Microbial conversion of jasmonates-hydroxylations by Aspergillus niger.

Area of Science:

• Microbial Biotechnology
• Natural Product Synthesis
• Enzymatic Hydroxylation

Background:

• (-)-Jasmonic acid (JA) is a plant hormone with diverse biological activities.
• Microbial biotransformations offer a sustainable route for modifying natural products.
• Understanding enzymatic modifications of JA is crucial for developing new derivatives.

Purpose of the Study:

• To investigate the hydroxylation capabilities of Aspergillus niger on jasmonic acid and its methyl ester.
• To identify the specific products formed during microbial transformation of JA.
• To characterize potential side reactions such as allylic rearrangement.

Main Methods:

• Cultivation of Aspergillus niger with (-)-jasmonic acid (JA) and methyl jasmonate (JA-Me).
• Isolation and purification of transformation products.
• Chemical structure elucidation of hydroxylated and rearranged compounds.

Main Results:

• Aspergillus niger hydroxylates the pentenyl side chain of JA to yield (11S)-(-)-hydroxy-JA and (11R)-(-)-hydroxy-JA (2:1 ratio), along with (-)-11,12-didehydro-JA.
• Methyl jasmonate (JA-Me) is hydrolyzed to JA before hydroxylation.
• Allylic rearrangement of the 11-hydroxy-(9Z)-pentenyl side chain can occur, forming (10E)-9-hydroxy- and (9E)-11-hydroxy-isomers under specific conditions.
• Hydroxylation of (+/-)-9,10-dihydro-JA occurs at C-11, yielding 11 xi-hydroxy-9,10-dihydro-JA, with methyl dihydro-JA requiring hydrolysis prior to hydroxylation.

Conclusions:

• Aspergillus niger possesses enzymatic machinery for the regioselective hydroxylation of jasmonic acid derivatives.
• The study highlights the potential for isomerization during microbial processing, necessitating careful control of cultivation and isolation.
• These findings contribute to the understanding of microbial metabolism of plant hormones and the development of biocatalytic routes for JA modification.