Total synthesis of a natural cerebroside from euphorbiaceae

Article abstract of DOI:10.1002/hlca.200790032

The regioselective total synthesis of the natural cerebroside (2R,15Z)-N-{(1S,2S,3R,4R,5Z)-1-[(β-D-glucopyranosyloxy)methyl]-2,3, 4-trihydroxyheptadec-5-en-l-yl)-2-hydroxytetracos-15-enamide (2), originally isolated from Euphorbiaceae, is reported in full

Full text of DOI:10.1002/hlca.200790032

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Total Synthesis of a Natural Cerebroside from Euphorbiaceae
by Francesca Cateni*, Marina Zacchigna, Jelena Zilic, and Gabriella Di Luca
Department of Pharmaceutical Sciences, University of Trieste, P.zle Europa 1, I-34127 Trieste
(phone: +39-040-5583720; fax: +39-040-52572; e-mail: cateni@units.it)
The regioselective total synthesis of the natural cerebroside (2R,15Z)-N-{(1S,2S,3R,4R,5Z)-1-[(b-D-
glucopyranosyloxy)methyl]-2,3,4-trihydroxyheptadec-5-en-1-yl}-2-hydroxytetracos-15-enamide
originally isolated from Euphorbiaceae, is reported in full detail.
(2),
Introduction. – Lipids and sphingoglycolipids play significant roles in numerous
biological processes. They have been considered to be present at the outer layer of bio-
logical cell membranes and to take part in antigen–antibody reactions and in the com-
munication between cells [1].
In our previous work [2], we described the isolation, identification, and biological
evaluation of several cerebrosides from Euphorbiaceae. Complex sphingoglycolipids,
in which a tetrahydroxy ꢀlong-chain baseꢁ (LCB) occurs as part of the cerebroside moi-
ety, were isolated from Euphorbia characias L. [3] and E. wulfenii HOPPE ex KOCH [4],
and characterized by physical and chemical methods. Unfortunately, sphingoglycolipids
are usually available from natural sources in only limited quantities as often hardly sep-
arable mixtures, especially in terms of their fatty acid compositions. Hence, a versatile
synthesis of these important natural products is of importance, especially for biochem-
ical investigations.
The C18 sphingosine (2S,3S,4R,5R,6Z)-2-aminooctadec-6-ene-1,3,4,5-tetrol (C18-
sphingoside; 1) present in the natural cerebroside 2, has been isolated from the latex
of Euphorbiaceae. Various syntheses of 1 have been described, either starting from
D-mannose [5], D-glutamic acid [6], or, more recently, from D-allosamines [7]. Herein,
we report the total synthesis of the more-complex cerebroside 2 from Euphorbiaceae
to confirm the structure of the natural isolate and to obtain higher quantities for bio-
logical studies.
Results and Discussion. – A retrosynthetic analysis is outlined in Scheme 1. Bond
disconnection of 2 leads to D-glucose (D-Glc), C18-sphingosine (1), and (15Z)-2-hydrox-
ytetracos-15-enoic acid (3) as building blocks. Whereas D-Glc is a readily available nat-
ural product, a suitably protected derivative of 1 had to be prepared from L-serine (L-
Ser) via the oxazolidine 4 [8], to which 2-(trimethylsilyl)-1,3-thiazole (5) was added
according to Dondoni et al. [9]. Since the way to connect the three building blocks,
Glc, 1, and 3, is somewhat problematic, this was performed in a convergent manner,
i.e., (1+3)+Glc ! 2.
ꢂ 2007 Verlag Helvetica Chimica Acta AG, Zürich

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Scheme 1
First, the C18-sphingosine derivative 6 was prepared according to [9]. Thus, the oxa-
zolidinecarbaldehyde 4 was treated with 5, which afforded, after desilylation of the ini-
tial adduct, the corresponding a-hydroxyalkylthiazole with a high level of diastereose-
lectivity. The anti-configured alcohol was separated from the syn adduct, and then sub-
jected to the following aldehyde-releasing four-step sequence: 1) OH protection as
benzyl (Bn) ether, which gave essentially the anti-isomer; 2) N-methylation of the thia-
zole ring with MeI affording the N-methylthiazolium salt; 3) reduction with NaBH4 to
the corresponding thiazolidine; and 4) Hg-mediated hydrolysis to the aldehyde 7 in
high yield [9]. Hence, 5 is a formyl-anion synthon adding to the aldehyde in a stereo-
selective manner, creating a new stereogenic center. Thus, repetition of the above proc-
esses, i.e., stereoselective addition of 5 followed by aldehyde release, over three consec-
utive cycles, each proceeding with high stereo-induction and chemical yield, finally pro-
vided compounds 8 [9] and 9.
Next, the aldehyde 9 was subjected to Wittig reaction using dodecylidenetriphenyl-
phosphorane generated in situ from the appropriate phosphonium salt and BuLi in the
presence of ꢀhexamethylphosphoramideꢁ (HMPA) so as to ensure cis selectivity [10].
