Polyketide-derived alkaloids

Biological Activity of Tropane Alkaloids Distribution of Tropane Alkaloids Piperidine Alkaloids Alkaloids from Piper Species Piperine Alkaloids Involving Condensation with Acetate/Malonate Sedum Alkaloids Lobelia Alkaloids Lycopodium Alkaloids Piperidine Alkaloids in Insects Polyketide-Derived Alkaloids Coniine... 

A number of polyketide-derived alkaloids are known to occur. Probably best known among these are coniine (48) and related compounds, found primarily in the Apiaceae (mostly in the genus Conium) (Leete, 1971). Other alkaloids with similar origin are pinidine (49) from pines, the Galbuli-... 

Polyketide-Derived Alkaloids from Coniothyrium cereale... 

Over the past quarter-century more than 10,000 compounds have been reported from marine-derived organisms. These compounds encompass a wide variety of chemical structures including acetogenins, polyketides, terpenes, alkaloids, peptides and many compounds of mixed biosynthesis. A number of excellent books and reviews document the diversity of both structures and bioactivities which have been observed for marine-derived compounds. ... 

Acetate is also a precursor of several groups of alkaloids in the form of a polyketide chain that interacts with an unknown nitrogen source (as in the terpene alkaloids). Examples of acetate-derived alkaloids are coniine—the toxic principle of Conium maculatum, pinidine—from several Pinus species, and the naphthy-lisoquinoline alkaloids (e.g., ancistrocladine)—showing antimalarial and anti-HIV activity. The latter alkaloids are apparently derived from the oxidative coupling of two pentaketide units. Huperzine A, currently in clinical trials for the treatment of Alzheimer s disease and isolated from the club moss (Serrata huperzia), is derived from a polyacetate precursor (Fig. 46). 

The excellent reviews of Berlinck [1-5] have surveyed a great number of guanidine-type natural products. In addition, some guanidine-derived marine alkaloids have been reviewed by Kobayashi and Ishibashi [6,7]. Also, a recent book gave accounts of marine alkaloids including the phakellins, palau amines and oroidin-like dimers derived from bromopyrroles and polyketide-derived polycyclic guanidine alkaloids [8]. 

Pyne et al. proposed an alternative biosynthetic pathway for pyrido[l,2-fl] azepine stemona alkaloids starting from the polyketide derivative 21. Condensation of the latter with 1,4-diaminopropane, a biosynthetic product from the HSS production of homospermidine 3, could provide the piperidine ring intermediate 22. 

Phytoalexins are low molecular weight products which are produced in response to elicitors such as microbial, herbivorous or environmental stimuli (Poulev et al. 2003). Once plants detect a pathogen signal, a complex mixture of secondary metabolites is produced to control the invader. These molecules are synthesized de novo, and thus involve the activation of certain genes and enzymes required for their synthesis (Kuc 1995). Phytoalexins are chemically diverse and may include many chemical classes such as simple phenylpropanoid derivatives, alkaloids, gly-costeroids, flavonoids, isoflavonoids, various sulphur products, terpenes and polyketides (Hammerschmidt 1999). There is no boundary between phytoalexins and phytoanticipins, and in one plant species a certain chemical can function as a phytoalexin, whereas it has the function of a phytoanticipin in another species (Junghanns et al. 1998). It is important to point out that the distinction between phytoanticipins and phytoalexins is not based on their chenucal structure but rather on how they are produced. Thus, the same chemical may serve as both phytoalexin and phytoanticipin, even in the same plant (VanEtten et al. 1994). 

This second volume on Biosynthesis follows the pattern of Volume 1, with the inclusion of a review of non alkaloidal nitrogenous compounds and the partition of plant phenolic compounds into the two principal divisions, polyketide-derived and shikimate-derived classes. 

There are several classes of alkaloids. Among these are purines such as xanthine and caffeine, ter-penes (Chapter 22), polyketides (Chapter 21), and alkaloids derived from amino acids. The basic amino acids ornithine, arginine, histidine, and lysine as well as the aromatic amino acids, anthranilate, and nicoti-nate are some of the starting materials.199 201 Robinson202 203 in 1917 recognized that many alkaloids are derived directly from aromatic amino acids. He proposed that alkaloids arise from Mannich reactions (Eq. 25-12) in which an amine and an aldehyde (probably through a Schiff base) react with a nucleophilic carbon such as that of an enolate anion. Many of the... 

Biosynthesis of Polyketides Phenolic Compounds derived from Shikimate. The Biosynthesis of CB - Cjg Terpenoid Compounds Trrterpenoids Steroids, and Carotenoids Non-protein Amino-acids, Cyanogenic Glycosides, and Glucosinolates Biosynihesis of Alkaloids. 

The majority of alkaloids have been found to be derived from amino acids, such as tyrosine, phenylalanine, anthranilic acid, tryptophan/tryptamine, ornithine/arginine, lysine, histidine and nicotinic acid (Fig. 2.1). However, alkaloids maybe derived from other precursors such as purines in case of caffeine, terpenoids, which become aminated after the main skeleton has been synthesized i.e. aconitine or the steroidal alkaloids, are found in the Solanaceae and Liliaceae. Alkaloids may also be formed from acetate-derived polyketides, where the amino nitrogen is introduced as in the hemlock alkaloid, coniine. 

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