Linolenic acid isomers

Tsuzuki,T.,Tokuyama,Y., Igarashi, M., and Miyazawa,T. 2004. Tumor growth suppression by alpha-eleostearic acid, a linolenic acid isomer with conjugated triene system, via lipid peroxidation. Carcinogenesis, 25,1-9. 

Chardigny, J.M., Bretihon, L., and Sebedio, J.L., 2001, New insights in health effects of trans a-linolenic acid isomers in humans. Fur. J. Lipid Sci. TechnoL, 103, 478. 

Lerch, S., Shingfield, K. J., Ferlay, A., Vanhatalo, A., Chilliard, Y. (2012). Rapeseed or linseed in grass-based diets effects on conjugated linoleic and conjugated linolenic acid isomers in milk fat from Holstein cows over 2 consecutive lactations. Journal of Dairy Science, 95,1269-11% . 

Thll oil fatty acids (TOFA) are available as commodity products having resin acid contents of 0.5%-10% (fatty acid fractions having greater than 10% resin acids are clasified as distilled tall oil). American TOFA consists primarily of Cjg acids with the monoenoic (oleic) and dienoic (linoleic and isomers) acids predominating. Only small amounts of trienoic and saturated acids are present. The linoleic portion is mostly the c/5, d5-9,12-isomer accompanied by some isomerization products from processing. A 5,9-linoleic acid isomer, a 5,9,12-linolenic acid isomer, and mono-, di-, and tri-unsaturated eicosanoic acid derivatives (Chap. 6332) are present in small amounts in tall oil and pine extractives. Scandinavian tall oil fatty acids, however, contain over 10% of the 5,9,12-linolenic acid. 

Draw the structures of (a) all the possible triacylglycerols that can be formed from glycerol with stearic and arachidonic acid, and (b) all the phosphatidylserine isomers that can be formed from palmitic and linolenic acids. 

The major fatty acids present in plant-derived fatty substances are oleic acid (9-octadecenoic, C18 l), linoleic acid (9,12-octadecadienoic, C18 2) and the conjugated isomers thereof and linolenic acid (9,12,15-octadecatrienoic, C18 3) (Scheme 31.1). Their rates of oxygen absorption are 100 40 1, respectively, hence partial hydrogenation with consequent lowering of the iodine number would lead to a significant increase in oxidative stabihty, particularly when C18 3 is reduced. 

FIGURE B-1 Structures of some fatty acids of neurochemical interest (see also Fig. 3-7 and text). The n minus nomenclature for the position of the double bond(s) is given here. Note that the position of the double bond from the carboxyl end can be indicated by the symbol A, so that linoleic acid may be also be designated as 18 2A9,12. The linolenic acid shown is the a isomer. 

Miwa and Yamamoto (31) described a simple and rapid method with high accuracy and reliability for the determination of C8 0-C22 6 fatty acids, which occur in esterified forms in dietary fats and oils and in living cells [the biological effects of routinely consumed fats and oils are of wide interest because of their impact on human health and nutrition (28,29), in particular, the ratio of cu-3 polyunsaturated fatty acid to w-6 polyunsaturated fatty acids (w-3/cu-6) seems to be associated with atherosclerosis and breast and colon cancers (30)]. They report improved separation of 29 saturated and mono- and polyunsaturated fatty acids (C8-C22), including cis-trans isomers and double-bond positional isomers, as hydrazides formed by direct derivatization with 2-nitrophenylhydrazine hydrochloride (2-NPH HC1) of saponified samples without extraction. The column consisted of a J sphere ODS-M 80 column (particle size 4 /xm, 250 X 4.6-mm ID), packed closely with spherical silica encapsulated to reach a carbon content of about 14% with end-capped octadecyl-bonded-spherical silica (ODS), maintained at 50°C. The solvent system was acetonitrile-water (86 14, v/v) maintained at pH 4-5 by adding 0.1 M hydrochloric acid with a flow rate of 2.0 ml/min. Separation was performed within only 22 min by a simple isocratic elution (Fig. 6). The resolution of double-bond positional isomers, such as y-linolenic ( >-6) and a-linolenic acid ( >-3) hydrazides and w-9, >-12, and >-15 eicosenoic acid hydrazides was achieved by use of this column. 

The separation achieved with the isomeric dienes derived from oleic acid is shown in Fig. 14. Three peaks are apparent, the last of which is the natural 9-cis,12-cis isomer the first must be 9-trans,12-trans octadecadienoate, and the second peak is presumably a mixture of the 9-cis,12-trans and 9-trans,12-cis compounds. With the geometric isomers of linolenic acid six... 

