A modular synthetic approach to isosteric sulfonic acid analogues of the anticoagulant pentasaccharide idraparinux

Article abstract of DOI:10.3390/molecules21111497

Heparin-based anticoagulants are drugs of choice in the therapy and prophylaxis of thromboembolic diseases. Idraparinux is a synthetic anticoagulant pentasaccharide based on the heparin antithrombin-binding domain. In the frame of our ongoing research aimed at the synthesis of sulfonic acid-containing heparinoid anticoagulants, we elaborated a modular pathway to obtain a series of idraparinux-analogue pentasaccharides bearing one or two primary sulfonic acid moieties. Five protected pentasaccharides with different C-sulfonation patterns were prepared by two subsequent glycosylation reactions, respectively, using two monosaccharide and four disaccharide building blocks. Transformation of the protected derivatives into the fully O-sulfated, O-methylated sulfonic acid end-products was also studied.

Full text of DOI:10.3390/molecules21111497

molecules
Article
A Modular Synthetic Approach to Isosteric Sulfonic
Acid Analogues of the Anticoagulant
Pentasaccharide Idraparinux
Erika Mezo˝, Dániel Eszenyi, Eszter Varga, Mihály Herczeg and Anikó Borbás *
Department of Pharmaceutical Chemistry, University of Debrecen, Egyetem tér 1, H-4032 Debrecen, Hungary;
mezzo.erika@science.unideb.hu (E.M.); eszenyi.daniel@science.unideb.hu (D.E.); esztervargaa@gmail.com (E.V.);
herczeg.mihaly@science.unideb.hu (M.H.)
* Correspondence: borbas.aniko@pharm.unideb.hu; Tel.: +36-52-512-900
Academic Editor: Vito Ferro
Received: 7 September 2016; Accepted: 3 November 2016; Published: 11 November 2016
Abstract: Heparin-based anticoagulants are drugs of choice in the therapy and prophylaxis of
thromboembolic diseases. Idraparinux is a synthetic anticoagulant pentasaccharide based on
the heparin antithrombin-binding domain. In the frame of our ongoing research aimed at the
synthesis of sulfonic acid-containing heparinoid anticoagulants, we elaborated a modular pathway
to obtain a series of idraparinux-analogue pentasaccharides bearing one or two primary sulfonic acid
moieties. Five protected pentasaccharides with different C-sulfonation patterns were prepared by two
subsequent glycosylation reactions, respectively, using two monosaccharide and four disaccharide
building blocks. Transformation of the protected derivatives into the fully O-sulfated, O-methylated
sulfonic acid end-products was also studied.
Keywords: heparin; carbohydrates; glycosylation; sulfonic acid; uronic acid
1. Introduction
Venous and arterial thromboembolic disorders, including pulmonary embolism and deep
vein thrombosis represent a serious medical and socioeconomic problem worldwide. Untreated
thromboembolism leads to cardiac or cerebral infarction or, in more severe cases, to death.
Anticoagulants are used in the prevention and treatment of venous thrombosis and in the prevention
of systemic embolism [1–4]. The sulfated polysaccharide heparin and its fractionated derivatives have
successfully been used in anticoagulant therapy and thromboprophylaxis since the late 1930s until
today. Heparin derivatives indirectly inhibit the coagulation enzymes thrombin or factor Xa through
activation of the serine protease inhibitor antithrombin, which is an endogenous regulatory protein in
the coagulation cascade [5]. Despite their effectiveness in therapy, heparin polysaccharides may incur
side effects including inflammation, bleeding or heparin induced thrombocytopenia (HIT) due to its
highly polyanionic and heterogeneous nature [6].
After the antithrombin-binding pentasaccharide domain of heparin (
identified, its closely related synthetic analogue, fondaparinux , has been developed into a novel
antithrombotic under the name Arixtra [ ]. This pentasaccharide selectively inhibits factor Xa and
minimizes the bleeding risk and many other unfavorable factors in anticoagulant therapy. Further
1), termed DEFGH, was
2
7,8
research efforts led to the development of the non-glycosaminoglycan derivative, idraparinux
possessing a simplified structure and an increased anticoagulant activity compared to Arixtra.
3 [9],
The interaction between heparin and antithrombin are primarily mediated by negatively
charged groups of heparin and the positively charged lysine and arginine residues from the protein.
Structure-activity relationship (SAR) studies of synthetic analogues of heparin pentasaccharides
Molecules 2016, 21, 1497; doi:10.3390/molecules21111497
www.mdpi.com/journal/molecules

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revealed that the type of negative charge is crucial; the carboxylate groups cannot be exchanged for
sulfate esters, and sulfate moieties cannot be exchanged for phosphate groups without destroying the
anticoagulant activity [1,3].
With the aim of developing a novel class of heparinoid anticoagulants, our group has started a
programme to study whether the sulfate ester groups of the active pentasaccharide can be exchanged
with sulfonic acid moieties without detriment to the antithrombin-binding ability [10
pentasaccharide sulfonic acids ( and ) and the reference compound idraparinux
prepared until now. An in vitro coagulation study of clearly demonstrated that the position
and/or number of the sulfonic acid moieties have a substantial impact on the anticoagulant activity
(Figure 1). While the disulfonate analogue displayed higher activity than the reference compounds
and , the introduction of a third sulfonic-acid moiety to the terminal sugar unit of compound resulted
–
19]. Two
4
5
3 have been
2–5
4
2
3
5
in a dramatic decrease in anti-Xa activity [14]. The difference in the biological activity of the disulfonic
and trisulfonic acids was attributed to the different conformation of their L-iduronic-acid residues.
Compound
Anti-Xa Activity (U/mg)
Arixtra (2)
Idraparinux (3)
Pentasaccharide disulfonic acid 4
Pentasaccharide trisulfonic acid 5
1195 ± 189
1911 ± 193
2153 ± 153
384 ± 139
Figure 1. The antithrombin-binding pentasaccharide domain of heparin (1) and structures and factor
Xa inhibitory activities of the synthetic analogues 2–5.
These results prompted us to prepare a series of heparinoid pentasaccharides by systematic
replacement of the sulfate esters with a sodium sulfonatomethyl moiety for further structure-activity
relationship studies. To get an easy access to all possible sulfonic acid isosters of idraparinux bearing the
sulfonic acid moieties at primary positions, we elaborated a modular synthetic pathway based on the
retrosynthetic analysis of the targeted pentasaccharides (Figure 2). According to this modular approach,
the synthesis of all planned pentasaccharide sulfonic acids could be accomplished by using two DE
disaccharide donors, two
syntheses of the 6-deoxy-6-sulfonatomethyl-containing
F
building blocks and two GH disaccharide acceptors. Multigram-scale
DE and GH building blocks have been
F,
published recently [17]. Herein, we present the synthesis of the FGH acceptors and assembly of five
protected pentasaccharide sulfonic acids via [2 + 3] block syntheses. Our study to convert the protected
mono- and disulfonic acid derivatives into the corresponding fully O-sulfated and O-methylated
end-products via two different reaction sequences is also described.

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Figure 2. Retrosynthetic analysis for modular [2 + 3] block syntheses of the targeted pentasaccharide
sulfonic acids 6–10.
2. Results and Discussion
2.1. Synthesis of the Protected Pentasaccharides
The synthetic route to the FGH trisaccharide acceptors 20
–
22 is shown in Scheme 1. First,
the L-idose-containing diol 11
using (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) as the oxidant and [bis(acetoxy)iodo]benzene
(BAIB) as the co-oxidant [20 21]. The corresponding sulfonic acid isoster 14 17] was prepared
from 13 17] in an analogous way. Next, GH disaccharide acceptors 12 and 14 were reacted with
monosaccharide donors 15 16] and 16 18], respectively, in the presence of N-iodosuccinimide
[18] was converted to iduronide acceptor 12 by selective oxidation
,
[
[
F
[
[
(NIS) and trifluoromethanesulfonic acid (TfOH). This promoter system proved to be highly efficient
for stereoselective condensation of the phenylthio-glucoside donor 16 with either of the acceptors,
and the corresponding trisaccharides 18 and 19, with the required
obtained in 98% and 80% yields, respectively. NIS-TfOH-promoted glycosylation of 12 with the
sulfonatomethyl donor 15 also occurred with full -selectivity affording trisaccharide 17 as the only
α-interglycosidic linkage, were
α
product. However, the yield was moderate due to insufficient conversion of the acceptor. Fortunately,
by changing the promotors to NIS-AgOTf, the conversion could significantly be increased, and the
yield of 17 reached 73%. Liberation of the 4-OH group of the terminal glucose unit of the fully protected
trisaccharides 17–19 was accomplished by oxidative removal of the (2-naphthyl)methyl (NAP) group
using 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) as the reagent [22,23], furnishing the FGH
acceptors 20–22 in good to excellent yields.
To avoid inefficient glycosylations with glucuronic acid donors of inherent low reactivity, which
were observed in earlier syntheses [ 15 24], donors 23 17] and 24 13] containing a non-oxidized
precursor of the glucuronide unit were used for [2 + 3] block syntheses of the targeted pentasaccharides
(Scheme 2). Condensation reactions of the trisaccharide acceptors 20 22 with the disaccharide donors
23 and 24 were carried out upon NIS-AgOTf or NIS-TfOH activation, respectively. All reactions
9,
,
[
[
–
took place in a stereoselective way providing the protected pentasaccharides 6–10, with the required
β-linkage between units E and F, in good yields.

Molecules 2016, 21, 1497
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Scheme 1. Preparation of the FGH building blocks.
Scheme 2. Synthesis of the protected pentasaccharide derivatives.
2.2. Transformation of the Protected Pentasaccharides into the End-Products
Transformation of compounds 10 into the fully O-methylated and O-sulfated mono- and
6–
disulfonic acid end-products requires eight further synthetic steps including acetyl-, NAP- and
benzyl-deprotections, formation of the glucuronic acid unit, liberation of carboxylic and sulfonic esters
and the introduction of methyl ether and sulfate ester functions. We envisioned a reaction sequence in
which the introduction of methyl ethers precedes the oxidative formation of the glucuronide residue

Molecules 2016, 21, 1497
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E. To study the efficacy of this procedure, compound
9
was subjected to Zemplén deacetylation to
liberate the hydroxyls to be methylated (Scheme 3). Upon deacetylation with NaOMe, nucleophilic
cleavage of the sulfonic-acid ester of unit also occurred in some extent. Hence, the obtaining mixture
F
of the sulfonate ester and sodium sulfonate derivatives was unified by treating with sodium iodide in
acetone to give sulfonic acid salt 25 in an 81% yield over two steps. Introduction of the methyl ethers
to the liberated hydroxyls was accomplished by alkylation using methyl iodide and sodium hydride to
afford the desired 26 in a 67% yield. Subsequently, the 6-position of the penultimate glucose unit was
unmasked by oxidative de-O-(2-napthyl)methylation to produce 27 in 80%. TEMPO-BAIB mediated
oxidation of 27 proceeded slowly and required large amounts of the co-oxidant BAIB to eventually
produce, after 48 h, the glucuronide derivative 28, along with its partially debenzylated derivatives.
Compound 28 could not be separated from the by-products, thus, this mixture was subjected to the
remaining transformation, including basic hydrolysis of the iduronic ester, catalytic hydrogenolysis
and O-sulfation to furnish 29, a monosulfonic acid analogue of idraparinux.
Scheme 3. Transformation of 9 into final product 29, a novel sulfonic acid analogue of idraparinux.

