Biotransformation of sesquiterpenoids: a recent insight

Sesquiterpenoids have been identified as natural compounds showing remarkable biological activities found in medicinal plants. There is great interest in developing methods to obtain sesquiterpenoids derivatives and biotransformation is one of the alternative methods for structural modification of complex sesquiterpenes structures. Biotransformation is a great drug design tool offering high selectivity and green method. The present review describes a comprehensive summary of biotransformation products of sesquiterpenoids and its structural modification utilizing a variety of biocatalysts including microorganisms, plant tissue culture and enzymes. This review covers recent literatures from 2007 until 2020 and highlights the experimental conditions for each biotransformation process.

Biotransformation of 4-Chromanol, 4-Flavanol, Xanthydrol, and their Analogs by Tissue Cultured Cells

We conducted the biotransformation of 4-chromanol, 4-flavanol and xanthydrol using Italian parsley ( Petroselinum neapolitanum) callus or soybean ( Glycine max) callus as biocatalysts. The biotransformation of 4-chromanol using P. neapolitanum yielded 4-chromanone at 5% on day 3, 12% on day 5, 23% on day 8, 21% on day 11, 25% on day 14, 22% on day 17, and a final yield of 22% on day 20. Although the reaction appeared to level off between days 8 and 20, we verified that the oxidation reaction continued to progress, albeit very gradually, until day 20. Furthermore, biotransformation of 4-flavanol using G. max callus yielded flavanone at 24.8% after 70 days. Moreover, biotransformation of xanthydrol using G. max yielded xanthone at 19.8% on day 1, 72.8% on day 2, 93.1% on day 4, and 96.3% on day 6. Addition of NADP accelerated the reaction, suggesting that an oxidoreductase may be involved. In contrast, there were no observable reverse reactions for 4-chromanone, 4-flavanone, or xanthone using the respective biocatalysts. Therefore, callus cells can be used as biocatalysts for the oxidation of alcohols to ketones. Organic synthetic reactions mimic environmentally-friendly reactions using biocatalysts found in nature.

Improvement of a P450-Based Recombinant Escherichia coli Whole-Cell System for the Production of Oxygenated Sesquiterpene Derivatives

Sesquiterpenes are common constituents of essential oil in plants. Their oxygenated derivatives often possess desirable flavor, fragrance, and pharmaceutical properties. Recently, the CYP264B1-based recombinant Escherichia coli whole-cell system has been constructed for the oxidation of sesquiterpenes. However, limiting factors of this system related to the high volatility of substrates and the suitability of the P450 redox partner need to be addressed. In this work, the improvement of the system was implemented with (+)-α-longipinene as a model substrate. By using 2-hydroxypropyl-β-cyclodextrin and an alternative ferredoxin reductase, the conversion of (+)-α-longipinene was improved 77.1%. Applying the optimized conditions, the yields of the main products were 54.2, 34.2, and 47.2 mg L^-1, corresponding to efficiencies of 82.1, 51.8, and 71.5% for the conversion of (+)-α-longipinene, (-)-isolongifolene, and α-humulene, respectively, at a 200 mL scale. These products were characterized as 12-hydroxy-α-longipinene, isolongifolene-9-one, and 5-hydroxy-α-humulene, respectively, by nuclear magnetic resonance spectroscopy.

Suppression of SOS-inducing activity of chemical mutagens by metabolites from microbial transformation of (+)-longicyclene

In this study, biotransformation of (+)-longicyclene (1) by Aspergillus niger (NBRC 4414) and the suppressive effect on umuC gene expression by chemical mutagens 2-(2-furyl)-3-(5-nitro-2-furyl)acrylamide (furylfuramide) and aflatoxin B1 (AFB1) of the SOS response in Salmonella typhimurium TA1535/pSK1002 were investigated. Initially, compound 1 was converted to three new terpenoids, (-)-(10R)-10-hydroxy-longicyclic acid (2), (+)-(10S)-10-hydroxy-longicyclic acid (3), and (+)-10-oxo-longicyclic acid (4) by A. niger , and their conversion rates were 27, 23, and 30%, respectively. The metabolites suppressed the SOS-inducing activity of furylfuramide and AFB1 in the umu test. Compounds 1-4 were hardly showing a suppressive effect on umu gene expression of the SOS responses in S. typhimurium TA1535/pSK1002 against furylfuramid. However, metabolites showed a suppressive effect against AFB1. Compound 4 had gene expression by chemical mutagen AFB1, was suppressed 53% at <1.0 mM, and was the most effective compound in this experiment.