Higher Plant Lignans

KB EDso, 1.2 x IQ-Vg/ml MELTING point 246-248°C SPECTRAL data IR, PMR, Mass Spec organism Polygala macradenia Gray (Polygalaceae) location Texas reference 183 

MELTING point 162-163°C SPECTRAL data UV, IR, PMR, Mass Spec organism Uvaria cucuminata Oliv. (Annonaceae) reference 100 

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Higher plants have yielded many effective, clinically useful anticancer drugs, including those derived from Catharanthus alkaloids, Taxus diterpenes, Camptotheca alkaloids, and Podophyllum lignans. Research in this area has been reviewed extensively (3-13). 

Hall et al. [304] tested the effects of a diet supplemented with flaxseed, rich in a-linolenic acid and plant lignans, on a murine model of lupus nephritis, and observed that the percentage of flaxseed-fed mice with proteinuria was lower than the control and that spleen lymphocyte proliferation was significantly higher in the control group than in the flaxseed group. In addition, mortality was lower in the flaxseed-fed mice versus the control. 

A lot of anticancerous agents have been isolated from natural sources especially from microorganisms and plants. However, there is no one special type of compound for cancer therapy various types of substances are effective for various types of cancers and tumors, for instance, alkaloids, lignans, terpenes and steroids [1]. In this report, concentrates on those antitumor compounds isolated from higher plants. 

Bryophytes, constituents of (constituents of mosses). Bryophytes produce numerous secondary metabolites that have not yet been found in other plants. They are mostly phenolic compounds and terpenes, there are considerable differences between the individual classes of mosses. Homworts (Anthocerotae) are characterized by the presence of lignans, liverworts (Hepaticae) principally by terpenes, especially sesqulterpenes that are often enantiomers of the compounds found in higher plants and bibenzyl derivatives. Mosses (Musci) contain biflavonoids (see flavonoids), sphagnorubins (peat mosses) and cou-marin derivatives. Alkaloids are rare and have as yet only been found in liverworts. 

Interest in lignans and neolignans has risen sharply in the last few years. This is due chiefly to their powerful, varied biological activities (Table 7.3.1) exemplified by three of the most noteworthy representatives. First, the lignan podophyllotoxin (1), in the form of several semisynthetic derivatives, is one of the very few natural products from higher plants used clinically in cancer chemotherapy (30). Next kadsurenone (2), also isolated from an angiosperm species has been described as... 

Table 1 lists crude extracts (mother liquor) of the plants studied however, the lignans were generally isolated after re-extractions rather than directly from the crude extracts. Extraction and isolation details are provided in the references [68-88] given in Table 1. As seen from the table, crude extracts were prepared with a polar solvent, mostly ethanol, sometimes water, but higher diversity was obtained by working with a direct acetone extract of T. maireii twigs, considering the number of the lignans isolated. An early study of Taxus lignans by Erdtman and Tsuno reported a brief comparative examination of several Taxus woods [67].

The lignans are secondary plant metabolites biosynthetically derived from the shikimate pathway. They possess diverse structures, usually dimers of phenylpropanoid units, although compounds containing three, four or even five such units, have been reported. The number of higher oligomers identified is currently increasing. 

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