62
1
General Principles
selected over those of the L-family of structural isomers is not clear. It, however, is not likely
that it was a matter of chance. It has been known for many years that irradiation of a racemic
mixture of D- and L- isomers with circularly polarized light will selectively destroy one of
the two isomers, leaving the other more or less intact [1]. Circularly polarized light has been
observed when there is high sunspot activity. High levels of circularly polarized light have also
been observed coming from the Orion nebula [2]. The selection of D-carbohydrates could have
occurred by this type of irradiation when carbohydrates were first being formed on the earth.
3.2 Analogues of D-Glyceraldehyde
D-Glyceraldehyde has some derived analogues, such as the reduced sugar alcohol, glycerol, its
oxidized product, D-glyceric acid, and their phosphorylated analogues, 1-phospho-D-glycerol,
3-phospho-D-glyceraldehyde, and 3-phospho-D-glyceric acid, whose structures are shown as:
⊡ Scheme 2
Analogues and derivatives of the naturally occurring three-carbon carbohydrates
Glycerol is found as the backbone compound that is esterified by fatty acids to give a class
of lipids known as triacyl glycerols (glycerides), and glycerol-1-phosphate is the backbone of
a major class of phospholipids. 3-Phospho-D-glyceraldehyde, dihydroxy acetone phosphate,
and 3-phospho-D-glyceric acid are all found in both the reactions of photosynthesis and in the
degradative reactions of glycolysis.
3.3 The Formation of Carbohydrates
Containing More than Three Carbons
From a theoretical stand point, Professor Emil Fischer showed that by adding a new chiral carbon between the aldehyde group and the asymmetric carbon of D-glyceraldehyde, a chiral pair
of 4-carbon D-tetraoses would be obtained, namely, D-erythrose and D-threose. Adding another set of similar chiral carbons to each of the two D-tetraoses, gives four 5-carbon D-pentoses,
and likewise adding a similar set of chiral carbons to each of the four D-pentoses, gives eight
6-carbon D-hexoses. It should be noted that it is only the configuration of the last asymmetric
1
General Principles
selected over those of the L-family of structural isomers is not clear. It, however, is not likely
that it was a matter of chance. It has been known for many years that irradiation of a racemic
mixture of D- and L- isomers with circularly polarized light will selectively destroy one of
the two isomers, leaving the other more or less intact [1]. Circularly polarized light has been
observed when there is high sunspot activity. High levels of circularly polarized light have also
been observed coming from the Orion nebula [2]. The selection of D-carbohydrates could have
occurred by this type of irradiation when carbohydrates were first being formed on the earth.
3.2 Analogues of D-Glyceraldehyde
D-Glyceraldehyde has some derived analogues, such as the reduced sugar alcohol, glycerol, its
oxidized product, D-glyceric acid, and their phosphorylated analogues, 1-phospho-D-glycerol,
3-phospho-D-glyceraldehyde, and 3-phospho-D-glyceric acid, whose structures are shown as:
⊡ Scheme 2
Analogues and derivatives of the naturally occurring three-carbon carbohydrates
Glycerol is found as the backbone compound that is esterified by fatty acids to give a class
of lipids known as triacyl glycerols (glycerides), and glycerol-1-phosphate is the backbone of
a major class of phospholipids. 3-Phospho-D-glyceraldehyde, dihydroxy acetone phosphate,
and 3-phospho-D-glyceric acid are all found in both the reactions of photosynthesis and in the
degradative reactions of glycolysis.
3.3 The Formation of Carbohydrates
Containing More than Three Carbons
From a theoretical stand point, Professor Emil Fischer showed that by adding a new chiral carbon between the aldehyde group and the asymmetric carbon of D-glyceraldehyde, a chiral pair
of 4-carbon D-tetraoses would be obtained, namely, D-erythrose and D-threose. Adding another set of similar chiral carbons to each of the two D-tetraoses, gives four 5-carbon D-pentoses,
and likewise adding a similar set of chiral carbons to each of the four D-pentoses, gives eight
6-carbon D-hexoses. It should be noted that it is only the configuration of the last asymmetric