112
WERNER BERGMANN
names and properties of sterols of uncertain structure or uniformity
will be given in connection with general discussions of the sterols of
the phyla or classes of animals from which they have been obtained.
1. Group I (Structure I): A
5 >
7 -SteroL· or 7-Dehydrosterols with Specific
Rotations in Excess of [a\ D —90° *
The most characteristic structural feature of the sterols belonging to
this group is the system of conjugated double bonds in ring B. It not
only accounts for their highly negative rotation, but also for their very
characteristic ultraviolet absorption spectrum. It sets these sterols apart
from all others which do not absorb light in this region. It also makes
possible the detection and quantitative determination of very small
amounts of A
5 '
7 -sterols in mixtures. This spectrographic evidence, however, detects only the presence of conjugation in ring B and no other
structural features such as the size of the side chain. This should be
borne in mind when reviewing the older literature, which contains many
references to the occurrence of ergosterol or 7-dehydrocholesterol in mixtures, when the less specific term A
5,7 -sterol would have been more accurate. Relatively large quantities of sterols of type I with unknown
side chains are found in mollusks. They will be discussed in the chapter
dealing with the sterols of bivalves.
A conjugated system of double bonds is very reactive and prone to
undergo rearrangements and other reactions induced by physical and
chemical means. Of greatest biological significance is the action of ultraviolet light on A
57 -sterols which leads through a series of interesting rearrangements to the vitamins D. It is for this reason that A
57 -sterols have
been referred to as provitamins D, although they may not all acquire
antirachitic activity upon irradiation. In another light reaction, in the
presence of air and a photosensitizer A
5j7 -sterols absorb oxygen to
form nicely crystalline and rather stable peroxides (14).
7-Dehydrocholesterol (provitamin D 3 ) (I, R = A), C27H42O, m.p.
150°, [a] D —114°; acetate, m.p. 130°, [a] D —85°. It is probably the most
widely distributed provitamin D of the animal world. While it normally
accompanies cholesterol or other sterols in but small amounts, it may in
certain cases constitute as high as 27% of the sterol mixture (see under
Mollusks, Section VIII). 7-Dehydrocholesterol is technically prepared
from cholesterol for the manufacture of vitamin D 3 , of which large
quantities are needed in poultry raising.
24a-Methyl-7-dehydrocholesterol (22,23-dihydroergosterol; provitamin
D 4 ) (I, R = E), C 28 H 46 0, m.p. 153°, [a] D —109°; acetate, m.p. 158°,
[a] D —75°. It has only been obtained by a selective hydrogenation of the
* Unless stated otherwise, the rotations were taken in chloroform.
WERNER BERGMANN
names and properties of sterols of uncertain structure or uniformity
will be given in connection with general discussions of the sterols of
the phyla or classes of animals from which they have been obtained.
1. Group I (Structure I): A
5 >
7 -SteroL· or 7-Dehydrosterols with Specific
Rotations in Excess of [a\ D —90° *
The most characteristic structural feature of the sterols belonging to
this group is the system of conjugated double bonds in ring B. It not
only accounts for their highly negative rotation, but also for their very
characteristic ultraviolet absorption spectrum. It sets these sterols apart
from all others which do not absorb light in this region. It also makes
possible the detection and quantitative determination of very small
amounts of A
5 '
7 -sterols in mixtures. This spectrographic evidence, however, detects only the presence of conjugation in ring B and no other
structural features such as the size of the side chain. This should be
borne in mind when reviewing the older literature, which contains many
references to the occurrence of ergosterol or 7-dehydrocholesterol in mixtures, when the less specific term A
5,7 -sterol would have been more accurate. Relatively large quantities of sterols of type I with unknown
side chains are found in mollusks. They will be discussed in the chapter
dealing with the sterols of bivalves.
A conjugated system of double bonds is very reactive and prone to
undergo rearrangements and other reactions induced by physical and
chemical means. Of greatest biological significance is the action of ultraviolet light on A
57 -sterols which leads through a series of interesting rearrangements to the vitamins D. It is for this reason that A
57 -sterols have
been referred to as provitamins D, although they may not all acquire
antirachitic activity upon irradiation. In another light reaction, in the
presence of air and a photosensitizer A
5j7 -sterols absorb oxygen to
form nicely crystalline and rather stable peroxides (14).
7-Dehydrocholesterol (provitamin D 3 ) (I, R = A), C27H42O, m.p.
150°, [a] D —114°; acetate, m.p. 130°, [a] D —85°. It is probably the most
widely distributed provitamin D of the animal world. While it normally
accompanies cholesterol or other sterols in but small amounts, it may in
certain cases constitute as high as 27% of the sterol mixture (see under
Mollusks, Section VIII). 7-Dehydrocholesterol is technically prepared
from cholesterol for the manufacture of vitamin D 3 , of which large
quantities are needed in poultry raising.
24a-Methyl-7-dehydrocholesterol (22,23-dihydroergosterol; provitamin
D 4 ) (I, R = E), C 28 H 46 0, m.p. 153°, [a] D —109°; acetate, m.p. 158°,
[a] D —75°. It has only been obtained by a selective hydrogenation of the
* Unless stated otherwise, the rotations were taken in chloroform.