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For conversion of
6
into the final sulfated analogue, another reaction sequence, starting with the
formation of the glucuronide residue, was used. The NAP protecting group of unit
E was cleaved
with DDQ to afford 30. Oxidation of the liberated 6-OH by TEMPO and BAIB proceeded smoothly to
provide the required glucuronic acid-containing pentasaccharide 31 in 80%. Zemplén deacetylation
followed by deprotection of the sulfonic acid esters by nucleophilic displacement with sodium iodide
gave the trisodium salt 32. Methylation of the free hydroxyl groups by using methyl iodide and sodium
hydride afforded the desired 33, which possessed all of the required methyl ethers. Deprotection of the
carboxylic-ester group of 33 by saponification gave tetrasodium salt 34, de-O-benzylation of which, by
catalytic hydrogenolysis, furnished compound 35 in a high yield. O-Sulfation of the pentaol by using
SO3 Et3N was surprisingly sluggish and the use of a high excess reagent and a prolonged reaction time
·
were needed for completion of the sulfate ester formation. Finally, the reaction gave, after treatment
with Dowex Na+ ion-exchange resin, compound 36 as a new isosteric disulfonic acid analogue of
idraparinux (Scheme 4).
The 1H-NMR, and 13C-NMR spectra of the new compounds are reported in the Supplementary data.
Scheme 4. Transformation of 6 into the corresponding pentasaccharide disulfonic acid final product.
3. Materials and Methods
3.1. General Information
Optical rotations were measured at room temperature with a Perkin-Elmer 241 automatic
polarimeter. Thin layer chromatography (TLC) was performed on Kieselgel 60 F254 (Merck) with
detection by immersing into 5% ethanolic sulfuric acid solution followed by heating. Column
chromatography was performed on Silica gel 60 (Merck 0.063–0.200 mm). Organic solutions were
dried over MgSO4, and concentrated in a vacuum. The 1H-NMR (360 and 400 MHz) and 13C-NMR
(90.54 and 100.28 MHz) spectra were recorded with Bruker DRX-360 and DRX-400 spectrometers at

Molecules 2016, 21, 1497
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◦
25 C. Chemical shifts are referenced to Me4Si or 4,4-dimethyl-4-silapentane-1-sulfonic acid (DSS)
(0.00 ppm for H) and to the solvent signals (CDCl3: 77.00 ppm for 13C). The H- and 13C-NMR
assignments have been established from 1D-NMR spectra and for compounds
1
1
6,
7,
8,
9
,
10, 20 and
21 the proton-signal assignments were supported by analysis of two-dimensional 1H–1H correlation
spectra (COSY), as well as the carbon-signal assignments by two-dimensional 13C–1H correlation
maps (HSQC). Infrared (IR) spectra were recorded on a Perkin–Elmer 16 PC FTIR (Program counter
Fourier transform infrared) spectrometer. Matrix-assisted laser desorption/ionization-time-of-flight
mass spectrometric (MALDI-TOF MS analyses of the compounds were carried out in the positive
reflectron mode using a BIFLEX III mass 13 spectrometer (Bruker, Rheinstetten, Germany) equipped
with delayed-ion extraction. The matrix solution was a saturated 2,4,6-trihydroxy-acetophenone
(THAP) solution in MeCN. Elemental analyses (C, H, S) were performed using an Elementar Vario
MicroCube instrument.
3.2. General Method A for TEMPO-BAIB Oxidation (12, 28, 31)
To a vigorously stirred solution of the appropriate alcohol (1 mmol) in CH2Cl2 (3.5 mL) and H2O
(1.5 mL), TEMPO (0.2 mmol) and BAIB (2 mmol) were added and the reaction mixture was stirred
until TLC showed complete conversion of the starting material. The reaction time was 45 min for 12
24 h for 31 and 48 h for 28. The reaction mixture was quenched by the addition of 10% aq Na2S2O3
solution (20 mL). The mixture was then extracted twice with EtOAc (10 mL), and the combined organic
layers were dried, and concentrated.
,
3.3. General Method B for Glycosylation Reaction Using NIS-TfOH Promoter System (7, 17, 18, 19)
To a solution of donor (1.5 mmol) and acceptor (1 mmol) in dry CH2Cl2 (20 mL), 4 Å molecular
sieves were added. The stirred mixture was cooled to
−
60 ◦C (17
,
18
,
19) and
−
50 ◦C (
7
) under argon.
L)
). The reaction mixture
L), diluted with CH2Cl2 (100 mL) and the reaction mixture was extracted
After 30 min at this temperature, NIS (2.25 mmol) and TfOH (0.045 mmol) dissolved in THF (155
µ
◦
◦
20 C (7
were added. The temperature was increased to
was quenched with Et3N (50
−
50 C (17
,
18,
19) or
−
µ
with saturated Na2S2O3 solution (20 mL), saturated NaHCO3 solution (20 mL) and with distilled water
(20 mL). The organic phase was dried and concentrated.
3.4. General Method C for Glycosylation Using NIS-AgOTf Promoter System 6, (8, 9, 10, 17)
To a solution of acceptor (1 mmol) and donor (1.5 mmol) in dry CH2Cl2 (20 mL), 4 Å molecular
◦
◦
35 C under argon. After
sieves were added. The stirred mixture was cooled to between
−
60 C and
−
30 min at this temperature, 2.25 mmol NIS dissolved in THF (1 mL) and 0.36 mmol AgOTf dissolved in
to◦luene (1 mL) were added. After 1–4 h stirring at
−
50 ◦C (17),
−
20 ◦C (
9),
−
15 ◦C (
6
),
−
10 ◦C (10) or
0 C (8) Et3N (50 µL) was added. The reaction mixture was diluted with CH2Cl2 (100 mL) and filtered
through a pad of Celite. The filtrate was concentrated.
3.5. General Method D for Removal of the (2-Naphthyl)methyl Ether Group (20, 21, 22, 27, 30)
To a vigorously stirred solution of starting material (1 mmol) in CH2Cl2: H2O (9:1, 10 mL) DDQ
(1.5 mmol) was added. The reaction mixture was stirred at room temperature for 30–40 min, diluted
with CH2Cl2 (30 mL), washed successively with satd aq NaHCO3 solution (15 mL) and H2O (15 mL).
The organic phase was dried and concentrated.
3.6. Product Characterization
Methyl [methyl (2-O-acetyl-3-O-methyl-
α
-L-idopyranosyl)uronate](1
→
4)-2,3,4-tri-O-benzyl-α-D-glucopyranoside
(12). The starting material 11 [18] (3.20 g, 4.7 mmol) was oxidized according to general method A.
The crude uronic acid was dissolved in THF (4.5 mL) and treated with ethereal diazomethane at 0 ◦C.
After complete disappearance of the uronic acid, the mixture was concentrated. The crude product

Molecules 2016, 21, 1497
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was purified by column chromatography to give 12 (2.47 g, 74%) as a colourless syrup; Rf = 0.36
(7:3 n-hexane/acetone); [ 2.67 (c 1.00, CHCl3); IR max (KBr): 3480, 3474, 3031, 2936, 2902, 1744,
1633, 1496, 1454, 1372, 1225, 1167, 1103, 1045, 911, 890, 854, 740, 700, 605 cm−1; 1H-NMR (360 MHz,
CDCl3) 7.37–7.20 (m, 15H, arom.), 5.08 (s, 1H), 4.98 (d, J = 11.4 Hz, 2H), 4.87 (s, 1H), 4.81 (d, J = 11.4 Hz,
1H, PhCH2), 4.67 (d, J = 12.0 Hz, 1H, PhCH2), 4.56–4.49 (m, 4H), 3.99–3.80 (m, 3H), 3.78–3.70 (m, 2H),
3.67–3.62 (m, 1H), 3.57 (dd, J = 9.4, 3.6 Hz, 1H), 3.50–3.44 (m, 1H), 3.47, 3.40, 3.34 (3s, 9H, 3 CH3),
2.68 (d, J = 11.8 Hz, 1H, OH), 2.01 (s, 3H, COCH3) ppm; 13C-NMR (91 MHz, CDCl3)
169.7, 169.2
α
]
−
ν
D
δ
×
δ
(COOCH3, COCH3), 139.0, 138.0, 138.0 (3C, Cq arom.), 128.4, 128.4, 128.2, 128.1, 127.9, 127.6, 127.6,
127.2, 127.0 (15C, arom.), 98.0, 97.6 (C-1-H, C-1-G), 80.3, 79.7, 76.8, 74.7, 70.1, 68.0, 67.2, 67.1 (C-2-G,
C-2-H, C-3-G, C-3-H, C 4 G, C-4-H, C-5-G, C-5-H), 74.8, 73.4, 73.3 (3
×
PhCH2), 68.5 (C-6-H), 58.1
(OCH3, C-3-G), 55.2 (OCH3, C-1-H), 51.9 (COOCH3), 21.00 (COCH3) ppm; MALDI-TOF MS: m/z 733.16
[M + Na]+ (Calcd. 733.28); Anal. Calcd. for C38H46O13 (710.29): C, 64.21; H, 6.52; O, 29.26. Found:
C, 64.28; H, 6.55.
Methyl [2,3-di-O-Benzyl-4-O-(2-naphthyl)methyl-6-deoxy-6-C-(ethylsulfonatomethyl)-α-D-glucopyranosyl]-
(1→4)-[methyl (2-O-acetyl-3-O-methyl-α-L-idopyranosyl)uronate]-(1→4)-(2,3,6-tri-O-benzyl-α-
D-glucopyranoside) (17)
I
. To a solution of acceptor 12 (2.80 g, 3.94 mmol) and donor 15
[
16] (3.85 g, 5.91 mmol) in dry
CH2Cl2 (20 mL), 4 Å molecular sieves (0.50 g) were added. The stirred mixture was cooled to
under argon and activated by method B. The reaction mixture was allowed to warm up to
in 1 h. The crude product was purified by column chromatography (7:3 n-hexane/EtOAc) to give 17
(2.35 g, 46%). Unreacted 12 (1.11 g, 28%) was recovered as a colourless syrup.
−
60 ◦C
50 ◦C
−
II. To a solution of acceptor 12 (1.11 g, 1.41 mmol) and donor 15 (1.37 g, 2.11 mmol) in dry CH2Cl2
(20 mL), 4 Å molecular sieves (0.50 g) were added. The stirred mixture was cooled to
argon and activated by method . The reaction mixture was allowed to warm up to
The crude product was purified by column chromatography (7:3 n-hexane/EtOAc) to give 17 (1.47 g,
73%) as a white foam; Rf = 0.34 (6:4 n-hexane/EtOAc); [ ]D +11.30 (c 0.81, CHCl3); IR (KBr): 3447,
3087, 3061, 3030, 2933, 1763, 1737, 1636, 1604, 1497, 1455, 1369, 1357, 1238, 1169, 1107, 1028, 1002, 917,
857 cm−1; 1H-NMR (360 MHz, CDCl3)
7.83–7.66 (m, 4H, arom.), 7.49–7.42 (m, 2H, arom.), 7.39–7.16
−
60 ◦C under
50 ◦C for 1 h.
C
−
α
ν
max
δ
(m, 26H, arom.), 5.13 (s, 1H), 5.03 (d, J = 11.3 Hz, 1H, ArCH2), 4.93 (m, 2H), 4.85–4.72 (m, 7H), 4.66
(t, J = 12.6 Hz, 2H), 4.60–4.54 (m, 3H), 4.12 (q, J = 7.1 Hz, 2H, SO3CH2CH3), 3.96–3.61 (m, 9H), 3.54
(dd, J = 9.4, 3.5 Hz, 1H), 3.44–3.34 (m, 1H), 3.41, 3.36, 3.34 (3s, 9H, 3
2.36–2.24 (m, 1H, H-7a), 2.00–1.83 (m, 4H, COCH3, H-7b), 1.25 (t, J = 7.1 Hz, 3H, SO3CH2CH3) ppm;
13C-NMR (91 MHz, CDCl3)
170.1, 169.4 (2 CO), 139.1, 138.4, 138.1, 138.1, 138.1, 135.6, 133.3, 133.0
(8C, Cq arom.), 128.6, 128.5, 128.4, 128.4, 128.2, 128.2, 128.0, 127.9, 127.9, 127.7, 127.6, 127.3, 127.1, 126.5,
126.2, 126.0, 125.7 (32C, arom.), 98.7, 98.0, 97.7 (3 C-1), 81.5, 81.2, 80.4, 80.2, 79.8, 76.5, 74.7, 74.7, 70.1,
69.5, 68.3, 67.7 (12C, skeleton carbons), 75.5, 75.1, 74.9, 73.6, 73.4, 73.4 (6 ArCH2), 68.5 (C-6-F), 66.2
×
OCH3), 3.24–3.05 (m, 3H),
δ
×
×
×
(SO3CH2CH3), 58.3, 55.2, 51.8 (3
×
OCH3), 46.5 (C-7-H), 25.9 (C-6-H), 21.1 (COCH3), 15.1 (SO3CH2CH3)
ppm; MALDI-TOF MS: m/z 1321.57 [M + Na]+ (Calcd. 1321.50); Anal. Calcd. for C72H82O20S (1298.51):
C, 66.55; H, 6.36; O, 24.62; S, 2.47. Found: C, 66.62; H, 6.40; S, 2.45.
Methyl [2,3,6-tri-O-benzyl-4-O-(2-naphthyl)methyl-
-L-idopyranosyl)uronate]-(1 4)-2,3-di-O-benzyl-6-deoxy-6-C-(ethylsulfonatomethyl)-
18. To a solution of acceptor (14) [17] (620 mg, 0.85 mmol) and donor 16 17] (874 mg, 1.28 mmol) in dry
CH2Cl2 (20 mL) 4 Å molecular sieves (0.50 g) were added. The stirred mixture was cooled to
60 ◦C
under argon and activated by method . The reaction mixture was allowed to warm up to
50 ◦C for
1 h. The crude product was purified by column chromatography (7:3 n-hexane/EtOAc) to give 18
(1.07 g, 98%) as a white foam; Rf = 0.63 (1:1 n-hexane/ EtOAc); [ ]D +6.62 (c 0.35, CHCl3); IR
(KBr): 3446, 3087, 3061, 3030, 2931, 2869, 1739, 1636, 1604, 1497, 1455, 1362, 1236, 1165, 1107, 1045, 1028,
1004, 917, 857, 818 cm−1; 1H-NMR (360 MHz, CDCl3)
7.85–7.67 (m, 3H, arom.), 7.55 (s, 1H, arom),
7.49–7.41 (m, 2H, arom.), 7.38–7.14 (m, 26H, arom.), 5.25 (s, 1H), 4.99–4.35 (m, 16H), 4.27 (q, J = 7.1 Hz,
α
-D-glucopyranosyl]-(1
→
4)-[methyl (2-O-acetyl-3-O-methy-
α
→
α
-D-glucopyranoside
[
−
B
−
α
ν
max
δ

