Plants antimetabolites from

Anticancer drugs act on cells in active proliferation and may interfere with a specific phase of the cell cycle or act independently from it. Some of these drugs are naturally occurring compounds, identified in plants or microorganisms, some are synthetic chemicals. Among the major classes of chemotherapeutics include antimetabolites, alkylating agents, inhibitors of the... 

Drags used to treat cancer are subdivided into six groups antimetabolites, alkylating agents, antibiotics, drags isolated from plants, hormones, and a group of substances not included in the classifications listed above, which are examined in another section. 

Finally, it may be worthwhile to point out that one of the most successful chemotherapeutic drugs provided by nature may be considered as a non-classical active-site-directed irreversible inhibitor This drug is penicillin (70). As a non-classical antimetabolite of D-alanyl-D-alanine, it first forms a reversible complex with the enzyme peptidoglycan transpeptidase, and then by a ringopening reaction of its p-lactam moiety, it forms a covalently linked penicil-loyl-enzyme complex97. However, the reaction involves the acylation of a sulfhydryl group in the active site of the enzyme in this respect, 70 resembles the classical-type endoalkylating antimetabolites, azaserine and DON (8 and 9, see Section 2.2.). Some of the more recently discovered antibiotics and natural products from plants with antitumor activity (e.g., camptothecin) are... 

Thus, a large number of substances have been tested as inhibitors for the steps in purine and pyrimidine metabolism (Cory, in Devlin, 1986, p. 674 0. Inclnded are both synthetic compounds and compounds isolated from plants, bacteria, fungi, etc. The substances may be further classed as glutamine antagonists, antifolates, and antimetabolites. Whereas the first-mentioned substances are toxic in the extrane, the latter two classifications have been of main concern although they are toxic enough in their own right. 

According to Ladonin and Spesivtsev (1974), maize tolerant to chloro-5-triazines stores the triazine taken up in the cytoplasm and in the sensitive pea it is stored in the nucleus, chloroplasts and mitochondria. They assume that the triazines are thus incorporated into proteins and nucleic acids as antimetabolites during the biosynthesis of internuclear nucleic acids. This may also be one of the explanations of the different sensitivity of plants to triazines. Black currant is also tolerant to 4 ppm simazine. According to Shone and Wood (1972) triazine translocated into the leaves of black currant cannot get from the tissue system into the mesophyll. The simazine taken up remains in the leaf veins and does not enter the chloroplasts. 

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