder, F.; Wood, R. Cancer Res. 1969, 29, 251–257.
5. Pugliese, P. T.; Jordan, K.; Cederberg, H.; Brohult, J. J. Altern. Complement Med.
1998, 4, 87–99.
NMR (100 MHz, CDCl3–D2O, 7:0.1)
d 132.74 (C=CHCH2CH2),
124.15 (CHCH2CH@C), 80.22 (CHOCH3), 73.39 (HOCHCH2OCH2),
73.14 (OCH2CHOCH3), 70.44 (CHOH), 63.85 (CH2OH), 57.23
(OCH3), 31.90, 29.66, 29.63 (2), 29.55 (2), 29.34 (2), 28.36
(CH3OCHCH2C@), 27.37 (@CCH2CH2), 22.68 (CH2CH3), 14.10 (CH3)
ppm.
6. Deniau, A. L.; Mosset, P.; Pedrono, F.; Mitre, R.; Le Bot, D.; Legrand, A. B. Mar.
Drugs 2010, 8, 2175–2184.
7. Blank, M. L.; Cress, E. A.; Smith, Z. L.; Snyder, F. Lipids 1991, 26, 166–169.
8. Das, A. K.; Holmes, R. D.; Wilson, G. N.; Hajra, A. K. Lipids 1992, 27, 401–405.
9. Hichami, A.; Duroudier, V.; Leblais, V.; Vernhet, L.; Le Goffic, F.; Ninio, E.;
Legrand, A. Eur. J. Biochem. 1997, 250, 242–248.
10. Bakes, M. J.; Nichols, P. D. Compd. Biochem. Physiol. B 1995, 110, 267–275.
11. Deprez, P. P.; Volkman, J. K.; Davenport, S. R. Aust. J. Mar. Fresh. Res. 1990, 41,
375–387.
12. Hayashi, K.; Takagi, T. B. Jpn. Soc. Sci. Fish. 1982, 48, 1345–1351.
13. Hallgren, B.; Stallberg, G. Acta Chem. Scand. 1967, 21, 1519–1529.
14. Hallgren, B.; Niklasson, A.; Stallberg, G.; Thorin, H. Acta Chem. Scand. B 1974, 28,
1029–1034.
15. Stallberg, G. A. M. Acta Chem. Scand. 1990, 44, 368–376.
16. Hallgren, B.; Stallberg, G.; Thorin, H. Acta Chem. Scand. 1971, 25, 3781–3784.
17. Boeryd, B.; Hallgren, B.; Stallber, G. Brit. J. Exp. Pathol. 1971, 52, 221–230.
18. Hallgren, B.; Stallberg, G.; Boeryd, B. Prog. Chem. Fats Other Lipids 1978, 16, 45–
58.
4.1.6. Preparation of (20R)-1-O-(20-methoxyhexadecyl)-sn-
glycerol 2
A suspension of (Z)-(20R)-1-O-(20-methoxyhexadec-40-enyl)-sn-
glycerol 1 (35 mg, 0.102 mmol) and 10% Pd in activated charcoal
(7 mg) in absolute ethanol (25 ml) was placed in a PARR reactor
under a hydrogen pressure (1 atm) and stirred for 2 h and 30 min
at room temperature. The reaction mixture was filtered over a
pad of Celite and flushed with diethyl ether. Solvent removal in va-
cuo afforded the pure product 2 as a white wax (34 mg, 96% yield).
½
a 2D0
ꢂ
¼ ꢀ3:0 (c 0.89, chloroform); IR(KBr) 3420 (O–H), 2918 (C–H),
1121 (C–O–C) cmꢀ1; HRMS (ESI): m/z calcd for C20H42O4 + H:
347.3156; found 347.3159 amu. 1H NMR (400 MHz, CDCl3–D2O,
7:0.1): d 3.88–3.83 (m, 1H, CHOH), 3.69 (dd, J = 11.5, 3.9 Hz, 1H,
19. Wang, H.; Rajagopal, S.; Reynolds, S.; Cederberg, H.; Chakrabarty, S. J. Cell.
Physiol. 1999, 178, 173–178.

C. D. Magnusson, G. G. Haraldsson / Tetrahedron: Asymmetry 21 (2010) 2841–2847
2847
20. Reynolds, S.; Cederberg, H.; Chakrabarty, S. Clin. Exp. Metastasis 2000, 18, 309–
25. Baer, E.; Fischer, H. O. L. J. Biol. Chem. 1941, 140, 397–410.
26. Baumann, W. J.; Mangold, H. K. J. Org. Chem. 1964, 29, 3055–3057.
27. Stallberg, G. Chem. Scripta 1975, 7, 31–41.
312.
21. Hallgren, B. In Ether Lipids: Biochemical and Biomedical Aspects; Mangold, H. K.,
Paltauf, F., Eds.; Academic Press: New York, 1983; pp 261–275.
22. Hallgren, B.; Niklasson, A.; Stallberg, G.; Thorin, H. Acta Chem. Scand. B 1974, 28,
1035–1040.
23. D’Ambrosio, M.; Guerriero, A.; Pietra, F. Experientia 1996, 52, 624–627.
24. Alam, N.; Bae, B. H.; Hong, J.; Lee, C. O.; Shin, B. A.; Im, K. S.; Jung, J. H. J. Nat.
Prod. 2001, 64, 533–535.
28. Yamaguchi, M.; Hirao, I. Tetrahedron Lett. 1983, 24, 391–394.
29. Eis, M. J.; Wrobel, J. E.; Ganem, B. J. Am. Chem. Soc. 1984, 106, 3693–3694.
30. Ugelstad, J.; Ellingsen, T.; Berge, A. Acta Chem. Scand. 1966, 20, 1593–1598.
31. Yu, C. C.; Lee, Y. S.; Cheon, B. S.; Lee, S. H. Bull. Korean Chem. Soc. 2003, 24, 1229–
1231.
32. Dale, J. A.; Dull, D. L.; Mosher, H. S. J. Org. Chem. 1969, 34, 2543–2549.