A facile, one-step conversion of 6-O-trityl and 6-O-TBDMS monosaccharides into the corresponding formate esters

Article abstract of DOI:10.1080/07328300600859668

A convenient method has been developed for a facile and high-yield conversion of 6-O-tert-butyldimethylsilyl and 6-O-trityl protected monosaccharides to their formate esters, which may serve as useful intermediates for the replacement of the primary hydro

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A Facile, One‐Step Conversion of 6‐O‐Trityl
and 6‐O‐TBDMS Monosaccharides into the
Corresponding Formate Esters
Dr. Dimitri Komiotis a , George Agelis a , Stella Manta a , Niki Tzioumaki a
Evangelia Tsoukala a & Kostas Antonakis b
,
a Department of Biochemistry and Biotechnology, Laboratory of Organic
Chemistry, University of Thessaly, Larissa, Greece
b Ecole Nationale Superieure de Chimie de Paris, Paris, France
Version of record first published: 22 Sep 2006.
To cite this article: Dr. Dimitri Komiotis, George Agelis, Stella Manta, Niki Tzioumaki, Evangelia Tsoukala &
Kostas Antonakis (2006): A Facile, One‐Step Conversion of 6‐O‐Trityl and 6‐O‐TBDMS Monosaccharides into the
Corresponding Formate Esters, Journal of Carbohydrate Chemistry, 25:6, 441-450
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Journal of Carbohydrate Chemistry, 25:441–450, 2006
Copyright # Taylor & Francis Group, LLC
ISSN: 0732-8303 print 1532-2327 online
DOI: 10.1080/07328300600859668
A Facile, One-Step
Conversion of 6-O-Trityl
and 6-O-TBDMS
Monosaccharides into
the Corresponding
Formate Esters
Dimitri Komiotis, George Agelis, Stella Manta, Niki Tzioumaki,
and Evangelia Tsoukala
Department of Biochemistry and Biotechnology, Laboratory of Organic Chemistry,
University of Thessaly, Larissa, Greece
Kostas Antonakis
Ecole Nationale Superieure de Chimie de Paris, Paris, France
A convenient method has been developed for a facile and high-yield conversion of 6-O-
tert-butyldimethylsilyl and 6-O-trityl protected monosaccharides to their formate
esters, which may serve as useful intermediates for the replacement of the primary
hydroxyl group of sugars by other functional groups.
Keywords Formate ester, Formic acid, Trityl, tert-Butyldimethylsilyl, O-branched
chain reactions
INTRODUCTION
Multiple use of protecting groups is a critical part of many synthetic schemes
that involve carbohydrate, nucleoside, and natural product chemistry. Trityl
and silyl ethers, including the tert-butyldimethylsilyl group (TBDMS), have
Received December 28, 2005; accepted May 30, 2006.
Address correspondence to Dr. Dimitri Komiotis, Department of Biochemistry and Bio-
technology, Laboratory of Organic Chemistry, University of Thessaly, Ploutonos 26,
41221 Larissa, Greece. E-mail: dkom@bio.uth.gr
441

