Acetylenic acids crepenynic

Another alteration of unsaturated fatty acids is the formation of acetylenic groups (-OC-). This apparently occurs by dehydrogenation of -CH=CH- Examples of naturally occurring acetylenes are crepenynic acid (p. 381), alloxanthin (p. 1240), and the following remarkable hydrocarbon from the common cornflower Centaurea cyanusm ... 

Oleic and linoleic acids are precursors for acetylenes in microorganisms and plants (Fig. 3.1), but crepenynic and dehydrocrepenynic acids also are incorporated into most acetylenic compounds. Crepenynic acid (1) is the first acety-... 

The acetylenic epoxy-acid (9), c/,s-9,10-epoxyoctadec-12-ynoic acid, discovered along with other epoxy-acids and other acetylenic acids in the seed oil of Helichrysum bracteatum may be an intermediate in the bioconversion of crepenynic acid (8) to helenynolic acid (10), both of which had been identified previously in this source. 

Acetylenic Crepenynic acid 18 2AM2yne Crepis foetida Polymers -... 

The most important monoacetylenic acids are tariric (18 1 6a) and crepenynic (18 2 9cl2a) though other examples have also been recognized. Tariric acid has long been known as a component of seed oils of the Picramnia species. Its isomer, stearolic acid, though easily made in the laboratory from oleic acid, occurs only rarely as a minor component in Santalaceae seed oils where more unsaturated mono- and poly-acetylenic compounds are also present (see below). Two rare acids related to stearolic acid are 17 1 (8 ) and 18 2 (9al7e). 

A large series of compounds are derived by modification of crepenynic acid and related Cig acetylenic fatty acids. Whereas these acids may be accumulated in seed oils as components of triacylglycerols, modified derivatives usually are found in vegetative portions of plants. The biosynthesis of matricaria ester (4) and dehydromatricaria ester (5) (both with 10 carbon atoms in the acid portion of the molecule) (Fig. 3.1) is typical for this series of compounds. In this instance, fatty acids with chain lengths of less than 18 carbon atoms do not serve as precursors. 

Crepis alpina seeds have oils (triacylglycerols) where 65-80% of the fatty acids consist of crepenynic (9-octadecen-12-yonic, 18 1 A) acid. We have studied the formation of 18 1 A in developing seeds from Crepis alpina and can, for the first time, present evidence for the in-vitro activity of an acetylenic forming enzyme (acetylenase) and the partial characterization of this enzyme and its substrate. 

Some plant species synthesise fatty acids with one or more double bonds of the frans-configuration (e.g. frans-9,frans-12-octadecenoic acid), with conjugated double bond systems (e.g. cis-9,trans-, trans- Z-octadecatrienoic or a-eleostearic acid), or with acetylenic bonds (e.g. octadec-c/s-9-en-12-ynoic or crepenynic acid). The natural occurrence of such fatty acids has been reviewed [71,856],... 

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