General Properties, Occurrence, and Preparation
1.2
71
in the sweet exudates of many trees, such as larch, Douglas fir, Virginia pine, and poplars.
Mild acid hydrolysis of melezitose gives D-glucose and the reducing disaccharide, turanose,
[α-D-glucopyranosyl-(1→3)-D-fructose].
Several sucrose analogues have been enzymatically synthesized in the laboratory. Levansucrase can transfer a D-fructofuransoyl unit from raffinose to D-xylose, giving a nonreducing sucrose disaccharide analogue, xylsucrose [α-D-xylopyranosyl-(1→2)-D-fructofuranoside] and the reducing disaccharide, melibiose [α-D-galactopyranosyl-(1→6)-D-glucose [5]. A similar reaction of levansucrase with raffinose and D-galactose gives galactosucrose [α-D-galactopyranosyl-(1→2)-D-fructofuranoside] (also referred to as galsucrose) and
melibiose [6]. Reaction of sucrose and lactose with levansucrase gives D-glucose and the
nonreducing trisaccharide, lactosucrose [4 Glc -β-D-galactopyranosyl sucrose] [7]. Reaction
of dextransucrase with sucrose and D-fructose gives an unusual reducing disaccharide, leucrose, containing an α-(1→5) linkage of D-glucopyranosyl linked (1→5) to D-fructopyranose
[α-D-glucopyranosyl-(1→5)-D-fructopyranose] [8,9].
A relatively large number of sucrose derivatives have been chemically synthesized [10].
Some notable chloro derivatives have been obtained by the reaction of sucrose with sulfuryl chloride in pyridine/chloroform at low temperatures, for example 4,6,1 ,6 -tetrachloro4,6,1 ,6 -tetradeoxy-glactosucrose, 4,6,6 -trichloro-4,6,6 -trideoxy-sucrose, and many others
were formed [11,12,13,14,15]. These chloro-compounds of sucrose were 10–100 times sweeter than sucrose. One of them, Sucralose (4,1 ,6 -trichloro-4,1 ,6 -trideoxy-galactosucrose),
was 650-times sweeter than sucrose, with no after-taste, and a sweet-taste identical to sucrose.
It is used commercially as a noncariogenic and noncaloric sweetener in soft drinks, candies,
cookies, jellies, and many other prepared foods, as well as a general substitute for table
sugar. Sucralose is enzymatically inert and passes through the human body without being
metabolized or absorbed.
4.2.3 Properties and Occurrence of D-Glucose Combined
with D-Galactose to Give Lactose and Higher Oligosaccharides
Lactose is a disaccharide composed of β-D-galactopyranose linked (1→4) to D-glucose and is
found in the milk of mammals, where it serves as a source of energy and nourishment for the
newborn. Lactose is a reducing disaccharide because the D-glucopyranose residue has a free
hemiacetal group at C1. Human milk contains 85 g L −1 lactose and cow’s milk contains about
50 g L −1 .
Human milk also contains lactose oligosaccharides in which various different monosaccharide
residues are attached to the D-galactopyranosyl residue. α-L-Fucose (6-deoxy-L-galactose) is
attached (1→2) to the galactose moiety [16], α-N-acetyl-D-neuraminic acid is attached (2→3)
to the galactose moiety [16,17], and the β-N-acetyl-D-glucosamine residue is attached either
(1→3) or (1→6) to the galactose moiety [18]. The latter serves to produce a core structure
that can be further extended by the addition of β-D-galactopyranose residues linked either
(1→2) or (1→4) [19]. The β-D-galactopyranosyl-β-N-acetyl-D-glucosamine disaccharide is
often added in multiples to give a repeated core structure to which α-N-acetyl-D-neuraminic
acid and α-L-fucose residues are added to the ends of the oligosaccharides. The so called
human blood group determinants (see > Sect. 14) have structural similarities to the human
milk oligosaccharides [19] and it is thought that through this relationship the milk oligosac-
1.2
71
in the sweet exudates of many trees, such as larch, Douglas fir, Virginia pine, and poplars.