Molecules 2016, 21, 1497
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2H, SO3CH2CH3), 3.97–3.63 (m, 7H), 3.62–3.24 (m, 4H), 3.47, 3.40, 3.32 (3
×
OCH3), 3.16–3.04 (m, 1H),
2.44–2.32 (m, 1H, H-7a), 2.03 (s, 3H, COCH3), 2.01–1.85 (m, 1H, H-7b), 1.37 (t, 3H, SO3CH2CH3) ppm;
13C-NMR (91 MHz, CDCl3)
170.2, 169.6 (2 CO), 139.0, 138.7, 138.3, 138.1, 138.0, 136.3, 133.3, 132.9
(8C, Cq arom.), 128.5, 128.4, 128.2, 128.1, 128.0, 127.9, 127.7, 127.2, 126.1, 125.9, 125.8, 125.6 (32C, arom.),
99.6, 98.0, 98.0 (3 C-1), 81.8, 80.3, 80.0, 79.5, 78.6, 77.0, 75.1, 71.4, 69.2, 68.4, 68.1, 57.9 (12C, skeleton
carbons), 75.5, 75.2, 74.7, 73.5, 73.5, 73.4 (6 ArCH2), 68.1 (C-6-H), 66.2 (SO3CH2CH3), 58.7, 55.6, 51.9
δ
×
×
×
(3 × OCH3), 46.7 (C-7-F), 26.0 (C-6-F), 21.1 (COCH3), 15.2 (SO3CH2CH3) ppm; MALDI-TOF MS: m/z
1321.57 [M + Na]+ (Calcd. 1321.50); Anal. Calcd. for C72H82O20S (1298.51): C, 66.55; H, 6.36; O, 24.62;
S, 2.47. Found: C, 66.50; H, 6.42; S, 2.51.
Methyl [2,3,6-tri-O-benzyl-4-O-(2-naphthyl)methyl-
α
-D-glucopyranosyl]-(1
→
4)-[methyl (2-O-acetyl-3-O-methyl-
α
-L-idopyranosyl)uronate]-(1 4)-(2,3,6-tri-O-benzyl-α
→
-D-glucopyranoside) (19). To a solution of acceptor
12 (1.50 g, 2.10 mmol) and donor 16 (2.16 g, 3.16 mmol) in◦dry CH2Cl2 (20 mL) 4 Å molecular sieves
(0.50 g) were added. The stirred mixture was cooled to
−
60 C under argon and activated by method B.
The reaction mixture was allowed to warm up to
by column chromatography (7:3 n-hexane/EtOAc) to give 18 (2.41 g, 80%) as a white foam. Rf = 0.47
(6:4 n-hexane/EtOAc).
−
50 ◦C for 30 min. The crude product was purified
Methyl [2,3-di-O-benzyl-6-deoxy-6-C-(ethylsulfonatomethyl)-
O-methyl- -L-idopyranosyl)uronate]-(1 4)-(2,3,6-tri-O-benzyl-
(2.50 g, 1.92 mmol) was converted to 20 according to general method
purified by column chromatography (7:3 n-hexane/EtOAc) to give compound 20 (1.55 g, 70%) as a
white foam; Rf = 0.40 (1:1 n-hexane/EtOAc); [ ]D +13.46 (c 0.56, CHCl3); IR (KBr): 3502, 3088,
3063, 3031, 2933, 1738, 1629, 1497, 1455, 1370, 1356, 1236, 1168, 1108, 1047, 1028, 917, 820, 740, 698,
606, 545, 466 cm−1; 1H-NMR (400 MHz, CDCl3)
7.38–7.19 (m, 25H, arom.), 5.15 (s, 1H, H-1-G), 4.93
α
-D-glucopyranosyl]-(1
-D-glucopyranoside) (20). Compound 17
. The crude product was
→
4)-[methyl (2-O-acetyl-3-
α
→
α
D
α
ν
max
δ
(d, J = 11.4 Hz, 2H, BnCH2), 4.85–4.76 (m, 4H, H-2-G, H-5-G, H-1-F, BnCH2), 4.75–4.61 (m, 4H, BnCH2),
4.55 (m, 3H, H-1-H, BnCH2), 4.24 (q, J = 7.1 Hz, 2H, SO3CH2CH3), 3.94–3.79 (m, 3H, H-3-H, H-4-G),
3.77–3.59 (m, 6H, H-3-G, H-3-F, H-5-F, H-4-H, H-6a,b-H), 3.54 (dd, J = 9.3, 3.5 Hz, 1H, H-2-H), 3.43–3.31
(m, 2H, H-2-F, H-5-H), 3.40, 3.37, 3.34 (3s, 3
2.33–2.21 (m, 1H, H-6a-F), 1.93 (s, 3H, COCH3), 1.98–1.84 (m, 1H, H-6b-F), 1.35 (t, J = 7.1 Hz, 3H,
SO3CH2CH3) ppm; 13C-NMR (101 MHz, CDCl3)
170.0, 169.3 (2 CO), 139.1, 138.5, 138.1, 138.0,
×
CH3) 3.28–3.09 (m, 3H, H-4-F, H-7a,b), 2.48 (s, 1H, OH),
δ
×
137.9 (5C, Cq arom.), 128.6, 128.5, 128.4, 128.3, 128.1, 128.1, 128.0, 127.9, 127.8, 127.8, 127.7, 127.5, 127.3,
127.1 (25C, arom.), 98.5 (C-1-F), 98.0 (C-1-H), 97.7 (C-1-G), 80.6 (C-3-F), 80.1 (C-2-H), 79.9 (C-2-F), 79.8
(C-3-H), 79.8 (C-4-G), 76.5 (C-5-F), 74.8 (C-2-G), 74.4 (C-4-F), 75.0, 74.9, 73.4, 73.3, 73.2 (5
×
PhCH2),
70.1 (C-4-H), 69.8 (C-5-H), 68.5 (C-3-F), 68.4 (C-6-H), 68.0 (C-5-G), 66.2 (SO3CH2CH3), 58.4, 55.2, 51.7
(3 × OCH3), 46.3 (C-7-F), 25.8 (C-6-F), 21.0 (COCH3), 15.1 (SO3CH2CH3) ppm; MALDI-TOF MS: m/z
1181.59 [M + Na]+ (Calcd. 1181.44); Anal. Calcd. for C61H74O20S (1158.45): C, 63.20; H, 6.43; O, 27.60;
S, 2.77. Found: C, 63.25; H, 6.37; S, 2.72.
Methyl [2,3,6-tri-O-benzyl-
(1 4)-2,3-di-O-benzyl-6-deoxy-6-C-(ethylsulfonatomethyl)-
0.83 mmol) was converted to 21 according to general method
column chromatography (65:35 n-hexane/acetone) to give compound 21 (807 mg, 85%) as a white
foam; Rf = 0.38 (65:35 n-hexane/acetone); [ ]D +14.44 (c 0.04, CHCl3); IR (KBr): 3481, 3063,
3031, 2929, 1740, 1626, 1497, 1455, 1370, 1234, 1167, 1105, 1046, 1028, 926, 820, 739, 698, 606, 548, 460,
418 cm−1; 1H-NMR (400 MHz, CDCl3)
7.30–7.08 (m, 25H, arom.), 5.17 (d, J = 3.3 Hz, 1H, H-1-G),
α
-D-glucopyranosyl]-(1
→
4)-[methyl(2-O-acetyl-3-O-methyl-
-D-glucopyranoside (21). Compound 18 (1.06 g,
. The crude product was purified by
α-L-idopyranosyl)uronate]-
→
α
D
α
ν
max
δ
4.86–4.65 (m, 3H, H-1-F, H-2-G, H-5-G, BnCH2), 4.59 (m, 3H, BnCH2), 4.50–4.34 (m, 4H, H-1-H, BnCH2),
4.18 (q, J = 7.1 Hz, 2H, SO3CH2CH3), 3.85–3.14 (m, 13H, skeleton protons), 3.36, 3.29, 3.23 (3s, 9H,
OCH3), 3.05–2.95 (m, 1H, H-7b-H), 2.46 (s, 1H, OH), 2.34–2.24 (m, 1H, H-6a-H), 1.93 (s, 3H, COCH3),
1.89–1.76 (m, 1H, H-6b-H), 1.28 (t, J = 7.1 Hz, 3H, SO3CH2CH3) ppm; 13C-NMR (101 MHz, CDCl3)
δ
170.2, 169.6 (2
×
CO), 139.0, 138.8, 138.2, 138.1, 138.0 (5C, Cq arom.), 128.6, 128.5, 128.4, 128.2, 128.0,
127.9, 127.8, 127.8, 127.3 (25C, arom.), 99.5 (C-1-F), 98.1 (C-1-H), 98.0 (C-1-G), 81.1, 80.2, 79.5, 79.5, 78.9,

