Esters of Glucose-2-Phosphate: Occurrence and Chemistry

Article abstract of DOI:10.3390/molecules25122829

Phosphodiesters of glucose-2-phosphate (G2P) are found only in few natural compounds such as agrocinopine D and agrocin 84. Agrocinopine D is a G2P phosphodiester produced by plants infected by Agrobacterium fabrum C58 and recognized by the bacterial periplasmic binding protein AccA for being transported into the bacteria before cleavage by the phosphodiesterase AccF, releasing G2P, which promotes virulence by binding the repressor protein AccR. The G2P amide agrocin 84 is a natural antibiotic produced by the non-pathogenic Agrobacterium radiobacter K84 strain used as a biocontrol agent by competing with Agrobacterium fabrum C58. G2P esters are also found in irregular glycogen structures. The rare glucopyranosyl-2-phophoryl moiety found in agrocin 84 is the key structural signature enabling its action as a natural antibiotic. Likewise, G2P and G2P esters can also dupe the Agrobacterium agrocinopine catabolism cascade. Such observations illustrate the importance of G2P esters on which we have recently focused our interest. After a brief review of the reported phosphorylation coupling methods and the choice of carbohydrate building blocks used in G2P chemistry, a flexible access to glucose-2-phosphate esters using the phosphoramidite route is proposed.

Full text of DOI:10.3390/molecules25122829

molecules
Article
Esters of Glucose-2-Phosphate: Occurrence
and Chemistry
Qiang Zhang, Si-Zhe Li, Mohammed Ahmar, Laurent Soulère and Yves Queneau *
Univ Lyon, Université Claude Bernard Lyon 1, CNRS, INSA Lyon, CPE Lyon, ICBMS, UMR 5246, Bât. E. Lederer,
1 rue Victor Grignard, F-69622 Villeurbanne, France; qiang.zhang@insa-lyon.fr (Q.Z.);
s.li@lic.leidenuniv.nl (S.-Z.L.); mohammed.ahmar@univ-lyon1.fr (M.A.); laurent.soulere@insa-lyon.fr (L.S.)
* Correspondence: yves.queneau@insa-lyon.fr; Tel.: +33-(0)-4-81-92-99-00
ꢀꢁꢂꢀꢃꢄꢅꢆꢇ
ꢀꢁꢂꢃꢄꢅꢆ
Academic Editor: László Somsák
Received: 26 May 2020; Accepted: 17 June 2020; Published: 19 June 2020
Abstract: Phosphodiesters of glucose-2-phosphate (G2P) are found only in few natural compounds
such as agrocinopine D and agrocin 84. Agrocinopine D is a G2P phosphodiester produced by plants
infected by Agrobacterium fabrum C58 and recognized by the bacterial periplasmic binding protein
AccA for being transported into the bacteria before cleavage by the phosphodiesterase AccF, releasing
G2P, which promotes virulence by binding the repressor protein AccR. The G2P amide agrocin 84
is a natural antibiotic produced by the non-pathogenic Agrobacterium radiobacter K84 strain used
as a biocontrol agent by competing with Agrobacterium fabrum C58. G2P esters are also found in
irregular glycogen structures. The rare glucopyranosyl-2-phophoryl moiety found in agrocin 84 is
the key structural signature enabling its action as a natural antibiotic. Likewise, G2P and G2P esters
can also dupe the Agrobacterium agrocinopine catabolism cascade. Such observations illustrate the
importance of G2P esters on which we have recently focused our interest. After a brief review of the
reported phosphorylation coupling methods and the choice of carbohydrate building blocks used
in G2P chemistry, a flexible access to glucose-2-phosphate esters using the phosphoramidite route
is proposed.
Keywords: agrocinopine; glucose-2-phosphate; phosphodiesters; agrocin 84; Agrobacterium fabrum
1. Introduction
Glucose-2-phosphate esters are rare structures, found in only a few natural compounds, among
which agrocinopine D and agrocin 84. Agrocinopines are a family of opines, which are plasmid-coded
enzyme products produced by pathogenic bacteria of the genus of Agrobacterium. Agrobacterium fabrum
are Gram negative bacteria which cause tumors in plants, causing diseases such as crown gall, hairy
root, and cane gall. In the process of infection by Agrobacterium fabrum C58, agrocinopines serve as
nutrients and as relays in the production of quorum-sensing autoinducers. These latter subsequently
control the expression of virulence genes and bacterial population [
1,
2]. Four agrocinopines (A, B, C
and D, Figure 1) have been identified and are specific to A. fabrum strains C58 and strains Bo542 [
2].
They differ in structure by being either glucose or arabinose phosphodiesters, connected with sucrose,
glucose or fructose moieties (Figure 1). In Agrobacterium fabrum, the agrocinopine catabolism cascade
involves several proteins notably AccA and AccF which are responsible for the import of agrocinopine
back into the bacteria, and for the cleavage of its phosphodiester linkage, respectively.
A phosphoramidate analog of agrocinopines is the natural antibiotic agrocin 84 produced by
Agrobacterium radiobacter K84 which is a non-pathogenic bacterial strain competing with Agrobacterium
fabrum C58. If agrocin 84 enters into Agrobacterium fabrum C58 cells, its phosphodiester linkage is
cleaved by AccF, releasing the toxic TM84 fragment acting as a leucine synthase inhibitor resulting in
bacterial death [3]. Agrobacterium radiobacter can thus be used as a biocontrol agent.
Molecules 2020, 25, 2829; doi:10.3390/molecules25122829
www.mdpi.com/journal/molecules

