Regioselective and stereocontrolled syntheses of protected L-glycosides from L-arabinofuranosides

Article abstract of DOI:10.1016/j.carres.2019.107901

Synthesis of novel mono- and di-O-protected L-arabinofuranoside derivatives was described via regioselective base-catalyzed acylations of methyl α- and β-L-arabinofuranosides with acyl chlorides. A new method for selective 3(2)-O-acylation of 5-O-silyl (trityl) L-arabinofuranosides was investigated based upon generation of organoboron compounds using L-Selectride and subsequent reaction of salt carbohydrate species with pivaloyl or 4-chlorobenzoyl chloride as the electrophile. Syntheses of methyl 2,3-anhydro-L-furanosides were accomplished from selectively protected methyl L-arabinofuranosides. 2(3)-Deoxy-L-pentofuranosides, including 2-deoxy-L-ribofuranoside, and their 5-O-blocked derivatives were prepared by stereoselective reductions of 2,3-anhydro-L-furanosides with L-Selectride.

Full text of DOI:10.1016/j.carres.2019.107901

Journal Pre-proof
Regioselective and stereocontrolled syntheses of protected L-glycosides from L -
arabinofuranosides
Grigorii G. Sivets
PII:
S0008-6215(19)30639-1
DOI:
https://doi.org/10.1016/j.carres.2019.107901
CAR 107901
Reference:
To appear in: Carbohydrate Research
Received Date: 29 October 2019
Revised Date: 20 December 2019
Accepted Date: 20 December 2019
Please cite this article as: G.G. Sivets, Regioselective and stereocontrolled syntheses of protected L-
glycosides from L -arabinofuranosides, Carbohydrate Research (2020), doi: https://doi.org/10.1016/
j.carres.2019.107901.
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition
of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of
record. This version will undergo additional copyediting, typesetting and review before it is published
in its final form, but we are providing this version to give early visibility of the article. Please note that,
during the production process, errors may be discovered which could affect the content, and all legal
disclaimers that apply to the journal pertain.
© 2019 Published by Elsevier Ltd.

1

Regioselective and stereocontrolled syntheses of protected
arabinofuranosides
L
-glycosides from -
L
Grigorii G.Sivets
Institute of Bioorganic Chemistry, National Academy of Sciences of Belarus, 5/2 Acad. Kuprevicha, Minsk 220141, Belarus, E-mail:
gsivets@mail.ru
Declarations of interest: none
Abstract: Synthesis of novel mono- and di-O-protected
catalyzed acylations of methyl α- and β- -arabinofuranosides with acyl chlorides. A new method for selective 3(2)-O-acylation
of 5-O-silyl (trityl) -arabinofuranosides was investigated based upon generation of organoboron compounds using -Selectride
and subsequent reaction of salt carbohydrate species with pivaloyl or 4-chlorobenzoyl chloride as the electrophile. Syntheses of
methyl 2,3-anhydro- -furanosides were accomplished from selectively protected methyl -arabinofuranosides. 2(3)-Deoxy-
pentofuranosides, including 2-deoxy- -ribofuranoside, and their 5-O-blocked derivatives were prepared by stereoselective
reductions of 2,3-anhydro- -furanosides with -Selectride.
L-arabinofuranoside derivatives was described via regioselective base-
L
L
L
L
L
L-
L
L
L
Keywords: L-arabinofuranosides / protecting groups / regioselective acylation reactions / anhydro- L-furanosides /stereoselective reduction / L-
Selectride
1.Introduction
Carbohydrates are an interesting class of biomolecules which play essential roles in various biological processes and
exploit as scaffolds for the generation of different bioactive compounds. As the most abundant natural resource, they
have found widespread application in constructing pharmaceuticals, polymers, oligosaccharides and
glycoconjugates. Selective modifications of
D-monosaccaharides are widely studied and include regioselective
functionalization on hydroxyl groups, using different methods [1-4] based upon organotin catalysis [5], metal- and
organo-catalysis [6], organoboron reagents [7] and enzyme-mediated selective protection of unprotected glycosides
[8] or deprotection of fully acylated glycoside [9]. Selectively protected
used as both intermediates and building blocks for further use in glycosylation reactions [10,11]. A set of modified
-pentose derivatives have been prepared by different chemical methods and utilized in the development of
nucleosides as antiviral agents [12]. Identification of several modified nucleosides derived from -sugars as potent
antiviral agents with lower toxicity compared to the -nucleosides and medicinal application of some -enantiomers
D- and L-monosaccharide derivatives can be
L
L-
L
D
L
of natural nucleosides have emerged important outcome of broad investigations in the past decades [13].
Fig.1.
Fig.1. L-Pentofuranoside derivatives as versatile intermediates in synthesis of modified L-sugars and oligosaccharides deriving from L-arabinose
The most active
ribofuranosyl)thymine (β- -thymidine, telbivudine), and
antiviral activities approved for use in therapy of acute and chronic hepatitis B infections, and HIV. Various
approaches have been reported for preparation of unnatural -monosaccharides, especially -ribose and
deoxyribose derivatives, which are valuable precursors for the synthesis of -pentofuranonucleosides [12,14]. It
should be emphasized that naturally occurring -deoxy sugars belonging to different classes of deoxygenated hexose
L-nucleoside analogues,
L-3′-thiacytidine (lamivudine,
L-TC), 1-(2-deoxy-β-L-
L
L
-5-fluoro-3-thiacytidine ( -FTC) with potent and selective
L
L
L
L-
L
L
derivatives were found to be constituents of oligosaccharide moieties in glycoconjugates or antibiotics with
antibacterial or antitumor activity [15].
Furthermore, it has been shown that 2-deoxy-
Noteworthy also is another important aspect of synthetic use of
agents. So selectively protected α- -arabinofuranoside derivatives, as well as their
L
-ribose and its analogues displayed antitumor activities [16]
-monosaccharides in development of antibacterial
-enantiomers, have been used as
L
D
L
building blocks in the synthesis of a series of arabinofuranosyl-containing oligosaccharides [10,11,17-20] that are
key structural motif in mycobacterial arabinogalactan and lipoarabinomannan [21] found in the wall cell of
2

mycobacteria. Synthetic routes to 2,3-anhydrofuranose derivatives have been studied from
-glytamic acid [22-25], and 2,3-anhydro- -sugar thioglycosides have found implementation as intermediates in the
synthesis of C-2 functionalized oligosaccharides [26, 27] and 2-deoxy-glycosides. To the best our knowledge, there
have been no reports on syntheses of various isomeric 2,3-anhydro- -furanosides. Thus, the study of synthetic
approaches to diverse protected -pentofuranoside derivatives (Fig.1) useful for glycosylation reactions and building
-nucleosides and -furanose-containing oligosaccharides is of considerable interest from
D-xylose, -arabinose or
L
D
L
L
modified
L
-sugars,
-arabinose.
The present paper describes synthetic base-catalyzed routes to different selectively protected α- and β-
arabinofuranosides, syntheses of isomeric 2,3-anhydro- -furanosides and novel deoxy- -pentofuranoside derivatives
using regio- and stereoselective transformations of methyl -arabinofuranosides readily available from -arabinose.
Special attention in this research was directed to regioselective protection of hydroxyl groups of
arabinofuranosides with various protecting groups and elaboration of new synthetic methods for preparation of
L
L
available
L
L-
L
L
L
L
L-
methyl 2(3)-deoxy-α-L-pentofuranoside derivatives via epoxide ring opening of 2,3-anhydro-L-furanosides by a
complex hydride.
2. Results and discussion
2.1.Regioselective transformations of methyl α-L-arabinofuranoside (1a)
2.1.1. Regioselective acylations of α-
In continuation of our previous investigations into regioselective syntheses of various
selective acylations of individual unprotected methyl α- and β- -arabinofuranosides 1a and 1b prepared by
methanolysis of -arabinose were studied under different reaction conditions with acyl chlorides. It is interesting to
note that a number of reports have been described regioselective acylations of mainly -hexopyranoside derivatives
L-arabinofuranosides with acyl chlorides
L
-pentose derivatives, [28]
L
L
D
with application of the different acylating agents to prepare selectively protected (benzoylated, pivaloylated and
acetylated) carbohydrates using organocatalytic processes [1, 29-33]. However, preparation of mono- and di-O-
acylated L-arabinofuranosides was little explored [11, 17, 18, 28, 34]. As reported earlier, selective acylation of α-L-
arabinofuranoside 1a with pivaloyl chloride in a mixture of solvents in the presence of pyridine as a catalyst resulted
in the 3,5-di-O-pivloyl derivative 2 as the main product [28]. The regioselectivity of this reaction was established
after separation of a mixture of O-acylated L-arabinosides by column chromatography on silica gel (Scheme 1,
conditions a1, table 1, entry 1). The formation of the 3,5-di-O-pivalate 2 together with 2,5-di- (3), 2,3,5-tri- (4) and
5-O-pivaloyl (5) derivatives was observed in a ratio of 6:2:2.2:1 in combined 78% overall yield as a result of the
acylation reaction with 2 equiv of pivaloyl chloride. Additionally, selective acylation of 1a with 2.1 equiv of
0
pivaloyl chloride in pyridine at 0 C gave the 5-O-pivaloyl-α-
L-arabinofuranoside (5) in 64% yield as the main
product along with the di-O-pivaloyl derivatives 2 and 3 (17%) in a ratio of 2:1 (table 1, entry 2). In contrast to
unsuccessful, selective 6-O-pivaloylation of a number of methyl hexopyranosides [35], regioselective acylation of
1a with pivaloyl chloride in pyridine proceeds selectively on the primary 5-OH group over secondary hydroxyl
groups in α-L-arabinofuranoside. Regioselective acylation of 1a with the bulky electrophile in pyridine may be
explained by a higher reactivity of the primary 5-OH group compared to secondary hydroxyl groups. It has
previously shown [28] that a simple two-step acylation of triol 1a using an overall twofold excess of 4-
chlorobenzoyl chloride as acylating agent in the presence of pyridine resulted in the target 3,5- and 2,5-di-O-
chlorobenzoylated α-
L-arabinofuanosides after chromatography on silica gel of regioisomeric products.
Alternatively, direct regioselective acylation of methyl α-
L-arabinofuranoside (1a) with 1 equiv of 4-chlorobenzoyl
chloride in a mixture of anhydrous methylene chloride and pyridine at room temperature followed by the same
3

acylation at 0 oC→rt furnished a mixture of acylated glycosides with 67% overall yield (a ratio of the di-O-acylated
L-glycosides - 2.5:1) and more lower regioselectivity than in the previous experiment (table 1, entries 4 and 3).
Scheme 1
o
Scheme 1. Reagents and conditions. a1) ref. 28 i) 1a, 1 equiv PivCl, CH2Cl2 1.5 equiv Py, 0 C→rt, ii) 1 equiv PivCl, CH2Cl2 1 equiv Py, 0
oC→rt; a2) 2.1 equiv PivCl, Py 0 0C, 6 h and 2h, rt; b1) ref. 28, 1a, 4ClBzCl, CH2Cl2, Py, 0 oC→rt; b2) i) 1 equiv 4ClBzCl, CH2Cl2 1equiv Py, rt,
o
ii) 1 equiv 4ClBzCl, CH2Cl2 1 equiv Py, 0 C→rt; c1) i) 1a, 1.9 equiv BzCl, THF/Py, 1 equiv DIPEA, rt, 5 h; ii) 1 equiv Et3N, 48 h rt; c2) i) 1a,
o
2.7 equiv BzCl, THF/Py, 1 equiv DIPEA, rt, 18 h; ii) 1 equiv Et3N, 18 h, rt; and then 3 h at 35-37 C; d) i) 9, 1.5 equiv 4ClBzCl, CH2Cl2, 2.1
equiv Py, 0 0C→rt, 1 h and then 20 h, rt; ii) 1 equiv 4ClBzCl, CH2Cl2, rt, 3 h.
The acylation reaction of 1a with 1.9 equiv of benzoyl chloride in a mixture of tetrahydrofuran/pyridine in
the presence of iPr2NEt and Et3N gave a mixture of 3,5- and 2,5-di-O-benzoylated L-arabinofuanosides 10 and 11 in
a ratio of 1:1 and 5-O-benzoyl derivative 9 (37%) after chromatography on silica gel (conditions c1, entry 5). The
use of 2.7 equiv of benzoyl chloride in the reaction under consideration in the presence of two amines gave rise to
the 5-O-benzoyl derivative 9 as the main product (64%) and a mixture of the regioisomeric dibenzoyl derivatives 10
and 11 (25%) (table 1, entry 6, conditions c2). Further, selective acylation of 5-O-benzoyalated α-L-
arabinofuranoside 9 with 2.5 equiv of 4-chlorobenzoyl chloride (entry 7, conditions d) in anhydrous methylene
chloride and pyridine afforded a mixture of regioisomeric di-O-benzoates 12 and 13 in 60% overall yield, and the
tri-O-benzoate 14 (6%) after chromatography on silica gel. It should be noted that the formation of mixtures of
acylated L-glycoside derivatives was observed under pyridine-catalysed acylations of 1a (Table 1) in all cases. The
target 3,5 and 2,5-di-O-acyl arabinofuranoside derivatives 2-3 and 6-7 were prepared as individual compounds after
acylation of the starting glycoside with pivaloyl or 4-chlorobenzoyl chloride in a mixture of solvents followed by
chromatographic separation of acylated products. We have found that synthesized isomeric the 3,5- and 2,5-di-O-
benzoylated arabinofuranoside derivatives 10 and 11, 12 and 13 in contrast to the di-O-pivalates (2 and 3) and the
di-O-chlorobenozoates (6 and 7) were inseparable by chromatography on silica gel in different tested conditions.
Table 1. Selective acylations of α-
L-arabinofuranoside 1a and its 5-O-benzoyl derivative 9
Entry
L
-arabinoside
Products (isolated yields, %)
(conditionsa)
Acyl
chloride
PivCl
3,5-di-
2,5-di-
2,3,5-tri-
5-O-acyl
1a (a1)
1a (a2)
1a (b1)c
1a (b2)
1a (c1)
1a (c2)
9 (d)
2(42)
3 (13)
4 (16)
5 (7)
5 (64)
-
-
9 (37)
9 (62)
-
1
2
3
4
5
6
7
PivCl
2/3 (17, ratio 2:1)b
-
8 (24)
8 (14)
-
ClBzCl
ClBzCl
BzCl
BzCl
ClBzCl
6 (40)
6 (38)
10/11 (25, ratio 1:1) b
10/11 (28, ratio 1:1.4) b
12/13 (60, ratio 1.7:1) b
7 (12)
7 (15)
-
14 (6)
a Conditions according to Scheme 1.
bSelectivity ratios were determined by 1H NMR data in CDCl3.
c Yields from ref.28.
2.1.2. Syntheses of selectively protected α-L-arabinofuranosides, 2,3-anhydro-α-L-furanosides and 2(3)-deoxy-α-L-
pentofuranosides
Next, investigation on selective protection of hydroxyl groups in 1a was undertaken to prepare 3,5-di-O-
protected derivatives with different type of protecting groups. Treatment of -glycoside 1a with tert-
butylchlorodiphenylsilane in pyridine gave 5-O-silyl derivative 15 in 82% yield. Regioselective acylation of the
protected α-L-arabinoside in the presence of -Selectride was studied with acyl chlorides (Scheme 2). It can be
L
L
assumed that reactivity difference of the secondary hydroxyl groups in the glycoside 15 with a complex hydride due
to steric hindarance or stereoelectonic effects may be utilized for selective generation of O-activated carbohydrate
4