This reaction led exclusively to the (Z)-alkene 10, which was isolated in relatively mod-
est overall yield (35%) after flash chromatography. The (Z)-configuration of the newly

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Scheme 2
a) 1. 5, CH2Cl2; 2. BnBr, NaH; 3. MeI, NaBH4, Hg2+, H2O. b) Me(CH2)11(Ph3)P+BrÀ, BuLi, HMPA,
A
À788. c) TFA, H2O.
generated C=C bond of 10 was verified by NMR spectroscopy. Thus, two distinct down-
field signals were observed in the 1H-NMR spectrum at d(H) 5.70 (dd, J=10.3, 8.4 Hz,
HÀC(5’)) and 5.59 (dd, J=10.4, 9.0 Hz, HÀC(4’)); and in the 13C-NMR spectrum, a
typical chemical shift of d(C) 27.7 was found for the CH2 group adjacent to the olefinic
C(6’), which is expected to resonate at d(C) ca. 33.0 in the (E)-configured long-chain
isomer. Finally, one-pot deprotection of 10 with TFA/H2O 9 :1 afforded the target
tris(O-benzyl)-protected C18-sphingosine derivative 6.
The next step was the synthesis of the Bn-protected 2-hydroxytetracos-15-enoic
acid 11 (Scheme 3). Treatment of 12-bromododecan-1-ol with (tert-butyl)diphenylsilyl
chloride (TBSCl) gave 12. The latter was heated with Ph3P at 1208 [11] to yield the cor-
responding phosphonium salt 13. After deprotonation with BuLi, the resulting phos-
phorane was subjected to Wittig reaction with the aldehyde 14, an oxidized, acetal-pro-
tected derivative of D-mannitol [12], which afforded 15 in 60% yield as a mixture of
geometric isomers. Hydrogenation with H2/PtO2 gave 16 in 85% yield, and silyl depro-
tection of the latter with Bu4NF (TBAF), followed by oxidation of the resulting OH
group with pyridinium chlorochromate (PCC), provided the aldehyde 17 in 87%
yield. Next, Wittig reaction between 17 and nonyl(triphenyl)phosphonium bromide
in the presence of BuLi at À708 gave a mixture of geometric isomers, which were easily
separated by flash column chromatography on silica gel. The major (Z)-isomer 18 (40%
yield) was then converted to the benzyl ether 19 in satisfactory overall yield through the
following sequence: 1) acetal deprotection followed by re-protection with
PhCH(OMe)2 to 20, and 2) selective reduction of 20 with (i-Bu)2AlH (DIBALH), gen-

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285
erating the mono-bezylated target compound 19. Finally, the primary OH group of 19
was oxidized with PCC to afford the corresponding aldehyde 21, and then further oxi-
dized to the target synthon 11, which was obtained in an overall yield of 59%.
Scheme 3
t
a) Bu(Ph)2SiCl (TBSCl), CH2Cl2. b) Ph3P, 1208. c) BuLi, À308. d) H2/PtO2, MeOH. e) 1. Bu4NF
(TBAF), THF; 2. pyridinium chlorochromate (PCC), CH2Cl2. f) Me(CH2)7CH2(Ph3)P+BrÀ, BuLi,
THF, À708. g) AcOH, H2O, 2N H2SO4, PhCH(OMe)2, TFA, CH2Cl2. h) DIBALH, toluene. i) PCC,
t
CH2Cl2. j) BuOH, 2-methylbut-2-ene; 2. H2O, NaClO2, NaH2PO4.
The next stage of the synthesis was the coupling of the building blocks 6 and 11
(Scheme 4). The reaction furnished the protected ceramide 22 in 50% yield upon cou-
pling with DCC/HOBt (DCC=dicyclohexylcarbodiimide, HOBt=1-hydroxy-1H-ben-
zotriazole) in THF. b-Glucosidation of 22 with the protected Glc derivative 23 under
Koenigs–Knorr conditions in the presence of Hg(CN)2 in nitromethane afforded 24
in 50% yield [13]. Finally, removal of the Ac protecting groups upon alkaline hydrol-
ysis, followed by debenzylation with lithium naphthalenide, afforded the target cere-
broside 2 in 85% yield [14].
The structure of compound 2 was secured by EI-MS, FAB-MS, 1H-NMR, 13C-NMR,
and 1H,13C-COSY experiments (see Exper. Part). Also, the high-field NMR data of the
synthetic material were found to be identical with those reported for the compound iso-
lated from natural sources [3][4].

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Scheme 4
a) HOBT, DCC, THF. b) Benzene, Hg(CN)2. c) 1. 5% KOH in MeOH; 2. Li naphthalenide, THF,
À258.
Experimental Part
General. All solvents were distilled before use, and all reactions were carried out under N2 atmos-
phere. Column chromatography (CC): Kieselgel 60 (70–230 mesh; Merck). Thin-layer chromatography
(TLC): pre-coated Kieselgel 60 F254 plates (Merck). Melting points (m.p.): Büchi-510 micro-melting-point
apparatus; uncorrected. FT-IR Spectra: Jasco IR-700 spectrometer, in cmÀ1. 1H-and 13C-NMR Spectra:
Varian Gemini-200 and Unity-400 spectrometers, in CDCl3 or C5D5N soln.; d in ppm rel. to Me4Si, J in Hz.
