A versatile synthesis of αGalCer and its analogues exploiting a cyclic carbonate as phytosphingosine 3,4-diol protecting group

Article abstract of DOI:10.1016/j.carres.2018.11.005

A convenient synthetic strategy to αGalCer and some relevant analogues by using a handily protected phytosphingosine is reported here. The conversion of the phytosphingosine amino group to azide and the protection of 3,4-diol as cyclic carbonate group, cl

Full text of DOI:10.1016/j.carres.2018.11.005

CarbohydrateResearch472(2019)50–57
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Carbohydrate Research
journal homepage: www.elsevier.com/locate/carres
A versatile synthesis of αGalCer and its analogues exploiting a cyclic
carbonate as phytosphingosine 3,4-diol protecting group
Luigi Panzaa, Federica Compostellab, Daniela Imperioa,∗
a Dipartimento di Scienze del Farmaco, Università del Piemonte Orientale, L. go Donegani 2, 28100, Novara, Italy
b Dipartimento di Biotecnologie Mediche e Medicina Traslazionale, Università degli Studi di Milano, Via Saldini 50, 20133, Milano, Italy
A R T I C L E I N F O
A B S T R A C T
Keywords:
A convenient synthetic strategy to αGalCer and some relevant analogues by using a handily protected phyto-
sphingosine is reported here. The conversion of the phytosphingosine amino group to azide and the protection of
3,4-diol as cyclic carbonate group, cleavable in mild basic conditions but resistant to acidic treatment, afforded
quickly an excellent glycosyl acceptor. Its glycosylation with a proper galactosyl donor, gave a versatile inter-
mediate in high yield and excellent stereoselectivity. To demonstrate the potentiality of the intermediate, three
immunologically relevant compounds were chosen as model targets: αGalCer, dansyl alpha-galactosylceramide
and 7DW8-5. These products were easily obtained in few steps and high yields to validate the synthetic route.
α-Galactosylceramide analogues
Glycosylation
Glycosphingolipids
Phytosphingosine acceptor
1. Introduction
chain or of the phytosphingosine moiety allowing to understand the
structural features essential or relevant for the immmunological ac-
Invariant natural killer T (iNKT) cells are a unique type of innate
immune cells (T lymphocytes) that express an invariant α,β T-cell re-
ceptor. They recognize a range of foreign and endogenous lipids pre-
sented by CD1d glycoprotein (non-polymorphic MHC class I-like an-
tigen presenting molecule). When activated they can influence the
immune system with various effector and regulatory functions [1].
α-Galactosylceramide (αGalCer or KRN7000 1, Fig. 1), a synthetic
glycolipid derived by the chemical simplification of Agelasphin, a
natural product isolated from the marine sponge Agelas mauritianus, is
composed of a galactose α-linked to a phytosphingosine acylated with a
long-chain fatty acid [2]. This glycolipid is the most extensively studied
ligand for iNKT cells as it acts as a strong stimulator when bound to the
CD1d glycoprotein. αGalCer is the reference compound for the eva-
luation of new CD1d ligands due to its potency and good biological
characterisation. The complex between CD1d and αGalCer is re-
cognised by the T-cell receptor of iNKT cells and induces the production
of different cytokines that promote both an inflammatory response
called T helper 1 (Th1), which governs the antitumor and antimicrobial
activities, and an immunomodulatory response named T helper 2 (Th2),
which can ameliorate various autoimmune diseases [3].
tivity.
In particular, some of the analogues showed a tendency in switching
immune responses towards Th1 or Th2 dominance with respect to
αGalCer, depending on the structural modifications introduced. For
example, an αGalCer derivative with a shortened sphingosine moiety
(OCH analogue) [5], showed a Th2-biased NKT cell activation profile
while the C-glycoside derivative of αGalCer showed Th1-polarizing
action and an increased activity against malaria and B16-melanoma in
mice [6].
The biological interest towards modified αGalCer structures
prompted the development of a huge number of synthetic approaches,
in which researchers tried to optimize the synthetic schemes toward
this class of compounds in term of yields, efficient glycosylation reac-
tions and an overall reduced number of steps [7]. A first crucial aspect
is the challenging stereoselective construction of 1,2-cis galactopyr-
anosyl linkages. α-Gal-type glycosides can be formed by exploiting the
anomeric effect and in situ anomerization [8], by using appropriate
solvents, and non-participating protecting groups at the C2-OH [9],
such as benzyl groups. Of particular interest are trimethylsilyl pro-
tecting groups [8b,c] which can give a rapid access to αGalCer struc-
tures. Often, galactosyl donors bearing a 4,6-O-benzylidene [10] (or
4,6-O-silylene [11]) protecting group are exploited as it can contribute
to direct the attack of the acceptor from the α side, probably due to
steric hindrance [12]. Moreover, a 4,6-O-arylidene protecting group
For these reasons, iNKT cells represent a striking target for devel-
oping new therapeutics able to influence the human immune system in
a broad range of settings [1,4]. Many analogues of αGalCer have been
developed to date, by varying the structures of the sugar, of the acyl
∗ Corresponding author.
E-mail address: daniela.imperio@uniupo.it (D. Imperio).
https://doi.org/10.1016/j.carres.2018.11.005
Received 23 October 2018; Received in revised form 6 November 2018; Accepted 6 November 2018
Availableonline15November2018
0008-6215/©2018ElsevierLtd.Allrightsreserved.

L. Panza et al.
CarbohydrateResearch472(2019)50–57
Fig. 1. Structures of αGalCer and its analogues.
allows an easy access to the C-6 position of galactose, for the devel-
opment of αGalCer 6-OH modified analogues, which have been shown
to have good or even enhanced biological activity [13,14].
used as glycosyl acceptors in glycosylation reactions.
Commercial phytosphingosine 4 was converted into the azide 5a by
diazo-transfer [25] or into the tetrachlorophthalimido derivative 5b
according to our previously published procedure [15]. Differently from
the approach described in Ref. [24], 3,4-cyclic carbonate was in-
troduced directly on triols 5a,b as reported in Scheme 1. Each of the
intermediates 5a or 5b, was dissolved in dry pyridine and added
dropwise to a solution of an excess of trichloromethyl chloroformate in
dichloromethane (DCM) at 0 °C. The reaction proceeded fast, and the
mixture was quenched by pouring into ice-water after 30 min. After
chromatographic purification, the cyclic carbonate 6a was obtained in
an acceptable 63% yield [26], while 6b was isolated in 82% yield by
crystallisation.
The other important aspect in the synthesis of αGalCer is re-
presented by the choice of the sphingolipid acceptor for the glycosy-
lation. For example, the use of ceramide allows quick access to αGalCer
derivatives but usually with fair to low yields [5]. In fact, the presence
of the amide on ceramide reduces the nucleophilicity of the primary
hydroxyl group because of a hydrogen bond with the amide NH [15].