derivatives on the first step followed by the acylation reaction with the electrophile. Thus, acylation of 5-O-
protected α- -arabinofuranoside 15 in the presence of 1.1 equiv of 1 Li(i-Bu)3BH (L-Selectride) in THF and a
excess of pivaloyl chloride (Scheme 2, conditions b1) resulted in only the 3-O-pivalate 17 (43%) and the 2,3-di-O-
pivalate 18 (57%) after column chromatography on silica gel. The formation of acylated -arabinofuranosides 17
L
M
L
and 18 proceeds via generation of intermediate organoboron compound 16 on the first step as result of reaction of 5-
O-protected arabinoside 15 with L-Selectride in THF. The use of 4-chlobenzoyl chloride instead of pivaloyl chloride
in this reaction gave the 3-O-benzoate 19 (40%) and the 2,3-di-O-benzoate 20 (50%) (conditions b2). The removal
of silyl group in 17 with ammonium fluoride in methanol furnished new 3-O-pivaloyl-α-arabinofuranoside (21) in
88% yield (Scheme 2, conditions c).
5-O-Protected methyl 2,3-anhydro-α-
using sodium methoxide in methanol. The same reaction of mesyl derivative 23 gave also rise to compound 26
(97%) after chromatography on silica gel (Scheme 2, conditions f). Methyl 2,3-anhydro-α- -ribofuranoside (25) was
prepared in 73% yield using two-step process involved mesylation of the 3,5-di-O-pivalate 2 followed by basic
treatment of the intermediate 2-OMs derivative. Reduction of unprotected 2,3-anhydrosugar 25 with an excess of
Selectride gave methyl 2-deoxy-α- -ribofuranoside (28) in 93% yield after column chromatography on silica gel.
L-ribofuranoside 26 was prepared from the mesylate 22 in 80% yield
L
L-
L
The stereoselective reaction of unprotected 2,3-epoxide 25 likely to proceed via generation of intermediate
organoboron compound 27 as a result of interaction of a complex hydride with 5-OH group followed by reduction of
the 2,3-anhydrocycle with
a complex hydride in THF afforded 5-O-protected methyl 2-deoxy-α-
simple treatment of the reaction mixture. Removal of the 2-O-chlorobenzoyl protecting group in protected
arabinoside 23 with methanolic ammonia followed by reduction of intermediate 2-OMs- -arabinoside derivative 24
L-Selectride in THF. Stereospecific reduction of 5-O-silyl derivative of epoxysugar 29 by
L-ribofuranoside 29 in 99% yield after a
L
gave
L-2-deoxyriboside derivative 28 in 73% overall yield (conditions i) from 24.
Scheme 2
Scheme 2. Reagents and conditions. a) 1a, TBDPSCl, Py 82%; b1) i) 15, 1.08 equiv 1M Li(iBu)3BH in THF, 0 oC→rt, 30 min, 2 equiv PivCl, 0
oC; 5 h, rt; ii) 1.4 equiv. PivCl, 0 oC; 18 h, rt, 57% to 18 and 43% to 17 taking account 28% recovery of 15; b2) (i) 15, 1 equiv 1M Li(i-Bu)3BH
o
o
in THF, 0 C→rt, 30 min, (ii) 2.1 equiv 4ClBzCl in THF, 0 C→rt, 4 h, 50% to 20 and 40% to 19 taking account 19% recovery of 15; c) 17,
o
o
o
NH4F, MeOH, 29-30 C, 88%; d) 17, MsCl/Py, DMAP, 0 C→rt, 2 h, 92% to 22; 19, MsCl/Py, DMAP, 0 C→rt, 18 h, 97% to 23; e) MeONa,
MeOH, rt, 80% to 26 from 22; 97% to 26 from 23; f) i) 2, MsCl/Py, ref.28; ii) MeONa, MeOH, rt, 73 % to 25; g) TBDPSCl, Py 85%; h1)
Li(iBu)3BH in THF, -78 oC→rt, 1h, 93% to 28 from 25; h2) Li(iBu)3BH in THF, -78 oC→rt, 15 min, 99% to 29 from 26; i) i) 23, NH3/MeOH, rt,
4 h; ii) 24, Li(iBu)3BH in THF/DME, -78 oC→rt, 18 h, 77% to 29.
Synthesis of methyl 5-O-trityl-2,3-anhydro-α-
Mitsunobu reaction with triphenylphospine (Ph3P) and diisopropylazodicarboxylate (DIAD) starting from 5-O-trityl
-arabinoside derivative 30 (Scheme 3) prepared by tritylation of 1a according the literature protocol described for
-enantiomer [36]. The reduction of the 2,3-epoxy ring in 31 with an excess of -Selectride gave only 5-O-protected
3-deoxy-α- -threo-pentofuranoside 32 which was prepared in 91% yield after column chromatography on silica gel.
L-lyxofuranoside (31) was carried out in 94% yield via the
L
D
L
L
Scheme 3
Scheme 3. Reagents and conditions. a) ref. 36; b) Ph3P, DIAD, THF, rt, reflux,1h, 94%; c) Li(iBu)3BH in THF, -78 oC→rt, 175 min, 91%; d) aq.
CH3COOH, 55 0C, 30 min, 82%; e) ref.22; f) Li(iBu)3BH in THF, -78 oC→rt, 50 min, 92%.
Mild removal of the trityl protecting group in the latter with aqueous acetic acid afforded 3-deoxy-α-
arabinoside 33 in 82% yield. Alternative two-step approach to 33 was studied from arabinoside 1a. 2,3-Anhydro-α-
-lyxofuranoside 34 was synthesized via epoxidation of 1a with Ph3P/DIAD under the Mitsunobu conditions [22].
Selectride reduction of epoxide 34, which proceeds via formation of intermediate 5-O-activated derivative 35
(Scheme 3) under treatment of 2,3-anhydro-α- -lyxofuranoside with an excess of -Selectride, gave methyl 3-
deoxy-α- -arabinofuranoside (33) in 92% yield after chromatography on silica gel.
L-
L
L
L
L
5

The structure of 3-deoxy L-glycoside 33 was confirmed by NMR spectral data. The anomeric proton having
the small value of H-1,2 coupling constant (< 1.0 Hz), characteristic of trans-relationship H1 and H2, displayed as a
singlet at δ 4.8 ppm and signals of protons at C-3 were observed as ddd at δ 2.34 (J = 5.9, J = 9.9, J = 13.4 Hz) and δ
1.66 ppm (J = 1.8, J = 4.8, J = 13.4 Hz), respectively, in the 1H NMR spectrum (CD3OD). The 13C NMR spectrum
of 33 showed C-1 and C-3 at δ 111.12 and δ 35.16 ppm, respectively. The resonances for the anomeric hydrogen of
isomeric 2-deoxy
L-sugar 28 appeared as a double doublet at δ 5.09 ppm (J1,2´ < 1.0, J1,2 = 4.6 Hz) and while did
1
protons at C-2 as ddd and a doublet at δ 2.11 and 2.0 ppm, respectively, in the H NMR spectrum (CDCl3,
experimental part). NMR spectral data of 2-deoxy-
earlier [37].
L-glycoside 29 are very close to those of D-enantiomer described
The results of the selectride reductions of 5-O-protected epoxides 26 and 31 with bulky blocking groups,
and unprotected 2,3-anhydro-α- -ribo- and lyxo-furanosides 25 and 34 indicate that stereoselective cleavages of the
L
2,3-epoxy rings by a complex hydride at C-2 or C-3 are governed by steric factors and polar effects of the
substituents at C-1 and C-4 (5-silyl(trityl)hydroxymethyl/5-hydroxymethyl and α-methoxy groups) as in the case of
the reactivity of epoxide ring in 2,3-anhydro-
epoxide 34 and its trityl derivative 31 reductive reactions occurs exclusively at C-3 due to the stereochemistry of the
substituent at anomeric center with formation of 3-deoxy- -furanosides. Stereoselective ring-opening reactions of
2,3-anhydro-α- -ribofuranoside 25, its silyl derivative 26 with a bulky reducing agent like -Selectride as well as the
2-deoxygenation procedure for 2-OMs α- -arabinofuranoside [28] studied earlier in the similar reaction conditions
proceed in high yields to give 2-deoxy-α- -ribofuranoside derivative. Preferential attack of the reagent at C-2 can be
D-pentofuranosides with various nucleophilic agents [38]. For α-lyxo-
L
L
L
L
L
explained by steric hindrances of the substituents at C-4 and minimal polar effects of α-methoxy group. It should be
noted that application of the sterically bulky selectride at low reaction temperature in the hydride reductions also
favored 2-reduction in α-
2.2. Regioselective transformations of methyl β-
2.2.1. Syntheses of selectively protected β- -arabinofuranosides, 2,3-anhydro-β-
-threo-pentofuranosides
Next, regioselective acylation of methyl β-
chlorobenzoyl chloride in the presence of pyridine under conditions used for α-
L-ribo epoxides.
L
-arabinofuranoside (1b)
L
L-lyxofuranosides and 2(3)-deoxy-
L
L-arabinofuranoside (1b) was conducted with 2.0 equiv of 4-
L
-arabinofuranoside 1a to give rise to
three acylated products (Scheme 4, conditions a). Unlike the α-anomer 1a, predominant formation of 2,5-di-O-
chlorobenzoyl derivative 36 (38% isolated yield) was achieved in this case. Besides, 2,3,5-tri- (37) and 2,3-di-O-
benzoyl (38) β-
accordingly. It is interesting that the direct pyridine-catalyzed acylation of isomeric
in essential differences in regioselectivity (Table 2, entries 1 and 2) which was lower for α-
both -arabinofuranosides were predominantly benzoylated to give regioisomeric the di-O-chlorobenzoyl protected
derivatives without generation of monoacylated -glycosides in the acylation reaction. Benzoylation of unprotected
-glycosides 1a and 1b proceeded in moderate overall yields probably because of low solubility of the starting
sugars in a mixture of solvents. Regioselective acylation of 5-O-trityl β- -arabinofuranoside 39, prepared by
tritylation of methyl L-glycoside 1b according to the literature protocol described for -enantiomer [36], was
exploited via generation of organoboron carbohydrate derivatives in the presence of -Selectride, and subsequent
treatment of intermediate salt species with 2 equiv of 4-chlobenzoyl chloride (Scheme 4, conditions c) similarly to
synthesis of the 3,5-di-O-protected α- -arabinofuranoside 19.
L
-arabinofuranoside derivatives were also isolated by column chromatography in 8% and 3% yields,
-glycosides 1a and 1b resulted
-arabinofuranoside. The
L
L
L
L
L
L
D
L
L
Scheme 4
6

Scheme 4. Reagents and conditions. a) i) 1 equiv. 4ClBzCl, CH2Cl2 1.0 equiv Py, rt, 20 h ii) 1 equiv. 4ClBzCl, CH2Cl2 1 equiv Py, 0 0C→rt, 22 h;
b) ref. 36; c) (i) 1 equiv 1M Li(iBu)3BH in THF, 0 oC→rt, 30 min, (ii), 2.0 equiv 4ClBzCl in THF, 0 oC→rt; d) MsCl/Py, DMAP, 0 oC→rt, 18 h,
88%; e) MeONa, MeOH, rt, 91%; f) TBDPDSCl, Py, rt, 80%; g) Li(iBu)3BH in THF, -78 oC→rt, 99%; h) i) Li(iBu)3BH in THF, -78 oC→rt, 90
min, ii) 10% aq. NaOH, 30% aq.H2O2, 51%.
2-O-Benzoate 43 (64%) as the major reaction product and 2,3-di-O-benzoate 44 (30%) were isolated after
the acylation and column chromatography on silica gel. The main direction of the selective acylation reaction at the
2-OH in β-
L-arabinofuranoside 39 is unexpected fact since this hydroxyl group is more sterically hindered than 3-
OH. Results of regioselective acylations of 5-O-protected α-and β-
L-arabinofuranoside derivatives with acyl
chlorides summarized in Table 2 can be explained by reactivity differences of 2-OH and 3-OH in
(entries 3,4 and 5).
L-sugars 15 and 39
Table 2. Regioselective acylations of methyl α-and β-
L-arabinofuranosides and their 5-O-protected derivatives
Entry
L-arabinoside,
Products (isolated yields, %)
(conditionsa, acyl
chloride)
2,5-di-
7 (15)
2,3,5-tri-
8 (14)
2,3-di-
(3,5-di- or 3-)
2-O-acyl
1a (b2, ClBzCl)
6 (38)
1
2
1b (a, ClBzCl)
36 (36)
37 (8)
38 (2)
15 (b1, PivCl)
15 (b2, ClBzCl)
39 (c, ClBzCl)
-
-
-
-
17 (57)
19 (50)
44 (30)
18 (43)
20 (40)
-
-
*
3
4
5
43 (64)
a Conditions according to Schemes 1-2,4.
*The formation of 2-O-chlorobenzoyl derivative was detected as a minor product (a ratio of 3-/2-substituted -10:1)
according to 1H NMR data
A higher reactivity of the 2-OH group in 5-O-trityl-β-L-arabinofuranoside 39 relative to that of 3-OH is due
to a higher acidity of 2-OH which could be attributed to the intramolecular hydrogen bond network in nonpolar
solvent. The anomeric β-methoxy group of 39 and an oxygen atom of the furanose ring probably participates in the
formation of hydrogen bonds with 2-hydroxy group to result in the 2-O-acylated glycoside as predominant product
(entry 5). In the case of 5-O-silyl-α-L-arabinofuranoside derivative 15, the steric factor of the 5-O-protecting group
along with the internal hydrogen bonding between α-methoxy and 3-OH groups may influence on the
regioselectivity of the acylation reactions (entries 3 and 4). The reversal of selectivity for monobenzoylation of 5-O-
protected
and 3-OH in
studied acylation reactions in the presence of basic organoboron reagent. Treatment of diol 39 with 1 equiv of
L
-glycosides 15 and 39 was observed under the similar reaction conditions. Different acidities of 2-OH
L-sugars 15 and 39 should be considered as the important factor determining the regioselectivity of the
L-
Selectride resulted in preferential formation of the 2-O-activated organoboron compound 40 which, in turns, may
converts to 2-O-anions 41 and 42 via producing intermediate alkylborane complexes with 2-hydroxyl group [39] or
β-methoxy group. Reaction of salt species 40-42 with acyl chloride on the next step gave rise to the 2-O-benzoylated
derivative 43. The formation of the di-O-benzoate 44 proceeds via generation of intermediate 2,3-di-O-Li
carbohydrate species from intermediate 40 or 41 followed by acylation reaction with chlorobenzoyl chloride. This
study demonstrates that
regioselective acylation of cis-1,2-diol groups in carbohydrates (
differentiation of secondary hydroxyl groups of 5-O-protected -arabinofuranosides by acyl chlorides.
The mesylation of individual selectively protected β- -glycoside 36 with methanesulfonyl chloride in
pyridine in the presence of DMAP yielded 3-O-mesyl-β- -arabinoside 45 in 88% yield (Scheme 4). Methyl 2,3-
anhydro-β- -lyxofuranoside (46) was prepared by treatment of the intermediate 3-OMs derivative with sodium
L-Selectride as well as other known organoboron reagents [31,40] described earlier for
D-hexopyranoside derivatives) can be used for
L
L
L
L
methoxide in methanol in 91% yield. NMR spectral data of 46 is close to that of the D-enantiomer [22] described
7

