Natural Sources and Bioactivities of 2,4-Di-Tert-Butylphenol and Its Analogs.

2,4-Di-tert-butylphenol or 2,4-bis(1,1-dimethylethyl)-phenol (2,4-DTBP) is a common toxic secondary metabolite produced by various groups of organisms. The biosources and bioactivities of 2,4-DTBP have been well investigated, but the phenol has not been systematically reviewed. This article provides a comprehensive review of 2,4-DTBP and its analogs with emphasis on natural sources and bioactivities. 2,4-DTBP has been found in at least 169 species of bacteria (16 species, 10 families), fungi (11 species, eight families), diatom (one species, one family), liverwort (one species, one family), pteridiphyta (two species, two families), gymnosperms (four species, one family), dicots (107 species, 58 families), monocots (22 species, eight families), and animals (five species, five families). 2,4-DTBP is often a major component of violate or essential oils and it exhibits potent toxicity against almost all testing organisms, including the producers; however, it is not clear why organisms produce autotoxic 2,4-DTBP and its analogs. The accumulating evidence indicates that the endocidal regulation seems to be the primary function of the phenols in the producing organisms.

Endocide-Induced Abnormal Growth Forms of Invasive Giant Salvinia (Salvinia molesta).

Giant salvinia (Salvinia molesta) is one of the most noxious invasive species in the world. The fern is known to have primary, secondary, and tertiary growth forms, which are also commonly hypothesized as growth stages. The identification of these forms is primarily based on the size and folding status of the floating leaves. However, we identified 12 forms in the greenhouse and the field. Our experiments showed that the folding of floating leaves is a reversible trait dependent on water access. The floating leaves quickly fold in response to water shortage, reducing water loss and needs, decreasing growth, and avoiding trichome damage. The leaves re-open to allow trichomes repel water and enhance growth when having adequate water supply. Larger secondary or tertiary forms do not produce small-leaf primary forms without high intensity stress. These results do not support the hypothesis that three growth forms represent sequential growth stages. The abnormal small-leaf forms are the result of endocide-induced autotoxicity and some of them never grow into other forms. The development of abnormal forms and reversible leaf folding strategy in response to high stress along with rapid asexual reproduction are major adaptive traits contributing to the invasiveness of S. molesta.

Endocidal Regulation of Secondary Metabolites in the Producing Organisms.

Secondary metabolites are defined as organic compounds that are not directly involved in the normal growth, development, and reproduction of an organism. They are widely believed to be responsible for interactions between the producing organism and its environment, with the producer avoiding their toxicities. In our experiments, however, none of the randomly selected 44 species representing different groups of plants and insects can avoid autotoxicity by its endogenous metabolites once made available. We coined the term endocides (endogenous biocides) to describe such metabolites that can poison or inhibit the parent via induced biosynthesis or external applications. Dosage-dependent endocides can selectively induce morphological mutations in the parent organism (e.g., shrubbiness/dwarfism, pleiocotyly, abnormal leaf morphogenesis, disturbed phyllotaxis, fasciated stems, and variegation in plants), inhibit its growth, development, and reproduction and cause death than non-closely related species. The propagule, as well as the organism itself contains or produces adequate endocides to kill itself.

Chemical constituents from Pterocarpus soyauxii.

Three new benzofurans (1-3) and one new isoflavan (4), pteroyanin G, H, I and J, together with 21 known compounds, were isolated from the heartwood of Pterocarpus soyauxii. Their structures were determined by the NMR and MS spectral data in comparison with literature data. Compounds (1-25) did not show cytotoxicity against three human cancer cell lines, A549, Panc-28, and HCT-116 (Gl50 > 50 µM).

Chemical constituents from the fruit body of Chlorophyllum molybdites.

A new glycoxyuracil and 15 known compounds were isolated from the fruit body of Chlorophyllum molybdites. The structures were determined from their NMR and MS data and by comparison with literature data. Compounds 2-5, 10-11, 13, and 15-16 were isolated from the genus Chlorophyllum for the first time. Compounds (1-9) did not show cytotoxicity against two human cancer cell lines, A549 and Panc-28 (GI50 > 50 microM).

Cytotoxic compounds from invasive giant salvinia (Salvinia molesta) against human tumor cells.

Giant salvinia (Salvinia molesta) is one of the most noxious invasive species in the world. Our bioactivity-guided fractionation of ethanol extract of giant salvinia led to the isolation of 50 compounds. Of the six new compounds (1-6), salviniol (1) is a rare abietane diterpene with a new ferruginol-menthol coupled skeleton and both salviniside I (2) and salviniside II (3) are novel benzofuran glucose conjugates with unique 10-membered macrodiolide structures. Sixteen abietane diterpenes (1, 7-17, and 19-22) demonstrated in vitro activities against human tumor cells, and 7 and 8 showed selective cytotoxicity to tumor cells over normal cells.

