Facile conversion of glycosyloxymethyl-furfural into γ-keto- carboxylic acid building blocks towards a sustainable chemical industry

Article abstract of DOI:10.1039/c3gc40185e

Carbohydrates, as cheap mass-products, promise to be outstanding candidates as sustainable raw materials (F. W. Lichtenthaler and S. Peters, C. R. Chim., 2004, 7, 65-90). To achieve the goal of carbohydrate utilisation as industry raw materials, environmental low impact conversions from sugars to high value reactive intermediates are needed. Here we present the facile access to γ-keto-carboxylic acid building blocks from the sucrose-based glycosyloxymethyl-furfural (GMF). Employing an oxidative ring opening strategy under careful selection of reaction conditions, allows for high yield conversions of the furan aglycon into γ-keto-carboxylic acid moieties without alteration of the sugar moiety attached. The resulting glycosylated building blocks were converted into selected heterocyclic products of the pyridazinone and benzodiazepinone type to exemplify the synthetic potential of these building blocks. All synthetic manipulations employed low environmental impact solvents, reagents, oxidants and protecting group free conversions.

Full text of DOI:10.1039/c3gc40185e

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Facile conversion of glycosyloxymethyl-furfural into
γ-keto-carboxylic acid building blocks towards a
sustainable chemical industry†
Cite this: Green Chem., 2013, 15, 1368
Andreas Brust*a,b and Frieder W. Lichtenthalerb
Carbohydrates, as cheap mass-products, promise to be outstanding candidates as sustainable raw
materials (F. W. Lichtenthaler and S. Peters, C. R. Chim., 2004, 7, 65–90). To achieve the goal of carbo-
hydrate utilisation as industry raw materials, environmental low impact conversions from sugars to high
value reactive intermediates are needed. Here we present the facile access to γ-keto-carboxylic acid build-
ing blocks from the sucrose-based glycosyloxymethyl-furfural (GMF). Employing an oxidative ring
opening strategy under careful selection of reaction conditions, allows for high yield conversions of the
furan aglycon into γ-keto-carboxylic acid moieties without alteration of the sugar moiety attached. The
resulting glycosylated building blocks were converted into selected heterocyclic products of the pyrid-
azinone and benzodiazepinone type to exemplify the synthetic potential of these building blocks. All
synthetic manipulations employed low environmental impact solvents, reagents, oxidants and protecting
group free conversions.
Received 24th January 2013,
Accepted 21st March 2013
DOI: 10.1039/c3gc40185e
www.rsc.org/greenchem
Introduction
Mankind is facing the end of cheap oil, with the peak of pro-
duction already passed.2 The chemical industry is heavily
reliant on oil or coal based hydrocarbons, which form the
foundation of our modern lifestyle. This discrepancy creates
the inevitable necessity for a progressive changeover towards
renewable and, hence, sustainable feedstock to fulfil the
industry’s raw material needs.3 Carbohydrates are by far the
most abundant organic compounds and represent the major
portion of the renewable biomass. Carbohydrate utilization for
the production of low cost and eco-friendly chemicals of versa-
tile industrial applicability is of central importance for reliev-
ing the industry’s reliance on petrochemical raw materials.1,3–7
The conversion of carbohydrates into chemical raw
materials requires dehydration to utilize the sugar-inherent
carbon backbone. These kinds of initial down-functionalizing
conversions include fermentation to ethanol or lactic acid, oxi-
dation to carboxylic acids, introduction of keto-moieties or
poly-dehydration to furan compounds (Scheme 1).8
Scheme 1 Synthesis of furfurals (1, 2, 3) from bulk carbohydrates.
performed on an industrial scale from biomass-derived
D-xylose, building the foundation of industrial furan chemistry.9
Due to economic reasons, the hexose-derived 5-hydroxymethyl-
furfural (HMF, 2) is not yet commercially viable. But progress
has been made to realize its industrial use, as HMF (2) has
been recognized as a potential building block for a range of
industrial applications.10–13 An analogous dehydration of the
fructose part of disaccharides is possible.14 In particular, iso-
maltulose, produced enzymatically from sucrose in industrial
Furans represent prototypes of industrially useful building
blocks and the conversion to furfural (1) has already been
aInstitute of Molecular Bioscience, University of Queensland, Brisbane, Australia.