earlier. Formation of methyl 2,3-anhydro-β-
di-O-benzoyl β- -glycoside prepared by selective acylation of 1b. Silylation of 2,3-ahhydro-
with tert-butylchlorodiphenylsilane in pyridine gave 5-O-silyl derivative 47 in 80% yield. Methyl 5-O-tert-
butyldiphenylsilyl-2-deoxy-β- -threo-pentofuranoside (48) was synthesized using regioselective reduction of the
epoxide ring in 5-O-silyl 2,3-anhydrosugar derivative 47 with -Selectride in THF (Scheme 4, conditions g) in 99%
yield. Reduction of unprotected methyl 2,3-anhydro-β- -lyxofuranoside (43) with an excess a complex hydride in
similar reaction conditions for 2,3-anhydro-α- -lyxofuranoside 34 followed by oxidative workup of the reaction
mixture and chromatography on silica gel gave rise to a mixture of two isomeric products such as 2-deoxy-β-
L-lyxofuranoside from the mesylate 45 confirms the structure of the 2,5-
L
L-lyxofuranoside 46
L
L
L
L
L-
threo-pentofuranoside 50 and 3-deoxy-β-L-threo-pentofuranoside 51 in overall 51% yield (a ratio of 2-deoxy and 3-
1
deoxy-furanosides - 1:1.1 according to H/13C NMR data) (conditions h). The assignment of the proton signals for
1
50 in NMR spectrum of prepared mixture was made using H NMR spectral data [41] for methyl 2-deoxy-α/β-
L-
xylofuranoside synthesized from
D
-sorbitol. It is interesting to note essential differences in selectivity for reductive
-sugars 47 and 46 by -Selectride. These findings
epoxide opening of protected and unprotected 2,3-anhydro-β-
L
L
cannot be explained by steric and polar factors of the substituents adjacent to the epoxy ring in anhydrosugars and
important role likely to play ability of the reducing agent to form intermediate complex organoboron derivatives via
adduct 49 during the reductive process of epoxide 46.
The structures of synthesized
data. In all cases, the trans-arrangement of H-1 and H-2 protones in α-
L
-sugars were supported by 1H NMR, 13C NMR, HRMS and IR spectroscopic
L-arabinofuranoside derivatives was indicated
1
by characteristic coupling constants (J1,2< 1.0 Hz) and appearance of the H-1 signal as a singlet in the H NMR
spectra. The structural assignments of the anomeric configurations of β-
L
-arabinofuranosides were made on basis of
-arabinofuranosides.
L-glycosides resonated between 106 and 109 ppm while did
3
the JH-1,H-2 magnitudes (4.5-4.7 Hz), which are significantly different from those of the α-
L
Furthermore, in the 13C NMR spectra C-1 signals of α-
the anomeric carbons of the β-isomers at 101 ppm.
3. Conclusion
In summary, a series of new 5-O, 3,5 and 2,5-di-O-protected
regioselective base-catalyzed acylations of methyl α- and β-
chlorobenzoyl chlorides. A new method for selective 3(2)-O-acylation of 5-O-tert-butyldiphenylsilyl (trityl)
arabinofuranosides was investigated through the tandem acylation reaction including generation of intermediate
organoboron compounds by -Selectride/acylation by acyl chloride. Significant differences in regioselectivity of the
acylation reactions were found for methyl α-and β- -arabinofuranosides and their 5-O-protected derivatives under
the similar reaction conditions. 3-O-Pivaloyl α- -arabinofuranoside derivative was obtained using the protection-
deprotection strategy. Syntheses of methyl 2,3-anhydro- -furanosides were accomplished from selectively 3,5-, 2,5-
and 5-O-protected methyl -arabinofuranosides derived from -arabinose. A simple and efficient procedure for the
preparation of 2(3)-deoxy- -pentofuranosides was developed via selectride reduction of the epoxy ring in 2,3-
anhydro- -furanosides and their 5-O-blocked derivatives. It was shown that different methyl -glycosides can be
synthesized via regio- and stereoselective transformations of -arabinofuranosides. -Deoxypentofuranoside
derivatives and -2,3-anhydrofuranosides can serve as useful intermediates for the synthesis of modified
monosaccharides and -nucleoside analogues. Selectively protected -arabinofuranosides may be used as building
L-arabinofuranoside derivatives were synthesized via
L-arabinofuranosides with pivaloyl, benzoyl and 4-
L-
L
L
L
L
L
L
L
L
L
L
L
L
L-
L
blocks (glycosyl acceptors) in the regioselective glycosylation reactions [44,45,11,18] for preparation of L-
arabinofuranosyl-containing di-, trisaccharides.
4.Experimental
8

4.1.General methods. Column chromatography was performed on silica gel 60 H (70-230 mesh; Merck, Darmstadt,
Germany), and thin-layer chromatography (TLC) on silica gel plates (Silufol, Czechoslovakia) and Merck silica gel
aluminum 60 F254 precoated plates with visualization of the spots of L-sugars by heating. All commercially available
reagents were used without further purification. The anhydrous solvents were distilled over CaH2, P2O5 or
magnesium prior to the use. L-Arabinofuranoside derivatives were coevaporated twice with anhydrous toluene
before acylation reactions. 1H and 13C 1NMR spectra were recorded in CDCl3, CD3OD and DMSO-d6 with a Bruker
Avance-500-DRX spectrometer at 500.13, and 126.76 MHz, respectively. 1H and 13C NMR chemical shifts (δ, ppm)
are relative to internal chloroform peak (7.26 ppm for 1H and 77.0 for 13C NMR). Chemical shifts are also reported
downfield from internal SiMe4 (1H). Melting points were determined on a Boetius apparatus and were uncorrected.
Optical rotations were measured with Autopol III automatic polarimeter. IR spectra were measured on Perkin-Elmer
Spectrum 100FT-IR spectrometer. High resolution mass spectra (HRMS) were recorded on an Agilent Q-TOF 6550
Instrument (USA) using ESI (electrospray ionization).
4.2. Regioselective transformations of methyl α-
4.2.1. Regioselective acylations of α- -arabinofuranosides with acyl chlorides
a1. Acylation with pivaloyl chloride. Pivaloyl chloride (0.22 ml, 1.79 mmоl) in anhydrous CH2Cl2 (3 ml) was
L-arabinofuranoside (1a)
L
added dropwise to a solution of methyl α-L-arabinoside 1a (295 mg, 1.79 mmol) in anhydrous CH2Cl2 (3 ml) and
o
pyridine (0.29 ml, 3.71 mmol) at 0 С (ice and sodium chloride). The reaction mixture was stirred for 1 h under
cooling and then 18 h at room temperature. Pyridine (0.14 ml, 1.79 mmol) and pivaloyl chloride (0.22 ml, 1.79
o
mmоl) in anhydrous CH2Cl2 (3 ml) were consequently added at 0 С. After stirring for 2 h under cooling, the
reaction mixture was stirred for 21 h at room temperature. The solution was diluted with CH2Cl2 (30 ml), water (10
ml), the aqueous phase was extracted with CH2Cl2 (3x30 ml). The combined organic extracts were washed 1
M HCl
(3x10 ml), dried over anh. Na2SO4 and evaporated to dryness. The residue was chromatographed on silica gel, using
mixtures of petroleum ether - EtOAc to afford (121 mg, 16%) of 2,3,5-tri-O-pivaloyl-α-
L
-arabinofuranoside (4) as a
syrup. IR (film, CHCl3): ν 2977, 2937, 1738, 1285, 1146 cm-1. [α]D –45.8 (c 1.0, CHCl3). H NMR (500 MHz,
CDCl3) δ: 4.99 (d, 1Н, Н-2), 4.96 (m, 1H, Н-3), 4.84 (s, 1Н, Н-1), 4.32 (dt, 1Н, Н-4), 4.19-4.23 (m, 2Н, H-5 and H-
5′), 3.37 (s, 3H, OCH3), 1.22, 1.20 and 1.96 [3s, 27H, 3x(СОС(СН3)3]. 13C NMR (125 MHz, CDCl3) δ: 178.17,
177.7 and 177.4 [(C=O, 3хСОС(СН3)3], 106.86 (С-1), 81.5 and 80.0 (C-2, С-3), 76.89 (C-4), 63.19 (С-5), 54.8
(ОСН3), 38.9, 38.73 and 38.71 [3х(СОС(СН3)3], 27.3, 27.2, and 27.15 [3х(СОС(СН3)3]. HRMS (ESI+): m/z calcd
for [C21H36O8+Na]+: 439.2308, found 439.2314.
20
1
(80 mg, 13%) of 2,5-di-O-pivaloyl derivative 3 as a syrup. IR (film, CHCl3): ν 3492, 2975, 1734, 1285, 1159 cm-1.
[α]D20 –47.1 (c 1.0, CHCl3). 1 Н NMR (500 MHz, CDCl3) δ: 4.95 (br. s, 1Н, Н-1), 4.77 (d, 1Н, J = 2.5 Hz, Н-2), 4.2-
4.32 (m, 3Н, Н-5, Н-5′ and Н-4), 3.84-3.87 (m, 1Н, Н-3), 3.39 ( s, 3Н, ОСН3), 3.19 (d, 1Н, 3-OH), 1.21 and 1.20
(2s, 18Н, 2хСОС(СН3)3]. 13С NMR (125 MHz, CDCl3) δ: 179.1 and 178.3 [(C=O, 2хСОС(СН3)3], 106.37 (C-1),
85.44, 81.58, 77.55 (C-2, C-4, С-3), 63.25 (C-5), 55.04 (OCH3), 38.95 and 38.81 [2x(СОС(СН3)3], 27.26 and 27.14
[2x(СОС(СН3)3]. HRMS (ESI+): m/z calcd for [C16H28O7+Na]+: 355.1733, found 355.1728.
(251 mg, 42%) of 3,5-di-O-pivaloyl derivative 2 as a syrup. 1 Н NMR (500 MHz, CDCl3) δ: 4.91 (s, 1Н, Н-1), 4.58
(dd, 1Н, J = 6.4, J = 2.8 Hz, Н-3), 4.35 (dm, 1Н, Н-5), 4.24-4.24 (m, 2Н, Н-4, Н-5′), 4.04 (d, 1Н, Н-2), 3.39 (s, 3H,
OCH3), 1.23 and 1.22 (2s, 18Н, СОС(СН3)3]. 13C NMR (125 MHz, CDCl3) δ: 179.69, 178.11 [(C=O,
2хСОС(СН3)3], 108.66 (С-1), 81.52, 81.4, 78.6 (С-4, C-3, С-2), 63.1 (С-5), 54.97 (ОСН3), 38.84, 38.86
[2х(СОС(СН3)3], 27.15, 27.96 [2х(СОС(СН3)3].
Further elution with a mixture of methylene chloride/methanol (5:1) gave (27 mg, 6%) of 5-O-pivaloyl derivative
(5) as a syrup. IR (film, CHCl3): ν 3441, 2970, 2934, 1725, 1169, 1109, 1040 cm-1. [α]D20 –16.6 (c 0.6, CHCl3). Н
1
9

NMR (500 MHz, CDCl3) δ: 4.87 (s, 1Н, Н-1), 4.28 (dd, 1Н, Н-5), 4.25 (dd, 1Н, Н-5′), 4.14 (m, 1Н, Н-4), 4.14 (m,
1Н, Н-2), 3.27 (dd, 1Н, Н-3), 3.39 (s, 3Н, ОСН3), 1.21 [s, 9Н, СОС(СН3)3]. 13С NMR (125 MHz, CDCl3) δ: 178.8
[(C=O, СОС(СН3)3], 108.71 (C-1), 82.9 (C-4), 80.5, 78.1 (C-2, С-3), 64.1 (C-5), 55.17 (OCH3), 39.0 [(СОС(СН3)3],
27.26 [(СОС(СН3)3]. HRMS (ESI+): m/z calcd for C11H20O6 [M+Na]+: 271.1158, found 271.1162; C10H17O5 [M-
OCH3]+: 217.1076, found 217.1084
a2. Pivaloyl chloride (0.18 ml, 1.46 mmоl) in anhydrous pyridine (0.8 ml) was added dropwise to a stirred solution
o
of methyl α-
L
-arabinoside (1a) (114 mg, 0.69 mmol) in anhydrous pyridine (2.0 ml) at 0 С in three portion. The
reaction mixture was stirred for 6 h under cooling and then 2 h at rt, diluted with water, extracted with chloroform.
The combined organic extracts were washed with 1 N HCl, 5%-aqueous NaHCO3, dried over anhydrous Na2SO4
and evaporated to dryness. The residue was chromatographed on silica gel, using a mixture of 3:1 petroleum ether-
EtOAc to afford a mixture of the dipivaloyl L-arabinofuranoside derivatives (40 mg, 17%, 2:1) (2 and 3) as a syrup.
Further elution with a mixture of methylene chloride-methanol (5:1) gave (110 mg, 64%) of 5-O-pivaloyl derivative
(5) as a syrup.
b2. Acylation with 4-chlorobenzoyl chloride. A solution of methyl α-L-arabinoside 1a (365 mg, 2.22 mmol) in
anhydrous CH2Cl2 (4.7 ml) and pyridine (0.17 ml, 2.2 mmol) was stirred for 20 min at rt, then 0.28 ml (2.18 mmоl)
4-chlorobenzoyl chloride in 2.9 ml anhydrous CH2Cl2 was added dropwise. The reaction mixture was stirred for 18 h
at room temperature. Anhydrous pyridine (0.17 ml, 2.2 mmol) and solution of 4-chlorobenzoyl chloride (0.28 ml,
0
2.18 mmоl) in anhydrous CH2Cl2 (2.9 ml) were consequently added to a prepared solution at 0 С. After stirring
during 45 min under cooling, the reaction mixture was stirred for 20 h at room temperature. The solution was diluted
CH2Cl2 (40 ml), water (10 ml), the aqueous phase was extracted with CH2Cl2 (3x30 ml). The combined organic
extracts was washed 1 N HCl (10 ml), 5% aq NaHCO3, dried over anhydrous Na2SO4 and evaporated to dryness.
The residue was chromatographed on silica gel using a mixture of 6:1, 4:1 and 2.5:1 hexane - EtOAc to afford (175
mg, 14%) of methyl 2,3,5-tri-O-4-chlorobenzoyl-α-
chlorobenzoyl-α- -arabinofuranoside (6) and (150 mg, 15%) of methyl 2,5-di-O-4-chlorobenzoyl derivative (7).
c1. Acylation with benzoyl chloride. To a solution of methyl α- -arabinoside 1a (151 mg, 0.92 mmol) in anhydrous
L-arabinofuranoside (8), (370 mg, 38%) of methyl 3,5-di-O-4-
L
L
THF (7.0 ml) and pyridine (0.22 ml), N,N-diisopropylethylamine (1.4 ml, 0.9 mmol) was added and a mixture was
stirred for 30 min at rt, then benzoyl chloride (0.16 ml, 1.38 mmol) was added dropwise to prepared solution. The
reaction mixture was stirred for 5 h at rt and then 0.13 ml (0.93 mmоl) triethylamine was added dropwise. The
reaction mixture was stirred for 48 h at room temperature. The precipitate was filtered off and washed THF (5 ml),
the filtrate was diluted with CH2Cl2 (40 ml), water (10 ml), the aqueous phase was extracted with CH2Cl2 (2x30 ml)
and the combined organic extracts were dried over anh. Na2SO4 and evaporated to dryness. The residue was
chromatographed on a silica gel, using a mixture of 5:1, 3:1 and 1:1 hexane - EtOAc to afford (85 mg, 25%) (a ratio
1
of 1:1 according to H NMR data) of a mixture of methyl 3,5-di-O-benzoyl-α-
L-arabinofuranoside (10) and methyl
2,5-di-O-benzoyl derivative 11. 1Н NMR (500 MHz, CDCl3) δ: 7.37-8.13 (m, 20H, Bz), 5.23 (s, 1Н, Н-1, 2,5-di-O-
Bz), 5.19 (br.d, 1Н, J = 2.3 Hz, Н-2), 5.10 (dd, 1Н, J = 2.7 Hz, Н-3, 3,5-di-O-Bz), 5.08 (s, 1H, Н-1, 3,5-di-O-Bz),
4.74-4.78 ( m, 1Н, Н-4), 4.70 (dd, 1Н, Н-5), 4.46-4.69 (m, 2Н, 2Н-5), 4.57 (dd, 1Н, Н-5´), 4.47-4.50 (m, 1Н, Н-4),
4.38 (br.d, 1Н, Н-2), 4.30 (dd, 1Н, Н-3), 3.52 (s, 3Н, ОСН3), 3.48 (s, 3Н, ОСН3). 13С NMR (125 MHz, CDCl3) δ:
167.30, 166.63, 166.44, 165.40 (4C=O, СОC6H5), 133.71, 133.23, 133.17, 129.91, 129.88, 129.76, 128.62, 128.55,
128.46, 128.38 (СОC6H5) 109.03 (С-1, 3,5-di-O-Bz), 106.57 (C-1, 2,5-di-O-Bz), 85.46, 81.98, 77.23 (С-4, C-2, C-3,
2,5-di-O-Bz), 82.16, 81.33, 79.02 (С-4, C-2, C-3, 3,5-di-O-Bz), 63.88 (С-5), 64.01 (C-5), 55.17 (ОСН3). HRMS
(ESI+): m/z calcd for [C20H20O7+Na]+: 395.1098, found 395.1127.
10