Molecules 2016, 21, 1497
10 of 19
77.0, 75.0, 71.2, 70.9, 69.8 (12C, skeleton carbons), 75.3, 75.1,73.7, 73.6, 73.3 (5
×
PhCH2), 69.3 (C-6-F),
69.0, 68.2, 66.3 (SO3CH2CH3), 58.9, 55.6, 51.9 (3
×
OCH3), 46.8 (C-7-H), 25.9 (C-6-H), 21.1 (COCH3),
15.2 (SO3CH2CH3) ppm; MALDI-TOF MS: m/z 1181.64 [M + Na]+ (Calcd. 1181.44); Anal. Calcd. for
C61H74O20S (1158.45): C, 63.20; H, 6.43; O, 27.60; S, 2.77. Found: C, 63.34; H, 6.47; S, 2.79.
Methyl [2,3,6-tri-O-benzyl-
(1 4)-(2,3,6-tri-O-benzyl-
to 22 according to general method
n-hexane/EtOAc) to give compound 22 (1.26 g, 59%) as a white foam; Rf = 0.33 (6:4 n-hexane/EtOAc);
α
-D-glucopyranosyl]-(1
-D-glucopyranoside) (22) [15]. Compound 19 (2.4 g, 1.87 mmol) was converted
. The crude product was purified by column chromatography (7:3
→
4)-[methyl-(2-O-acetyl-3-O-methyl-α-L-idopyranosyl)uronate]-
→
α
D
[
α
]D +8.41 (c 0.62, CHCl3) (lit. [15] [
α
]D +2.3 (c 0.10, CHCl3); IR
ν
(KBr): 3087, 3062, 3031, 2932, 2906,
max
1739, 1605, 1497, 1455, 1371, 1237, 1104, 1046, 1028, 908, 738, 697, 606, 538, 459, 419 cm−1. The NMR
spectroscopic and analytical data of 22 are consistent with those given in the literature [15].
Methyl [2,3,4-tri-O-methyl-6-deoxy-6-C-(ethylsulfonatomethyl)-
O-(2-naphthyl)methyl- -D-glucopyranosyl]-(1 4)-[2,3-di-O-benzyl-6-deoxy-6-C-(ethylsulfonatomethyl)-
D-glucopyranosyl]-(1 4)-[methyl (2-O-acetyl-3-O-methyl- -L-idopyranosyl)uronate]-(1 4)-2,3,6-tri-O-
benzyl- -D-gluco-pyranoside ( ). To a solution of acceptor 20 (630 mg, 0.54 mmol) and donor 23
(660 mg, 0.82 mmol) in dry CH2Cl2 (20 mL), 4 Å molecular sieves (0.50 g) were added. The stirred
α
-D-glucoopiranosyl]-(1
→
4)-[2,3-di-O-acetyl-6-
β
→
α-
→
α
→
α
6
mixture was cooled to
allowed to warm up to
(6:4 n-hexane/EtOAc) to give
−
40 ◦C under argon and activated by method
15 ◦C for 4 h. The crude product was purified by column chromatography
(626 mg, 62%) as a colourless syrup; Rf = 0.26 (1:1 n-hexane/EtOAc);
]D +23.69 (c 0.14, CHCl3); 1H-NMR (400 MHz, CDCl3)
7.84–7.75 (m, 3H, arom.), 7.65 (s, 1H, arom.),
7.48–7.40 (m, 2H, arom.), 7.37–7.13 (m, 26H, arom.), 5.18 (t, J = 9.2 Hz, 1H, H-3-E), 5.11 (s, 1H, H-1-G),
4.99–4.46 (m, 19H, H-1-D, H-2-E, H-5-G, H-2-G, H-1-E, H-1-H, H-1-F, 12 ArCH2), 4.27, 4.07 (2q,
C. The reaction mixture was
−
6
[
α
δ
×
4H, SO3CH2CH3), 3.93–3.77 (m, 5H, H-4-H, H-4-E, H-3-F, H-4-G, H-3-H), 3.76–3.59 (m, 5H, H-5-H,
H-5-F, H-6a,b-H, H-3-G), 3.58–3.17 (m, 9H, H-2-F, H-6a,b-E, H-5-D, H-4-F, H-2-H, H-3-D, H-5-E, H-7a-F),
3.52, 3.48, 3.40, 3.36, 3.33, 3.31 (6s, 18H, 6
(m, 2H, H-2-D, H-7b-D), 2.65 (t, J = 9.2 Hz, 1H, H-4-D), 2.33–2.21 (m, 1H, H-6a-F), 2.21–2.08 (m, 1H,
H-6a-D), 2.05, 1.99, 1.94 (3s, 9H, 3 COCH3), 1.86–1.71 (m, 2H, H-6b-D, H-6b-F), 1.38, (t, J = 7.1 Hz, 3H,
SO3CH2CH3), 1.25 (t, J = 6.8 Hz, 3H, SO3CH2CH3) ppm; 13C-NMR (101 MHz, CDCl3)
170.1, 169.8,
169.8, 169.3 (4 CO), 139.1, 138.9, 138.0, 137.9, 137.7, 135.3, 133.2, 132.9 (8C, Cq arom.), 128.4, 128.3,
×
OCH3), 3.18–3.03 (m, 2H, H-7b-F, H-7a-D), 2.93–2.81
×
δ
×
128.2, 128.1, 128.0, 128.0, 127.9, 127.8, 127.8, 127.6, 127.5, 127.1, 127.0, 126.4, 126.1, 125.8, 125.6 (32C,
arom.), 101.1 (C-1-H), 98.0 (C-1-E), 97.8 (C-1-F), 97.4 (C-1-G), 96.8 (C-1-D), 83.2 (C-4-D), 82.3 (C-3-D),
82.1 (C-4-F), 81.9 (C-2-D), 80.0 (C-2-F), 79.7 (C-2-H), 79.6 (C-4-G), 79.4 (C-3-F), 76.0 (C-3-G), 75.1 (C-5-E),
74.7, 74.3, 73.6, 73.4, 73.2, 73.2, (6 × ArCH2), 74.5 (C-3-E), 74.5 (C-4-H), 74.4 (C-4-E), 74.0 (C-3-H), 72.5
(C-2-E), 70.0 (C-5-H), 69.2 (C-5-D), 68.9 (C-5-F), 68.3 (C-6-H), 68.2 (C-5-G), 67.7 (C-6-E), 67.3 (C-2-G),
66.2, 65.8 (2
×
SO3CH2CH3), 60.5, 60.5, 58.9, 58.1, 55.1, 51.7 (6
×
OCH3), 46.6 (C-7-D), 46.4 (C-7-F), 26.0
(C-6-D), 25.7 (C-6-F), 21.0, 20.8, 20.5 (3
m/z 1877.77 [M + Na]+ (Calcd. 1877.68); Anal. Calcd. for C94H118O34S2 (1854.69): C, 60.83; H, 6.41; O,
×
COCH3), 15.0, 15.0 (2
×
SO3CH2CH3) ppm; MALDI-TOF MS:
29.31; S, 3.46. Found: C, 60.69; H, 6.35; S, 3.41.
Methyl [2,3,4-tri-O-methyl-6-deoxy-6-C-(ethylsulfonatomethyl)-
O-(2-naphthyl)methyl- -D-glucopyranosyl]-(1 4)-[2,3,6-tri-O-benzyl-
(2-O-acetyl-3-O-methyl- -L-idopyranosyl)uronate]-(1 4)-2,3-di-O-benzyl-6-deoxy-6-C-(ethylsulfonatomethyl)-
-D-glucopyranoside ( ). To a solution of acceptor 21 (720 mg, 0.62 mmol) and donor 23 (752 mg,
0.93 mmol) in dry CH2Cl2 (20 mL) 4 Å molecular sieves (0.50 g) were added. The stirred mixture
α
-D-glucopyranosyl]-(1
→
4)-[2,3-di-O-acetyl-6-
β
→
α
-D-glucopyranosyl]-(1
→
4)-[methyl
α
→
α
7
was cooled to
to warm up to
n-hexane/EtOAc) to give
+32.21 (c 0.14, CHCl3); H-NMR (400 MHz, CDCl3)
−
50 ◦C under argon and activated by method
20 ◦C for 3 h. The crude product was purified by column chromatography (65:35
B. The reaction mixture was allowed
−
7
(726 mg, 63%) as a colourless syrup; Rf = 0.21 (1:1 n-hexane/EtOAc); [
α]
D
1
δ
7.83–7.71 (m, 3H, arom.), 7.62 (s, 1H, arom.),
7.44 (m, 2H, arom.), 7.41–7.12 (m, 26H, arom.), 5.21 (d, J = 2.3 Hz, 1H, H-1-G), 5.10–4.99 (m, 1H,
H-3-E, ArCH2), 4.96–4.76 (m, 6H, H-1-D, H-2-G, H-2-E, H-1-F, 2 ArCH2), 4.75–4.63 (m, 5H, H-5-G,
×

Molecules 2016, 21, 1497
11 of 19
4
×
ArCH2), 4.60–4.38 (m, 7H, H-1-E, H-1-H, 5
×
ArCH2), 4.29 (q, J = 7.1 Hz, 2H, SO3CH2CH3), 4.06
(q, J = 7.1 Hz, 2H, SO3CH2CH3), 3.95 (t, J = 9.4 Hz, 1H, H-4-H), 3.91–3.67 (m, 8H, H-4-G, H-4-E, H-6a-E,
H-5-H, H-3-H, H-3-F, H-6a-F, H-5-F), 3.67–3.25 (m, 9H, H-3-G, H-6b-F, H-6b-E, H-4-F, H-5-D, H-2-H,
H-2-F, H-3-D, H-7-H), 3.57, 3.53, 3.43, 3.41, 3.33 (5s, 15H, 5
H-7a-H), 2.97–2.87 (m, 2H, H-2-D, H-7b-D), 2.69 (t, J = 9.2 Hz, 1H, H-4-D), 2.44–2.30 (m, 1H, H-6a-H),
2.30–2.14 (m, 1H, H-6a-D), 2.02, 1.96, 1.95 (3s, 9H, 3 COCH3), 2.06–1.74 (m, 2H, H-6b-D, H-6b-H),
1.40 (t, J = 7.1 Hz, 3H, SO3CH2CH3), 1.23 (t, J = 7.4 Hz, 3H, SO3CH2CH3) ppm. 13C-NMR (101 MHz,
CDCl3) 170.3, 170.0, 169.7, 169.6 (4 CO), 139.4, 139.0, 138.3, 138.1, 137.6, 135.8, 133.4, 133.0 (8C,
×
OCH3), 3.23–3.04 (m, 3H, H-5-E, H-7a-D,
×
δ
×
Cq arom.), 128.8, 128.6, 128.5, 128.4, 128.4, 128.2, 128.2, 128.1, 128.0, 127.9, 127.8, 127.6, 127.3, 126.4,
126.1, 125.9, 125.8 (32C, arom.), 99.8 (C-1-E), 99.6 (C-1-F), 98.0 (C-1-H), 97.8 (C-1-G), 96.9 (C-1-D), 83.5
(C-4-D), 82.7 (C-3-D), 82.2 (C-2-D), 80.3 (C-4-F), 79.7 (C-3-H), 79.4 (C-3-F), 79.3 (C-2-F), 78.6 (C-2-H),
76.7 (C-4-H), 76.5 (C-3-G), 75.3 (C-5-E), 74.9 (C-4-G), 74.9 (C-3-E), 74.9 (C-4-E), 72.5 (C-2-E), 71.1 (C-5-F),
69.5 (C-5-D), 69.3 (C-5-G), 68.2 (C-5-H), 68.2 (C-2-G), 75.3, 75.1, 73.9, 73.7, 73.6, 73.6 (6
(C-6-E), 67.4 (C-6-F), 66.3, 66.1 (2 SO3CH2CH3), 60.8, 60.8, 59.2, 58.8, 55.6, 52.0 (6 OCH3), 46.8, 46.8
SO3CH2CH3)
×
ArCH2), 68.1
×
×
(C-7-D, C-7-H), 26.2 (C-6-D), 26.0 (C-6-H), 21.1, 21.0, 20.8 (3
×
COCH3), 15.2, 15.1 (2
×
ppm; MALDI-TOF MS: m/z 1877.77 [M + Na]+ (Calcd. 1877.68); Anal. Calcd. for C94H118O34S2
(1854.69): C, 60.83; H, 6.41; O, 29.31; S, 3.46. Found: C, 60.90; H, 6.44; S, 3.51.
Methyl [2,3,4-tri-O-methyl-6-deoxy-6-C-(ethylsulfonatomethyl)-
6-O-6-O-(2-naphthyl)methyl- -D-glucopyranosyl]-(1 4)-[2,3,6-tri-O-benzyl-
[methyl-(2-O-acetyl-3-O-methyl- -L-idopyranosyl)uronate]-(1 4)-(2,3,6-tri-O-benzyl-α
α
-D-glucopyranosyl]-(1
-D-glucopyranosyl]-(1
-D-glucopyranoside)
→
4)-[2,3-di-O-acetyl-
β
→
α
→
4)-
α
→
(
8
). To a solution of acceptor 22 (1.18 g, 1.03 mmol) and donor 23 (1.25 g, 1.55 mmol)◦in dry CH2Cl2
(40 mL), 4 Å molecular sieves (1 g) were added. The stirred mixture was cooled to
−
50 C under argon
and activated by method
product was purified by column chromatography (6:4 n-hexane/EtOAc) to give
colourless syrup; Rf = 0.51 (94:6 CH2Cl2/acetone); [
]D +24.44 (c 0.05, CHCl3); 1H-NMR (400 MHz,
CDCl3) 7.86–7.71 (m, 3H, arom.), 7.62 (s, 1H, arom.), 7.44 (m, 2H, arom.), 7.40–7.11 (m, 31H, arom.),
5.15 (d, J = 2.7 Hz, 1H, H-1-G), 5.05 (m, 2H, H-3-E, ArCH2), 4.95–4.75 (m, 7H, H-1-D, H-2-E, H-1-F,
H-2-G, 3 ArCH2), 4.74–4.65 (m, 5H, H-5-G, 4 ArCH2), 4.62–4.46 (m, 6H, H-1-H, 5 ArCH2),
C
. The reaction mixture was allowed to warm up to 0 ◦C for 4 h. The crude
(1.29 g, 68%) as a
8
α
δ
×
×
×
4.45–4.40 (m, 2H, H-1-E, ArCH2), 4.05 (q, J = 7.1 Hz, 2H, SO3CH2CH3), 3.95 (t, J = 9.4 Hz, 1H, H-4-F),
3.91–3.45 (m, 16H, H-4-G, H-4-H, H-4-E, H-3-H, H-5-F, H-6a,b-H, H-3-F, H-5-H, H-3-G, H-6a,b-E,
H-6a,b-F, H-5-D, H-2-H), 3.57, 3.53, 3.41, 3.35, 3.34, 3.32 (6s, 18H, 6
H-3-D, H-5-E, H-7a-D), 2.97–2.85 (m, 2H, H-2-D, H-7b-D), 2.69 (t, J = 9.2 Hz, 1H, H-4-D), 2.26–2.15 (m,
1H, H-6a-D), 2.01, 1.91, 1.89 (3s, 9H, 3 COCH3), 1.87–1.75 (m, 1H, H-6b-D), 1.23 (t, J = 7.1 Hz, 3H,
SO3CH2CH3) ppm; 13C-NMR (91 MHz, CDCl3)
170.2, 170.0, 169.7, 169.6 (4 CO), 139.5, 139.2, 138.3,
×
OCH3), 3.44–3.27 (m, 4H, H-2-F,
×
δ
×
138.3, 138.1, 137.7, 135.8, 133.4, 133.0 (9C, Cq arom.), 128.8, 128.5, 128.4, 128.2, 128.2, 128.0, 127.9, 127.8,
127.8, 127.6, 127.5, 127.3, 127.1, 126.4, 126.1, 125.9, 125.8 (37C, arom.), 99.8 (C-1-E), 99.7 (C-1-F), 98.1
(C-1-H), 97.8 (C-1-G), 96.9 (C-1-D), 83.6 (C-4-D), 82.7 (C-3-D), 82.2 (C-2-D), 80.1 (C-2-H), 79.9 (C-3-H),
79.8 (C-3-F), 79.3 (C-2-F), 76.8 (C-3-G), 76.5 (C-4-F), 75.3 (C-5-E), 75.1 (C-3-E), 75.1 (C-4-E), 74.9 (C-4-G),
74.9 (C-4-H), 75.1, 75.1, 75.1, 73.8, 73.6, 73.5, 73.5 (7
69.5 (C-5-D), 69.2 (C-5-G), 68.5 (C-2-G), 68.3 (C-6-F), 68.3 (C-6-E), 67.4 (C-6-H), 66.0 (SO3CH2CH3),
×
ArCH2), 72.5 (C-2-E), 71.0 (C-5-F), 70.2 (C-5-H),
60.8, 60.8, 59.2, 58.8, 55.3, 51.8 (6
×
OCH3), 46.8 (C-7-D), 26.2 (C-6-D), 21.1, 21.1, 20.8 (3
×
COCH3),
15.1 (SO3CH2CH3) ppm; MALDI-TOF MS: m/z 1862.75 [M + Na]+ (Calcd. 1863.02); Anal. Calcd. for
C98H118O32S (1840.03): C, 63.97; H, 6.46; O, 27.82; S, 1.74. Found: C, 64.03; H, 6.49; S, 1.68.
Methyl-[6-O-benzyl-2,3,4-tri-O-methyl-
-D-glucopyranosyl]-(1 4)-[2,3-di-O-benzyl-6-deoxy-6-C-(ethylsulfonatomethyl)-
[methyl-(2-O-acetyl-3-O-methyl- -L-idopyranosyl)uronate]-(1 4)-(2,3,6-tri-O-benzyl-
). To a solution of acceptor 20 (1.20 g, 1.04 mmol) and donor 24 (1.23 g, 1.55 mmol) in dry CH2Cl2
α
-D-glucopyranosyl]-(1
→
4)-[2,3-di-O-acetyl-6-O-(2-naphthyl)methyl-
-D-glucopyranosyl]-(1 4)-
-D-glucopyranoside)
β
→
α
→
α
→
α
(
9
◦
(40 mL), 4 Å molecular sieves (1 g) were added. The stirred mixture was cooled to
argon and activated by method . The reaction mixture was allowed to warm up to
−
35 C under
C
−
20 ◦C for 4 h.