EI-MS (4 kV, 70 eV) and FAB-MS (8 kV, Xe): Kratos MS-80-RFA apparatus; FAB-MS in MeOH soln.
with glycerol/NaCl matrix; all values in m/z (rel. %).
tert-Butyl (4S)-4-[(1S)-1-(Benzyloxy)-2-oxoethyl]-2,2-dimethyl-1,3-oxazolidine-3-carboxylate (7).
Prepared according to [15], and purified by CC (SiO2; hexane/AcOEt 7:3). Yield: 1.6 g (85%). Colorless
powder. M.p. 170–1718. IR (KBr): 1735, 1700, 1170. 1H-NMR (CDCl3)1): 1.46 (s, Me); 1.51 (br. s, tBu);
1.60 (s, Me); 3.40 (m, HÀC(1’)); 3.80–4.20 (m, CH2(5), HÀC(4)); 4.40–4.80 (m, PhCH2); 7.30 (m, 5
arom. H); 9.60 (d, CHO). 13C-NMR (CDCl3): 22.2–28.1 (Me); 58.1 (C(4)); 65.0 (C(5)); 65.5 (CMe3);
73.7 (PhCH2); 82.3 (BnOCH); 123.0–128.0 (arom. C); 137.0; 173.0 (O=CÀO); 200.2 (CHO). EI-MS:
349 (15, M+), 320 (100, ([MÀ29]+), 247 (71).
tert-Butyl (4S)-4-[(1S,2S)-1,2-Bis(benzyloxy)-3-oxopropyl]-2,2-dimethyl-1,3-oxazolidine-3-carboxy-
late (8). Prepared according to [15] from 7 (0.9 g, 2.57 mmol) and 5 (0.2 g, 1.5 mmol). Repetition of
the usual functionalization–unmasking sequence afforded 8 (ribo configuration) in 85% yield, together
with 15% of the arabino-configured isomer. IR (film): 1739, 1700, 1665, 1170. 1H-NMR (CDCl3): 1.45 (s,
Me); 1.50 (br. s, tBu); 1.61 (s, Me); 3.42–3.60 (m, HÀC(1’), HÀC(2’)); 3.82–4.22 (m, CH2(5), HÀC(4));
4.45–4.89 (m, 2 PhCH2); 7.30 (m, 10 arom. H); 9.75 (br. s, CHO). 13C-NMR (CDCl3): 26.2–29.3 (Me);
58.3 (C(4)); 64.7 (C(5)); 65.6 (Me3C); 72.9, 73.9 (2 PhCH2); 79.3 (BnOCH); 80.7, 84.2 (BnOCH);
123.0–128.0 (arom. C); 137.2; 173.1 (O=CÀO); 201.2 (CHO). EI-MS: 469 (20, M+), 440 (100, [MÀ29]+).
1
)
Arbitrary atom numbering for all compounds (see Schemes 2–4).

Helvetica Chimica Acta – Vol. 90 (2007)
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tert-Butyl (4S)-2,2-Dimethyl-4-[(1S,2S,3S)-1,2,3-tris(benzyloxy)-4-oxobutyl]-1,3-oxazolidine-3-car-
boxylate (9). Repetition of the usual functionalization–unmasking sequence according to [15] with 8
1
afforded 9 (0.5 g, 78%) as an oil. IR (film): 1739, 1700, 1660, 1175. H-NMR (CDCl3): 1.46 (s, Me);
t
1.55 (br. s, Bu); 1.65 (s, Me); 3.45–3.70 (m, HÀC(1’), HÀC(2’), HÀC(3’)); 3.83–4.50 (m, H2(5), HÀ
C(4)); 4.60–4.80 (m, 3 PhCH2); 7.32–7.40 (m, 15 arom. H); 9.35 (s, CHO). 13C-NMR (CDCl3):
26.0–29.5 (Me); 58.0 (C(4)); 63.7 (C(5)); 65.9 (Me3C); 72.2, 73.3 (2 PhCH2); 74.6; 75.6 (BnOCH);
80.2 (PhCH2); 82.2, 82.4 (2 BnOCH); 127.0–128.0 (arom. C), 137.0; 176.1 (O=CÀO); 201.0 (CHO).
EI-MS: 589 (15, M+), 560 (100, ([MÀ29]+), 487 (70).
(4S)-2,2-Dimethyl-4-[(1S,2R,3R,4Z)-1,2,3-tris(benzyloxy)hexadec-4-en-1-yl]-1,3-oxazolidine (10).
To a suspension of dodecyl(triphenyl)phosphonium bromide (0.43 g, 0.85 mmol) in anh. THF (20 ml)
and HMPA (1.5 ml) at À788 was added under N2 a 1.6M soln. of BuLi in hexane (0.6 ml, 0.90 mmol).
The mixture was stirred at this temp. for 1 h. Then, a soln. of 9 (0.5 g, 0.85 mmol) in THF (10 ml) was
added dropwise under stirring at À788, and the resulting mixture was stirred at this temp. for 1 h.
