Biotransformation of (−)‐( R )‐ α ‐Phellandrene: Antimicrobial Activity of Its Major Metabolite

Terpene derivatives converted by microbial biotransformation constitute an important resource for natural pharmaceutical, fragrance, and aroma substances. In the present study, the monoterpene α ‐phellandrene was biotransformed by 16 different strains of microorganisms (bacteria, fungi, and yeasts). The transformation metabolites were initially screened by TLC and GC/MS, and then further characterized by NMR spectroscopic techniques. Among the six metabolites characterized, 6‐hydroxypiperitone, α ‐phellandrene epoxide, cis‐p ‐menth‐2‐en‐1‐ol, and carvotanacetone, which originated from (−)‐( R )‐ α ‐phellandrene, are reported for the first time in this study. Additionally, the substrate and the metabolite 5‐ p ‐menthene‐1,2‐diol were subjected to in vitro antibacterial and anticandidal tests. The metabolite showed moderate‐to‐good inhibitory activities ( MIC s=0.125 to >4 mg/ml) against various bacteria and especially against Candida species in comparison with its substrate (−)‐( R )‐ α ‐phellandrene and standard antimicrobial agents.