E-mail: a.brust@imb.uq.edu.au
bClemens-Schoepf Institut für Organische Chemie und Biochemie, Technische
Universität Darmstadt, Darmstadt, Germany
scales,1,5 is readily converted into
a glycosyl-substituted
†Part 46 of the series Sugar-Derived Building Blocks. (Part 45)25
hydroxymethylfurfural derivative. In this process, an acid
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catalyzed dehydration of the fructose moiety of isomaltulose is
performed under conditions retaining the intersaccharidic
linkage.1,5,14 This conversion has been validated on an indus-
trial pilot scale in a continuous flow reactor with an acidic ion
exchange resin in DMSO at 120 °C.1,5 Thus, 5-α-D-glucosyloxy-
methyl-furfural (α-GMF, 3)14,15 is of particular interest as it is
potentially accessible on the industrial scale and as it com-
bines a carbohydrate moiety with a furfural aglycon promising
for the production of chemical raw materials with novel
characteristics.
In contrast to this already well-established access to furfur-
als, further processing towards reactive intermediates is still
under-investigated, in particular, with regard to sustainable
low environmental impact pathways.
We have reported in the past on the conversions of carbo-
hydrates and carbohydrate derived furfurals into nitrogen
heterocycles.16–18 This work focuses on the conversion of GMF
(3) into glycosylated analogues of γ-keto-carboxylic acids,
which are not only suitable building blocks for the synthesis
of heterocycles but also have potential to be used for the
synthesis of e.g. γ-amino acids, or biopolymer building
blocks.19–21
Scheme 2 Conversion of GMF (3) into ketocarboxylic acids of type 4, 5 and 6.
Oxidation conditions and reaction media determine the chemical entity formed.
The table shows the NMR assignment of selected signals indicative of the
structure.
quantitative and resulted in a homogeneous product so that a
further purification step was not necessary. These protecting
group free, high yielding entry reactions represent straight-
forward conversions to novel building blocks with a high
potential as raw materials for industrial applications.
Results
In a previous work we could show how oxidative ring opening
All structures of products 4, 5 and 6 were investigated by 1H
of furans can lead to synthetically interesting 1,4-diketo build- and 13C NMR. The table in Scheme 2 summarizes a selection
ing blocks as intermediates towards heterocycles of the of NMR signals obtained for the aglycon portion of the syn-
pyrrole, thiophene, pyridazine and benzodiazepine type.18 In thesized γ-keto-carboxylic acids. The obtained chemical shifts
this report we focus on the direct conversion of GMF (3) and coupling constants confirm clearly the proposed struc-
without the use of protecting groups and how the selection of tures of building blocks 4, 5 and 6.
oxidation conditions and the reaction environment can be
Particularly indicative is the comparison of the 13C chemi-
used to obtain a variety of useful γ-keto-carboxylic acid build- cal shift of carbon-4 in compound 4 relating to a hydroxy-
ing blocks in high yields and industrial conversion feasibility. furanone-actal chemical environment (105.7 ppm) while
Per-acetylated-GMF15,18 can be oxidized in organic aprotic compounds 5 and 6 show a strong deep field shift (211.5 ppm
media (dichloromethane) employing m-CPBA resulting in oxi- with respect to 180 ppm) indicative of a open chain ketone-
dative ring opening under decarboxylation and intramolecular chemical environment. Both compounds 5 and 6 show a
ring closure to the hydroxyl-furanone product 418 (Scheme 2). proton coupling constant between H-2 and H-3 of 5.7 Hz,
While this reaction is straightforward and high yielding which relates to a Z-configuration fixated structure. The levuli-
(overall yield 85%) we were interested in making improvements nic acid analogue 6 is clearly determined by the C-2 and C-3
towards more environmentally friendly alternatives, employing methylene signals (32.1, 32.5 ppm) and the C-4 chemical shift
benign solvents, reagents and oxidants.
