Some alkaloids

Synthesis of some alkaloids using allyl boron derivatives 99KGS1015. 

Tandem cyclization-cycloaddition of diazoketones in the synthesis of some alkaloids 97F303. 

Cholesterol is probably the best known steroid because of its association with atherosclerosis. However, biochemically it is also of significance because it is the precursor of a large number of equally important steroids that include the bile acids, adrenocortical hormones, sex hormones, D vitamins, cardiac glycosides, sitosterols of the plant kingdom, and some alkaloids. 

Figure 1 shows fhe molecular structures of some alkaloids that have been studied in recent years for their transformations through microorganisms. 

Hydrophobic compounds such as sesquiterpene lactones and some alkaloids penetrate into cells and binds with various compartments (Roshchina, 2004 2005b). This observation permits to analyze the possible target of the substance acted. 

Moisture. Moisture increased the extraction yield of some alkaloids as demonstrated for black tea and mat6 tea leaves (Saldana and others 1999). This can be explained considering that water can act as a cosolvent for the extraction of slightly polar compounds, whereas the presence of water is favorable at about 10-15% to increase extraction yield. 

Functionalized 5,6-dihydro-4// -oxazines are direct precursors of a series of useful products, for example, of proline derivatives (539), unnatural amino acids (540), and some alkaloids (541). 

Some alkaloids do not fall into the simple classification that we have used, nor do they fall into the categories that we have decided to exclude. In this chapter,... 

Figure 14.15. Structures of some alkaloids from Cinchona bark...

Gong, Z. L., Zhang, Y., Zhang, H., and Cheng, J. K. (1999). Capillary electrophoresis separation and permanganate chemiluminescence on-line detection of some alkaloids with beta-cyclodextrin as an additive.. Chromatogr. A 855, 329—335. 

Most other alkaloids shown to have AChE inhibitory activity have been isolated from plants used in traditional medicine. Coptis chinensis Franch has been used in TCM for several conditions including age-related cognitive and memory decHne. Some alkaloids found in this species e.g. berberine (43), coptisine (44) and palmatine (45) are reported to also be antiChE. Coptis chinensis extract improved a scopolamine-induced learning and memory deficit in rats and this is likely to be due to the alkaloids present thus raising ACh levels. Berberine (43) has been shown to selectively inhibit AChE compared with Bu ChE and it has been shown to improve scopolamine-induced amnesia in rats. ... 

Although it is comparatively easy to explain the fact that some alkaloids inhibit AChE because of their molecular features, it is not easy to correlate chemical structure and activity for some other phytochemical types for which AChE inhibition has recently been reported. 

Kuznetsova LP, Nikol skaya EB, Sochilina EE, Inhibition of human blood acetylcholinesterase and butyrylcholinesterase by some alkaloids,/EvolBiochem Physiol 38 35-39, 2002. 

Many tremendous hopes, raised up in the past by the discovery of very powerful antitumor chemicals, vanished actually to some extent when it was shown that these drugs were not specific enough of the cancerizcd part of the body but were also attacking some other healthy organs in such a disastrous manner that the patient dies cured. . . This is the case, for example, with several platinum dru which induce nephrotoxicity (kidney damage), of nitrosoureas (bone marrow depletion) and of some alkaloids (heart diseases). 

Figure 2. Some alkaloids isolated by pharmaceutists Pierre Joseph Pelletier and Joseph Beiname Caventou during 1817-1821. They did not know the exact structures. Their compounds thus isolated are combinations of alkaloids rather than one pure alkaloid.

Alkaloid biosynthesis needs the substrate. Substrates are derivatives of the secondary metabolism building blocks the acetyl coenzyme A (acetyl-CoA), shikimic acid, mevalonic acid and 1-deoxyxylulose 5-phosphate (Figure 21). The synthesis of alkaloids starts from the acetate, shikimate, mevalonate and deoxyxylulose pathways. The acetyl coenzyme A pathway (acetate pathway) is the source of some alkaloids and their precursors (e.g., piperidine alkaloids or anthraniUc acid as aromatized CoA ester (antraniloyl-CoA)). Shikimic acid is a product of the glycolytic and pentose phosphate pathways, a construction facilitated by parts of phosphoenolpyruvate and erythrose 4-phosphate (Figure 21). The shikimic acid pathway is the source of such alkaloids as quinazoline, quinoline and acridine. 

The sesquiterpene pyridine alkaloids have antifeedant and insecticidal activ-ihes. Some alkaloids, such as triptonine B, hypoglaunine B, hyponine B and wilfortrine, have antivirus activity potential. Others, such as emarginatines A-B, E-G and emarginatine, have cytotoxic activity. Ebenifoline and cangorinine have immunosuppressive activity. 

Alkaloids are non-toxic in vacuoles where they are stored but toxic when they escape from the vacuoles. They have to change their chemical configurations and biological activity in different cells and tissues according to pH changes. This means that some alkaloids can have different biological activity in different cell... 

Figure 85 presents antibacterial activity by some alkaloids. There are clearly different minimum inhibitory amount of alkaloids for this activity. It is also clear that alkaloid antibacterial activity is selective. 

Figure 85. Activity of some alkaloids on Gram-positive Staphylococcus aureus, 1) and Gram-negative Klebsiella pneumoniae, 2) bacteria. Explanations Observe that the value for Scutianine E and Xanthoxyline is the same (12.5pg). Alkaloids indicated in 1 but not in 2 have values of more than 100 pg. In the case of Penduline there is no data available (Refs [388, 389, 390, 394 ]).

Figure 86. Some alkaloids from Strychnos species.

Some alkaloids (Table 23) are still used in medicine They... 

Some alkaloids are active in a and /3-adrenergic receptors (e.g. ephedrine), a receptors (e.g. ergotamine), uterine a2 receptors (e.g. ergometrine) or presy-naptic a2 adrenoreceptors (e.g. yohimbine). Ephedrine increases blood pressure... 

Table 25 Some alkaloids produced by cell cultures...

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