An efficient asymmetric synthesis of furofuran lignans: (+)-sesamin and (−)-sesamin

Enantioselective total synthesis of furofuran lignans via Pd-catalyzed asymmetric allylic cycloadditon of vinylethylene carbonates with 2-nitroacrylates

Herein, a practical and efficient approach to tetrahydrofurans with three-stereocenters has been developed through Pd-catalyzed asymmetric allylic cycloaddition of vinylethylene carbonates (VECs) with 2-nitroacrylates under mild conditions. By using this asymmetric catalytic reaction as a key step, several furofuran lignans with stereodivergency have been effectively synthesized through 5- or 6-step sequences from readily available starting materials.

Synthetic studies on optically active furofuran and diarylbutane lignans*

Lignans are a large class of naturally occurring secondary metabolites which are widely spread within the plant kingdom. Their diverse structures and variety of biological activities have fascinated organic chemists. For synthesizing optically active lignans, we have developed the novel asymmetric dimerization of cinnamic acid derivatives, and applied it to the enantioselective syntheses of furofuran lignans (yangambin, sesamin, eudesmin, caruilignan A) and diarylbutane lignans (sauriols A and B). This review summarizes the methodology of our asymmetric dimerization of cinnamic acid derivatives, and efficient total syntheses of furofuran and diarylbutane lignans reported by our and other groups.

Absorption, distribution, metabolism, and excretion of [14 C]sesamin in rats

SCOPE

Sesamin is a major lignan in sesame seeds and has various physiological effects. Although metabolism of sesamin by cytochrome P450 or intestinal microflora has been reported, little is known concerning the mass balance, pharmacokinetics, and tissue distribution of sesamin.

METHODS AND RESULTS

Absorption, distribution, metabolism, and excretion of [¹⁴ C]sesamin were investigated after a single oral dose of 5 mg/kg in rats. Sesamin was absorbed with peak plasma radioactivity at 1.0 h and declined with a terminal half-life 4.7 h. The cumulative excretion of radioactivity was 37.5 ± 3.1% in urine and 58.7 ± 4.8% in feces. In bile duct-cannulated rats, the cumulative excretion of radioactivity was 66.3 ± 8.4% in bile and 27.8 ± 10.2% in urine. Tissue distribution was investigated using quantitative whole-body autoradiography. Radioactivity was widely distributed over the whole body and was highly detected in the liver and kidney. The metabolites profile was examined using radiochromatography. Sesamin was mainly distributed in the form of conjugate metabolites.

CONCLUSIONS

Sesamin was absorbed efficiently and distributed over the whole body. In particular, sesamin was highly distributed in the form of the metabolites in the liver and kidney. The results of this study are useful in elucidating the action mechanism of sesamin.

Evaluation of plant growth regulatory activity of furofuran lignan bearing a 7,9':7',9-diepoxy structure using optically pure (+)- and (-)-enantiomers

The plant growth regulatory activity of furofuran lignan (7,9':7',9-diepoxylignan) was evaluated by employing optically pure synthesized (+)- and (-)-enantiomers. (+)-Sesamin possessing a 3,4-methylenedioxy group on the aromatic rings and 7-aryl structure showed growth promotion activity against lettuce roots (EC50 = 0.50 mM); on the other hand, growth inhibitory activity was observed against lettuce shoots (EC50 = 0.38 mM). Against ryegrass shoots, (-)-sesamolin, which has 3,4-methylenedioxy groups on the aromatic rings and a 7-acetal structure, was effective in showing growth inhibitory activity (EC50 = 0.23 mM). Different activity levels were observed between (+)- and (-)-enantiomers. It was assumed that the 3,4-methylenedioxy group on the aromatic ring was more potent for the plant growth regulatory activity.

The dihydrofuran template approach to furofuran synthesis

Flash vacuum pyrrolysis of vinyl epoxides provides cis-dihydrofuran carboxylic esters in good yields and diastereoselectivities, which, on base-promoted epimerisation afford the complementary trans series. The compounds provide a viable template for a Lewis acid promoted cyclisation to provide the 2,6-diaryl-3,7-dioxabicyclo[3.3.0]octane core found in the furofuran series of natural lignans. This strategy is stereodivergent and can be controlled to provide the exo-exo, exo-endo or endo-endo stereochemistries. The approach has been exemplified in syntheses of the sesamyl furofurans (+/-)-epiasarinin and (+/-)-asarinin.