Damascenone

Biosynthesis

The biosynthesis for β-damascenone begins when farnesyl pyrophosphate (FPP) and isopentenyl pyrophosphate (IPP) react to produce geranylgeranyl pyrophosphate (GGPP). The enzyme phytoene synthase (PSY) condenses two GGPP molecules together to produce phytoene, removing diphosphate with a proton shift. :[[File:GGPP Synthesis.svg|frameless|upright=2|GGPP Synthesis]]

Phytoene then undergoes a series of dehydrogenation reactions. phytoene desaturase (PDS) first desaturates phytoene to produce phytofluene, then ζ-carotene. Other enzymes have been found to catalyze this reaction including CrtI and CrtP.{{cite journal Then ζ-Carotene desaturase (ZDS) catalyzes further desaturation to produce neurosporene followed by lycopene. Other enzymes that are able to catalyze this reaction include CtrI and CrtQ. The desaturation concludes when lycopene β-cyclase catalyzes lycopene cyclization, first producing γ-carotene, then β-carotene: :[[File:Beta Carotene Synthesis.svg|frameless|upright=2|Beta Carotene Synthesis]] The cyclization mechanism is as follows: :[[File:Beta-Carotene Mechanism.svg|frameless|upright=2|Beta-Carotene Mechanism]]

Next, β-carotene reacts with and the enzyme β-carotene ring hydroxylase, producing zeaxanthin.{{cite journal | doi-access = free Zeaxanthin then reacts with , NADPH, a reduced ferredoxin cluster, and the enzyme zeaxanthin epoxidase (ZE) to produce antheraxanthin which reacts in a similar fashion to produce violaxanthin. Violaxanthin then reacts with the enzyme neoxanthin synthase to form neoxanthin, the main β-damascenone precursor:{{cite journal :[[File:Neoxanthin Synthesis.svg|frameless|upright=2|Neoxanthin synthesis]]

In order to generate β-damascenone from neoxanthin there are a few more modifications needed. First, neoxanthin undergoes an oxidative cleavage to create the grasshopper ketone. The grasshopper ketone then undergoes a reduction to generate the allenic triol. At this stage, there are two main pathways the allenic triol can take to produce the final product. The allenic triol can undergo a dehydration reaction to generate either the acetylenic diol or the allenic diol. Finally, one last dehydration reaction of either the acetylenic diol or the allenic diol produces the final product β-damascenone:{{cite journal :[[File:Beta-Damascenone Synthesis.svg|frameless|upright=2|Beta-damascenone synthesis]] The proposed mechanism for the conversion of the allenic triol to the acetylenic diol is: :[[File:Acetylenic Diol Mechanism.svg|frameless|upright=2|Acetylenic diol mechanism]] The proposed mechanism for the conversion of the acetylenic diol to the final product is: :[[File:Beta-Damascenone Mechanism.svg|frameless|upright=2|Beta-damascenone mechanism]] This mechanism is known as a Meyer-Schuster rearrangement.

References

References

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7. (April 21, 2007). "Which Impact for β-Damascenone on Red Wines Aroma?". Journal of Agricultural and Food Chemistry.