The roots of Lithospermum erythrorhizon Sieb. and Zucc., (violet root, Japanese name, Shikon) contain shikonin and its esters as purple pigments. The coloring matter of the root of Alkanna tinctoria in Europe is a mixture of the enantiomeric alkannin and its esters. The racemic compound of shikonin and alkannin was named shikalkin by R. Kuhn and H. Brockmann. From ancient times these purple pigments have been well-known as valuable materials having antiinflammatory, antibacterial, antitumor actions, and as ancient purple deys and cosmetics. Here, the history, structural determination, synthesis and pharmacology of shikonin, alkannin, and their derivatives will be reviewed.
From the medicinal plants Gelsemium, various skeletal type of indole alkaloids were isolated. Along the biogenetic speculation of these alkaloids, some of the structurally complex compounds, involving sarpagine-, humantenine-, koumine-, and gelsedine-type, were prepared from ajmaline and the Gardneria alkaloids. In the second half of this article, recent synthetic studies on the sarpagine type alkaloids and on a principal Gelsemium alkaloid, gelsemine, are reviewed.
Total synthesis of eudistomins has been reviewed. Various approaches to the oxathiazepine ring system are summarized and the natural products have been synthesized from Nb-hydroxytryptamine and D-cysteinal.
Recent development in synthetic chemistry of the sugar moiety of nucleosides as potential anti-HIV agents has been reviwed. These include the chemical transformation of the sugar moiety of naturally-occurring nucleosides and the synthesis of carbocyclic nucleosides. Total syntheses of (-) -oxetanocin and its derivatives are also discussed.
Several derivatives of heterocyclic-oxy phenoxy propionic acid have been known as selective herbicides. During extensive investigations on this series with various condensed heterocyclic moieties, the quinoxalinyloxy phenoxy propionic acid derivatives were found to show an excellent herbicidal activity against grass weeds. Among them, ethyl 2- [4- (6-chloro-2-quinoxalinyloxy) phenoxy] propionate, (code No.NC-302, quizalofop ethyl) showed a potent herbicidal activity. It is commercialized as a novel post-emergence herbicide. In this paper, facile syntheses of substituted quinoxalines and quizalofop ethyl derivatives are described in detail.