116
WERNER BERGMANN
methyl group of the C-24 branch has been found to be cis-oriented
with respect to the isopropyl group. A synthetic product with a trans
orientation at this point is also known (43). Sargasterol (20-isofucosterol), (II, R = N), C 29 H 48 0, m.p. 132-133.5°, [a] D -47.5°; acetate,
m.p. 138-139°, [a] D —53°. This sterol, as yet isolated only from Sargassum seaweed, has been assigned an isoconfiguration at C-20 on the
basis of degradative (22) and synthetic evidence (44). It is believed
that a similar isomerism occurs in other sterols. Since their structures
have not definitely been established they will be dealt with under the
animals from which they have been derived.
3. Group HI (Structure HI): A
7 -Sterols with Specific Rotations of
[a] D -20° to +10°
The A
7 -sterols, formerly also called "y"-sterols belong to the most
readily recognizable sterols. Without additional unsaturation their specific rotations are near zero, but more negative with a second double
bond in the side chain. The differences between the molecular rotations
of the sterols and their acetates and their benzoates are —15 ± 15 and
+20 db 14, respectively (31). These sterols are relatively easily separated
from sterol mixtures by chromatography of their azoyl esters (11). Small
quantities of A
7 -sterols in mixtures may be detected and estimated by
means of colorimetric methods. One of them makes use of a modified
Schoenheimer and Sperry reagent (11), and the other of the reduction
of the colorless selenious acid to colored selenium (45).
A
7 -Cholestenol (lathosterol) (III, R = A), C 27 H 46 0, m.p. 126°, [a] D
+6°, infrared spectrum (26); acetate, m.p. 119°, [a] D +2°. After it had
been known for some time as a synthetic product, this sterol was first
found in nature as a companion of cholesterol in commercial preparations (45). It was subsequently isolated from the skin of animals and
was found in particularly high concentrations in the skin sterols of
rodents (11). A
7 -Cholestenol is the principal sterol of certain primitive
mollusks, and it is believed to be identical with hitodesterol from certain starfish sterol mixtures. It has also been shown to function as a precursor of cholesterol (46).
A
7 -Ergostenol (fungisterol; 24a-methyl-A
7 -cholestenol) (III, R = E),
C 28 H 48 0, m.p. 146°; [a] D 0°; acetate, m.p. 160°; [a] D —5°; and 5,6dihydroergosterol (α-dihydroergosterol;
24a-methyl-A
7 '
22 -cholestadienol)
(III, R = F), C 28 H 46 0, m.p. 176°, [a] D -19°; acetate, m.p. 180°, [a] D
—20°. Both sterols are minor components of yeast sterol mixtures. It is
probable that they also accompany their 24/?-methyl epimers (vide
infra) in starfish sterol mixtures.
24ß-Methyl-A
7 -cholestenol
(stellastenol) (III, R = G), and 24ß-
WERNER BERGMANN
methyl group of the C-24 branch has been found to be cis-oriented
with respect to the isopropyl group. A synthetic product with a trans
orientation at this point is also known (43). Sargasterol (20-isofucosterol), (II, R = N), C 29 H 48 0, m.p. 132-133.5°, [a] D -47.5°; acetate,
m.p. 138-139°, [a] D —53°. This sterol, as yet isolated only from Sargassum seaweed, has been assigned an isoconfiguration at C-20 on the
basis of degradative (22) and synthetic evidence (44). It is believed
that a similar isomerism occurs in other sterols. Since their structures
have not definitely been established they will be dealt with under the
animals from which they have been derived.
3. Group HI (Structure HI): A
7 -Sterols with Specific Rotations of
[a] D -20° to +10°
The A
7 -sterols, formerly also called "y"-sterols belong to the most
readily recognizable sterols. Without additional unsaturation their specific rotations are near zero, but more negative with a second double
bond in the side chain. The differences between the molecular rotations
of the sterols and their acetates and their benzoates are —15 ± 15 and
+20 db 14, respectively (31). These sterols are relatively easily separated
from sterol mixtures by chromatography of their azoyl esters (11). Small
quantities of A
7 -sterols in mixtures may be detected and estimated by
means of colorimetric methods. One of them makes use of a modified
Schoenheimer and Sperry reagent (11), and the other of the reduction
of the colorless selenious acid to colored selenium (45).
A
7 -Cholestenol (lathosterol) (III, R = A), C 27 H 46 0, m.p. 126°, [a] D
+6°, infrared spectrum (26); acetate, m.p. 119°, [a] D +2°. After it had
been known for some time as a synthetic product, this sterol was first
found in nature as a companion of cholesterol in commercial preparations (45). It was subsequently isolated from the skin of animals and
was found in particularly high concentrations in the skin sterols of
rodents (11). A
7 -Cholestenol is the principal sterol of certain primitive
mollusks, and it is believed to be identical with hitodesterol from certain starfish sterol mixtures. It has also been shown to function as a precursor of cholesterol (46).
A
7 -Ergostenol (fungisterol; 24a-methyl-A
7 -cholestenol) (III, R = E),
C 28 H 48 0, m.p. 146°; [a] D 0°; acetate, m.p. 160°; [a] D —5°; and 5,6dihydroergosterol (α-dihydroergosterol;
24a-methyl-A
7 '
22 -cholestadienol)
(III, R = F), C 28 H 46 0, m.p. 176°, [a] D -19°; acetate, m.p. 180°, [a] D
—20°. Both sterols are minor components of yeast sterol mixtures. It is
probable that they also accompany their 24/?-methyl epimers (vide
infra) in starfish sterol mixtures.
24ß-Methyl-A
7 -cholestenol
(stellastenol) (III, R = G), and 24ß-