Y-linoleic acid

In general for the C20 series, maximal activity is achieved with amides of arachidonic acid (1) [81], mead acid (199) [149], and dihomo-y-linoleic acid (200) [150] (see Table 6.18). Decreasing the unsaturation (201), (202), or abolishment of the n-pentyl chain (203) [150] led to less active or inactive compounds. Variable results were seen with longer chains. The C22 4 n-6 analogue (204) is as active as AEA (1) whereas the C22 6 n-3 analogue (205) is less active than the C20 5 n-3 analogue (203) [150]. Replacement of the double bonds with triple bonds (206) resulted in loss of activity [150] (see Table 6.18). Forcing the fatty acid chain into a hairpin conformation by cyclisation (207) also resulted in inactive compounds [151]. 

Because homo-y-linolenic acid lacks a double bond in position 5 but has a double bond in position 13, all derivatives of PGG, the primary prostaglandin of the homo-y-linoleic acid series, are designated PG, followed by a letter A-I and the number 1 which denotes only one double bond in the molecule. 

A total of approx 400 t of seeds are processed each year in the United States and Canada. One major supplier of OEP derives the oil from specially selected and hybridized forms of Oenothera species (6). OEP in oral tablets or capsules usually range from 500 to 1300 mg. Most commercial products are standardized for a y-linoleic acid content of 9% (2). Dosage forms include oral formulations (capsules, tablets, oil swallowed directly or mixed with another liquid/food) and topical (7). 

Main components Resin, mucilage, tannins, soluble silicic acid, ascorbic acid, y-linolic acid, pyrrolizidine alkaloids and traces of essential oil of unknown composition. 

Fig. 9. Accumulation of y-linoleic acid (y-18 3) by zygotic embryos of Borago officinalis cultured in basal medium supplemented with various sucrose concentrations (%, w/v, indicated in inset) from 6 to 16 d post anthesis. Data from liquid and semisolid media are combined. After Whipkey et al. [76]...

The enzymes involved in Scheme 3.3 are the same for the (0-3 and (0-6 PUFAs. The AMesaturase enzyme installs a C6-C7 cis double bond on hnoleic add (4) and a-linolenic acid (5), which forms y-linolenic acid (9) and stearidonic add (10), respectively. Then an elongase transforms these two fatty acids to the two C20 fatty acids dihomo-y-linoleic add (11) and eicosatetraenoic acid (12), respectively. Claisen-type condensation reactions of thioesters are again involved. Desaturation on dihomo-y-linoleic acid (11) by the A -desaturase enzyme installs a C5-C6 cis double bond that leads to arachidonic acid (8). If the A -desaturase enzyme uses eicosatetraenoic acid (12) as the substrate, EPA (6) is formed (Scheme 3.3). 

The role of (w-3) fatty acids in health promotion and disease prevention is well known. Phospholipids containing eicosa pentaenoic acid (EPA) (C20 5) and docosahexaenoic acid (DHA) (C22 6) at the 2-position can be easily digested and have nutritional and medical value. Na et al. [59] have incorporated these PUFAs into the 2-position of a phosphotidylcholine (PC) by a phospholipase A2-catalyzed process in a w/o microemulsion. In another study, Osterberg et al. [58] incorporated y-linoleic acid into an unhindered triglyceride through lipase-catalyzed transesterification. 

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