D. Ekeberg et al. / Carbohydrate Research 342 (2007) 1992–1997
1993
aldose–ketose transformation. Isomerisation of glucose
to fructose was reported in a patent in 1964.15 Since
then, this method has also been used in the isomerisation
of reducing disaccharides, lactulose has been prepared
from lactose16 and maltose has been converted to maltu-
pyridine under the same conditions as those used for
the aldoses.
2. Results and discussion
lose in aluminate solution17 and on aluminate resin.18
A
possible mechanism for the isomerisation of glucose to
fructose has been suggested19 on the basis of the known
capability of aluminate to form complexes with mono-
saccharides.20 Increased yield of fructose from glucose
in alkaline solution on the addition of aluminate is
explained by stronger ability of the ketose to form alu-
minate complex.19 In a previous paper from our labora-
tory, the isomerisation of aldoses of the arabino and lyxo
series in aluminate solution was reported.21 The results
supported the suggested19 mechanism, based on stabili-
sation of a trans-1,2-enediol intermediate by 1,3-alumi-
nate complexation.
In our recently reported work on isomerisation of
aldoses in pyridine with aluminium oxide,14 the aldoses
investigated, especially glucose and xylose, belong to the
most stable ones, and they are not expected to give the
highest yields of ketoses. To get more information about
the potential of this improved reaction for preparation
of less common ketoses, we decided to examine the effect
of aluminium oxide on the isomerisation of several other
aldoses in pyridine.
Whereas production of aldohexoses by enzyme-cataly-
sed isomerisation of 2-hexuloses has been reported,22–24
ketoses are not suitable as starting materials for prepa-
ration of aldoses by isomerisation in pyridine, mainly
because two 2-epimeric aldoses are formed, and in addi-
tion, 3-epimerisation of the ketose occurs. However,
since the presence of aluminium oxide has been found
to increase the reaction rate of aldose–ketose transfor-
mation, it seemed of interest to also investigate the effect
of this catalyst on the reverse reaction. Therefore, two
2-hexuloses have been treated with aluminium oxide in
As a method for qualitative and quantitative analysis of
the monosaccharides in the reaction mixtures, GC–MS
of their O-isopropylidene derivatives was chosen. Under
certain conditions, most monosaccharides dealt with in
this work, with the exception of altrose, idose and
talose, give exclusively or mainly one derivative.25 As a
result, less complex gas chromatograms are obtained
than those of, for example, trimethylsilyl derivatives or
acetates. In addition, the mass spectra of O-isopropylid-
ene derivatives are more characteristic and, unlike those
from trimethylsilyl derivatives and acetates, often dis-
criminate between configurational isomeric sugars.26
EI mass spectra of the derivatives of most of the
common monosaccharides have been reported,26–28
and mass spectral data of the derivatives of the less
common aldoses altrose, gulose, idose and talose are
shown in Table 1. From altrose, 1,2:5,6- and 1,2:3,4-
di-O-isopropylidene derivatives are formed in a ratio
of about 2:1 under the derivatisation conditions applied
in this work, whereas 1,2:5,6 and 2,3:5,6 derivatives are
obtained from talose.29 Contrary to what is the situation
with glucose, a 1,2:3,5-di-O-isopropylidene derivative is
formed in substantial amounts from its 5-epimeric
aldose, idose, in addition to the main 1,2:5,6-di-O-iso-
propylidene derivative. This difference may at least in
part be explained by the fact that the 2,2-dimethyl-
1,3-dioxane ring, involving C-3, C-4, C-5 in the idose
derivative, may adopt a chair conformation without
unfavourable 1,3-diaxial C–C interactions, as seen by
inspection of a molecule model. In the 1,2:3,5-di-O-iso-
propylidene derivative of glucose on the other hand, this
is impossible, and this glucose derivative is formed in
Table 1. Mass spectral data for the acetals of altrose, gulose, idose and talose
1,2:4,5-Di-O-isopropylidene-b-D-altrofuranose m/z (% rel. int.): 245 (63), 187 (16), 159 (24), 143 (16), 131 (13), 127 (29), 101 (68), 85 (32),
73 (52), 59 (62), 55 (48) 43 (100)
1,2:3,4-Di-O-isopropylidene-b-D-altropyranose: 245 (24), 229 (4), 187 (27), 185 (7), 171 (16), 144 (5), 127 (23), 113 (43), 100 (55), 85 (53),
71 (38), 59 (73), 43 (100)
2,3:5,6-Di-O-isopropylidene-L-gulofuranose: 245 (88), 187 (36), 141 (13), 129 (11), 127 (24), 115 (12), 109 (14), 101 (100), 99 (19), 85 (30),
81 (27), 72 (25), 59 (88), 43 (100)
1,2:5,6-Di-O-isopropylidene-b-D-idofuranose: 245 (74), 187 (46), 159 (9), 131 (13), 129 (26), 127 (38), 113 (12), 101 (100), 85 (27), 59 (74),
55 (25), 43 (100)
1,2:3,5-Di-O-isopropylidene-b-D-idofuranose: 245 (59), 229 (12), 187 (22), 171 (11), 129 (52), 127 (33), 113 (100), 109 (15), 100 (67), 85 (62),
72 (19) 69 (20), 59 (96), 57 (19), 55 (17), 43 (100)
2,3:5,6-Di-O-isopropylidene-D-talofuranose: 245 (40), 187 (34), 159 (5), 141 (7), 129 (29), 127 (13), 115 (7), 101 (100), 95 (15), 85 (20), 81 (16),
73 (32), 59 (81), 55 (17), 43 (100)
1,2:5,6-Di-O-isopropylidene-b-D-talofuranose: 245 (97), 187 (5), 185 (11), 167 (9), 159 (35), 129 (10), 115 (8), 113 (13), 101 (92), 99 (21),
85 (23), 73 (36), 72 (31), 59 (100), 55 (77), 43 (100)
1,2:5,6-Di-O-isopropylidene-a-D-glucofuranose: 245 (79), 187 (73), 159 (46), 145 (21), 131 (44), 129 (41), 127 (75), 113 (32), 101 (100), 85 (72),
72 (49), 69 (51), 59 (88), 55 (40), 43 (73)
1,2:3,5-Di-O-isopropylidene-a-D-glucofuranose: 245 (29) 229 (5), 187 (5), 171 (13), 142 (24), 129 (42), 127 (18), 113 (100), 109 (8), 101 (16),
100 (24), 85 (44), 69 (17), 59 (91), 57 (18), 55 (18), 43 (100)