Then, the temp. was allowed to rise to À108 within 2 h, the mixture was quenched by addition of
brine (10 ml), and extracted with Et2O (3”20 ml). The combined org. extracts were dried (Na2SO4)
and concentrated in vacuo. The residue was purified by CC (SiO2; hexane/AcOEt 4 :1) to yield 10
(0.22 g, 35%) as an oil. A small amount of the corresponding (E)-isomer was obtained by further elution.
1
IR (film): 2970, 1700, 1630. H-NMR (CDCl3): 0.87 (t, J=6.0, Me(CH2)10); 1.23 (br. s, 9 CH2); 1.46 (s,
t
Me); 1.57 (br. s, Bu); 1.65 (s, Me); 2.30 (m, CH2ÀCH=); 3.50–3.70 (m, HÀC(1’), HÀC(2’), HÀC(3’));
3.80–4.55 (m, CH2(5), HÀC(4)); 4.63–4.79 (m, 3 PhCH2); 5.59 (dd, J=10.4, 9.0, HÀC(4’)); 5.70 (dd,
J=10.3, 8.4, HÀC((5’)); 7.30–7.40 (m, 15 arom. H). 13C-NMR (CDCl3): 14.3 (Me(CH2)10); 22.0–26.1
(Me); 27.7 (C(6’)); 28.1–30.0 (CH2); 58.3 (C(4)); 63.8 (C(5)); 66.0 (Me3C); 70.4, 73.3 (2 PhCH2); 73.8;
74.8 (BnOCH); 80.1 (PhCH2); 81.7, 82.1 (2 BnOCH); 123.6 (C(5’)); 127.0–128.0 (arom. C); 136.0
(C(4’)); 137.0; 175.6 (O=CÀO). EI-MS: 725 (22, M+), 584 (60, [MÀC10H21]+).
(2S,3S,4R,5R,6Z)-6-Octadecasphingenine (=(2S,3S,4R,5R,6Z)-2-Amino-3,4,5-tris(benzyloxy)octa-
dec-6-en-1-ol; 6). A mixture of trifluoroacetic anhydride (10 ml), H2O (1 ml), and 10 (0.28 g, 0.37
mmol) was stirred at r.t. for 1 h. Then, the mixture was washed with sat. aq. NaHCO3 soln. and brine,
and extracted with CH2Cl2 (3”5 ml). The combined org. extracts were dried (Na2SO4) and concentrated
in vacuo. The residue was purified by CC (SiO2; hexane/AcOEt 4 :1) to afford 6 (0.16 g, 90%) as an oil.
[a]2D0 =À33.6 (c=0.2, CHCl3). IR (film): 3390, 3300, 3250, 1585, 1045. 1H-NMR (CDCl3): 0.88 (t, J=6.0,
Me(18)); 1.27 (br. s, 9 CH2); 1.73 (br. s, OH, NH2); 2.05 (m, CH2(8)); 2.88 (m, HÀC(2)); 3.65 (br. d,
J=5.0, CH2(1)); 3.60–3.78 (m, HÀC(3), HÀC(4), HÀC(5)); 4.65–4.80 (m, 3 PhCH2); 5.56 (dd,
J=10.5, 9.0, HÀC(6)); 5.75 (dd, J=10.3, 8.4, HÀC(7)); 7.10–7.50 (m, 15 arom. H). 13C-NMR
(CDCl3): 14.2 (C(18)); 22.7–31.8 (CH2); 27.8 (C(8)); 52.9 (C(2)); 59.1 (C(1)); 70.7, 72.2, 72.8 (3
PhCH2); 73.3, 75.5, 81.2 (3 BnOCH); 125.3 (C(7)); 128.2–129.3 (arom. C); 136.1 (C(6)); 137.6. EI-
MS: 601 (23, M+), 460 (73, [MÀC10H21]+).
[(12-Bromododecyl)oxy](tert-butyl)diphenylsilane (12). A soln. of 12-bromododecanol (4.0 g, 15
t
mmol) in anh. CH2Cl2 (20 ml) containing BuPh2SiCl (TBSCl; 3.2 ml, 12.4 mmol) and 1H-imidazole
(1.7 g, 2.2 mmol) was stirred for 12 h at r.t. The mixture was then poured into ice-cooled aq. NaHCO3
soln. and extracted with CH2Cl2 (3”50 ml). The combined org. extracts were dried (Na2SO4) and concen-
trated in vacuo. The residue was purified by CC (SiO2; hexane) to afford 12 (7 g, 95%) as colorless nee-
dles. M.p. 131–1328. IR: 1585, 1440, 1110, 1065. 1H-NMR (CDCl3): 1.08 (s, tBu); 1.20–1.70 (br. s, 10 CH2);
3.42 (t, J=6.2, CH2(1)); 3.65 (m, CH2(12)); 7.30–7.50 (m, 6 arom. H); 7.60–7.80 (m, 4 arom. H). EI-MS:
503 (30, M+).
(12-{[(tert-Butyl)(diphenyl)silyl]oxy}dodecyl)(triphenyl)phosphonium Bromide (13). A mixture of
Ph3P (0.16 g, 0.6 mmol) and 12 (0.3 g, 0.6 mmol) was stirred under N2 at 1208 for 12 h. The resulting Wittig
salt 13 was used in the next step without further purification.
