Analysis of car-3-en-5-hydroperoxide

Area of Science:

• Biochemistry
• Natural Products Chemistry
• Analytical Chemistry

Background:

• Enzymatic transformations of monoterpenes are important for natural product synthesis.
• Lipoxygenase-like peroxidation of polyunsaturated fatty acids involves radical intermediates and hydroperoxides.
• The detection of terpene hydroperoxides in complex mixtures like essential oils is challenging.

Purpose of the Study:

• To investigate the volatile products of (+)-car-3-ene transformation by a Pleurotus sapidus dioxygenase.
• To identify and characterize any hydroperoxide intermediates formed during the enzymatic reaction.
• To evaluate the stability and detectability of terpene hydroperoxides using various analytical techniques.

Main Methods:

• High-resolution gas chromatography-mass spectrometry (HRGC-MS) with split/splitless injection.
• Thin-layer chromatography (TLC) with hydroperoxide-specific staining.
• Liquid chromatography-mass spectrometry (LC-MS) using atmospheric pressure chemical ionization (APCI+).
• Preparative high-performance liquid chromatography (prep-HPLC) for isolation and further analysis.

Main Results:

• The dioxygenase transformed (+)-car-3-ene to car-3-en-5-one and car-3-en-5-ol.
• Hydroperoxides were indicated by TLC but not definitively identified by HRGC-MS due to degradation.
• APCI(+)-LC-MS unequivocally identified car-3-en-5-hydroperoxides.
• Degradation of car-3-en-5-hydroperoxide to the corresponding ketone and alcohol during chromatography was confirmed.

Conclusions:

• Terpene hydroperoxides may be more prevalent in essential oils than previously thought.
• Standard analytical methods like capillary GC and UV/vis LC-detection are often insufficient for detecting these labile compounds.
• APCI(+)-LC-MS is a powerful tool for the identification of terpene hydroperoxides.