Flexible, polymer-supported synthesis of sphingosine derivatives provides ceramides with enhanced biological activity

Article abstract of DOI:10.1016/j.bmc.2014.07.024

A polymer-supported route for the synthesis of sphingosine derivatives is presented based on the C-acylation of polymeric phosphoranylidene acetates with an Fmoc-protected amino acid. The approach enables the flexible variation of the sphingosine tail through a deprotection-decarboxylation sequence followed by E-selective Wittig olefination cleavage. d-Erythro-sphingosine analogs have been synthesized by diastereoselective reduction of the keto group employing LiAlH(O-tBu)₃as reducing agent. The effect of ceramides and keto-ceramides on the proliferation of three cancer cell lines HEP G-2, PC-12 and HL-60 was investigated and a ceramide containing an aromatic sphingosine tail was identified as being most active.

Full text of DOI:10.1016/j.bmc.2014.07.024

Bioorganic & Medicinal Chemistry 22 (2014) 5506–5512
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry
journal homepage: www.elsevier.com/locate/bmc
Flexible, polymer-supported synthesis of sphingosine derivatives
provides ceramides with enhanced biological activity
Adeeb El-Dahshan b, Samer I. Al-Gharabli c, Silke Radetzki b, Taleb H. Al-Tel d, Pradeep Kumar e,
Jörg Rademann a,b,
⇑
a Institute of Pharmacy, Free University Berlin, Königin-Luise-Str. 2+4, 14195 Berlin, Germany
b Leibniz Institute for Molecular Pharmacology (FMP), Robert-Rössle-Str. 10, 13125 Berlin, Germany
c Chemical-Pharmaceutical Engineering, School of Applied Medical Sciences, German-Jordanian University, P.O. Box 35247, Amman 11180, Jordan
d College of Pharmacy, University of Sharjah, P.O. Box 27272, Sharjah, United Arab Emirates
e Organic Chemistry Division, National Chemical Laboratory, Homi Bhabha Road, Pune 411 008, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A polymer-supported route for the synthesis of sphingosine derivatives is presented based on the C-acyl-
ation of polymeric phosphoranylidene acetates with an Fmoc-protected amino acid. The approach
enables the flexible variation of the sphingosine tail through a deprotection–decarboxylation sequence
Received 20 May 2014
Revised 15 July 2014
Accepted 16 July 2014
Available online 24 July 2014
followed by E-selective Wittig olefination cleavage. D-Erythro-sphingosine analogs have been synthesized
by diastereoselective reduction of the keto group employing LiAlH(O-tBu)3 as reducing agent. The effect
of ceramides and keto-ceramides on the proliferation of three cancer cell lines HEP G-2, PC-12 and HL-60
was investigated and a ceramide containing an aromatic sphingosine tail was identified as being most
active.
Keywords:
Lipids
Sphingosine
Ceramide
Apoptosis
Lipid rafts
Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction
phosphatidyl ceramide, is the major phosphosphingolipid of
eukaryotic cells. It is cleaved by sphingomyelinases releasing cera-
Sphingolipids are the sphingosine-containing components of cell
membranes. They are part of structured membrane areas denomi-
nated as lipid rafts1 and as such they are involved in numerous
specific cellular functions including important events of inter- as
well as intracellular signal transduction.2 In agreement with their
functional relevance, genetic defects in several enzymes of the
sphingolipid metabolism have been linked to a number of well-
characterized monoallelic diseases.3 In addition, functional links of
the sphingolipid metabolism with several polyallelic diseases have
been established including cancer,4 diabetes,5 and bacterial infec-
tions.6 Major subclasses of sphingolipids, are glycosphingolipids
and phosphosphingolipids. Glycosphingolipids constitute impor-
tant extracellular signals being responsible for cell adhesion and
among others recognition of cancer cells by the immune system.
mide, which can be further degraded to sphingosine by ceramidases.
Phosphorylation of sphingosine provides sphingosine-1-phosphate
(S1P). S1P superagonists acting via the G-protein coupled S1P-
receptors induce cell growth and prodrugs thereof are clinically
admitted for the pharmaceutical treatment of multiple sclerosis.8
Ceramide, on the contrary, induces apoptosis via release of cyto-
chrome c from mitochondria and activation of caspases.9 This path-
way towards apoptosis is essential for the prevention of cancer as
the programmed cell death eliminates cells with genetic defects.
In >95% of all malignant tumours, however, the pathway towards
apoptosis is blocked by mutations, for example, of the oncogene
p53 which in its native form recognizes DNA damage and thus
induces the programmed cell death of aberrant cells. As a conse-
quence ceramides are investigated for combination therapy of can-
cerous diseases especially in cases in which cancer cells have
acquired resistance towards anti-cancer drugs such as cell-cycle
inhibitors.10
a-Galactosylceramide, for example, activates invariant natural
killer T-cells (iNKT) and has been under clinical investigation for
treatment of hepatitis C infections.7 Sphingomyeline, or choline
In view of these results, there has been considerable interest in
structurally modified sphingosines.11 It has been shown that some
of their analogues induce morphological changes in neuronal
cells12 and also behave as enzyme inhibitors.13 Because of limited
⇑
Corresponding author. Tel.: +49 30 838 53272; fax: +49 30 838 459829.
E-mail address: joerg.rademann@fu-berlin.de (J. Rademann).
URL: http://www.bcp.fu-berlin.de/ag-rademann (J. Rademann).
http://dx.doi.org/10.1016/j.bmc.2014.07.024
0968-0896/Ó 2014 Elsevier Ltd. All rights reserved.

A. El-Dahshan et al. / Bioorg. Med. Chem. 22 (2014) 5506–5512
5507
Table 1
O
OH
syn/anti
C-acylations followed by Wittig reaction leading to 4E-ketoceramides 10a–e
R/S
NH
R´
R
R/S
NH
R´
R
R´´
Entry
Compound
R
Yielda (%)
R´´
1
2
10a
10b
47
49
C13H27
O
1a-e
10a-e
O
3
4
5
10c
10d
10e
C8H17
62
79
68
Ph
Ph
O
Ph
Ph
P
P
R
OTMSE
OTMSE
FmocHN
R/S
a
Yields of isolated products.
