Geometric isomer analogs

Although benzoxazolium salts are more acidic than their benzothiazol analogs in position 2, isolation of the corresponding dioxa-diazafulvalenes was unsuccessful (72LA126). Comparable to the 1,3-dithiolium- and 1,3-thiazolium salts, 1,2,4-dithiazolium salts yielded on treatment with triethylamine in acetonitrile at 0°C mixed geometrical isomers of the TTDAF... 

The report by Kitagawa and coworkers [112] examined C. viridis and found the same three compounds (88-90) plus the expected fourth C5-C8 diene geometrical isomer (91). In this and a subsequent report by this group, the new PG-analogs were called the claviridenones A-D , a name which has not been generally accepted. Their structures were determined principally by NMR... 

Unlike desferrioxamine analogs designed for specific therapeutic purposes described above, chiral DFO analogs that form conformationally unique complexes with iron(lll) were designed to serve as chemical probes of microbial iron(lll) uptake processes. As mentioned above, ferrioxamine B can form a total of five isomers when binding trivalent metal ions, each as a racemic mixture. Muller and Raymond studied three separate, kinetically inert chromium complexes of desferrioxamine B (N-cis,cis, C-cis,cis and trans isomers), which showed the same inhibition of Fe-ferrioxamine B uptake by Streptomyces pilosus. This result may indicate either that (i) ferrioxamine B receptor in this microorganism does not discriminate between geometrical isomers, or that (ii) ferrioxamine B complexes are conformationally poorly defined and are not optimal to serve as probes. 

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