Alternative approaches use other types of phytosphingosine acceptors
prepared either by protection of commercially available phyto-
sphingosine or by synthesis from naturally occurring chiral precursors.
In both cases, different steps of protection and deprotection are in
general required. Commonly used protecting groups for the 2,3-OH
groups of phytosphingosine are benzoyl [16], benzyl [17], iso-
propylidene [18], silyl [11,19], etc. In addition, p-methoxybenzyl
ethers have found a convenient application in the synthesis of αGalCer
derivatives [20]. One further different approach to αGalCer exploits the
construction of the sphingoid backbone after the glycosylation of ga-
lactose with a proper phytosphingosine precursor, such as a protected D-
lyxose derivative. This strategy allows the access to different sphingo-
sine analogues but does not permit to introduce modifications on the
sugar part [18,21].
4-Methylphenyl 2,3-di-O-benzyl-4,6-O-benzylidene-1-thio-β-D-ga-
lactopyranoside 7 [27] was selected as glycosyl donor because of its
stability, ease of preparation and for the α-directing effect of the ben-
zylidene protecting group. The glycosylation reaction was performed on
both acceptors 6a and 6b using Me2S2-Tf2O as the promoter, according
to the procedure reported by Fügedi [28]. (Scheme 2) and already
exploited with the same donor but on a different acceptor in a previous
synthesis of αGalCer analogues [29].
We were very pleased to obtain the expected products in high yield
and complete stereoselectivity. Either a good match of donor-acceptor
reactivity and the use of a buffered medium to perform the glycosyla-
tion contributed to our excellent results. We demonstrated that com-
pounds 6a and 6b are feasible acceptors in the glycosylation with donor
7 that resulted more reactive than previously reported [29]. We then
focused our attention on the introduction of the acyl chain on phyto-
sphingosine.
In view of the above considerations, we developed a versatile
synthesis for αGalCer and some analogues through a new versatile
galactosyl sphingosine intermediate. To demonstrate the efficiency of
the approach, we focused our efforts towards three representative
structures (Fig. 1) characterized by biological interest: αGalCer, 7DW8-
5 2, a derivative characterized by a superior adjuvant activity on HIV
and malaria vaccines in mice [22], and the dansylated αGalCer 3 as a
useful tool to monitor αGalCer uptake by cells [23].
Disappointingly, when compound 8b was submitted to standard
tetrachlorophthalimide deprotection protocol (ethylendiamine in
ethanol [30]), a complex mixture was obtained. Despite many attempts
to deprotect either the NTCP or the cyclic carbonate or both in various
conditions (ethylendiamine or hydrazine [31] in different conditions of
solvent and temperature, sodium methoxide, potassium carbonate in
methanol, sodium borohydride followed by treatment with acetic acid
[32]), complex mixtures were always obtained. So intermediate 8b was
discarded. On the other hand, the azido intermediate 8a, behaved as
expected (Scheme 3). The azido group of 8a was reduced by mild cat-
alytic hydrogenation with Lindlar catalyst to the corresponding amine,
which was condensed with hexacosanoic acid or with 11-(4-
2. Results and discussion
Our attention was initially focused on the sphingoid moiety. Key
phytosphingosine acceptors were synthesized exploiting a cyclic car-
bonate as the protecting group for the 2,3-hydroxyl groups of phyto-
sphingosine and masking the amino group as an azide or a tetra-
chlorophtalimide. The introduction of the carbonate 3,4-diol protecting
group on phytosphingosine was reported only once in the literature
[24] but never exploited to obtain phytosphingosine derivatives to be
51

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CarbohydrateResearch472(2019)50–57
Scheme 1. Phytosphingosine acceptors synthesis.
fluorophenyl)undecanoic acid 19 in the presence of 1-ethyl-3-(3-di-
methylaminopropyl)carbodiimide (EDC), N,N-diisopropylethylamine
(DIPEA), and hydroxybenzotriazole (HOBt), to give compounds 9 and
10 [17].
Acid 19 was prepared as shown in Scheme 4 in 71% yield over two
steps, following a modified literature procedure [33]. Commercially
available iodide 16 and alkyne 17 were coupled via Sonogashira reac-
tion to give the alkyne 18 which afforded the carboxylic acid 19 by
catalytic hydrogenation.
The hydrolysis of the cyclic carbonate on compounds 9 and 10
proceeded in mild conditions under Zémplen-like conditions with a
catalytic amount of potassium hydroxide in methanol [34]. The so
obtained diols 11 and 12 were directly subjected to catalytic
Scheme 2. Glycosylation reaction.
Scheme 3. Synthesis of the final compounds.
52

L. Panza et al.
CarbohydrateResearch472(2019)50–57
a Stuart Scientific SMP3 apparatus and remain uncorrected. Optical
rotations were measured on a JASCO P1010 polarimeter at 20 °C.
4.1. (2S,3S,4R)-2-azidooctadecan-1-ol-cyclic 3,4-carbonate (6a)
Diphosgene (2.53 g, 12.80 mmol) was dissolved under Argon at-
mosphere in DCM (20 mL) and cooled at 0 °C. A solution formed by
compound 5a (0.88 g, 2.56 mmol) dissolved in Py (40 mL) was then
added dropwise in 20’. After 30’ the reaction mixture was slowly
poured into ice (100 mL) and stirred for 1 h. It was then transferred into
a washing funnel, the layers separated and the aqueous was extracted
with DCM (2 × 100 mL), the organics combined and washed with HCl
1N (100 mL), brine, dried over Na2SO4 and concentrated under va-
cuum. The residue was purified by flash chromatography (toluene/
ethyl acetate 8:2) to obtain 0.60 g of a white solid (yield: 63%). Mp:
54–56 °C. [α]2D0: +48.5° (c 1.0, CHCl3).
Scheme 4. Synthesis of the acid 19.
hydrogenation to give the final compounds 1 and 2 in high yields.
The synthesis of compound 3 was more complex. Removal of the
benzylidene protecting group from intermediate 9 in acidic conditions,
using a mixture of TFA/DCM/H2O, afforded diol 13. The tosyl group
was selectively introduced at the primary hydroxyl group of galactosyl
moiety followed by nucleophilic substitution with sodium azide to
obtain the 6-azido derivative 14 [35]. The azide was reduced to amine
using the Staudinger reaction and directly submitted to sulphonylation
by treatment with commercially available dansyl chloride in di-
chloromethane-triethylamine. Hydrolysis of the cyclic carbonate with
potassium carbonate in methanol and final catalytic hydrogenation
afforded in good yield the dansylated αGalCer 3.
