Eicosapentaenoic acid synthesis pathway

Figure 12-6 Eicosapentaenoic acid synthesis pathway from alpha-linolenic acid. Note that the enzymes necessary to the process are delta-6-desaturase and delta-5-desaturase. (From http //www.asthmaworld.org/OMEGA3.htm)...

Hybridalactone, a novel marine derived eicosanoid from Laurencia hybrida, appears to be biosynthesized by a unique pathway from eicosapentaenoic acid. The synthesis of hybridalactone was carried out enantiospecifically from (+)-bicyclo[3.2.0]hept-4-ene-l-one so as to provide proof of stereochemistry (Ref. 4). 

FIGURE 4.1 Pathway for the synthesis of to-6 and to-3 fatty acids. Note GLA = Y-linolenic acid, DGLA = dihomo-y-linolenic acid, AA = arachidonic acid, EPA = eicosapentaenoic acid, DPA = docosapentaenoic acid, DHA = docosohexanoic acid. Source Adapted from Arterbum et al. (2006)." ... 

There are three groups of eicosanoids that are synthesized from C20 eicosanoic acids derived from the essential fatty acids linoleate and a-linolenate, or directly from dietary arachidonate and eicosapentaenoate (Figure 23-5). Arachidonate, usually derived from the 2 position of phospholipids in the plasma membrane by the action of phospholipase Aj (Figure 24-6)—but also from the diet—is the substrate for the synthesis of the PG2, 1X2 series (prostanoids) by the cyclooxygenase pathway, or the LT4 and LX4 series by the lipoxygenase pathway, with the two pathways competing for the arachidonate substrate (Figure 23-5). 

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