D. Komiotis et al.
442
become popular protecting groups for hydroxyl functions during complex mul-
tistep syntheses, especially when orthogonal protection/deprotection steps are
required.[1,2] These ethers display a unique set of properties, ranging from their
easy introduction to their good stability under a wide range of conditions and
possible one-step deprotection.[1,2] Nevertheless, if performed on multifunc-
tional or sensitive molecules, one-step O-trityl and O-TBDMS deprotection
may be problematic.[3,4] Alternatively, innovative two-step procedures inter-
converting trityl and TBDMS ethers to a different kind of protected ether
followed by its smooth hydrolysis could also be of interest.
O-Formylation could be the method of choice for protecting an alcoholic
group in a complex synthetic sequence because it can be selectively introduced
to primary hydroxyl groups[5] and deformylation can be effected selectively in
the presence of other ester-protecting groups.[6,7] Further, if the alcoholic
group is planned to be oxidized, the formylated alcoholic group need not be
deprotected and direct oxidation under Oppenauer conditions can be
realized.[8,9] In some steroidal transformations formylation has been found to
be superior to acetylation.[8] Formate esters also serve as useful synthetic
reagents and intermediates, and specifically for O-branched chain extension
reactions through Wittig type olefinations.[10–14] Despite these uses and
considerable potential, the formyl-protecting group has been rather overlooked.
Various one-step formylation methods have been reported over the years,
using formylation agents such as formyl fluoride, formic acetic anhydride,[15]
2-(N-methyl-N-formylamino)pyridine, dimethylchloromethyl-ammonium chlor-
ide, N-formylbenzotriazole,[16] and N,N-dimethylformamide,[17] among many
others.[18] However, there are serious limitations for the preparation of
formate esters due to the hard experimental conditions, the use of uncommon
reagents, and formation of undesirable or toxic byproducts. Recently the one-
step conversion of silyl ethers into the corresponding formates has been
reported using PPh3/CBr4 in HCOOEt/H2O[19] or POCl3/DMF.[20–23]
In this work a new highly efficient, simple, and low-cost method for such
conversion is described and its mechanism is tentatively proposed. Thus,
6-O-TBDMS and 6-O-trityl monosaccharides were converted into the corre-
sponding formate esters. Besides, the potential usefulness of such transform-
ation for subsequent O-branched chain extension is exemplified.
RESULTS AND DISCUSSION
Methyl b-D-galactopyranoside, methyl a-D-mannopyranoside, and methyl a-D-
glucopyranoside were tritylated or silylated and then acetylated, one pot, to
give in over 85% yield trityl derivatives 1, 3, and 5, and silyl derivatives 2, 4,
and 6, respectively. Treatment of the trityl derivatives 1, 3, and 5 with a 1/1
mixture of concentrated formic acid/diethyl ether at reflux temperature for

Conversion of 6-O-Trityl and 6-O-TBDMS Sugars into Formate Esters
443
30 min afforded formate esters 7 (86%), 8 (90%), and 9 (87%), respectively
(Sch. 1). Likewise, the same compounds were obtained in over 80% yield
upon reaction for 60 min in a 1.5/1 formic acid/diethyl ether mixture of silyl
derivatives 2, 4, and 6, respectively.
1
These results were confirmed by H NMR spectroscopy, which indicated
a singlet at around 8 ppm corresponding to the formate proton and a deshield-
ing of the protons at position 6 by an average of 0.40 ppm as commonly observed
for such transformation.[23] Moreover, when products 7–9 were deformylated
under conventional conditions,[6] the corresponding 2,3,4-tri-O-acetylated
Scheme 1: Reagents and conditions: i. (R ¼ Tr) HCOOH/diethyl ether (1/1), reflux, 30 min;
ii. (R ¼ TBDMS) HCOOH/diethyl ether (1,5/1), 60 min; iii. MeOH, 3 days, 258C.

D. Komiotis et al.
444
derivatives 10[24] (92%), 11[25] (96%), and 12[26] (94%) were isolated,
respectively. The overall good yields of 10–12 thus obtained ascertained that
no acetyl migration had occured. It is interesting to note that the four-step
transformation of the methyl glycosides provides the tri-O-acetylated
products in higher yield (68% to 77%) than the more familiar three-step route
(37% to 62%),[24–26] reinforcing the potential of the described methodology.
Of note, when the formylation reaction was attempted on compounds 1 to 6
at rt for 7 and 15 min, the detritylated and desilylated derivatives (10–12),
respectively, were mainly obtained.[27] The reaction mechanism probably
involves the oxonium cation formed by the self-dissociation of formic acid in
nonaqueous media. Addition of the formic oxonium cation to the trityl or
TBDMS ether gave the intermediate 13. Elimination of TrOH or TBDMSOH
affords the corresponding formate 15 via the intermediate 14 (Sch. 2). It is
hypothesized that the elimination step is fast at high temperature, but slow
at room temperature, and hydrolysis of intermediate 13 will occur during the
aqueous work-up.
Methyl 2,3,4-tri-O-acetyl-6-O-formyl-a-D-glucopyranoside (9) was treated
with carbomethoxymethylene triphenylphosporane in toluene to afford, in
a Wittig-type reaction,[10–14] the methyl acrylate derivative 16 (Sch. 3).
1H NMR data for this compound (J ¼ 12,7 Hz) confirmed the presence of the
E isomer only.
In conclusion, the reported procedure describes a one-step formylation of
primary 6-O-TBDMS and 6-O-trityl monosaccharides into their corresponding
formate esters. The method provides several advantages, including operational
simplicity, mild reaction conditions, low cost of the reagents, and high yields of
the formylated products. Formates can serve as intermediates for the replace-
ment of the primary hydroxyl group of sugars by other functional groups such
as aldehydes[28] and vinyl ethers.[14] In particular, their conversion to Wittig-
Horner products may allow the introduction of additional diversity based on
the choice of the Wittig-Horner reagent. Thus, formates and their Wittig-
Horner products could be very useful intermediates for coupling of
Scheme 2

