Structure-plant growth inhibitory activity relationship of lariciresinol

Effect of further substitutions at 5-, 6-, 7-, or 8-position of 3-[3-(4-methoxyphenyl)-1-hydroxyprop-2-yl]coumarin on phytotoxicity

Derivatives of the coumarin ring in (R)-3-[3-(4-methoxyphenyl)-1-hydroxyprop-2-yl]coumarin 2, which is a lignan structure, were synthesized to clarify their structure-phytotoxicity relationships. The growth-inhibitory activity of the 8-OCH3 derivative 8 (IC50=228 µM) was more potent against the roots of lettuce seedlings than the compound without substituents 2. As for the roots of Italian ryegrass seedlings, the presence of the methoxy group at the 7- or 8-position was extremely effective for inhibiting growth (7-OCH3 7: IC50=121 µM, 8-OCH3 8: 56.7 µM). Methyl derivatives at the 5- or 8-position showed activity levels similar to those of the compound without substituents 2 (5-CH3 13: IC50=214 µM, 8-CH3 16: IC50=225 µM). The activities of OH- and F-derivatives were not observed or were lower.

Anti-hyperglycemic potential and chemical constituents of Aristolochia triangularis Cham. leaves - A medicinal species native to Brazilian forests

ETHNOPHARMACOLOGICAL RELEVANCE

Aristolochia triangularis Cham. has been used in Brazilian traditional medicine for various therapeutic purposes, including as a leaf-based infusion for diabetes management.

AIM OF THE STUDY

This study was designed to chemically characterize an infusion of in natura A. triangularis leaves and evaluate the in vivo anti-hyperglycemic properties of this infusion.

MATERIALS AND METHODS

Chemical composition was examined using liquid-liquid extraction procedure, chromatographic methods, NMR, and LC-MS/MS. The in vivo anti-hyperglycemic activity of the freeze-dried infusion of A. triangularis leaves (Inf-L-At) was assessed using oral glucose tolerance test (OGTT). Initially, normoglycemic male rats were pre-treated with orally administered Inf-L-At at doses of 62.5, 125, and 250 mg/kg for two consecutive days. On the day of the OGTT, fasting animals received a glucose load (4 g/kg) 30 min after treatment with Inf-L-At, and the blood glucose levels were verified at 15, 30, 60, and 180 min. Intestinal maltase, lactase, and sucrase activities and muscle and liver glycogen contents were also assessed after the OGTT.

RESULTS

Inf-L-At extract led to glycemic reduction with no dose-response at 15, 30, and 60 min comparable to that of the antidiabetic drug glibenclamide and was accompanied by an increase in hepatic and muscle glycogen contents. Additionally, there was a significant statistically decrease in the in vitro activity of disaccharidases. Maltase and sucrase activities were inhibited at all doses, whereas lactase activity was inhibited only at 62.5 and 250 mg/kg. In total, 75 compounds were found in the infusion, including seven new ones, (7S*,8S*,7ꞌS*,8ꞌR*)-4,4ꞌ-dihydroxy-3,3ꞌ-dimethoxy-7,9ꞌ-epoxylignan-7ꞌ-ol; 4ꞌ-hydroxy-3ꞌ-methoxy-3,4-methylenedioxy-7,9ꞌ-epoxylignan-9,7ꞌ-diol; triangularisines A, B, and C; N-ethyl-N-methyl-affineine; and N-methyl pachyconfine, and one previously not described as a natural product, epi-secoisolariciresinol monomethyl ether.

CONCLUSION

The results demonstrated the anti-hyperglycemic activity of the infusion from A. triangularis leaves and showed that it is a rich source of lignoids, alkaloids, and glycosylated flavonoids, which are known to exhibit antidiabetic effects and other biological properties that can be beneficial for patients with chronic hyperglycemia, thus certifying the popular use of this herbal drink.

Mactanamide and lariciresinol as radical scavengers and Fe2+ ion chelators - A DFT study

A DFT based kinetic study of OOH radical scavenging potency of mactanamide (MA) and lariciresinol (LA), two natural polyphenols, indicates their nearly equal potential via the proton coupled electron transfer (PCET) mechanism in lipid media. Contribution of C-H bond breaking to this potency is negligible compared to O-H bond breaking, contrary to recent claims. The predicted potency of both compounds is not sufficient to protect biological molecules from oxidative damage in lipid media. In aqueous media, the scavenging potency of MA and LA phenoxide anions via the single electron transfer (SET) mechanism is much higher and may contribute to the protection of lipids, proteins, and DNA from OOH radical damage. Also, MA and LA have the potential to chelate catalytic Fe2+ ions, thus suppressing the formation of dangerous OH radicals via Fenton-type reactions. The monoanionic species of MA and LA show stronger monodentate chelating ability with Fe2+ ion compared to its neutral form. The dianionic specie LA2- exhibited the highest chelation ability with Fe2+ ion via bidentate 1:2 coordination. However, direct radical scavenging and metal chelation could be rarely operative in vivo because MA and LA presumably achieve very low concentrations in systemic circulation.

