Synthesis of enantiomerically pure, sn-1 modified sn-2-deoxy-2-amido- glycero-3-phospholipids

Article abstract of DOI:10.1016/S0009-3084(00)00156-0

The synthesis of two types of enantiomerically pure sn-2-deoxy-2-amido- glycero-phospholipids differing in the connection of the alkyl chain at the sn-1-position is described. Both types of lipids were prepared from l-serine- methylester as the chiral starting material. (C) 2000 Published by Elsevier Science Ireland Ltd.

Full text of DOI:10.1016/S0009-3084(00)00156-0

Chemistry and Physics of Lipids
107 (2000) 121–129
www.elsevier.com/locate/chemphyslip
Synthesis of enantiomerically pure, sn-1 modified
sn-2-deoxy-2-amido-glycero-3-phospholipids
Markus Bartel, Bernd Rattay *, Peter Nuhn
Institut fu¨r Pharmazeutische Chemie, Martin-Luther-Uni6ersita¨t Halle-Wittenberg, Wittenberg, Germany
Received 25 February 2000; received in revised form 2 May 2000; accepted 15 May 2000
Abstract
The synthesis of two types of enantiomerically pure sn-2-deoxy-2-amido-glycero-phospholipids differing in the
connection of the alkyl chain at the sn-1-position is described. Both types of lipids were prepared from L-serine-
methylester as the chiral starting material. © 2000 Published by Elsevier Science Ireland Ltd.
Keywords: sn-2-Deoxy-2-amido-glycero-phospholipids; Enantiomer; Alkyl chain
1. Introduction
apy of inflammation and allergic diseases. For this
purpose nonhydrolyzable phospholipids are valu-
able tools since they allow the study of interac-
tions with the PLA2 without the disturbing effects
due to the hydrolysis products in the case of
hydrolyzable lipids.
Phospholipase A2 (PLA2) is an enzyme that
stereospecifically hydrolyzes the fatty acid ester
bond from the sn-2-position of naturally occur-
ring phospholipids. Because mainly unsaturated
fatty acids are esterified at this position (e.g.
arachidonic acid) the reaction is the basis for the
biosynthesis of physiologically and pathophysio-
logically important mediators as prostaglandines,
leukotrienes and thromboxanes. Therefore, the
investigation of the mechanism of the enzyme
reaction and the search for opportunities to influ-
ence this process is of great interest for the ther-
In front of this background, we describe the
synthesis of the enantiomerically pure non-
hydrolyzable
sn-2-amide-phospholipids
1–4
(Scheme 1). sn-2-Amide analogs of phospholipids
* Corresponding author. Tel.: +49-345-5525185; fax: +49-
345-5527026.
Scheme 1. Structures of the synthesized sn-2-amide-phospho-
E-mail address: rattay@pharmatie.uni-halle.de (B. Rattay).
lipids.
0009-3084/00/$ - see front matter © 2000 Published by Elsevier Science Ireland Ltd.
PII: S0009-3084(00)00156-0

122
M. Bartel et al. / Chemistry and Physics of Lipids 107 (2000) 121–129
Scheme 2. Synthesis of (S)-N-palmitoyl-serine-hexadecylester (9).
are known as strong inhibitors of the secretory
phospholipase A2 when they have an ester, ether,
thioether bond or an alkyl chain at the sn-1-posi-
tion of the original glycerol backbone (Bonsen et
al., 1972; Davidson et al., 1986; Yu et al., 1986; de
Haas et al., 1990). In contrast to these compounds
sphingomyelins (that bear a free hydroxy group at
the ‘sn-1-position’) do not inhibit the PLA2 al-
though they are amide phospholipids too (Yu et
al., 1986). Thereby the sn-1 position seems to be
sensitive with respect to the inhibitory properties
of sn-2-amide-phospholipids. The synthesized
phospholipid analogs should also help to investi-
gate the influence of particular structural elements
on the adsorption of the PLA2 at the supramolec-
ular membrane structures and on the inhibition of
the hydrolysis reaction.
