Usnic acid

Since its first isolation in 1844, usnic acid [2,6-diacetyl-7,9-dihydroxy-8,9b-dimethyl-1,3(2H,9bH)-dibenzo-furandione] has become the most extensively studied lichen metabolite and one of the few that is commercially available. Usnic acid is uniquely found in lichens, and is especially abundant in genera such as Alectoria, Cladonia, Usnea, Lecanora, Ramalina and Evernia. Many lichens and extracts containing usnic acid have been utilized for medicinal, perfumery, cosmetic as well as ecological applications. Usnic acid as a pure substance has been formulated in creams, toothpaste, mouthwash, deodorants and sunscreen products, in some cases as an active principle, in others as a preservative. In addition to antimicrobial activity against human and plant pathogens, usnic acid has been shown to exhibit antiviral, antiprotozoal, antiproliferative, anti-inflammatory and analgesic activity. Ecological effects, such as antigrowth, antiherbivore and anti-insect properties, have also been demonstrated. A difference in biological activity has in some cases been observed between the two enantiomeric forms of usnic acid. Recently health food supplements containing usnic acid have been promoted for use in weight reduction, with little scientific support. The emphasis of the current review is on the chemistry and biological activity of usnic acid and its derivatives in addition to rational and ecologically acceptable methods for provision of this natural compound on a large scale.     

Usnic acid derivatives are effective inhibitors of tyrosyl-DNA phosphodiesterase 1

The synthesis of (+)-usnic acid derivatives is described. The derivatives contain one or two cyano groups, connected to the acetophenone fragment of dibenzofuran core by linkers of different length and character, or some other modifications. The influence of these compounds on the activity of recombinant human tyrosyl-DNA phosphodiesterase 1 and MCF-7 tumor cells’ viability has been estimated. The data indicate a distinct dependence of functional characteristics of the compounds on their structure.     

松萝酸提取工艺的研究

以破茎松萝为材料,分别以碱水或碱醇直接提取、制备松萝酸钠,并对松萝酸钠提取影响因素进行探究。对所得提取物进行分离和定性鉴定,并利用高效液相层析技术测定提取物中松萝酸的含量。通过单因素实验考察了NaOH和Na2CO3浓度对松萝酸提取的影响,用HPLC测定不同浓度碱液提取物中松萝酸的含量。实验结果说明,1.5%NaOH和75%乙醇+4%Na2CO3提取松萝酸效果较好,松萝酸提取得率最高,分别为1.75%和1.99%,破茎松萝材料中松萝酸含量为2.4%。     

Protocatechuic acid derivatives from Hemizonia lobbii

From the external leaf resin of Hemizonia lobbii, 3,4-dihydroxy-5-(2-isopentenyl)-benzoic acid (5-prenylprotocatechuic acid) and two related compounds have been isolated.     

Ellagic acid derivatives from Rhabdodendron macrophyllum

Rhabdodendron macrophyllum contains 24-methylenecycloartenol in the leaves, as well as 3-O-acetylaleuritolic acid and glycosides of oleanolic acid, hederagenin and arjunolic acid in the branches. Accompanied by 5′-methoxy-3,4,3′-tri-O-methylflavellagic acid, 3,4,?'-tri-O-methylflavellagic acid and ellagic acid (possibly in the form of methyl ethers), such saponins also occur in the roots. Chemically the Rhabdodendraceae would fit into the Rosiflorae or even better into the Myrtiflorae.     

Kaurenic acid derivatives from Stevia eupatoria

Two kaurene type diterpenes were isolated from the aerial part of Stevia euphoria. Their structures and stereochemistry were established by carbon and ¹H NMR, chemical transformation and correlation with known compounds.     

Bioactive caffeic acid derivatives from Wedelia trilobata

Two new caffeic acid derivatives, p-hydroxyphenyl caffeate (1) and methyl 3-(7-methoxy-dihydrocaffeoyl)-5-caffeoyl quinate (2), were isolated from the whole plant of Wedelia trilobata, along with four known ones, neochlorogenic acid methyl ester (3), methyl 4,5-di-O-caffeoyl quinate (4), methyl 3,5-di-O-caffeoyl quinate (5) and chlorogenic acid methyl ester (6). Their structures were elucidated on the basis of detailed spectroscopic analysis. They were all isolated from plant W. trilobata for the first time. Compounds 1, 2, 4 and 5 showed significantly in vitro α-glucosidase inhibitory activity with IC₅₀ values from 0.029 to 0.362 mM, which were more potent than the reference compound acarbose (IC₅₀ 0.410 mM). Compound 1 was further revealed to show interesting in vitro tyrosinase inhibitory activity (IC₅₀ 2.00 μM) much stronger than positive control kojic acid (IC₅₀ 12.55 μM).     