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Figure 1. Structures of agrocinopines A, B, C and D, d-glucose-2-phosphate (G2P) and its esters G2P
lactate, its amide agrocin 84.
The carbohydrate signature of the agrocinopines is therefore the key for the three
protein-carbohydrate recognition events, first through specific recognition by the periplasmic binding
proteins AccA. Then, once imported, it is recognized and hydrolyzed by the phosphodiesterase
AccF. Finally, the resulting fragment binds with the repressor protein AccR responsible for virulence
activation through the activation of quorum sensing signals synthesis [3].
If agrocin 84 can act as a natural antibiotic, it is because it shares the rare pyranose-2-phosphate
chemical signature with agrocinopines. Agrocin 84 structure was first proposed to be a glucofuranose
1-O-phosphate though not ruling out other connections [
glucopyranosyl-2-phosphoryl derivative after X-ray crystallography diffraction studies of its complex
with AccA [ ]. The ability of G2P esters to dupe the acc cascade of Agrobacterium fabrum was also
4,5]. Its structure was fully identified as a
6
confirmed using the G2P lactic acid ester (G2LP) found to be the first non-natural G2P ester to mimic
the role of natural agrocinopine A [7].
Considering the importance of the G2P motif in plant pathogens, and their originality in biology
compared to glucose-1-phosphates (G1P) or glucose-6-phosphates (G6P), we have further focused our
attention on their chemical synthesis. Below we briefly review the chemistry of G2P and its esters,
discussing the phosphorylation methods and possible carbohydrate building blocks, before applying
an updated sequence to the synthesis of a short series of derivatives.
2. Results
Although phosphate esters are very frequent in biologically relevant carbohydrates [8], there
are only a handful of G2P phosphodiesters reported in the literature. Apart from the family of
agrocinopines and analogues mentioned above, the G2P motif was only found in glycogen, together
with G3P and the more common G6P. Glycogen-bound phosphate influences glycogen architecture
with different branching and chain length. Even if glucose phosphates are structurally similar, G1P
and G6P are involved in the processes of glycogen degradation and synthesis, respectively. Oppositely,
G2P or G3P residues cannot be confirmed by biochemical enzymatic assays as there is no known
enzyme with specific activity towards these two phosphates [
itself was used for studying phosphate stability or hydrolysis rates [
the hydrolyzed monomeric forms of glycogen to understand the metabolism of the phosphate in
this biopolymer [ 14]. The quite uncommon d-glucose-2-phosphate (G2P), which refer to phosphate
9–
11]. Actually, glucose-2-phsophate
8,12,13], or for identification of
9,
covalently bonded glucose hydroxyl at C-2 position, was firstly and unequivocally synthesized by
Farrar [15] in 1949. The hydrolysis of the cyclic glucose-1,2-phosphate (GCP) can afford a mixture of
G2P and G1P. During hydrolysis, G2P esters exhibit higher stability versus G1P [12,15].

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2.1. Phosphorylation and Coupling Methods
In the synthesis of G2P and its phosphodiesters, a first issue is the choice between various
methods for installing the phosphorus on the glucose residue and further connecting the other moiety.
Several methods have been developed in the field of carbohydrates and oligonucleotide [16], glycoside
and peptide synthesis, but only few have been applied to the case of G2P and its esters. Farrar’s
first unequivocal G2P synthesis [15] involved diphenyl chlorophosphate (3 days in pyridine) as
phosphorylation reagent (Scheme 1). The method used by Lindberg and Oscarson [17] for reaching
an agrocinopine C precursor was the condensation of sucrose derivative and hydrogenphosphate in
pyridine, while for reaching an agrocinopine D precursor, they performed the condensation of glucose
derivative with a phosphonic acid in pyridine, activated by an acyl chloride [18,19]. The use of excess
glucose building block was needed to make the reaction complete. The purification of the highly polar
phosphonate diesters intermediates (in their salt form) requires consecutive ion exchange columns.
Scheme 1. Previous synthesis of the precursors of agrocinopine C and D, G2P and G2LP.

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In the chemistry of agrocinopines A and B [20], which involve an arabinose building block
instead of a glucose one in agrocinopines C and D, Thiem and coworkers used trichloroethyl
phosphorodichloridate with 1,2,4-triazole in pyridine as coupling reagent. More recently, our team
has used the convenient phosphoramidite strategy for constructing the phosphodiester both in the
arabinose and glucose series [6,7]. This method combines easiness and flexibility for a diversity-oriented
strategy towards a variety of agrocinopine analogs from various sugars and alcohols.
2.2. Building Blocks
The overall efficiency of these syntheses relies also on the availability of the carbohydrate
building blocks possessing the appropriate partial protection required for selective phosphorylation
at C-2. Several 2-OH free glucoses have been reported in literature, most of them with
benzyl and/or acetyl groups at O-1, 3, 4 and 6. In the synthesis of G2P, Farrar [15] used
1,3,4,6-tetraacetyl-
by reaction of 3,4,6-tri-O-acetyl-1,2-anhydro-
purification by crystallization makes this sequence quite efficient. Alternatively, the hydrolysis of
halogenated acetoglucose can also lead to tetraacetyl glucose with only 2-OH free [22 24] (Scheme 2b,c).
β-glucose, which was prepared following Hardegger and Pascual procedure [21
]
α
-d-glucopyranose with HOAc (Scheme 2a). The easy
–
Scheme 2. Previous synthetic routes for acetylated glucose with 2-OH free [21–24].
However, considering the risk of acetyl group migrations, leading to undesired mixtures of
regioisomers in the course of the phosphorylation step, less labile protecting groups should be
preferred. For example, one of us reported an allyl glucoside with only the 2-OH free as other
positions are protected as a 4,6-O-benzylidene and a 3-O-allyl ether [25]. Even more appropriate is
the use of benzyl ethers, both at the anomeric and other positions, in order to keep an easy final and
practical deprotection procedure. Therefore, benzyl 3,4,6-tri-O-benzyl-d-glucopyranoside appears as
the ideal glucose precursor. In the only previously reported synthesis of agrocinopine D, Lindberg
and Oscarson [17] used this building block as its
β anomer. They relied on a 5 steps synthesis
starting from tetra-O-acetyl- -d-glucopyranosyl bromide, formation of the 1,2-orthoester, Zemplén
α
deacetylation followed by Williamson etherification using benzyl bromide to the tri-O-benzyl orthoester,
then HgBr2-mediated glycosylation with benzyl alcohol and deacetylation to tetrabenzyl derivative
1
(Scheme 3a). The
endo-type 1,2-O-benzylidene acetal [26] or using the elegant reductive selective 2-O-debenzylation
promoted by triisobutyl aluminum (TIBAL) [27] of perbenzyl glucose [ ] (Scheme 3b,c). However,
this latter debenzylation step only proceeds on the anomer, limiting significantly the overall yield
α anomer benzyl 3,4,6-tri-O-benzyl-α-d-glucopyranoside 2 can be made from
6,7
α

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when mixtures of anomers are used as substrate as all the
β
anomer remains untransformed. The
shortest and most efficient sequence appears to be based on the Lewis acid-catalyzed opening reaction
of the readily available 1,2-anhydro- -d-glucopyranose [28 29] leading to in high yield within only 2
α
,
1
steps from the commercially available benzylated glucal (Scheme 3d). Based on this survey, this latter
access to 1 was used in the following work towards G2P and G2P esters.
Scheme 3. Various accesses to tetrabenzylated glucose with 2-OH free [26–29].