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.

(-)-Lariciresinol Isolated from the Roots of Isatis indigotica Fortune ex Lindl. Inhibits Hepatitis B Virus by Regulating Viral Transcription

Chronic hepatitis induced by hepatitis B virus (HBV) infection is a serious public health problem, leading to hepatic cirrhosis and liver cancer. Although the currently approved medications can reliably decrease the virus load and prevent the development of hepatic diseases, they fail to induce durable off-drug control of HBV replication in the majority of patients. The roots of Isatis indigotica Fortune ex Lindl., a traditional Chinese medicine, were frequently used for the prevention of viral disease in China. In the present study, (-)-lariciresinol ((-)-LRSL), isolated from the roots of Isatis indigotica Fortune ex Lindl., was found to inhibit HBV DNA replication of both wild-type and nucleos(t)ide analogues (NUCs)-resistant strains in vitro. Mechanism studies revealed that (-)-LRSL could block RNA production after treatment, followed by viral proteins, and then viral particles and DNA. Promoter reporter assays and RNA decaying dynamic experiments indicated that (-)-LRSL mediated HBV RNA reduction was mainly due to transcriptional inhibition rather than degradation. Moreover, (-)-LRSL in a dose-dependent manner also inhibited other animal hepadnaviruses, including woodchuck hepatitis virus (WHV) and duck hepatitis B virus (DHBV). Combining the analysis of RNA-seq, we further found that the decrease in HBV transcriptional activity by (-)-LRSL may be related to hepatocyte nuclear factor 1α (HNF1α). Taken together, (-)-LRSL represents a novel chemical entity that inhibits HBV replication by regulating HNF1α mediated HBV transcription, which may provide a new perspective for HBV therapeutics.

Selective tumor cell growth inhibition by lignans and a seco-triterpenoid from Combretum mellifluum

Two new tetrahydrofuran lignans 1-2, along with 2,3-seco-lup-20(29)-en-2,3-dioic acid (3), (-)-larreatricin (4), and 15 additional compounds were isolated from Combretum mellifluum (Combretaceae). Their structures were determined by 1D- and 2D- NMR spectroscopic data and HRESIMS. Another 15 compounds were identified after HPLC-DAD-MS/MS analysis. Tested against HT-29 (colon) neoplastic cells, lignan 1 showed marked cytotoxicity (GI₅₀ = 3.9 µM) and high selectivity (SI > 227), compared with non-neoplastic NIH/3T3 cells, while 2 proved less cytotoxic, despite exhibiting SI > 75. Seco-triterpene 3 was strongly cytotoxic to 786-0 (kidney) and HT-29 cells (GI₅₀ = 0.5 and 2.9 µM, respectively), proving roughly 107 and 18 times more selective for these cell lines, respectively, than for NIH/3T3 cells. After 48 h of incubation, 1-3 exhibited potent cytostatic activity against HT-29 cells at all concentrations tested, while 3 had a cytocidal effect on 786-0 cells at 25 µg.mL^-1.

Insights into Lignan Composition and Biosynthesis in Stinging Nettle (Urtica dioica L.)

Stinging nettle (Urtica dioica L.) has been used as herbal medicine to treat various ailments since ancient times. The biological activity of nettle is chiefly attributed to a large group of phenylpropanoid dimers, namely lignans. Despite the pharmacological importance of nettle lignans, there are no studies addressing lignan biosynthesis in this plant. We herein identified 14 genes encoding dirigent proteins (UdDIRs) and 3 pinoresinol-lariciresinol reductase genes (UdPLRs) in nettle, which are two gene families known to be associated with lignan biosynthesis. Expression profiling of these genes on different organs/tissues revealed a specific expression pattern. Particularly, UdDIR7, 12 and 13 displayed a remarkable high expression in the top internode, fibre tissues of bottom internodes and roots, respectively. The relatively high expression of UdPLR1 and UdPLR2 in the young internodes, core tissue of bottom internode and roots is consistent with the high accumulation of lariciresinol and secoisolariciresinol in these tissues. Lignan quantification showed a high abundance of pinoresinol in roots and pinoresinol diglucosides in young internodes and leaves. This study sheds light on lignan composition and biosynthesis in nettle, providing a good basis for further functional analysis of DIRs and PLRs and, ultimately, engineering lignan metabolism in planta and in cell cultures.

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.