Fig. 15 Separation of the phenacyl derivatives of the geometrical isomers of (A) linoleic and (B) linolenic acids by HPLC in the silver ion mode. The column temperature was 38°C, and the mobile phase was 1,2-dichloroethane/dichloromethane/acetonitrile (49.75 49.75 0.5 v/v/v) at a flow rate of 0.75 ml/min, with detection at 242 nm. Note the change of scale on the time axis.

Linoleic acid and a-linolenic acid are two naturally occurring unsaturated fatty acids that are components of fats. Explain how many cis-trans isomers exist for each of these fatty acids. Interestingly, only the all-cis isomers of each occur naturally. Draw the structure of the naturally occurring stereoisomer of linoleic and a-linolenic acid using skeletal structures. 

Gas chromatography is the most accurate means of quantifying the trans isomers present in fatty acid mixtures. In the GC trace the trans peaks appear broader because they contain isomers whose complete resolution is difficult. Virgin olive oils may show, in the sum of the trans-oleic acid-isomers, a maximum value of 0.05% and in the sum of /ran.v-linoleic and linolenic acid the same maximum value of 0.05%. Lower grade olive oils and refined olive oils are allowed wider limits for fatty acid trans isomers (see Table 2.2). 

Table 4.6 Formation of geometrical isomers of y-linolenic acid in borage oil deodorized at different temperatures as determined by gas liquid chromatography of fatty acid isopropyl esters on a 30 m long DB-wax capillary column...

Wolff, R.L. (1993b) Further studies on artificial geometrical isomers of a-linolenic acid in edible linolenic acid containing oils. J. Am. Oil Chem. Soc., 70, 219-224. 

Most of the major metabolites of linolenic acid, listed in Figure 35, contain the cyclopentane (or -ene) ring and the two side chains arrayed in the cis fashion on the ring. Some of the metabolites, however, take the tram arrangement. Although isomerization to the trans isomer during isolation/purification is a likely process, a... 

Calibration Standard curves are prepared for added linoleic acid, linolenic acid, arachidonic acid and internal standards. Results are calculated using the ratio of the peak-height of the 18 2(9-cis,l 1-trans) biological isomer to that of the internal standard and multiplying by the concentration of the internal standard added. 

Yeast-derived saturated short-medium chain and branched-chain aldehydes are formed from sugar metabolism, fatty acid metabolism and branched-chain amino acid metabolism (Fig 8D.7). In addition, hexanal, as well as hexenal isomers, are formed during the pre-fermentative stages of winemaking by the sequential action of grape lipoxygenase and hydroperoxide cleavage enzyme on linoleic and linolenic acid, respectively (Crouzet 1986). 

Fatty acids with two or more conjugated double bonds are found in some plants and animals. In tissues of ruminant animals (and, hence, in meat and dairy products), fatty acids with conjugated diene system were detected as intermediates or by-products in the biohydrogenation of linoleic acid by microorganisms in the rumen. The main isomer, 9-cis, ll-fran -octadecadienoic acid, may account for up to 1% of the total fatty acids of milk fat. 9-cis, ll-fran5-15-cw-octadecatrienoic acid, derived from a-linolenic acid, is present in ruminant tissues only in trace levels. This fatty acid has been shown to have several medical properties, especially anti-cancer and anti-atherosclerosis effects. 

The list of natural fatty acids exceeds 1000, but commercial interest is limited to a smaller number— perhaps around 20. Ignoring the lipid membrane, rich in ot-lino-lenic acid and present in all green tissue, the three dominant acids in the plant kingdom are palmitic, oleic, and linoleic, sometimes accompanied by stearic acid and by linolenic acid. Others, occuring in specialty oils, include myristic, lauric, erucic, hexadecenoic, petroselinic, y-linolenic acid, eleostearic and isomers, ricinoleic, and vemolic (Table 1). 

Reaction sequence 45 shows this process at C-13 of linolenic acid for simplicity, but comparable cyclization also occurs at C-10 in linolenic acid and at C-8, C-9, C-11, and C-12 in arachidonic acid (252). The cyclic product mixes of oxidized Ln and An typically show multiple positional and geometric isomers (227, 266). In the interest of space, the isomerization and racemization that accompanies cyclization will not be discussed here. The reader is referred to papers by Gardner (6, 267) and Porter (7, 11, 252, 268) for more details. 

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