Quinolizidine alkaloid biosynthesis: recent advances …
Therefore, we also found two transcripts were highly expressed, one encoding the putrescine methyltransferase, which participates in alkaloid biosynthesis ; the other encoding the GDP-D-mannose 3,5-epimerase (GME), which is generally considered to be a key enzyme of the major ascorbate biosynthesis pathway in higher plants through converting GDP-d-mannose to GDP-l-galactose .
In the biosynthesis of alkaloids, ..
With respect to qualitative differences in alkaloid profiles (as opposed to quantitative variation in total alkaloid concentrations), variation is substantial among Pinus species (Tallent, 1955; ; ; ), to the extent that euphococcinine, rather than pinidine, is the dominant alkaloid in some species. In contrast, within ponderosa pine, little intraspecific qualitative variation that could be sorted into chemotypes was observed. Intraspecific differences in alkaloid profiles of other plants do occur with geography (), and there was some evidence for this in the stacked bars of Fig. . The Fort Lewis and Mendocino seedlings had slightly lower proportions of pinidine in the total, otherwise the differences within and among regions were primarily a matter of quantity rather than composition. Euphococcinine, the secondary end-product of alkaloid biosynthesis in ponderosa pine, appeared consistently in very minor proportions (3–6 %) across the regions. This same alkaloid is synthesized de novo by a bean beetle (Epilachna varivestis) for deployment as a feeding deterrent (), but the minor quantities found in ponderosa pine suggest euphococcinine has not been selected for. suggested that trade-offs in production of particular monoterpenes within the total pool can occur where resources are limited, and this situation would lead to negative correlations between terpenes. They did find strong negative correlations for three major monoterpenes of field-sampled ponderosa pine. In the present case, however, log-transformed pinidine and euphococcinine concentrations related weakly, but positively with one another (R2 = 13·1 %, simple linear regression, P
Pinus ponderosa produces a suite of piperidine alkaloids in most tissues (; ; ; ). Biosynthesis involves several pathways and intermediates leading to one predominant and stable end-product (pinidine) in mature foliage (; ; , ). Alkaloid variation due to combined environmental and genetic effects, as measured in an observational field study of ponderosa pine, is dependent on site to the extent that alkaloids may be entirely absent (). Environmental influences on ponderosa pine alkaloids were documented in a field fertilization study that showed the potential for nitrogen availability to influence alkaloid variation (). To our knowledge, the genetic basis for intraspecific variation in conifer alkaloid production has not yet been explored. Intraspecific variation of other types of alkaloids in disparate plant genera have exhibited moderate () to high levels of heritability, more so, for example, than terpenes of Pinus (Table in ).
Shahjalal University of Science and Technology
Methodology followed . Briefly, a 0·5 g sample of oven-dried, ground foliage was extracted in aqueous acid then centrifuged; the supernatant was basified and the alkaloids partitioned into chloroform using an Extrelut® solid-phase column. The eluate was reduced, an internal standard added, and the solution increased to a known volume. The following piperidine alkaloids (Fig. ) were identified and quantified using gas chromatography–mass spectrometry (GC-MS): pinidine; pinidinone; 6-epi-pinidinone; pinidinol; 1,2-dehydropinidinone; 1,2-dehydropinidinol; euphococcinine; and RT 6·80. Pinidine is the primary end-product of alkaloid biosynthesis in ponderosa pine, and euphococcinine is an alternative end-product (, ). The remaining alkaloids listed are intermediates. Although it has never been officially described, RT (retention time) 6·80 very probably is 1,6-dehydropinidinone (), based on the molecular ion (153 m/z) and mass spectrum. Another unknown, probable alkaloid with molecular ion 167 m/z, was observed but not incorporated in the data analysis (because it has not been properly described, and was a minor, sporadic component). The presence of the 6-epi form of pinidinone is interesting because, heretofore, only cis-2,6-disubstituted piperidines have been found in Pinus species (; ). Both isomers of pinidinone occurred sporadically at low concentrations in a quarter to a third of the samples.
Glycogen Synthase Kinase-3 (GSK-3)-Targeted Therapy …
Reports have showed that the exposure or ingestion of certain plant alkaloids could provoke harmful outcomes. Insects and herbivores are often repulsed by the potential toxicity and bitter taste of alkaloids. For instance, lupin alkaloids are feeding deterrents and lethal to certain species of insects, especially aphids (). Also, quinolizidine alkaloids toxicity to insects and vertebrates is attributable to the interactions of sparteine or lupanine (alkaloids) with N-acetylcholine receptors (nAChR) (sparteine or lupanine activates nAChR), Na+/K+- channels and interference with protein biosynthesis (). The anti-nutrients attributes of alkaloids are in connection with their actions in the central nervous system, which disrupt or cause inappropriate transmission of electrochemical signals. Specifically, massive intake of tropane alkaloids elicits rapid heartbeat, paralysis and in fatal case, leads to death. Likewise, high dose of tryptamine alkaloids cause staggering gate and death (). Strychnine alkaloids are used as rat poison (). The molecular configurations of some common alkaloids are shown in .
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12. S. E. O’Connor and J. J. Maresh, Chemistry and biology of monoterpene indole alkaloid biosynthesis, Natural product reports, 2006, 23, 532 – 547.