Molecules 2016, 21, 1497
12 of 19
The crude product was purified twice by column chromatography (
I. 6:4 n-hexane/EtOAc II. 96:4
CH2Cl2/EtOAc) to give
(c 0.06, CHCl3); 1H-NMR (400 MHz, CDCl3)
(m, 2H, arom.), 7.38–7.11 (m, 31H, arom), 5.22 (t, J = 9.3 Hz, 1H, H-3-E), 5.12–5.03 (m, 2H, H-1-G,
H-1-D), 4.95 (t, J = 12.3 Hz, 2H, 2 ArCH2), 4.89–4.48 (m, 15H, H-2-E, H-5-G, H-2-G, H-1-E, H-1-F,
H-1-H, 9 ArCH2), 4.40 (d, J = 10.9 Hz, 2H, 2 ArCH2), 4.26 (m, 3H, SO3CH2CH3, ArCH2), 3.98–3.43
(m, 14H, H-4-E, H-4-H, H-4-G, H-3-F, H-3-H, H-5-F, H-5-H, H-6a,b-H, H-3-G, H-6a,b-E, H-2-H, H-5-D),
3.55, 3.39, 3.39, 3.38, 3.34, 3.30 (6s, 18H, 6 OCH3) 3.43–2.99 (m, 9H, H-6a,b-D, H-4-F, H-5-E, H-2-F,
H-3-D, H-7a,b-F, H-4-D, H-2-D), 2.31–2.20 (m, 1H, H-6a-F), 2.04, 1.99, 1.93 (3s, 9H, 3 OCH3), 1.85–1.70
(m, 1H, H-6b-F), 1.39 (t, J = 7.1 Hz, 3H, SO3CH2CH3) ppm; 13C-NMR (91 MHz, CDCl3)
170.3, 170.0,
169.9, 169.5 (4 CO), 139.2, 139.1, 138.2, 138.1, 138.1, 137.9, 136.0, 133.3, 133.0 (9C, Cq arom.), 128.5,
9
(1.20 g, 63%) as colourless; Rf = 0.33 (1:1 n-hexane/EtOAc); [
α]D +26.28
δ
7.84–7.71 (m, 3H, arom.), 7.63 (s, 1H, arom.), 7.50–7.41
×
×
×
×
×
δ
×
128.5, 128.4, 128.4, 128.3, 128.2, 128.1, 128.0, 127.8, 127.7, 127.3, 127.2, 126.7, 126.2, 126.1, 125.9, 125.6
(37C, arom.), 101.1 (C-1-E), 98.3 (C-1-F), 98.1 (C-2-H), 97.9 (C-1-D), 97.6 (C-1-G), 83.2 (C-3-D), 82.1
(C-4-F), 81.8 (C-2-D), 80.2 (C-2-H), 79.9 (C-3-H), 79.8 (C-2-F), 79.5 (C-3-F), 79.3 (C-4-D), 76.1 (C-3-G),
75.1 (C-5-E), 75.0 (C-3-E), 74.8 (C-4-H), 74.5 (C-4-E), 74.2 (C-4-G), 74.9, 74.6, 73.8, 73.5, 73.4, 73.4, 73.4
(7
×
ArCH2), 72.9 (C-2-E), 71.2 (C-5-D), 70.2 (C-5-F), 69.1 (C-5-H), 68.6 (C-6-E), 68.5 (C-6-H), 68.4
OCH3), 46.6
COCH3), 15.2 (SO3CH2CH3) ppm; MALDI-TOF MS: m/z
(C-5-G), 68.3 (C-6-D), 67.4 (C-2-G), 66.3 (SO3CH2CH3), 60.7, 60.4, 59.4, 58.2, 55.3, 51.9 (6
×
(C-7-F), 25.9 (C-6-F), 21.2, 21.0, 20.7 (3
1862.74 [M + Na]+ (Calcd. 1863.02); Anal. Calcd. for C98H118O32S (1840.03): C, 63.97; H, 6.46; O, 27.82;
S, 1.74. Found: C, 63.95; H, 6.51; S, 1.78.
×
Methyl [6-O-benzyl-2,3,4-tri-O-methyl-
α
-D-glucopyranosyl]-(1
4)-[2,3,6-tri-O-benzyl- -D-glucopyranosyl]-(1
-L-idopyranosyl)uronate]-(1 4)-2,3-di-O-benzyl-6-deoxy-6-C-(ethylsulfonatomethyl)-
→
4)-[2,3-di-O-acetyl-6-O-(2-naphthyl)methyl-
4)-[methyl-(2-O-acetyl-3-O-methyl-
-D-glucopyranoside
β
-D-glucopyranosyl]-(1
→
α
→
α
→
α
(
10). To a solution of acceptor 21. (720 mg, 0.62 mmol) and donor 24 (737 mg, 0.93 mmol) in dry
CH2Cl2 (20 mL), 4 Å molecular sieves (0.50 g) were added. The stirred mixture was cooled to
−
40 ◦C
◦
10 C for
under argon and activated by method
90 min. The crude product was purified twice by column chromatography (
6:4 n-hexane/EtOAc) to give 10 (825 mg, 72%) as a colourless syrup; Rf = 0.31 (1:1 n-hexane/EtOAc);
]D +35.45 (c 0.05, CHCl3); 1H-NMR (400 MHz, CDCl3)
7.82–7.69 (m, 3H, arom.), 7.62 (s, 1H, arom.),
7.48–7.09 (m, 30H, arom.), 5.21 (d, J = 5.0 Hz, 1H, H-1-G), 5.12–5.03 (m, 3H, H-3-E, H-1-D, ArCH2),
4.92–4.76 (m, 5H, H-2-E, H-1-F, H-2-G, 2 ArCH2), 4.75–4.61 (m, 5H, H-5-G, 4 ArCH2), 4.59–4.51
(m, 3H, 3 ArCH2), 4.49–4.37 (m, 5H, H-1-E, H-1-H, 3 ArCH2), 4.34–4.25 (m, 3H, SO3CH2CH3,
C
. The reaction mixture was allowed to warm up to
−
I. 9:1 CH2Cl2/EtOAc II
.
[
α
δ
×
×
×
×
ArCH2), 4.01–3.84 (m, 3H, H-4-H, H-4-E, H-4-G), 3.83–3.67 (m, 7H, H-3-H, H-5-F, H-6a-F, H-6a,b-E,
H-5-H, H-3-F), 3.66–3.52 (m, 3H, H-3-G, H-5-D, H-6b-F), 3.50–3.26 (m, 7H, H-6a,b-D, H-2-H, H-4-F,
H-3-D, H-2-F, H-7a-H), 3.59, 3.44, 3.42, 3.41, 3.33, 3.32 (6s, 18H, 6
H-4-D, H-7a-H, H-2-D), 2.42–2.32 (m, 1H, H-6a-H), 2.01, 1.96, 1.94 (3s, 9H, 3
1H, H-7b-H) 1.39 (t, J = 12.7 Hz, 3H, SO3CH2CH3) ppm; 13C-NMR (101 MHz, CDCl3)
169.7, 169.6 (4 CO), 139.4, 139.0, 138.4, 138.1, 138.1, 137.7, 136.2, 133.4, 133.0 (9C, Cq arom.), 128.8,
×
OCH3), 3.26–3.02 (m, 4H, H-5-E,
COCH3),1.98–1.93 (m,
170.3, 170.0,
×
δ
×
128.6, 128.4, 128.4, 128.3, 128.2, 128.1, 128.0, 127.8, 127.7, 127.6, 127.3, 127.2, 126.0, 125.9, 125.7 (37C,
arom.), 99.8 (C-1-E), 99.6 (C-1-F), 98.0 (C-1-H), 97.9 (C-1-G), 97.9 (C-1-D), 83.3 (C-3-D), 81.9 (C-2-D),
80.3 (C-4-F), 79.8 (C-5-H), 79.8 (C-3-F), 79.4 (C-4-D), 79.4 (C-3-H), 79.2 (C-2-F), 78.6 (C-2-H), 76.7
(C-3-G), 76.5 (C-4-H), 75.1 (C-4-G), 75.1 (C-4-E), 75.1 (C-5-E) 74.9 (C-3-E), 75.3, 75.1, 73.9, 73.7, 73.6, 73.4,
73.4 (7
(C-2-G), 67.4 (C-6-F), 66.2 (SO3CH2CH3), 60.8, 60.5, 59.3, 58.8, 55.6, 51.9 (6
(C-6-H), 21.1, 21.0, 20.8 (3
COCH3), 15.2 (SO3CH2CH3) ppm; ESI-MS: m/z 1862.75 [M + Na]+ (Calcd.
×
ArCH2), 72.7 (C-2-E), 71.4 (C-5-D), 71.1 (C-5-F), 69.3 (C-5-G), 68.9(C-6-E), 68.6 (C-6-D), 68.2
×
OCH3), 46.8 (C-7-H), 26.1
×
1863.02); Anal. Calcd. for C98H118O32S (1838,73): C, 63.97; H, 6.46; O, 27.82; S, 1.74. Found: C, 64.07;
H, 6.53; S, 1.82.
Methyl
glucopyranosyl]-(1
[6-O-benzyl-2,3,4-tri-O-methyl-
α
-D-glucopyranosyl]-(1
→
4)-[6-O-(2-naphthyl)-methyl-
-D-glucopyranosyl)]-(1
β
-D-
4)-
→
4)-[sodium (2,3-di-O-benzyl-6-deoxy-6-C-sulfonato-methyl-
α
→