1H NMR (CDCl3, 300 MHz) δ 4.71 (m, 1H), 4.58 (dd, J1 = 10.1 Hz,
J2 = 7.1 Hz, 1H), 4.12 (dd, J1 = 11.6 Hz, J2 = 2.8 Hz, 1H), 3.95 (dd,
J1 = 11.6 Hz, J2 = 5.6 Hz, 1H), 3.71 (m, 1H), 2.10 (bs, 1H), 1.68 (m,
4H), 1.30–1.10 (m, 22H), 0.87 (t, J = 6.1 Hz, 3H); 13C NMR (CDCl3,
75 MHz) δ 153.8, 79.7, 75.8, 62.7, 59.8, 32.0, 29.79, 29.77, 29.75,
29.69, 29.6, 29.5, 29.3, 29.0, 25.6, 22.8, 14.2. MS (ESI) m/z Calculated
for C19H35N3O4: 369; Found: 392 [M+Na]+. HRMS(ESI) calcd for
[C19H35N3O4 + Na]+: 392.2525, found: 392.2527.
IR (neat, cm−1): 2918, 2850, 2144, 2103, 1789.
4.2. (2S,3S,4R)-2-tetrachlorophthalimidooctadecan-1-ol-cyclic 3,4-
carbonate (6b)
3. Conclusions
Diphosgene (0.42 g, 2.12 mmol) was dissolved under Argon atmo-
sphere in DCM (25 mL) and cooled at 0 °C. A solution formed by com-
pound 5b (0.50 g, 0.85 mmol) dissolved in Py (5 mL) was then added
dropwise in 20’. After 30’ the reaction mixture was slowly poured into
ice (100 mL) and stirred for 1 h. It was then transferred into a washing
funnel, the layers separated and the aqueous was extracted with DCM
(2 × 100 mL), the organics combined and washed with HCl 1N
(100 mL), brine, dried over Na2SO4 and concentrated under vacuum.
The residue was crystallized by hot ethanol to obtain 0.43 g of a yellow
solid (yield: 82%). Mp: 148–150 °C. [α]2D0: +9.5° (c 1.0, CHCl3). 1H
NMR (CDCl3, 300 MHz) δ 5.60 (dd, J1 = 10.5 Hz, J2 = 7.0 Hz, 1H),
4.73–4.55 (m, 2H), 4.10 (d, J = 6.1 Hz, 2H), 1.89–1.62 (m, 2H), 1.54
(d, J = 3.9 Hz, 1H), 1.40–1.10 (m, 24H), 0.87 (t, J = 6.7 Hz, 3H). 13C
NMR (CDCl3, 75 MHz) δ 163.6, 141.0, 130.3, 127.0, 79.4, 74.8, 60.4,
52.0, 32.0, 29.7, 29.5, 29.4, 29.0, 28.7, 25.3, 22.8, 14.3. MS (ESI) m/z
Calculated for C27H35Cl4NO6: 611; Found: 610 [M-1]-. HRMS(ESI) calcd
for [C27H3535Cl4NO6 + Na]+: 632.1116, found: 632.1116.
In conclusion, the synthetic route herein described allows an easy
and convenient access to reported relevant αGalCer analogues. A new
phytosphingosine acceptor was developed and obtained with
a
straightforward 2-steps synthesis. It performed satisfactorily in the
glycosylation reaction to give the αGalCer backbone which was effi-
ciently transformed into the target αGalCer derivatives 1, 2, and 3.
Indeed, the flexibility of our approach would permit the introduction of
various acyl chains on the ceramide moiety as well as modifications of
the sugar part, so improving the access to αGalCer and analogues
thereof.
4. Experimental section
Reagents were used as supplied without further purification unless
otherwise stated. All reagents and solvents were purchased from TCI or
Carlo Erba.
Thin layer chromatography was performed on silica gel plates with
fluorescent indicator. Visualization was accomplished by UV light (254
and/or 365 nm) and/or by staining in ceric ammonium molybdate or
sulfuric acid solution. Anhydrous solvents were obtained using acti-
vated molecular sieves (0.3 or 0.4 nm depending on the type of sol-
vent). All reactions (if not specifically containing water as reactant,
solvent or co-solvent) were performed under Argon atmosphere, in
oven dried glassware. Flash column chromatography was performed
following the procedure indicated on J. Org. Chem., 1978, 43,
2923–2925, with 230–400 mesh silica gel. NMR spectra were recorded
using a JEOL ECP 300 MHz spectrometer. Chemical shifts (δ) are quoted
in parts per million referenced to the residual solvent peak. The mul-
tiplicity of each signal is designated using the following abbreviations:
s, singlet; d, doublet; t, triplet; q, quartet; quint, quintet; sext, sextet;
hept, heptet; m, multiplet; br, broad. Coupling constants (J) are re-
ported in Hertz (Hz). Mass spectra were recorded on a Thermo
Finningan LCQ-deca XP-plus mass spectrometer equipped with an ESI
source and an ion trap detector. High-resolution mass spectra were
collected by electrospray ionization (ESI) spectroscopy on a QTof
SYNAPT G2Si Mass Spectrometer Melting points were determined using
IR (neat, cm−1) 3433, 2918, 2051, 1754, 1718, 1470, 1389, 1364,
1350, 1095, 736.
4.3. (2S,3S,4R)-1-O-(2,3-di-O-benzyl-4,6-O-benzylidene-α-D-
galactopyranosyl)-2-azido-octadecan-1-ol-cyclic-3,4-carbonate (8a)
Preparation of Me2S2-Tf2O (1.0 M): to a solution of dimethyl dis-
ulphide (1 mL, 11.3 mmol), in 7.5 mL of dry DCM cooled at −10 °C was
added triflic anhydride (1.7 mL, 10 mmol). The mixture was stirred for
30’ and the Me2S2-Tf2O was obtained.
