Chiral discrimination of ( R )-(-)-linalool and characterization of new key marker constituent homalomenol D in Homalomena aromatica (Spreng.) Schott essential oil

Homalomena aromatica (Spreng.) Schott, or “Sugandhmantri,” is known to biosynthesize the valuable essential oil, which finds several applications in perfumery. This study offers a comprehensive analysis of essential oil of the plant collected from two different geographical locations in India. An extensive investigation using gas chromatography, enantioselective gas chromatography, mass spectrometry and NMR experiments led to the identification of (R)-(-)-linalool as single predominant enantiomer and characterization of a new compound, homalomenol D (HMD). A total of over 49 compounds (covering 82.94-92.70% of the oil) were identified, with linalool (40.2-54.4%) as the major constituent, followed by terpinen-4-ol (3.7-5.3%), δ-cadinene (2.4-5.2%), τ-muurolol (2.4-4.6%) and α-cadinol (6.2-7.3%). Chiral analysis showed the (R)-(-)-linalool proportions >96.7% in the oil, which is quite high compared to Karlovo Kashmir lavender (91.9%). In addition, oil samples also contained <3.3% (S)-(+)-linalool, well below the EP5 12.0% maximum limit. Besides, isolation followed by extensive NMR experiments led to characterization of a sesquiterpene epoxide identified as 5-isopropyl-2,8-dimethyl-11-oxatricyclo[5.3.1.0(2,6)]undecan-8-ol, or HMD (5.4-6.5%) in the oil. The present findings insights the usefulness of this plant as an alternative source of natural linalool.