Identification of (all-cis)-6,9,12,15-octadecatetraenoic acid in Ribes nigrum and fish oils: chemical and physical characterization.

In this report, we show that the non-conjugated octadecatetraenoic acid found in the oil of the seeds from Ribes nigrum is identical to the C18-polyunsaturated fatty acid previously isolated in a number of fish oils and seed oils. Evidence obtained from mass spectral data of its triazolopyridine derivative clearly indicates the presence of methylene-interrupted double bonds. Comparison with authentic material prepared by chemical synthesis provides further confirmation of the (all-cis)-6,9,12,15-octadecatetraenoic acid structure. The (all-cis)-4,8,12,15-structural arrangement erroneously attributed to this acid in several literature reports is thus definitely ruled out.