共查询到20条相似文献，搜索用时 15 毫秒
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Ronald K. Pickerill 《Ichnos》2013,20(2)
(See Color Plate V) 相似文献
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Abstract «Pinus mugo» Turra and «Pinus uncinata» Miller in Piedmont. Critical notes and distribution. — The Authors have carried on a research on the distribution of Pinus mugo Turra (sensu Fl. Eur.) and Pinus uncinata Miller in all Piedmont Alpes and, having observed the extreme variability of the characters which are employed in the keys of determination to differentiate these two species, they suggest other and more constant characters. These are:
Il Pinus Mugo Turra Ed Il Pinus Uncinata Miller in Piemonte. Note Critiche e Distribuzione
Published online:
14 September 2009Table 相似文献
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《Nucleosides, nucleotides & nucleic acids》2013,32(4):419-435
Abstract 5′-O-Mesyl-2′,3′-O-isopropylidene ribonucleosides (4 and 12) were converted to their 5′-substituted nucleosides in good yields by reacted with NaN3 or KI. 2′,3′-O-Isopropylidene ribonucleosides (3 and 11) were prepared in good yields from ribonucleosides 1 and 2 with a reaction mixture of acetone and triethyl orthoformate instead of using acetone diethyl acetal. Compound 1 or 2 was treated with 2-acetoxyisobutyryl halide (Cl or Br) to give 1-[2-O-acetyl-3-halo-3-deoxy-5-O-(2,5,5-trimethyl-1,3-dioxolan-4-on-2-yl)-β-D-xylofuranosyl]-1,2,4-triazole-3-carboxamide (19, 22, and 23) in high yields. Instead of using 2-acetoxyisobutyryl bromide, the mixture of 2-acetoxyisobutyryl chloride and NaBr was employed in the synthesis of 22 and 23. Treatment of 19 with an activated Zn/Cu couple and deprotection gave 2′,3′-anhydro nucleoside (21), and treatment of 22 and 23 with an activated Zn/Cu couple and a little of HOAc and deprotection gave corresponding 2′,3′-unsaturated triazole nucleosides (24 and 25), respectively. The biological activity of the compounds (7 ～ 10, 15 ～ 18, and 24) was examined in human liver cancer cells (A-549), lung cancer cells (BEL-7402), and Flu-A cells.
Synthesis of Triazole Nucleoside Derivatives
Published online:
07 February 2007 Compound 1. 相似文献
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Plant-derived antioxidants are essential in our diet, and antioxidant composition is a key determinant of the quality of plant extracts of interest to the pharmaceutical and food industries. By using carnosic acid as an example of a key antioxidant constituent of rosemary and sage extracts, we discuss the importance of studying non-transgenic approaches to enhancing antioxidant levels in plants and improving the antioxidant composition of plant extracts. In contrast to other terpenoids or phenolic compounds, carnosic acid has only been found in some Labiatae species, such as rosemary and sage. Carnosic acid has medicinal properties; it is a potent antioxidant and protects skin cells against UV-A radiation and cancer. Furthermore, it has been used as a preservative in food and non-food products, displaying important antimicrobial effects. However, the key steps involved in its biosynthesis remain largely unknown, and thus non-transgenic approaches are required to increase its level in plant extracts. Dried rosemary or sage leaves can contain between 0.1% and 7% carnosic acid, depending on the species and variety, but also on plant growth conditions, sample treatment and mode of extract preparation. Furthermore, leaf age, salinity and ionic interactions can also have a significant effect on biosynthesis and therefore have a strong impact on the total antioxidant potential of rosemary and sage extracts. Non-transgenic approaches, used in these or other species, can significantly increase antioxidant levels and therefore provide very significant improvements in the quality of several botanical extracts used in industry, and can be applied as either an alternative or a complement to transgenic approaches.
Enhanced Phenolic Diterpenes Antioxidant Levels Through Non-transgenic Approaches
Published online:
26 October 2012FIG. 1 Chemical structure of synthetic and natural plant-derived antioxidants. Note that the hydroxyl groups in the ortho-position at C11 and C12 of the carnosic acid molecule provide high antioxidant properties (color figure available online). 相似文献
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Exposure to petroleum constituents at contaminated sites may occur through a variety of pathways, including inhalation of vapors and particulates, ingestion of water and soils, and dermal contact with water and soils. Accurately assessing the human health risks from such exposures requires information on the medium‐ and route‐specific bioavailability of petroleum constituents (e.g., how well these chemicals enter the body via the gastrointestinal tract and skin). For example, when the medium or exposure route in an animal toxicity assay (e.g., ingestion of water) differs from the actual route of human exposure at the petroleum contaminated site (e.g., dermal contact with soil), adjustments should be made that reflect the relative bioavailability of the chemical in the different media. The focus of this article is on (1) the availability of oral and dermal absorption data for one PAH (benzo[a]pyrene, (B[a]P) and three VOCs in soil (benzene, toluene, and xylene); (2) factors affecting the uptake of these PAHs and VOCs from soil; and (3) ways to incorporate bioavailability data into human health risk assessments. Based on our review, we recommend the following default values for the oral and dermal absorption of B[a]P, benzene, toluene, and xylene from soil:
A review of the bioavailability of petroleum constituents
Published online:
02 December 2008Site‐specific information such as chemical concentrations in soil, soil characteristics, soil loadings on the skin, contact site, and contact time could result in modifications of these numbers. As shown, our default absorption values are generally less than those recommended by the U.S. EPA (1991a,b,c). The implications of these estimates of bioavailability for risk assessment and for the selection of soil cleanup levels at petroleum‐contaminated sites are discussed. 相似文献