Conversion of 6-O-Trityl and 6-O-TBDMS Sugars into Formate Esters
445
Scheme 3
carbohydrates to biologically important molecules as well as important key
precursors to oligosaccharide or glycoconjugate mimics.[29–36]
EXPERIMENTAL
Melting points were recorded in a Mel-Temp apparatus and are uncorrected.
TLC was performed on Silica Gel (240–400 mesh, Merck). NMR spectra
were recorded at rt with a Brucker 250-MHz spectrometer in CDCl3 with
internal TMS. Mass spectra were obtained with a Micromass Platform LC
(ESI-MS).
Methyl 2,3,4-tri-O-acetyl-6-O-trityl-b-D-galactopyranoside (1). A solution
of methyl b-D-galactopyranoside (1 g, 5.1 mmol) and trityl chloride (1.55 g,
5.4 mmol) in pyridine (5 mL) was heated for 3 h at 1008C, and then kept over-
night at rt. To the solution, acetic anhydride (4 mL, 42.4 mmol) was added, and
the mixture was kept for 24 h at rt. It was then poured into ice water, and the
solid was filtered off, washed with water, and dried. The product was recrystal-
lized from ether-petroleum ether to give 1 (2.49 g, 86%). NMR spectra were
identical to those described.[24] m.p. 139–1418C, lit.[24] m.p. 1388C.
Methyl 2,3,4-tri-O-acetyl-6-O-trityl-a-D-mannopyranoside (3). Compound 3
was prepared from methyl a-D-mannopyranoside as for 1 in 89% yield, and
crystallized from ethanol. NMR spectra were identical to those described.[25]
m.p. 99–1018C, lit.[25] m.p. 97–988C.
Methyl 2,3,4-tri-O-acetyl-6-O-trityl-a-D-glucopyranoside (5). Compound
5 was prepared from methyl a-D-glucopyranoside as for 1 in 89% yield, and
crystallized from ethanol. NMR spectra were identical to those described.[26]
m.p. 134–1368C, lit.[26] m.p. 132–1358C.