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2.3. Alternative Flexible Access to G2P and Esters
Aiming at proposing a more general and flexible access able to lead to G2P or its esters, we thus
applied the phosphoramidite coupling strategy to the 3,4,6-tri-O-benzyl- -d-glucopyranoside building
block . Reaction with benzyloxy bis(diisopropylamino)phosphine gave selectively the monoaminated
phosphoramidite in 81% yield in the presence of diisopropylammonium tetrazolide as mild and
β
1
3
hindered base preventing double diisopropylamino displacement [30]. The phosphoramidite 3 was
then used in coupling reactions with different alcohols, as shown in Table 1.
Table 1. Synthesis of the precursors of glucose-2-phosphate and derivatives.
Yield (%) (Diastereomeric
Ratio) a
Entry
ROH
Product 4
1
benzyl alcohol
88
2
3
cetearyl alcohol
cholesterol
90 (1/1.1)
70 (1/1.3)
74 (1/1.4)
53
4
5
5
α
-cholestan-3β-ol
benzyl
3,4,6-tri-O-benzyl-
β-
d-glucopyranoside
a. Measured by 31P-NMR.
The conversion of phosphoramidite
3
into phosphotriesters
4
was conducted in a two-step one-pot
procedure, involving firstly the reaction with the alcohol leading to an intermediate phosphite, and
secondly the oxidation of the phosphite to the phosphate using tert-BuOOH. The reaction with benzyl
alcohol gave the fully protected G2P 4a in 88% yield. The reaction was also conducted with a short
scope of primary or secondary alcohols including cetearyl alcohol, cholesterol, 5
(dihydrocholesterol) and glucoside having only 2-OH available. All gave fair to good yields, with
primary alcohols showing logically higher reactivity, while secondary suffer from steric hindrance.
α-cholestan-3β-ol
1

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Owing to the chiral center of the phosphorus atom, phosphates 4b
,
4c and 4d were obtained as a
mixture of the two diastereoisomers in nearly 1:1 ratio determined by 31P-NMR spectra.
Considering the interest of agrocinopine D, and its symmetrical structure, we investigated a
one-pot access to the protected phosphodiester 4e from the glucose building block
intermediate bis-glucosyl phosphite was not isolated (Scheme 4). This step was optimized with respect
to the stoichiometry between substrate , phosphoramidite and tetrazole. When the reaction was
carried out with only 1.0 equivalent phosphoramidite (compared to the 2.0 equivalents of substrate
), low conversion of substrate was observed. Increasing the amount of phosphoramidite to 2.0
equivalents led mainly to the formation of monoaminated phosphoramidite . The most favorable
conditions were found to be 1.2 equivalents of phosphoramidite and 3 equivalents of 1H-tetrazole.
1 in which the
1
1
1
3
Scheme 4. Synthesis of the precursor of agrocinopine D in one-pot.
The fully deprotected targets G2P (5a) and agrocinopine D (5b) were obtained after
palladium-catalyzed hydrogenolysis from compounds 4a and 4e respectively, using 1 atm H2 and
Pd/C in methanol (Scheme 5). G2P 5a was obtained in high yield and purity after debenzylation in
ethyl acetate. Agrocinopine D 5b was obtained in 78% yield as its ammonium salt after ion exchange
chromatography on a DEAE-Sephadex column. Both compounds exhibited identical data as compared
to literature [6,17].
Scheme 5. Deprotection of the phosphate precursors.
3. Materials and Methods
3.1. General Methods
All commercial reagents and solvents were used without further purification. Analytical thin layer
chromatography was performed on aluminum-backed plates coated with Macherey-Nagel Kieselgel 60
XtraSIL G/UV254. Macherey-Nagel Kieselgel 60 M silica was used for flash chromatography. Synthetic
products were visualized under UV light (at 254 nm) or stained using concentrated sulfuric acid. NMR
spectra were recorded on a Bruker 300 MHz or a Bruker 500 MHz spectrometer. Chemical shifts (ppm)