O
O
5
6
Scheme 1. Variation of sphingosine analogs based on solid phase synthesis
employing phosphoranylidene acetate resin 5.
to ceramide derivatives on solid support (Scheme 1). C-acylation of
resin 5 should enable the introduction of various amino acid side
chains R in both sterical orientations (R/S), Fmoc-deprotection of
6 and N-acylation should be feasible with various carboxylic acids.
availability of sphingosine and its derivatives from natural sources
and purity requirements for biological testing, interest in develop-
ing efficient and diverse methods for their synthesis still continues
unabated.14 A number of methods have been reported for their
synthesis so far. Asymmetric methods are based mainly on the
2. Results and discussion
In the proposed retrosynthesis (Scheme 1), various ceramide
derivatives 1a–e can be obtained by stereoselective reduction of
ketoceramides 10a–c, which in turn were derived from a general
resin-bound intermediate 6. This protected amino acyl phosphor-
anylidene acetate ester could be formed via C-acylation of the
already reported polymeric phosphoranylidene acetate 5. Crucial
for the variability of this synthesis is especially the step from com-
pound 6 to 10a–e involving the deprotecting of the ester function-
ality in 6 followed by decarboxylation and the versatile Wittig
cleavage which allows for the introduction of different substitu-
ents, affording the natural product and derivatives. Thus, the main
advantage of this strategy is its high versatility, allowing the
synthesis of not only sphingosine but also a range of structural
analogues from a common precursor. It is worth mentioning that
compounds 5 and 6 are versatile building blocks that could be
manipulated and eventually differentiated from two directions
leading to plethora of variants of 1. Since the lipophilic ceramide
tail acts as a membrane anchor, while the hydrophilic head group
such as saccharide or phosphate, which is predominantly located
on the external surface of the membrane, is associated with the
use of the chiral pool, particularly amino acids (L
-serine)15 and car-
bohydrates.16 Alternatively, chiral auxiliaries such as sulfoxides,17
chiral aziridines,18 or chiral sulfur19 and nitrogen20 ylides have
been used. The asymmetric catalytic methods employ, for example,
Sharpless asymmetric epoxidation21 and dihydroxylation reac-
tions.18,22 Besides the aldol reaction,23 organocatalytic proce-
dures24 have also been reported. Though extensive research
efforts have resulted in several synthetic approaches to sphingoid
bases and structural analogs, however, an efficient, concise and
diversity oriented synthesis of these molecule is still desirable.
Recently, we reported efficient procedures for the racemization-
free C-acylations of polymer bound phosphoranylidene acetates
with Fmoc-protected amino acids leading to the synthesis of a vari-
ety of Fmoc amino acyl phosphoranylidene acetates.25,26 This
method was further used in the synthesis of cis-peptide mimetics
by metal free, regioselective triazole formation employing a reac-
tion of a suitable azide with phosphoranylidene acetate.27 While
working with phosphoranylidene acetates of type 5 we envisioned
that these intermediates could allow for a novel and flexible access
O
FmocHN
OH
OTMSE
(5 eq)
Br
(5 eq)
Br
Ph
Ph
O
Ph
Ph
O
OtBu
Ph
Ph
P
P
2
O
(5 eq) TEA, DCM
P
OTMSE
OTMSE
(5 eq) MSNT
,
100°C, 15 min, MW
TMSE=
RT
2 h
3
5
(4.9 eq) 2,6-lutidine
12 h, RT
4
Si
Ph
O
Ph
Ph
O
Ph
Ph
Ph
O
O
O
P
O
P
O
P
1. Piperidine/DMF(20%)
2. Ac2O/DMF, 30 min
1. 3 eq (TAS-F)
2. THF, 3h, RT
OTMSE
OTMSE
FmocHN
N
H
N
H
O
O
O
8
7
6
Scheme 2. C-acylations of polymer-supported 2-phosphoranylidene acetates.

5508
A. El-Dahshan et al. / Bioorg. Med. Chem. 22 (2014) 5506–5512
Table 2
Diastereoselective reduction of 4E-ketoceramides 10a–e to protected ceramides 11a,c–e
Entry
Starting material
Reduction conditions
Yield of 11a,c–ea (%)
anti/syn
1
2
3
4
5
6
7
10a
10a
10a
10b
10c
10d
10e
Zn(BH4)2, THF, À78 °C, 15 min
70
49
85
0.0
80
56
73
4:1
3:2
L-Selectride, THF, À78 °C, 15 min
LiAlH(O-tBu)3, EtOH, À78 °C, 15 min
LiAlH(O-tBu)3, EtOH, À78 °C, 15 min
LiAlH(O-tBu)3, EtOH, À78 °C, 15 min
LiAlH(O-tBu)3, EtOH, À78 °C, 15 min
LiAlH(O-tBu)3, EtOH, À78 °C, 15 min
>95% anti
Decomp.
100:00
95 :5 anti/syn
95 :5 anti/syn
a
Yields of isolated products.
molecular recognition process, a variation in this tail may be of
importance to enhance the activity of this class of compounds.
Therefore, a flexible strategy is needed that would permit the
synthesis of sphingolipids with different substituents and chain
lengths. As illustrated in Scheme 2, phosphonium salt 4 could be
obtained from 2-(trimethylsilyl)ethyl (@TMSE) 2-bromoacetate
ester 2 and the commercially available triphenylphosphane resin
3 under gentle microwave heating for 15 min., followed by the
deprotonation with triethylamine to afford phosphoranylidene
acetate 5. Efficient C-acylations could be performed with 1-(2-mes-
itylenesulfonyl)-3-nitro-1H-1,2,4-triazole (MSNT)28,29 by reacting
compound 5 with the Fmoc-protected amino acid serine Fmoc-
Ser(tBu)-OH. The coupling yield of acylated product 6 (90%) was
determined by spectrophotometric quantification of Fmoc groups
cleaved off a dried resin sample. Acylation of amino acids activated
with MSNT and lutidine proceeded without racemization as proven
by total hydrolysis and chiral separation of the products30 and did
not cleave standard side-chain protecting groups used in peptide
synthesis such as tert-butyl and others. Replacement of tert-butyl
protection by trityl could be an alternative, if deprotection under
mildly acidic conditions is required. Following to the C-acylation
reaction, the removal of the protective Fmoc group of 6 was
effected with 20% piperidine in DMF. N-acetylation with acetic
anhydride furnished N-acetyl-2-serinyl-2-phosphoranylidene
acetate 7. Deprotection of the TMSE ester was first attempted with
tetrabutylammonium fluoride (TBAF).31 Under these basic reaction
conditions, however, the molecule was destroyed. Therefore, the
reaction was buffered by the addition of acetic acid. Removal of
tetrabutylammonium ions from the resin and the products, how-
ever, failed even with prolonged washings as indicated by NMR
analysis. Only when tris(dimethylamino) sulfonium difluoro-
trimethylsilicate (TAS-F)32 was employed as desilylating reagent, the
TMSE removal succeeded smoothly without washing problems.
The intermediary carboxylic acid decarboxylated spontaneously
to the amino acyl phosphoranylidene methane (acylphosphorane)
8. Compound 8 was subjected to Wittig olefination employing a
variety of aldehydes yielding the protected ketoceramides 10a–e
(Table 1, Scheme 3). Reaction of resin 8 with 5 equiv of 1-tetrade-
canal in THF at room temperature for 8 h afforded the ketocera-
mide 10a with the E isomer as the single detectable product in
the NMR spectrum of the crude (Table 1). Removal of excess start-
ing material afforded 10a with 47% yield over four steps. The scope
of this methodology was extended to the synthesis of compound
10b using the a,b-unsaturated aldehyde (E)-2-butenal. Next, inter-
mediate 8 was coupled with various aromatic aldehydes. Product
10c formed from benzaldehyde at rt could be isolated in a very
good yield over four steps (62%). Compounds 10d and 10e were
synthesized from 4-substitued benzaldehydes at 60 °C also in good
yields (Table 1).