(tert-Butyl)({(12Z)-13-[(4R)-2,2-dimethyl-1,3-dioxolan-4-yl]tridec-12-en-1-yl}oxy)diphenylsilane
(15). A 1.6M BuLi soln. in hexane (0.4 ml, 0.6 mmol) was added to a stirred suspension of crude 13 (0.46 g,
0.6 mmol) in anh. THF (30 ml) under N2 at À308, and the mixture was stirred for 1 h at this temp. Then, a
soln. of 2,3-O-isopropylidene-D-glyceraldehyde (14; 0.05 g, 0.43 mmol) in anh. THF (10 ml) was added,
and stirring was continued for 1 h at À308, and for 2 h at 08. The mixture was poured into ice-cooled sat.
NH4Cl soln. (15 ml) and extracted with Et2O (3”25 ml). The combined org. extracts were washed with

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brine, dried (Na2SO4), filtered, and concentrated in vacuo. The residue was purified by CC (SiO2; hexane/
AcOEt 10 :1) to afford a mixture of (E)-and ( Z)-15 (4.8 g, 60%). IR (film): 1589, 1466, 1430, 1380, 1110.
t
1H-NMR (CDCl3): 1.10 (s, Bu); 1.25 (br. s, 8 CH2); 1.32, 1.37 (2s, Me2C); 1.65 (m, CH2(6)); 2.22 (m,
CH2(5)); 3.49–4.70 (m, CH2(1), HÀC(2), CH2(15)); 5.30–5.60 (m, CH=CH); 7.30–7.50 (m, 6 arom.
H); 7.60–7.80 (m, 4 arom. H). 13C-NMR (CDCl3): 19.2 (SiC); 22.0–26.0 (Me); 28.2–30.1 (CH2), 32.3
(CH2ÀCH=); 64.0 (CH2OSi); 69.5 (C(1)); 72.1 (C(2)); 109.0 (Me3C); 127.1 (C(3)); 128.0–136.1
(arom. C); 135.3 (C(4)); 134.0. EI-MS: 536 (20, M+), 479 (79, [MÀC4H9]+).
(tert-Butyl)({13-[(4R)-2,2-dimethyl-1,3-dioxolan-4-yl]tridecyl}oxy)diphenylsilane (16). A soln. of 15
(2.5 g, 4.65 mmol) in anh. MeOH (50 ml) was hydrogenated at 100 atm H2 over PtO2 (1.2 g) at r.t. When
the reaction was complete (GC control), the pressure was released, and the catalyst was removed by fil-
tration. The filtrate was concentrated in vacuo to afford 16 (2.2 g, 85%) as an oil, which was used in the
next step without purification. IR (film): 1600, 1110. 1H-NMR (CDCl3): 1.10 (s, tBu); 1.26 (br. s, 12 CH2);
1.31, 1.36 (2s, Me2C); 3.50–4.65 (m, CH2(1), HÀC(2), CH2(15)); 7.30–7.50 (m, 6 arom. H); 7.60–7.80 (m,
4 arom. H). EI-MS: 538 (12, M+).
13-[(4R)-2,2-Dimethyl-1,3-dioxolan-4-yl]tridecanal (17). a) A 1M soln. of Bu4NF (TBAF) in THF (6
ml, 6.0 mmol) was added to a soln. of 16 (1.6 g, 3.0 mmol) in THF (50 ml), and the mixture was stirred for
3 h at r.t. Then, the mixture was diluted with CHCl3 and washed with sat. aq. NH4Cl soln. The aq. layer
was re-extracted with CHCl3, the combined org. layers were washed with brine, dried (Na2SO4), and con-
centrated in vacuo. The residue was purified by CC (SiO2; hexane/AcOEt 7:3) to afford 13-[(4R)-2,2-
dimethyl-1,3-dioxolan-4-yl]tridecan-1-ol (0.8 g, 89%).
b) A soln. of the above intermediary alcohol (0.8 g, 2.6 mmol) in CH2Cl2 (15 ml) was added to a stir-
red suspension of pyridinium chlorochromate (PCC; 0.6 g, 2.7 mmol) in anh. CH2Cl2 (20 ml), and the
mixture was stirred at r.t. for 2 h. The mixture was treated with Celite, extracted with Et2O (3”20 ml),
and the combined org. extracts were filtered through a short plug of SiO2, and concentrated in vacuo.
The resulting residue was subjected to CC (SiO2; hexane/AcOEt 5 :1) to afford 17 (0.7 g, 87%) as an
oil. IR (film): 2750, 1730, 1430, 1115. 1H-NMR (CDCl3): 1.28 (br. s, 12 CH2); 1.30, 1.36 (2s, Me2C);
2.40 (m, CH2(14)); 3.50–4.05 (m, CH2(1), HÀC(2)); 9.70 (s, CHO). 13C-NMR (CDCl3): 24.1, 24.3
(Me2C); 27.0–31.9 (CH2); 62.1 (C(14)); 69.5 (C(1)); 72.3 (C(2)); 108.7 (Me2C); 204.0 (CHO). EI-MS:
298 (25, M+), 269 (100, [MÀ29]+).