Compound
7
(0.83 g, 1.50 mmol), compound 6a (0.83 g,
2.25 mmol) and 2,6-di tertbutyl-4-methyl pyridine (0.30 g, 1.50 mmol)
were dissolved in dry THF (12.5 mL) under argon atmosphere and
molecular sieves 4A° were added. The mixture was stirred at rt for 1 h
then cooled to −10 °C in a salt-ice bath before adding Me2S2-Tf2O
(1.0 M, 3 mL). After stirring for 20’, the reaction was quenched with
Et3N (0.7 mL), diluted with DCM (20 mL). The organic layer was wa-
shed with water (2 × 40 mL), brine, dried over Na2SO4 and con-
centrated. The residue was purified by flash chromatography (toluene/
ethyl acetate 95:5) to obtain 1.05 g of a white waxy compound (yield:
53

L. Panza et al.
CarbohydrateResearch472(2019)50–57
88%). [α]2D0: +46.2° (c 1.0, CHCl3). 1H NMR (CDCl3, 300 MHz) δ
7.52–7.25 (m, 15H), 5.49 (s, 1H), 5.01 (d, J = 3.7 Hz, 1H), 4.87 (d,
J = 11.6 Hz, 1H), 4.79 (d, J = 11.6 Hz, 1H) 4.78 (m, 1H), 4.74 (d,
J = 12.2 Hz, 1H), 4.64 (d, J = 11.3 Hz, 1H), 4.54 (ddd, J1 = 10.2 Hz,
J2 = 7.3 Hz, J3 = 2.8 Hz, 1H), 4.28–4.08 (m, 4H), 4.07–3.93 (m, 2H),
3.76 (dd, J1 = 11.1 Hz, J2 = 4.4 Hz, 1H), 3.67 (br s, 1H), 3.54 (ddd,
J1 = 10.1 Hz, J2 = 4.2 Hz, J3 = 2.4 Hz, 1H), 1.76–1.52 (m, 3H),
1.39–1.21 (m, 23H), 0.89 (t, J = 6.7 Hz, 3H). 13C NMR (CDCl3,
75 MHz) δ 153.5, 138.8, 138.7, 137.9, 129.0, 128.6, 128.4, 128.3,
127.90, 127.85, 127.8, 127.7, 126.4, 101.2, 100.0, 79.4, 75.9, 75.7,
75.1, 74.7, 73.8, 72.2, 69.4, 68.4, 63.4, 57.9, 32.0, 29.8, 29.7, 29.6,
29.5, 29.3, 29.0, 25.6, 22.8, 14.2. MS (ESI) m/z Calculated for
down to ambient. The solution was diluted with diethyl ether and
washed with a 1N solution of HCl, a saturated solution of NaHCO3,
water and brine. After drying with MgSO4, solvent was evaporated
under vacuum and the crude was purified by flash chromatography,
(cyclohexane/ethyl acetate 8:2) to give 0.53 g of pure 9 as waxy solid,
in 80% yield. [α]2D0: +60.9° (c 1.0, CHCl3). 1H NMR (CDCl3, 300 MHz) δ
7.52–7.25 (m, 15H), 6.00 (d, J = 8.9 Hz, 1H), 5.49 (s, 1H), 5.03 (d,
J = 3.1 Hz, 1H), 4.90 (d, J = 11.0 Hz, 1H), 4.82–4.66 (m, 3H), 4.61 (d,
J = 11.0 Hz, 1H), 4.44–4.18 (m, 4H), 4.11 (dd, J1 = 10.1 Hz,
J2 = 3.0 Hz, 1H), 4.10–3.80 (m, 2H), 3.74 (m, 2H), 3.61 (sapp, 1H), 2.03
(m, 2H), 1.70–1.50 (m, 5H), 1.40–1.10 (m, 67H), 0.88 (t, J = 6.5 Hz,
6H). 13C NMR (CDCl3, 75 MHz) δ 172.8, 154.0, 138.6, 138.2, 137.8,
129.1, 128.7, 128.5, 128.3, 128.2, 128.0, 127.9, 127.8, 126.4, 101.2,
100.0, 79.8, 76.10, 75.96, 74.6, 74.1, 71.5, 69.4, 67.8, 63.2, 47.6, 36.8,
32.0, 29.8, 29.6, 29.54, 29.48, 29.4, 29.2, 25.7, 25.6, 22.8, 14.2. MS
C
46H61N3O9: 799; Found: 822 [M+Na]+
. HRMS(ESI) calcd for
[C46H61N3O9 + Na]+: 822.4306, found: 822.4309. IR (neat, cm−1):
2923, 2853, 2104, 1807, 1454, 1099, 1050, 1028, 997, 740, 697.
(ESI) m/z Calculated for C72H113NO10: 1152; Found: 1175 [M+Na]+
.
4.4. (2S,3S,4R)-1-O-(2,3-di-O-benzyl-4,6-O-benzylidene-α-D-
galactopyranosyl)-2-tetrachlorophthalimidooctadecan-1-ol-cyclic 3,4-
carbonate (8b)
HRMS(ESI) calcd for [C72H113NO10
+
Na]+
: 1174.8262, found
1174.8270. IR (neat, cm−1): 3274, 2917, 2850, 1829, 1541, 1469,
1101, 1053.
Preparation of Me2S2-Tf2O (1.0 M): to a solution of dimethyl dis-
ulphide (1 mL, 11.3 mmol), in 7.5 mL of dry DCM cooled at −10 °C was
added triflic anhydride (1.7 mL, 10 mmol). The mixture was stirred for
30’ and the Me2S2-Tf2O was obtained.
4.6. (2S,3S,4R)-1-O-(2,3-di-O-benzyl-α-D-galactopyranosyl)-2-
(hexacosanoyl)amino-octadecan-1-ol-cyclic-3,4-carbonate (13)
Compound 9 (160 mg, 0.14 mmol) was dissolved in a mixture of
DCM (11 mL) and water (0.5 mL). After cooling at 0 °C, trifluoracetic
acid (1 mL) was added and the mixture was left at 0 °C for 2 h and at rt
for 2 h. The organic phase was washed with water (2 × 10 mL), brine,
dried over MgSO4 and concentrated under vacuum. The crude was
purified by flash chromatography (cyclohexane/ethyl acetate 4:6) to
give 117 mg of pure 13 as waxy solid, in 80% yield. [α]2D0: +52.3° (c
1.0, CHCl3). 1H NMR (CDCl3, 300 MHz) δ 7.38–7.32 (m, 10H), 6.31 (d,
J = 9.2 Hz, 1H), 4.87 (d, J = 3.0 Hz, 1H), 4.84–4.67 (m, 4H), 4.59 (d,
J = 11.4 Hz, 1H), 4.55–4.45 (m, 1H), 4.38 (m, 1H), 4.11 (br s, 1H),
3.94–3.66 (m, 6H), 3.70 (dd, J1 = 11.3 Hz, J2 = 3.1 Hz, 1H), 2.49 (br s,
2H), 2.10 (m, 2H), 1.73 (m, 1H), 1.54 (m, 4H), 1.24 (m, 67H), 0.87 (t,
J = 6.1 Hz, 6H). 13C NMR (CDCl3, 75 MHz) δ 173.1, 154.2, 138.0,
137.97, 128.7, 128.6, 128.3, 128.1, 128.0, 99.6, 80.0, 77.4, 76.1, 74.0,
72.5, 70.2, 68.7, 68.4, 62.9, 57.8, 47.5, 36.6, 32.0, 29.8, 29.6, 29.5,
28.6, 25.7, 22.8, 14.2. MS (ESI) m/z Calculated for C65H109NO10: 1064;
Compound
7
(1.00 g, 1.80 mmol), compound 6b (1.43 g,
2.34 mmol) and 2,6-di tertbutyl-4-methyl pyridine (0.37 g, 1.80 mmol)
were dissolved in dry THF (15 mL) under argon atmosphere and mo-
lecular sieves 4A° were added. The mixture was stirred at rt for 1 h then
cooled to −10 °C in a salt-ice bath before adding Me2S2-Tf2O (1.0 M,
3.6 mL). After stirring for 20’, the reaction was quenched with Et3N
(0.8 mL), diluted with DCM (20 mL). The organic layer was washed
with water (2 × 40 mL), brine, dried over Na2SO4 and concentrated.
