D. Carotenoids
41
1. CAROTENES
To the nonspecialist carotene is the pigment that is responsible for the
color of carrots and which is the biochemical precursor of vitamin A. Appropriately enough, when the crystalline coloring matter of carrots was
first isolated in 1831 it was named carotene. Much later, with refined isolation
techniques, it was recognized that carrots contained two isomeric pigments.
The minor constituent, an optically active substance, was eluted ahead of the
optically inactive major constituent during chromatography. Because of this
elution sequence the minor component was named α-carotene and the major
component ß-carotene. ^-Carotene (95) has emerged as the most abundant
and as one of the most widespread of the carotenes. The standard numbering
system, which follows the isoprenoid construction of the molecule, is shown
in formula 95.
IS'
4
'
16 17
Τ
Τ
15
Ι
I
II
20'
19'
17' 16'
95
In contrast to the wide distribution of ß-carotene (95), ε-carotene (96) is a
rarely encountered hydrocarbon; it differs from the common ^-isomer by
having a-ionone (97) instead of ß-ionone (98) end groups. ε-Carotene was
first isolated from the colonial marine diatom Navicula torquatum by Strain
and Manning (1943), and was subsequently detected in a green alga, Bryopsis
corticulans (Strain, 1951). Chapman and Haxo (1963) reisolated ε-carotene
from both marine sources as well as from the cultured unicellular flagellate
Cryptomonas ovata var. palustris and showed it to be identical with a carotene
96
97
98
41
1. CAROTENES
To the nonspecialist carotene is the pigment that is responsible for the
color of carrots and which is the biochemical precursor of vitamin A. Appropriately enough, when the crystalline coloring matter of carrots was
first isolated in 1831 it was named carotene. Much later, with refined isolation
techniques, it was recognized that carrots contained two isomeric pigments.
The minor constituent, an optically active substance, was eluted ahead of the
optically inactive major constituent during chromatography. Because of this
elution sequence the minor component was named α-carotene and the major
component ß-carotene. ^-Carotene (95) has emerged as the most abundant
and as one of the most widespread of the carotenes. The standard numbering
system, which follows the isoprenoid construction of the molecule, is shown
in formula 95.
IS'
4
'
16 17
Τ
Τ
15
Ι
I
II
20'
19'
17' 16'
95
In contrast to the wide distribution of ß-carotene (95), ε-carotene (96) is a
rarely encountered hydrocarbon; it differs from the common ^-isomer by
having a-ionone (97) instead of ß-ionone (98) end groups. ε-Carotene was
first isolated from the colonial marine diatom Navicula torquatum by Strain
and Manning (1943), and was subsequently detected in a green alga, Bryopsis
corticulans (Strain, 1951). Chapman and Haxo (1963) reisolated ε-carotene
from both marine sources as well as from the cultured unicellular flagellate
Cryptomonas ovata var. palustris and showed it to be identical with a carotene
96
97
98