indicative of a keto-function (180 ppm). Thus, a ring–chain
A range of oxidation agents/solvent pairs was investigated tautomerisation is not observed for 6.
to perform the furfural oxidations. Unprotected GMF (3) was
The formation of different γ-keto-carboxylic acids can be
treated with photochemically created singlet oxygen in metha- sufficiently explained by the proposed mechanism (Scheme 3)
nol. Methylene blue was used as a photocatalytic reagent and of oxidative ring opening and the solvent properties employed.
irradiation was performed with a conventional 50 W halogen
Oxidative conversion of per-acetylated-GMF (Ac4-GMF)15 is
light source at −40 °C.18 Complete conversion was monitored performed under aprotic conditions with m-CPBA.18 The oxi-
after 5 h to deliver the unsaturated open chain γ-keto-carb- dative ring opening22 results in a keto-aldehyde 4a intermedi-
oxylic acid 5 in 93% yield.
ate which is further oxidized to an unstable keto-carboxylic
The product obtained was chromatographically homo- acid, which immediately decarboxylates to a α,β unsaturated
geneous and further purification was not necessary. When per- aldehyde 4b. Further oxidation yields the final unsaturated
forming the oxidation of GMF (3) in an aqueous solution of keto-carboxylic acid 4 with the cyclic 5-hydroxy-2(5H)-furanone
30% hydrogen peroxide a 5-glycosyloxy-analogue of levulinic form as the most stable end product under the applied aprotic
acid (6) was formed in 98% yield. Also this reaction was conditions.
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Conclusion
Access to reactive synthesis intermediates is necessary to in-
corporate renewable carbohydrates into chemical production
processes for the chemical industry. The formation of furfurals
from pentoses, hexoses and disaccharides is an ideal entry
reaction as it down functionalizes the carbohydrate moiety,
making them amenable for further chemical modifications.
While the formation of furfurals 1, 2 and 3 is well investigated,
their further transformation into industrially viable products,
from 2 and particularly 3 is considerably less developed
mainly due to the simultaneous presence of an aromatic furan
skeleton and multiple hydroxyl groups. Thus with the oxidative
ring opening strategy presented here we are able to arm the
furan system, generating highly reactive γ-keto-carboxylic acid
synthesis intermediates (4, 5, 6), with outstanding potential as
building blocks for the chemical industry. The developed reac-
tion pathways from renewable sugars have potential for direct
industrial applicability, employing low cost, low environmental
impact reagents, solvents and oxidants. The generated build-
ing blocks have been validated for their synthetic potential by
producing pyridazinone (7) as well as benzodiazepinone
heterocycles (8 and 9) in only 2 steps from GMF (3). We are
herewith clearing the path towards the generation of fully
green and sustainable products from carbohydrate sources.
Scheme 3 Selection of reaction conditions (oxidant and media) determines
the product formation due to different mechanistic pathways.
When performing the same reaction in water with hydrogen
peroxide, instead of oxidation of the α,β unsaturated aldehyde
intermediate, an aldehyde hydrate is formed (6c), preventing
further oxidation. Further tautomerization finally yields the
levulinic acid analogue 6. During the singlet oxidation23,24 of
GMF (3) in methanol a bicyclic endo-peroxide 5a is formed.
Induced by the formation of a methanol hemiacetal followed
by elimination of formic acid–methylester, the final α,β-un-
saturated keto-carboxylic acid 5 is formed.
Experimental
Analytical instrumentation used: melting points (uncorrected
values) recorded on a Bock monoskop instrument. Spectral
measurements were performed on: Perkin Elmer 241
(rotations), Varian MAT 311 A (MS), Bruker WM 300 instru-
ments (1H at 300, 13C NMR at 75.5 MHz, respectively). A
Perkin-Elmer 240 elemental analyzer was used for compound
microanalysis and purity confirmation. TLC on Kieselgel 60
F254 plastic sheets (Merck) was used to monitor the reactions
and to ascertain the purity of the products (a single point on a
TLC plate); eluents employed and Rf values observed are given
in the appropriate experiment; detection of TLC plates was
performed with UV-light or by charring with sulfuric
acid. Column chromatography: Kieselgel 60 (63-200 mesh,
Macherey-Nagel).
