1. FATTY ACID OCCURRENCE AND DISTRIBUTION
7
thus sarmentosus (25) and cis-12,13-epoxyoctadec-cis-9-enoic acid occurs in quantity in the seed oils of Vernonia anthelmintica (26). All
these oxygenated acids are optically active.
The naturally occurring n-even-numbered carbon monoethenoid
acids range from Ci 0 to C 30 . In general the lower members are found in
milk fats, those of intermediate range (Ci 6 -C 24 ) in the oils of aquatic
species, and the higher members in waxes, phosphatides, and unusual
seed fats.
An odd-numbered acid, heptadec-cw-9-enoic acid, has been isolated
from lamb caul fat, and evidence for the occurrence of a C15 unsaturated acid has been obtained (27). In the free fatty acids of human
hair fat the full range of monoethenoid acids from Cn to Ci 8 has been
observed (28).
b. Diethenoid Acids. The most commonly occurring diethenoid acid
is linoleic (octadeca-cis-9,cis-12-dienoic) acid, which is found in most
seed fats. Other diethenoid acids include deca-frans-2,ds-4-dienoic acid
found in Stillingia oil (29, 30).
c. Triethenoid Acids. Linolenic (octadeca-cis-9,cis-12,c£s-15-trienoic)
acid occurs in quantity in many vegetable oils. Other nonconjugated
triethenoid acids include an isomer of linolenic acid, octadeca-6,9,12trienoic acid, present in the seed fats of Oenothera biennis (31); a
closely related Ci 6 acid, hexadeca-7,10,13-trienoic acid occurs in rape
leaf glycerides (32).
α-Eleostearic acid, oct£Ldeca.-cis-9,trans-ll,trans-13~tnenoic acid, is
the chief acid in tung oil and in some other drying oils; punicic acid,
octadeca-m-9,£rans-ll,cis-13-trienoic acid, which is isomeric with a-eleostearic acid, occurs in pomegranate seed oils (33-35). Other acids
closely related to α-eleostearic, which occur in certain seed fats, include
α-kamlolenic acid, which is 18-hydroxy-a-eleostearic (36) acid, and
licanic acid, which is 4-keto-a-eleostearic acid (37, 38). Parinaric acid,
which is octadeca-9,ll,13,15-tetraenoic acid (39), contains two or three
trans bonds (40).
d. Polyothenoid Acids. The best-known acid in this class, arachidonic
(eicosa-5,8,ll,14-tetraenoic) acid, is present in very small quantities in
many animal fats and in larger amounts in the organ fats, especially in
the phospholipid fractions. C 20 and C 22 unsaturated acids with four,
five, or six double bonds also occur, especially in fish liver oils.
In animal fats these polyenoic acids are mainly of the linoleic type,
that is, .with the first double bond between the sixth and seventh carbons from the methyl group end, whereas in fish oils they are mainly
of the linolenic type with the first double bond between the third and
fourth carbons from the methyl group end (41). In all instances the
7
thus sarmentosus (25) and cis-12,13-epoxyoctadec-cis-9-enoic acid occurs in quantity in the seed oils of Vernonia anthelmintica (26). All
these oxygenated acids are optically active.
The naturally occurring n-even-numbered carbon monoethenoid
acids range from Ci 0 to C 30 . In general the lower members are found in
milk fats, those of intermediate range (Ci 6 -C 24 ) in the oils of aquatic
species, and the higher members in waxes, phosphatides, and unusual
seed fats.
An odd-numbered acid, heptadec-cw-9-enoic acid, has been isolated
from lamb caul fat, and evidence for the occurrence of a C15 unsaturated acid has been obtained (27). In the free fatty acids of human
hair fat the full range of monoethenoid acids from Cn to Ci 8 has been
observed (28).
b. Diethenoid Acids. The most commonly occurring diethenoid acid
is linoleic (octadeca-cis-9,cis-12-dienoic) acid, which is found in most
seed fats. Other diethenoid acids include deca-frans-2,ds-4-dienoic acid
found in Stillingia oil (29, 30).
c. Triethenoid Acids. Linolenic (octadeca-cis-9,cis-12,c£s-15-trienoic)
acid occurs in quantity in many vegetable oils. Other nonconjugated
triethenoid acids include an isomer of linolenic acid, octadeca-6,9,12trienoic acid, present in the seed fats of Oenothera biennis (31); a
closely related Ci 6 acid, hexadeca-7,10,13-trienoic acid occurs in rape
leaf glycerides (32).
α-Eleostearic acid, oct£Ldeca.-cis-9,trans-ll,trans-13~tnenoic acid, is
the chief acid in tung oil and in some other drying oils; punicic acid,
octadeca-m-9,£rans-ll,cis-13-trienoic acid, which is isomeric with a-eleostearic acid, occurs in pomegranate seed oils (33-35). Other acids
closely related to α-eleostearic, which occur in certain seed fats, include
α-kamlolenic acid, which is 18-hydroxy-a-eleostearic (36) acid, and
licanic acid, which is 4-keto-a-eleostearic acid (37, 38). Parinaric acid,
which is octadeca-9,ll,13,15-tetraenoic acid (39), contains two or three
trans bonds (40).
d. Polyothenoid Acids. The best-known acid in this class, arachidonic
(eicosa-5,8,ll,14-tetraenoic) acid, is present in very small quantities in
many animal fats and in larger amounts in the organ fats, especially in
the phospholipid fractions. C 20 and C 22 unsaturated acids with four,
five, or six double bonds also occur, especially in fish liver oils.
In animal fats these polyenoic acids are mainly of the linoleic type,
that is, .with the first double bond between the sixth and seventh carbons from the methyl group end, whereas in fish oils they are mainly
of the linolenic type with the first double bond between the third and
fourth carbons from the methyl group end (41). In all instances the