Usnic acid,as a biotic factor,changes the ploidy level in mosses

Lichens and mosses often share the same environmental conditions where they compete for substrate and other essential factors. Lichens use secondary metabolites as allelochemicals to repel surrounding plants and potential rivals. In mosses, endoreduplication leads to the occurrence of various ploidy levels in the same individual and has been suggested as an adaptation to abiotic stresses. Here, we show that also biotic factors such as usnic acid, an allelochemical produced by lichens, directly influenced the level of ploidy in mosses. Application of usnic acid changed the nuclei proportion and significantly enhanced the endoreduplication index in two moss species, Physcomitrella patens and Pohlia drummondii. These investigations add a new aspect on secondary metabolites of lichens which count as biotic factors and affect ploidy levels in mosses.     

Three new resorcylic acid derivatives from Sporotrichum laxum

Sporotrichum laxum ATCC 15155 is the producing strain of the potent anti-Helicobacter pylori natural product spirolaxine (1). Investigation of the secondary metabolites in this fungus led to the isolation of five phthalides (1, 2, 3, 6 and 9) and five resorcylic acid derivatives (4, 5, 7, 8 and 10), among which 5, 7 and 8 are new compounds. The structures were elucidated by spectroscopic analyses, and the absolute configurations of 7 and 8 were determined by Mosher’s method. Addition of soy flour into the potato dextrose agar has led to the increased production of 4–10. A biosynthetic pathway consisting of a highly reducing polyketide synthase (PKS), a nonreducing PKS and a series of tailoring enzymes was proposed to produce these fungal natural products. The resorcylic acid derivatives are proposed to result from early hydrolysis of the polyketide chain or incorporation of a longer fatty acyl starter unit.     

Three new phenolic acid derivatives from Oenothera biennis

Three new phenolic acid derivatives, 1-methyl glyceric acid-2-vanillic acid ether (1), methyl 2-hydroxy-6-(3-methoxy-3-oxoprop-1-en-2-yloxy) benzoate (2), methyl 2-hydroxy-6-(1-Carboxyvinyloxy) benzoate (3) and five known compounds namely 4-hydroxymellein (4), mellein methyl ether (5), 2-methyl-5,7-dihydroxychromone (6), latifolicinin C (7) and oresbiusin A (8) were isolated from Oenothera biennis L. The structures of these secondary metabolites were elucidated using different spectroscopic techniques, including ¹H, ¹³C NMR, HR-ESI-MS, ECD and comparison with published data.     

松萝酸研究进展

自从松萝酸于1844年第一次被分离出来,它已经成为研究最广泛的地衣物质之一。对于松萝酸的抗菌功能、化学性质及其在医药、环境监控等各个领域的应用研究,可见于各种外文文献的报道。美国、日本及德国的应用研究较多;而中国、智利、南斯拉夫、印度尼西亚等国仍然在致力于松萝酸的提取、抗菌、抗病毒等基础方面的研究。中文文献不多。目前发现松萝酸只存在于地衣中,在以下种属中较为丰富：树发属、石蕊属、茶渍衣属、松萝属、树花属及扁枝衣。     

Ellagic acid derivatives and cytotoxic cucurbitacins from Elaeocarpus mastersii

Bioassay-guided investigation of the bark of Elaeocarpus mastersii using KB (human oral epidermoid carcinoma) cells as a monitor led to the isolation of two cucurbitacins, cucurbitacin D and cucurbitacin F as cytotoxic principles, together with two ellagic acid derivatives, 4'-O-methylellagic acid 3-(2",3"-di-O-acetyl)-alpha-L-rhamnoside (1) and 4,4'-O-dimethylellagic acid 3-(2",3"-di-O-acetyl)-alpha-L-rhamnoside (2). These compounds were evaluated against a panel of human tumor cell lines.