3. Synthetic procedures and results
3.1. Materials and methods
L
-serine-methylester, methanesulfonic acid chlo-
ride, dibutyltin dichloride, choline tosylate, N-
Boc-ethanolamine and the
R-a-methoxy-
a-trifluoromethylphenyl-acetic acid (R-Mosher’s
acid) were purchased from Aldrich. Phosphorous
2. Synthetic schemes
For the preparation of enantiomerically pure
sn-2-amide analogs of phospholipids (Scheme 1)
derivatives of serine are convenient chiral starting
materials because they already own important
structural moieties of the target molecules (Chan-
drakumar and Hajdu, 1981; Chandrakumar and
Hajdu, 1983; Bhatia and Hajdu, 1988; Dijkman et
al., 1990). In our preparations
L-serine-
methylester (5) was the starting material (Schemes
2 and 3).
Scheme 3. Synthesis of the 1-O-alkyl-sn-2-amide-phospho-
choline (4).

M. Bartel et al. / Chemistry and Physics of Lipids 107 (2000) 121–129
123
trichloride, phosphorous oxychloride and pivaloyl
3.3. (S)-3-O-(tert-butyl-diphenylsilyl)-N-
palmitoyl-serine-hexadecylester (8) (Scheme 2,
sequence [A])
chloride were Acros products, hexadecanol was
from Fluka. Trityl chloride (Aldrich) was recrys-
tallized before use from hexane under addition of
thionylchloride. Hexadecylmethanesulfonate was
prepared by reaction of hexadecanol with
methanesulfonic acid chloride/trimethylamine as
described by Prinz et al. (1985). 1,1,3,3-tetra-n-bu-
tyl-1-isothiocyanato-3-hydroxy-1,3-distannoxan
was synthesized from dibutyltin dichloride ac-
cording to Okawara and Wada (1963), Wada et
al. (1965). (S)-N-palmitoyl-serine-methylester (6)
was synthesized in the same manner as described
by Chandrakumar and Hajdu (1981). (S)-N-trityl-
3-O-trityl-serine-methylester (13) and 2-N-trityl-2-
amino-2-deoxy-3-O-trityl-sn-glycerol (14) were
synthesized in the same manner as described by
Dijkman et al. (1990).
A solution of 7 (1.03 g; 1.73 mmol) and hexade-
canol (2.1 g; 8.65 mmol) in 10 ml dry toluene was
mixed with 1,1,3,3-tetra-n-butyl-1-isothiocyanato-
3-hydroxy-1,3-distannoxane (96 mg; 0.173 mmol,
10 mol% in relation to 7). The mixture was
refluxed for 12 h. After that the solvent was
removed in vacuum. The crude product was
purified by chromatography in the same manner
as described for 7 to give a white crystalline solid.
Yield, 1.25 g (90%); TLC (petroleum ether/ether
5:2 v/v); Rf, 0.46; m.p. 52°C; [a]2D0, 19.6°; (c, 5%
1
m/6 in CHCl3). H NMR (500 MHz; CDCl3), l
0.9 (t, 6H, CH3), 1.0 (s, 9H, t-bu), 1.3 (s, 50H,
CH2), 1.6 (m, 4H, b-CH2), 2.15 (t, 2H, ꢀCH2ꢀ
CONH), 3.83–3.92 (m, 1H, ꢀCHH
4.0–4.2 (m, 3H, ꢀCHHꢀCH(NH)ꢀCOOꢀCH2ꢀ),
4.6–4.7 (m, 1H, ꢀCH(NH)ꢀ), 6.2 (d, 1H, ꢀNH),
6 ꢀCH(NH)ꢀ),
6
3.2. (S)-3-O-(tert-butyl-diphenylsilyl)-N-
palmitoyl-serine-methylester (7) (Scheme 2,
sequence [A])
6
6
7.30–7.62 (m, 10H, 2 phenyl). Elemental analysis,
calculated for C51H87NO4Si, C, 75.97; H, 10.87;
N, 1.74; found, C, 76.00; H, 11.08; N, 1.63.
