Other Nitrogen-Containing Natural Products

00001 ppm. Related pyrazines, probably formed by the pyrolysis of amino acids during the process of cooking, are also important in the aroma of roasted meats. Several polyalkyl pyrazines are insect pheremo-nes, for example 2-ethyl-3,6-dimethylpyrazine is the major component of the trail pheremone of the South American leaf-cutting ant. 

Some fungal metabolites from Streptomyces species include the quaternary salt pyridazinomycin. Divi-cine, present as a glucoside in broad beans and related plants, is the toxic agent responsible for favism , a serious hemolytic reaction in genetically susceptible people (of Mediterranean origin). 

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Stereoselective additions to C=N bonds are of prime importance for the synthesis both of alkaloids and also of a host other nitrogen-containing natural products. Nature s own ability to synthesize complex alkaloids is awe-inspiring. A relatively simple example where the sequence of synthetic steps has been well elucidated is the biosynthesis of nicotine (8) from nicotinic acid (vitamin B,) [43]. As outlined in Figure 11.1, the enzyme-mediated... 

The ease with which amines are extracted into aqueous acid, combined with their regeneration on treatment with base, makes it a simple matter to separate amines from other plant materials, and nitrogen-containing natural products were among the earliest organic compounds to be studied. Their basic... 

Acyl nitroso compounds react with 1, 3-dienes as N-O heterodienophiles to produce cycloadducts, which have found use in the total synthesis of a number of nitrogen-containing natural products [21]. The cycloadducts of acyl nitroso compounds and 9,10-dimethylanthracene (4, Scheme 7.3) undergo thermal decomposition through retro-Diels-Alder reactions to produce acyl nitroso compounds under non-oxidative conditions and at relatively mild temperatures (40-100°C) [11-14]. Decomposition of these compounds provides a particularly clean method for the formation of acyl nitroso compounds. Photolysis or thermolysis of 3, 5-diphenyl-l, 2, 4-oxadiazole-4-oxide (5) generates the aromatic acyl nitroso compound (6) and ben-zonitrile (Scheme 7.3) [22, 23]. Other reactions that generate acyl nitroso compounds include the treatment of 5 with a nitrile oxide [24], the addition of N-methyl morpholine N-oxide to nitrile oxides and the decomposition of N, O-diacylated or alkylated N-hydroxyarylsulfonamides [25-29]. 

Fused-ring aziridines have found broad application to the synthesis of complex natural products. The ability of these fused-ring aziridines to be converted to other nitrogen-containing molecules under mild conditions with wide functional group compatibility makes these heterocycles quite useful. 

In today s world, some plant-derived secraidary metabolites play a great role in pharmaceutical production, among them nitrogen-containing natural compounds called alkaloids. Some alkaloids are produced by synthesis or enzymatic methods and others are obtained from plants. Unfortunately, overexploitation of these plants has made them endangered species. Therefore, appropriate technologies for sustainable use and sufficient focus on the biosynthetic routes and methods of isolation of these secondary metabolites derived from the plants are required. 

Diastereoselective intramolecular cycloaddition of nitrones is useful for constructing nitrogen- containing cyclic structures. The reaction serves as a key step in a number of natural product syntheses.63 Tufarriello and coworkers have used this strategy for preparing cocaine and other alkaloids.74 As a classical example, enantioselective total synthesis of (+)-luciduline is presented in Scheme 8.13, in which a useful feature of the 1,3-dipolar addition of nitrones is nicely illustrated.75... 

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