Lunularic Acid Research Articles

Spatial Distribution, Antioxidant Capacity, and Spore Germination-Promoting Effect of Bibenzyls from Marchantia polymorpha.

Liverworts, considered to be the first plant type to successfully make the transition from water to land, can resist different oxidative stress. As characteristic constituents of liverworts, the bibenzyls are efficient antioxidants. In this study, spatial distributions of the bibenzyls within Marchantia polymorpha L., the model species of liverworts, were mapped using airflow-assisted desorption electrospray ionization imaging mass spectrometry. Bibenzyls were found to largely exist in the female receptacle of M. polymorpha, where lunularic acid was found to focus in the central region and bisbibenzyls were enriched in the periphery. The region-specific gene expression and antioxidant activities were characterized. In line with the spatial feature of bibenzyls, higher MpSTCS1A and Mp4CL expression levels and antioxidant ability were exhibited in the archegoniophore. The expression level of MpSTCS1A, and the content of total phenolic acid was increased after UV-B irradiation, suggesting bibenzyls play an important role in UV-B tolerance. Moreover, lunularic acid and extract of archegoniophore at a certain concentration can stimulate the spore germination under normal conditions and UV-B stress. These works broaden our understanding of the significance of bibenzyls in spore propagation and environmental adaptation.

Interaction of PKR with STCS1: an indispensable step in the biosynthesis of lunularic acid in Marchantia polymorpha.

Unlike bibenzyls derived from the vascular plants, lunularic acid (LA), a key precursor for macrocyclic bisbibenzyl synthesis in nonvascular liverworts, exhibits the absence of one hydroxy group within the A ring. It was hypothesized that both polyketide reductase (PKR) and stilbenecarboxylate synthase 1 (STCS1) were involved in the LA biosynthesis, but the underlined mechanisms have not been clarified. This study used bioinformatics analysis with molecular, biochemical and physiological approaches to characterize STCS1s and PKRs involved in the biosynthesis of LA. The results indicated that MpSTCS1s from Marchantia polymorpha catalyzed both C2→C7 aldol-type and C6→C1 Claisen-type cyclization using dihydro-p-coumaroyl-coenzyme A (CoA) and malonyl-CoA as substrates to yield a C6-C2-C6 skeleton of dihydro-resveratrol following decarboxylation and the C6-C3-C6 type of phloretin in vitro. The protein-protein interaction of PKRs with STCS1 (PPI-PS) was revealed and proved essential for LA accumulation when transiently co-expressed in Nicotiana benthamiana. Moreover, replacement of the active domain of STCS1 with an 18-amino-acid fragment from the chalcone synthase led to the PPI-PS greatly decreasing and diminishing the formation of LA. The replacement also increased the chalcone formation in STCS1s. Our results highlight a previously unrecognized PPI in planta that is indispensable for the formation of LA.

Front Cover: Synthesis and SAR of 2,3‐Dihydro‐1‐benzofuran‐4‐carboxylates: Potent Salicylic Acid‐Based Lead Structures against Plant Stress (Eur. J. Org. Chem. 14/2022)

The Front Cover shows one set of crop species thriving in comparison to the other – despite both enduring cold and drought conditions – as it has been treated with new compounds developed by Frackenpohl and colleagues. Notes on the Lewis acid-mediated cyclization used to synthesize these have been left on the pot of hydrangea flowers, the roots of which contain hydrangeic acid and the plant hormone lunularic acid, which inspired this work. Cover artwork by Ronald W. Brown. More information can be found in the Research Article by J. Frackenpohl et al.

Synthesis and SAR of 2,3‐Dihydro‐1‐benzofuran‐4‐carboxylates: Potent Salicylic Acid‐Based Lead Structures against Plant Stress

AbstractNew 2,3‐dihydro‐1‐benzofuran‐4‐carboxylic acid derivatives have been identified as potent lead structures against drought and cold stress in crops starting from the synthetic exploration of stabilized analogs of the natural product lunularic acid. An optimized Lewis‐acid mediated cyclization gave a short and efficient access to the envisaged 2,3‐dihydro‐1‐benzofuran‐4‐carboxylates. Enantioselective approaches were investigated to assess the potential impact of the chiral center on in vivo activity. Whilst 2,3‐dihydro‐1‐benzofuran‐4‐carboxamides and 2,3‐dihydro‐1‐benzofuran‐4‐carboxylates carrying phenyl substituents with electron‐withdrawing groups exhibited only low to moderate in vivo activity, the corresponding 2,3‐dihydro‐1‐benzofuran‐4‐carboxylates carrying optimized electron‐donating substituents in the phenyl moiety revealed strong in vivo activity, both against drought stress in several broad‐acre crops, as well as against cold stress in corn. Remarkably, several 2,3‐dihydro‐1‐benzofuran‐4‐carboxylates showed stronger efficacy than the internal standards used in our in vivo SAR study.