N-palmitoyl-serine-methylester (6) (2.145 g; 6
mmol) was dissolved in 30 ml dry
dichloromethane. Pyridine (0.97 ml; 12 mmol)
and 4-dimethyl-aminopyridine (DMAP; 242 mg;
1.98 mmol) were added and the solution was
cooled to 0°C. tert-Butyl-diphenylsilyl chloride
(2.47 g; 2.34 ml; 9 mmol) was dropped into the
solution and the mixture was stirred for 2 days at
room temperature. HCl (5 ml, 1 N) was added
and the organic layer was separated in a separa-
tion funnel. The aqueous phase was washed with
3×10 ml dichloromethane and the combined or-
ganic phases were washed with 20 ml water por-
tions until the pH was neutral. After drying over
Na2SO4 the solvent was evaporated in vacuum.
The crude product was purified by chromatogra-
phy over a dry column of silica gel (20 g silica gel
per 1 g crude product) with petroleum ether/di-
ethylether 5:2 (v/v) as eluent. The product was
obtained as colorless oil. Yield, 2.7 g (75.5%); thin
layer chromatography (TLC, petroleum ether/
ether 5:2 v/v); Rf, 0.21. Elemental analysis, calcu-
lated for C36H57NO4Si, C, 72.56; H, 9.64; N, 2.35;
found, C, 72.77; H, 9.69; N, 2.39.
3.4. Deprotection of the TBDPS group (8“9)
(Scheme 2, sequence [A])
To a solution of 8 (1.13 g; 1.4 mmol) in 15 ml
of dry THF 1.624 ml (1.624 mmol) of an 1 M
solution of tetrabutylammoniumfluoride in THF
were added and the mixture was stirred overnight
at room temperature. After neutralization with
acetic acid the crude product was precipitated by
addition of water and was filtered off by suction.
Further purification was carried out by column
chromatography (CHCl3/ether 8:2 v/v). Yield, 0.7
g (88%); the analytical data are the same as
described in Section 3.5.
3.5. (S)-N-palmitoyl-serine-hexadecylester (9)
(Scheme 2, sequence [B])
(S)-N-palmitoyl-serine-methylester (6) (1.7 g;
4.75 mmol) and hexadecanol (5.76 g; 23.75 mmol)
were dissolved in 17 ml dry toluene and 1,1,3,3-
tetra-n-butyl-1-isothiocyanato-3-hydroxy-1,3-dis-
tannoxane (270 mg; 0.48 mmol, 10 mol% in rela-

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M. Bartel et al. / Chemistry and Physics of Lipids 107 (2000) 121–129
tion to 6) was added. The mixture was refluxed
for 12 h and the solvent was then evaporated in
vacuum. The purification of the product was car-
ried out by chromatography on silica gel using
heptane/chloroform 1:1 (v/v) as starting eluent for
the elution of lipophilic impurities. The main
product was eluted with heptane/chloroform 7:3
as well as a mixed fraction containing hexade-
canol and 9. From this fraction pure 9 could be
separated by a repeated passage through a silica
gel column. Yield, 2.13 g (79%) as a white crys-
talline solid; m.p. 98°C. TLC (CHCl3/ether 8:2
v/v); Rf, 0.39; [a]D20, 10°; (c, 4.8% m/6 in CHCl3).
1H NMR (500 MHz; CDCl3), l 0.9 (t, 6H, CH3);
1.3 (s, 50H, CH2); 1.6 (m, 4H, b-CH2); 2.2 (t, 2H,
CH2ꢀCONH); 3.9 (d, 2H, HOꢀCH2ꢀCHNH);
4.15 (t, 2H, CH2ꢀOOC); 4.65 (m, 1H,
OꢀCH2ꢀCHNH); 4.88 (m, 1H, CH6 NH); 6.0 (d,
1H, ꢀNH6 ); 7,4 (m, 5H, phenyl).
1H NMR (500 MHz; CDCl3); (R,R)-
diastereomere, l 4.65 (m, 2H, OꢀCH2ꢀCHNH);
4.84 (m, 1H, CH6 NH); 6.10 (d, 1H, ꢀNH6
). 19F
NMR (188 MHz; CDCl3); (S,R)-diastereomere
and (R,R)-diastereomere, l -73.189 (s).