The residue was purified by flash chromatography (cyclohexane/ethyl
acetate 9:1) to obtain 1.64 g of a white solid (yield: 87%). Mp:
103–105 °C. [α]2D0: +19.0° (c 1.0, CHCl3). 1H NMR (CDCl3, 300 MHz) δ
7.58–6.90 (m, 15H), 5.59 (dd, J1 = 10.7 Hz, J2 = 7.0 Hz, 1H), 5.44 (s,
1H), 4.85 (d, J = 3.2 Hz, 1H), 4.82–4.60 (m, 4H), 4.33 (s, 2H),
4.28–4.16 (m, 2H), 4.12 (d, J = 3.0 Hz, 1H), 4.01 (d, J = 12.6 Hz, 1H),
3.95–3.84 (m, 2H), 3.80 (dd, J1 = 10.0 Hz, J2 = 3.2 Hz, 1H), 3.64 (s,
1H), 1.83–1.64 (m, 1H), 1.60–1.48 (m, 1H), 1.30–1.10 (m, 24H), 0.88
(t, J = 6.6 Hz, 3H). 13C NMR (75 MHz, CDCl3) δ 163.7, 153.4, 140.7,
138.8, 138.2, 137. 9, 129.8, 128.9, 128.5, 128.20, 128.17, 127.8,
127.7, 127.5, 127.0, 126.4, 126.2, 101.0, 99.3, 79.4, 76.3, 76.0, 74.7,
74.6, 73.0, 72.6, 69.4, 65.8, 63.4, 50.1, 32.0, 29.76, 29.72, 29.54,
29.46, 29.4, 29.1, 28.7, 25.4, 22.8, 14.2. MS (ESI) m/z Calculated for
Found:
1087
[M+Na]+
.
HRMS(ESI)
m/z
calcd
for
[C65H109NO10 + Na]+: 1086.7949, found 1086.7950. IR (neat, cm−1):
3728, 2918, 2850, 1801, 1467, 1364, 1047.
4.7. (2S,3S,4R)-1-O-(6-azido-6-deoxy-2,3-di-O-benzyl-α-D-
galactopyranosyl)-2-(hexacosanoyl)aminooctadecan-1-ol-cyclic-3,4-
carbonate (14)
C
51H61Cl4NO11: 1042; Found: 1065 [M+Na]+. HRMS(ESI) calcd for
[C51H61Cl435NO11 + Na]+: 1062.2896, found 1062.2902. IR (neat,
cm−1): 2923, 2853, 1806, 1723, 1454, 1392, 1371, 1349, 1099, 1053,
739.
To a solution of 9 (117 mg, 0.11 mmol) in 2.5 mL of anhydrous DCM
was added TsCl (63 mg, 0.33 mmol) followed by Et3N (77 μL,
0.55 mmol) at 0 °C. The reaction mixture was raised up to rt and stirred
for 8 h. Saturated aqueous NH4Cl was slowly added to neutral. Two
layers were separated, and the aqueous layer was extracted with DCM
(3 × 20 mL). The organics were combined and dried over MgSO4, and
then concentrated in vacuo. The resulting residue was purified by flash
chromatography (cyclohexane/ethyl acetate 8:2) to afford the inter-
mediate 6-tosylate (117 mg, 87%, white solid). 1H NMR (CDCl3,
300 MHz) δ 7.75 (d, J = 8.0, 2H), 7.34 (m, 12H), 6.26 (d, J = 8.8 Hz,
1H), 4.77 (d, J = 11.6 Hz, 1H), 4.71 (m, 5H), 4.57 (d, J = 11.5 Hz, 1H),
4.35 (m, 1H), 4.2–4.0 (m, 3H), 3.98 (m, 2H), 3.81 (m, 2H), 3.63 (d,
J = 10.1 Hz, 1H), 2.4 (s, 3H), 2.13 (m, 2H), 1.62 (m, 8H), 1.24 (m,
65H), 0.87 (t, J = 6.4 Hz, 6H). To a solution of the intermediate
(110 mg, 0.09 mmol) in 4.7 mL of anhydrous DMF was added NaN3
(17 mg, 0.27 mmol). The reaction mixture was stirred at 80 °C overnight
and cooled to rt. The reaction was diluted with 10 mL of water and
diethyl ether (1:1), the phases separated. The aqueous was extracted
with diethyl ether (2 × 10 mL). The organics combined were washed
4.5. (2S,3S,4R)-1-O-(2,3-di-O-benzyl-4,6-O-benzylidene-α-D-
galactopyranosyl)-2-(hexacosanoyl)amino-octadecan-1-ol-cyclic-3,4-
carbonate (9)
Under Ar atmosphere 0.63 g (0.79 mmol) of 8a were dissolved in
60 mL of ethyl acetate and carefully degassed. Lindlar catalyst (0.63 g)
was added and the reaction was stirred under H2 atmosphere overnight.
After restoring Ar atmosphere, solution was filtered through a plug of
Celite and solvent was removed on vacuum. The amine was directly
used without any further purification and split in two batch. Part of the
crude, (0.46 g, 0.59 mmol) was then dissolved under Ar atmosphere in
16.7 mL of anhydrous DCM. The obtained solution was added to a so-
lution previous prepared dissolving (under Ar atmosphere at 0 °C) the
hexacosanoic acid (0.41 g, 1.04 mmol), DIPEA (0.34 g, 2.6 mmol), EDC
(0.33 g, 1.73 mmol), HOBt (0.23 g, 1.73 mmol), in DMF (8.4 mL). The
solution was stirred overnight at 40 °C and then it was allowed to cool-
54

L. Panza et al.
CarbohydrateResearch472(2019)50–57
with water (2 × 10 mL), brine, dried over MgSO4 and concentrated in
vacuo. The crude was purified by flash chromatography (cyclohexane/
ethyl acetate 8:2) to afford 14 (76 mg, 78%, yellow oil). [α]2D0: +47.9°
(c 1.0, CHCl3).