With five different ketoceramides in hand, the diastereoselec-
tive reduction of the keto group was investigated. Diastereoselec-
tivity of the reduction step was determined based on 1H NMR
spectra of the product mixture by integration of the signals for
the proton at C-3 and was confirmed by comparison with literature
data.15d Initially the reduction of 10a was attempted by reaction
with freshly prepared Zn(BH4)2 at À78 °C in THF (Table 2).15d The
diastereoselectivity obtained, however, was only moderate with
an anti/syn ratio of 4:1. Moreover, the reaction afforded the pro-
tected dihydrosphingosine (sphinganine) as the main product with
the double bond being reduced.
Next, compound 10a was subjected to reduction with
L-selectride33 obtaining unsatisfactory diastereoselectivity with
an anti/syn ratio of 3:2. Finally, 10a was reduced diastereoselec-
34
tively using the bulky hydride reducing agent LiAlH(OtBu)3 in
dry EtOH at À78 °C. With excess LiAlH(OtBu)3 (2.0 equiv) the ery-
thro amino alcohol 1a was isolated following to deprotection with
TFA in 90% yield with >95% anti-diastereoselectivity. Similarly
treatment of compound 10c with LiAlH(OtBu)3 afforded compound
11c in 80% yield, with >95% diastereoselectivity in favor of the anti
product. Compounds 10d and 10e also underwent smooth reduc-
tion affording compound 11d and 11e in excellent selectivity
anti/syn (95:5).
R
O
OH
O
LiAlH(O-tBu)3
EtOH,
-78 °C, 15 min
H
8
1, 10-12a: R =
1, 10-12b: R =
1, 10-12c: R =
O
R
O
R
C13H27
THF, 8 h
HN
O
HN
O
10a-e
11c-e
TFA/DCM
(95:5, v:v)
TFA/DCM
(95:5, v:v)
C8H17
O
OH
O
1, 10-12d: R =
1, 10-12e: R =
HO
R
HO
R
HN
O
HN
12a,c-e
1a,c-e
Scheme 3. Wittig reaction leading to diverse ketoceramides and sphingosine.

A. El-Dahshan et al. / Bioorg. Med. Chem. 22 (2014) 5506–5512
5509
Table 3
key steps include the enantioselective C-acylation of a polymer-
supported phosphorane with the amino acid -serine, cleavage
Anti-proliferative effects of sphingosine analogs against HEP G-2, PC-12, and HL-60
L
and decarboxylation of an ester, the Wittig reaction between of a
resin-bound phosphorus ylide and various appropriate aldehydes
and the diastereoselective reduction of keto functionality using
LiAlH(OtBu)3 as reducing agent. The noteworthy feature of this
strategy is its flexibility which permits the divergent synthesis of
sphingolipids from different starting amino acids, from different
aliphatic and aromatic aldehydes with different lengths and substi-
tutions resulting in variations in the sphingosine chain, and finally
with variation of the N-acyl substituents.39
Entry
Compound
IC50 (lM)
HEP G-2
PC-12
HL-60
1
2
3
4
5
6
7
8
1a
1c
1d
1e
12a
12c
12d
12e
58
31
98
40
26
11
a
a
a
—
—
—
—
—
—
a
a
a
175
65
>200
41
>200
70
42
43
—
48
50
59
This flexibility has been demonstrated here for a small selection
of aldehydes used in the Wittig reaction step. The obtained synthe-
sized ketoceramides and ceramides have been tested in the Alamar
Blue cell proliferation assay employing three human cancer cell
lines, HEP G-2, derived from a hepatocarcinoma, PC-12, derived
from a neuroendocrine tumor, and HL-60, a human leukemia cell
line. Biological results indicate that arylic substituents integrated
in or even replacing the sphingosine chain show significant inhibi-
tion of cell proliferation, partially even stronger than the reference
compound N-acetyl sphingosine. It remains to be investigated how
these arylic substitutions affect the solubility and the ADME
properties of these compounds and if these novel sphingosine
derivatives can synergize the effect of other antineoplastic drugs
on tumor cells.
a
Decomposed during deprotection.
HL60-cells
4
12e (50 µM)
1c (11 µM)
1a (23 µM)
12a (43 µM)
3
2
1
0
1.0
1.5
2.0
Log [compound]
4. Experimental section
4.1. General methods
Figure 1. Inhibition of cancer cell proliferation in the presence of various ceramides
as determined in the Alamar Blue assay by incubation of cells with 6.25–200
compounds for 4 h.
lM of
Unless otherwise stated, all reagents were obtained from com-
mercial suppliers and used without further purification. Dry sol-
vents were purchased and stored over molecular sieves. Solid
phase chemistry was performed in plastic syringes equipped with
teflon filters. Resins were purchased from Fluka (triphenylphos-
phine polystyrene). Microwave-assisted solid-phase reactions were
performed on a Personal Chemistry Smith Synthesizer. Resins were
washed with DMF, THF, toluene and CH2Cl2 unless otherwise sta-
ted. Resin loadings were determined by photometric determination
after Fmoc cleavage. Solid-phase reactions were monitored through
FT-ATR-IR spectra of the resins with Thermo Nicolet Impact 400
SplitPea ATR unit. Absorptions are reported in wave numbers
(cmÀ1). Purification of cleaved intermediates and products was car-
The obtained products were finally deprotected with TFA yield-
ing the isolated ceramide and ketoceramide derivatives 1a–e and
12a–e, respectively (Scheme 3). While all four deprotected
ketoceramides were obtained as stable products, the reduced cera-
mides 1d and 1e with aromatic side chains were isolated with
reduced yields and partially decomposed during deprotection. All
stable products were dissolved in DMSO to investigate their anti-
proliferative effects against three different human cell lines. HEP
G-2, a liver adenocarcinome, PC-12, a cell line from a neuroendo-
crine tumour, and HL-60 leukaemia cells were treated with at com-
pound concentrations between 6.25 and 200 lM and tested for cell
proliferation employing the Alamar Blue assay35 after either 24 h
or 4 h. All assays were conducted in triplicate and results obtained
are displayed in Table 3 and in Figure 1. The reference compound
1a was active towards all three cell lines with IC50 values in a sim-
ilar range as reported for comparable proliferation assays.36,37
Induction of apoptosis by this and other compounds could be
observed already at lower concentrations than required for com-
plete cell death.38 The anti-proliferative effect of the corresponding
ketosphingosine 12a was also detected for all cell lines, however,
the reported, strongly enhanced activity of this derivative37 could
not be confirmed.
ried out on a semipreparative HPLC column (10
l
m, 250 Â 20 mm,
Grom-SIL 300 ODS-5 ST RP-C18) employing individual gradients
derived from analytical runs. Purities were determined by HPLC/
MS and NMR and were >95% for all isolated products. ESI/MS were
recorded on an Agilent 1100Series (Agilent Technologies).