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were reported relative to residual solvent signals. Multiplicities are abbreviated as follows: s, singlet;
d, doublet; t, triplet; m, multiplet. Coupling constants were measured in Hertz (Hz). High-resolution
mass spectra (HRMS) were performed by a Finnigan Mat 151xL mass spectrometer using electrospray
(see supplementary materials).
3.2. Synthesis of benzyl 3,4,6-tri-O-benzyl-2-O-[benzyloxy(diisopropylamino)phosphanyl]-β-D-
glucopyranoside (or benzyl ((2R,3R,4S,5R,6R)-2,4,5-tris(benzyloxy)-6-((benzyloxy)methyl)tetrahydro-
2H-pyran-3-yl) diisopropylphosphoramidite) 3
Benzyl 3,4,6-tri-O-benzyl-
3,4,6-tri-O-benzyl-d-glucal as previously reported [26
resulting product as white solid was subjected to the next step. To a solution of diisopropylammonium
β-d-glucopyranoside (1) was synthesized from commercially available
,27]. After recrystallization from ethanol, the
1
tetrazolide salt, prepared by mixing tetrazole (1.0 eq, 4.2 mL of a 0.45M solution in MeCN) with
diisopropylamine (1.2 eq, 0.33 mL) and benzyloxy bis(diisopropylamino)phosphine (0.96 g, 2.7 mmol,
1.5 eq.) in 10 mL DCM, was added benzyl 3,4,6-tri-O-benzyl-β-d-glucopyranoside (1, 1 g, 1.8 mmol),
which was dissolved in 10 mL DCM at 0 ◦C. Then the mixture was stirred overnight at room temperature.
The reaction was monitored by TLC (EtOAc-pentane 1:9 with 1% Et3N as eluent. When the starting
material was consumed, the solid salt was filtered. The organic phase was collected, concentrated and
purified by silica gel chromatography (EtOAc-pentane 1:9 with 1% Et3N) to give 1.2 g of the desired
1
product (yield 81%). Rf = 0.56. H-NMR (CDCl3, 500 MHz):
δ
(ppm) 7.38–7.09 (m, 23H, Ph), 7.07–7.00
HPh), 4.74–4.43 (m, 8H, 4 2Ph), 4.40 (d, J =
7.5 Hz, 1H, H-1), 3.84 (m, 1H, H-2), 3.66–3.51 (m, 6H, H6a, H6b, H-4, H-3, 2 CH), 3.42 (m, 1H, H-5),
1.07–0.96 (m, 12H, 4 (ppm) 139.9 (C-Ph), 139.6 (C-Ph), 138.8
CH3); 13C-NMR (126 MHz, CDCl3)
(m, 2H, Ph), 4.93 (m, 1H, C
H
HPh), 4.84 (m, 1H, C
H
×
CH
×
×
δ
(C-Ph), 138.3 (C-Ph), 137.7 (C-Ph), 128.4 (Ph), 128.4 (Ph), 128.4 (Ph), 128.3 (Ph), 128.2 (Ph), 128.2 (Ph),
128.1 (Ph), 128.0 (Ph), 128.0 (Ph), 128.0 (Ph), 127.9 (Ph), 127.8 (Ph), 127.8 (Ph), 127.8 (Ph), 127.7 (Ph),
127.7 (Ph), 127.6 (Ph), 127.6 (Ph), 127.6 (Ph), 127.4 (Ph), 127.3 (Ph), 127.2 (Ph), 127.1 (Ph), 127.0 (Ph),
127.0 (Ph), 102.0 (C1), 101.7 (d, JC-P = 2.9 Hz, C10), 85.5 (d, JC-P = 2.8 Hz, C3), 85.4 (C30), 78.1 (C4), 76.2
(d, JC-P = 10.9 Hz, C2’), 75.9 (d, JC-P = 5.2 Hz, C2), 75.2 (
H2Ph), 70.8 ( H2Ph), 43.1 (CH), 43.0 (CH), 24.7 (CH3), 24.6 (CH3), 24.6
H2Ph), 69.2 (C6, C60), 65.5 (
(CH3), 24.5 (CH3). 31P-NMR (CDCl3,122 MHz):
(ppm) 151.44, 150.23 (ratio 1/1.3). HR-MS (ESI):
CH2Ph), 75.0 (C5, C5’), 74.9 (CH2Ph), 73.5
(C
C
C
δ
C47H59NO8P [M + H3O]+ requires: 796.3973; found: 796.3976.
3.3. General Procedure for the two-step Synthesis of Phosphotriesters 4a–e
To a solution of phosphoramidite 3 (155 mg, 0.2 mmol) in 2 mL DCM was added corresponding
alcohol (0.2 mmol) dissolved in 1 mL DCM, 1H-tetrazole (4.5 mL of a 0.45 M solution in MeCN, 0.2
mmol) at rt. Then the mixture was stirred for 5 h at rt. After completion of the reaction, t-BuOOH (43
µL of a 5.6 M solution in decane, 0.24 mmol) was added. After 1 h, the white solid was filtered. The
organic phase was collected, concentrated and purified by silica gel chromatography.
3.3.1. Benzyl 3,4,6-tri-O-benzyl-2-O-dibenzylphosphonato-β-D-glucopyranoside [or dibenzyl
((2R,3R,4S,5R,6R)-2,4,5-tris(benzyloxy)-6-((benzyloxy)methyl)tetrahydro-2H-pyran-3-yl)
phosphate] 4a
From benzyl alcohol (20
1:3 as eluent, flash chromatography of the crude product (1:3 EtOAc-pentane) afforded 4a (yield 88%)
as a white solid. Rf = 0.43. 1H-NMR (CDCl3, 500 MHz):
(ppm) 7.31 (m, 8H, Ph), 7.25–7.13 (m,
16H, Ph), 7.12–7.01 (m, 6H, Ph), 4.93–4.85 (m, 4H, 2 2Ph), 4.82 (m, 1H, C HPh), 4.79–4.68 (m, 3H,
HPh, C 2Ph), 4.61–4.55 (m, 2H, C 2Ph), 4.51 (d, J = 10 Hz, 1H, H1), 4.50–4.47 (m, 2H, C 2Ph),
4.45–4.39 (m, 1H, H2), 3.70–3.62 (m, 4H, H6a, H6b, H3, H4), 3.45 (m, 1H, H5); 13C-NMR (CDCl3, 126
MHz): (ppm) 138.3, 138.1, 137.9, 136.9, 136.2, 136.1, 128.4, 128.4, 128.4, 128.4, 128.3, 128.2, 128.2, 128.0,
127.9, 127.8, 127.8, 127.7, 127.7, 127.7, 127.6, 127.5, 100.1 (d, JC-P = 3.7 Hz, C1), 83.7 (d, JC-P = 4.0 Hz,
C3), 79.1 (d, JC-P = 6.9 Hz, C2), 77.8 (C4), 75.2 (C5), 75.1 (O H2Ph), 75.0 (O H2Ph), 73.6 (O H2Ph),
µL) following general procedure, TLC monitoring using EtOAc-pentane
δ
×
CH
H
C
H
H
H
H
δ
C
C
C