In initial experiments we have used the α,β-unsaturated-4-
keto-carboxylic acid building block 5 as a synthetic precursor
for the synthesis of some selected heterocycles to exemplify
their potential use (Scheme 4).
Treatment of 5 dissolved in water (pH 4 adjusted with
acetic acid) with phenyl hydrazine affords the phenyl hydra-
zone, which readily cyclized under slightly acidic conditions to
the phenyl-pyridazinone 7. While in a previous work18 we have
used the building block 4 as a reactive intermediate for the
synthesis of benzodiazepinones, we now use the α,β-unsatu-
rated keto-carbonic acid 5 in a protecting group free approach.
Thus, reaction with 1,2-diaminobenzene or 1,2-diamino-4,5-
dichloro-benzene in methanol (0 °C) delivered in good yield
(55% and 48%) the benzodiazepinones 8 and 9.18
5-(α-D-Glucopyranosyloxy)-4-oxo-pent-2-enoic acid (5)
A stirred and cooled (−40 °C) solution of GMF (3, 4.0 g,
13.9 mmol) in tri-MeOH (50 mL) was irradiated in the pres-
ence of a few crystals of methylene-blue with a halogen lamp
(Tungsram, 500 W). Oxygen gas was transferred into the solu-
tion under vigorous magnetic stirring and TLC indicates com-
plete transformation into product 5 after 5 hours (5: Rf 0.45,
1 : 1 CHCl3–MeOH). Deoxygenating with nitrogen gas (30 min)
was followed by the addition of Me2S (0.86 g, 14 mmol), a
temperature increase to ambient, and decolourization with
activated charcoal. Evaporation of the resulting clear filtrate
yields 3.77 g (93%) chromatographic homogeneous (TLC) 5 in
Scheme 4 Conversion of the γ-keto-carboxylic acid building block into select
heterocycles of the pyridazinone (7) and benzodiazepinone (8, 9) type.
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the form of a colourless hard foam. (Found: C, 45.20; H, 5.50; 4R- and 4S-[(α-D-Glucopyranosyloxy)-acetyl]-1,3,4,5-tetrahydro-
O, 49.30% C11H16O9 requires C, 45.21; H, 5.52; O, 49.27%); 2H-1,5-benzodiazepin-2-one (8a and 8b)18
δ
1H NMR (300 MHz, CD3OD): 3.25–3.42 (m, 4 H, 2′-H, 3′-H,
A cooled (0 °C) solution of the α,β-unsaturated keto-carbonic
acid 5 (0.24 g, 0.8 mmol) in abs. MeOH (10 mL, molecular
sieve 3 Å) was treated in portions with o-phenylenediamine
(80 mg, 0.8 mmol). TLC monitoring indicated disappearance
of starting material after 2 hours of reaction. After filtration
the solvent was removed in vacuo resulting in a crude product
which was purified on silica gel (3 × 20 cm) with CHCl3–MeOH
(5 : 1) as the eluent. Evaporation of fractions with Rf 0.5
[CHCl3–MeOH (1 : 1)] yielded 8 (167 mg, 55%) in the form of a
colourless foam as a 1 : 1 mixture of its diastereomers 8a and
8b. (Found: C, 53.40; H, 5.80; N, 7.30, O, 33.50% C17H22N2O8
requires C, 53.40; H, 5.80; N, 7.33 O, 33.47%).
4′-H, 5′-H), 3.55–3.70 (m, 2 H, 5-Ha, 6′-Ha), 3.75–3.85 (m, 2 H,
5-Hb, 6′-Hb), 4.76 (d, 1 H, 1′-H), 6.20 (d, 1 H, 2-H), 7.48 (d, 1 H,
3-H). J2,3 = 5.7 Hz; δ 13C NMR (75 MHz, CD3OD): 62.6 (C-6′),
70.6 (C-5), 71.6 (C-4′), 73.5 (C-5′), 74.1 (C-3′), 74.8 (C-2′), 100.5
(C-1′), 124.8 (C-2), 155.2 (C-3), 172.7 (COOH), 211.5 (C-4). MS
(FD): m/z = 292 (M+).
