9,10,18-Trihydroxyoctadecanoic acid

Phosphorus-Hydrlodic acid Zn-HCl-CHsOH. An efficient method for the replacement of primary and secondary hydroxyl groups by hydrogen has proved useful in the investigation of hydroxy acid constituents of fats. Thus an acid eventually characterized as 9,10,18-trihydroxyoctadecanoic acid (1) was refluxed with red phosphorus and hydriodic acid for 16 hrs. and the reduced product was recovered by ether extraction and refluxed with methanolic hydrochloric acid and zinc. The product was identified as methyl stearate (2). 

It has been reported that the major aliphatic monomers of suberin polymers from several tree barks are fatty acids with both a>- and mid-chain oxygenation (192). These monomers include 9,10-epoxy-18-hydroxyoctadecanoic acid and 9,10,18-trihydroxyoctadecanoic acid, both of which are common components of cutin polymers (232). For example, 9,10-epoxy-18-hydroxyoctadecanoic acid was reported to be the major monomer (31%) of Quercus ilex bark suberin and... 

Trihydroxyoctadecanoic acid was generated from 9,10-epoxy-18-hy-droxyoctadecanoic acid by a 3000-g particulate fraction obtained from the skin of the young fruit of Malus pumila (91). This enzyme activity did not require any cofactors and showed fairly stringent substrate specificity. It catalyzed the hydration of the m-epoxide to the /ireo-product and this stereospecificity is consistent with the natural occurrence of the /Areo-product in cutin. The trihydroxy Cig acid thus generated probably is the biosynthetic precursor of 9,10-dihy-droxyoctadecanedioic acid, which has been found in several suberin polymers (244). 

The building units of cutin are called cutin acids, which include mono-, di- and trihydroxycarboxylic fatty acids and also higher dicarboxylic, dihy-droxydicarboxylic and also other acids. The characteristic monomers are 18-hydroxyoctadeca-9,12-dienoic, 10,16-dihydroxyhexadecanoic and threo-9,10,18-trihydroxyoctadecanoic acids. 

The major components of the C16 cutins are 9- or 10,16-dihydroxyhexadecanoic acid, and 16-hydroxyhexadecanoic acid. 16-Hydroxy-10-oxo-C16 acid and 16-oxo-9 or 10-hydroxy C16 acid are monomers in only some cases. The major components of the C18 family of monomers are 18-hydroxy-9,10-epoxyoctadecanoic acid and 9,10,18-trihydroxyoctadecanoic acid, together with their monounsaturated homologs. Omega hydroxyacids and their derivatives are the main components of cutin, which are interhnked via ester bonds, forming a polyester polymer of indeterminate size [211]. 

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