H2 for 17 h. at rt. The reaction mixture was then filtered through a
Celite pad, the Celite was washed thoroughly with CHCl3/EtOH (3/2,
v/v), and the filtrate concentrated. The residue was purified by chro-
matography column (CH2Cl2/MeOH 9:1) obtaining
a yellow wax
1H NMR (CDCl3, 300 MHz) δ 7.35 (m, 10H), 6.16 (d, J = 9.3 Hz,
1H), 4.87 (d, J = 3 Hz, 1H), 4.83–4.67 (m, 4H), 4.59 (d, J = 11.3 Hz,
1H), 4.49 (t, J = 8.2 Hz, 1H), 4.39 (t, J = 9.2 Hz, 1H), 3.97 (br s, 1H),
3.83 (m, 4H), 3.73 (dd, J1 = 11.3 Hz, J2 = 2.9 Hz, 1H), 3.62 (m, 1H),
3.37 (dd, J1 = 12.5 Hz, J2 = 4.3 Hz, 1H), 2.4 (br s, 1H), 2.11 (m, 2H),
1.58 (m, 5H), 1.25 (m, 67H), 0.87 (t, J = 5.8, 6H). 13C NMR (CDCl3,
75 MHz) δ 172.8, 154.0, 137.9, 137.8, 128.8, 128.7, 128.3, 128.2,
128.1, 128.0, 99.4, 79.9, 77.1, 76.0, 74.1, 72.7, 69.5, 69.0, 67.7, 51.6,
47.3, 37.2, 32.0, 29.8, 29.5, 29.46, 29.4, 29.2, 28.6, 25.7, 22.8, 14.2.
MS (ESI) m/z Calculated for C65H108N4O9: 1089; Found: 1112 [M
(37 mg, 90% yield over two steps). 1H NMR (Pyridine-d-5, 300 MHz) δ
9.73 (1H, t, J = 5.0 Hz), 9.02 (d, J = 8.6 Hz, 1H), 8.58 (d, J = 7.0 Hz,
1H), 8.53 (d, J = 8.3 Hz, 1H), 8.43 (d, J = 8.6 Hz, 1H), 7.50 (m, 2H),
7.11 (d, J = 7.6 Hz, 1H), 5.44 (d, J = 3.1 Hz, 1H), 5.23 (m, 1H), 4.52
(m, 3H), 4.30–4.28 (m, 3H), 4.23 (dd, J1 = 9.8 Hz, J2 = 2.8 Hz, 1H),
4.16 (dd, J1 = 11.3 Hz, J2 = 5.5 Hz, 1H), 3.85 (t, J = 5.5 Hz, 2H), 2.72
(s, 6H), 2.44 (m, 3H), 1.82 (m, 5H), 1.31–1.23 (m, 66H), 0.86 (t,
J = 6.7 Hz, 6H). 13C NMR (Pyridine-d-5, 75 MHz) δ 173.0, 152.0,
137.4, 130.4, 130.3, 129.9, 128.9, 128.0, 120.3, 115.5, 101.1, 76.7,
72.3, 71.1, 71.0, 70.8, 69.7, 68.3, 50.9, 45.1, 44.8, 36.7, 34.4, 32.0,
30.3, 30.1, 29.9, 29.5, 26.4, 26.3, 22.8, 14.2. MS (ESI) m/z Calculated
+Na]+. HRMS(ESI) calcd for [C65
H
108
N4O9 + Na]+: 1111.8014,
found 1111.8022. IR (neat, cm−1): 2918, 2848, 2100, 1802, 1655,
1540, 1467, 1264, 1055.
for C62H111N3O10S: 1090; Found: 1091 [M+1]+
.
4.10. 11-(4-fluorophenyl)undec-9-ynoic acid (18) [32]
4.8. (2S,3S,4R)-1-O-(6-deoxy-6[N-(5-[dimethylamino]napth-1-
ylsulfonyl)amino]2,3-di-O-benzyl-α-D-galactopyranosyl)-2-(hexacosanoyl)
amino-octadecan-1-ol-cyclic-3,4-carbonate (15)
4-Fluoroiodobenzene (2.44 g, 11.00 mmol) was dissolved in dry
THF under argon atmosphere (10 mL), Pd(PPh3)2Cl2 (0.10 g,
0.14 mmol, 2.5 mol %), CuI (50 mg, 0.27 mmol, 5 mol %), iPr2NH
(1.67 g, 16.46 mmol) and the undec-10-ynoic acid (1.00 g, 5.49 mmol)
were sequentially added. The mixture was stirred at rt for 3 h. The
mixture was diluted with ethyl acetate and washed with HCl 1N
(2 × 100 mL), water, brine, dried over MgSO4 and concentrated under
vacuum. The crude was purified by flash chromatography (toluene/
ethyl acetate 6:4) to give 1.27 g of a pure yellow solid, in 76% of yield.
MP: 66–68 °C.
PMe3 (10 μL, 0.096 mmol) was added to a solution of compound 14
(75 mg, 0.064 mmol) in THF (2 mL) at r.t. The resulting solution was
stirred for 5 h. H2O (10 μL) was then added and the reaction mixture
was stirred for 1 h before being concentrated under reduced pressure.
The residue was diluted in ethyl acetate and washed with water, brine,
dried over MgSO4 and evaporated to give the intermediate 6-amine. 1
H
NMR (CDCl3, 300 MHz) δ 7.50–7.27 (m, 10H), 6.60 (d, J = 8.9 Hz, 1H),
4.89 (d, = 3.2 Hz, 1H), 4.85–4.70 (m, 4H), 4.60 (d, J = 11.3 Hz, 1H),
4.45 (m, 1H), 4.33 (m, 1H), 4.15 (br s, 1H), 3.96 (dd, J1 = 9.8 Hz, J2 =
3.3 Hz, 1H), 3.86–3.56 (m, 4H), 3.05 (br s, 2H), 2.86 (br s, 3H), 2.07
(m, 2H), 1.77–1.45 (m, 5H), 1.40–1.00 (m, 67H), 0.87 (t, J = 6.3 Hz,
6H).
1H NMR (CDCl3, 300 MHz) δ 10.2 (br s, 1H), 7.35 (m, 2H), 6.97 (m,
2H), 2.37 (m, 4H), 1.62 (m, 4H), 1.34 (m, 8H). 13C NMR (CDCl3,
75 MHz) δ 180.5, 162.1 (d, JCF = 246 Hz), 133.35 (d, JCF = 7.9 Hz),
120.2 (d, JCF = 2.9 Hz), 115.4 (d, JCF = 21.8 Hz), 90.1, 79.6, 34.2,
29.2, 29.1, 29.0, 28.9, 28.8, 24.7, 19.4. 19F (CDCl3, 282 MHz) δ −112,
MS (ESI) m/z Calculated for C17H21FO2: 276; Found: 275 [M-1]-.
