Conversion and Hydrothermal Decomposition of Major Components of Mint Essential Oil by Small-Scale Subcritical Water Treatment.

Thermal stabilities of four major components (l-menthol, l-menthone, piperitone, and l-menthyl acetate) of Japanese mint essential oil were evaluated via subcritical water treatment. To improve experimental throughput for measuring compound stabilities, a small-scale subcritical water treatment method using ampoule bottles was developed and employed. A mixture of the four major components was treated in subcritical water at 180-240 °C for 5-60 min, and then analyzed by gas chromatography. The results indicated that the order of thermal resistance, from strongest to weakest, was: l-menthyl acetate, l-menthol, piperitone, and l-menthone. In individual treatments of mint flavor components, subsequent conversions of l-menthyl acetate to l-menthol, l-menthol to l-menthone, l-menthone to piperitone, and piperitone to thymol were observed in individual treatments at 240 °C for 60 min. As the mass balance between piperitone and thymol was low, the hydrothermal decomposition of the components was considered to have occurred intensely during, or after the conversion. These results explained the degradation of mint essential oil components under subcritical water conditions and provided the basis for optimizing the extraction conditions of mint essential oils using subcritical water.

Enantioselective Diels-Alder reaction of 1,2-dihydropyridines with aldehydes using ß-amino alcohol organocatalyst.

The enantioselective Diels-Alder reaction of 1,2-dihydropyridines with aldehydes using an easily prepared optically active ß-amino alcohol catalyst was found to provide optically active isoquinuclidines, an efficient synthetic intermediate of pharmaceutically important compounds such as oseltamivir phosphate, with a satisfactory chemical yield and enantioselectivity (up to 96%, up to 98% ee). In addition, the obtained highly optically pure isoquinuclidine was easily converted to an optically active piperidine having four successive carbon centers.

Enzyme-assisted Extraction of Bioactive Phytochemicals from Japanese Peppermint (Mentha arvensis L. cv. 'Hokuto').

In this study, we provide a method for obtaining essential oil from Mentha arvensis L. in large quantities. Three types of polysaccharide-degrading enzymes were investigated, namely cellulase A "Amano" 3, cellulase T "Amano" 4, and hemicellulase "Amano" 90. The optimum extraction conditions were the combined use of 2 wt% cellulase T and 2 wt% hemicellulase 90, and 3 h of incubation. Enzymeassisted extraction increased the amount of the essential oil from 2.2 mL to 3.0 mL, compared with the amount extracted without an enzyme.

Utilization of the Japanese Peppermint Herbal Water Byproduct of Steam Distillation as an Antimicrobial Agent.

The present study provides valuable data that the herbal water byproduct of Japanese peppermint, produced during the steam distillation extraction of an essential oil, can be utilized as an antibacterial agent. The major ingredient in the herbal water from Japanese peppermint 'Hokuto' was menthol, with a concentration close to its water solubility. The herbal water produced showed excellent antibacterial efficacy against typical gram-negative and gram-positive bacterial strains of Escherichia coli and Staphylococcus aureus, respectively, and the antibacterial efficacy was maintained even when the herbal water was diluted up to an appropriate concentration of 50%. The efficacy of the herbal water against E. coli was higher than that against S. aureus, which is likely because of the difference in the efficacy of menthol against these two different bacterial strains. The excellent antibacterial efficacy of the herbal water is mainly attributed to the function of menthol, while other trace ingredients also contributed to the antibacterial efficacy. The Japanese peppermint herbal water byproduct, generally treated as industrial waste and disposed, can be easily commercialized as an antibacterial agent if efforts are made to maintain a constant menthol concentration throughout the steam distillation essential oil extraction process.

A novel chiral oxazolidine organocatalyst for the synthesis of an oseltamivir intermediate using a highly enantioselective Diels-Alder reaction of 1,2-dihydropyridine.

Enantioselective Diels-Alder reactions of 1,2-dihydropyridines with acroleins using a novel chiral oxazolidine organocatalyst afforded chiral isoquinuclidines that is an efficient synthetic intermediate of oseltamivir, with fairly good chemical yield and excellent enantioselectivity (90%, up to >99% ee).