3.7. Preparation of the sn-3-H-phosphonate (10)
To an ice cold solution of imidazole (1.88 g;
26.55 mmol) in 40 ml dry acetonitril at first
phosphorous trichloride (1.045 g; 0.67 ml; 7.61
mmol) and then triethylamine (2.62 g; 3.6 ml;
25.85 mmol) were added dropwise. After stirring
for 15 min a solution of 9 (1.00 g; 1.77 mmol) in
100 ml toluene was dropped into the mixture over
a period of 25 min followed by 7 h of stirring
under argon atmosphere at room temperature
(control of the conversion by TLC). The reaction
was stopped by addition of 20 ml water and the
mixture stirred for further 30 min. The solvent
was evaporated in vacuum. Then 100 ml of pyri-
dine/triethylamine (80:20; v/v) were added and
evaporated again. The crude product was dis-
solved in 100 ml chloroform and washed with 100
ml water. The organic phase was separated and
the aqueous layer was washed with 3×20 ml
chloroform. After drying the collected organic
layers with Na2SO4 and evaporation of the sol-
vent in vacuum a white waxy product was ob-
tained which was used without further
purification. TLC (CHCl3/MeOH 35:15 v/v); Rf,
0.44; (CHCl3/MeOH/acetic acid 35:15:2 v/v/v);
Rf, 0.62. +ES−MS m/z 632.7 (M+H+); m/z
654.7 (M+Na+).
ꢀCH6 (NH)ꢀ); 6.4 (d, 1H, ꢀNH6 ). Elemental analy-
sis, calculated for C35H69NO4, C, 74.07; H, 12.17;
N, 2.47; found, C, 74.03; H, 11.94; N, 2.43.
3.6. Preparation of the diastereomeric Mosher
ester (9M)
The S-enantiomere of 9 (0.3 g; 0.53 mmol) was
dissolved in 8 ml dry dichloromethane. While
stirring the mixture R(+)-a-methoxy-a-trifl-
uoromethyl-phenyl-acetic acid (145.2 mg; 0.62
mmol) and DMAP (12 mg; 0.01 mmol) in 1.5 ml
DMF were added and the solution was cooled to
0°C. Then 1.75 ml (0.85 mmol) of a 10% solution
of dicyclohexylcarbodiimide in dichloromethane
was dropped into the reaction mixture. After
warming up to room temperature stirring was
continued for 3 h (TLC control). The precipitated
dicyclohexyl-urea was filtered off and the solvent
was evaporated in vacuum. The crude product
was purified by column chromatography
(petroleum ether/ether 5:2 v/v). The (R,R)-
diastereomere and the mixture of the
diastereomeres were prepared in the same way
using the R-enantiomere and the racemate of 9,
respectively. Yield, 0.33 g (79%); TLC (petroleum
ether/ether 5:2 v/v); Rf, 0.30. 1H NMR (500
MHz; CDCl3); (S,R)-diastereomere, l 0.85 (t, 6H,
CH3); 1.25 (s, 50H, CH2); 1.6 (m, 4H, b-CH2);
2.15 (t, 2H, CH2ꢀCONH); 3.45 (s, 3H, OCH3);
4.1 (m, 2H, CH2ꢀOOC); 4.64 (m, 2H,
3.8. Preparation of the phosphoethanolamine (1)
The sn-3-phosphonate 10 (1.77 mmol) and N-
Boc-ethanolamine (0.428 g; 0.41 ml; 2.655 mmol)
were dissolved in 20 ml of dry pyridine and
pivaloyl chloride (0.43 ml; 3.54 mmol) was added.
