An octadecatrienoic acid from Lamium purpureum L. seed oil containing 5,6-allenic and trans-16-olefinic unsaturation

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Abstract
1. Lamium purpureum L. (Labiatae) seed oil contains 16% of a new acid characterized as (−)-octadeca-5,6-trans-16-trienoic acid (proposed trivial name ‘lamenallenic acid’) (Ia). The acid was isolated as its methyl ester by countercurrent distribution by using a combination of recycle–single withdrawal techniques. Methyl lamenallenate (Ib) is strongly laevorotatory. 2. The structure was established by infrared spectroscopy, nuclear-magnetic-resonance spectroscopy, quantitative hydrogenation and oxidative cleavage data of the original acid and of hydrazine partial reduction products. 3. Other unsaturated esters identified by their cleavage products were oleate, linoleate and linolenate. 4. A very small amount (less than 1%) of methyl laballenate [(−)-methyl octadeca-5,6-dienoate] was also isolated and identified.