(4R)-4-[(13Z)-Docos-13-en-1-yl]-2,2-dimethyl-1,3-dioxolane (18). A 1.6M BuLi soln. in hexane (1.5
ml, 2.4 mmol) was added to a stirred suspension of nonyl(triphenyl)phosphonium bromide (1.12 g, 2.4
mmol) in anh. THF (30 ml) and HMPA (3 ml) under N2 at À788, and the mixture was stirred for 40
min at this temp. Then, a soln. of 17 (0.65 g, 2.2 mmol) in anh. THF (20 ml) was added, and stirring
was continued for 1 h at À788, and for 2 h at 08. The mixture was poured into ice-cooled brine (20
ml), and extracted with Et2O (3”20 ml). The combined org. extracts were dried (Na2SO4), filtered,
and concentrated in vacuo. The residue was purified by CC (SiO2; hexane/AcOEt 9 :1) to afford pure
18 (0.35 g, 40%) as an oil, together with a small amount (0.09 g, 10%) of the (E)-isomer (oil). IR
(film): 1650, 1120. 1H-NMR (CDCl3): 0.90 (t, Me); 1.26 (br. s, 17 CH2); 1.31, 1.36 (2s, Me2C);
1.90–2.15 (m, CH2(14), CH2(17)); 3.50–4.05 (m, CH2(1), HÀC(2)); 5.35 (dd, J=9.0, 9.2, CH=CH).
13C-NMR (CDCl3): 14.0 (Me); 24.1, 24.3 (Me2C); 26.2–31.3 (CH2); 27.8 (C(14)); 27.9 (C(17)); 69.4
(C(1)); 72.5 (C(2)); 108.9 (Me2C); 130.0 (CH=CH). EI-MS: 408 (12, M+), 295 (100, [MÀC8H17]+).
(4R)-4-[(13Z)-Docos-13-en-1-yl]-2-phenyl-1,3-dioxolane (20). a) A soln. of 18 (0.35 g, 0.80 mmol) in
THF (3.6 ml), AcOH (20 ml), H2O (12 ml), and 2N aq. H2SO4 (10 ml) was stirred at r.t. for 24 h. The mix-
ture was washed with sat. aq. NaHCO3 soln. (20 ml), and extracted with CH2Cl2 (3”25 ml). The com-
bined org. extracts were dried (Na2SO4) and concentrated in vacuo, and the resulting crude diol, i.e.,
(2R,15Z)-tetracos-15-ene-1,2-diol, was used in the next step without further purification.
b) A mixture of the above crude diol (0.2 g, 0.5 mmol) in CH2Cl2, benzaldehyde dimethyl acetal
(PhCH(OMe)2; 0.12 ml, 0.80 mmol), and CF3CO2H (TFA; 0.1 ml) was stirred under N2 at 508 for 2 h.
The mixture was then washed with sat. aq. NaHCO3 soln. (10 ml), and extracted with CH2Cl2 (3”20
ml). The combined org. extracts were washed with brine, and concentrated in vacuo. The resulting res-
idue was purified by CC (SiO2; hexane/Et2O 10 :1) to afford 20 (0.12 g, 50%) as an oil. A small amount
1
(20 mg) of the (E)-isomer was also obtained by further elution. IR (film): 1650, 1590, 1110. H-NMR
(CDCl3): 0.90 (t, Me); 1.27 (br. s, 17 CH2); 1.90–2.10 (m, CH2(14), CH2(17)); 3.40–4.20 (m, CH2(1),

Helvetica Chimica Acta – Vol. 90 (2007)
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HÀC(2)); 5.35 (m, CH=CH); 5.80 (s, PhCH); 7.35 (m, 3 arom. H); 7.50 (m, 2 arom. H). 13C-NMR
(CDCl3): 14.0 (Me); 26.0–30.9 (CH2); 27.8 (C(14)); 27.9 (C(17)); 69.5 (C(1)); 72.6 (C(2)); 107.1
(PhCH); 130.1 (CH=CH); 128.0–135.0 (arom. C). EI-MS: 456 (30, M+), 343 (100, [MÀC8H17]+).
(2R,15Z)-2-(Benzyloxy)tetracos-15-en-1-ol (19). A soln. of 20 (0.1 g, 0.2 mmol) was added to a 1M
suspension of diisobutylaluminum hydride (DIBALH) in toluene (2 ml, 2 mmol), and the mixture was
stirred at r.t. for 24 h. The reaction was quenched with MeOH, the mixture was washed with sat. aq.
NaHCO3 soln. (5 ml), and extracted with CH2Cl2 (3”10 ml). The org. extracts were combined, dried
(Na2SO4), and concentrated under reduced pressure. The residue was purified by CC (SiO2; hexane/
Et2O 1:1) to afford 19 (73 mg, 80%) as colorless needles. M.p. 95–968. IR (KBr): 3400, 1650, 1585,
1
1110. H-NMR (CDCl3): 0.90 (t, Me); 1.26 (br. s, 17 CH2); 1.90–2.10 (m, CH2(14), CH2(17)); 3.41 (m,
HÀC(2)); 4.20–4.72 (m, CH2(1), PhCH2); 5.30–5.50 (m, CH=CH); 7.30–7.50 (m, 5 arom. H). EI-MS:
458 (20, M+), 345 (80, [MÀC8H17]+).