5-(α-D-Glucopyranosyloxy)-4-oxo-pentanoic acid (6)
A solution of GMF (3, 1.0 g, 3.5 mmol) in 40 mL of 30% hydro-
gen peroxide solution was stirred at room temperature for
18 hours. Removal of the solvent was performed under
reduced pressure at 50 °C. Residual water was removed by
azeotropic co-evaporation with toluene. The crude syrup was
finally dried under high vacuum to deliver the product 6 in the
form of a colourless hard foam (1 g, 98%). The obtained
product did not require further purification due to its chromato-
graphic homogeneity. The product was highly hygroscopic
and required storage in a desiccator over P2O5. – Rf 0.22
(CHCl3–MeOH 1 : 1). – [α]2D0 + 94.5 (c 0.85, MeOH). (Found: C,
44.80; H, 6.20; O, 49.00% C11H18O9 requires C, 44.90; H, 6.17;
1
δ H NMR (300 MHz, CD3OD): 2.85 (m, 1 H, 3-Ha), 3.05 (m,
1 H, 3-Hb), 3.12–3.50 (m, 6 H, 2′-H, 3′-H, 4′-H, 5′-H, 6′-H2),
4.20–4.52 (m, 3 H, 4-H, OCH2CO), 4.85 (d, 1 H, 1′-H), 6.68–7.36
(m, 4 H, C6H4). – J1′,2′ = 3.8 Hz; δ 13C NMR (75.5 MHz, CD3OD):
δ 40.3 (C-3), 50.7, 50.8 (C-4 of diastereomers 8a and 8b), 60.9
(C-6′), 70.0 (C-2′, C-5′), 71.7 (OCH2CO), 73.0 (C-4′), 73.1 (C-3′),
98.7 (C-1′), 117.6, 124.1, 127.7, 128.0 (C-6, C-7, C-8, C-9), 133.5,
136.2 (C-5a, C-9a), 168.3 (C-2), 205.8, 205.9 (4-CO of diastereo-
mers 8a and 8b). MS (FD): m/z = 382 (M+).
1
O, 48.93%); δ H NMR (300 MHz, CD3OD): 2.52–2.54 (m, 2 H,
3-H2), 2.61–2.64 (m, 2 H, 2-H2), 3.34 (dd, 1 H, 4′-H), 3.47 (dd,
1 H, 2′-H), 3.62 (m, 1 H, 5′-H), 3.63 (dd, 1 H, 3′-H), 3.78 (dd, 1
H, 6′-Ha), 3.81 (dd, 1 H, 6′-Hb), 5.11 (d, 1 H, 1′-H), 5.37, 5.39
4R- and 4S-7,8-Dichloro-4-[(-α-D-glucopyranosyloxy)-acetyl]-
1,3,4,5-tetrahydro-2H-1,5-benzodiazepin-2-one (9a and 9b)18
Benzodiazepine 9 was synthesized under identical conditions
as 8. The reaction of 5 (0.24 g, 0.8 mmol) with 3,4-dichloro-
phenylenediamine (140 mg, 0.8 mmol) and column purifi-
cation on silica gel (3 × 20 cm) with CHCl3–MeOH (10 : 1) as
the eluent yielded product 9. Evaporation of fractions with Rf
0.85 [CHCl3–MeOH (2 : 1)] yielded 9 (172 mg, 48%) as a colour-
less mixture of both diastereomers 9a and 9b.
(2 d je 1 H, 5-CH2). Jgem, 5-H2 = 6.4, J1′,2′ = 3.6, J2′,3′ = 9,8, J3′,4′
=
9.2, J4′,5′ = 9.2, J5′,6′a = 2.3, Jgem,
= 12.0 Hz. δ 13C NMR
6′-H2
(75.5 MHz, CD3OD): 32.1, 32.5 (C-2, C-3), 63.6 (C-6′), 72.6
(C-4′), 72.9 (C-2′), 74.8 (C-3′, C-5′), 87.9 (C-5), 100.8 (C-1′), 175.5
(COOH), 179.9 (C-4). MS (FD): m/z = 294 (M+).
