Fatty acids with conjugated unsaturation occur in many seed oiIs. Thirty of these acids are reviewed with emphasis on their detection, isolation, and structure determination. Their distribution among plant families is shown, and a botanical source of each acid is given. Some reactions, derivatives, and methods of determining configuration are described. Current theories of their biosynthesis in the seed, involving oxygenated precursors, are summarized.

No abstract

The seed oil of Tragopogon porrifolifoliz~s I,. was found to contain about 4y0 of conjugated diene hydroxy fatty acids, identified as 9-hydroxy-10,12-and 13-hydroxy-9,ll-octadecadienoic acids. On dehydration, the products were 8,10,12-and 9,11,13-octadecatrienoic acids. The diene acids were cis,trans or lra?rs,cis and the trierle acids were judged to be all-trans.The conjugated triene acid of Calendr~la ofici?zalis L. seed oil was isolated and identihed as trans,8:trans,l0:cis,12-octadecatrienoic acid by spectral analysis, by the structure of the il~aleic anhydride adduct, and by ideiltification of degradation products. All-tra?rs-8,10,12-octadecatrienoic acid was found to react with rnaleic anhydride a t both the 8.11 and 10,13 positions.

Seed oils of nine species of Cucurbitaceae were analyzed by gas chromatography and other techniques. The oil of Ecballiz~m elaterium yielded 227, of punicic acid; Cucumis dipsaceus and Cucurbita jicijolia had the ordinary palmitic-oleic-linoleic composition; a variety of iVoinordica charantia had 5iYo of U-eleostearic acid. Occurrence of punicic acid as the major acid of Trichosanthes anguina was confirmed. KO evidence could be found for the existence of a n isomer of linoleic acid in Teuairia pedata oil. The fatty acid composition was determined quantitatively for the above oils and for those of Cucumis melo, Lagenaria siceraria, and L u . a cylindrica. The 4-bromophenacyl esters of a-eleostearic and punicic acids were prepared.Seed oils of the Cucurbitaceae family fall into two distinct groups, one having the ordinary palmitic-oleic-linoleic composition, the other having a considerable proportion of conjugated triene fatty acids in the glycerides. The first group includes the common cultivated cucurbits. The second or conjugated oil group consists of certain species of Cucurbita, ,Vomordica, Telfairia, and Trichosanthes.Nine species of the family were exanlined in the present work to ascertain or co~lfirnl the identity of the conjugated acids and to resolve certain anomalies in previous studies. Ecballium elaterium, Czlcumis dipsaceus, and Cz~curbita ficifolia had not been analyzed previously. The percentage co~nposition of each oil was determined by gas-liquid chromatography (GLC) of the methyl esters, in conjunction with ultraviolet absorption analysis. The conjugated acids, when present in substantial amount, were isolated and purified-by crystallization a t low temperatures. They were identified by orthodox chemical methods. KESULTS A N D DISCUSSIONPreliminary data are shown in Table I. The high refractive indices of the first three oils indicate conjugated unsaturation and this was confirmed by their ultraviolet spectra and by isolation of conjugated triene fatty acids (see Table 11). None of the oils had an absorption peak in the region of 233 mp; thus they contained no appreciable amount of conjugated diene acid.In the analysis of the methyl esters by GLC, neither myristic nor linolenic acid was observed, although these two acids had been reported in some species by earlier workers (11,15,16). The results suggest that seed oils of Cucurbitaceae contain little or no linolenic acid. No acids other than those shown in Table I1 were observed. The infrared spectra did not disclose any evidence of oxygenated acids and GLC analysis showed that C20 and C22 acids were absent.There was evidently some loss of conjugated triene ester on the GLC column during the analysis. Accordingly, the content of conjugated triene was determined by ultraviolet absorption analysis and the amount of each non-conjugated acid was calculated as a percentage of the remainder.

The major fatty acid of the seed oil ofTrewia nudiflora is shown to be ॅ‐kamlolenic acid, not ॅ‐eleostearic acid as believed earlier. Other conjugated acids were found and identified in seed oils not previously studied, viz., ॅ‐eleostearic acid inParinari insularum andRicinodendron rautanenii; trans,8‐trans,10‐cis,12‐octadecatrienoic acid inCalendula stellata. The identity of the conjugated acids in four other seed oils was established, viz., ॅ‐eleostearic acid inPrunus yedoensis andValeriana officinalis; punicic acid inCucurbita digitata andC. palmata.