The crude amine was dissolved in dry DCM, and dansyl chloride
(17 mg, 0.064 mmol) and triethylamine (0.32 mmol) were sequentially
added. The mixture was stirred at rt for 4 h, the solvent was evaporated
and the crude was directly purified by flash chromatography (cyclo-
hexane/ethyl acetate 7:3) to afford 15 (65 mg, 78% over two steps,
yellow wax). [α]2D0: +38.4° (c 0.5, MeOH). 1H NMR (CDCl3, 300 MHz) δ
8.56 (d, J = 7.8 Hz, 1H), 8.25 (d, J = 8.8 Hz, 1H), 8.23 (d, J = 7.4 Hz,
1H), 7.53 (m, 2H), 7.38 (m, 10H), 7.18 (d, J = 7.3 Hz, 1H), 6.29 (d,
J = 8.6 Hz, 1H), 5.48 (br s, 1H), 4.72 (m, 5H), 4.55 (m, 2H), 4.39 (m,
1H), 3.97 (br s, 1H), 3.91 (m, 1H), 3.82–3.62 (m, 4H), 3.12 (m, 2H),
2.89 (s, 6H), 2.35 (br s, 1H), 2.14 (m, 2H), 1.65–1.45 (m, 5H), 1.25 (m,
67H), 0.87 (t, J = 6.5 Hz, 6H). 13C NMR (CDCl3, 75 MHz) δ 173.1,
154.3, 151.5, 138.0, 137.9, 134.6, 130.6, 129.8, 129.7, 128.7, 128.6,
128.5, 128.2, 128.1, 128.0, 127.95, 123.5, 119.1, 115.5, 99.4, 80.1,
77.3, 75.9, 73.9, 72.5, 68.9, 67.6, 47.5, 45.6, 43.9, 36.7, 32.0, 29.8,
29.7, 29.6, 29.5, 29.2, 28.6, 25.73, 25.69, 22.8, 14.2. MS (ESI) m/z
Calculated for C77H121N3O11S: 1296; Found: 1297 [M+1]+. HRMS
(ESI) calcd for [C77H121N3O11S + Na]+: 1318.8620, found 1318.8610.
IR (neat, cm−1): 3352, 2922, 2852, 1804, 1658, 1531, 1457, 1320,
1143, 1049, 791.
4.11. 11-(4-fluorophenyl)undecanoic acid (19) [32]
Pd(OH)2 on carbon (0.30 g) was added to a solution of compound
18 (1.20 g, 4.3 mmol), dissolved in a mixture of MeOH (30 mL) and
acetic acid (1.5 mL) and the reaction stirred under H2 for 17 h. at rt. The
mixture was then filtered through Celite, the Celite was washed thor-
oughly with methanol and the filtrate was concentrated. The residue
was concentrated obtaining a white solid. (1.13 g, 94% yield). MP:
70–72 °C. 1H NMR (CDCl3, 300 MHz) δ 11.0 (br s, 1H), 7.11 (m, 2H),
6.95 (m, 2H), 2.57 (t, J = 7.6 Hz, 2H), 2.35 (t, J = 7.4 Hz, 2H), 1.62 (m,
4H), 1.34 (m, 12H). 13C NMR (CDCl3, 75 MHz) δ 180.5, 161.2 (d,
J
CF = 241 Hz), 138.5 (d, JCF = 2.3 Hz), 129.7 (d, JCF = 7.6 Hz), 114.9
(d, JCF = 20.8 Hz), 35.2, 34.2, 31.7, 29.6, 29.52, 29.48, 29.3, 29.2,
29.1, 24.8. 19F (CDCl3, 282 MHz) δ −118. MS (ESI) m/z Calculated for
C17H25FO2: 280; Found: 279 [M-1]-.
4.12. (2S,3S,4R)-1-O-(2,3-di-O-benzyl-4,6-O-benzylidene-α-D-
galactopyranosyl)-2-[11-(4-fluorophenyl)undecanoyl]amino-octadecan-1-
ol-cyclic 3,4-carbonate (10)
4.9. (2S,3S,4R)-1-O-(6-deoxy-6[N-(5-[dimethylamino]napth-1-
ylsulfonyl)amino]-α-D-galactopyranosyl)-2-(hexacosanoyl)amino-
octadecan-1,3,4-triol (3) [23b]
The second part of the crude amine produced after reduction of 8a,
(150 mg, 0.19 mmol) was then dissolved under Ar atmosphere in 5 mL
of anhydrous DCM. The obtained solution was added to a solution
previously prepared dissolving (under Ar atmosphere at 0 °C) the
compound 19 (87 mg, 0.31 mmol), DIPEA (100 mg, 0.77 mmol), EDC
(99 mg, 0.52 mmol), HOBt (70 mg, 0.52 mmol), in DMF (2.5 mL). The
solution was stirred overnight at 40 °C and then it was allowed to cool-
down to ambient. The solution was diluted with diethyl ether and
washed with a 1N solution of HCl, a saturated solution of NaHCO3,
water and brine. After drying with MgSO4, the solvent was evaporated
To a solution of compound 15 (50 mg, 0.038 mmol) in MeOH
(0.8 mL) was added K2CO3 (5 mg, 0.038 mmol, 1.0 equiv). After stirring
at rt overnight, the mixture was diluted with ethyl acetate and organic
layer washed with HCl 1N (10 mL), water, brine, dried over MgSO4 and
concentrated to provide the diol in quantitative yield. Pd(OH)2 on
carbon (10 mg) was added to a solution of the crude dissolved in a
mixture of CHCl3/EtOH (5 mL, 3/2, v/v) and the reaction stirred under
55