Chemical Constituents and Anti-inflammatory Principles from the Fruits of Forsythia suspensa

Fifty compounds were isolated from the fruits of Forsythia suspensa, including 13 new compounds characterized as eight new diterpenoids (1-8), three new lignans (9-11), a new iridoid (12), and a new triterpenoid (13). Their structures were established on the basis of spectroscopic and spectrometric analysis. Most of the isolated compounds were examined for their anti-inflammatory activity in vitro. The results showed that several compounds displayed significant inhibition of fMLP/CB-induced superoxide anion generation and elastase release, with IC₅₀ values ranging from 0.6 ± 0.1 to 8.6 ± 0.8 μg/mL and from 0.8 ± 0.3 to 7.3 ± 1.1 μg/mL, respectively.

Antioxidant efficacy and the upregulation of Nrf2-mediated HO-1 expression by (+)-lariciresinol, a lignan isolated from Rubia philippinensis, through the activation of p38

The aim of the present study was to examine the antioxidative activity of (+)-lariciresinol (LRSL), an optically active lignan isolated from Rubia philippinensis in several in vitro assays. LRSL was also subjected to evaluate its inhibitory effect against the generation of reactive oxygen species (ROS) in murine macrophage (RAW 264.7) cells. The results showed that LRSL possessed very strong radical scavenging activity and reducing power, as well as inhibited ROS generation in a dose-dependent manner without showing any cytotoxicity. The transcriptional and translational levels of superoxide dismutase (SOD), glutathione peroxidase (GPx) and catalase (CAT) were markedly higher in the sample treated group. LRSL treatment also increased the transcriptional and translational activities of NF-E2-related factor-2 (Nrf-2) with a corresponding increase in the transcriptional and translational activities of the heme oxygenase-1 (HO-1). LRSL activated p38 and treatments with SB239063 (a p38 inhibitor) suppressed the LRSL-induced activation of Nrf2, resulting in a decrease in HO-1 expression. Collectively, the data demonstrated that LRSL has potent antioxidative activity, decreasing ROS generation in RAW 264.7 cells and increasing the transcriptional and translational levels of antioxidant enzymes by activating Nrf2-mediated HO-1 induction via p38 signaling.

Enantioselective syntheses of both enantiomers of 9'-dehydroxyimperanene and 7,8-dihydro-9'-dehydroxyimperanene and the comparison of biological activity between 9-norlignans and dihydroguaiaretic acids

To estimate the effect of methyl group of dihydroguaiaretic acid, which shows many kinds of biological activities, on biological activity, both enantiomers of 9'-dehydroxyimperanene (5, 6) and 7,8-dihydro-9'-dehydroxyimperanene (7, 8) lacking one of the methyl groups of dihydroguaiaretic acid were synthesized. (S)-7,8-Dihydro-9'-dehydroxyimperanene (7) showed 4-6-fold higher cytotoxic activity than all stereoisomers of dihydroguaiaretic acid (2-4). The IC50 values of (S)-7,8-dihydro-9'-dehydroxyimperanene (7) against HL-60 and HeLa cells were 6.1μM and 5.6μM, respectively. Though only one of three stereoisomers of dihydroguaiaretic acid showed antibacterial activity against a gram negative bacterium, both enantiomers of 5-8 showed antibacterial activity against a gram negative bacterium. This is a Letter on biological activity of 9-norlignan, in which one of methyl groups of lignan is absent.

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.

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

The synthesized 7-aryl derivatives of (7R,7'S,8S,8'S)-(+)-verrucosin were applied to growth inhibitory activity test against ryegrass at 1mM. 7-(3-Ethoxy-4-hydroxyphenyl) derivative 12 and 7-(2-hydroxyphenyl) derivative 4 showed comparable activity to those of (+)-verrucosin against the root (-95%) and the shoot (-60%), respectively. The growth inhibitory activity test against lettuce using synthesized 7-aryl derivatives of (7S,7'R,8R,8'R)-(-)-verrucosin at 1mM showed that the activities of 7-(3-hydroxyphenyl) derivative 20 and 7-(3-ethoxy-4-hydroxyphenyl) derivative 28 are similar to that of (-)-verrucosin against the root (-95%). Against the shoot, 7-(3-hydroxyphenyl) derivative 20 showed higher activity (-80%) than that of (-)-verrucosin (-60%). As the next step, (7S,7'R,8R,8'R)-7-(3-hydroxyphenyl)-7'-aryl-(-)-verrucosin derivatives, in which the most effective 3-hydroxyphenyl group is employed as 7-aromatic ring, were synthesized for the assay against lettuce. In this experiment, 7'-(2-hydroxyphenyl) derivative 37 and 7'-(3-hydroxyphenyl) derivative 38 showed similar activity to that of derivative 20. The effect of 7- and 7'-aryl structures of 7,7'-epoxylignanes on the plant growth inhibitory activity was clarified. The 7- and 7'-aryl structures were simplified to show comparable activity to or higher activity than that of (-)-verrucosin. The plant growth inhibitory activity of a nutmeg component, (+)-fragransin C3b, was estimated as -80% inhibition at 1mM against ryegrass roots.