After stirring the mixture for 15 min iodine (0.90
g, 3.54 mmol) dissolved in 20 ml of pyridine/water
(98:2 v/v) was added and stirring was continued
for 5 min. The solution was mixed with 300 ml
chloroform, 70 ml 5% aqueous sodium hydrogen

M. Bartel et al. / Chemistry and Physics of Lipids 107 (2000) 121–129
125
sulfite and 50 ml methanol. After shaking in a
separation funnel the organic layer was separated
and the aqueous phase was washed with 3×30 ml
chloroform. The collected organic layers were
dried with Na2SO4 and the solvent was evapo-
rated in vacuum. Traces of pyridine and water
were removed by repeated evaporation with dry
toluene yielding a yellowish oil. The removal of
the protecting group was carried out with trifl-
uoroacetic acid/dichloromethane (Alcaraz et al.,
1996). Yield (from 9), 650 mg (53%). TLC
(CHCl3/MeOH/NH3 35:15:2 v/v/v); Rf, 0.29; +
ES−MS m/z 691.5 (M+H+); m/z 713.5 (M+
4.05 (m, 2H, CH2ꢀOOC); 4.20 (m, 2H, ꢀCH2ꢀ
CHNH); 4.30 (m, 2H, OꢀPO3ꢀCH2ꢀCH2ꢀN); 4.60
(m, 1H, ꢀCH6 (NH)ꢀ); 7.90 (d, 1H, ꢀCH(NH6 )ꢀ).
3.10. 1-O-hexadecyl-2-N-trityl-2-amino-2-deoxy-
3-O-trityl-sn-glycerol (15)
A suspension of NaH (542 mg 55%; 12.42
mmol) in 20 ml dry THF was cooled to 0°C.
Under an argon atmosphere a solution of the
alcohol 14 (6.5 g; 11.29 mmol) in 10 ml THF was
dropped slowly into the suspension. The mixture
was stirred for 1 h at room temperature and
stirring was continued overnight at 50°C. The
reaction was then cooled to 0°C and a solution of
hexadecane methanesulfonate (3.98 g; 12.42
mmol) in 15 ml dry THF was added dropwise.
The mixture was refluxed for 12 h and was stirred
for further 10 h at room temperature (TLC con-
trol). The liquid was mixed with the same volume
of ice cold water. The organic phase was sepa-
rated and the aqueous phase was washed with
3×40 ml ether. The combined organic phases
were dried with Na2SO4 and evaporated in vac-
uum. The crude product was used for the detrity-
lation without further purification. TLC
(petroleum ether/diethylether 5:2 v/v); Rf, 0.58
(UV-detection).
1
Na+). H NMR (500 MHz; CD3OD/CDCl3), l
0.85 (t, 6H, CH3); 1.25 (s, 50H, CH2); 1.60 (m,
4H, b-CH2); 2.20 (m, 2H, CH2ꢀCONH); 3.10 (m,
2H, CH2ꢀNH+3 ); 4.0–4.20 (m, 6H, CH2ꢀOOC;
CH2ꢀCH(NH); PO3ꢀCH2); 4.65 (m, 1H,
ꢀCH6
(NH)ꢀ). 31P NMR, l 0.890.
3.9. Preparation of the phosphocholine (2)
The sn-3-H-phosphonate 10 (1.77 mmol) and
choline tosylate (0.98 g; 3.54 mmol) were dis-
solved in 20 ml of dry pyridine and pivaloyl
chloride (0.43 ml; 3.54 mmol) was added. After
stirring the mixture for 15 min iodine (0.90 g; 3.54
mmol) dissolved in 20 ml of pyridine/water (98:2
v/v) was added and stirring was continued for 5
min. The solution was mixed with 300 ml chloro-
form, 70 ml 5% aqueous sodium hydrogen sulfite
and 50 ml methanol. After shaking in a separa-
tion funnel the organic layer was separated and
the aqueous phase was washed with 3×30 ml
chloroform. The collected organic layers were
dried with Na2SO4 and the solvent was evapo-
rated in vacuum. Traces of pyridine and water
were removed by repeated evaporation with dry
3.11. 1-O-hexadecyl-2-amino-2-deoxy-sn-glycerol
(16)
The stereospecific preparation of 1-O-alkyl-seri-
nols has been described in literature using a differ-
ent synthetic sequence (Chandrakumar and
Hajdu, 1983). In our case, we used the following
procedure.
toluene yielding
a
yellowish oil. The crude
Crude product 15 (approximately 11.3 mmol)
was dissolved in 250 ml dry dichloromethane and
cooled to 0°C. BF3 (20 ml) solution (10% in
methanol) was added and the mixture was stirred
at room temperature until the TLC showed the
complete detritylation. The solution was washed
twice with ice cold water and the organic phase
was dried (Na2SO4) and evaporated in vacuum.