Molecules 2016, 21, 1497
13 of 19
[methyl (3-O-methyl-
NaOMe (36 mg) was added to the solution of compound
α
-L-idopyranosyl)uronate]-(1
→
4)-(2,3,6-tri-O-benzyl-
α
-D-glucopyranoside)
(25).
9
(1.22, 0.66 mmol) in MeOH (35 mL) at
room temperature and stirred for 24 h. The reaction mixture was quenched by the addition of acetic
acid (1–2 drops) and the solution was concentrated. Then, NaI (149 mg, 0.99 mmol) was added to the
solution of crude product in acetone (40 mL) and the mixture was stirred at room temperature for
24 h. The mixture was concentrated and purified by gel chromatography (Sephadex LH-20, MeOH)
to give 25 (919 mg, 81% for two steps) as a colourless syrup; Rf = 0.28 (95:5 CH2Cl2/MeOH); [
+33.7 (c 0.11, CHCl3); 1H-NMR (CDCl3, 400 MHz):
(ppm) 7.79–7.07 (m, 37H, arom.), 5.34–4.21 (m,
19H, 7 ArCH2, 5 H-1), 3.98–2.87 (m, 49H, 20 skeleton protons, 6 OCH3, 3 H-6a,b, H-7a,b
OH), 2.43–2.38 (m, 1H, H-6a-F), 2.13–2.03 (m, 1H, H-6b-F); 13C-NMR (CDCl3, 100 MHz):
(ppm)
171.3 (CO), 140.7, 140.1, 139.4, 139.3, 138.9, 137.4, 134.6, 134.3 (9 Cq arom.), 129.4–126.8 (37C, arom.),
104.3, 102.2, 99.5, 98.9, 96.0 (5 C-1), 84.6, 83.5, 81.7, 81.3, 81.2, 80.7, 80.3, 79.7, 78.0, 76.3, 75.9, 75.6,
72.6, 72.3, 71.6, 70.8, 69.2, 67.9 (20C, skeleton carbons), 75.7, 74.9, 74.4, 74.2, 73.9 (7 ArCH2), 69.8
α]
D
δ
×
×
×
×
×
,
3
×
δ
×
×
×
(3
×
C-6) 60.9, 60.8, 59.8, 58.5 (4
MALDI-TOF MS: m/z 1729.72 [M + Na]+ (Calcd. 1729.64). Anal. Calcd. for C90H107NaO29S (1707.85):
×
OCH3), 55.5 (C-1-OCH3), 52.9 (COOCH3), 48.2 (C-7-F), 27.6 (C-6-F);
C, 63.29; H, 6.31; S, 1.88. Found: C, 63.37; H, 6.40; S, 1.97.
Methyl [6-O-benzyl-2,3,4-tri-O-methyl-
-D-glucopyranosyl]-(1 4)-[sodium (2,3-di-O-benzyl-6-deoxy-6-C-sulfonatomethyl-
(1 4)-[methyl (2,3-di-O-methyl- -L-idopyranosyl)uronate]-(1 4)-(2,3,6-tri-O-benzyl-α
α
-D-glucopyranosyl]-(1
→
4)-[2,3-di-O-methyl-6-O-(2-naphthyl)methyl-
-D-glucopyranosyl)]-
-D-glucopyranoside)
β
→
α
→
α
→
(
26). An amount of 60 m/m% NaH (68 mg, 1.68 mmol) was added to the soluti◦on of compound 25
(798 mg, 0.467 mmol) in dry N,N-dimethylmethanamide (DMF) (15 mL) at 0 C. After 30 min of
stirring at room temperature, MeI (105 µL, 1.68 mmol) was added to the reaction mixture and it was
stirred for 4 h. The reaction mixture was quenched by the addition of MeOH (4–5 drops). The solution
was concentrated and the crude product was purified by gel chromatography (Sephadex LH-20 in
MeOH) to give 26 (550 mg, 67%) as a colourless syrup; Rf = 0.58 (9:1 CH2Cl2/MeOH); [
(c 0.26, CHCl3); 1H-NMR (CDCl3, 400 MHz):
(ppm) 7.79–7.12 (m, 37H, arom.), 5.58 (d, J = 3.6 Hz,
1H), 5.21 (d, J = 5.6 Hz, 1H), 5.00–4.33 (m, 17H), 3.86–2.98 (m, 55H, 20 skeleton protons, 9 OCH3,
H6a,b, H-7a,b), 2.48–2.39 (m, 1H, H-6a-F), 2.02–2.01 (m, 1H, H-6b-F); 13C-NMR (CDCl3, 100 MHz):
(ppm) 169.8 (CO), 139.3, 138.9, 138.3, 138.2, 138.1, 138.0, 136.1, 133.2, 132.8 (9 Cq arom.), 128.3–125.6
(37C, arom.), 103.0, 100.1, 99.7, 98.0, 96.0 (5 C-1), 86.3, 84.8, 83.3, 81.6, 80.7, 80.2, 79.8, 79.6, 79.5, 79.1,
78.3, 76.4, 74.3, 74.2, 72.0, 71.5, 70.7, 70.2, 69.9, 69.6 (20C, skeleton carbons), 75.2, 75.1, 74.6, 73.5, 73.3,
α] +49.4
D
δ
×
×
3
×
δ
×
×
73.2, 72.9 (7
×
ArCH2), 69.1, 68.3, 68.0 (3
×
C-6), 60.6, 60.4, 60.2, 59.7, 59.6, 59.4, 59.3 (7
×
OCH3),
55.2 (C-1-OCH3), 51.7 (COOCH3), 46.8 (C-7-F), 26.4 (C-6-F); MALDI-TOF MS: m/z 1771.76 [M + Na]+
(Calcd. 1771.69). Anal. Calcd. for C93H113NaO29S (1749.93): C, 63.83; H, 6.51; S, 1.83. Found: C, 63.92;
H, 7.03; S, 2.01.
Methyl [6-O-benzyl-2,3,4-tri-O-methyl-
(1 4)-[sodium (2,3-di-O-benzyl-6-deoxy-6-C-sulfonatomethyl-
methyl- -L-idopyranosyl)uronate]-(1 4)-(2,3,6-tri-O-benzyl-
(550 mg, 0.314 mmol) was converted to 27 according to general method
purified by column chromatography (9:1 CH2Cl2/MeOH) to give 27 (404 mg, 80%) as a colourless
syrup; Rf = 0.52 (9:1 CH2Cl2/MeOH); [ (ppm)
+24.2 (c 0.06, CHCl3); 1H-NMR (CDCl3, 400 MHz):
7.35–7.24 (m, 30H, arom.), 5.50 (s, 1H), 5.18 (s, 2H), 4.82–4.57 (m, 15H), 3.94–3.15 (m, 55H, 20 skeleton
protons, 9 OCH3, 3
H-6a,b, H-7a,b), 2.52–2.41 (m, 1H, H-6a-F), 2.08–1.99 (m, 1H, H-6b-F); 13C-NMR
(CDCl3, 100 MHz): (ppm) 171.7 (CO), 140.3–139.5 (6 Cq arom.), 129.5–128.4 (30C, arom.), 103.5,
100.6, 99.0, 97.8, 97.0 (5 C-1), 87.6, 86.4, 84.4, 83.0, 81.7, 81.4, 80.9, 80.6, 80.5, 80.4, 79.7, 76.8, 76.6 (20C,
skeleton carbons), 76.6, 76.0, 74.9, 74.5, 74.1 (6 ArCH2), 70.0, 69.7, 62.8 (3 C-6), 61.0, 60.8, 60.6, 59.9,
59.7 (7
α
-D-glucopyranosyl]-(1
-D-glucopyranosyl)]-(1
-D-glucopyranoside) (27). Compound 26
. The crude product was
→
4)-[2,3-di-O-methyl-
β
-D-glucopyranosyl]-
→
α
→
4)-[methyl (2,3-di-O-
α
→
α
D
α
]
δ
D
×
×
δ
×
×
×
×
×
OCH3), 55.6 (C-1-OCH3), 52.6 (COOCH3), 49.0 (C-7-F), 27.8 (C-6-F); MALDI-TOF MS: m/z
1631.77 [M + Na]+ (Calcd. 1631.63). Anal. Calcd. for C82H105NaO29S (1609.75): C, 61.18; H, 6.57; S, 1.99.
Found: C, 61.24; H, 6.59; S, 2.08.

Molecules 2016, 21, 1497
14 of 19
Methyl-(6-O-benzyl-2,3,4-tri-O-methyl-
α
-D-glucopyranosyl)-(1
→
4)-[sodium (2,3-di-O-methyl-
β
-D-glucopyranosyl)
uronate]-(1
→
4)-(sodium (2,3-di-O-benzyl-6-deoxy-6-C-sulfonatomethyl- -D-glucopyranosyl)-(1
α
→
4)-[methyl
(2,3-di-O-methyl-
α
-L-idopyranosyl)uronate]-(1 4)-(2,3,6-tri-O-benzyl-α-D-glucopyranoside) (28). To a
→
vigorously stirred solution of 27 (40 mg, 0.025 mmol) in CH2Cl2 (2.0 mL) and H2O (1.0 mL), TEMPO
(0.8 mg, 0.005 mmol, 0.2 equiv.) and BAIB (32 mg, 0.099 mmol, 4 equiv.) were added. After 24 h, the
TLC (9:1 CH2Cl2/MeOH) indicated moderate conversion of the starting material. Another portion
of BAIB (32 mg, 0.099 mmol, 4 equiv.) were added and the stirring was continued for a further
24 h. The reaction mixture was quenched by the addition of 10% aq Na2S2O3 solution (4 mL). The
mixture was then extracted twice with EtOAc (8 mL), and the combined organic layers were dried,
and concentrated. The residue was purified by column chromatography (9:1 CH2Cl2/MeOH) to
give a colourless syrup (31 mg). The mass spectrum contained peaks corresponding to 28 and its
partially debenzylated derivatives; this mixture was used in the subsequent reaction without further
purification. MALDI-TOF MS for C82H102Na2O30S (1644.60): m/z 1667.65 [M + Na]+ (Calcd. 1667.59);
1379.56 [M + Na (−3Bn)]+ (Calcd. 1379.45); 1487.56 [M + Na (−2Bn)]+ (Calcd. 1487.49).
Nona sodium [methyl (2,3,4-tri-O-methyl-6-O-sulfonato-
methyl- -D-glucopyranosyl)uronate]-(1 4)-[sodium (2,3-di-O-sulfonato-6-deoxy-6-C-sulfonatomethyl-
D-glucopyranosyl)-(1 4)-[sodium (2,3-di-O-methyl- -L-idopyranosyl)uronate]-(1 4)-2,3,6-tri-O-sulfonato-
D-glucopyranoside (29). An amount of 0.5 M NaOH solution (0.30 mL) was added to the solution of
28 (30 mg) in a mixture of THF (0.30 mL) and MeOH (0.30 mL) and stirred at room temperature for
24 h. The reaction was quenched by the addition of 1 N HCl solution (1 drop) and the mixture was
concentrated. The crude product was converted to sodium salt by ion exchange resin (Dowex, MeOH)
to give a colourless syrup (28 mg). The syrupy residue was dissolved in 96% EtOH (3.0 mL) and 10%
α
-D-glucopyranosyl)-(1
→
4)-[sodium (2,3-di-O-
β
→
α
-
-
→
α
→
α
Pd/C (10 mg) and acetic acid (100 µL) were added. The mixture was stirred at room temperature for
24 h under a 10 bar H2 atmosphere. The mixture was diluted with MeOH, the catalyst was filtered off
through a pad of Celite and the filtrate was concentrated. The crude product was purified by column
chromatography (7:6:1 CH2Cl2/MeOH/H2O, Rf = 0.13) and gel chromatography (Sephadex G-25,
H2O) to give the corresponding pentaol (9 mg) which was characterized by MALDI MS. (MALDI-TOF
MS for C39H63Na3O30S (1112.28): m/z 1091.39 [M
−
Na + 2H]+ (Calcd. 1091.31), 1113.39 [M + H]+
(Calcd. 1113.29), 1135.42 [M + Na]+ (Calcd. 1135.27). To the solution of the pentaol derivative (9 mg) in
dry DMF (0.6 mL), SO3 Et3N complex (44 mg, 0.040 mmol) was added and the reaction mixture was
·
stirred at 50 ◦C for 48 h. The reaction was quenched with satd. aq. NaHCO3 (21 mg, 0.24 mmol). The
solution was concentrated. The crude product was treated with Dowex ion-exchange resin (Na+ form),
and then purified by Sephadex G-25 column chromatography eluting with H2O to give 29 (7 mg, 17%
from 27) as a white solid. ESI-MS for C39H57Na9O48S7 (1723.91): m/z 795.110 [M
−
6Na + 4H]2−
(Calcd. 795.00); 522.451 [M − 7Na + 4H]3− (Calcd.: 522.34).
Methyl [2,3,4-tri-O-methyl-6-deoxy-6-C-(ethylsulfonatomethyl)-
-D-glucopyranosyl]-(1 4)-[2,3-di-O-benzyl-6-deoxy-6-C-(ethylsulfonatomethyl)-
[methyl (2-O-acetyl-3-O-methyl- -L-idopyranosyl)uronate]-(1 4)-(2,3,6-tri-O-benzyl-
30). Compound (975 mg, 0.53 mmol) was converted to 30 according to general method
crude product was purified by column chromatography (94:6 CH2Cl2/acetone) to give compound
30 (612 mg, 68%) as a colourless syrup; Rf = 0.26 (93:7 CH2Cl2/acetone); [ ]D +30.56 (c 0.10, CHCl3);
1H-NMR (360 MHz, CDCl3)
7.45–7.17 (m, 25H, arom.), 5.23 (t, J = 9.3 Hz, 1H, H-3-E), 5.11 (s, 1H,
H-1-G), 5.00 (d, J = 3.6 Hz, 1H, H-1-D), 4.96–4.49 (m, 16H, H-2-E, H-5-G, H-2-G, H-1-E, H-1-H, H-1-F,
10 PhCH2), 4.29 (q, J = 7.1, 1.2 Hz, 4H, 2 SO3CH2CH3), 3.93–3.07 (m, 21H, skeleton protons), 3.55,
3.52, 3.41, 3.41, 3.34, 3.31 (6s, 18H, 6 OCH3), 3.01 (dd, J = 9.8, 3.6 Hz, 1H, H-2-D), 2.72 (t, J = 9.3 Hz,
1H, H-4-D), 2.34–2.22 (m, 2H, H-6a-D, H-6a-F), 2.03, 2.01, 1.96 (3s, 9H, 3 COCH3), 1.94–1.75 (m, 3H,
H-6b-D, H-6b-F, OH), 1.41 (m, 6H, 2 170.2, 170.0,
SO3CH2CH3) ppm; 13C-NMR (91 MHz, CDCl3)
169.6, 169.6 (4 CO), 139.1, 139.0, 138.1, 138.1, 137.9 (5C, Cq arom.), 128.6, 128.6, 128.4, 128.4, 128.2,
128.1, 127.9, 127.8, 127.6, 127.3, 127.1, 126.1 (25C, arom.), 100.9, 98.4, 98.0, 97.6, 96.8 (5 C-1), 83.8, 82.8,
α
-D-glucopyranosyl]-(1
-D-glucopyranosyl]-(1
-D-glucopyranoside)
. The
→
4)-[2,3-di-O-acetyl-
β
→
α
→
4)-
α
→
α
(
6
D
α
δ
×
×
×
×
×
δ
×
×