Bis-bibenzyls, Bibenzyls, and Terpenoids in 33 Genera of the Marchantiophyta (Liverworts): Structures, Synthesis, and Bioactivity.

The Marchantiophyta (liverworts) are rich sources of phenolic substances, especially cyclic and acyclic bis-bibenzyls, which are rare natural products in the plant kingdom, together with bibenzyls and characteristic terpenoids. At present, more than 125 bis-bibenzyls have been found in liverworts. They are biosynthesized from the dimerization of lunularic acid via dihydrocoumaric acid and prelunularin. The structurally unusual cyclic and acyclic bis-bibenzyls show various biological activities such as antimicrobial, antifungal, cytotoxic, muscle relaxation, antioxidant, tubulin polymerization inhibitory, and antitrypanosomal activities, among others. The present review article deals with the distribution and structure of bis-bibenzyls, bibenzyls, and several characteristic ent-sesqui- and diterpenoids in liverworts. Furthermore, the biosynthesis and total syntheses and biological activities of bis-bibenzyls are also surveyed.

Valuable building block for the synthesis of lunularic acid, hydrangeic acid and their analogues

A new functionalised sulphone-based building block has been synthesised that enabled C-C bond formation through Julia olefination. The utility of developed building block was demonstrated by successful synthesis of two natural products lunularic acid, hydrangeic acid and initial libraries of their analogues.

2-Carboxy-dihydrostilbene and flavan glycosides from Desmodium heterocarpon

A new 2-carboxy-dihydrostilbene glucoside, 2-carboxy-3,5,4′-trihydroxydihydrostilbene 3-O-β-d-glucopyranoside (1) and a new flavan diglycoside, (2S)-5,7,4′-trihydroxyflavan 7-O-β-d-apiofuranosyl-(1→6)-O-β-d-glucopyranoside (3) were isolated from the aerial portion of Thai origin Desmodium heterocarpon together with five known compounds, lunularic acid 4′-O-β-d-glucopyranoside (2), vitexin (4), isovitexin (5), (−)-epi-catechin 3-O-β-d-glucopyranoside (6), and (−)-epi-afzelachin 3-O-β-d-glucopyranoside (7). The structure determinations were based on physical data and spectroscopic evidence including 1D- and 2D-NMR experiments. The presence of 2-carboxy-dihydrostilbene derivatives from this species added the information data of this compound-type to the plant kingdom.

Abscisic acid-induced gene expression in the liverwort Marchantia polymorpha is mediated by evolutionarily conserved promoter elements.

Abscisic acid (ABA) is a phytohormone widely distributed among members of the land plant lineage (Embryophyta), regulating dormancy, stomata closure and tolerance to environmental stresses. In angiosperms (Magnoliophyta), ABA-induced gene expression is mediated by promoter elements such as the G-box-like ACGT-core motifs recognized by bZIP transcription factors. In contrast, the mode of regulation by ABA of gene expression in liverworts (Marchantiophyta), representing one of the earliest diverging land plant groups, has not been elucidated. In this study, we used promoters of the liverwort Marchantia polymorpha dehydrin and the wheat Em genes fused to the β-glucuronidase (GUS) reporter gene to investigate ABA-induced gene expression in liverworts. Transient assays of cultured cells of Marchantia indicated that ACGT-core motifs proximal to the transcription initiation site play a role in the ABA-induced gene expression. The RY sequence recognized by B3 transcriptional regulators was also shown to be responsible for the ABA-induced gene expression. In transgenic Marchantia plants, ABA treatment elicited an increase in GUS expression in young gemmalings, which was abolished by simultaneous disruption of the ACGT-core and RY elements. ABA-induced GUS expression was less obvious in mature thalli than in young gemmalings, associated with reductions in sensitivity to exogenous ABA during gametophyte growth. In contrast, lunularic acid, which had been suggested to function as an ABA-like substance, had no effect on GUS expression. The results demonstrate the presence of ABA-specific response mechanisms mediated by conserved cis-regulatory elements in liverworts, implying that the mechanisms had been acquired in the common ancestors of embryophytes.