The chromatographic purification of the product
was carried out on a dry silica gel column with
product was purified by chromatography on silica
gel (chloroform/methanol/water 35:15:2 v/v/v).
Yield (from 9), 700 mg (54%). TLC (CHCl3/
MeOH/NH3 35:15:2 v/v/v); Rf, 0.22; +ES−MS
m/z 733.6 (M+H+); m/z 755.7 (M+Na+); m/z
1467 (2M+H+). H NMR (500 MHz; CDCl3), l
1
0.85 (t, 6H, CH3); 1.25 (s, 50H, CH2); 1.60 (m,
4H, b-CH2); 2.20 (t, 2H, CH2ꢀCONH); 3.22 (s,
9H, ꢀN+(CH3)3); 3.72 (m, 2H, CH2ꢀN+(CH3)3);

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M. Bartel et al. / Chemistry and Physics of Lipids 107 (2000) 121–129
chloroform for the elution of the unpolar side
products. After elution of the side products chlo-
roform/methanol 9:1 (v/v) was used to elute the
product 16 as a white waxy solid. Pure 16 was
obtained by crystallization from diethylether.
Yield (from 15), 2.8 g (80%); m.p. 68°C. TLC
(CHCl3/CH3OH 9:1 v/v); Rf, 0.17. [a]2D0, 1.8°; (c,
10% m/6 in CHCl3). +ES−MS m/z 316.6 (M+
white crystalline substance. Yield, 489 mg (65%);
TLC (CHCl3/MeOH/NH3 35:15:2 v/v/v); Rf, 0.21.
+ES−MS, m/z 742.1 (M+Na+). 1H NMR
(500 MHz; CDCl3), l 0.85 (t, 3H, CH3), 1.25 (s,
50H, CH2), 1.6 (m, 4H, b-CH2), 2.1 (t, 2H,
CH2ꢀCONH), 3.35 (s, 9H, N+(CH3)3), 3.35–3.55
(m, 4H, CH2ꢀOꢀCH2), 3.77 (m, 2H, CH2ꢀN+
(CH3)3), 3.9 (m, 2H, CH2ꢀOꢀPO3), 4.1 (m, 1H,
1
H+). H NMR (500 MHz; CD3OD), l 1.8 (t, 3H,
ꢀCH
6
(NH)ꢀ), 4.3 (m, 2H, OꢀPO3ꢀCH2ꢀCH2ꢀN),
CH3); 2.25 (s, 26H, CH2); 2.55 (m, 2H,
7.0 (d, 1H, ꢀCH(NH
6
)ꢀ). 31P NMR, l 0.619.
OꢀCH2ꢀCH2); 2.97–3.10 (m, 1H, CH
6 NH2); 3.33–
3.64 (m, 7H, HOꢀCH2ꢀCH(NH2)ꢀCH2ꢀOꢀCH2).
6
Elemental analysis, Calculated for C19H41NO2, C,
72.25; H, 12.99; N, 4.43; found, C, 71.96; H,
12.99; N, 4.33.
3.12. 1-O-hexadecyl-2-amino-2-deoxy-sn-glycero-
3-phosphocholine (3)
The synthesis of 3 was carried out according to
the procedure of Deigner and Fyrnys (1992).
