Two new (3 and 5), as well as three known (1, 2, and 4), polyynes were isolated from Devil's Club (Oplopanax horridus; Araliaceae), a medicinal plant of North America. The structures were established by 1H and 13C NMR. The absolute configurations of 2 and 5 were determined by application of Mosher's method. All the polyynes exhibited significant anti-Candida, antibacterial, and antimycobacterial activity, with an ability to kill Mycobacterium tuberculosis and isoniazid-resistant Mycobacterium avium at 10 micrograms/disk in a disk diffusion assay.
The primary metabolic fate of phenylalanine, following its deamination in plants, is conscription of its carbon skeleton for lignin, suberin, flavonoid, and related metabolite formation. Since this accounts for ϳ30 -40% of all organic carbon, an effective means of recycling the liberated ammonium ion must be operative. In order to establish how this occurs, the uptake and metabolism of various N NMR, and gas chromatography-mass spectrometry analyses. It was found that the ammonium ion released during active phenylpropanoid metabolism was not made available for general amino acid/protein synthesis. Rather it was rapidly recycled back to regenerate phenylalanine, thereby providing an effective means of maintaining active phenylpropanoid metabolism with no additional nitrogen requirement. These results strongly suggest that, in lignifying cells, ammonium ion reassimilation is tightly compartmentalized.The successful colonization of land by vascular plants, from their aquatic forerunners, was in large measure due to elaboration of the phenylpropanoid/phenylpropanoid-acetate pathways. At this critical juncture in evolution, phenylalanine (tyrosine) became the portal entry of phenols into lignins, lignans, flavonoids, suberins, and proanthocyanidins. Vascular plants thus have a very high Phe/Tyr turnover, since ϳ30 -40% of all assimilated carbon in photosynthesis is of phenylpropanoid/ phenylpropanoid-acetate origin (1-5).Phenylpropanoid metabolism is not only a feature of normal development, but can also be induced. For example, when loblolly pine (Pinus taeda) cell suspension cultures are exposed to high levels of sucrose (6), there is an induction of lignin synthesis. Curiously, little attention has been paid to the issue of the relationship between phenylpropanoid and nitrogen metabolism (7). This is surprising since there are many indications from physiological studies of significant metabolic relations between nitrogen depletion and the build-up of aromatic compounds, e.g. Lotus pendunculatus produces flavolans under nitrogen-limiting conditions, but not when nitrogen is provided (8).Scrutiny of the prearomatic pathway, leading to Phe/Tyr, and subsequent phenylpropanoid/phenylpropanoid-acetate metabolism reveals some noteworthy features. First, prephenate accepts an amino group from glutamate via transamination, constituting the point whereby nitrogen is introduced (9 -15). Second, when Phe/Tyr are committed to phenylpropanoid metabolism, rather than to protein or alkaloid synthesis, nitrogen (as the ammonium ion) is immediately removed via the appropriate lyase reaction (16 -18) (Scheme 1). Third, for every mole of cinnamate (p-hydroxycinnamate) formed, an equimolar amount of ammonium ion is generated. Consequently, an efficient means of nitrogen recycling must exist within cells undergoing active phenylpropanoid metabolism, otherwise severe nitrogen deficiency would result. A possible mechanism for recycling is shown in Scheme 2, where the ammonium ion released during lysis is metabolized via glutamine synthet...
An increasing number of phytochemicals, including phenols, terpenoids, polyketides, and alkaloids, are being recognized as photochemically active substances or photosensitizers. These compounds, unlike the photosynthetic pigments or the phytochromes, do not have any known functions in the plant species in which they occur. However, when introduced into other biological systems, e.g., cells or complex organisms, many of them arc extremely toxic in light. The cellular targets and the photochemical processes for some of them have been defined. In one type of process there is cycloaddition of the photosensitizer with a nucleic acid base, e.g., the formation of a photoadduct of a furanocoumarin such as 8-methoxypsoralen with thymine in a nucleic acid. Certain alkaloids including furanoquinolines. β-carbolines, canthinones, and certain furanochromones and chromenes appear to be of this type; they are photogenotoxic, giving rise to gross chromosomal aberrations in light. A second type of photoreaction, inherently bimolecular, often leads to oxidations. A very large group of phytochemicals, particularly the polyacetylenes and their thiophene derivatives, belong here. These compounds, characteristic of the Compositae and about 20 other families of flowering plants as well as basidiomycetous fungi, are powerful photosensitizers whose main targets in the phototoxicity process arc cell membranes. A number of natural derivatives of the chlorophylls are also in this class. The uses of some of these photosensitizers in photochemotherapy are presented. In contrast to these phototoxic reactions there are other photochemical processes occurring in plants whose significance is not yet understood. One of these processes leads to structural change in molecules, e.g., synthesis of vitamin D in plants. A fourth process is the light-directed E→Z (trans–cis) isomerism of cinnamic acid derivatives. This important stereochemical change may account for phototropism and spatial orientation in some plants.
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