Biotransformation of (+)-(1R,2S,4R)-borneol and (−)-(1S,2R,4S)-borneol by Spodoptera litura (common cutworm) larvae

• The biotransformation of (+)- and (−)-borneols by insect Spodoptera litura larvae was investigated.
• Eight new products were obtained.
• A fatty acid conjugation reaction was the main metabolic pathway.

In this study, we investigated the use of insects as biocatalysts for the biotransformation of monoterpenoids such as (+)-(1R,2S,4R)-borneol (1) and (−)-(1S,2R,4S)-borneol (2) by the larvae of Spodoptera litura. The substrates were administrated to the fourth instar larvae of S. litura through food, and the metabolites were collected in the feces. Analysis showed that substrate 1 was converted into the following 12 metabolites: (+)-(1R,2S,4R)-borneol linoleate (1–1), (+)-(1R,2S,4R)-borneol linolenate (1–2), (+)-(1R,2S,4R)-borneol-2-O-β-d-glucopyranoside (1–3), (+)-(1R,2S,4R,5S)-5-endo-hydroxyborneol (1–4), (+)-(1R,4R,5S)-5-endo-hydroxycamphor (1–5), (+)-(1R,2S,4R,5R)-5-exo-hydroxyborneol (1–6), (+)-(1R,4R,5R)-5-exo-hydroxycamphor (1–7), (+)-(1R,2S,4R,7R)-8-hydroxyborneol (1–8), (+)-(1R,4R,7R)-8-hydroxycamphor (1–9), (+)-(1R,2S,4R,7S)-9-hydroxyborneol (1–10), (+)-(1R,2S,4R)-10-hydroxyborneol (1–11), and (+)-(1R,2R,3S,4S)-3-endo-hydroxyborneol (1–12). The metabolism of substrate 2 generated 12 enantiomers of the above metabolites, namely 2–1 to 2–12. Compounds 1–1, 1–2, 1–3, 2–1, 2–2, 2–8, 2–10, and 2–12 are novel compounds. The main metabolites were generated by phase II reactions such as esterification or glucosidation of the parent substrates. The minor metabolites originated from phase I reactions such as hydroxylation or oxidation, probably by cytochrome P450 enzymes. These fatty acid and glucose conjugation reactions are new metabolic pathways, compared with those reported in previous studies on monoterpenoids in S. litura.

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