1H and 13C NMR spectra were recorded on a Bruker AVANCE
300 MHz instrument and chemical shifts were measured in parts
per million (ppm). Instrument used for HRMS measurements is
an Agilent 6220 accurate mass TOF-MS equipped with an
electrospray source.
Interestingly, variation of the sphingosine chain led to signifi-
cant changes in the bioactivity. The strongest effect was observed
for the N-acetyl-4-(n-octyl)-phenyl sphingosine 1c for all three cell
lines, while the corresponding ketosphingosine 12c was slightly
less active. The sphingosines bearing an entirely aromatic chain
(1d and 1e) were partially decomposed during deprotection. Thus,
only the parent ketosphingosines 12d,e were tested and showed
anti-proliferative activity in the same range.
4.2. Alamar Blue assay
Cells were plated in black 96-well plates (5000 cells per well in
45 lL medium) and incubated for 24 h at 37 °C/5% CO2 before addi-
tion of compounds/dimethylsulfoxide (DMSO) for control wells.
Five microliters of diluted sample were added to give a final DMSO
concentration of 0.5% in the assay. Cells were incubated for
additional 24 h at 37 °C. Alamar Blue reagent was added directly
to each well to a final concentration of 10%. The plates were then
further incubated at 37 °C. The fluorescence signal was measured
after 4 h and 24 h at 535 nm (excitation) and 590 nm (emission)
on a SAFIRE II plate reader.
3. Conclusions
We have developed an efficient, flexible and diastereoselective
approach to the synthesis of erythro-sphingosine analogs. The

5510
A. El-Dahshan et al. / Bioorg. Med. Chem. 22 (2014) 5506–5512
4.2.1. 2-(Trimethylsilyl) ethyl 2-bromoacetate (2)
4.4. A general procedure for the preparation of N-acylated
To a solution of 2-bromoacetic acid (5.7 g, 41 mmol) in dry
CH2Cl2 (30 mL) at 0 °C was added, 2-(trimethylsilyl)ethanol
(2.37 g, 20 mmol) and 4-(dimethylamino)pyridine (200 mg). To
the stirred solution, DCC (9.5 g, 42 mmol) was added carefully in
small portions over 5 min. The resulting mixture was stirred at
0 °C for 1 h. The solid was filtered and the remaining filter cake
was washed with hexane/ether (100 mL, 4:1 v:v) and KHCO3 solu-
tion. The organic layers were dried over sodium sulphate, and sol-
vents removed under reduced pressure. The crude product thus
obtained was distilled under high vacuo and characterized by
NMR. 1H NMR (CDCl3) d = 0.08 (s, 9H, (CH3)3Si), 1.1 (m, 2H, COOCH2
CH2Si), 3.9 (s, 2H, BrCH2CO), 4.2 (m, 2H, COOCH2CH2Si), 13C NMR:
(CDCl3) d = 0.001, 18.7, 27.6, 66.3, 168.8. Yield: (4.0 g, 83.4%).
ketosphingosines via polymer bound Wittig reaction
To a suspension of 8 (200 mg, 1.27 mmol/g, 0.254 mmol) in dry
THF was added the aldehyde (0.76 mmol, 3 equiv) and the mixture
stirred for 8 h in THF at 60 °C for aromatic aldehydes and at rt for
aliphatic aldehydes. The product was purified on column chroma-
tography (hexane/ethyl acetate) or as needed with semiprepara-
tive HPLC column (10
RP-C18), and characterized by MS and NMR.
l
M, 250 Â 20 mm, Grom-SIL 300 ODS-5 ST
4.5. Oxidation of 1-tetradecanol to 1-tetradecanal (9) with IBX
To 1-tetradecanol (2.7 g, 12.6 mmol, 1 equiv) in EtOAc was
added IBX (10.6 g, 3 equiv) at rt and the reaction mixture was
refluxed at 70 °C until the starting material was consumed as
shown by TLC (1 h). After completion of the reaction, the mixture
was filtered and concentrated under reduced pressure to give alde-
hyde 9, which was characterized by NMR; 1H NMR (300 MHz,
CDCl3): d = 0.86 (t, 3H, J = 7.3 Hz), 1.25 (s, 20H), 1.26 (m, 2H),
2.35 (m, 2H), 9.75 (t, 1H, J = 2.4 Hz); 13C NMR (75.49 MHz, CDCl3)
d 14.5, 22.5, 23.1, 25.1, 29.4, 29.6, 29.7, 30.0, 32.3, 34.3, 44.3,
203.0. Yield: 2.57 g (96%).
4.2.2. 2-Phosphoranylidene-2-(trimethylsilyl)ethyl acetate (5)
Triphenylphosphine polystyrene resin 3 (0.5 g, 1.6 mmol/g,
0.8 mmol, 1% divinyl benzene, 100–200 mesh) was weighed into
a microwave vial and suspended in dry toluene (4 mL). After addi-
tion of 2-(trimethylsilyl) ethyl 2-bromoacetate (991 mg, 4 mmol,
5 equiv), the vial was sealed and heated at 100 °C for 15 min in a
microwave synthesizer. The vial was cooled to room temperature
before opening, the resin was filtered and washed with dry toluene
and CH2Cl2. The polymeric phosphonium salt 3 thus obtained was
resuspended in dry CH2Cl2 (5 mL) and TEA (557
l
L, 4 mmol,
4.5.1. N-Acetyl-(S,E)-2-amino-1-tert-butoxy-octadec-4-ene-3-
one (10a)
5 equiv) was added. After shaking for 2 h at rt the yellow-coloured
resin 4 was filtered, washed and dried in vacuo. Resin loading after
alkylation was determined by elemental analysis (quantitative). IR
Following the general procedure as described above, for the N-
acylated ketosphingosine, the Wittig reaction of 8 with 1-tetrade-
canal afforded compound 10a. Flash chromatographic purification
over silica gel (1:1 v/v EtOAc/hexanes) afforded 10a as a white
solid. 1H NMR (300 MHz, CDCl3): d = 0.86 (t, 3H, CH3ACH2,
J = 7.3 Hz), 1.07–1.50 (m, 31H, (CH2)11, and C(CH3)3), 2.02 (s, 3H,
CH3CO), 2.20–2.23 (m, 2H, CH2-olefin) 3.57 (dd, 1H, J = 9.2 Hz,
9.3 Hz), 3.74 (dd, 1H, J = 8.5 Hz, 9.7 Hz), 4.85–4.90 (m, 1H), 6.52
(ATR) after the deprotonation:
m
(cmÀ1) = 3056, 3025, 2923, 2852,
1725, 1600, 1493, 1452, 1437, 1380, 1310, 1249, 1183, 1116,
835, 751, 698, 542.
