Structure-plant phytotoxic activity relationship of 7,7'-epoxylignanes, (+)- and (-)-verrucosin: simplification on the aromatic ring substituents

Syntheses of Tetrahydropyran Type 8,7'-Neolignans Using a Ring-Expansion Reaction and Tetrahydrofuran Type 8,7'-Neolignans to Discover a Novel Phytotoxic Neolignan

One novel tri-substituted tetrahydropyran type 8,7'-neolignan and its enantiomer with higher enantiomeric excess were synthesized from all cis-tetra-substituted tetrahydrofuran with an iodomethyl group by a hydride or H2 ring-expansion reaction. The normal hydride reductions of C-I bonds of tetra-substituted tetrahydrofurans bearing iodomethyl groups were observed in other 2,3-cis-stereoisomers of tetra-substituted tetrahydrofurans to give tetra-substituted tetrahydrofurans bearing 7,8-cis and 8,7'-neolignan structures. The phytotoxicities of their synthesized compounds were compared with previously synthesized 7,8-trans-8,7'-neolignans bearing tetra-substituted tetrahydrofurans to find out the highest phytotoxic tri-substituted tetrahydropyran type 8,7'-neolignan.

Plant Growth Suppressive Activity of (R)-3-(7'-Aryl-9'-hydroxyprop-8'-yl)coumarin, Structural Isomer of Z-2-Hydroxybenzylidene-γ-butyrolactone-type Lignan

3-(7'-Aryl-9'-hydroxyprop-8'-yl)coumarin, which is a structural isomer of a Z-2-hydroxybenzylidene-γ-butyrolactone-type lignan, was stereoselectively synthesized and subjected to plant growth regulation examination. (R)-4'-Methoxyphenyl derivative 3 showed stereospecific plant growth suppressive activity. The significance of the presence of hydroxy group at the 9'-position for the activity was clarified. The effect of the substituent at the 7'-aryl group was also shown. The 3'-methoxy, 4'-methoxy, and 4'-trifluoromethyl derivatives 10, 3, and 22 led to the most significant growth suppression of Italian ryegrass roots. The 2'-methoxy derivative 9 and 4'-methoxy derivative 3 provided the most growth suppressive activity against lettuce shoots and roots, respectively.

Stereocontrolled syntheses of (-)- and (+)-γ-diisoeugenol along with optically active eight stereoisomers of 7,8'-epoxy-8,7'-neolignan

It was shown that reduction of the tertiary benzylic hydroxy group of (2R,3S,4R,5S)-3,5-bis(4-benzyloxy-3-methoxyphenyl)-2,4-dimethyltetrahydro-3-furanol 17 followed by the intramolecular Friedel-Crafts reaction gave exclusively indane with (7S,7'S,8R,8'R)-2,7'-cyclo-7,8'-neolignan structure 18 along with (7S,7'R,8S,8'R)-7,8'-epoxy-8,7'-neolignan structure 19. Indane 18 was converted to (-)-γ-diisoeugenol ((-)-4). On the other hand, (2S,3R,4R,5S)-3,5-bis(4-benzyloxy-3-methoxyphenyl)-2,4-dimethyltetrahydro-3-furanol 22 did not afford indane, but the tetrahydrofuran structure with (7S,7'S,8S,8'S)-7,8'-epoxy-8,7'-neolignan structure 23 and 7'-epi-23.

Effects of Substituents on the Aromatic Ring of Lignano-9,9'-lactone on Plant Growth Inhibitory Activity

The relationship between the structure of lignano-9,9'-lactone (2,3-dibenzylbutyrolactone) and its activity as a plant growth regulator has been clarified. Derivatives with higher plant growth inhibitory activity than natural dimethylmatairesinol 4 were synthesized. The 2-hydroxy-7- Z-ene derivative 42 displayed growth inhibitory activity against both the shoots (IC50 = 0.65 mM) and roots (IC50 = 0.43 mM) of lettuce seedlings. Regiospecific activity was observed. The 2,3-dihydroxy derivative 24 showed the highest growth inhibitory activity against both the shoots (IC50 = 0.36 mM) and roots (IC50 = 0.13 mM) of Italian ryegrass seedlings. A similar level of activity to 24 against just the roots of Italian ryegrass seedlings was maintained when the hydroxy group at position 3 of the 2,3-dihydroxy derivative 24 was replaced by a fluorine atom. The (2-hydroxy,4-fluoro)-derivative 33 also showed growth inhibitory activity against both the shoots (IC50 = 0.79 mM) and roots (IC50 = 0.14 mM) of Italian ryegrass seedlings. The level of activity was found to depend on the positions of the two hydroxy groups or the hydroxy group and fluorine atom on the aromatic ring. The importance of the lignano-9,9'-lactone structure was also shown.

Effect of the structure of dietary epoxylignan on its cytotoxic activity: relationship between the structure and the activity of 7,7′-epoxylignan and the introduction of apoptosis by caspase 3/7

We compared the cytotoxic activities of dietary epoxylignans and their stereoisomers and found (−)-verrucosin, which is (7S,7′R,8R,8′R)-7,7′-epoxylignan, to be the most cytotoxic epoxylignan against HeLa cells (IC50 = 6.6 μM). On the other hand, the activity was about a factor of 10 less against HL-60. In this research on the relationship between the structure and cytotoxic activity of (−)-verrucosin 13, the 7-(4-methoxyphenyl)-7′-(3,4-dimethoxyphenyl) derivative 60, for which the activity (IC50 = 2.4 μM) is three times greater than (−)-verrucosin 13, was discovered. The induction of apoptosis by caspase 3/7 was observed upon treatment with the (−)-verrucosin derivative.

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.