Current Organic Chemistry - Volume 4, Issue 12, 2000

Marine opisthobranchs represent a very interesting source of bioactive natural products, which exhibit an extraordinary variety of chemical structures. Opisthobranchs are naked molluscs, apparently unprotected by the physical constrain of a shell. In spite of this, they appear to be free of predation. Their survival is assured by a series of alternative defensive strategies which include the use of chemicals. These bioactive compounds, which are often localized in selected parts of body and in the defensive mucous secretion, can be derived from the diet or de novo biosynthesized. Terpenes represent the major group of secondary metabolites isolated from opisthobranchs. Most of these compounds show both interesting biological properties and unique chemical structures. In particular, diterpenes include some of the most interesting examples of bioactive molecules. This review covers the chemistry of diterpenes from marine opisthobranchs, until approximately 1999. Isolation, synthesis and biosynthesis are separately discussed throughout the paper. Relevant data regarding biological activities are also reported.

More than three decades ago, Kashman and coworkers [1,2] reported for the first time a class of closely related compounds from avocados (Lauraceae). This class of compounds contains several highly oxygenated long-chain acetylenic and olefinic natural products derived from fatty acids (e.g. possibly C- 18 oleic, linoleic, linolenic, or stearic acid as precursors). These products form part of a group of compounds known as the “biologically active aliphatic acetogenins”, the distribution of which is thought to be restricted to the Annonaceae and Lauraceae. Current studies indicate that the Lauraceous acetogenins are synthesized during early plant development from specialized idioblast oil cells and transported from the oil cells to other parts of the plant. While idioblast oil cells are found throughout the plant kingdom, their function in many plant families has been the focus of considerable speculation because little is known about the chemistry or biological activity of the oil in the cells. Until recently, the idioblast cells were generally viewed simply as unusual storage organs. In avocados, increasing evidence indicates that the cells, and the oil they contain, may play an important defensive role against pathogens and insects. Several of the compounds produced in avocado oil cells, reported to occur almost exclusively in the genus Persea, are now known to have antibacterial, antifungal, and insecticidal activity. In the present paper we review the distribution, synthesis, biological activity, and mode of action of the most studied Lauraceous acetogenins: the diene persin, (12Z, 5Z)-1-acetoxy-2-hydroxy-4-oxo-heneicosa-12,15-diene, and the persin-derived furans known as avocadofurans.

The Botrytis species belong to the most geographically widespread group of plant pathogens and saprophytes, and cause serious losses to very many commercial crops. These phytopathogenus fungi are the agents of the disease known as grey mould. They biosynthesise characteristic metabolites that, in vitro, produce the grey mould symptoms. The recent discovery that oxidative forces are involved when B. cinerea infects plant and the relevance of toxins for pathogenicity, have increased the interest for these compounds, in order to determinate the potential links to the plant oxyradical metabolism and the induction of oxidative stress. This review describes the metabolites isolated from Botrytis species, the spectroscopic data, grouping together by structural family, synthesis and chemical transformation, specially those carried out on botryane skeleton. The basic skeleton of botrydial is a bicyclic, non isoprenoid sesquiterpene system which has provided the stimulus for many investigations into the biosynthetic pathway to this skeleton. The biosynthetic studies carried out and the approaches to the asymmetric synthesis on this skeleton are reported in this paper. On the other hand, a detailed study on biological activity showed for these metabolites and the structure-activity relationship of metabolites with the botryanes skeleton is included.

Southern Africa is one of two world centres of diversity in the Hyacinthaceae, harbouring approximately half the worlds family representatives. Some 368 species in 27 genera are locally represented. Plants are well distributed throughout the region, with a predominance in the Western Cape of South Africa. Some 23 species in nine genera have been phytochemically investigated, revealing compounds belonging to a diverse range of chemical classes. The chemical constituents from plants of this family have been divided into four classes, namely, homoisoflavanones, steroidal compounds, bufadienolides and miscellaneous compounds. A single report on the occurrence of Amaryllidaceae alkaloids in Urginea altissima is questioned following a reinvestigation of this species. Plants are employed for traditional medicinal purposes ranging from the treatment of hangovers, rheumatic fever, sprains and syphilis to cancer. A number of species have been toxicologically assessed following human deaths and livestock losses after ingestion. The bioactivity and ethnobotany of southern African hyacinthacs is reviewed, as is the pharmacology of isolated constituents and crude extracts.