3-(α-D-Glucopyranosyloxymethyl)-1-phenyl-6(1H)-pyridazinone
(7)
(Found: C, 45.30; H, 4.50; N, 6.20% C17H20Cl2N2O8 requires
C, 45.25; H, 4.47; N, 6.21; O, 28.36; Cl, 15.71%).
A solution of keto-pentenoic acid 5 (0.42 g, 1.44 mmol) in
10 mL of water/acetic acid (pH 4) was treated with phenyl-
hydrazine (0.15 mL, 1.44 mmol) at room temperature. TLC
indicated complete transformation into the product. Removal
of water under reduced pressure resulted in an orange syrup
which was purified on silica gel (3 × 20 cm) with CHCl3–MeOH
5 : 1 as the eluent. Combined fractions with Rf 0.22 yielded
after the evaporation of the solvent 0.35 g (70%) an orange
hard foam of the pyridazinone 7. (Found: C, 56.10; H, 5.50; N,
7.70; O, 30.7% C17H20N2O7 requires C, 56.04; H, 5.53; N, 7.69,
δ
1H NMR (300 MHz, CD3OD): 2.85 (m, 1 H, 3-Ha),
3.05–3.19 (m, 2 H, 3-Hb, 5′-H), 3.25 (m, 3 H, 3′-H, 4′-H, 6′-Hb),
4.10 (d, 1 H, OCH2aCO), 4.20 (d, 1 H, OCH2bCO), 4.23 (m, 1 H,
4-H), 4.74 (d, 1 H, 1′-H), 6.87 (s, 2 H, 6-H, 9-H). – J1′2′ = 3.8,
J2′,3′ = 9.6 Jgem,
= 17.1 Hz, δ 13C NMR (75.5 MHz,
OCH2CO
CD3OD): δ 40.3 (C-3), 50.7, 50.8 (C-4 of diastereomers 9a and
9b), 60.8 (C-6′), 70.0 (C-2′, C-5′), 71.7 (OCH2CO), 73.0 (C-4′),
73.1 (C-3′), 98.7 (C-1′), 113.8, 115.4 (C-6, C-9), 118.2 (C-7), 123.9
(C-8), 125.9, 134.1 (C-5a, C-9a), 166.3 (C-2), 205.8 (4-CO). MS
(FD): m/z = 450 (M+).
1
O, 30.74%); δ H NMR (300 MHz, DMSO): 3.05–3.15 (m, 1 H,
5′-H), 3.20–3.30 (m, 1 H, 2′-H), 3.40–3.50 (m, 3 H, 3′-H, 4′-H,
6′-H2a), 3.65–3.68 (m, 1 H, 6′-H2b), 4.45 (d, 1 H, 3–CH2a), 4.48
(t, 1 H, 6′-OH), 4.56 (d, 1 H, 3-CH2b), 4.77–4.81 (m, 3 H, 3 OH),
7.11 (d, 1 H, 4-H), 7.39–7.56 (m, 5 H, C6H5), 7.64 (d, 1 H, 5-H).
Acknowledgements
J4,5 = 9.5, Jgem, 3-CH = 12.5, J1′,2′ = 5.7 Hz. δ 13C NMR (75.5 MHz, This work was financially supported by the Südzucker AG,
2
DMSO): 61.2 (C-6′), 67.5 (3-CH2), 70.6 (C-5′), 72.2 (C-2′), 73.6 Mannheim/Ochsenfurt, and by grants 94 NR 078-F and 99 NR
(C-4′, C-3′), 99.1 (C-1′), 126.5, 128.3, 129.0, 141.7 (C6H5), 131.2, 063 from the Ministry of Nutrition, Agriculture and Forestry,
133.0 (C-4, C-5), 145.6 (C-3), 159.3 (C-6). MS (FD): m/z = 364 Bonn, administered by the Fachagentur Nachwachsende
(M+), 202 (M+ − C6H11O5).
Rohstoffe, Gülzow.
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