4.2.3. 2-Acyl-2-phosphoranylidene-2-(trimethylsilyl) ethyl
acetate (6)
Resin 5 (200 mg, 1.43 mmol/g, 0.286 mmol) was pre-swollen in
dry CH2Cl2. The Fmoc-Ser(tBu)-OH (1.53 g, 1.43 mmol, 5 equiv)
was suspended in dry CH2Cl2 (4 mL) and dissolved under addition
a
(d, 1H, J = 7.3 Hz), 6.90–7.10 (m, 1H, C H); 13C NMR (75.49 MHz,
CDCl3) d 13.6, 22.1, 22.7, 24.4, 26.7, 27.5, 28.8, 28.7, 28.8, 28.9,
29.0, 29.0, 29.1, 29.1, 29.2, 31.4, 32.1, 56.6, 61.5, 72.8, 126.2,
149.0, 169.3, 195.6. HRMS (ESI): Calcd for C24H46NO3 [M+H]+:
396.35. Found: 396.29. Yield: 47.3 mg (47%).
of 2,6-lutidine (162.7 lL, 1.40 mmol, 4.9 equiv). The clear solution
obtained after addition of 1-(2-mesitylenesulfonyl)-3-nitro-1H-
1,2,4-triazole (MSNT) (423.7 mg, 1.43 mmol, 5 equiv) was directly
mixed with the resin suspension and shaken overnight at rt. The
resin was washed after the coupling step and dried in vacuo.
Acylation yields were determined after Fmoc cleavage of small
samples (90%). IR (ATR, after the acylation with Fmoc-Ser(tBu)-
4.5.2. N-Acetyl-(2S,4E,6E)-2-amino-1-(tert-butoxy)-octa-4,6-
diene-3-one (10b)
Following the general procedure as described above, for the
N-acylated ketosphingosine, the Wittig reaction of 8 with crotonal-
dehyde was carried out. Flash chromatographic purification over
silica gel (1:3 v/v EtOAc/hexanes) afforded compound 10b as a
bright yellow solid. 1H NMR (300 MHz, CDCl3): d = 1.03 (s, 9H),
1.82 (d, 3H, J = 4.8 Hz), 1.98 (s, 3H), 3.54–3.77 (m, 2H); 4.84 (d,
J = 13.4 Hz, 1H), 6.13–7.20 (4H) 13C NMR (75.49 MHz, CDCl3) d
18.4, 22.8, 26.7, 56.9, 61.5, 72.9, 123.5, 129.8, 141.3, 144.1, 187.9,
HRMS (ESI): Calcd for C14H23NO3 [M+H]+: 254.30. Found: 254.29.
Yield: (49.0%).
OH):
m
(cmÀ1) = 3424, 3396, 3058, 3025, 2923, 2853, 1718, 1654,
1559, 1492, 1451, 1437, 1384, 1248, 1195, 1117, 1080, 835, 742,
723, 698, 613, 541.
4.3. General procedure for Fmoc-protecting group cleavage and
N-acetylation
To a suspension of resin 6 (200 mg, 1.27 mmol/g, 0.254 mmol)
in DMF was added piperidine/DMF (20%, v:v) (8 mL) two times
every 6 min and shaken. The resin was filtered, washed and dried
in vacuo. Deprotection of Fmoc was verified by the Kaiser-test.
Acetylation was carried out in Ac2O/DMF (8 mL, 2:8, v:v) and
stirred for 30 min at rt. The obtained resin 7 was washed with
DMF, THF and DCM.
4.5.3. N-Acetyl-(2S,4E)-2-amino-1-(tert-butoxy)-5-(4-
octylphenyl)-pent-4-ene-3-one (10c)
Following the general procedure as described above, for the N-
acylated ketosphingosine, the Wittig reaction of 8 with 4-octyl
benzaldehyde. Compound 10c was purified on a semipreparative
HPLC (Eluent A = water, Eluent B acetonitrile)10%B?90B) afforded
compound 10c. 1H NMR (300 MHz, CDCl3): d = 0.86 (t, 3H,
(CH3A(CH2)7, J = 6.1 Hz), 1.10 (s, 9H, (CH3)3AC), 1.2–1.4 and 1.6–1.7
(br s, 14H), 2.05 (s, 3H), 2.65 (t, 2H, 7.3 Hz), 3.65 (d, 1H,
J = 9.7 Hz), 3.85 (dd, 1H, J = 9.7 Hz, 8.55 Hz), 4.95 (m, 1H), 6.65 (d,
1H, J = 7.3 Hz), 6.85 (d, 1H, J = 7.3 Hz), 7.20 (d, 1H, J = 7.3 Hz), 7.5
(d, 1H, J = 7.3 Hz), 7.72 (d, 1H, J = 15.8 Hz), 13C NMR (75.49 MHz,
CDCl3) d 13.6, 22.1, 22.8, 26.7, 28.7, 28.8, 31.3, 35.4, 57.1, 61.5,
4.3.1. N-Acetyl-3-amino-2-oxo-1-phosphoranylidene propane 8
To a suspension of resin 7 (200 mg, 1.27 mmol/g, 0.254 mmol)
in dry DMF was added tris(dimethylamino)sulphur (trimethyl-
silyl)difluoride (210 mg, 0.762 mmol, 3 equiv) and the mixture
stirred for 3 h at rt. The resin was filtered, washed and dried in
vacuo. IR (ATR):
m = 3059, 3025, 2926, 2851, 2149, 1731, 1599,
1492, 1451, 1437, 1256, 1185, 1111, 751, 698, 569, 517, 512.

A. El-Dahshan et al. / Bioorg. Med. Chem. 22 (2014) 5506–5512
5511
72.9, 121.3, 128.0, 128.6, 131.3, 143.6, 145.9, 169.3, 195.6. HRMS
(ESI): Calcd for C21H32NO2 [MÀ(t-but)+H]+: 346.2377. Found:
346.2370. Yield: 54.5 mg (62%).
C17H25NO3 [M+HÀH2O]+: 274.2. Found: 274.1. Yield: 81.5 mg
(56%).