In vitro Anti-erythrocyte Sickling Effect of Lunularic Acid of Natural Origin

In vitro Anti-erythrocyte Sickling Effect of Lunularic Acid of Natural Origin

Two new compounds from Hicriopteris glauca and their potential antitumor activities

Chemical examination of the EtOAc extract from the stems of Hicriopteris glauca (Thunb) Ching. led to the isolation of two new compounds: lunularic acid 4′-glucoside (1) and 2,9-dihydroxy-4,7-megastigmadiene-3-O-β-glucoside (2). Their structures were elucidated on the basis of spectral analysis and by comparing their spectral data with those in literature. Two compounds, along with the petroleum ether, chloroform, EtOAc, and n-BuOH extracts, were tested for cytotoxic activities. Only the n-BuOH extract showed antitumor activity against human melanoma A375 cells with IC50 values of 0.80 μg/ml.

Directed Ortho-Metalation of Unprotected Benzoic Acids. Methodology and Regioselective Synthesis of Useful Contiguously 3- and 6-Substituted 2-Methoxybenzoic Acid Building Blocks

[reaction: see text] By treatment with s-BuLi/TMEDA at -78 degrees C, unprotected 2-methoxybenzoic acid is deprotonated exclusively in the position ortho to the carboxylate. A reversal of regioselectivity is observed when the acid is treated with n-BuLi/t-BuOK. These results are of general utility for the one-pot preparation of a variety of very simple 3- and 6-substituted 2-methoxybenzoic acids that are not easily accessible by conventional means. The potential usefulness of the method is demonstrated by the expedient synthesis of lunularic acid.

Inhibition of endothelial cell functions by novel potential cancer chemopreventive agents

Endothelial cells (EC) play a major role in tumor-induced neovascularization and bridge the gap between a microtumor and growth factors such as nutrients and oxygen supply required for expansion. Immortalized human microvascular endothelial cells (HMEC-1) were utilized to assess anti-endothelial effects of 10 novel potential cancer chemopreventive compounds from various sources that we have investigated previously in a human in vitro anti-angiogenic assay. These include the monoacylphloroglucinol isoaspidinol B, 1,2,5,7-tetrahydroxy-anthraquinone, peracetylated carnosic acid (PCA), isoxanthohumol, 2,2′,4′-trimethoxychalcone, 3′-bromo-2,4-dimethoxychalcone as well as four synthetic derivatives of lunularic acid, a bibenzyl found in mosses [Int. J. Cancer Prev. 1 (2004) 47]. EC proliferation was inhibited with half-maximal inhibitory concentrations from 0.3 to 49.6μM, whereas EC migration was affected by most compounds at sub-micromolar concentrations. PCA and the bibenzyl derivative EC 1004 potently prevented differentiation of HMEC-1 into tubule-like structures. Overall, our data indicate that inhibition of endothelial cell function contributes to various extents to the chemopreventive or anti-angiogenic potential of these lead compounds.

Stilbenecarboxylate biosynthesis: a new function in the family of chalcone synthase-related proteins

Chalcone (CHS), stilbene (STS) synthases, and related proteins are key enzymes in the biosynthesis of many secondary plant products. Precursor feeding studies and mechanistic rationalization suggest that stilbenecarboxylates might also be synthesized by plant type III polyketide synthases; however, the enzyme activity leading to retention of the carboxyl moiety in a stilbene backbone has not yet been demonstrated. Hydrangea macrophylla L. (Garden Hortensia) contains stilbenecarboxylates (hydrangeic acid and lunularic acid) that are derived from 4-coumaroyl and dihydro-4-coumaroyl starter residues, respectively. We used homology-based techniques to clone CHS-related sequences, and the enzyme functions were investigated with recombinant proteins. Sequences for two proteins were obtained. One was identified as CHS. The other shared 65–70% identity with CHSs and other family members. The purified recombinant protein had stilbenecarboxylate synthase (STCS) activity with dihydro-4-coumaroyl-CoA, but not with 4-coumaroyl-CoA or other substrates. We propose that the enzyme is involved in the biosynthesis of lunularic acid. It is the first example of a STS-type reaction that does not lose the terminal carboxyl group during the ring folding to the end product. Comparisons with CHS, STS, and a pyrone synthase showed that it is the only enzyme exerting a tight control over decarboxylation reactions. The protein contains unusual residues in positions highly conserved in other CHS-related proteins, and mutagenesis studies suggest that they are important for the structure or/and the catalytic activity. The formation of the natural products in vivo requires a reducing step, and we discuss the possibility that the absence of a reductase in the in vitro reactions may be responsible for the failure to obtain stilbenecarboxylates from substrates like 4-coumaroyl-CoA.

