Isoxanthopterin carboxylic acid

One of the earliest attempts to prepare analogues of FA as potential inhibitors involved the synthesis of 2-amino-4,7-dihydroxypteridine-6-carboxylyl-p-ami-nobenzoic acid (612) (in which the change from the structure of FA itself is exchange of the methylene bridge for a carbonyl group, and oxidation of position 7 to a lactam). This compound, which was a surprisingly effective inhibitor, was prepared from isoxanthopterin carboxylic acid (611) by in situ conversion to its acid chloride with a mixture of phosphorus oxychloride and phosphorus pentachloride, followed by addition of p-aminobenzoylglutamic acid (Scheme 3.132) [115]. 

Cyprino-purple B Isoxanthopterin-6-carboxylic acid 6-(l, 2 -Dihydroxypropyl)isoxanthopterin —... 

Isotubaic acid — see Benzofuran-5-carboxylic acid, 4-hydroxy-2-isopropyl-Isouramil occurrence, 3, 144 5-Isoxalones potentiometry, 6, 11 Isoxanthopterin, 6-acetonyl-structure, 3, 276 Isoxanthopterin, 3,8-dimethyl-rearrangements, 3, 309 Isoxanthopterin, 6-methoxy-3,8-dimethyl-synthesis, 3, 297 Isoxanthopterin, 6-methyl-bromination, 3, 301 Isoxanthopterin, 8-methyl-synthesis, 3, 319 Isoxanthopterin, 6-phenacyl-structure, 3, 276... 

Isoxanthopterin-6-carboxylic acid chlorination, 3, 296 synthesis, 3, 304 Isoxanthopterins catabolism, 3, 322 chlorination, 3, 296 degradation, 3, 308 occurence, 3, 323 oxidation, 3, 287 8-riboside synthesis, 3, 319 silylation, 3, 297 structure, 3, 264, 273 synthesis, 3, 298 Isoxazole, 3-acetohydroximoyl-synthesis, 6, 409 Isoxazole, 5-acetyl-3-chloro-oxidation, 6, 53... 

More simple transformations to highly functionalized pyrazines and pteridines have been documented by the syntheses of xanthopterin and isoxanthopterin <75JOC234i>, pterin-6-carboxaldehyde <80JOC2485>, pteridine-6-carboxylic acids (393) <88JHC1737>, biopterin <74JA6781>, and euglenapterin (Scheme 63) <8iJOC54i6>. 

Another wing pterin was found to be an isomer of xanthopterin and given the name isoxanthopterini. The synthesis of this colorless pterin was accomplished by condensation of ethyl mesoxalate with 2,4,5-triamino-6-hy-droxypyrimidine followed by decarboxylation of the intermediate as indicated in the above equations . A small amount of xanthopterin-7-carboxylic acid was also formed in the initial step, but in the presence of sulfuric acid, the products consist of 42% xanthopterin-7-carboxylic acid and 29% iso-xanthopterin-6-carboxyhc acid. Xanthopterincarboxylic add could not be decarboxylated but conversion to a dihydro derivative, decarboxylation of the dihydro derivative, and catalytic oxidation gave xanthopterin. Leuco-pterin can be reduced to a dihydroxanthopterin and reoxidized to xanthopterin. On the basis of absorption spectra of related derivatives, leucopterin and isoxanthopterin appear to have structures in which all of the hydroxyl groups indicated are in the lactam configuration . 

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