Mild acid hydrolysis of melezitose gives D-glucose and the reducing disaccharide, turanose,
[α-D-glucopyranosyl-(1→3)-D-fructose].
Several sucrose analogues have been enzymatically synthesized in the laboratory. Levansucrase can transfer a D-fructofuransoyl unit from raffinose to D-xylose, giving a nonreducing sucrose disaccharide analogue, xylsucrose [α-D-xylopyranosyl-(1→2)-D-fructofuranoside] and the reducing disaccharide, melibiose [α-D-galactopyranosyl-(1→6)-D-glucose [5]. A similar reaction of levansucrase with raffinose and D-galactose gives galactosucrose [α-D-galactopyranosyl-(1→2)-D-fructofuranoside] (also referred to as galsucrose) and
melibiose [6]. Reaction of sucrose and lactose with levansucrase gives D-glucose and the
nonreducing trisaccharide, lactosucrose [4 Glc -β-D-galactopyranosyl sucrose] [7]. Reaction
of dextransucrase with sucrose and D-fructose gives an unusual reducing disaccharide, leucrose, containing an α-(1→5) linkage of D-glucopyranosyl linked (1→5) to D-fructopyranose
[α-D-glucopyranosyl-(1→5)-D-fructopyranose] [8,9].
A relatively large number of sucrose derivatives have been chemically synthesized [10].
Some notable chloro derivatives have been obtained by the reaction of sucrose with sulfuryl chloride in pyridine/chloroform at low temperatures, for example 4,6,1 ,6 -tetrachloro4,6,1 ,6 -tetradeoxy-glactosucrose, 4,6,6 -trichloro-4,6,6 -trideoxy-sucrose, and many others
were formed [11,12,13,14,15]. These chloro-compounds of sucrose were 10–100 times sweeter than sucrose. One of them, Sucralose (4,1 ,6 -trichloro-4,1 ,6 -trideoxy-galactosucrose),
was 650-times sweeter than sucrose, with no after-taste, and a sweet-taste identical to sucrose.
It is used commercially as a noncariogenic and noncaloric sweetener in soft drinks, candies,
cookies, jellies, and many other prepared foods, as well as a general substitute for table
sugar. Sucralose is enzymatically inert and passes through the human body without being
metabolized or absorbed.
4.2.3 Properties and Occurrence of D-Glucose Combined
with D-Galactose to Give Lactose and Higher Oligosaccharides
Lactose is a disaccharide composed of β-D-galactopyranose linked (1→4) to D-glucose and is
found in the milk of mammals, where it serves as a source of energy and nourishment for the
newborn. Lactose is a reducing disaccharide because the D-glucopyranose residue has a free
hemiacetal group at C1. Human milk contains 85 g L −1 lactose and cow’s milk contains about
50 g L −1 .
Human milk also contains lactose oligosaccharides in which various different monosaccharide
residues are attached to the D-galactopyranosyl residue. α-L-Fucose (6-deoxy-L-galactose) is
attached (1→2) to the galactose moiety [16], α-N-acetyl-D-neuraminic acid is attached (2→3)
to the galactose moiety [16,17], and the β-N-acetyl-D-glucosamine residue is attached either
(1→3) or (1→6) to the galactose moiety [18]. The latter serves to produce a core structure
that can be further extended by the addition of β-D-galactopyranose residues linked either
(1→2) or (1→4) [19]. The β-D-galactopyranosyl-β-N-acetyl-D-glucosamine disaccharide is
often added in multiples to give a repeated core structure to which α-N-acetyl-D-neuraminic
acid and α-L-fucose residues are added to the ends of the oligosaccharides. The so called
human blood group determinants (see > Sect. 14) have structural similarities to the human
milk oligosaccharides [19] and it is thought that through this relationship the milk oligosac-