4.6.3. N-Acetyl-(2S,3R,4E)-2-amino-1-(tert-butoxy)-5-(4-
biphenyl)-pent-4-ene-3-ol (11e)
4.5.4. N-Acetyl-(2S,4E)-2-amino-1-(tert-butoxy)-5-phenyl-pent-
4-ene-3-one (10d)
1H NMR (300 MHz, DMSO): d = 1.20 (s, 9H, tBu), 1.94 (s, 3H,
CH3CO), 3.52–3.66 (m, 2H, CH2AO-tBu), 4.02–4.10 (m, 1H, CHAOH),
Following the general procedure as described above for the N-
acylated ketosphingosine, the Wittig reaction of 8 with benzalde-
hyde afforded compound 10d. 1H NMR (300 MHz, CDCl3):
d = 1.09 (s, 9H tBu), 2.08 (s, 3H, CH3CO), 3.82 (d, 1H, CH2AO-tBu,
J = 3.66 Hz), 3.85 (d, 1H, CH2AO-tBu, J = 3.67 Hz), 4.96–5.02 (m,
a
4.35 (t, 1H, J = 6.78 Hz, C H), 6.33 (dd, 1H, CHA(OH)CH@CH,
J = 15.81 Hz, J = 6.77 Hz), 6.5 (d, 1H, CHA(OH)CH@CH,
J = 15.85 Hz), 7.28–7.64 (m, 9H, aromatics). MS (ESI): Calcd for
C
23H29NNaO3: [M+Na]+: 390.2. Found: 390.0. Yield: 133 mg (73%).
a
1H, C H), 6.70–6.73 (d, 1H, NH, J = 6.11), 6.89 (d, 1H, CH-olefin,
J = 15.88 Hz), 7.38–7.39, 7.53–7.56, 7.66 and 7.72 (br s, 6H, aromat-
ics and olefin). 13C NMR (75.49 MHz, CDCl3) d: 22.6, 26.7, 57.3,
61.44, 73.1, 122.1, 128.0, 128.5, 130.39, 133.82, 143.73, 170.05,
195.44. MS (ESI): Calcd for C17H24NO3 [M+H]+: 290.1751. Found:
290.1760. Yield: 58.2 mg (79%).
4.7. Cleavage of the tert-Bu protecting group
The ceramides 11a,c–e or the N-acylated keto sphingosines
10,c–e (50 mg) were treated with TFA:CH2Cl2 (95:5, v:v) for 5 h
to remove the tert-butyl group. TFA was removed in vacuo and
the product was chromatographed using EtOAc/hexane (1:4, v:v)
yielding ceramides 1a,c–e and ketoceramides 12a,c–e.
4.5.5. N-Acetyl-(2S,4E)-2-amino-5-(4-biphenyl)-1-(tert-butoxy)-
pent-4-ene-3-one (10e)
Following the general procedure as described above for the N-
acylated ketosphingosine, the Wittig reaction of 8 with 4-phenyl
benzaldehyde afforded compound 10e. 1H NMR (300 MHz, CDCl3):
d = 1.13 (s, 9H, tBu), 2.08 (s, 3H, CH3CO), 3.85 (d, 1H, CH2AO-tBu,
J = 3.66 Hz), 3.88 (d, 1H, CH2AO-tBu, J = 3.67 Hz), 4.99–5.04 (m,
4.7.1. N-Acetyl-(2S,3R,4E)-2-amino-octadec-4-ene-1,3-diol (1a)
1H NMR (300 MHz, CDCl3): d = 0.86 (t, 3H, CH3ACH) 1.26–1.37
(m, 22H, CH2ACH2A), 2.05–2.07 (m, 5H, CH2-olefin, and CH3 CO),
2.76 (br s, 1H, NHACH), 3.71 (d, 1H, CbH2, J = 10.99), 3.90–3.99
a
(m, 1H, C H), 4.33 (br s, 1H CHAOH), 5.51, 5.56 (dd, 1H, CH-olefin,
a
1H, C H), 6.58–6.60 (d, 1H, NH, J = 7.33), 6.95 (d, 1H, CH-olefin,
J = 6.11, J = 7.33), 5.74–5.82 (m, 1H, CH-olefin), 6.33 (d, 1H, NH).
J = 15.88 Hz), 7.44–7.77 (m, 10H, aromatics and olefin). 13C NMR
(75.49 MHz, CDCl3) d: 22.8, 26.8, 57.2, 61.61, 73.0, 122.1, 126.6,
127.2, 128.5, 128.5, 132.8, 139.6, 143.1, 169.3, 195.7. HRMS (ESI):
HRMS (ESI): Calcd for C
20H39NO3 [M+H]+: 342.3003. Found:
342.2973; [M+Na]+ Calcd 364.2822. Found 364.2819. Yield:
38.7 mg (90%).
C
23H27NO3 [M+Na]+: 388.1883. Found: 388.1885. Yield: 63.1 mg
(68%).
4.7.2. N-Acetyl-(2S,3R,4E)-2-amino-5-(4-octylphenyl)-pent-4-
ene-1,3-diol (1c)
4.6. General procedure for the diastereoselective reduction of
ketosphingosine 11a,c–e with lithium-tri-tert-
butoxyaluminium hydride to (11a,c–e)
1H NMR (300 MHz, CDCl3): d = 0.80 (t, 3H, J = 7.33 Hz), 1.20–
1.23, 1.52 (br s, 14 H), 1.98 (s, 3H), 2.52 (t, 2H, J = 8.55 Hz), 3.48
(d, 1H, J = 8.5 Hz), 3.71 (d, 1H, J = 7.33 Hz), 4.05 (d, 1H, J = 8.5),
4.33 (dd, 1H, J = 8.53, 7.33 Hz), 6.10 (d, 1H, J = 4.88 Hz) 6.11 (d,
1H, J = 6.11 Hz), 6.31 (d, 1H, J = 8.55 Hz), 6.63 (d, 1H, J = 15 Hz),
7.06 (d, 1H, J = 7.32 Hz), 7.22 (d, 1H, J = 8.55 Hz); HRMS (ESI): Calcd
for C21H33NO3 [M+H]+: 348.2533. Found: 348.2530. Calcd for
[M+Na]+: 370.2353. Found 370.2369. Yield: 25.8 mg (60%).
To a stirred mixture of 10a,c–e (0.5 mmol) in dry ethanol (1 mL)
at À78 °C under N2 atmosphere lithium-tri-tert-butoxyaluminium
hydride (1 mmol, 2 equiv) was added portion-wise. After the reac-
tion mixture was stirred at the same temperature for 15 min, 1 N
HCl was added. The mixture was extracted with ethyl acetate,
and the extract was washed with brine, dried over MgSO4 and con-
centrated in vacuo to give the crude product. Silica gel chromatog-
raphy using hexane/ethyl acetate as eluent (8:2) gave 11c–e as a
yellow oil.