Further elution with EtOAc-methanol (6:1) gave (89 mg, 36%) of 5-O-benzoyl derivative 9 as a syrup. IR (film,
CHCl3): ν 3434, 2937, 1719, 1278, 1106, 950 cm-1. [α]D20 –50 (c 1.0, CHCl3). 1Н NMR (500 MHz, CDCl3) δ: 7.45-
8.09 (3m, 5H, Bz), 4.97 (s, 1Н, Н-1), 4.60 (dd, 1Н, Н-5), 4.56 (dd, 1Н, Н-5′), 4.34 (m, 1Н, Н-4), 4.20 (br.d, 1Н, Н-
2), 4.08 (dd, 1Н, Н-3), 3.73 (br.s, 2H, 2-OH and 3-OH), 3.45 (s, 3Н, ОСН3). 13С NMR (125 MHz, CDCl3) δ: 165.77
(C=O, СОC6H5), 133.34, 130.08, 129.77, 128.52 (СОC6H5), 108.78 (С-1), 82.96 (С-4), 80.76, 78.07 (C-3 and С-2),
64.55 (С-5), 55.23 (ОСН3). HRMS (ESI+): m/z calcd for [C13H16O6+Na]+: 291.0845, found 291.0845.
c2. To a solution of methyl α-L-arabinoside (1a) (147 mg, 0.89 mmol) in anhydrous THF (5.5 ml) and pyridine (0.17
ml, 2.2 mmol) was added a solution previously prepared by adding benzoyl chloride (0.22 ml, 2.43 mmol) to N,N-
diisopropylethylamine (0.14 ml, 0.9 mmol) in abhydrous THF (0,7 ml). The reaction mixture was stirred for 5 h at rt
and then triethylamine (0.12 ml, 0.86 mmоl) was added dropwise to prepared solution. The reaction mixture was
0
stirred for 18 h at room temperature and then 3 h at 35-37 C. After cooling the precipitate was filtered off and
washed THF (5 ml), the filtrate was diluted with CH2Cl2 (40 ml), water (10 ml), the aqueous phase was extracted
with CH2Cl2 (2x30 ml), and the combined organic extracts were dried over anh. Na2SO4 and evaporated to dryness.
The residue was chromatographed on a silica gel, using a mixture of 5:1, 3:1 and 1:1 hexane-EtOAc to afford (93
mg, 28%, a ratio of 1:1.4 according to 1H NMR data) of a mixture of methyl 3,5-di-O-benzoyl-α-
L-
arabinofuranoside (10) and 2,5-di-O-benzoyl derivative 11.
Further elution with EtOAc-methanol (6:1) gave (150 mg, 62%) of 5-O-benzoyl derivative 9 as a syrup.
4.2.2. Selective acylation of methyl 5-O-benzoyl-α-
4-Chlorobenzoyl chloride (0.022 ml, 0.171 mmоl) in anhydrous CH2Cl2 (0.22 ml) was added dropwise to a solution
of methyl 5-O-benzoyl-α- -arabinofuranoside (9) (46 mg, 0.171 mmol) in anhydrous CH2Cl2 (2 ml) and pyridine
L-arabinofuranoside (9) with 4-chlorobenzoyl chloride.
L
(0.03 ml, 0.38 mmol) at 0 oС (ice and sodium chloride). The reaction mixture was stirred for 1 h under cooling and
then for 20 h at room temperature. A solution of 4-chlorobenzoyl chloride (0.022 ml, 1.79 mmоl) in anhydrous
CH2Cl2 (0.8 ml) was added to a prepared solution at rt. After stirring for 2 h the reaction mixture was diluted with
CH2Cl2 (30 ml), water (10 ml), and the aqueous phase was extracted with CH2Cl2 (3x30 ml). The combined organic
extracts were washed with 5% aq. NaHCO3, dried over anhydrous Na2SO4 and evaporated to dryness. The residue
was chromatographed on a silica gel, using a mixture of 7:1, 6:1, 4:1 and 2:1 hexane-EtOAc to afford as the first
20
fraction (6 mg, 6%) of methyl 2,3-di-O-4-chlorobenzoyl-5-O-benzoyl-α-L-arabinofuranoside (14) as a syrup. [α]D
+39 (c 1.0, CHCl3). 1Н NMR (500 MHz, CDCl3) δ 7.33 - 8.08 (m, 13H, C6H5CO, 2x СОC6H4Cl), 5.59 (br.d, 1H, H-
3), 5.52 (d, 1Н, Н-2), 5.21 (s, 1Н, Н-1), 4.90 (dd, 1Н, Н-5), 4.71 (dd, 1Н, Н-5′), 4.52-4.65 (m, 1Н, Н-4), 3.54 (s, 3H,
OCH3). 13С NMR (125 MHz, CDCl3) δ: 165.15, 164.97 and 164.61 [3C=O, СОC6H5, СОC6H4Cl], 140.13, 140.09,
133.16, 131.33, 131.20, 131.07, 129.73, 128.33, 128.05, 127.48, 127.40 (СОC6H5, СОC6H4Cl), 106.72 (С-1), 82.27,
80.72, 78.06 (C-2, С-3, C-4), 63.51 (С-5), 55.04 (ОСН3). HRMS (ESI+): m/z calcd for [C27H22O8Cl2+Na]+:
567.0584, found 567.0578.
The second fraction was a mixture of methyl 3-O-4-chlorobenzoyl-5-O-benzoyl derivative 12 and methyl 2-O-4-
1
chlorobenzoyl-5-O-benzoyl derivative 13 (42 mg, 60%) (a ratio of 12:13 = 1.7:1 according to H NMR data). 1Н
NMR (500 MHz, CDCl3) δ: 7.39-8.10 (m, 13H, C6H5CO, СОC6H4Cl), 5.22 (s, 0.49Н, Н-1, 2,5-di-O-Bz), 5.16 (dd,
0.49Н, J = 2.4 Hz, Н-2), 5.08 (dd, 1Н, J = 2.5 Hz, Н-3, 3,5-di-O-Bz), 5.07 (s, 1Н, Н-1, 3,5-di-O-Bz), 4.74 (dd, 1Н,
Н-5), 4.69 (dd, 0.5Н, Н-5), 4.60-4.67 (m, 2Н, Н-4 and H-5’), 4.56 (dd, 0.6Н, Н-5’), 4.45-4.49 (m, 0.5Н, Н-4), 4.36
(dd, 1Н, Н-2), 4.28 (dd, 0.5Н, Н-3), 3.52 (s, 1.6Н, ОСН3), 3.48 (s, 3Н, ОСН3). 13С NMR (125 MHz, CDCl3) δ:
166.43, 166.40, 166.35, 166.76 [(4 x C=O, СОC6H5 and СОC6H4Cl], 140.27, 133.30, 133.23, 131.56, 131.28,
131.23, 129.88, 129.77, 128.99, 128.94, 128.87, 128.74 (СОC6H5), 108.96 (С-1, 3,5-di-O-Bz), 106.40 (C-1, 2,5-di-
O-Bz), 85.53, 82.03, 77.25 (С-4, C-2, C-3, 2,5-di-O-Bz), 82.40, 81.38, 78.90 (С-4, C-2, C-3, 3,5-di-O-Bz), 63.89
11

(С-5, 3,5-di-O-Bz) 63.77 (C-5, 2,5-di-O-Bz), 55.21 (2xОСН3). HRMS (ESI+): m/z calcd for [C20H19O7Cl+Na]+:
429.0717, found 429.0714.
4.2.3. Methyl 5-O-tert-butyldiphenylsilyl-α-L-arabinofuranoside (15).
To a solution of methyl α-
L-arabinoside (1a) (260 mg, 1.58 mmol) in pyridine (7.2 ml) was added tert-
o
butylchlorodiphenylsilane (0.62 ml, 2.37 mmol) at 0 С and then the reaction mixture was stirred for 48 h and
evaporated, diluted with CH2Cl2 and poured into 5% aq NaHCO3, aqueous phase was extracted with CH2Cl2 (3x50
ml), the combined organic extracts were dried and evaporated. The residue was chromatographed on a silica gel,
using for elution a mixture of hexane-ethylacetate 6:1 and 4:1, 1:1 to give (522 mg, 82%) of 5-O-silyl α-L-
arabinofuranoside derivative 15 as a colorless oil IR (film, CHCl3): ν 3421, 2931, 2861, 1113, 1073, 1003 cm-1.
20
[α]D +47.7 (c 1.3, CHCl3). 1H NMR (500 MHz, CDCl3) δ: 7.40-7.71 [2m, 10H, (CH3)3CSi(C6H5)2], 4.99 (s, 1H, H-
1), 4.01-4.20 (m, 4Н, Н-2, H-3, H-4 and OH), 3.84 (dd (1Н, J5,4 = 2.2 Hz, J5,5′ = 11.4 Hz, Н-5), 3.75 (dd, 1Н, J5′,4
=
1.2 Hz, Н-5′), 3.42 (s, 3Н, OCH3), 2.95 (d, 1H, OH), 1.06 (s, 9H, (CH3)3C-). 13С NMR (125 MHz, CDCl3) δ:
135.79, 135.72, 130.33, 130.21, 128.13, 128.07 [(CH3)3CSi(C6H5)2], 109.54 (C-1), 87.57 (C-4), 78.57, 78.13 (C-3,
С-2), 64.18 (C-5), 55.01 (OCH3), 26.80 (CH3)3C-, 19.16 (CH3)3C-. HRMS (ESI+): m/z calcd for C22H30SiO5Na
[M+Na]+: 425.1760, found 425.1765.
4.2.4. Acylation of 5-O-silyl derivative α-
L-arabinofuranoside 15 with acyl chlorides.
Acylation with pivaloyl chloride. -Selectride (0.49 ml 1 M solution in THF, 0.49 mmol) was added dropwise
L
to a solution of 5-O-silyl derivative of methyl arabinoside 15 (180 mg, 0.45 mmol) in anhydrous THF (2.7 ml) at 0
0С (ice and sodium chloride). The solution was stirred at 0 0C for 30 min with gradually raising temperature to room
and then, it was stirred for 30 min. Pivaloyl chloride (0.11 ml, 0.89 mmol) was added to prepared solution under
cooling 0 0С. The reaction mixture was stirred for 5 h at room temperature, then cooled to 0 0С and pivaloyl chloride
(0.08 ml, 0.65 mmol) was added to it. The reaction mixture was stirred for 18 h at room temperature, poured in
cooled 5% aq NaHCO3, the aqueous phase was extracted with CH2Cl2 (3x30 ml). The combined organic extracts
was washed water, dried over anh. Na2SO4, and evaporated to dryness. The residue was chromatographed on silica
gel, using for elution a mixture of hexane-ethylacetate 8:1, 6:1 and 4:1, and ethylacetate as the eluent to give (106
mg, 57%) of methyl 5-O-tert-butyldiphenylsilyl-2,3-di-O-pivaloyl-α-L-arabinofuranoside (18) as a syrup. IR (film,
CHCl3): ν 2967, 2938, 2865, 1739, 1285, 1143, 1110, 1073 cm-1. [α]D20 –29 (c 1.0, CHCl3). 1H NMR (500 MHz,
CDCl3) δ: 7.26-7.71 [2m, 10H, (CH3)3CSi(C6H5)2], 5.14 (dd, 1Н, J2,3 = 1.8 Hz, J3,4 = 5.4 Hz, Н-3), 4.97 (d, 1H, H-2),
4.85 (br.s, 1Н, Н-1), 4.17 (m, 1Н, Н-4), 3.84 (dd, 1Н, J5,4 = 4.7 Hz, J5,5′ = 11.1 Hz, Н-5), 3.81 (dd, 1Н, J5′,4 = 5.3 Hz,
Н-5′), 3.39 (s, 3Н, OCH3), 1.88 and 1.17 (2s, 9H, (CH3)3C(CO)-, 1.07 (s, 9H, (CH3)3C-). 13C NMR (125 MHz,
CDCl3) δ: 177.40 (CO), 177.29 (CO), 135.62, 133.29, 133.21, 129.67, 127.66 [(CH3)3CSi(C6H5)2], 106.78 (C-1),
82.38, 81.46, 76.79 (C-2, C-3 , С-4), 63.51 (C-5), 54.66 (OCH3), 38.54 (CH3)3C(CO)-, 26.93, 26.77 [(CH3)3C-,
(CH3)3C(CO)-], 19.26 (CH3)3C-). HRMS (ESI+): m/z calcd for C32H46SiO7Na [M+Na]+: 593.2911, found 593.2908.
methyl 5-O-tert-butyldiphenylsilyl-3-O-pivaloyl-α-
L-arabinofuranoside (17) (68 mg, 43%) as a syrup. IR (film,
1
CHCl3): ν 3457, 2964, 2934, 2861, 1729, 1288, 1162, 1056, 1000 cm-1. [α]D20 –44 (c 1.1, CHCl3). Н NMR (500
MHz, CDCl3) δ: 7.38-7.712 [m, 10H, (CH3)3CSi(C6H5)2], 4.99 (s, 1H, H-1), 4.92 (dd, 1Н, J2,3 = 1.0 Hz, J3,4 = 3.6 Hz,
Н-3), 4.08-4.11 (m, 2Н, Н-2 and H-4), 3.90 (dd, 1Н, J5,4 = 2.6 Hz, J5,5′ = 11.2 Hz, Н-5), 3.85 (dd, 1Н, J5′,4 = 2.64 Hz,
Н-5′), 3.39 (s, 3Н, OCH3), 3.74 (d, 1H, 2-OH), 1.88 and 1.08 [2s, 9H, (CH3)3C(CO)-, CH3)3C-]. 13С NMR (125
MHz, CDCl3) δ: 178.87 (CO), 135.62, 129.97, 129.89, 127.87, 127.80 (CH3)3CSi(C6H5)2, 109.36 (C-1), 83.38,
80.11, 78.97 (C-3, C-4, С-2), 63.96 (C-5), 54.69 (OCH3), 38.56 (CH3)3C(CO)-, 26.89, 26.76 [(CH3)3C-,
(CH3)3C(CO)-], 19.15 (CH3)3C-. HRMS ((ESI+): m/z calcd for C27H38SiO6Na [M+Na]+: 509.2335, found 509.2331.
and (50 mg, 28%) of the starting L-arabinoside 15
12

