Analysis of Car-3-en-5-hydroperoxide

Abstract

HRGC-MS, using split/splitless injection (230°C), showed that a dioxygenase from Pleurotus sapidus regio-selectively transformed (+)-car-3-ene to car-3-en-5-one as the major volatile product to minor amounts of the corresponding alcohol, and to some other volatiles. Thus, the reaction was assumed to be radical mediated and similar to the lipoxygenase catalyzed peroxidation of polyunsaturated fatty acids, but the expected car-3-ene-hydroperoxides were not detected. TLC of the reaction products, followed by hydroperoxide specific staining, visually indicated the presence of hydroperoxides. TLC spots were eluted and re-analyzed using cool on-column injection, but only tailing peaks showing a mixed mass spectrum of car-3-en-5-ol/one were obtained. An unequivocal identification of car-3-en-5-hydroperoxides was achieved only after using APCI +-LC-MS. Upon structural confirmation, the car-3-en-5-hydroperoxide was accumulated by preparative HPLC, re-injected cool on-column, and the continuing degradation of the hydroperoxide to monoterpene ketone and alcohol during chromatography was verified. It was concluded that terpene hydroperoxides may occur in essential oils more frequently than anticipated, but are not recognized due to the principal blindness of capillary gas chromatography techniques and UV/vis LC-detectors.

Quantification of hydroperoxides by gas chromatography‐flame ionization detection and predicted response factors

“…Early papers reported the use of UV detectors, but they were only suitable for the species bearing a chromophore, which led Berger et al . to suspect, that ‘terpene hydroperoxides may occur in essential oils more frequently than anticipated’ . To circumvent this detection difficulty, the use of a post‐column reaction has been proposed.…”

“…Alternatively, the oxidized reagent can become luminescent . The use of mass‐spectrometric (MS) detection is also reported . It is noteworthy that an MS only allows detection, and subsequent quantification, of known hydroperoxides, because there is no fragment characteristic of the hydroperoxide function in general.…”