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70.8 (O
(CDCl3, 122 MHz,):
C48H49NaO9P [M + Na]+ requires: 823.3006; found: 823.3006.
C
H2Ph), 69.2 (d, JC-P = 5.2 Hz, O
C
H2Ph), 69.1 (d, JC-P = 5.3 Hz, O
C
H2Ph), 68.7 (C6); 31P-NMR
δ
(ppm)
−
1.71. [α]2D4
=
25.1 (c = 0.4, acetone). mp: 83.1~83.4 ◦C. HR-MS (ESI):
−
3.3.2. Benzyl 3,4,6-tri-O-benzyl-2-O-[(benzyl)(hexadecyl)phosphonato]-β-D-glucopyranoside [or
benzyl hexadecyl ((2R,3R,4S,5R,6R)-2,4,5-tris(benzyloxy)-6-((benzyloxy)methyl)tetrahydro-2H-
pyran-3-yl) phosphate] 4b
From cetearyl alcohol (48 mg) following general procedure, TLC monitoring using EtOAc-pentane
1:3 as eluent, flash chromatography of the crude product (1:1 EtOAc-pentane) afforded 4b (yield 90%)
1
as a white solid. Rf = 0.4. H-NMR (CDCl3, 500 MHz):
δ
(ppm) 7.46–7.41 (m, 1H, Ph), 7.41–7.12 (m,
24H, Ph), 5.08–4.88 (m, 4H, 2
(m, 2H, CH2Ph), 4.57 (d, J = 8.3 Hz, 1H, H1), 4.56–4.53 (m, 2H, CH2Ph), 4.45 (m, 1H, H2), 3.94–3.81 (m,
×
CH2Ph), 4.88–4.81 (m, 1H, CHHPh), 4.81–4.75 (m, 1H, CHHPh), 4.70–4.61
2H, OCH2), 3.79–3.68 (m, 4H, H3, H4, H6a, H6b), 3.51 (m, 1H, H5), 1.51–1.37 (m, 2H, CH2), 1.28 (m,
26H, 13 δ (ppm) 138.3 (Ph), 138.1
CH2), 0.90 (t, J = 6.9 Hz, 3H, CH3); 13C-NMR (CDCl3, 126 MHz):
×
(Ph), 137.9 (Ph), 137.0 (Ph), 136.3 (Ph), 128.6 (Ph), 128.5 (Ph), 128.4 (Ph), 128.4 (Ph), 128.4 (Ph), 128.3
(Ph), 128.3 (Ph), 128.3 (Ph), 128.2 (Ph), 128.1 (Ph), 128.1 (Ph), 128.0 (Ph), 128.0 (Ph), 127.9 (Ph), 127.8
(Ph), 127.8 (Ph), 127.8 (Ph), 127.7 (Ph), 127.7 (Ph), 127.6 (Ph), 127.6 (Ph), 127.4 (Ph), 100.1 (d, JC-P = 3.6
Hz, C1, C1’), 83.7 (t, JC-P = 3.6 Hz, C3, C3’), 78.9 (t, JC-P = 7.5 Hz, C2, C2’), 77.8 (C4, C4’), 75.2 (C5, C5’),
75.0 (OCH2Ph), 73.5 (OCH2Ph), 70.8 (OCH2Ph), 69.2 (d, JC-P = 8.2 Hz, OCH2Ph), 69.1 (d, JC-P = 5.4 Hz,
OC’H2Ph), 69.0 (OCH2Ph), 68.7 (C6, C60), 68.2 (d, JC-P = 10.3 Hz, OCH2), 68.2 (d, JC-P = 6.0 Hz, OC’H2),
32.0, 30.1, 29.8, 29.7, 29.7, 29.7, 29.6, 29.5, 29.4, 29.1, 25.4, 25.3, 22.7, 14.2; 31P-NMR (CDCl3,122 MHz):
δ
(ppm)
−
1.55,
1.80 (ratio 1/1.1). HR-MS (ESI): C57H75NaO9P [M + Na]+ requires: 957.5041; found:
−
957.5038.
3.3.3. Benzyl 3,4,6-tri-O-benzyl-2-O-[(benzyl)(cholesteryl)phosphonato]-β-D-glucopyranoside [or
benzyl cholesteryl ((2R,3R,4S,5R,6R)-2,4,5-tris(benzyloxy)-6-((benzyloxy)methyl)tetrahydro-2H-
pyran-3-yl) phosphate] 4c
From cholesterol (79 mg) following general procedure, TLC monitoring using EtOAc-pentane
1:3 as eluent, flash chromatography of the crude product (1:4 EtOAc-pentane) afforded 4c (yield 70%)
as a white solid. Rf = 0.56. 1H-NMR (CDCl3, 500 MHz):
δ
(ppm) 7.35–7.00 (m, 25H, Ph), 5.12 (m,
2Ph), 4.78–4.66 (m, 2H, C 2Ph), 4.62–4.52 (m, 2H,
2Ph), 4.47 (d, J = 6 Hz, 1H, H1), 4.46–4.42 (m, 2H, C 2Ph), 4.34 (m, 1H, H2), 4.05 (m, 1H, OCH-Chol),
1H, C=CH-Cholesterol), 4.98–4.79 (m, 4H, 2
×
CH
H
C
H
H
3.69–3.57 (m, 4H, H3, H4, H6a, H6b), 3.41 (m, 1H, H5), 2.34–2.11 (m, 2H, CH2-Chol), 1.98–1.65 (m, 5H,
Chol), 1.63–1.12 (m, 12H, Chol), 1.11–0.63 (m, 21H, Chol), 0.60–0.53 (m, 3H, Chol); 13C-NMR (CDCl3,
126 MHz):
128.0, 127.9, 127.8, 127.7, 127.6, 127.4, 122.7 (C=
C-P = 3.7 Hz, C3), 78.9 (t, JC-P = 6.7 Hz, C2, C2’), 78.6 (d, JC-P = 6.0 Hz, OCH-Chol), 78.5 (d, JC-P = 5.8
Hz, OC’H-Chol), 77.8 (C4, C4’), 75.1 (C5, C5’), 75.0 (O H2Ph), 74.9 (O H2Ph), 73.5 (O H2Ph), 70.8
(O H2Ph), 69.0 (d, JC-P = 5.5 Hz, O H2Ph), 68.7 (C6, C6’), 56.7, 56.2, 49.8, 42.3, 39.8, 39.6, 36.7, 36.6,
36.3, 36.2, 35.8, 31.9, 31.8, 29.4, 29.3, 28.3, 28.1, 24.3, 23.9, 22.9, 22.6, 21.0, 19.3, 19.2, 18.8, 11.9. 31P-NMR
(CDCl3, 202 MHz): (ppm) 2.60,
2.98 (ratio 1/1.3). HR-MS (ESI): C68H88O9P [M + H]+ requires:
1079.6160; found: 1079.6170.
δ
(ppm) 139.5 (
C
=CH, Chol), 138.4, 138.1, 137.9, 137.1, 136.4, 128.6, 128.4, 128.3, 128.2, 128.1,
C
H, Chol), 100.2 (d, JC-P = 3.5 Hz, C1, C1’), 83.7 (d,
J
C
C
C
C
C
δ
−
−
3.3.4. Benzyl 3,4,6-tri-O-benzyl-2-O-[(benzyl)(5α-cholestan-3β-yl)phosphonato]-β-D-glucopyranoside
[or benzyl cholestanyl ((2R,3R,4S,5R,6R)-2,4,5-tris(benzyloxy)-6-((benzyloxy)methyl)tetrahydro-2H-
pyran-3-yl) phosphate 4d
From 5α-cholestan-3β-ol (79 mg) following general procedure, TLC monitoring by TLC using
EtOAc-pentane 1:3 as eluent, flash chromatography of the crude product (1:3 EtOAc-pentane) afforded
1
4d (yield 74%) as a white solid. Rf = 0.37. H-NMR (CDCl3, 500 MHz):
δ
(ppm) 7.46–7.09 (m, 25H, Ph),
2Ph), 4.70–4.61 (m, 2H, C 2Ph), 4.57–4.56
2Ph), 4.54 (d, J = 8.3 Hz, 1H, H1), 4.45–4.40 (m, 1H, H2), 4.23–4.09 (m, 1H, OCH-Chol),
4.97 (m, 3H, C
H
HPh, CH
2Ph), 4.92–4.74 (m, 3H, C
H
HPh, CH
H
(m, 2H, C
H

