2. STEROLS: STRUCTURE AND DISTRIBUTION
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sterol has with certainty been isolated only from plants, its structural
relationship to other sterols found in invertebrates makes its occurrence
in animals quite probable.
24a-Methyl-22-dehydrocholesterol
(brassicasterol)
(II, R = F),
C 28 H 4G 0, m.p. 148°, [ a ] D -64°; acetate, m.p. 157° [a] D -65°. First
obtained from rapeseed oil, this sterol has been isolated from several
invertebrates, among which it appears to be fairly widely distributed.
24ß-Methyl-22-dehydrocholesterol
(II, R = H). A sterol, chalinasterol, which had originally been assigned this structure has been shown
to be 24-methylenecholesterol (II, R = D) (38). There seems to be
little doubt that a sterol of structure (II, R = H) is present in some of
the more complex sterol mixtures. Its isolation in a reasonable state of
purity, however, has not yet been accomplished.
24a-Ethylcholesterol (ß-sitosterol) (II, R = J), C 29 H 50 O, m.p. 137°,
[a] D —37°, infrared spectrum (26); acetate, m.p. 127° [a] D —42°.
Widely distributed among plants and described under a variety of
names (18) this sterol generally occurs in mixtures from which it can
be separated only with great difficulties. It is generally accompanied by
its 24/?-epimer. A reliable reference sample is best prepared by selective
hydrogenation of stigmasterol (II, R = K) (42). Its occurrence in mollusks has been reported.
24ß-Ethyhholesterol
[γ-sitosterol; clionasterol (?)] (II, R = L),
C 29 H 50 O, m.p. 148°, [a] D —43°; acetate, m.p. 144°, [ a ] D —45°. In
plants, this sterol is found mainly mixed with its 24a-epimer as minor or
major component. It is difficult to obtain pure. The same holds true for
clionasterol, which is widely distributed among invertebrates and which
may well be identical with γ-sitosterol and possess structure (II,
R = L) (17).
Stigmasterol (24a-ethyl-22-dehydrocholesterol) (II, R = K), C 29 H 48 0,
m.p. 170°, [a] D —46°, infrared spectrum (26); acetate, m.p. 144°,
[a] D —49°. Like other sterols first known from plants it also appears to
occur in invertebrate sterol mixtures.
24ß-Ethyl-22-dehydrocholesterol
(poriferasterol) (II, R = M), C 29
H 48 0, m.p, 156°, [a] D —49°, infrared spectrum (26); acetate, m.p. 147°,
[a] D —53°. This 24-epimer of stigmasterol is readily separated through
its acetate tetrabromides. It appears to be widely distributed among
marine invertebrates.
24-Ethylidenecholesterol
(fucosterol) (II, R = I), C 29 H 48 0, m.p.
124°, [a] D —40°, infrared spectrum (26); acetate, m.p. 118°, [a] D —45°.
This typical sterol of the brown algae, Phaeophyceae (18), has not yet
been found in animals. It may be regarded as an intermediate in the
biosynthesis of sterols of the types (II, R = J) and (II, R = L). The
115
sterol has with certainty been isolated only from plants, its structural
relationship to other sterols found in invertebrates makes its occurrence
in animals quite probable.
24a-Methyl-22-dehydrocholesterol
(brassicasterol)
(II, R = F),
C 28 H 4G 0, m.p. 148°, [ a ] D -64°; acetate, m.p. 157° [a] D -65°. First
obtained from rapeseed oil, this sterol has been isolated from several
invertebrates, among which it appears to be fairly widely distributed.
24ß-Methyl-22-dehydrocholesterol
(II, R = H). A sterol, chalinasterol, which had originally been assigned this structure has been shown
to be 24-methylenecholesterol (II, R = D) (38). There seems to be
little doubt that a sterol of structure (II, R = H) is present in some of
the more complex sterol mixtures. Its isolation in a reasonable state of
purity, however, has not yet been accomplished.
24a-Ethylcholesterol (ß-sitosterol) (II, R = J), C 29 H 50 O, m.p. 137°,
[a] D —37°, infrared spectrum (26); acetate, m.p. 127° [a] D —42°.
Widely distributed among plants and described under a variety of
names (18) this sterol generally occurs in mixtures from which it can
be separated only with great difficulties. It is generally accompanied by
its 24/?-epimer. A reliable reference sample is best prepared by selective
hydrogenation of stigmasterol (II, R = K) (42). Its occurrence in mollusks has been reported.
24ß-Ethyhholesterol
[γ-sitosterol; clionasterol (?)] (II, R = L),
C 29 H 50 O, m.p. 148°, [a] D —43°; acetate, m.p. 144°, [ a ] D —45°. In
plants, this sterol is found mainly mixed with its 24a-epimer as minor or
major component. It is difficult to obtain pure. The same holds true for
clionasterol, which is widely distributed among invertebrates and which
may well be identical with γ-sitosterol and possess structure (II,
R = L) (17).
Stigmasterol (24a-ethyl-22-dehydrocholesterol) (II, R = K), C 29 H 48 0,
m.p. 170°, [a] D —46°, infrared spectrum (26); acetate, m.p. 144°,
[a] D —49°. Like other sterols first known from plants it also appears to
occur in invertebrate sterol mixtures.
24ß-Ethyl-22-dehydrocholesterol
(poriferasterol) (II, R = M), C 29
H 48 0, m.p, 156°, [a] D —49°, infrared spectrum (26); acetate, m.p. 147°,
[a] D —53°. This 24-epimer of stigmasterol is readily separated through
its acetate tetrabromides. It appears to be widely distributed among
marine invertebrates.
24-Ethylidenecholesterol
(fucosterol) (II, R = I), C 29 H 48 0, m.p.
124°, [a] D —40°, infrared spectrum (26); acetate, m.p. 118°, [a] D —45°.
This typical sterol of the brown algae, Phaeophyceae (18), has not yet
been found in animals. It may be regarded as an intermediate in the
biosynthesis of sterols of the types (II, R = J) and (II, R = L). The