Acylation with 4-chlorobenzoyl chloride. L-Selectride (0.46 ml 1 M solution in THF, 0.46 mmol) was added
dropwise to a solution of 5-O-silyl derivative of arabinoside 15 (184 mg, 0.46 mmol) in anhydrous THF (3.0 ml) at 0
0С. The solution was stirred at 0 0C (ice and sodium chloride) for 30 min with gradually raising temperature to room
and then, it was stirred for 20 min. 4-Chlorobenzoyl chloride (0.12 ml, 0.95 mmol) in anhydrous THF (0.7 ml) was
added dropwise to a solution under cooling 0 0С. The reaction mixture was stirred under cooling for 30 min and then
4 h at room temperature, poured in cooled 5% aq NaHCO3, the aqueous phase was extracted with EtOAc (3x30 ml).
The combined organic extracts was washed water, dried over anh. Na2SO4, and evaporated to dryness. The residue
was chromatographed on silica gel, using for elution a mixture of hexane-ethylacetate 8:1, 6:1 and 4:1, and
ethylacetate as the eluent to give (126 mg, 50%) of methyl 5-O-tert-butyldiphenylsilyl-2,3-di-O-4-chlorobenzoyl-α-
L
-arabinofuranoside (20). M.p.40–42 °С. IR (KBr): ν 2957, 2931, 1729, 1596, 1268, 1106 cm-1. [α]D20 –48 (c 1.0,
1
CHCl3). H NMR (500 MHz, CDCl3) δ: 7.33-7.99 [4m, 18H, (CH3)3CSi(C6H5)2, ClBz], 5.61 (dd, 1Н, J3,2 = 1.1 Hz,
J3,4 = 5.3 Hz, Н-3), 4.42 (d, 1Н, Н-2), 5.11 (s, 1H, H-1), 4.35 (m, 1Н, Н-4), 4.04 (dd,. 1Н, J5,4 = 4.6 Hz, J5,5′ = 11.3
Hz, Н-5), 3.99 (dd, 1Н, J5′,4 = 4.2 Hz, Н-5′), 3.47 (s, 3Н, OCH3), 1.06 [s, 9H, (CH3)3Si(C6H5)2]. 13C NMR (125
MHz, CDCl3) δ: 164.77 (CO), 164.64 (CO), 139.87, 135.62, 133.26, 133.15, 131.27, 129.70, 128.74, 127.86, 127.67
[(CH3)3CSi(C6H5)2, Cl-C6H4CO], 106.75 (C-1), 82.68, 82.58, 77.79 (C-3, C-2, С-4), 63.38 (C-5), 54.83 (OCH3),
26.76 (CH3)3C-, 19.31 (CH3)3C-. HRMS (ESI+): m/z calcd for C36H36O7SiCl2Na [M+Na]+: 701.1505, found
701.1502.
methyl 5-O-tert-butyldiphenylsilyl-3-O-4-chlorobenzoyl-α-
L-arabinofuranoside (19) (80 mg, 40%) as a syrup. IR
1
(film, CHCl3): ν 3447, 2954, 2931, 2861, 1722, 1272, 1112 cm-1. [α]D20 –56 (c 1.0, CHCl3). H NMR (500 MHz,
CDCl3) δ: 7.38-7.95 [3m, 14H, (CH3)3CSi(C6H5)2, ClBz], 5.30 (dd, 1Н, J2,3 = 0.9 Hz, J3,4 = 3.6 Hz, Н-3), 5.04 (s, 1H,
H-1), 4.24-4.28 (m, 2Н, Н-2 and H-4), 3.97 (dd, 1Н, J5,4 = 2.5 Hz, J5,5′ = 12.7 Hz, Н-5), 3.91 (dd, 1Н, J5′,4 = 2.7 Hz,
Н-5′), 3.42 (s, 3Н, OCH3), 3.78 (d, 1H, 2-OH), 1.09 [s, 9H, (CH3)3Si(C6H5)2]. 13C NMR (125 MHz, CDCl3) δ: 165.8
(CO), 139.89, 135.63, 132.38, 132.33, 131.2, 130.02, 129.94, 128.79, 127.90, 127.84 [(CH3)3CSi(C6H5)2, ClBz],
109.52 (C-1), 83.87, 80.84, 79.02 (C-4, C-3, С-2), 63.9 (C-5), 54.98 (OCH3), 26.78 (CH3)3C-, 19.16 (CH3)3C-.
HRMS (ESI+): m/z calcd for C29H33O6SiClNa [M+Na]+: 563.1633, found 563.1628.
and the starting L-arabinoside 12 (35 mg, 19%).
4.2.5. Methyl 3-O-pivaloyl-α-L-arabinofuranoside (21)
To a solution of 17 (38 mg, 0.078 mmol) in anhydrous methanol (1.5 ml) was added NH4F (14 mg, 0.38 mmol). The
0
solution was stirred at 29-30 C for 85 min, and then the reaction mixture was evaporated. The residue was
chromatographed on a silica gel, using for elution a mixture of 6:1, 4:1 hexane-EtOAc and CHCl3:MeOH - 5:1 to
give (17 mg, 88%) of methyl 3-O-pivaloyl-α-
L-arabinofuranoside (21) as a colorless oil. IR (film, CHCl3): ν 3418,
1
2974, 2934, 1729, 1292, 1166, 1112, 990 cm-1. [α]D20 –75 (c 0.43, CHCl3). Н NMR (500 MHz, CDCl3) δ: 4.98 (s,
1Н, Н-1), 4.80 (dd, 1Н, J3,2 = 2.0 Hz, J3,4 = 5.0 Hz, Н-3), 4.19-4.21 (dt, 1Н, Н-4), 4.13( br.d, 1Н, Н-2), 3.96 (dd, 1Н,
Н-5, J5,4 = 2.6 Hz, J5,5′ = 11.9 Hz, Н-5), 3.89 (dd, 1Н, J5′,4 = 2.7 Hz, Н-5′), 3.43 (s, 3Н, ОСН3), 1.25 [s, 9Н,
СОС(СН3)3]. 13С NMR (125 MHz, CDCl3) δ: 179.33 СОС(СН3)3, 109.26 (C-1), 82.51, 80.23, 79.96 (C-4, C-2, С-
3), 61.75 (C-5), 54.84 (OCH3), 38.63 СОС(СН3)3, 26.93 СОС(СН3)3. HRMS (ESI+): m/z calcd for C11H20O6
[M+Na]+: 271.1158, found 271.1153.
4.2.6. Methyl 2,3-anhydro-α-L-ribofuranoside (25)
To a solution of intermediate 2-O-mesylate (238 mg, 0.58 mmol), prepared from the 3,5-di-O-pivaloate 2 according
to the previous work [28] in anhydrous methanol (2.5 ml) was added 1 M solution of NaOCH3 in methanol (0.43
ml). The reaction mixture was stirred at room temperature for 18 h, and then was neutralized with glacial acetic acid
and evaporated to dryness, coevaporated with a mixture of ethanol-toluene (25 ml). The residue was
13

chromatographed on a silica gel, using for elution chloroform, CHCl3-petroleum ether-methanol (15:7:2) to give (68
20
mg, 80%) of methyl 2,3-anhydro-α-
L
-ribofuranoside (25) as a colorless oil. [α]D –17.7 (c 1.2, H2O); lit for
D-
23
1
isomer [24]. [α]D +19.2 (c 2.3, H2O). H NMR (500 MHz, CDCl3) δ: 5.21 (br.s, 1Н, J1,2 < 1.0 Hz, Н-1), 4.33 (t,
1Н, J4,5 = 3.8 Hz, J4,5′ = 3.9 Hz, Н-4), 3.80 (dd, 1Н, J1,2 = 0.7 Hz, J2,3 = 2.8 Hz, Н-2), 3.77 (dd, 1Н, J5,5′ = 11.5 Hz, Н-
5), 3.70 (d, 1Н, J3,2 = 2.8 Hz, Н-3), 3.66 (dd, 1Н, Н-5′), 3.50 (s, 3Н, OCH3). 13C NMR (125 MHz, CDCl3) δ: 102.73
(C-1), 78.99 (C-4), 63.18 (C-5), 57.98 (C-3), 56.84 (OCH3), 56.47 (C-2). HRMS (ESI+): m/z calcd for C6H10O4Na
[M+Na]+: 169.0477, found 169.0481.
4.2.7. Methyl 5-O-tert-butyldiphenylsilyl-2,3-anhydro-α-L-ribofuranoside (26)
d. To a solution of
L-arabinoside derivative 17 (55 mg, 0.11 mmol) and 4-dimethylaminopyridine (9 mg, 0.07
0
mmol) in anhydrous pyridine (2.0 ml) was added methanesulfonyl chloride (0.03 ml, 0.39 mmоl) at 0 C. The
reaction mixture was stirred for 2 h at rt, the prepared solution was diluted CH2Cl2 (10 ml), washed water (4 ml), the
aqueous phase was extracted with CH2Cl2 (20 ml). The combined organic extracts were washed with 1 N HCl (3x30
ml), 5% aq NaHCO3, dried over anhydrous Na2SO4, and evaporated to dryness. The residue was purified by
chromatography on silica gel, using mixture of 5:1 and 4:1 hexane-EtOAc to afford (59 mg, 92%) of intermediate
mesylate 22 as a syrup. 1H NMR (500 MHz, CDCl3) δ: 7.37-7.70 [3m, 10H, CH3)3CSi(C6H5)2], 5.15 (br.d, 1Н, J3,2
=
4.2 Hz, Н-3), 5.11 (s, 1H, H-1), 4.80 (br.s, 1Н, Н-2), 4.16 (m, 1Н, Н-4), 3.87 (dd, 1Н, J5,4 = 4.4 Hz, J5,5′ = 11.2 Hz,
Н-5), 3.83 (dd, 1Н, J5′,4 =4.7 Hz, Н-5′), 3.39 (s, 3Н, OCH3), 3.09 (s, 3Н, -SO2CH3), 1.95 [s, 9H, (CH3)3C(CO)], 1.07
[s, 9H, (CH3)3CSi(C6H5)2]. HRMS (ESI+): m/z calcd for C22H28O4SiNa [M+Na]+: 407.1655, found 407.1664.
To a solution of intermediate 2-O-mesylate 22 (48 mg, 0.098 mmol) in anhydrous methanol (4.5 ml) was added 1 M
solution of NaOCH3 in methanol (0.065 ml). The reaction mixture was stirred at room temperature for 18 h, and
then neutralized with glacial acetic acid and evaporated to dryness, coevaporated with a mixture of ethanol-toluene
(25 ml). The residue was chromatographed on a silica gel, using for elution a mixture of 10:1 and 7:1 hexane-EtOAc
to afford (30 mg, 80%) of methyl 5-O-tert-butyldiphenylsilyl-2,3-anhydro-α-L-ribofuranoside (26) as a colorless oil.
1
[α]D20 –46 (c 1.0, CHCl3). H NMR (500 MHz, CDCl3) δ: 7.38-7.68 [m, 10H, (CH3)3CSi(C6H5)2], 5.25 (s, 1Н, J1,2
<1.0 Hz, Н-1), 4.32 (t, 1Н, J = 4.3 Hz, J = 2.6 Hz, Н-4), 3.82 (dd, 1Н, J5,5′ = 11.2 Hz, Н-5), 3.78 (d, 1Н, J2,3 = 2.7 Hz,
Н-2), 3.72 (dd, 1Н, Н-5`), 3.71 (d, 1Н, Н-3), 3.52 (s, 3Н, OCH3), 1.07 [s, 9H, (CH3)3Si(C6H5)2]. 13C NMR (125
MHz, CDCl3) δ: 135.68, 135.61, 132.97, 130.14, 130.02, 128.0, 127.96 (CH3)3CSi(C6H5)2, 103.15 (C-1), 78.79 (C-
4), 64.81 (C-5), 57.11 (OCH3), 57.07, 56.35 (C-3, C-2), 26.95 (CH3)3C-, 19.26 (CH3)3C-.
d. To a solution of
L-arabinoside derivative 19 (35 mg, 0.065 mmol) and 4-dimethylaminopyridine (5 mg, 0.04
0
mmol) in anhydrous pyridine (2.0 ml) was added methanesulfonyl chloride (0.03 ml, 0.39 mmоl) at 0 C. The
reaction mixture was stirred at rt for 18 h, then diluted CH2Cl2 (10 ml), washed water (4 ml), the aqueous phase was
extracted with CH2Cl2 (20 ml). The combined organic extracts were washed 5% aq NaHCO3, dried over anhydrous
Na2SO4, and evaporated to dryness. The residue was purified by chromatography on silica gel, using a mixture of
1
10:1 and 7:1 hexane-EtOAc to afford (39 mg, 97%) of intermediate mesylate 23 as a syrup. H NMR (500 MHz,
CDCl3) δ: 7.33-7.99 [4m, 14H, (CH3)3CSi(C6H5)2, Cl-Bz], 5.43 (dd, 1Н, J = 1.2 Hz, J = 5.4 Hz, Н-3), 5.18 (s, 1H, H-
1), 5.01 (br.s, 1Н, Н-2), 4.30 (m, 1Н, Н-4), 3.98 (dd, 1Н, J5,4 = 4.3 Hz, J5,5′ = 11.3 Hz, Н-5), 3.92 (dd, 1Н, J5′,4 = 4.4
Hz, Н-5′), 3.42(s, 3Н, OCH3), 3.12 (s, 3Н, -SO2CH3), 1.05 [s, 9H, (CH3)3Si(C6H5)2].
To a solution of intermediate 2-O-mesylate 23 (37 mg, 0.059 mmol) in anhydrous methanol (2.0 ml) was added 1 M
solution of NaOCH3 in methanol (0.039 ml). The reaction mixture was stirred at room temperature for 18 h, and
then was diluted with CH2Cl2 (5 ml) and neutralized with glacial acetic acid and evaporated to dryness,
coevaporated with a mixture of ethanol-toluene (25 ml). The residue was chromatographed on a silica gel, using for
14