L. Panza et al.
CarbohydrateResearch472(2019)50–57
under vacuum and the crude was purified by flash chromatography,
(cyclohexane/ethyl acetate 8:2) to give 181 mg of pure 10 as yellow
solid, in 90% yield. [α]2D0: +72.9° (c 1.0, CHCl3). MP 70–72 °C. 1H NMR
(CDCl3, 300 MHz) δ 7.53–7.33 (m, 15H), 7.10 (t, J = 8.0 Hz, 2H), 6.94
(t, J = 8.4 Hz, 2H), 6.03 (br d, J = 7.4 Hz, 1H), 5.49 (s, 1H), 5.02 (d,
J = 2.5 Hz, 1H), 4.90 (d, J = 11.1 Hz, 1H), 4.77–4.69 (m, 3H), 4.61 (d,
J = 11.3 Hz, 1H), 4.37 (m, 2H), 4.28–3.88 (m, 5H), 3.73 (br s, 2H),
3.67 (br s, 1H), 2.56 (t, J = 7.6 Hz, 2H), 2.04 (m, 2H), 1.54 (m, 7H),
1.20 (m, 35H), 0.88 (t, J = 6.3 Hz, 3H). 13C NMR (CDCl3, 75 MHz) δ
J1 = 10.1 Hz, J2 = 2.4 Hz, 1H), 3.66 (br s, 1H), 3.52 (s, 1H), 3.45 (m,
2H), 2.27 (br s, 1H), 2.14 (t, J = 7.4 Hz, 2H), 1.58 (m, 4H), 1.26 (m,
68H), 0.88 (t, J = 6.1 Hz, 6H). 13C NMR (CDCl3, 75 MHz) 173.0, 138.4,
137.9, 137.8, 129.1, 128.6, 128.5, 128.3, 128.2, 127.85, 127.78, 126.4,
101.2, 99.6, 76.5, 76.3, 75.2, 74.7, 74.1, 73.4, 71.6, 69.9, 69.4, 63.1,
49.2 37.0, 33.5, 32.0, 29.8, 29.5, 25.9, 22.8, 14.2. MS (ESI) m/z
Calculated for C71H115NO9: 1126 Found: 1149 [M+Na]+. IR (neat,
cm−1): 3415, 2919, 2850, 1738, 1620, 1544, 1497, 1101, 1054, 796.
Pd(OH)2 on carbon (13 mg) was added to a solution of the crude dis-
solved in a mixture of CHCl3/MeOH (4 mL, 1/1, v/v) and the reaction
stirred under H2 for 17 h. at rt. The reaction mixture was then filtered
through Celite, the Celite was washed thoroughly with hot CHCl3/
MeOH (1/1, v/v), and the filtrate was concentrated under vacuum. The
crude was purified by column chromatography (CH2Cl2/MeOH 9:1)
obtaining a white solid (1). (45 mg, yield 90%). Analytical data in
agreement with literature report [36].
172.8, 161.1 (d,
JCF = 249 Hz), 154.0, 138.6, 138.5, 138.47 (d,
J
CF = 3 Hz), 138.2, 137.8, 129.72 (d, JCF = 7.5 Hz), 129.1, 128.7,
128.5, 128.2, 127.8, 126.4, 115.0 (d, JCF = 20.3 Hz), 101.2, 100.0,
79.9, 77.2, 76.1, 76.0, 74.6, 74.1, 71.6, 69.4, 67.7, 63.2, 47.6, 36.7,
35.2, 30.4, 30.1, 29.8, 29.6, 29.54, 29.48, 29.38, 29.30, 27.0, 25.7,
22.8, 14.2. 19F (CDCl3, 282 MHz) δ −118. MS (ESI) m/z Calculated for
C
63H86FNO10: 1036; Found: 1059 [M+Na]+. HRMS(ESI) calcd for
[C63H86FNO10 + Na]+: 1058.6133, found 1058.6143. IR (neat, cm−1):
3527, 3374, 2918, 2850, 1800, 1686, 1509, 1095, 1073, 1040, 748.
Conflicts of interest
4.13. (2S,3S,4R)-1-O-(α-D-galactopyranosyl)-2-[11-(4-fluorophenyl)
There are no conflicts to declare.
Acknowledgements
undecanoyl]amino-octadecan-1,3,4-triol (2) [22b]
To a solution of compound 10 (158 mg, 0.15 mmol) in MeOH (6 mL)
was added KOH (2 mg, 0.03 mmol). After stirring at rt overnight, 1 mL
of water was added and the white solid 12 was filtered and washed with
water and methanol and directly used for the next step. (110 mg, yield:
72%) 1H NMR (CDCl3, 300 MHz) δ 7.51–7.32 (m, 15H), 7.10 (t,
J = 7.6 Hz, 2H), 6.94 (t, J = 8.6 Hz, 2H), 6.28 (br s, 1H), 5.47 (s, 1H).
4.97 (d, J = 2.7 Hz, 1H), 4.94 (d, J = 11.6 Hz, 1H), 4.76 (s, 2H), 4.67
(d, J = 11.2 Hz, 1H), 4.21 (m, 3H), 4.08 (m, 1H), 3.95 (m, 3H), 3.82
(m, 1H), 3.47 (m, 3H), 2.56 (t, 1H, J = 7.4 Hz, 2H), 2.13 (m, 2H), 1.57
(m, 6H), 1.26 (m, 36H), 0.88 (t, 1H, J = 5.5 Hz, 3H). MS (ESI) m/z
Calculated for C62H88FNO9: 1009; Found: 1010 [M+1]+. Pd(OH)2 on
carbon (24 mg) was added to a solution of the crude dissolved in a
mixture of CHCl3/EtOH (8 mL, 1:1) and the reaction stirred under H2
for 17 h. at rt. The reaction mixture was then filtered through Celite,
which was thoroughly washed with CHCl3/EtOH (1:1), and the filtrate
was concentrated. The residue was purified by chromatography column
(CH2Cl2/MeOH 9:1) to give (2) as a colourless wax. [α]2D0: +26.2° (c
0.5, CH3OH:CHCl3 1:1). 1H NMR (Pyridine-d-5, 300 MHz) δ 8.56 (d,
J = 8.6 Hz, 1H), 7.16–7.07 (m, 4H), 5.55 (d, J = 3.7 Hz, 1H), 5.24 (m,
1H), 4.64 (m, 2H), 4.50 (m, 2H), 4.43–4.35 (m, 4H), 4.30 (br s, 2H),
2.51 (t, J = 7.4 Hz, 2H), 2.43 (t, J = 7.4 Hz, 2H), 2.27 (br s, 1H),
1.89–1.66 (m, 3H), 1.51 (m, 2H), 1.22 (m, 36H), 0.85 (t, J = 6.7 Hz,
3H). 13C NMR (Pyridine-d-5, 75 MHz) δ 173.1, 161.4 (d, JCF = 240 Hz),
We thank Università del Piemonte Orientale for support.
Appendix A. Supplementary data
Supplementary data to this article can be found online at https://
doi.org/10.1016/j.carres.2018.11.005.
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138.95 (d,
JCF = 3.1 Hz), 130.2 (d, JCF = 7.5 Hz), 115.2 (d,
JCF = 20.2 Hz), 115.0, 101.4, 76.6, 72.9, 72.4, 71.5, 70.9, 70.2, 68.5,
62.5, 51.3, 36.6, 35.1, 34.2, 32.0, 31.7, 30.2, 30.0, 29.9, 29.8, 29.7,
29.62, 29.58, 29.5, 29.3, 26.4, 26.2, 22.8, 14.2. 19F (Pyridine-d-5,
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