Efficient production of the flavoring agent zingerone and of both (R)- and (S)-zingerols via green fungal biocatalysis. Comparative antifungal activities between enantiomers

Abstract

Zingerone (1) and both chiral forms of zingerol (2) were obtained from dehydrozingerone (3) by biotransformation with filamentous fungi. The bioconversion of 3 with A. fumigatus, G. candidum or R. oryzae allowed the production of 1 as the sole product at 8 h and in 81%-90% at 72 h. In turn, A. flavus, A. niger, C. echinulata, M. circinelloides and P. citrinum produced 1 at 8 h, but at 72 h alcohol 2 was obtained as the major product (74%-99%). Among them, A. niger and M. circinelloides led to the anti-Prelog zingerol (R)-2 in only one step with high conversion rates and ee. Instead, C. echinulata and P. citrinum allowed to obtain (S)-2 in only one step, with high conversion rates and ee. Both chiral forms of 2 were tested for antifungal properties against a panel of clinically important fungi, showing that (R)-, but not (S)-2 possessed antifungal activity.

Scheme 1

Possible products in the biotransformation of dehydrozingerone 3. * Chiral carbon.

Figure 1

Biotransformation of dehydrozingerone 3 with ten different filamentous fungi during 72 h. The percentages (%) of each product zingerone 1 or zingerol 2 are showed in different rows. The front row shows the percentage of the remainder substrate 3 in each biotransformation process.

Figure 2

Time-course of the biotransformation of dehydrozingerone 3 with A. fumigatus (A) and A. niger (B). * Chiral carbon.

Figure 3

¹H NMR spectra of (S)-(−)-MTPA esters with: (A) a mixture enriched with the alcohol (R)-2 obtained by biotransformation of 3 with A. niger; (B) a mixture enriched with the alcohol (S)-2 obtained by biotransformation of 3 with P. citrinum; and (C) rac-2.

Figure 4

Configuration correlation model for (S)-MTPA esters of (R)-2 (A) and (S)-2 (B).

Figure 5

Chromatograms obtained by chiral HPLC of rac-2 (A); (R)-2, Retention Time (RT) = 15.7 min (B) and (S)-2; RT = 18.7 min (C).

Figure 6

Comparative antifungal activities of (S)- (94% ee) and (R)-zingerol (98% ee) against yeasts and filamentous fungi. Ca: Candida albicans ATCC 10231; Sc: Saccharomyces cerevisiae ATCC 9763; Cn: Cryptococcus neoformans ATCC 32264; Mg: Microsporum gypseum CCC 115; Tr: Trichophyton rubrum CCC 110; Tm: Trichophyton mentagrophytes ATCC 9972. MICs of terbinafine against Mg, Tr and Tm = 0.04, 0.01 and 0.04 µg/mL, respectively. MICs of Amphotericin B against Ca, Sc and Cn = 1.00, 0.50 and 0.25 µg/mL, respectively.