(2R,15Z)-2-(Benzyloxy)tetracos-15-enal (21). Prepared from 19 (0.7 g, 1.5 mmol) in analogy to the
procedure described for the preparation of 17 (see above). Yield: 0.62 g (90%). IR (film): 2745, 1730,
1
1650, 1585, 1110. H-NMR (CDCl3): 0.90 (t, Me); 1.27 (br. s, 17 CH2); 1.90–2.15 (m, 2 CH2); 3.75 (m,
1 H); 4.50–4.75 (m, PhCH2); 5.35 (m, CH=CH); 7.30–7.45 (m, 5 arom. H); 9.60 (s, CHO). 13C-NMR
(CDCl3): 14.3 (Me); 26.0–30.6 (CH2); 73.3 (PhCH2); 83.8; 128.1, 130.0 (CH=CH); 130.3–135.1 (arom.
C); 204.1 (CHO). EI-MS: 456 (10, M+), 427 (100, ([MÀ29]+), 314 (65, [MÀ29ÀC8H17]+).
(2R,15E)-2-(Benzyloxy)tetracos-15-enoic Acid (11). Aldehyde 21 (4.3 g, 9.6 mmol) was dissolved in
tBuOH (20 ml) and 2-methylbut-2-ene (4.8 ml). A soln. of NaClO2 (0.8 g, 8.8 ml) and NaH2PO4 (1.0 g, 6.6
mmol) in H2O (8 ml) was added over 10 min. The pale-yellow mixture was stirred at r.t. overnight. The
volatile components were removed under reduced pressure. The residue was dissolved in H2O (20 ml),
and the soln. was extracted with hexane (3”20 ml). The aq. layer was acidified to pH 2 with 2N HCl,
and extracted with Et2O (3”20 ml). The combined org. layers were washed with H2O, dried (Na2SO4),
1
and concentrated to afford 11 (2.6 g, 59%) as an oil. IR (film): 3060, 1730, 1650, 1580, 1110. H-NMR
(CDCl3): 0.90 (t, Me(23)); 1.27 (br. s, 17 CH2); 1.90–2.10 (m, CH2(14), CH2(17)); 3.75 (m, HÀC(2));
4.50–4.75 (m, PhCH2); 5.35 (m, CH=CH); 7.30–7.45 (m, 5 arom. H); 12.1 (br. s, COOH). 13C-NMR
(CDCl3): 14.2 (C(24)); 26.0–30.6 (CH2); 27.8 (C(14)); 27.9 (C(17)); 73.2 (PhCH2); 83.7 (C(1)), 128.0
(CH=CH); 130.0, 130.2–135.0 (arom. C); 220.1 (COOH). EI-MS: 472 (15, M+), 359 (50, [MÀC8H17]+).
(2R,15Z)-2-(Benzyloxy)-N-[(1S,2S,3R,4R,5Z)-2,3,4-tris(benzyloxy)-1-(hydroxymethyl)heptadec-5-
en-1-yl]tetracos-15-enamide (22). To a soln. of 6 (1 g, 1.6 mmol) and 11 (0.7 g, 1.6 mmol) in anh. THF (20
ml) was added a soln. of 1,3-dicyclohexylcarbodiimide (DCC; 0.4 g, 2 mmol) and 1-hydroxy-1H-benzo-
triazole (HOBt; 0.3 g, 2 ml) in anh. THF (15 ml), and the mixture was stirred for 48 h at r.t. The solvent
was evaporated at reduced pressure, and the residue was purified by CC (SiO2; hexane/AcOEt 8 :2).
Yield: 0.76 g (50%). Colorless oil. IR (film): 3442, 1739, 1670. 1H-NMR (CDCl3): 0.88 (m, Me(18),
Me(24’)); 1.28 (br. s, 21 CH2); 1.90–2.20 (m, CH2(8), CH2(14’), CH2(17’)); 3.50–4.27 (m, CH2(1), HÀ
C(2), HÀC(3), HÀC(4), HÀC(5), HÀC(2’)); 4.52–4.82 (m, 4 PhCH2); 5.24–5.90 (m, HÀC(6), HÀ
C(7), HÀC(15’), HÀC(16’)); 7.10–7.41 (m, 20 arom. H, NH). 13C-NMR (CDCl3): 14.0, 14.2 (C(18),
C(24’)); 23.9–30.7 (CH2); 27.8, 27.9, 28.1 (C(8), C(14’), C(17’)); 51.7 (C(2)); 62.3 (C(1)); 70.2
(PhCH2); 72.2 (BnOCH); 74.3 (PhCH2); 74.4 (PhCH2); 74.6 (PhCH2); 79.9 (BnOCH); 80.3
(BnOCH); 80.5 (BnOCH); 126.1–130.2 (arom. C); 137.5, 131.0–138.2 (C(6), C(7), C(15’), C(16’));
179.2 (C(1’)). EI-MS: 1056 (10, M+).