Molecules 2020, 25, 2829
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3.81–3.66 (m, 4H, H3, H4, H6a, H6b), 3.51 (m, 1H, H5), 1.95 (m, 1H, Chol), 1.86–1.73 (m, 2H, Chol),
1.63–1.50 (m, 4H, Chol), 1.44 (d, J = 7.4 Hz, 1H, Chol), 1.41–0.94 (m, 20H, Chol), 0.93–0.84 (m, 9H, Chol),
0.82–0.70 (m, 2H, Chol), 0.69–0.60 (m, 6H, Chol), 0.55–0.39 (m, 1H, Chol); 13C-NMR (CDCl3, 126 MHz):
δ
(ppm) 138.4, 138.1, 137.9, 137.2, 136.5, 128.4, 128.3, 128.3, 128.3, 128.3, 128.3, 128.0, 128.0, 128.0, 127.9,
127.8, 127.8, 127.8, 127.8, 127.7, 127.7, 127.7, 127.5, 127.4, 100.2 (d, JC-P = 1.9 Hz, C1, C1’), 83.7 (d, JC-P
3.7 Hz, C3, C3’), 78.9 (d, JC-P = 7.2 Hz, C2), 78.8 (d, JC-P = 7.0 Hz, C20), 78.6 (d, JC-P = 6.0 Hz, O
H-Chol),
77.8 (C4, C4’), 75.1 (C5, C5’), 75.0 (O H2Ph), 74.7 (O H2Ph), 73.5 (O H2Ph), 70.8 (O H2Ph), 69.0 (d,
C-P = 5.4 Hz, O H2Ph), 68.7 (C6), 56.5, 56.3, 54.0, 44.3, 42.6, 40.0, 39.6, 36.6, 36.2, 35.8, 35.6, 35.1, 32.0,
=
C
C
C
C
C
J
C
29.3, 29.1, 28.5, 28.3, 28.1, 24.2, 23.9, 22.9, 22.6, 21.2, 18.7, 12.2, 12.1. 31P-NMR (CDCl3,122 MHz)
δ (ppm)
−2.47, −2.85 (ratio 1/1.4). HR-MS (ESI): C68H90O9P [M + H]+ requires: 1081.6317; found: 1081.6309.
3.3.5. Benzyl 3,4,6-tri-O-benzyl-2-O-[(benzyl)[(1,3,4,6-tetrabenzyl-β-d-glucopyranos-2-
yl)phosphonato]-β-d-glucopyranoside [or benzyl bis((2R,3R,4S,5R,6R)-2,4,5-tris(benzyloxy)-6-
((benzyloxy)methyl)tetrahydro-2H-pyran-3-yl) phosphate] 4e
From compound
1 (108 mg) following general procedure, TLC monitoring using EtOAc-pentane
1:3 as eluent, flash chromatography of the crude product (1:3 EtOAc-pentane) afforded 4e (yield 53%)
1
as a white solid. Rf = 0.36. H-NMR (CDCl3 500 MHz):
δ
(ppm) 7.49–7.41 (m, 4H, Ph), 7.37–7.27 (m,
2Ph), 4.73 (d, J = 10.8 Hz, 2H,
2Ph), 4.44–4.39 (m, 1H, H2), 4.35 (m, 1H,
H20), 4.30 (d, J = 6.9 Hz, 1H, H1), 4.29 (d, J = 6.9 Hz, 1H, H10), 3.68 (m, 2H, H6), 3.61 (m, 2H, H60),
3.53–3.36 (m, 4H, H4, H40, H3, H30), 3.35–3.26 (m, 2H, H5, H50); 13C-NMR (CDCl3,126 MHz):
(ppm)
26H, Ph), 7.25–7.12 (m, 13H, Ph), 7.07 (m, 2H, Ph), 5.01–4.84 (m, 6H, 3
×
CH
C
H
2Ph), 4.71–4.66 (m, 2H, C 2Ph), 4.66–4.45 (m, 8H, 4
H
×
CH
δ
138.5, 138.2, 138.0, 137.3, 137.3, 128.4, 128.4, 128.3, 128.3, 128.3, 128.2, 128.2, 127.9, 127.9, 127.8, 127.8,
127.8, 127.7, 127.7, 127.7, 127.6, 127.5, 127.5, 127.4, 127.4, 100.2 (d, JC-P = 2.9Hz, C10), 99.8 (d, JC-P = 4.2
Hz, C1), 83.6 (d, JC-P = 4.8 Hz, C30), 83.5 (d, JC-P = 3.6 Hz, C3), 79.1 (d, JC-P = 7.4 Hz, C20), 78.6 (d, JC-P
= 6.8 Hz, C2), 77.7 (C4’), 77.6 (C4), 75.0 (C5), 74.8 (C5’), 74.8 (O
74.7 (O H2Ph), 73.4 (O H2Ph), 73.4 (O H2Ph), 70.9 (O H2Ph), 70.2 (O
(ppm) 3.64. HR-MS (ESI): C75H77NaO14P [M
C
H2Ph), 74.8 (OCH2Ph), 74.7 (OCH2Ph),
C
C
C
C
C
H2Ph), 69.3 (d, JC-P = 5.0 Hz,
O
C
H2Ph), 68.7 (C6, C60); 31P-NMR (CDCl3,122 MHz)
δ
−
+ Na]+ requires: 1255.4943; found: 1255.4949.
3.4. Procedure for the one-step Synthesis of 4e
To a solution of benzyl 3,4,6-tri-O-benzyl-
β-d-glucopyranoside (1) (783 mg, 1.45 mmol, 2 eq.) and
benzyloxy bis(diisopropylamino)phosphine (297 mg, 0.88 mmol, 1.2 eq.) in 9 mL of acetonitrile was
added 1H-tetrazole (4.95 mL of a 0.45 solution in MeCN, 2.2 mmol, 3 eq.) at rt. Then the mixture was
stirred overnight at rt. After full conversion of the starting glucoside (TLC using EtOAc-pentane 1:4.5
as eluent, intermediate phosphite Rf = 0.3), the mixture was cooled to 0 ◦C, then t-BuOOH (170
µL,
0.88 mmol, 1.2 eq.) dissolved in 15 mL of DCM was added and the reaction mixture was allowed to
warm to rt. After 4 h, TLC using EtOAc-pentane 1:3 as eluent indicated that the product 4e (Rf = 0.36)
was formed and no starting material remained. The white solid was filtered, the organic phase was
collected, concentrated and purified by silica gel chromatography, same as in previous section.
3.5. Procedure for the Debenzylation of Phosphodiesters 4a and 4e
3.5.1. d-Glucose-2-phosphate (G2P) 5a
To a solution of phosphate 4a (100 mg, 0.12 mmol) in 5 mL of EtOAc was added 10% Pd/C (60 mg).
The mixture was stirred under 1 atm H2 at rt. After 24 h, Pd/C was filtered with a celite layer. The
organic phase was concentrated to afford G2P as a white solid, which is showing high purity as seen
1
by NMR(90% yield,
J = 7.6 Hz, 0.6H, H1
(t, J = 7.7 Hz, 0.6H, H3
α
/
β
= 5:3). H-NMR (D2O, 300 MHz)
δ
(ppm) 5.33 (d, J = 3.3 Hz, 1H, H1
), 3.86–3.59 (m, 5.8H, H2 , H3 , H5 , H6 , H6
), 3.47–3.36 (m, 2.2H, H4 , H4 , H5 ). NMR data were consistent with the
α
), 4.69 (d,
β
), 3.98–3.88 (m, 1H, H2
α
β
α
α
α
β), 3.58
β
α
β
β
reported [6].