4.7.3. N-Acetyl-(2S,3R,4E)-2-amino-5-phenyl-pent-4-ene-1,3-
diol (1d)
1H NMR (750 MHz, DMSO): d = 1.81 (s, 3H, CH3CO), 3.44–3.55
(m, 2H, CH2AOAH), 4.35–4.39 (m, 1H, CHAOH), 4.58–4.78 (m,
a
1H, C H), 6.05–6.19 (m, 1H, CHA(OH)CH@CH), 6.52–6.63 (m, 1H,
4.6.1. N-Acetyl-(2S,3R,4E)-2-amino-1-(tert-butoxy)-5-(4-
octylphenyl)-pent-4-ene-3-ol (11c)
CHA(OH)CH@CH, J = 16.54 Hz), 7.28–7.64 (m, 5H, aromatics)
HRMS(ESI): Calcd for
C
13H17NO3[M]+: 235.1214. Found:
1H NMR (300 MHz, CDCl3): d = 0.86 (t, 3H, J = 5.9 Hz), 1.19 (s,
9H), 1.27–1.30, 1.55–1.60 (br s, 12 H), 2.05 (s, 3H), 2.59 (t, 2H,
J = 8.55 Hz), 3.56 (dd, 2H, J = 10.1 Hz), 3.79 (dd, 1H, J = 9.66 Hz),
4.14 (dd, 1H, J = 8.53 Hz), 4.40–4.45 (br s, 1H), 6.21 (dd, 1H,
J = 17.09 Hz), 6.38 (d, 1H, J = 8.55 Hz), 6.70 (d, 1H, J = 15 Hz), 7.14
(d, 2H, J = 7.33 Hz), 7.29 (d, 2H, J = 8.55 Hz); 13C NMR
(75.49 MHz, CDCl3) d 13.6, 22.2, 23.0, 26.9, 28.8, 28.9, 31.4, 35.2,
51.6, 61.8, 73.8, 74.5, 125.9, 127.8, 128.2, 130.3, 133.6, 142.2.
235.1208. Yield: 10 mg (20%), partially decomposed.
4.7.4. N-Acetyl-(2S,3R,4E)-2-amino-5-(4-biphenyl)-pent-4-ene-
1,3-diol (1e)
1H NMR (300 MHz, DMSO): d = 1.80 (s, 3H, CH3CO), 3.43–3.96
(m, 2H, CH2AOAH), 4.26–4.39 (m, 1H, CHAOH), 4.62–4.74 (m,
a
1H, C H), 6.25 (dd, 1H, CHA(OH)CH@CH, J = 15.24 Hz,
J = 6.07 Hz), 6.54 (d, 1H, CHA(OH)CH@CH, J = 16.54 Hz), 7.28–
7.64 (m, 9H, aromatics) (ESI): Calcd for C19H19NO2 [M+HÀH2O]+:
293.1412. Found: 293.1416. Yield: 15 mg (30%), partially
decomposed.
HRMS (ESI): Calcd for
404.3164. Yield: 139.3 mg (80%).
C
25H41NO3 [M+H]+: 404.3159. Found:
4.6.2. N-Acetyl-(2S,3R,4E)-2-amino-1-(tert-butoxy)-5-phenyl-
pent-4-ene-3-ol (11d)
4.7.5. N-Acetyl-(S,E)-2-amino-1-oxy-octadec-4-ene-3-one (12a)
1H NMR (300 MHz, CDCl3): d = 0.86 (t, 3H, CH3ACH2,
J = 7.30 Hz), 1.24–1.62 (m, 22H, (CH2)11), 2.01 (s, 3H, CH3CO),
2.36–2.52 (m, 2H, CH2-olefin) 3.10–3.13, and 3.53–3.55 (m, 2H,
1H NMR (300 MHz, DMSO): d = 1.21 (s, 9H), 1.92 (s, 3H, CH3CO),
3.50–3.65 (m, 2H, CH2AO-tBu), 4.01–4.09 (m, 1H, CHAOH), 4.33 dt,
a
1H, J = 6.96 Hz, J = 0.84 Hz, C H), 6.27 (dd, 1H, CHA(OH)CH@CH,
a
J = 15.47 Hz, J = 7.28 Hz), 6.6 (d, 1H, CHA(OH)CH@CH,
J = 15.47 Hz), 7.18–7.42 (m, 5H, aromatic) (ESI): Calcd for
CbH2), 4.61–4.64 (m, 1H, C H), 6.31 (br s, 1H, CH-olefin), 6.57–
6.66 (d, 1H, J = 15.88 Hz, CH-olefin); 13C NMR (75.49 MHz, CDCl3)

5512
A. El-Dahshan et al. / Bioorg. Med. Chem. 22 (2014) 5506–5512
9. (a) Hannun, Y. A.; Obeid, L. M. Trends Biochem. Sci. 1995, 20, 73; (b) Mathias, S.;
Pena, L. A.; Kolesnick, R. N. Biochemistry 1998, 335, 465; (c) Birbes, H.; Bawab, S.
E.; Obeid, L. M.; Hannun, Y. A. Adv. Enzyme Regul. 2002, 42, 113; (d) Posse de
Chaves, E. I. Biochim. Biophys. Acta 2006, 1758, 1995.
10. (a) Fillet, M. et al Biochem. Pharmacol. 2003, 65, 1633; (b) Swanten, C. Cancer
Cell 2007, 11, 498; (c) Chapman, J. V. et al Biochem. Pharmacol. 2010, 80, 308.
11. Sawatzki, P.; Kolter, T. Eur. J. Org. Chem. 2004, 11, 3693. and references therein.
12. van Echten-Deckert, G.; Zschosche, A.; Bär, T.; Schmidt, R. R.; Raths, A.;
Heinemann, T.; Sandhoff, K. J. Biol. Chem. 1997, 272, 15825.
d 13.6, 22.1, 22.7, 26.7, 29.1, 31.4, 32.1, 33.4, 56.6, 61.5, 72.8, 126.2,
149.1, 169.4, 177.9, 195.6. HRMS (ESI): Calcd for C20H37NO3;
[M+H]+: 340.2846. Found: 340.2838, Calcd for [M+Na]+:
362.2666. Found 362.2654. Yield: 25.8 mg (62%).
4.7.6. N-Acetyl-(2S,4E)-2-amino-5-(4-octylphenyl)-1-oxy-pent-
4-ene-3-one (12c)
13. Brodesser, S.; Sawatzki, P.; Kolter, T. Eur. J. Org. Chem. 2003, 2021.
14. (a) Koskinen, P. M.; Koskinen, A. M. P. Synthesis 1998, 1075; (b) Howell, A. R.;
Ndakala, A. J. Curr. Org. Chem. 2002, 6, 365.
1H NMR (300 MHz, CDCl3): d = 0.86 (t, 3H, (CH3A(CH2)7,
J = 6.1 Hz), 1.2–1.4 and 1.6–1.7 (br s, 14H), 2.05 (s, 3H), 2.65 (t,
2H, 7.3 Hz), 3.65 (d, 1H, J = 9.7 Hz), 3.85 (dd, 1H, J = 9.7 Hz,
8.55 Hz), 4.95 (m, 1H), 6.65 (d, 1H, J = 7.3 Hz) 6.85 (d, 1H,
J = 7.3 Hz), 7.20 (d, 1H, J = 7.3 Hz), 7.5 (d, 1H, J = 7.3 Hz), 7.72 (d,
1H, J = 15.8 Hz), 13C NMR (75.49 MHz, CDCl3) d 13.6, 21.2, 22.3,
26.9, 28.8, 31.3, 35.4, 33.1, 57.1, 57.5, 61.5, 72.8, 72.9, 121.6,
128.0, 129.0, 131.3, 142.9, 145.9, 169.3, 195.8. HRMS (ESI): Calcd
15. (a) Chun, J.; Lee, G.; Byun, H.-P.; Bittman, R. Tetrahedron Lett. 2002, 43, 375; (b)
Yadav, J. S.; Geetha, V.; Raju, A. K.; Gnaneshwar, D.; Chandrasekhar, S.