D. Komiotis et al.
446
Methyl 2,3,4-tri-O-acetyl-6-O-tert-butyldimethylsilyl-b-D-galactopyra-
noside (2). A solution of methyl b-D-galactopyranoside (1 g, 5.1 mmol) and
TBDMS chloride (1 g, 6.6 mmol) in pyridine (10 mL) was stirred for 1 h at
0–58C, and then kept overnight at rt. To the solution, acetic anhydride
(4 mL, 42.4 mmol) was added, and the mixture was kept for 24 h at rt. Then
MeOH (4 mL) was added and the solvent was removed under reduced
pressure. Column chromatography (EtOAc/hexane 1/9) of the residue gave
compound 2 (2.62 g, 98%). Rf 0.44 (EtOAc/hexane 1/9); 1H NMR (CDCl3,
250 MHz) d 5.44 (d, 1H, J ¼ 3.4 Hz, H-4), 5.15 (dd, 1H, J ¼ 10.4 Hz,
J ¼ 7.9 Hz, H-2), 5.01 (dd, 1H, J ¼ 3.4 Hz, J ¼ 10.4 Hz, H-3), 4.36 (d, 1H,
J ¼ 7.9 Hz, H-1), 3.70 (m, 2H, H-6), 3.61 (m, 1H, H-5), 3.47 (s, 3H, OMe),
2.09, 2.02, 1.94 (3s, 9H, 3Ac) ppm; ESI-MS (m/z): Found 435.85 (M þ Hþ).
Anal. Calcd. for C19H34O9Si: C, 52.52; H, 7.89. Found C, 52.36; H, 7.52.
Methyl 2,3,4-tri-O-acetyl-6-O-tert-butyldimethylsilyl-a-D-mannopyra-
noside (4). Compound 4 was prepared from methyl a-D-mannopyranoside as
1
for 2 (87%). Rf 0.40 (EtOAc/hexane 1/9); H NMR (CDCl3, 250 MHz), d 5.32
(dd, 1H, J ¼ 3.2 Hz, J ¼ 10.0 Hz, H-3), 5.23 (t, 1H, J ¼ 10.0 Hz, H-4), 5.18
(dd, 1H, J ¼ 1.7 Hz, J ¼ 3.2 Hz, H-2), 4.67 (d, 1H, J ¼ 1.7 Hz, H-1), 3.69
(m, 2H, H-6), 3.62 (m, 1H, H-5), 3.40 (s, 3H, OMe), 2.10, 2.08, 2.01 (3s, 9H,
3Ac) ppm; ESI-MS (m/z): Found 435.85 (M þ Hþ). Anal. Calcd. for
C19H34O9Si: C, 52.52; H, 7.89. Found C, 52.86; H, 7.44.
Methyl 2,3,4-tri-O-acetyl-6-O-tert-butyldimethylsilyl-a-D-glucopyrano-
side (6). Compound 6 was prepared from methyl a-D-glucopyranoside as for
2 (86%). Rf 0.45 (EtOAc/hexane 1/9); NMR spectra were identical to those
already described.[22]
Methyl 2,3,4-tri-O-acetyl-6-O-formyl-b-D-galactopyranoside (7). a)
From 1: A solution of 1 (0.5 g, 0.89 mmol) was dissolved in a 1/1 mixture of
HCOOH/diethyl ether (16 mL). The mixture was refluxed for 30 min and
diluted with diethyl ether, neutralized with solid hydrogen carbonate, washed
successively with brine and water, dried over magnesium sulfate, and concen-
trated. Column chromatography (EtOAc/hexane 3/7) of the residue gave
compound 7 (0.27 g, 86%). Rf 0.40 (EtOAc/hexane 4/6).
b) From 2: A solution of 2 (0.5 g, 1.15 mmol) was dissolved in a 1,5/1 mixture
of HCOOH/diethyl ether (22 mL). The mixture was refluxed for 60 min and
diluted with diethyl ether, neutralized with solid hydrogen carbonate,
washed successively with brine and water, dried over magnesium sulfate,
and concentrated. Column chromatography (EtOAc/hexane 2/8) of the
residue gave compound 7 (0.33 g, 83%). 1H NMR (CDCl3, 250 MHz) d 8.03
(s, 1H, HCOO), 5.41 (d, 1H, J ¼ 2.9 Hz, H-4), 5.23 (dd, 1H, J ¼ 10.8 Hz,