(2R,15Z)-2-(Benzyloxy)-N-((1S,2S,3R,4R,5Z)-2,3,4-tris(benzyloxy)-1-{[(2,3,4,6-tetra-O-acetyl-b-D-
glucopyranosyl)oxy]methyl}heptadec-5-en-1-yl)tetracos-15-enamide (24). Anh. benzene was added to a
soln. of 22 (150 mg, 0.14 mmol) in nitromethane (13 ml), and the resulting soln. was stirred at 1108 to
remove moisture azeotropically. The mixture was concentrated to a volume of ca. 15 ml, and cooled
under N2. Then, 2,3,4,6-tetra-O-acetyl-a-D-glucopyranosyl bromide (23; 82.2 mg, 0.2 mmol) and HgCN2
(50 mg, 0.2 mmol) were added, and stirring was continued for 2 h at 908 under N2. After cooling, the mix-
ture was diluted with CHCl3, and washed with a sat. soln. of H2S. The black precipitate (HgS) was filtered
off (Celite), the filtrate was washed with sat. aq. NH4Cl soln. and brine, dried (Na2SO4), and concentrated
in vacuo. The residue was purified by CC (SiO2; CHCl3/AcOEt 15 :1). Yield: 95.8 mg (50%). The com-
pound was used in the next step without further purification.

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Helvetica Chimica Acta – Vol. 90 (2007)
(2R,15Z)-N-{(1S,2S,3R,4R,5Z)-1-[(b-D-Glucopyranosyloxy)methyl]-2,3,4-trihydroxyheptadec-5-en-
1-yl}-2-hydroxytetracos-15-enamide (2). a) A soln. of crude 24 in MeOH (10 ml) was treated with 5%
KOH in MeOH (10 ml). The mixture was stirred at r.t. for 30 min, and then neutralized with Dowex
50 WX8 (H+ form). The resin was removed by filtration, the filtrate was concentrated under reduced
pressure, and the residue was purified by CC (SiO2; CHCl3/MeOH 10 :1) to afford a colorless powder
(60 mg; intermediate). Meanwhile, in a separate flask, to a soln. of naphthalene (30 mg, 0.28 mmol) in
THF (1.5 ml) was added Li (1.5 mg, 0.2 mmol) in small pieces. The mixture was stirred at r.t. under N2
atmosphere until the metal was completely dissolved (ca. 3 h) [11]. The resulting dark-green lithium
naphthalenide soln. was cooled to À258. Then, a soln. of the above colorless powder (60 mg, 0.05
mmol) in THF (2 ml) was added dropwise over 5 min. The resulting mixture was stirred at À258 for 2
h. Then, sat. aq. NH4Cl soln. (0.5 ml) and H2O (0.5 ml) were added. The mixture was extracted with
Et2O (3”5 ml). The combined org. extracts were washed with H2O and brine, dried (Na2SO4), filtered,
and concentrated. The crude product was purified by CC (SiO2; CHCl3/MeOH 5 :1) to afford the target
cerebroside 2 (0.36 g, 85%). [a]2D0 =+13.2 (c=0.3, MeOH). IR (film): 3500, 1740, 1670. 1H-NMR
(C5D5N)1): 0.86 (m, Me(18), Me(24’)); 1.25 (br. s, 21 CH2); 1.90–2.40 (m, CH2(8), CH2(14’),
CH2(17’)); 3.68 (m, HÀC(5’’)); 3.90 (t, J=7.5 Hz, HÀC(2’’)); 4.10 (obscured, HÀC(4)); 4.13 (obscured,
HÀC(3’’)); 4.15 (obscured, HÀC(4’’)); 4.23 (m, HÀC(3)); 4.29 (dd, J=11.7, 5.7, HbÀC(6’’)); 4.45 (dd,
J=11.7, 2.2, HaÀC(6’’)); 4.48 (dd, HbÀC(1)); 4.55 (dd, J=7.8, 3.7, HÀC(2’)); 4.66 (dd, J=10.8, 6.6,
HaÀC(1)); 4.78 (m, HÀC(5)); 4.92 (d, J=8.0, HÀC(1’’)); 5.22 (m, HÀC(2)); 5.50 (m, CH=CH); 5.60
(m, HÀC(7)); 5.80 (dd, J=10.0, 9.7, HÀC(6)); 8.51 (d, J=9.0, NH). 13C-NMR (C5D5N): 14.0, 14.2
(C(18), C(24’)); 23.0–30.5 (CH2); 27.8, 27.9, 28.1 (C(8), C(14’), C(17’)); 51.7 (C(2)); 62.6 (C(6’’)); 67.6
(C(5)); 70.2 (C(1)); 71.5 (C(4’’)); 72.4 (C(2’)); 75.1 (C(2’’)); 75.9 (C(3), C(4)); 78.4 (C(3’’), C(5’’));
105.4 (C(1’’)); 130.2–131.0 (C(6), C(7), C(15’), C(16’)); 175.6 (C(1’)). FAB-MS: 881 (15, [M+Na]+),
679 (20, [MÀ179]+), 661 (35, [MÀ179ÀH2O]+), 516 (100, [C24H47NO9 +Na]+), 314 (50, C18H36NOþ3 ),
296 (45, C18H34NOþ2 ).
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Received October 2, 2006