Total Synthesis of Lunularic Acid and Lunularine, a New Approach to Natural Dihydrostilbenes

The natural polyketide lunularic acid (6) was prepared in six steps starting from 4-methoxystilbene and methyl 2,6-dihydroxybenzoate Lunularine (10) is available in an analogous manner in three steps starting from 4-methoxystilbene and 3-methoxyphenol. Key step of both syntheses is a hydroboration/ palladium-catalyzed cross-coupling protocol, that offers a convenient approach to dihydrostilbenes starting from a styrene and a phenolic building block.

Cytochromes P-450 catalyze the formation of marchantins A and C in Marchantia polymorpha

Two specific cytochrome P-450 enzymes were detected in cell suspension cultures of Marchantia polymorpha; the first catalyzes the coupling of two molecules of lunularic acid to form marchantin C and CO 2 and the second hydroxylates marchantin C to marchantin A. Cell free experiments using 3 H/ 14 C doubly-labeled substrates demonstrated that lunularic acid, and neither lunularine nor prelunularic acid, is the sole substrate for the coupling reaction. Both enzymes are dependent on the presence of oxygen and NADPH. Both reactions were inhibited in the presence of CO in the dark; this inhibition was partially reversed by white light. In addition, both reactions were inhibited by typical inhibitors of cytochrome P-450 enzymes such as cytochrome c and ancymidol.

Sesquiterpene lactones and bisbibenzyl derivatives from the neotropical liverwort Frullania convoluta

The new germacranolide epi-isocostunolide and two new bisbibenzyls, 2′-(11-hydroxy-1-bibenzyl-oxy)-1′-methoxy-6′,10′,11′-trihydroxy-7′,8′-dihydro-phenanthrene and 2′-(10,11-dihydroxy-1-bibenzyl-oxy)-1′-methoxy-6′,10′,11′-trihydroxy-7′,8′-dihydrophenanthrene, along with the known eudesmanolides, α-cyclocostunolide, brothenolide, nepalensolide A and nepalensolide B, the bisbibenzyls, perrottetin E, perrottetin F, perrottetin G, 7′,8′-dehydroperrottetin F, and the bibenzyls, lunularic acid and lunularin, have been isolated from the neotropical liverwort Frullania convoluta. Their structures were elucidated by NMR spectroscopy.

Aromatic compounds from the liverwort Plagiochila spinulosafn1fn1Part 7 in the series NMR Fingerprinting of Liverworts. For part 6 see Soderstrom et al., 1999.

Abstract Two known and five novel 9,10-dihydrophenanthrene derivatives, two orsellinic acid derivatives and a lunularic acid derivative have been isolated from the liverwort Plagiochilaspinulosa and identified following NMR studies. A further known 9,10-dihydrophenanthrene derivative has been identified using 1H NMR fingerprinting of the extracts.

ChemInform Abstract: Ethynylation of Aryl Halides by a Modified Suzuki Reaction: Application to the Syntheses of Combretastatin A‐4 (VII), A‐5 (X), and Lunularic Acid (XIII).

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Ethynylation of Aryl Halides by a Modified Suzuki Reaction: Application to the Syntheses of Combretastatin A‐4, A‐5 and Lunularic Acid

AbstractOn treatment with trimethyl borate sodium acetylide undergoes a palladium‐catalyzed cross coupling with functionalized aryl halides or triflates in reasonable to good yields. The ethynylarenes thus obtained serve as building blocks for the formation of the highly effective tubulin polymerization inhibitors combretastatin A‐4 (1) and A‐5 (2) as well as for the synthesis of the plant‐growth regulator lunularic acid (36).

Inhibiting Effects of Lunularic Acid Analogs on the Growth of Liverwort, Watercress, and Timothy Grass

A number of analogs of lunularic acid varying in the number of methylene carbons between the two benzene rings and in the substituents on their rings were prepared, and their effects on the growth of liverwort gemmaling, watercress, and timothy grass were investigated. Almost all the analogs tested were more inhibitory than lunularic acid, and a correlation between the structure and activity was observed. The differences in the growth-inhibition activity of analogs between higher and lower plants are also discussed.