Biologically active neolignans from

YOSHIDA Biologically Active Neolignans from Amazonian Trees... 

A stereocontrolled synthesis of the biologically active neolignan (+)-dehydrodiconiferyl alcohol, which was isolated from several Taxus species, was achieved via Evans asymmetric aldol condensation [58] using ferulic acid amide derived from D-phenylalanine. The reaction steps are shown in Fig. 9. This stereocontrolled reaction is also useful for preparing the enantiomer of (+)-dehydroconiferyl alcohol using chiral auxiliary oxazolidinone prepared from L-phenylalanine. This reaction also enables the syntheses of other natural products that possess the same phenylcoumaran framework. 

From the viewpoint of organic synthesis, nature provides us with a number of target molecules, which have novel structures and a variety of biological activities. As already shown in Section II.A, electrochemical oxidation of phenols has been applied successfully to natural products synthesis. Hypervalent (diacyloxyiodo)benzenes have also been proved to be effective for natural products synthesis. Generally, oxidation of o- and p-methoxyphenols in MeOH provides the corresponding o- and p-quinone monoketals, respectively. They are utilized as promising synthons for natural products and related bioactive compounds, as demonstrated by Swenton . Recently, these quinone monoketals have been utilized for syntheses of terpenoids, neolignans, anthraquinones, alkaloids and related compounds. 

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... 

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