Molecules 2020, 25, 2829
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3.5.2. Agrocinopine D 5b
To a solution of phosphate 4e (100 mg, 0.08 mmol) in 5 mL of methanol was added 10% Pd/C (60
mg). The mixture was stirred under 1 atm H2 at rt for 1 day. TLC monitoring using DCM, acetone,
MeOH, H2O 4:3:3:1 (vol.) shows formation of 5b (Rf = 0.48). After filtration with a celite layer, the
organic phase was concentrated to afford a white solid, which was further purified by ion exchange
chromatography on a DEAE-Sephadex column pre-washed with water. The column was then eluted
with a 5% to 100% gradient 1M ammonium carbonate. Freeze-drying the resulting fractions allows to
1
get 5b as a white solid in 78% yield. H-NMR (D2O, 500 MHz)
δ
(ppm) 5.39 (d, J = 3.6 Hz, 1H, H1
), 3.93–3.60 (m, 6H, H2 , H3 , H3 , H5 , H6
). HR-MS (ESI) [M
H]−: 421.0753; found: 421.0735. NMR
α),
α,
4.75 (d, J = 7.9 Hz, 0.5H, H1
H6 ), 3.51–3.43 (m, 2H, H4
β
), 4.09–3.96 (m, 1H, H2
, H4 , H5
data were consistent with the reported [17]. HR-MS (ESI): C12H22O14P [M
found: 421.0735.
α
β
α
β
α
β
α
β
β
−
−
H]− requires: 421.0753;
4. Conclusions
A short and flexible access to the rare glucose-2-phosphate G2P esters including agrocinopine D is
proposed. It relies on the combination of the use of benzyl 3,4,6-tri-O-benzyl- -d-glucopyranoside
β
prepared in two steps from the commercially available tri-O-benzyl-d-glucal and the phosphoramidite
coupling strategy. It is applied to short and easy accesses to G2P itself and agrocinopine D.
Supplementary Materials: The following are available online, NMR spectra for all new compounds.
Author Contributions: Conceptualization, Y.Q., L.S. and M.A., methodology, Y.Q., L.S., Q.Z., S.-Z.L. and M.A.;
validation, Y.Q., L.S., Q.Z., S.-Z.L. and M.A.; formal analysis, Y.Q., L.S., Q.Z., S.-Z.L. and M.A.; investigation, Y.Q.,
L.S., Q.Z., S.-Z.L. and M.A.; writing—original draft preparation, Q.Z. and Y.Q.; writing—review and editing, Y.Q.;
supervision, Y.Q., L.S. and M.A.; project administration, Y.Q.; funding acquisition, Y.Q. and L.S. All authors have
read and agreed to the published version of the manuscript.
Funding: This research received no additional external funding.
Acknowledgments: The authors are grateful to CNRS and MESRI for financial support and to the China
Scholarship Council program for a scholarship to Qiang Zhang.
Conflicts of Interest: The authors declare no conflict of interest.
References
1.
Beck Von Bodman, S.; Hayman, G.T.; Farrand, S.K. Opine catabolism and conjugal transfer of the nopaline Ti
plasmid pTiC58 are coordinately regulated by a single repressor. Proc. Natl. Acad. Sci. USA 1992, 89, 643–647.
[CrossRef] [PubMed]
2.
3.
4.
5.
6.
Ellis, J.G.; Kerr, A.; Petit, A.; Tempe, J. Conjugal transfer of nopaline and agropine Ti-plasmids-the role of
agrocinopines. Mol. Gen. Genet. 1982, 186, 269–274. [CrossRef]
Reader, J.S.; Ordoukhanian, P.T.; Kim, J.-G.; de Crécy-Lagard, V.; Hwang, I.; Farrand, S.; Schimmel, P. Major
biocontrol of plant tumors targets tRNA synthetase. Science 2005, 309, 1533. [CrossRef] [PubMed]
Roberts, W.P.; Tate, M.E.; Kerr, A. Agrocin 84 is a 6-N-phosphoramidate of an adenine nucleotide analogue.
Nature 1977, 265, 379–381. [CrossRef]
Thompson, R.J.; Hamilton, R.H.; Pootjes, C.F. Purification and characterization of agrocin 84. Antimicrob.
Agents Chemother. 1979, 16, 293–296. [CrossRef]
El Sahili, A.; Li, S.-Z.; Lang, J.; Virus, C.; Planamente, S.; Ahmar, M.; Guimaraes, B.G.; Aumont-Nicaise, M.;
Vigouroux, A.; Soul
quorum-sensing regulation in Agrobacterium tumefaciens. PLoS Pathog. 2015, 11, e1005071. [CrossRef]
Li, S.-Z.; Vigouroux, A.; Ahmar, M.; El Sahili, A.; Soul re, L.; Sago, L.; Cornu, D.; Mor ra, S.; Queneau, Y.
Synthesis of a non-natural glucose-2-phosphate ester able to dupe the acc system of Agrobacterium fabrum.
Org. Biomol. Chem. 2019, 17, 1090–1096. [CrossRef]
ère, L.; et al. A pyranose-2-phosphate motif is responsible for both antibiotic import and
7.
8.
è
é
Mikkola, S. Hydrolysis and Isomerization of Sugar Phosphates and Carbohydrate Phosphodiesters. Curr.
Org. Chem. 2013, 17, 1525–1544. [CrossRef]

