Pyrazine alkaloids

and Kashman [122] used long-range data in the characterization 

Selective cytotoxicity of the marine sponge alkaloid asmarine-A (148) [123] triggered Kashmaris laboratory to undertake the synthesis of this unique diazepinopurine 

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Isolation and identification of pyrazine alkaloids (Table III) have been achieved in most cases by a combination of gas chromatography and mass spectrometry (35,36,38,69,97,142). Methyl-, 2,3,6-trimethyl-, and tetramethylpyrazines (23a, 21a, and 22a) from the melon fly are identified by utilizing a solid sampling technique in conjunction with gas chromatography-mass spectroscopy (147). Methylpyrazines show the molecule ion as a base peak. Fragmentation proceeds mainly by the loss of HCN or CH3CN from the molecular ion (141). Eth-... 

In 1999, Duran et al. isolated two pyrazine alkaloids ixQvaBotryllus leachi. Botryllazines... 

The Stille coupling of 2-chloro-6-tributyltinylpyrazine with 4-methoxybenzoylchloride produced a key intermediate 43 for the synthesis of pyrazine alkaloids botryllazine A-B [29]. 

Synthesis of pyrazine alkaloid, botryllazine A, involved a combination of the Stille and Suzuki coupling reactions. The Suzuki coupling of 6-substituted 2-chloropyrazine 69 with 4-methoxyboronic acid produced 2,6-diarylpyrazine 70 [29]. 

Pettit et al. (24), working on the marine worm Cephalodiscus gilchristi (order Cephalodisicida, phyla Hemichordata, class Pterobranchia) collected from the Indian Ocean off Southeast Africa, have isolated a number of bioactive bis-steroidal pyrazine alkaloids, the cephalostatins 1-15 (11-25). 

Ritterella tokioka Kott, a tunicate of the family Polyclinidae, collected from the Izu Peninsula 100 km southwest of Tokyo, on extraction and partitioning between a number of solvent systems followed by repeated chromatography, afforded another series of bis-steroidal pyrazine alkaloids, ritterazines A-M (26-38). Structures of these alkaloids were found to be related to the cephalostatins isolated from the hemichordate Cephalo-discus gilchristii. 

A total synthesis of the pyrazine alkaloid Botryllazine B from the red ascidian Botryllus leachi was accomplished, and a previously proposed structure was shown to be correct <04M333>. Also in the natural product arena, six new polyhydroxy-p-terphenyl pyrazinediol dioxide conjugates 98a-c and 99a-c related to sarcodonin were isolated from the fruiting bodies of the basidiomycete Sarcodon leucopus <04EJO592>. 

The family of dimeric steroid-pyrazine alkaloids isolated from Cephalodiscus and Ritteria now stands at thirty members. There are undoubtedly other examples of this group of steroidal alkaloids that have yet to be discovered, and it is probable that members common to both sources will be found. 

Hu and collaborators isolated a new indole-pyrazine alkaloid, colletotri-chumine A (97), with a novel Ci6N3-type skeleton from Colletotrichum capsid, a pathogenic fungus and a newly discovered source of natural products with heretofore unprecedented structural compositions (F ure 15) (14TL6093). 

Physiological Activity of Xanthine Derivatives Pyrazine Alkaloids Securinega Alkaloids Sesbania Alkaloids Betalains Biosynthesis Chemosystematic Value Betalains in Foods and Beverages Miscellaneous Alkaloids Trigonelline and an Unusual Pyrrole Histronionicotoxins Huperzine A References... 

Pyrazine alkaloids (Fig. 37.11) are known to occur in both Dlants and insects. These alkaloids serve as warning and ilarm substances from Iridomyrmex humilis ( driisena-neisen ) and Ondontomachus species ( Stachelameisen )... 

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