elution a mixture of hexane- EtOAc 8:1 and 6:1 to give (16 mg, 73%) of methyl 5-O-tert-butyldiphenylsilyl-2,3-
anhydro-α- -ribofuranoside (26) as a colorless oil.
L
g. tert-Butyldiphenylchlorosilane (0.12 ml, 0.469 mmol) was added to a solution of epoxide 25 (49 mg, 0.33 mmol)
in anhydrous pyridine (1.2 ml). The solution was stirred at room temperature for 48 h, and then the reaction mixture
was evaporated, coevaporated with toluene, the residue was dissolved in CH2Cl2 and washed with 5% aq NaHCO3,
dried over anhydrous Na2SO4 and evaporated. The residue was chromatographed on a silica gel, using for elution a
mixture of hexane- EtOAc 10:1 and 7:1 to give (110 mg, 85%) of methyl 5-O-tert-butyldiphenylsilyl-2,3-anhydro-
α-
4.2.8. Methyl 2-deoxy-α-
-Selectride (1.0 ml 1 M solution in THF, 1.0 mmol) was added dropwise under argon to a solution of epoxide 25
L-ribofuranoside (26) as a colorless oil.
L
-erythro-pentofuranoside (28)
L
(43 mg, 0.29 mmol) in anhydrous THF (0.18 ml) at -78 0С. The solution was stirred with gradually warmed to room
temperature and then, it was stirred for 1 h. Ethanol (2.5 ml) was added to the prepared solution under cooling, and
evaporated to dryness. The residue was chromatographed on a silica gel, using for elution chloroform, CHCl3-
petroleum ether-methanol (15:7:2) to give (40 mg, 93%) of methyl 2-deoxy-α-L-erythro-pentofuranoside (28) as oil.
[α]D20 –125 (c 1.0, MeOH). 1H NMR (500 MHz, CDCl3) δ: 5.09 (d, 1Н, J1,2´ < 1.0 Hz, J1,2 = 4.6 Hz, Н-1), 4.11-4.14
(m, 2Н, Н-3 and H-4), 3.71 (dd, 1Н, J4,5 = 3.7 Hz, J5,5′ = 11.8 Hz, Н-5), 3.61( dd, 1Н, J4,5′ = 4.6 Hz, Н-5′), 3.48 (d,
1H, OH), 3.38 (s, 3Н, OCH3), 2.11 (ddd, 1H, J2,3 = 6.3 Hz, Н-2′), 2.0 (d, 1Н, J2,2′ = 13.9 Hz, Н-2). 13C NMR (125
MHz, CDCl3) δ: 105.45 (C-1), 87.32 (C-4), 72.73 (C-3), 63.03 (C-5), 54.85 (OCH3), 41.50 (C-2). HRMS (ESI+):
m/z calcd for [C16H12O4+Na]+: 171.0628, found 171.0725.
4.2.9. Methyl 5-O-tert-butyldiphenylsilyl-2-deoxy-α-
L-erythro-pentofuranoside (29)
h2. -Selectride (1.6 ml 1 M solution in THF, 1.6 mmol) was added dropwise under argon to epoxide 26 (200 mg,
L
0
0.52 mmol) in 3.0 ml anhydrous THF at -78 С. The solution was stirred with gradually warmed to room
temperature and then, it was stirred for 1 h. Water (4 ml) was added to the prepared solution, the mixture was
extracted with CHCl3 (3x30 ml), combined extracts washed with 5% aq. NaHCO3, water, dried and evaporated to
dryness. The residue was dissolved in CCl4 and then filtered off, filtrate was evaporated. 2-Deoxy-α-L-erythro-
pentofuranoside (29) (200 mg, 99%) was prepared as a colorless oil. IR (film, CHCl3): ν 3457, 2958, 2934, 2857,
1
1432, 1112, 1079, 1039, 999, 702 cm-1. [α]D20 –58.7 (c 1.0, CHCl3). H NMR (500 MHz, CDCl3) δ: 7.37-7.67 [m,
10H, (CH3)3CSi(C6H5)2], 5.11 (d, 1Н, J1,2 = 4.6 Hz, Н-1), 4.30 (dd, 1Н, Н-3), 4.14-4.18 (m, 1Н, J4,5 = 3.5 Hz, J4,5′
=
4.6 Hz, Н-4), 3.75 (dd, 1Н, J5,5′ = 10.9 Hz, Н-5), 3.60 (dd, 1Н, Н-5′), 2.85 (d, 1H, 2-OH), 3.38 (s, 3Н, OCH3), 2.19
(m, 1Н, J = 4.6, J = 5.7, J = 13.0 Hz, Н-2′), 2.02 (d, 1Н, J2,2′ = 13.0 Hz, Н-2), 1.05 [s, 9H, (CH3)3CSi(C6H5)2]. 13C
NMR (125 MHz, CDCl3) δ: 135.6, 133.55, 133.18, 129.78, 129.72, 127.74, 127.71 (CH3)3CSi(C6H5)2), 105.63 (C-
1), 87.85 (C-4), 73.25 (C-3), 64.38 (C-5), 54.79 (OCH3), 41.11 (C-2), 26.79 (CH3)3C-, 19.22 (CH3)3C-. HRMS
(ESI+): m/z calcd for C22H30O4SiNa [M+Na]+: 409.1811, found 409.1811.
i. Methanol (3 ml) saturated at 0 oС with ammonia was added to a solution of the mesylate 23 (50 mg, 0.081 mmol)
in anhydrous methanol (4 ml). The reaction mixture was stirred at room temperature for 5 h, and then was
1
evaporated under diminished pressure. Intermediate 2-O-mesylate 24 was prepared as oil. Н NMR (500 MHz,
CDCl3) δ: 7.38-7.68 [m, 10H, (CH3)3CSi(C6H5)2], 5.04 (br.d, 1Н, Н-1), 4.84 (dd, 1Н, J2,1 = 1.5 Hz, J2,3 = 3.5 Hz, Н-
2), 4.35 (m, 1Н, Н-3), 4.07 (m, 1Н, J4,5 = 4.4 Hz, J4,5′ = 4.8 Hz, Н-4), 3.88 (dd, 1Н, J5,5′ = 11.2 Hz, Н-5), 3.84 (dd,
1Н, Н-5`), 3.41 (s, 3Н, OCH3), 3.03 (s, 3Н, SO2CH3), 2.64 (d, 1H, 3-OH), 1.08 [s, 9H, (CH3)3Si(C6H5)2]. 13С NMR
(125 MHz, CDCl3) δ: 135.61, 135.57, 129.82, 129.80, 127.76, 127.73 (CH3)3CSi(C6H5)2, 105.73 (C-1), 88.51, 83.1,
76.21 (C-4, C-2, С-3), 63.17 (C-5), 55.15 (OCH3), 38.07 (SO2CH3), 26.70 (CH3)3C-, 19.27 (CH3)3C-. L-Selectride
(0.27 ml 1 M solution in THF, 0.27 mmol) was added under argon to intermediate mesylate 24 in anhydrous THF
15

0
(0.3 ml) at -78 С. The solution was stirred with gradually warmed to room temperature and then, it was stirred for
19 h at room temperature. Water (2 ml) was added to the prepared solution, the mixture was extracted with CHCl3
(2x10ml), combined extracts were washed with 5% aq NaHCO3, dried and evaporated. The residue was
chromatographed on a silica gel, using for elution a mixture of hexane- EtOAc 10:1 and 7:1, 5:1 to afford (24 mg,
77%) of 2-deoxy
4.2.10. Methyl 5-O-trityl-2,3-anhydro-α-
DIAD (0.4 ml, 2.06 mmol) were added to a solution of methyl 5-O-trityl-α-
mmol) prepared according to the method described for -isomer [36] and Ph3P (540 mg, 2.06 mmol) in anhydrous
L-glycoside 29 as a colorless oil.
L
-lyxofuranoside (31)
L-arabinofuranoside (30) (400 mg, 0.98
D
THF (17 ml) at 0 0C and then a solution was stirred with gradually raising temperature to room and then the reaction
mixture was refluxed for 1 h, cooled down to rt and evaporated to dryness. The residue was chromatographed on a
silica gel, using for elution a mixture of hexane- EtOAc 10:1, 8:1, and 4:1 to give (364 mg, 94%) of trityl derivative
20
1
of methyl 2,3-anhydro-α-L-lyxofuranoside 31 as a colorless oil. [α]D +46 (c 1.0, CHCl3). H NMR (500 MHz,
CDCl3) δ: 7.25-7.52 (2m, 15H, Ar), 4.95 (s, 1H, H-1), 4.24 (dd, 1Н, Н-4), 3.94 (d, 1Н, Н-2), 3.71 (d, 1Н, Н-3), 3.45
(s, 3Н, OCH3), 3.4 (dd, 1Н, Н-5), 3.3 (dd, 1Н, Н-5′). 13C NMR (125 MHz, CDCl3) δ: 143.8, 128.7, 127.9, 127. 1
(C(C6H5)3, 102.19 (C-1), 86.97 [C(C6H5)3], 75.31 (С-4), 62.16 (C-5), 56.51, 55.54, 54.62 (C-2, C-3, OCH3). HRMS
(ESI+): m/z calcd for C25H24O4Na [M+Na]+: 411.1567, found 411.1570.
4.2.11. Methyl 5-O-trityl-3-deoxy-α-
L-threo-pentofuranoside (32)
L-Selectride (3.3 ml 1 M solution in THF, 3.3 mmol) was added under argon to 2,3-anhydrofuranose derivative 31,
0
(300 mg, 0.77 mmol) in 7 ml anhydrous THF at -78 С. The solution was stirred with gradually warmed to room
temperature and then it was stirred for 175 min. Reaction mixture was quenched with cooled 4% aqueous sodium
hydroxide, the aqueous phase was extracted with EtOAc (2x50 ml), combined organic extracts washed with water
(2x15 ml), dried over sodium hydride and evaporated to dryness. The residue was dissolved in CCl4 and then filtered
off, filtrate was evaporated. The product was chromatographed on a silica gel, using for elution a mixture of hexane-
20
EtOAc 5:1, 3:1, and 1:1 to give (272 mg, 91%) of
L
-3-deoxy sugar 32 as a colorless oil. [α]D –77 (c 1.0, CHCl3).
1H NMR (500 MHz, DMSO-d6) δ: 7.24-7.41 (m,15H, Ar), 5.00 (d, 1H, 2-OH), 4.70 (s, 1H, H-1), 4.14-4.19 (m, 1Н,
Н-4), 3.97 ( m, 1Н, Н-2), 3.23 (s, 3Н, OCH3), 3.14 (dd, 1Н, J5,4 = 6.5 Hz, J5′,5 = 9.5 Hz, Н-5), 2.97 (dd, 1Н, J5′,4 = 4.8
Hz, Н-5′), 2.16 (ddd, 1Н, J = 6.4 Hz, J = 8.0 Hz, J3,3’ = 13.2 Hz, Н-3), 1.44 (ddd, 1Н, J = 2.6 Hz, J = 5.7 Hz, Н-3’).
13C NMR (125 MHz, DMSO-d6) δ: 143.77, 128.22, 127.84 126.9 C(C6H5)3, 109.57 (C-1), 85.82 [C(C6H5)3], 76.85
(C-4), 74.03 (C-2), 66.61 (C-5), 53.87 (OCH3), 35.21 (С-3). HRMS (ESI+): m/z calcd for C25H26O4Na [M+Na]+:
413.1723, found 413.1728
4.2.12. Methyl 3-deoxy-α-L-threo-pentofuranoside (33)
d. A solution of trityl derivative 32 (210 mg, 0.55 mmol) in 63%-aqueous CH3COOH (7 ml) was stirred at 55 0C for
30 min, and then toluene was added, the reaction mixture was evaporated. The residue was chromatographed on a
silica gel, using for elution chloroform and a mixture of CHCl3:acetone - 1:1 to give (63 mg, 82%) of methyl 3-
20
1
deoxy-α-L-threo-pentofuranoside (33) as a colorless oil. [α]D –43 (c 1.0, CHCl3). Н NMR 500 MHz, CD3OD) δ:
4.8 (s, 1Н, Н-1), 4.21-4.26 (m, 1Н, Н-4), 4.70 (dd, 1Н, J2,3 = 1.8 Hz, J2,3’ = 5.9 Hz, Н-2), 3.68 (dd, 1Н, Н-5, J5,4 = 3.2
Hz, J5,5′ = 11.5 Hz, Н-5), 3.59 (dd, 1Н, J5′,4 = 4.7 Hz, Н-5′), 3.34 (s, 3Н, ОСН3), 2.34 (ddd,1H, J = 5.9 Hz, J = 8.7
Hz, J3,3’ = 13.4 Hz, H-3'), 1.66 (ddd, 1H, J = 1.8 Hz, J = 4.8 Hz, H-3). 13С NMR (125 MHz, CD3OD) δ: 111.12 (C-
1), 80.16 (C-4), 75.73 (C-2), 61.15 (C-5), 54.77 (OCH3), 35.16 (С-3). HRMS (ESI+): m/z calcd for C6H12O4
[M+Na]+: 171.0628, found 171.0625.
e.
L-Selectride (1.74 ml 1 M solution in THF) was added under argon to methyl 2,3-anhydro-α-
L-lyxofuranoside
(34) (75 mg, 0.457 mmol) prepared according to the known procedure from methyl α-
L-arabinoside 1a [22] in 0.6 ml
16

anhydrous THF at -780С. The reaction mixture was stirred with gradually warmed to room temperature and then it
was stirred for 50 min. To the prepared solution was added ethanol (5 ml) under cooling and it was evaporated. The
residue was chromatographed on a silica gel, using for elution chloroform and a mixture of CHCl3:acetone - 1:1 to
give (70 mg, 92%) of methyl 3-deoxy-α-
L-threo-pentofuranoside (33) as a colorless oil.
4.3. Synthesis of selectively protected β-
threo-pentofuranoside derivatives
L
-arabinofuranosides, 2,3-anhydro-β- -lyxofuranoside and 2-deoxy-L-
L
4.3.1. Acylation of β-L-arabinofuranoside 1b with 4-chlorobenzoyl chloride
To methyl β- -arabinoside (1b, 400 mg, 2.4 mmol) was added anhydrous CH2Cl2 (10 ml) and pyridine (0.2 ml, 2.4
L
mmol) and a solution was stirred for 30 min at room temperature, then 4-chlorobenzoyl chloride (0.32 ml, 2.5
mmоl) in anhydrous CH2Cl2 (3.5 ml) was added dropwise to prepared solution. The reaction mixture was stirred for
20 h at room temperature. Anhydrous pyridine (0.2 ml, 2.4 mmol) and solution of 4-chlorobenzoyl chloride (0.32
ml, 2.5 mmоl) in anhydrous CH2Cl2 (3.5 ml) were consequently added to the prepared solution at 0 0С. The reaction
mixture was stirred for 22 h at room temperature, and then was diluted CH2Cl2 (80 ml), water (15 ml), the aqueous
phase was extracted with CH2Cl2 (3x60 ml). The combined organic extracts was washed 0.5 N HCl (5 ml), 5% aq
NaHCO3, dried over anhydrous Na2SO4 and evaporated to dryness. The residue was chromatographed on a silica
gel, using for elution a mixture of 6:1, 4:1 and 2.5:1 hexane-EtOAc to afford (110 mg, 8%) of methyl 2,3,5-tri-O-4-
chlorobenzoyl-β-
L-arabinofuranoside (37) as a syrup. IR (film, CHCl3): ν 2950, 2931, 1732, 1599, 1404, 1268,
1
1093, 1020 cm-1. [α]D20 +102 (c 1.0, CHCl3). H NMR (500 MHz, CDCl3) δ: 7.36-8.02 (4m, 12H, 3 x СОC6H4Cl),
5.91 (dd, 1H, J3,2 = 7.0 Hz, J3,4 = 5.4 Hz, H-3), 5.45 (dd, 1Н, Н-2), 5.32 (d, 1Н, J1,2 = 4.6 Hz, Н-1), 4.73 (dd, 1Н, J5,4
= 4.6 Hz, J5,5′ = 11.6 Hz, Н-5), 4.60 (dd, 1Н, J5′,4 = 6.6 Hz, Н-5′), 4.45 (m, 1Н, Н-4), 3.37 (s, 3H, OCH3). 13C NMR
(125 MHz, CDCl3) δ: 165.32, 165.05 (C=O, 3хСОC6H4Cl), 140.24, 140.11, 139.63, 131.36, 131.20, 131.14, 128.92,
128.87, 128.71, 127.47, 127.37 (3хСОC6H4Cl), 101.35 (С-1), 78.58 (C-4), 77.63, 76.64 (C-2, С-3), 65.85 (С-5),
55.61 (ОСН3). HRMS (ESI+): m/z calcd for C27H21O8Cl3Na [M+Na]+: 601.0200, found 601.0201.
methyl 2,5-di-O-4-chlorobenzoyl-β-L-arabinofuranoside (36) (388 mg, 36%) as white solid. M.p.114–115 °С. IR
(KBr): ν 3426, 2953, 1722, 1594, 1285, 1266, 1095 cm-1. [α]D20 +28.7 (c 1.0, CHCl3). 1Н NMR (500 MHz, CDCl3)
δ: 8.00 and 7.42 (2m, 8H, 2 x ClBz), 5.17 (d, 1Н, J1,2 = 4.48 Hz, Н-1), 5.09 (dd, 1Н, J3,2 = 7.37 Hz, J1,2 = 4.5 Hz, Н-
2), 4.62 ( t, 1Н, Н-3), 4.55 (dd, 1Н, J5,4 = 4.5 Hz, J5,5′ = 11.8 Hz, Н-5), 4.47 (dd, 1Н, J5′,4 = 5.7 Hz, Н-5′), 4.28 (m,
1Н, Н-4), 3.35 (s, 3H, OCH3). 13C NMR (125 MHz, CDCl3) δ: 166.17 and 165.65 (C=O, 2хСОC6H4Cl), 140.15,
139.70, 131.32, 131.13, 128.85, 128.77, 128.17, 127.49 (2хСОC6H4Cl), 101.35 (С-1), 80.71, 79.95, 74.44 (С-4, C-
2, С-3), 65.58 (С-5), 55.42 (ОСН3). HRMS (ESI+): m/z calcd for C20H18O7Cl2Na [M+Na]+: 463.0327, found
463.0321.
methyl 2,3-di-O-4-chlorobenzoyl-β-L-arabinofuranoside (38) (20 mg, 2%) was isolated as a syrup after additional
separation of a mixture of dibenzoates 36 and 38 by column chromatography on a silica gel, using for elution
hexane-EtOAc 3:1. IR (film, CHCl3): ν 3471, 2938, 1725, 1592, 1404, 1275, 1096, 1016 cm-1. [α]D20 +181 (c 0.37,
CHCl3). 1Н NMR (500 MHz, CDCl3) δ: 7.99, 7.96, 7.42 and 7.40 (4d, 8H, 2 x СОC6H4Cl), 5.60 (dd, 1Н, J2,3 = 6.41
Hz, J2,1 = 4.71 Hz, Н-2), 5.46 (dd, 1Н, Н-3), 5.30 (d, 1Н, J1,2 = 4.71 Hz, Н-1), 4.24 (m, 1Н, Н-4), 3.92 (dd, 1Н, J5,4
=
4.0 Hz, J5,5′ = 12.0 Hz, Н-5), 3.87 (dd, 1Н, J5′,4 = 4.7 Hz, Н-5′), 3.43 (s, 3H, OCH3). 13C NMR (125 MHz, CDCl3) δ:
166.17 and 165.65 (C=O, 2хСОC6H4Cl), 140.19, 140.05, 131.31, 131.18, 128.87, 128.82, 128.68, 128.24
(2хСОC6H4Cl), 101.14 (С-1), 82.48, 78.03, 76.85 (С-4, C-2, С-3), 64.02 (С-5), 55.04 (ОСН3). HRMS (ESI+): m/z
calcd for C20H18O7Cl2 [M+Na]+: 463.0327, found 463.0322.
4.3.2. Acylation of 5-O-trityl β-
L
-arabinofuranoside 36 with 4-chlorobenzoyl chloride
17

