Fatty acids cyclopentene

Some natural fatty acids contain a carbocyclic unit which may have three (cyclopropane and cyclo-propene acids), five (prostaglandins-see Section 1.4 and cyclopentene acids) or six carbon atoms (cyclohexane acids). Aspects of this topic have been reviewed (Christie, 1970 Lie Ken lie, 1979 and Badami and Patil, 1982). Other cyclic acids occur in tall oil (Section 3.3.36). 

Secondary fatty acids may differ from common fatty acids in chain length, additional fimctional groups, e.g., hydroxy and hydroperoxy groups, or other structural elements (branches in the carbon chain, presence of cyclopropane or cyclopentene rings, etc.) (D 3.2). 

When unsaturated fatty acids are subjected to thermolytic cleavage, dimers, polymers and cyclic compounds are produced. The dimers include alicyclic mono-, di-, and triene dehydrodimers, saturated dimers with cyclopentene structures, tetrasubstituted cyclohexanes and bicyclic and tricyclic dimers (Nawar, 1985). Cyclic mononmers exhibit toxicity in experimental animals (Van Gastel et al, 1984), therefore, generation of cyclic monomers at high temperature frying with oils containing polyunsaturated fatty acids should be carefully monitored. 

Another group consists of cyclic fatty acids with saturated or unsaturated three-membered, five-membered and six-membered rings. The naturally occurring acids usually have the cyclopropane (3-24) or cyclopropene (3-25) ringin the middle ofthe hydrocarbon chain. The cyclopentene ring (3-26), as is the case of chaulmoogric... 

Cyclic unsaturated fatty acids with a cyclopentene ring at the end of the chain, such as chaulmoogric acid (3-26) and hydno-carpic acid, are present in the seeds of evergreen trees known as chaulmoogra Hydnocarpus, syn. Taraktogenos) of the Achariaceae... 

The unsaturated fatty acids are also transformed, via the radicals formed during heating to higher temperatures (e.g. during frying), into cyclic fatty acids with five- and six-membered rings. Cyclic acids derived from oleic acids are saturated compounds. The products formed from linoleic acid have one double bond. These products include cyclopentene acids and cyclopentane and cyclohexane acids with one cis double bond in the side chain. Linolenic acid forms products with two double bonds, such as cyclopentene and cyclohexene acids with one cis double bond in the side chain. 

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