Flavonoids and 3-arylcoumarin from Pterocarpus soyauxii.

Phytochemical study on the constituents of the heartwood of Pterocarpus soyauxii led to the isolation of five new isoflavonoids and one new 3-arylcoumarin, pterosonins A-F (1-6), together with 17 known analogues, among which 8, 9, and 18 were reported as natural products for the first time. Structure elucidation was achieved by way of spectroscopic measurements as well as by comparison with literature data. Only Compound 6 showed potent cytotoxicity against human non-small cell lung cancer (A549), pancreatic cancer (Panc-28), and colon carcinoma (HCT-116) cells with GI50 values at 7.39, 25, and 19.17 µM, respectively; the other isolates showed no cytotoxicity against the above tested cell lines with GI50 values > 50 µM.

Cytotoxic triterpenoid saponins from husks of Aesculus californica (Spach) Nutt.

Fifteen polyhydroxyoleanene saponins, aesculiosides C1-C15 (1-15), were isolated from husks of Aesculus californica. Their structures were established by extensive spectroscopic and chemical analyses. The triterpenoid saponins from A. californica have greater structural diversity than those from any other investigated species thus far in the genus Aesculus. The chemotaxonomic characteristic of aesculiosides C1-C15 is that the unit attached to the C-3 of the aglycone is a glucopyranosyl moiety, instead of a glucuronopyranosyl group in the saponins that have been isolated from other Aesculus species. The saponins isolated from A. californica then provide important evolutionary and chemotaxonomic knowledge of the Aesculus genus, a well-known intercontinental disjunct genus in the Northern hemisphere. Aesculiosides C1-C15 (1-15) showed cytotoxicity to human non-small cell lung tumor (A549) with GI50 ranged from 3.76 to >25µM.

Potent HGF/c-Met axis inhibitors from Eucalyptus globulus: the coupling of phloroglucinol and sesquiterpenoid is essential for the activity.

Eucalyptin A (1), together with two known compounds 2 and 3 exhibiting potent inhibition on HGF/c-Met axis, was discovered from the fruits of Eucalyptus globulus. 1 possessed an unprecedented carbon framework of phloroglucinol-coupled sesquiterpenoid, and its structure was elucidated by spectroscopic method and ECD calculation. A brief structure-activity relationship discussion indicated that the coupling of a phloroglucinol and a sesquiterpenoid is essential for the activity.

Limonoids from the stems of Toona ciliata var. henryi (Meliaceae).

Ten limonoids, toonacilianins A-J, and two norlimonoids, toonacilianins K and L, together with seven known compounds were isolated from the stems of Toona ciliata var. henryi (Meliaceae). Their structures were elucidated by spectroscopic analysis. Two compounds showed strong cytotoxic activities.

Four sesquiterpenoids from Chloranthus multistachys.

Four new sesquiterpenoids, chlomultins A-D (1-4), were isolated from the whole plant of Chloranthus multistachys. Their structures were established on the basis of spectroscopic analysis.

Sesquiterpenes and dimeric sesquiterpenoids from Sarcandra glabra.

Two new sesquiterpenes, sarcandralactones A (1) and B (2), and five new dimeric sesquiterpenoids, sarcandrolides A-E (3-7), along with 10 known compounds were isolated from the whole plants of Sarcandra glabra. Their structures were elucidated on the basis of spectroscopic analysis. Some of the new isolates exhibit significant cytotoxicities when tested against a small panel of tumor cell lines.

Antimicrobial diterpenes from Trigonostemon chinensis.

Five new diterpenes, trigonochinenes A-E (1-5), and two known ones, 3,4- seco-sonderianol (6) and 3,4- seco-sonderianic acid (7), were isolated from the aerial part of Trigonostemon chinensis. Compounds 1-4 possess a rare 3,4-seco-cleistanthanic skeleton, and compound 5 is a highly aromatized tetranorditerpene. Structures of these compounds were elucidated by spectroscopic analysis. The antimicrobial activities of compounds 1-7 were evaluated against a panel of bacteria and fungi.

Sesquiterpenoids from Hedyosmum orientale.

Five new guaiane-type sesquiterpenoids, hedyosumins A-E (1-5), together with five known ones (6-10), were isolated from the aerial parts of Hedyosmum orientale. Two known sesquiterpenoids, 10alpha-hydroxy-1,5alpha H-guaia-3,7(11)-dien-8alpha,12-olide and 9alpha-hydroxyasterolide, were obtained as natural products for the first time. Their structures were elucidated on the basis of spectroscopic methods. 9alpha-Hydroxyasterolide (7) showed moderate activities against A-549 and HL-60 tumor cell lines with the IC 50 values of 3.1 and 8.8 microM, respectively.