L-Selectride (0.6 ml 1 M solution in THF, 0.6 mmol) was added dropwise to a solution of 5-O-trityl β-L-arabinoside
39 [36] (255 mg, 0.627 mmol) in anhydrous THF (3.8 ml) at 0 0С (ice and sodium chloride). The solution was stirred
0
at 0 C for 30 min and then for 20 min at room temperature. 4-Chlorobenzoyl chloride (0.16 ml, 1.26 mmol) was
0
added dropwise to prepared solution at 0 С (ice and sodium chloride). The reaction mixture was stirred under
cooling for 35 min and then 210 min at room temperature, poured in cooled 5% aq NaHCO3, the aqueous phase was
extracted with EtOAc (3x30 ml). The combined organic extracts were washed with water, dried over anh. Na2SO4,
and evaporated to dryness. The residue was chromatographed on a silica gel, using for elution a mixture of hexane-
EtOAc 8:1, 6:1 and 4:1, and EtOAc as the eluent to give (130 mg, 30%) of methyl 5-O-trityl-2,3-di-O-4-
chlorobenzoyl-β-L-arabinofuranoside (44) as white solid. M.p.62–64 °С. IR (KBr): ν 3063, 3033, 1728, 1596, 1444,
1275, 1096, 758, 702 cm-1. [α]D20 +47 (c 1.0, CHCl3). 1H NMR (500 MHz, CDCl3) δ: 7.23-7.98 [m, 23H, (C6H5)3C,
2xClBz], 5.91 (dd, 1Н, J2,3 = 6.8 Hz, J3,4 = 5.7 Hz, Н-3), 5.33 (dd, 1Н, J2,1 = 4.5 Hz, Н-2), 5.25 (d, 1H, H-1), 4.22
(m, 1H, H-4), 3.48 (dd, 1Н, J5,4 = 5.5 Hz, J5,5′ = 9.9 Hz, Н-5), 3.44 (dd, 1Н, J5′,4 = 6.5 Hz, Н-5′), 3.27 (s, 3Н, OCH3).
13C NMR (125 MHz, CDCl3) δ: 165.09, 164.59 (C=O, 2хСОC6H4Cl), 143.75, 139.88, 131.36, 131.19, 128.67,
127.91, 127.7, 127.23 [(C6H5)3C, Cl-Bz], 101.2 (C-1), 86.81 (C6H5)3C, 79.34, 77.91, 76.64 (C-4, С-2, C-3), 65.44
(C-5), 55.34 (OCH3). HRMS (ESI+): m/z calcd for C39H32O7Cl2Na [M+Na]+: 705.1423, found 705.1419.
methyl 5-O-trityl-2-O-4-chlorobenzoyl-β-L
-arabinofuranoside (43) (220 mg, 64%) as oil. [α]D20 +56 (c 1.0, CHCl3).
1Н NMR (500 MHz, CDCl3) δ: 7.23-7.99 [m, 19H, (C6H5)3C, Cl-Bz], 5.15 (d, 1Н, J1,2 = 4.5 Hz, Н-1), 5.04 (dd, 1H,
J2,3 = 7.67 Hz, H-2), 4.99 (t, 1Н, Н-3), 4.10 (m, 1H, H-4), 3.38 (dd, 1Н, J5,4 = 5.7 Hz, J5,5′ = 9.8 Hz, Н-5), 3.30 (dd,
1Н, J5′,4 = 5.27 Hz, Н-5′), 3.28 (s, 3Н, OCH3). 13C NMR (125 MHz, CDCl3) δ: 165.97 (C=O, СОC6H4Cl), 143.81,
139.84, 131.31, 128.78, 128.67, 127.86, 127.1 [(C6H5)3C, Cl-Bz], 101.1 (C-1), 86.75 (C6H5)3C, 80.79 , 80.36, 74.85
(C-4, С-2, C-3), 65.44 (C-5), 55.34 (OCH3). HRMS (ESI+): m/z calcd for C32H29O6ClNa [M+Na]+: 567.1550, found
567.1559.
4.3.3. Methyl 3-O-methanesulfonyl-2,5-di-O-4-chlorobenzoyl-β-L-arabinofuranoside (45)
To a solution of 2,5-di-O-acyl-β-
L-arabinofuranoside 36 (360 mg, 0.82 mmol) in anhydrous pyridine (14 ml) and 4-
0
dimethylaminopyridine (50 mg, 0.4 mmol) was added methanesulfonyl chloride (0.3 ml, 3.8 mmоl) at 0 C. The
reaction mixture was stirred at rt for 3 h, then diluted CH2Cl2 (50 ml), washed with water (10 ml), the aqueous phase
was extracted with CH2Cl2 (50 ml). The combined organic extracts were washed with 1 N HCl (3x30 ml), 5% aq
NaHCO3, dried over anhydrous Na2SO4, and evaporated to dryness. The residue was purified by chromatography on
20
silica gel, using a mixture of 5:1 and 4:1 hexane -EtOAc to afford (370 mg, 88%) of mesylate 45 as a syrup. [α]D
+55.4 (c 1, CHCl3). 1Н NMR (500 MHz, CDCl3) δ: 1 Н NMR (CDCl3): 8.04, 8.02, 7.45 and 7.42 (4m, 8H, 2 x
ClBz), 5.56 (dd, 1Н, J3,2 = 7.2 Hz, J3,4 = 5.7 Hz, Н-3), 5.31 (dd 1Н, H-2), 5.26 (d, 1H, J1,2 = 4.5 Hz, Н-1), 4.64 (dd,
1Н, J5,4 = 4.7 Hz, J5,5′ = 11.7 Hz, Н-5), 4.53 (dd, 1Н, J5′,4 = 5.7 Hz, Н-5′), 4.48 (m, 1Н, Н-4), 3.33 (s, 3H, OCH3),
3.08 (s, 3Н, SO2CH3). 13С NMR (125 MHz, CDCl3) δ: 165.31, 164.78 (C=O, 2хСОC6H4Cl), 140.34, 139.79,
131.34, 131.23, 129.01, 128.80, 127.18, (2хСОC6H4Cl), 100.79 (C-1), 80.37 (C-3), 77.31 (C-4), 77.26 (С-2), 64.48
(C-5), 55.66 (OCH3), 38.66 (SO2CH3). HRMS (ESI+): m/z calcd for C29H20O9SCl2 [M+Na]+: 541.0103, found
541.0108.
4.3.4. Methyl 2,3-anhydro-β-L-lyxofuranoside (46)
1 M solution of NaOCH3 in methanol (1.2 ml) was added to a solution of mesylate (45, 360 mg, 0.69 mmol) in
anhydrous methanol (10 ml). The prepared solution was stirred at room temperature for 18 h, and then the reaction
mixture was neutralized with glacial acetic acid and evaporated to dryness, coevaporated with a mixture of ethanol-
toluene (40 ml). The residue was chromatographed on a silica gel, using for elution chloroform, CHCl3-petroleum
ether-methanol (16:8:2) to give (93 mg, 91%) of methyl 2,3-anhydro-β-L-lyxofuranoside (46) as a colorless oil.
18

[α]D20 +88 (c 1.1, CHCl3). Lit. for -isomer [42]. [α]D25 –106.8 (c 1.0, H2O). 1H NMR (500 MHz, CDCl3) δ: 5.02 (s,
D
1Н, J1,2 <1.0 Hz, Н-1), 4.01 (t, 1Н, J4,3 <1.0 Hz, J4,5 = 5.7 Hz, J4,5′ = 5.4 Hz, Н-4), 3.88 (dd, 1Н, J5,5′ = 11.4 Hz, Н-5),
3.85 (dd, 1Н, Н-5), 3.71 (br.d, 1Н, Н-3), 3.69 (br.d, 1Н, J2,3 = 2.9 Hz, Н-2), 3.51 (s, 3Н, OCH3). 13C NMR (125
MHz, CDCl3) δ: 102.35 (C-1), 76.68 (C-4), 61.81 (C-5), 56.88 (OCH3), 55.31 (C-2), 54.82 (C-3). HRMS (ESI+):
m/z calcd for C6H10O4Na [M+Na]+: 169.0477, found 169.0482.
4.3.5. Methyl 5-O-tert-butyldiphenylsilyl-2,3-anhydro-β-L-lyxofuranoside (47)
To a solution of epoxide 46 (31 mg, 0.21 mmol) in anhydrous pyridine (0.9 ml) was added tert-
butyldiphenylchlorosilane (0.08 ml, 0.31 mmol). The solution was stirred at room temperature for 48 h, and then the
reaction mixture was evaporated, coevaporated with toluene, then residue was dissolved in CH2Cl2 and washed with
5% aq NaHCO3, dried and evaporated to dryness. The residue was chromatographed on a silica gel, using for elution
a mixture of hexane-ethylacetate 10:1 and 7:1 to give (65 mg, 80%) of silyl derivative of methyl 2,3-anhydro-β-
L-
20
lyxofuranoside 47 as a colorless oil. IR (film, CHCl3): ν 2956, 2934, 2894, 2861, 1115, 1063, 1055 cm-1. [α]D
+53.6 (c 0.5, CHCl3). 1H NMR (500 MHz, CDCl3) δ: 7.37-7.71 [m, 10H, (CH3)3CSi(C6H5)2], 5.00 (d, 1Н, J1,2 = 0.5
Hz, Н-1), 4.04 (ddd, 1Н, J4,5 = 5.3 Hz, J4,5′ = 8.4 Hz, J4,3 = 0.8 Hz, Н-4), 3.91 (dd, 1Н, J5,5′ = 9.7 Hz, Н-5), 3.85 (dd,
1Н, J2,3 =3.0 Hz, Н-3), 3.84 (dd, 1Н, Н-5′), 3.72 (d, 1Н, Н-2), 3.46 (s, 3Н, OCH3), 1.08 (s, 9H, (CH3)3CSi(C6H5)2.
13C NMR (125 MHz, CDCl3) δ: 135.49, 133.35, 133.21, 129.71, 127.72, 127.69 (CH3)3CSi(C6H5)2, 102.32 (C-1),
76.75 (C-4), 62.07 (C-5), 56.67(OCH3), 55.92, 55.27 (C-3, C-2), 26.80 (CH3)3C-, 19.22 (CH3)3C-. HRMS (ESI+):
m/z calcd for C22H28O4SiNa [M+Na]+: 407.1655, found 407.1651.
4.3.6. Methyl 5-O-tert-butyldiphenylsilyl-2-deoxy-β-
L-threo-pentofuranoside (48)
L-Selectride (0.45 ml 1 M solution in THF, 0.45 mmol) was added under argon to epoxide 47 (60 mg, 0.156 mmol)
in anhydrous THF (0.5 ml) at -78 0С. The solution was stirred with gradually warmed to room temperature and then,
it was stirred for 1 h. Water (3 ml) was added to the prepared solution, the reaction mixture was extracted with
CHCl3 (2x20 ml), combined extracts washed with 5% aq NaHCO3, water, dried and evaporated to dryness. The
residue was dissolved in CCl4 and then filtered off, filtrate was evaporated. 2-Deoxy L-sugar 48 (60 mg, 99%) was
prepared as a colorless oil. IR (film, CHCl3): ν 3450, 2956, 2934, 2862, 1107, 1049, 1015, 805, 409 cm-1. [α]D20 +36
1
(c 0.67, CHCl3). Lit. for D-isomer [43]. [α]D20 –54 (c 0.31, CHCl3). H NMR (500 MHz, CDCl3) δ: 7.37-7.73 [m,
10H, (CH3)3CSi(C6H5)2], 5.04 (dd, 1Н, J1,2´ = 1.6 Hz, J1,2 = 3.7 Hz, Н-1), 4.33 (m, 1Н, Н-4), 4.10 (m, 1Н, Н-3), 4.05
(dd, 1Н, J4,5 = 5.7 Hz, J5,5′ = 10.6 Hz, Н-5), 3.87 (dd 1Н, J4,5′ = 5.8 Hz, Н-5′), 3.29 (s, 3Н, OCH3), 2.94 (d, J = 9.7
Hz, 3-OH), 2.10-2.14 (m, 2Н, Н-2 and Н-2′), 1.07 [s, 9H, (CH3)3CSi(C6H5)2]. 13C NMR (125 MHz, CDCl3) δ:
135.60, 133.39, 133.39, 129.65, 127.66 (CH3)3CSi(C6H5)2, 105.04 (C-1), 84.57 (C-4), 71.47 (C-3), 63.67 (C-5),
54.92 (OCH3), 41.39 (C-2), 26.80 (CH3)3C-, 19.17 (CH3)3C-. HRMS (ESI+): m/z calcd for C22H30O4SiNa [M+Na]+:
409.1811, found 409.1807.
4.3.7. Methyl 2-deoxy-β-
L
-threo-pentofuranoside (50) and methyl 3-deoxy-β-
L
-threo-pentofuranoside (51)
-lyxofuranoside (46)
L-Selectride (2.0 ml 1 M solution in THF) was added under argon to methyl 2,3-anhydro-β-
L
(90 mg, 0.61 mmol) in 0.7 ml anhydrous THF at -780С. The reaction mixture was stirred with gradually warmed to
room temperature and then it was stirred for 90 min. Reaction mixture was treated with 10% NaOH (3 ml) and 30%
0
H2O2 (2.1 ml) under 0 C ice-cooling and then was stirred for 10 min at rt and evaporated under high vacuum and
mild heating. The residue was chromatographed on a silica gel, using for elution chloroform and a mixture of
CHCl3:acetone - 1:1 to give a mixture (47 mg, a ratio of 2-deoxy and 3-deoxy-isomers - 1:1.1, 51%) of methyl 2-
1
deoxy-β-L-threo-pentofuranoside (50) and methyl 3-deoxy-β-
L
-threo-pentofuranoside (51) as a colorless oil. Н
NMR (500 MHz, CDCl3) δ: 5.04 (d, 1Н, J1,2 = 4.7 Hz, Н-1, 2-deoxy-derivative), 4.75 (d, 1.1 Н, J1,2 = 4.5 Hz, Н-1, 3-
deoxy-derivative), 4.37 (t, 1H, H-4), 4.19-4.26 (m, 2.2Н, Н-4 and H-3), 4.11 (t, 1H, H-3), 3.87 (d, 2H, 2H-5), 3.70
19

