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Chapter 20 681
Copyright © 2017 Pearson Education, Inc.
3.
l-Galactose is reduced to the same alditol that d-galactose is reduced to.
CH
2
OH
OH H
H HO
H HO
OH H
D
-galactose
the alditol of
D
-galactose
CH
2
OH
CH
2
OH
OH H
H HO
H HO
OH H
CH
2
OH
OH H
H HO
H HO
OH H
CH
2
OH
H HO
OH H
OH H
H HO
L
-galactose
rotate 180
°
C
H O
C
H O
C
H O
1. NaBH
4
2. H
3
O
+
1. NaBH
4
2. H
3
O
+
b. 1.
The ketohexose (d-tagatose) with the same configuration at C-3, C-4, and C-5 as d-talose forms
the same alditol (d-talitol) that d-talose forms. The other alditol (d-galactitol) that is formed has
the opposite configuration at C-2.
CH
2
OH
C
CH
2
OH
H HO
H HO
OH
H
D
-tagatose
CH
2
OH
CH
2
OH
H HO
H HO
H HO
OH
H
D
-talitol
O
CH
2
OH
CH
2
OH
OH H
H HO
H HO
OH H
D
-galactitol
+
1. NaBH
4
2. H
3
O
+
2.
Similarly, the ketohexose
(
d-psicose) with the same configuration at C-3, C-4, and C-5 as d-allose
forms the same alditol that d-allose forms. The other alditol (d-altritol) that is formed has the
opposite configuration at C-2.
CH
2
OH
C O
H OH
H OH
H OH
CH
2
OH
CH
2
OH
OH
H OH
H OH
H OH
CH
2
OH
H
CH
2
OH
H
H OH
H OH
H OH
CH
2
OH
HO
+
D
-psicose
D
-allitol
D
-altritol
1. NaBH
4
2. H
3
O
+