Tetrahedron Lett. 2003, 44, 2983; (c) Lombardo, M.; Capdevila, M. G.; Pasi, F.;
Trombini, C. Org. Lett. 2006, 8, 3303; (d) Lee, J.-M.; Lim, H.-S.; Chung, S.-K.
Tetrahedron: Asymmetry 2002, 13, 343; (e) Yamamoto, T.; Hasegawa, H.;
Hakogi, T.; Katsumura, S. Org. Lett. 2006, 8, 5569; (f) Masuda, Y.; Mori, K. Eur. J.
Org. Chem. 2005, 22, 4789; (g) Duffin, G. R.; Ellames, G. J.; Hartmann, S.;
Herbert, J. M.; Smith, D. I. J. Chem. Soc., Perkin Trans. 1 2000, 2237; (h) Mori, K.;
Masuda, Y. Tetrahedron Lett. 2003, 44, 9197.
for
C
21H31NO3 [M+H]+: 346.2377. Found 346.2370; [M+Na]+:
16. (a) Luo, S.-Y.; Thopate, S. R.; Hsu, C.-Y.; Hung, S.-C. Tetrahedron Lett. 2002, 23,
4889; (b) Chaudhari, V. D.; Kumar, K. S. A.; Dhavale, D. D. Org. Lett. 2005, 7,
5805; (c) Lin, C.-C.; Fan, G.-T.; Fan, J.-M. Tetrahedron Lett. 2003, 44, 5281; (d)
Chiu, H.-Y.; Tzou, D.-L. M.; Patkar, L. N.; Lin, C.-C. J. Org. Chem. 2003, 68, 5788;
(e) Plettenburg, O.; Bodmer-Narkevich, V.; Wong, C.-H. J. Org. Chem. 2002, 67,
4559; (f) Graziani, A.; Passancatelli, P.; Piancatelli, G.; Tani, S. Tetrahedron:
Asymmetry 2000, 11, 3921; (g) Wild, R.; Schmidt, R. R. Tetrahedron: Asymmetry
1994, 5, 2195; (h) Fan, G.-T.; Pan, Y.-S.; Lu, K.-C.; Cheng, Y.-P.; Lin, W.-C.; Lin, S.;
Lin, C.-H.; Wong, C.-H.; Fang, J.-M.; Lin, C.-C. Tetrahedron 2005, 61, 1855; (i)
Figueroa-Pérez, S.; Schmidt, R. R. Carbohydr. Res. 2000, 328, 95; (j) Compostella,
F.; Franchini, L.; De Libero, G.; Palmisano, G.; Ronchetti, F.; Panza, L.
Tetrahedron 2002, 58, 8703; (k) Duclos, R. I., Jr. Chem. Phys. Lipids 2001, 111,
111; (l) Milne, J. E.; Jarowickki, K.; Kocienski, P. J.; Alonso, J. Chem. Commun.
2002, 426; (m) Van den Berg, R. J. B. H. N.; Korevaar, C. G. N.; van der Marel, G.
A.; Overkleeft, H. S.; Van Boom, J. H. Tetrahedron Lett. 2002, 43, 8409.
17. Zhong, Y.-W.; Dong, Y.-Z.; Fang, K.; Izumi, K.; Xu, M.-H.; Lin, G.-Q. J. Am. Chem.
Soc. 2005, 127, 11956.
368.2196. Found 368.2188. Yield: 34.4 mg (80%).
4.7.7. N-Acetyl-(2S,4E)-2-amino-1-oxy-5-phenyl-pent-4-ene-3-
one (12d)
1H NMR (300 MHz, CDCl3): d = 2.10 (s, 3H, CH3CO), 4.00–4.02
a
(m, 2H, CH2AOH), 4.99–5.02 (m, 1H, C H), 5.92–5.93 (d, 1H, NH),
6.91 (d, 1H, CH-olefin, J = 16.48 Hz), 7.38–7.17, 7.79 (m, 6H, aro-
matics and olefin). 13C NMR (75.49 MHz, CDCl3) d: 22.6, 26.7,
57.3, 61.4, 73.1, 122.1, 128.0, 128.5, 130.3, 133.8, 143.7, 170.0,
195.4. HRMS (ESI): Calcd for C13H15NO3 [M+H]+: 234.1125. Found:
234.1123, [M+Na]+ Calcd 256.0944. Found 256.0941. Yield:
30.4 mg (65%).
18. Yoon, H. J.; Kim, Y.-W.; Lee, B. K.; Lee, W. K.; Kim, Y.; Ha, Y.-J. Chem. Commun.
2007, 79.
19. Morales-Serna, J. A.; Llaveria, J.; Diaz, Y.; Matheu, M. I.; Castillón, S. Org. Biomol.
Chem. 2008, 6, 4502.
4.7.8. N-Acetyl-(2S,4E)-2-amino-5-(4-biphenyl)-1-oxy-pent-4-
ene-3-one (12e)
1H NMR (300 MHz, CDCl3): d = 2.06 (s, 3H, CH3CO), 3.90 (d, 1H,
CH2AOH, J = 3.05 Hz), 3.88–3.89 (d, 1H, CH2AOH, J = 3.05 Hz),
20. Disadee, W.; Ishikawa, T. J. Org. Chem. 2005, 70, 9399.
21. (a) Olofsson, B.; Somfai, P. J. Org. Chem. 2003, 68, 2514; (b) Torssell, S.; Somfai,
P. Org. Biomol. Chem. 2004, 2, 1643; (c) Righi, G.; Ciambrone, S.; D’Achille, C.;
Leonelli, A.; Bonini, C. Tetrahedron 2006, 62, 11821.
22. (a) Martin, C.; Prünk, W.; Bortolussi, M.; Bloch, R. Tetrahedron: Asymmetry
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a
4.95–4.97 (m, 1H, C H), 6.78–6.80 (d, 1H, NH), 6.88 (d, 1H, CH-
olefin, J = 15.88 Hz), 7.44–7.77 (m, 10H, aromatics and olefin). 13C
NMR (75.49 MHz, CDCl3) d: 22.8, 26.8, 57.2, 61.6, 73.0, 122.1,
126.6, 127.2, 128.5, 128.5, 132.8, 139.6, 143.1, 169.3, 195.7 HRMS
(ESI): Calcd for C19H19NO3 [M+H]+: 310.1438. Found: 310.1441,
[M+Na]+ 332.1257. Found 332.1254. Yield: 28.5 mg (54%).
Supplementary data
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Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.bmc.2014.07.024.
These data include MOL files and InChiKeys of the most important
compounds described in this article.
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