Molecules 2016, 21, 1497
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82.1, 81.7, 80.2, 79.8, 79.4, 79.1, 76.1, 75.3, 74.8, 74.2, 72.6, 72.2, 70.2, 69.6, 69.2, 68.4, 67.5 (20C, skeleton
carbons), 74.6, 73.9, 73.4, 73.4, 73.4 (5 PhCH2), 68.4, 60.6 (C-6-H, C-6-E), 66.3, 66.1 (2 SO3CH2CH3),
60.8, 60.7, 59.5, 58.2, 55.3, 51.8 (6 OCH3), 46.8, 46.6 (C-7-D, C-7-F), 26.4, 25.5 (C-6-D, C-6-F), 21.1, 21.0,
20.6 (3 COCH3), 15.2, 15.2 (2
SO3CH2CH3) ppm; MALDI-TOF MS: m/z 1737.62 [M + Na]+ (Calcd.
×
×
×
×
×
1737.62); Anal. Calcd. for C83H110O34S2 (1714.63): C, 58.10; H, 6.46; O, 31.70; S, 3.74. Found: C, 58.21;
H, 6.41; S, 3.70.
Methyl
(2,3-di-O-acetyl-
D-glucopyranosyl]-(1
benzyl- -D-glucopyranoside) (31). Compound 30 (2.4 g, 1.87 mmol) was converted to 31 according
to general method . The reaction mixture was stirred for 24 h. The crude product was purified
by column chromatography (98:2 CH2Cl2/MeOH) to give 31 (528 mg, 80%) as a colourless syrup;
Rf = 0.50 (95:5 CH2Cl2/MeOH); [ 7.38–7.19
]D +29.26 (c 0.11, CHCl3); 1H-NMR (360 MHz, CDCl3)
(m, 25H, arom.), 5.26–5.18 (m, 1H), 5.08 (s, 1H, H-1-G), 5.00 (d, J = 3.5 Hz, 1H, H-1-D), 4.96–4.49 (m,
16H, 10 PhCH2, skeleton protons), 4.30, 4.28 (2q, 4H, 2 SO3CH2CH3), 4.04 (t, J = 8.8 Hz, 1H),
3.93–3.77 (m, 4H, skeleton protons), 3.77–3.60 (m, 4H, skeleton protons), 3.59–3.18 (m, 8H skeleton
protons), 3.56, 3.52, 3.42, 3.39, 3.34, 3.30 (6s, 18H, 6 OCH3), 3.16–3.05 (m, 1H, H-7b), 3.01 (dd, J = 9.8,
3.6 Hz, 1H, H-2-D), 2.72 (t, J = 9.3 Hz, 1H, H-4-D), 2.33–2.17 (m, 2H, H-6a-D, H-6a-F), 2.03, 2.01, 1.95
(3s, 9H, 3 COCH3), 1.91–1.77 (m, 2H, H-6b-D, H-6b-F), 1.39, 1.38 (m, 6H, 2 SO3CH2CH3) ppm;
13C-NMR (91 MHz, CDCl3)
170.4, 169.9, 169.5, 169.5, 169.0 (5 CO), 139.1, 138.7, 138.1, 138.1, 137.8
(5C, Cq arom.), 128.6, 128.5, 128.4, 128.2, 128.2, 128.1, 127.9, 127.8, 127.7, 127.6, 127.5, 127.3, 127.2
(25C, arom.), 100.8, 98.4, 98.0, 97.6, 97.6 (5 C-1), 83.8, 82.7, 81.9, 81.6, 80.2, 80.1, 79.8, 79.0, 76.2,
75.3, 74.7, 74.4, 74.4, 74.0, 72.4, 70.2, 69.5, 69.1, 68.3, 67.4 (20C, skeleton carbons), 74.9, 74.8, 73.8,
73.4, 73.4 (5 PhCH2), 68.5 (C-6-H), 66.6, 66.4 (2 SO3CH2CH3), 60.7, 60.7, 59.5, 58.2, 55.3, 51.9
OCH3), 46.6, 46.5 (C-7-D, C-7-F), 26.0, 25.7 (C-6-D, C-6-F), 21.1, 20.9, 20.6 (3 COCH3), 15.2, 15.2
SO3CH2CH3) ppm; MALDI-TOF MS: m/z 1773.53 [M + Na]+ (Calcd. 1773.58); Anal. Calcd. for
[2,3,4-tri-O-methyl-6-deoxy-6-C-(ethylsulfonatomethyl)-
-D-glucopyranosyl)uronate]-(1 4)-[2,3-di-O-benzyl-6-deoxy-6-C-(ethylsulfonatomethyl)-
4)-[methyl (2-O-acetyl-3-O-methyl- -L-idopyranosyl)uronate]-(1 4)-(2,3,6-tri-O-
α
-D-glucopyranosyl]-(1
→
4)-[sodium
β
→
α-
→
α
→
α
A
α
δ
×
×
×
×
×
δ
×
×
×
×
(6
(2
×
×
×
C83H107O35S2 (1714.63): C, 58.10; H, 6.46; O, 31.70; S, 3.74. Found: C, 58.21; H, 6.41; S, 3.70.
Methyl
-D-glucopyranosyl)uronate]-(1
4)-[methyl (3-O-methyl- -L-idopyranosyl)uronate]-(1
NaOMe (2 mg, 0.03 mmol) was added to the solution of compound 31 (500 mg, 0.29 mmol) and stirred
at room temperature for 24 h. The mixture was quenched by the addition of acetic acid (1–2 drops) and
then concentrated. The crude product was dissolved in acetone (20 mL) and NaI (128 mg, 0.86 mmol)
was added to the solution. The reaction mixture was stirred at room temperature for 24 h. The mixture
was concentrated and the crude product was purified by gel chromatography (Sephadex LH-20,
MeOH) to give 32 (386 mg, 84% for two steps) as a colourless syrup. Rf = 0.47 (7:3 CH2Cl2/MeOH);
[2,3,4-tri-O-methyl-6-deoxy-6-C-(sulfonatomethyl)-
4)-[2,3-di-O-benzyl-6-deoxy-6-C-(sulfonatomethyl)-
4)-(2,3,6-tri-O-benzyl- -D-glucopyranoside) (32).
α
-D-glucopyranosyl]-(1
→
4)-[sodium
(
(1
β
→
α
-D-glucopyranosyl]-
→
α
→
α
[α
]D +34.32 (c 1.66, CHCl3); 1H-NMR (360 MHz, CDCl3)
1H), 5.10 (s, 1H), 5.03 (d, J = 3.3 Hz, 1H), 5.02–4.50 (m, 14H, 5
(m, 22H, skeleton protons), 3.57, 3.52, 3.52, 3.46, 3.36, 3.35 (6s, 18H, 6
Hz, 1H, H-2-D), 3.08–2.95 (m, 2H, H-7a-D, H-7a-F), 2.84–2.75 (m, 1H, H-4-D), 2.43–2.31 (m, 1H, H-6a),
2.30–2.18 (m, 1H, H-6a), 2.11–1.78 (m, 2H, 2 177.8, 171.6
H-6b) ppm; 13C-NMR (91 MHz, CDCl3)
(2 CO), 140.2, 140.1, 139.5, 139.4, 139.0 (5C, Cq arom.), 129.6, 129.3, 129.2, 129.1, 128.9, 128.7, 128.4
(25C, arom.), 104.3, 102.3, 98.9, 98.2, 95.9 (5 C-1), 85.1, 83.7, 81.8, 81.2, 80.8, 80.4, 79.3, 78.4, 78.2, 76.2,
75.9, 75.7, 75.2, 73.6, 72.5, 71.7, 70.9, 70.7, 69.1, 67.8 (20C, skeleton carbons), 76.3, 76.1, 75.0, 74.5, 74.0
δ
7.44–7.15 (m, 25H, arom.), 5.51 (d, J = 3.5 Hz,
PhCH2, skeleton protons), 3.99–3.21
OCH3), 3.13 (dd, J = 9.8, 3.6
×
×
×
δ
×
×
(5
×
PhCH2), 69.8 (C-6-H), 60.8, 60.6, 59.3, 59.2, 58.5, 55.5 (6
×
OCH3), 28.3, 27.8 (C-6-D, C-6-F) ppm;
MALDI-TOF MS: m/z 1635.50 [M + Na]+ (Calcd. 1635.45); Anal. Calcd. for C73H91Na3O32S2 (1612.46):
C, 54.34; H, 5.68; Na, 4.27; O, 31.73; S, 3.97. Found: C, 54.23; H, 5.66; S, 4.03.

