Marine lipids
Table 1 - Sterol composition of Suberitidae sponges (for the meaning
of A to E, see Materials and methods).
Sterols
RRT
A
B
C
D
E
5α-Stanols
24-norcholestunol
0.78
0.5
0.8
1.7
0.7
1.8
Cholestanol
1.03
65.6
72.2
71.7
74.4
51.2
Campestanol
1.26
17.6
11.1
12.0
8.9
36.0
Stigmastanol
1.48
1.7
1.0
0.9
Tr.
7.0
Δ5 Sterols
Brassicasterol
1.10
Tr.
2.1
-
-
-
24-CH
2
-cholesterol
1.21
0.5
0.2
—
-
-
Campesterol
1.23
Tr.
0.5
2.2
1.6
-
Poriferasterol
1.35
1.0
1.0
Tr.
0.3
-
β-sitosterol
1.47
9.3
6.3
3.0
0.8
4.0
Δ7 Sterols
C26:1
0.72
—
—
-
0.3
-
C27:1
0.93
0.2
0.2
-
-
-
7-cholestenol
1.12
2.4
2.1
9.2
12.6
-
C28:1
1.18
—
1.9
—
0.3
-
7-campestenol
1.37
0.5
0.4
—
-
-
7-clionastenol
1.61
0.5
0.2
-
-
-
RRT: Retention time relative to cholesterol (1.00) on OV-1 (25 m). Tr.: traces (< 0.2%).
Stanols were readily identifïed as acetates from their relative retention
times and mass spectra, which displayed molecular ion peaks, in contrast
with the Δ5 sterol acetates. The base peak was m/z 215 in all spectra of
stanol acetates since electron impact at 20 eV insteacl of 70 eV enhanced
this major diagnostic ion. Five other diagnostic ions were produced,
which corresponded to losses of the methyl group, acetic acid, side
chain (sc) and D ring from the molecular ion. As an example, the mass
spectrum of 24-norcholestanyl acetate displayed the following additional
diagnostic fragment ions:
M + , m/z 416, [M-CH3}
+ , m/z 401, [M-AcOH] + , m/z 356,
[M-ACOH-CH 3 }
+ , m/z 341, [M-D ring-sc] + , m/z 275.
In all samples studied, cholestanol was the major component, accounting
for up to 75% of the total sterol mixture. The occurrence of A7 sterols
was also of interest. This may mean that the first stage in the biosynthesis sequence Δ5→Δ0→Δ7 is rapid, in contrast with the second
that does not appear to be very efficient. Thus, stanols are accumulated.
This sequence was previously demonstrated (Smith & Goad, 1975;
Sheikh & Djerassi, 1977).
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