(dd, 1Н, J4,5 = 2.9 Hz, J5,5’ = 11.8 Hz, Н-5), 3.48-3.51 (dd, 1Н, Н-5′), 3.49 (s, 3.3Н, ОСН3), 3.40 (s, 3H, ОСН3),
2.23-2.29 (ddd, 1H, H-3′), 2.16-2.21 (ddd, 1H, H-2′), 2.10 (dd, 1H, H-2), 1.74 (dt, 1H, H-3). 13С NMR (125 MHz,
CDCl3) δ: 104.99 (C-1, 2-deoxy), 102.48 (C-1, 3-deoxy), 83.34 (C-4), 78.5 (C-4), 72.69, 71.97 (C-2 and C-3), 65.23
(C-5, 3-deoxy), 62.58 (C-5, 2-deoxy), 54.78 (OCH3, 3-deoxy), 55.08 (OCH3, 2-deoxy), 41.83 (C-2, 2-deoxy), 32.20
(С-3, 3-deoxy). HRMS (ESI+): m/z calcd for C6H12O4 [M+Na]+: 171.0628, found 171.0631.
Supplementary data
Supplementary data associated with this article can be found, in the online version.
Acknowledgments
This work was supported from Chempharmsynthesis Program (Grant 2.49), National Academy of Sciences of
Belarus
References
[1] J. Lawandi, S. Rocheleau, N. Moitessier, Regioselective acylation, alkylation, silylation and glycosylation of
monosaccharides, Tetrahedron. 72 (2016) 6283-6319. https:// doi.org/10.1016/j.tet.2016.08.019.
[2] W. Muramatsu, Recent Advances in the Regioselective Functionalization of Carbohydrates Using Non-
Enzymatic Catalysts, Trends in Glycoscience and Glycotechnology. 28 (2016) E1-E11. https://
doi/10.4052/tigg1502.1E.
[3] M. Jager, A.J. Minnaard, Regioselective modification of unprotected glycosides, Chem. Commun. 52 (2016)
656-664. https://doi.org/10.1039/c5cc08199h.
[4] D. Lee, M.S. Taylor, Catalyst-Controlled Regioselective Reactions of Carbohydrates Derivatives, Synthesis. 44
(2012) 3421-3431. https://doi.org/10.1055/s-0032-1317483.
[5] W. Muramatsu, Y. Takemoto, Selectivity Switch in the Catalytic Functionalization of Nonprotected
Carbohydrates: Selective Synthesis in the Presence of Anomeric and Structurally Similar Carbohydrates under Mild
Conditions, J. Org. Chem. 78 (2013) 2336-2345. https://doi.org/10.1021/jo3024279.
[6] I-Hon. Chen, K.G.M. Kou, D.N. Le, C.M. Rathbun, V.M. Dong, Recognition and Site-Selective Transformation
of Monosaccharides by Using Copper (II) Catalysis, Chem. Eur. J. 20 (2014) 5013-5018. https://
doi.org/10.1002/chem.201400133.
[7] S. Rocheleau, J. Pottel, I. Huskic, N. Moitessier, Highly Regioselective Monoacylation of Unprotected
Glycopyranosides Using Transient Directing-Protecting Groups, Eur. J. Org. Chem. (2017) 646-656. https://
doi.org/10.1002/ejoc.201601457.
[8] J. Thiem, Applications of enzymes in synthetic carbohydrate chemistry, FEMS Microbiol. Reviews. 16 (1995)
193-211. https:// doi.org/10.1111/j.1574-6976.1995.tb00166.x.
[9] S.J. Jun, M.S. Moon, S.H. Lee, C.S. Cheong, K.S. Lim, Selective monoacetylation of methyl 2,3,5-tri-O-acetyl-
D-arabinofuranoside
using
biocatalyst,
Tetrahedron
Lett.
46
(2005)
5063-5065.
https://
doi.org/10.1016/j.tetlet.2005.05.120.
[10] A.K. Pathak, V. Pathak, W.J. Suling, J.R. Riordan, S.S. Gurcha, G.S. Besta, R.C. Reynolds, Synthesis of
deoxygenated α-(1-5)-linked arabinofuranose disaccharides as substrates and inhibitors of arabinosyltransferases of
Mycobacterium tuberculosis, Bioorg. Med. Chem. 17 (2009) 872-881. https://doi.org/10.1016/j.bmc.2008.11.027.
[11] H-Z. Li, J. Ding, Ch.-R. Cheng, Y. Chen, X-Y. Liang, β-
pyridinecarbonyl)- -arabinofuranosyl Trichloroacetimidate, Carbohydr. Res. 460 (2018) 1-7. https:
//doi.org/10.1016/j.carres.2018.02.006.
[12] J.J. Forsman, R. Leino, -Pentoses in Biological and medical Applications, Chem. Rev. 111 (2011) 3334-3357.
L-Arabinofuranosylation Conducted by 5-O-(2-
L
L
https://doi.org/10.1021/cr1002563.
[13] D.N. Standring, E.G. Bridges, L.T. Placidi, A. Faraj, A.G. Loi, C. Pierra, D. Dukhan, G. Gosselin, J.-L.
Imbach, B. Hernandez, A. Juodawlkis, B. Tennant, B. Korba, P. Cote, E. Cretton-Scott, R.F. Schinazi, M. Myers,
M.L. Bryant, J.-P. Sommadossi, Antiviral β-L-nucleosides specific for haepatitis B virus infection, Antiv. Chem. &
Chemother. 12 (2001) 119–129.
[14] C. Mathe, G. Gosselin, L-Nucleoside enantiomers as antiviral drugs: A mini-review, Antiviral Res. 71 (2006)
276-281. https://doi.org/10.1016/j.antiviral.2006.04.017.
[15] A. Kirschining, M. Jesberger, K-U. Schoning, Concept for the total synthesis of deoxy sugars, Synthesis. 4
(2001) 507-540. https://doi.org/10.1055/S-2001-12342.
[16] H. Uchimiya, T. Furukawa, M. Okamoto, Y. Nakajima, S. Matsushita, R. Ikeda, T. Gotanda, M. Hraguchi, T.
Sumizava, M, Ono, M. Kuwano, T. Kanzaki, S. Akiyama, Suppression of Thymidine Phosphorylase-mediated
Angiogenesis and Tumor Growth by 2-Deoxy-L-ribose, Cancer Res. 62 (2002) 2834-2839.
[17] Y. Kawabata, S. Kaneko, I. Kusakabe, Y. Gama, Synthesis of regioisomeric methyl α-L-arabinofuranobiosides,
Carbohydr. Res. 267 (1995) 39-47. https://doi.org/10.1016/0008-6215(94)00290-v.
20

[18] S. Kaneko, Y. Kawabata, T. Ishii, Y. Gama, I. Kusakabe, The core trisaccharide of
of methyl 3,5-di-O-α- -arabinofuranosyl-α- -arabinofuranoside, Carbohydr. Res. 268 (1995) 307-311.
https://doi.org/10.1016/0008-6215(94)00327-c.
L-arabinofuranan: Syntheses
L
L
[19] F.W. D’Souza, J.D. Ayers, P.R. McCarren, T.L. Lowary, Arabinofuranosyl Oligosaccharides from
Mycobacteria: Synthesis and Effect of Glycosylation on Ring Conformation and Hydroxymethyl Group Rotamer
Populations, J. Am. Chem. Soc. 122 (2000) 1251-1260. https://doi.org/10.1021/ja9935431.
[20] Y. Du, Q. Pan, F. Kong, An efficient and concise regioselective synthesis of α-(1‒5)-linked L-arabinofuranosyl
oligosaccharides, Carbohydr. Res. 329 (2000) 17-24. https://doi.org/10.1016/S0008-6215(00)00159-2.
[21] T.L. Lowary, Twenty Years of Mycobacterial Glycans: Furanosides and Beyond, Acc. Chem. Res. 49 (2016)
1379-1388. https://doi.org/10.1021/acs.accounts.6b00164.
[22] O. Schulze, J. Voss, G. Adiwidjaja, Preparation of methyl 2,3-Anhydro- and 2,3-O-Sulfinylfuranosides from
Unprotected Furanosides Using the Mitsunobu Reaction, Synthesis. 2 (2001) 229-234. https://doi.org/10.1055/S-
2001-10806.
[23] R.R. Gadikota, C.S. Callam, T.L. Lowary, Stereocontrolled Synthesis of 2,3-Anhydro-β-
Glycosides, Org. Lett. 3 (2001) 607-610. https://doi.org/10.1021/ol007008y.
D
-lyxofuranosyl
-ribofuranoside,
-Pentose
[24] C.S. Callam, R.R. Gadikota, T.L. Lowary, An efficient synthesis of methyl 2,3-anhydro-α-
D
Carbohydr. Res. 330 (2001) 267-270. https://doi.org/10.1016/s0008-6215(00)00227-9.
[25] M. Taniguchi, K. Koga, S.-I. Yamada, Stereochemical Studies. XXXI. Total Synthesis of Several
Derivatives. Stereochemical Courses for the Synthesis of Four Methyl 2,3-Anhydro-5-O-benzyl- -pentofuranosides
from -Clutamic Acid and Their Reactions with Nucleophiles, Chem. Pharm. Bull. 22 (1974) 2318-2323. https:
//doi.org/10.1248/cpb.22.2318.
[26] O.M. Cociorva, T.L. Lowary, 2,3-Anhydrosugars in glycoside bond synthesis. Application to the preparation of
C-2 functionalized α- -arabinofuranosides, Tetrahedron 60 (2004) 1481-1489.
https://doi.org/10.1016/j.tet.2003.12.022.
D
D
D
D
[27] D. Hou, H.A. Taha, T.L. Lowary, 2,3-Anhydrosugars in Glycoside Bond Synthesis: Mechanism of 2-deoxy-2-
thioaryl Glycoside Formation, J. Am. Chem. Soc. 131 (2009) 12937-12948. https://doi.org/10.1021/ja9029945.
[28] G.G. Sivets. Regio- and stereoselective syntheses of
(2018) 920-931. https://doi.org/10.1016/j.tet.2017.12.045.
L-pentose derivatives from L-arabinose, Tetrahedron. 74
[29] E.V. Evtushenko, Regioselective Benzoylation of Glycopyranosides by Benzoyl Chloride in the presence of
MoO2(acac)2, J. Carbohydr. Chem. 29 (2010) 369-378. https://doi.org/10.1080/07328303.2010.549258.
[30] T. Kawabata, W. Muramatsu, T. Nishio, T. Shibata, H. Schedel, A catalytic One-step Process for the Chemo-
and Regioselective Acylation of Monosaccharides, J. Am. Chem. Soc. 129 (2007) 12890-12895. https:
//doi.org/10.1021/ja074882e.
[31] K. Oshima, E.-I. Kitazano, Y. Aoyama, Complexation-induced activation of sugar OH groups. Regioselective
alkylation of methyl fucopyranoside via cyclic phenylboronate in the presence of amine, Tetrahedron Lett. 38
(1997) 5001-5004. https://doi.org/10.1016/S0040-4039(97)01070-8.
[32] J.M. Williams, A.C. Richardson, Selective acylation of pyranosides - I. Benzoylation of methyl α-D-
glycopyranosides of mannose, glucose and galactose, Tetrahedron. 23 (1967) 1369-1378.
https://doi.org/10.1016/0040-4020(67)85091-9.
[33] S.A. Blaszczyk, T.C. Homan, W. Tang, Recent advances in site-selective functionalization of carbohydrates
mediated by organocataltsis, Carbohydr. Res. 471 (2019) 64-67. https:// doi.org/10.1016/j.carres.2018.11.012.
[34] C.G.-D. Dellac, G.Gosselin, J.-L.Imbach, Preparation of new acylated derivatives of
deoxy- -erythro-pentofuranose as precursors for the synthesis of -pentofuranosyl nucleosides, Carbohydr. Res. 216
(1992) 249-255. https://doi.org/10.1016/0008-6215(82)84166-P.
L-arabinofuranose and 2-
L
L
[35] L. Jang, T.-H. Chan, Regioselective Acylation of Hexopyranosides with Pivaloyl Chloride, J. Org. Chem. 63
(1998) 6035-6938. https: // doi.org/10.1021/jo980294v.
[36] A.N. Cuzzupe, R. Di Florio, M.A. Rizzacasa, Enantiospecific Synthesis of the Phospholipase A2 Inhibitor (-)-
Cinatrin B, J. Org. Chem. 67 (2002) 4392-4398. https://doi.org/10.1021/jo016221k.
[37] P. Hansen, E.B. Pedersen, A simple synthetic route to silylated methyl 3-azido-2,3-dideoxy-α,β-D-erythro-
pentofuranoside, Acta Chem. Scandinavica. 44 (1990) P.522-523. https:// doi.org/10.3891/acta.chem.scand.44-0522.
[38] N.R. Williams. Advances in Carbohydrate Chemistry and Biochemistry, ed.by R.S. Tipson and D. Horton,
Academic Press, New York and London. 25 (1970) 109.
[39] P.J. Domaille, J.D. Druliner, L.W. Gosser, J.M. Read, E.R. Schmeizer, W.R. Stevens, Triphenylborane
methanolysis and equilibrium association between triphenyl borane or diphenylborinate esters and alcohols, J. Org.
Chem. 50 (1985) 189-194. https://doi.org/10.1021/jo00202a010.
[40] D. Lee, M.S. Taylor, Borinic Acid-Catalyzed Regioselective Acylation of Carbohydrate Derivatives, J. Am.
Chem. Soc. 133 (2011) 3724-3727. https://doi.org/10.1021/ja110332r.
[41] B.K. Chun, R.F. Schinazi, Y.-Ch. Cheng, Ch.K .Chu, Synthesis of 2´,3´-dideoxy-3´-fluoro-
L-ribonucleosides as
potential antiviral agents from
6215(99)00312-2.
D-sorbitol, Carbohydr. Res. 328 (2000) 49-59. https:// doi.org/10.1016/s0008-
[42] M.A. Thome, M.B. Giudicelli, D. Picq, D. Anker, An Improved Synthesis of methyl 2,3-Anhydro-α- and β-D-
lyxofuranosides, J. Carbohydr. Chem. 10 (1991) 923-926. https://doi.org/10.1080/0732830910854396.1.
21

[43] G.W.J. Fleet, J.C. Son, A.E. Derome, Methyl 5-O-tert-butyldiphenylsilyl-2-deoxy-αβ-D-threo-pentofuranoside
as a divergent intermediate for the synthesis of 3´-substituted-2´,3´-dideoxynucleosides: synthesis of 3´-azido-3´-
deoxythymidine, 3´-deoxy-3´-fluorothymidine and 3´-cyano-3´-deoxy-thymidine, Tetrahedron. 44 (1988) 625-636.
https://doi.org/10.1016/s0040-4020(01)85850-6.
[44] D.Hou, T.L. Lowary, Stereoselective Synthesis of 2-Deoxy-furanosides from 2,3-Anhydro-furanosyl
Thioglycosides, Org. Lett. 9 (2007) 4487-4490. https://doi.org/10.1021/ol7019108.
[45] Q-W. Liu, H-Ch. Bin, J.-S. Yang, β-Arabinofuranosylation Using 5-O-(2-Quinolinecarbonyl) Substituted Ethyl
Thioglycoside Donors, Org. Lett 15(2013) 3974-3977. https://doi.org/10.1021/ol401755e.
22

•
•
•
•
Novel mono- and di-O-protected L-arabinofuranoside derivatives were synthesized.
A method of selective acylation of 5-O-protected L-arabinosides was investigated.
Acylation reactions of α- and β-L-arabinofuranosides differ in regioselectivity.
2(3)-L-deoxyglycosides were prepared via stereoselective L-Selectride reductions.

Declaration of interests
☒ The authors declare that they have no known competing financial interests or personal relationships
that could have appeared to influence the work reported in this paper.
☐The authors declare the following financial interests/personal relationships which may be considered
as potential competing interests:
Declarations of interests: none