Diene conformation in the naturally occurring tricarboxylic acid, telfairic acid, by Raman spectroscopy

The conformational geometry of the two CC bonds in a naturally occurring dienetricarboxylic acid, telfairic acid, isolated from Xylaria telfairii, has been determined by Raman spectroscopy. This application of analytical Raman spectroscopy is important because infrared, UV and NMR spectroscopic techniques have failed to provide sufficient information for the determination of the diene geometry. Several specially synthesised model dienecarboxylic acids with known diene conformations were used to calibrate the Raman data. The natural extract from X. telfairii was shown to be a mixture of both cis (Z) and trans (E) forms whereas the purified extract was predominantly the trans isomer. Raman data also suggest that the established method for the preparation of a trans–trans sorbic acid is open to debate. Further applications of the Raman technique for the determination of diene conformation of fungal metabolite extracts are proposed.