TLC (MeOH/CHCl3/NH3 90:10:10 v/v/v); Rf,
0.25; +ES−MS, m/z 481.7 (M+H+); m/z
503.6 (M+Na+). 31P NMR (CD3OD), l −
1
3.029. H NMR (500 MHz; CD3OD); l 0.8 (t,
3H, CH3); 1.3 (s, 26H, CH2), 1.6 (m, 2H,
OꢀCH2ꢀCH2ꢀ), 3.2 (s, 9H, N+(CH3)3), 3.45–3.70
(m, 7H, CH2ꢀOꢀCH2ꢀCH(NH2)ꢀCHH
CH2ꢀCH2ꢀN), 4.1 (m, 2H, ꢀCH(NH2)ꢀ; CH
OꢀPO3), 4.3 (m, 2H, OꢀPO3ꢀCH2ꢀCH2ꢀN).
6
, OꢀPO3ꢀ
6
6
Hꢀ
3.13. 1-O-hexadecyl-2-N-palmitoyl-2-amino-2-
deoxy-sn-glycero-3-phosphocholine (4)
Palmitoyl chloride (0.43 g; 1.56 mmol) in 5 ml
of dry chloroform was added dropwise at 0°C to
a stirred solution of the amino-lysolipid 3 (500
mg; 1.04 mmol) and DMAP (190 mg; 1.56 mmol)
in 20 ml of dry chloroform. The mixture was
stirred for 48 h at room temperature. The solution
of the crude product was washed with water. The
organic layer was dried with Na2SO4 and the
solvent was evaporated in vacuum. The crude
product was purified by chromatography on silica
gel using chloroform/methanol/water 35:15:2 (v/v/
v) as eluent for the elution of the main product.
After evaporation 4 was dissolved in chloroform
and precipitated with acetone to yield a pure,
Fig. 1. 1H NMR data of the Mosher ester 9M. (a) S,R-
diastereomere; (b) mixture of the S,R- and R,R-
diastereomeres; (c) 9M from sequence [A] Scheme 2.

M. Bartel et al. / Chemistry and Physics of Lipids 107 (2000) 121–129
127
Scheme 4. Introduction of the phosphoethanolamine and phosphocholine residue.
4. Discussion
In sequence [A] (Scheme 2) the free hydroxyl
group of the 2-N-acyl-serine-methylester (6) was
blocked at first with TBDPS-Cl and subsequently
transesterified with hexadecanol. The TBDPS-
blocked intermediate could be easily isolated and
separated from the excess of hexadecanol by
column chromatography. For the deprotection of
the TBDPS-blocked hydroxy group the reaction
with tetrabutylammonium fluoride was used be-
cause this method is reported to give the best
yields (Zacharie et al., 1997). Although the depro-
tection was complete the resulting intermediate
A key steps in the synthesis of the 3-O-
trimethylammonioethyl-phosphoryl-2-N-acyl-ser-
ine-hexadecylester (1) and 3-aminoethyl-phos-
phoryl-2-N-acyl-serine-hexadecylester (2) is the
preparation of a hexadecylester of a serine deriva-
tive. We started with L-serine-methylester and car-
ried out a transesterification reaction during our
course of preparation. Because the free amino
group of the serine ester disturbs the following
reactions the fatty acid amide function in 2-posi-
tion was introduced at first (Scheme 2). For the
following transesterification with hexadecanol we
used a method described by Otera et al. (1986)
which allows the conversion with sterically hin-
dered and long chain alcohols in good yields. We
investigated two possible ways of preparation.
1
showed a partial racemisation as detected by H
NMR of the corresponding Mosher ester (Fig. 1).
This can be due to the high basicity of the fluoride
ion in the absence of water.
In sequence [B] (Scheme 2) 6 was transesterified
with hexadecanol without protection of the free

128
M. Bartel et al. / Chemistry and Physics of Lipids 107 (2000) 121–129
Acknowledgements
hydroxy group. When a 5-fold excess of hexade-
canol was used no concurrence reaction by the
serine hydroxy group was observed. The chro-
matographic separation of the excess hexade-
canol was more difficult but the yield of this
one-step approach was 79% in contrast to 48%
obtained by sequence [A]. The enantiomeric pu-
rity of the 2-N-acyl-serinehexadecylester could
Our work was supported by a grant from the
ministry of education of the state Sachsen-An-
halt/Germany.
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