Molecules 2016, 21, 1497
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Methyl-[sodium 2,3,4-tri-O-methyl-6-deoxy-6-C-(sulfonatomethyl)-
α
-D-glucopyranosyl]-(1
→
4)-[sodium
(2,3-di-O-methyl-
glucopyranosyl]-(1
β
-D-glucopyranosyl)uronate]-(1
4)-[methyl (2,3-di-O-methyl-
→
4)-[2,3-di-O-benzyl-6-deoxy-6-C-(sulfonatomethyl)-
-L-idopyranosyl)uronate]-(1 4)-2,3,6-tri-O-benzyl-
α
-D-
-D-
→
α
→
α
glucopyranoside (33). An amount of 60 m/m% NaH (55 mg, 1.38 mmol) was added to the solution
of compound 32 (370 mg, 0.23 mmol) in dry DMF (40 mL) at 0 ◦C. After 30 min of stirring at room
temperature, MeI (64 µL, 1.04 mmol) was added to the reaction mixture and it was stirred for 4 h. The
reaction mixture was quenched by the addition of MeOH and acetic acid (1–2 drops). The solution was
concentrated and the crude product was purified by gel chromatography (Sephadex LH-20, MeOH) to
give 33 (249 mg, 65%) as a colourless syrup; Rf = 0.53 (7:3 CH2Cl2/MeOH); [
1H-NMR (360 MHz, CDCl3)
7.49–7.10 (m, 25H, arom.), 5.15–4.51 (m, 17H, 5
10 PhCH2), 4.00–3.24 (m, 20H, skeleton protons), 3.57, 3.55, 3.53, 3.49, 3.46, 3.43, 3.38, 3.36, 3.35 (9s,
27H, 9 OCH3), 3.11 (dd, J = 9.7, 3.6 Hz, 1H, H-2-D), 3.09–2.77 (m, 2H, 2 H-7b), 2.56–2.38 (m, 1H,
H-6a), 2.30–2.17 (m, 1H, H-6a), 2.07–1.85 (m, 2H, 2 170.4,
H-6b) ppm; 13C-NMR (101 MHz, MeOD)
170.0 (2 CO), 139.3, 139.3, 138.5, 138.4, 138.4 (5C, Cq arom.), 128.8, 128.7, 128.6, 128.5, 128.3, 128.3,
128.2, 128.1, 128.0, 127.9, 127.6 (25C, arom.), 100.1, 100.0, 98.4, 96.7, 96.0 (5 C-1), 86.2, 84.2, 83.8,
83.5, 82.7, 82.1, 81.7, 81.4, 80.3, 79.5, 79.2, 78.9, 76.5, 74.7, 74.3, 71.6, 71.4, 70.7, 70.1, 68.8 (20C, skeleton
carbons), 75.7, 75.5, 75.2,73.8, 73.8 (5 PhCH2), 73.9 (C-6-H), 60.9, 60.9, 60.1, 60.0, 59.8, 59.3, 55.5, 53.0,
52.3, (9
α
]D +4.09 (c 0.81, CHCl3);
δ
×
H-1, H-5-E, H-5-G,
×
×
×
×
δ
×
×
×
×
COCH3), 47.6, 47.5 (C-7-D, C-7-F), 27.5, 27.3 (C-6-D, C-6-F) ppm; MALDI-TOF MS: m/z
1655.53 [M + Na]+ (Calcd. 1655.52); Anal. Calcd. for C76H97Na3O32S2 (1654.51): C, 55.13; H, 5.91; Na,
4.17; O, 30.92; S, 3.87. Found: C, 55.20; H, 5.97; S, 3.79.
Methyl [2,3,4-tri-O-methyl-6-deoxy-6-C-sulfonatomethyl-
methyl- -D-glucopyranosyl)uronate]-(1 4)-[2,3-di-O-benzyl-6-deoxy-6-C-(sulfonatomethyl)-
(1 4)-[sodium (2,3-di-O-methyl- -L-idopyranosyl)uronate]-(1 4)-(2,3,6-tri-O-benzyl- -D-glucopyranoside)
34). An amount of 0.5 M NaOH solution (2 mL) was added to the solution of compound 33 (206 mg,
α
-D-glucopyranosyl]-(1
→
4)-[sodium (2,3-di-O-
β
→
α-D-glucopyranosyl]-
→
α
→
α
(
0.12 mmol) in a mixture of THF (2 mL) and MeOH (2 mL) and stirred at room temperature for
24 h. The reaction was quenched by the addition of 1 N HCl solution (1–2 drops) and the mixture
was concentrated. The crude product was converted to sodium salt by ion exchange resin (Dowex,
MeOH) to give 34 (187 mg, 90%) as a colourless syrup; Rf = 0.24 (8:2 CH2Cl2/MeOH); [
(c 0.10, CHCl3); 1H-NMR (360 MHz, CDCl3)
7.43–7.20 (m, 25H, arom.), 5.46 (d, J = 3.6 Hz, 1H), 5.15
(d, J = 3.3 Hz, 1H), 5.10 (d, J = 3.9 Hz, 1H), 5.04–4.48 (m, 14H, 2 H-1, H-5-E, H-5-G, 10 PhCH2),
4.09–3.25 (m, 17H, skeleton protons), 3.58, 3.54, 3.53, 3.52, 3.50, 3.43, 3.35, 3.34 (8s, 24H, 8 OCH3),
α]D +42.81
δ
×
×
×
3.23–3.16 (m, 1H), 3.09 (dd, 1H, H-2-D), 3.07–3.86 (m, 2H, H-7b-D, H-7b-F), 2.81 (t, J = 9.8 Hz, 1H,
H-4-D), 2.60–2.48 (m, 1H, H-6a), 2.33–2.19 (m, 1H, H-6a), 1.98–1.82 (m, 2H, H-6b-D, H-6b-F) ppm;
13C-NMR (101 MHz, MeOD)
δ
171.1, 170.7 (2
129.4, 129.3, 129.2, 129.0, 129.0, 128.8, 128.7, 128.6, 128.4, 128.2, 128.0 (25C, arom.), 104.6, 100.5, 98.9,
96.8, 96.7 (5 C-1), 87.0, 85.4, 84.5, 84.1, 82.9, 82.8, 81.3, 81.2, 80.8, 80.6, 80.4, 76.6, 75.2, 74.9, 74.1,
71.6, 71.5, 71.0, 70.7 (20C, skeleton carbons), 76.0, 75.8, 74.5, 73.9, 73.8 (5 PhCH2), 69.6 (C-6-H), 61.2,
×
CO), 140.4, 140.2, 139.6, 139.5, 139.5 (5C, Cq arom.),
×
×
60.9, 60.6, 59.9, 59.5, 55.9, 55.9, 55.6 (8
1685.49 [M + Na]+ (Calcd. 1685.47); Anal. Calcd. for C75H94Na4O32S2 (1662.48): C, 54.15; H, 5.70; Na,
5.53; O, 30.78; S, 3.85. Found: C, 54.08; H, 5.67; S, 3.87.
×
OCH3), 30.7, 28.3 (C-6-D, C-6-F) ppm; MALDI-TOF MS: m/z
Methyl [2,3,4-tri-O-methyl-6-deoxy-6-C-sulfonatomethyl-
-D-glucopyranosyl)uronate]-(1 4)-[6-deoxy-6-C-sulfonatomethyl-
(2,3-di-O-methyl- -L-idopyranosyl)uronate]-(1 4)- -D-glucopyranoside (35). An amount of 10% Pd/C
(110 mg) and acetic acid (350 L) were added to the solution of compound 34 (180 mg, 0.11 mmol)
α
-D-glucopyranosyl]-(1
→
4)-[sodium (2,3-di-O-methyl-
β
→
α
-D-glucopyranosyl]-(1
→
4)-[sodium
α
→
α
µ
in 96 v/v % EtOH (10 mL). The mixture was stirred at room temperature for 24 h under a 10 bar H2
atmosphere. The mixture was diluted with MeOH and the catalyst was filtered off on Celite-pad.
The filtrate was concentrated. The crude product was purified by column chromatography (7:6:1
CH2Cl2/MeOH/H2O) and gel chromatography (Sephadex G-25, H2O) to give 35 (123 mg, 92%) as
1
a colourless syrup; Rf = 0.25 (7:6:1 CH2Cl2/MeOH/H2O); [
α
]
+21.82 (c 0.21, CHCl3); H-NMR
D

Molecules 2016, 21, 1497
17 of 19
(360 MHz, CDCl3)
δ
5.54 (s, 1H), 5.14 (s, 1H), 5.09 (s, 1H), 4.83 (s, 2H), 4.62 (s, 1H), 4.18 (s, 1H), 3.97–3.25
(m, 46H, skeleton protons, 8
H-6a), 2.29–2.16 (m, 1H, H-6a), 1.99–1.85 (m, 2H, H-6b, H-6b) ppm; 13C-NMR (91 MHz, CDCl3)
193.2 (2 CO), 103.5, 103.4, 100.1, 100.0, 96.2 (5 C-1), 86.8, 84.4, 83.9, 83.5, 82.3, 81.8, 80.4, 78.6, 78.1,
76.7, 73.9, 72.8, 72.6, 72.5, 72.4, 71.9, 71.6, 71.4, 70.3, 69.9 (20C, skeleton carbons), 61.2 (C-6-H), 61.5, 61.1,
×
OCH3), 3.18–2.96 (m, 5H), 2.90 (d, J = 2.7 Hz, 1H), 2.49–2.35 (m, 1H,
δ
193.3,
×
×
60.4, 60.4, 59.9, 59.6, 58.9, 55.9 (8
×
OCH3), 48.3, 48.2 (C-7-D, C-7-F), 27.3, 27.0 (C-6-D, C-6-F) ppm;
ESI-MS: m/z 561.46 [M + 2H]2− (Calcd. 561.15); Anal. Calcd. for C40H64Na4O32S2 (1212.24): C, 39.61;
H, 5.32; Na, 7.58; O, 42.21; S, 5.29. Found: C, 39.56; H, 5.29; S, 5.24.
Nona sodium [methyl (2,3,4-tri-O-methyl-6-deoxy-6-C-sulfonatomethyl-
methyl- -D-glucopyranosyluronate]-(1 4)-[2,3-di-O-sulfonato-6-deoxy-6-C-sulfonatomethyl-
(1 4)-[2,3-di-O-methyl- -L-idopyranosyluronate]-(1 4)-2,3,6-tri-O-sulfonato- -D-glucopyranoside (36).
α
-D-glucopyranosyl)]-(1
→
4)-[2,3-di-O-
β
→
α-D-glucopyranosyl]-
→
α
→
α
To the solution of compound 35 (58 mg, 0.047 mmol) in dry DMF (4 mL) sulfur trioxide–triethylamine
complex (215 mg, 1.187 mmol) was added and the reaction mixture was stirred at 50 ◦C for 72 h. The
reaction was quenched with satd. aq. NaHCO3 (262 mg, 3.12 mmol). The solution was concentrated.
The crude product was treated with Dowex ion-exchange resin (Na+ form), and then purified
by Sephadex G-25 column chromatography eluting with H2O to give 36 (28 mg, 36%) as a white
powder. Rf = 0.53 (7:4:1 CH2Cl2/MeOH/H2O); ESI-MS: m/z for C40H59Na9O47S7 (1721.94): 837.771
[M − 2Na]2− (Calcd. 837.979); 794.136 [M − 6Na + 4H]2− (Calcd. 794.015).
4. Conclusions
Five new idraparinux-analogue pentasaccharide precursors bearing one or two primary
sulfonatomethyl moieties at the
D, F or H glucose units have been prepared using four disaccharides
and two monosaccharides as the building blocks. The synthetic approach, including two subsequent
glycosylation steps proved to be highly efficient, and the glycosylation reactions proceeded in good
to excellent yields with complete stereoselectivity, regardless of the C-sulfonation pattern of the
building blocks.
Unexpectedly, the transformation of the protected pentasaccharides into the fully O-sulfated
and O-methylated end-products was troublesome. Upon synthesis of pentasaccharide 29 from
via a Zemplén deacetylation, O-methylation, NAP-deprotection and TEMPO-BAIB oxidation route,
the glucuronide formation proceeded with low efficacy. Fortunately, pentasaccharide could be
9
6
converted into the desired disulfonic acid product in an acceptable yield by applying a reaction
sequence in which the oxidative formation of the glucuronic acid residue preceded the introduction of
the methyl ether groups. A study to improve the yields of the synthetic procedures at a pentasaccharide
level is in progress in our laboratory.
Synthesis of further isosteric sulfonic acid analogues of idraparinux and evaluation of their
anticoagulant activity will be reported in due course.
Supplementary Materials: Supplementary materials can be accessed at: http://www.mdpi.com/1420-3049/21/
11/1497/s1. copies of 1H-NMR and 13C-NMR spectra of described compounds.
Acknowledgments: The authors gratefully acknowledge financial support for this research from the Mizutani
Foundation for Glycoscience (150091) and from the National Research, Development and Innovation Office of
Hungary (OTKA K 109208, K 105459 and PD 115645). The research was also supported by the EU and co-financed
by the European Regional Development Fund under the project GINOP-2.3.2-15-2016-00008.
Author Contributions: M.H. and A.B. conceived and designed the experiments; E.M., D.E. and E.V. performed
the experiments; E.M., M.H. and A.B. wrote the paper.
Conflicts of Interest: The authors declare no conflict of interest.
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Sample Availability: For availability of samples of compounds contact the corresponding author.
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