Sterculic acids

Sterculic acid and related substances are the subject of an article in the July 1982 is sue of Journal of Chemical Education (pp 539-543)... 

Double bonds are accommodated by rings of all sizes The smallest cycloalkene cyclo propene was first synthesized m 1922 A cyclopropene nng is present m sterculic acid a substance derived from one of the components of the oil present m the seeds of a tree (Sterculia foelida) that grows m the Philippines and Indonesia... 

Sterculiagum Sterculic acid Sterculic acid [738-87-4] Sterculic acids Stereolithography Stereon... 

Step-shear test, 21 708-709 Sterculic acid(s), 5 28, 36t Stereochemistry... 

Malvaceae). Malvalic acid is produced from sterculic acid by chain shortening from the carboxyl end (Figure 3.14). Sterculic acid is an inhibitor of the A9-desaturase which converts stearic acid into oleic acid and is potentially harmful to humans in that it can alter membrane permeability and inhibit reproduction. 

In other cases cyclopropenes have been obtained by direct reaction of an alkyne with a diazo-compound in. the presence of a suitable catalyst. Typical of these is the reaction of ethyl diazoacetate with alkynes in the presence of copper, which is reported to lead to about 40-50 % conversion to cyclopropene per equivalent of diazo-compound. This has been applied to the synthesis of the important naturally occurring cyclopropene, sterculic acid, (66) 56) ... 

However, the elimination may be achieved in high yield from either cis- or trans-, 2-di-iodo-1,2-dibutylcyclopropanes using one molecular equivalent of butyllithium at low temperature. Since no reaction occurred at the ester group under these conditions, this has been applied in synthesis esters as of sterculic acid, a-hydroxysterculic acid (55)108 and 56, a potential inhibitor of mycolic acid synthesis109 ... 

Bickerstaffe, R., Johnson, A.R. 1972. The effect of intravenous infusions of sterculic acid on milk fat synthesis. Br. J. Nutr. 27, 561-570. 

Sterculic acid is a potent inhibitor of several desaturases, which are the enzymes responsible for the formation of double bonds in long-chain acids used as fuels, membrane components, and other critical biological molecules. Consequently, vegetable oils containing sterculic acid must be hydrogenated or processed at high temperatures to reduce or destroy the cyclopropene ring. 

Many chemists once believed that a cyclopropene could never be made because it would snap open (or polymerize) immediately from the large ring strain. Cyclopropene was eventually synthesized, however, and it can be stored in the cold. Cyclopropenes were still considered to be strange, highly unusual compounds. Natural-product chemists were surprised when they found that the kernel oil of Sterculia foelida, a tropical tree, contains sterculic acid, a carboxylic acid with a cyclopropene ring. 

Glanded cottonseed kernels contain 1.1-1.3% gossypol (19) plus related pigments that affect nutritional properties and color of the oil and meal. Cottonseed also contains the cydoptopenoid acids, malvahc and sterculic acids, which exist as glycerides and are concentrated in the seed axis (32). 

This type of fatty acid is usually found at low levels (around 1%) in plant oils that contain cyclopropene acids. Cyclopropene acids are characteristic for oils from the Malvalaceae, Stercu-liaceae, Bombaceae, Tiliaceae, and Sapicidaceae families with sterculic acid (9,10-methyleneoctadec-9-enoic acid) and mal-valic acid (8,9-methyleneheptadec-8-enoic acid) as two major compounds. Sterculic acid is more abundant (about 50% of the total fatty acids in Sterculiafoetida oil). 2-Hydroxysterculic acid may also be present in this oil as a possible intermediate in the biosynthesis of malvalic acid (through a-oxidation of sterculic acid). 

Figure 5. Proposed mechanism for the formation of 1-decyne from the photooxidation of sterculic acid (18).

Cyclopropenoid Fatty Acids. Cotton, and other plants in the Malvaceae family, contain a pair of unique cyclopropene fatty acids (CPFA). These two fatty acids, sterculic and malvalic acid, are generally referred to collectively as cyclopropenoid fatty acids. Sterculic acid is the most active of the two fatty acids whose general action is to inhibit the desaturation of stearic to oleic fatty acid in the animal body with a resultant alteration in membrane permeability or an increase in the melting point of fats. 

Jones (36) reviewed the natural antinutrients of cottonseed protein products— gossypol and the cyclopropenoic fatty acids (CPFA malvalic and sterculic acids). The CPFAs participate in forming the pink color complex in the Halphen reaction, a test specific for the admixture of cottonseed oil with other oils and fats. They also inhibit A9 desamrase, an enzyme that converts stearic acid into oleic acid, and thus increase hardness of fats from animals (e.g., pig backfat and lard) raised or finished on feedstuffs containing high levels of polyunsamrated oils like corn. Feed industry practice is to limit cottonseed lipids to no more than 0.1-0.2% in the diet of laying hens to avoid pink discoloration of egg whites and alterations of the vitelline membrane that cause pasty yolks. 

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