2. STEROLS: STRUCTURE AND DISTRIBUTION
155
HO'
H 3 C
H,C CH,
CH
(VIII)
Squalene
HqC CH
(IX)
Lanosterol
CH.,
^
3
HoC CH.
HoC
CHo
(X)
(XI)
Zymosterol
H3C
CH^
(XII)
Lophenol
(XIII)
Cholesterol
of cholesterol, but among the vertebrate sterols they have largely if not
entirely disappeared. It is for such reasons that the term primitive sterol
has two meanings and hence should be used with caution if at all. Thus
cholesterol may be viewed as the more primitive sterol when compared
with 24-methylenecholesterol. Yet the latter is found as a major sterol
only in animals which may be viewed as more primitive than the
cholesterol-bearing vertebrates.
In plants the evolution of sterols has taken a different course which
has not led to a return to the preferential use of cholesterol. For a long
time it had been tacitly assumed that cholesterol was the typical animal
sterol and altogether absent from plants. It was shown only rather
recently that this is not true and that cholesterol is the principal sterol
155
HO'
H 3 C
H,C CH,
CH
(VIII)
Squalene
HqC CH
(IX)
Lanosterol
CH.,
^
3
HoC CH.
HoC
CHo
(X)
(XI)
Zymosterol
H3C
CH^
(XII)
Lophenol
(XIII)
Cholesterol
of cholesterol, but among the vertebrate sterols they have largely if not
entirely disappeared. It is for such reasons that the term primitive sterol
has two meanings and hence should be used with caution if at all. Thus
cholesterol may be viewed as the more primitive sterol when compared
with 24-methylenecholesterol. Yet the latter is found as a major sterol
only in animals which may be viewed as more primitive than the
cholesterol-bearing vertebrates.
In plants the evolution of sterols has taken a different course which
has not led to a return to the preferential use of cholesterol. For a long
time it had been tacitly assumed that cholesterol was the typical animal
sterol and altogether absent from plants. It was shown only rather
recently that this is not true and that cholesterol is the principal sterol