Conversion of 6-O-Trityl and 6-O-TBDMS Sugars into Formate Esters
447
J ¼ 7.9 Hz, H-2), 5.02 (dd, 1H, J ¼ 2.9 Hz, J ¼ 10.8 Hz, H-3), 4.29 (d, 1H,
J ¼ 7.8 Hz, H-1), 4.16 (m, 2H, H-6), 3.85 (m, 1H, H-5), 3.41 (s, 3H, OMe),
2.08, 2.04, 2.01 (3s, 9H, 3Ac) ppm; ESI-MS (m/z): Found 349.62 (M þ Hþ).
Anal. Calcd. for C14H20O10: C, 48.28; H, 5.79. Found C, 48.36; H, 5.82.
Methyl 2,3,4-tri-O-acetyl-6-O-formyl-a-D-mannopyranoside (8).Compound
8 was prepared from 3 (and 4) as for 7. Column chromatography (EtOAc/
hexane 3/7) of the residue gave compound 8 (90% from 3 and 84% from 4).
1H NMR (CDCl3, 250 MHz) d 8.06 (s, 1H, HCOO), 5.33 (dd, 1H, J ¼ 3.1 Hz,
J ¼ 9.9 Hz, H-3), 5.33 (t, 1H, J ¼ 9.9 Hz, H-4), 5.20 (dd, 1H, J ¼ 1.9 Hz,
J ¼ 3.1 Hz, H-2), 4.72 (d, 1H, J ¼ 1.9 Hz, H-1), 4.29 (m, 2H, H-6), 3.95
(m, 1H, H-5), 3.42 (s, 3H, OMe), 2.14, 2.10, 2.09 (3s, 9H, 3Ac) ppm; ESI-MS
(m/z): Found 349.74 (M þ Hþ). Anal. Calcd. for C14H20O10: C, 48.28; H, 5.79.
Found C, 48.25; H, 5.75.
Methyl 2,3,4-tri-O-acetyl-6-O-formyl-a-D-glucopyranoside (9). Compound
9 was prepared from 5 (or 6) as for 7. Column chromatography (EtOAc/hexane
3/7) of the residue gave compound 9. The product was crystallized from EtOAc-
hexane (87% from 5 and 84% from 6). m.p. 89–918C. 1H NMR (CDCl3, 250 MHz)
d 8.08 (s, 1H, HCOO), 5.50 (t, 1H, J ¼ 10.0 Hz, H-3), 5.05 (t, 1H, J ¼ 10.0 Hz,
H-4), 4.95 (d, 1H, J ¼ 3.6 Hz, H-1), 4.90 (dd, 1H, J ¼ 3.6 Hz, J ¼ 10 Hz, H-2),
4.29 (m, 2H, H-6), 4.04 (m, 1H, H-5), 3.43 (s, 3H, OMe), 2.08, 2.04, 2.01 (3s,
9H, 3Ac) ppm; ESI-MS (m/z): Found 349.62 (M þ Hþ). Anal. Calcd. for
C14H20O10: C, 48.28; H, 5.79. Found C, 48.34; H, 5.77.
Methyl 2,3,4-tri-O-acetyl-6-O-(methyl (2E) acrylate)-a-D-glucopyrano-
side (16). A solution of methyl 2,3,4-tri-O-acetyl-6-O-formyl-a-D-glucopyrano-
side (0.2 g, 0.57 mmol) and carbomethoxymethylene triphenylphosporane
(0.38 g, 1.14 mmol) in toluene (10 mL) was refluxed for 12 h and concentrated.
Column chromatography (EtOAc/hexane 2/8) of the residue gave compound 16
(0.17 g, 74%). Rf 0.40 (EtOAc/hexane 4/6). The product was crystallized from
1
EtOAc-hexane. m.p. 101–1028C. H NMR (CDCl3, 250 MHz) d 7.55 (d, 1H,
J ¼ 12.7 Hz, H0-3 acrylate), 5.48 (t, 1H, J ¼ 9.8 Hz, H-3), 5.23 (d, 1H,
J ¼ 12.7 Hz, H0-2 acrylate), 5.02 (d, 1H, J ¼ 9.8 Hz, H-4), 4.95 (d, 1H,
J ¼ 3.6 Hz, H-1), 4.87 (dd, 1H, 3.6 Hz, J ¼ 9.8 Hz, H-2), 4.25 (m, 2H, H-6),
4.01 (m, 1H, H-5), 3.70 (s, 3H, COOMe acrylate), 3.41 (s, 3H, OMe), 2.07,
2.02, 1.99 (3s, 9H, 3Ac)) ppm; ESI-MS (m/z): Found 405.49 (M þ Hþ). Anal.
Calcd. for C17H24O11: C, 50.49; H, 5.99. Found C, 50.44; H, 5.88.
ACKNOWLEDGMENT
This work was supported in part by the Greek General Secretariat for
Research and Technology Program No. 3245C. The authors are grateful to

D. Komiotis et al.
448
Dr. J. Herscovici (Ec. Nat. Sup. de Chimie de Paris; CNRS-FRE 2463) for
encouraging this work and to Dr. T. Halmos (Ec. Nat. Sup. de Chimie de
Paris) for the unstinted and fruitful aid.
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