Molecules 2020, 25, 2829
12 of 13
9.
Tagliabracci, V.S.; Heiss, C.; Karthik, C.; Contreras, C.J.; Glushka, J.; Ishihara, M.; Azadi, P.; Hurley, T.D.;
DePaoli-Roach, A.A.; Roach, P.J. Phosphate incorporation during glycogen synthesis and Lafora disease. Cell
Metab. 2011, 13, 274–282. [CrossRef]
10. Chikwana, V.M.; Khanna, M.; Baskaran, S.; Tagliabracci, V.S.; Contreras, C.J.; DePaoli-Roach, A.; Roach, P.J.;
Hurley, T.D. Structural basis for 20-phosphate incorporation into glycogen by glycogen synthase. Proc. Natl.
Acad. Sci. USA 2013, 110, 20976–20981. [CrossRef]
11. Young, L.E.A.; Brizzee, C.O.; Macedo, J.K.A.; Murphy, R.D.; Contreras, C.J.; DePaoli-Roach, A.A.; Roach, P.J.;
Gentry, M.S.; Sun, R.C. Accurate and sensitive quantitation of glucose and glucose phosphates derived from
storage carbohydrates by mass spectrometry. Carbohydr. Polym. 2020, 230, 115651. [CrossRef] [PubMed]
12. Kokesh, F.C.; Cameron, D.A.; Kakuda, Y.; Kuras, P.V. Hydrolysis of α-d-glucopyranose 1, 2-cyclic phosphate:
The effect of pH and temperature on the product distribution, and the position of opening of the phosphate
diester ring in formation of d-glucose 2-phosphate. Carbohydr. Res. 1978, 62, 289–300. [CrossRef]
13. Kokesh, F.C.; Stephenson, R.K.; Kakuda, Y. Inibition of potato starch phosphorylase by α-d-glucopyranose-1,
2-cyclic phosphate. Biochim. et Biophys. Acta 1977, 483, 258–262. [CrossRef]
14. Whiteside, T.; Carreira, L.; Hilal, S. Estimation of phosphate ester hydrolysis rate constants. II. Acid and
general base catalyzed hydrolysis. QSAR Comb. Sci. 2007, 26, 587–595. [CrossRef]
15. Farrar, K.R. Glucose-2 phosphate: Its preparation and characterisation by hydrolysis studies. J. Chem. Soc.
1949, 3131–3135. [CrossRef]
16. Roy, B.; Depaix, A.; P
érigaud, C.; Peyrottes, S. Recent trends in nucleotide synthesis. Chem. Rev. 2016, 116,
7854–7897. [CrossRef]
17. Lindberg, M.; Oscarson, S. Synthesis of d-Glucos-2-yl Sucros-2-yl Phosphate (Agrocinopin C) and bis
(d-glucos-2-yl) Phosphate (Agrocinopin D). J. Carbohydr. Chem. 1993, 12, 1139–1147. [CrossRef]
18. Froehler, B.C.; Matteucci, M.D. Nucleoside h-phosphonates: Valuable intermediates in the synthesis of
deoxyoligonucleotides. Tetrahedron Lett. 1986, 27, 469–472. [CrossRef]
19. Stawinski, J.; Thelin, M. Studies on the activation pathway of phosphonic acid using acyl chlorides as
activators. J. Chem. Soc. Perkin Trans. 2 1990, 849–853. [CrossRef]
20. Franzkowiak, M.; Thiem, J. Synthesen von Agrocinopin A und B. Liebigs. Ann. Chem. 1987, 1065–1071.
[CrossRef]
21. Hardegger, E.; De Pascual, J. Glucoside und
β-1,3,4,6-Tetraacetyl-glucose aus Triacetyl-glucosan-α<1, 2>
β<1, 5>. Helv. Chim. Acta 1948, 31, 281–286. [CrossRef] [PubMed]
22. Dick, W.E., Jr. Hydrolyses of intermediate acetoxonium ions derived from d-glucose. Carbohydr. Res. 1972
21, 255–268. [CrossRef]
,
23. Helferich, B.; Zirner, J. Zur Synthese von Tetraacetyl-hexosen mit freiem 2-Hydroxyl. Synthese einiger
Disaccharide. Chem. Ber. 1962, 95, 2604–2611. [CrossRef]
24. Wang, T.; Nigudkar, S.S.; Yasomanee, J.P.; Rath, N.P.; Stine, K.J.; Demchenko, A.V. Glycosyl nitrates in
synthesis: Streamlined access to glucopyranose building blocks differentiated at C-2. Org. Biomol. Chem.
2018, 16, 3596–3604. [CrossRef]
25. Lubineau, A.; Queneau, Y. Stereochemical variations in aqueous cycloadditions using glyco-organic substrates
as a consequence of chemical manipulations on the sugar moiety. Tetrahedron 1989, 45, 6697–6712. [CrossRef]
26. Suzuki, K.; Nonaka, H.; Yamaura, M. Reductive Ring-Opening Reaction of 1, 2-O-Benzylidene and
1,2-O-p-Methoxybenzylidene-α-d-glucopyranose Using Diisobutyl Aluminum Hydride. J. Carbohydr. Chem.
2004, 23, 253–259. [CrossRef]
27. Lecourt, T.; Herault, A.; Pearce, A.J.; Sollogoub, M.; Sinaÿ, P. Triisobutylaluminium and diisobutylaluminium
hydride as molecular scalpels: The regioselective stripping of perbenzylated sugars and cyclodextrins. Chem.
Eur. J. 2004, 10, 2960–2971. [CrossRef]
28. Gordon, D.M.; Danishefsky, S.J. Displacement reactions of a 1,2-anhydro-
α-d-hexopyranose: Installation of
useful functionality at the anomeric carbon. Carbohydr. Res. 1990, 206, 361–366. [CrossRef]

Molecules 2020, 25, 2829
13 of 13
29. Somasundaram, D.; Balasubramanain, K.K.; Shanmugasundaram, B. Simple and mild stereoselective
O-glycosidation using 1, 2-anhydrosugars under neutral conditions. Tetrahedron Lett. 2019, 60, 764–767.
[CrossRef]
30. Barone, A.D.; Tang, J.-Y.; Caruthers, M.H. In situ activation of bis-dialkylaminophosphines—a new method
for synthesizing deoxyoligonucleotides on polymer supports. Nucleic Acids Res. 1984, 12, 4051–4061.
[CrossRef]
Sample Availability: Not available.
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2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access
article distributed under the terms and conditions of the Creative Commons Attribution
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