Isoxanthopterin

Their physical properties closely resemble those of pterin, which has a basic pKt, of 2.20 and an acidic one of 7.86 associated with N-1 protonation and a hypsochromic shift of the long-wavelength absorption band in the UV spectrum, and N-3 deprotonation effecting a bathochromic shift respectively (Table 4). The xanthopterin (4) and isoxanthopterin types... 

The purely chemical analogy involving nucleophilic attack and subsequent oxidation can be achieved by hydrogen peroxide, which converts pteridin-6-one into pteridine-6,7-dione (52JCS1620), and xanthopterin (4) into leucopterin (6) (39LA(539)179). Isoxanthopterin (5) reacts with nitrous acid to give pteridine-2,4,6,7-tetrone (44LA(555)146). 

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

Asperopterin A 8-Methyl-6-(/3 -D-ribosyloxymethyl)isoxanthopterin 6-(l -Hydroxypropyl)-8-methylisoxanthopterin —... 

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... 

Isoxanthopterin (2-amino-4,7-dihydroxypteridine) [529-69-1] M 179.4, m>300°, pKj -0.5 (basic), pKj 7.34 (acidic), pKj 10.06 (acidic). Purified by repeated pptn from alkaline solutions by acid (preferably AcOH), filter, wash well with H2O then EtOH and dried at 100°. Purity is checked by paper chromatography [Rp 0.15 (n-BuOH, AcOH, H2O, 4 1 1) 0.33 (3% aq NH4OH). [Goto et al. Arch Biochem... 

Xanthopterin monohydrate (2-amino-4,6-dihydroxypteridine, 2-amino-pteridin-4,6(lff,5ff)-dione) [5979-01-1 (H2O), 119-48-8 (anhydr)] M 197.2, m <300", pK, 1.6 (basic), pKj 6.59 (acidic), PK3 9.31 (acidic)(anhydrous species), and pKj 1.6 (basic), pK2 8.65 (acidic), PK3 9.99 (acidic)(7,8-hydrated species). Purification as for isoxanthopterin. Crystd by acidifying an ammoniacal soln, and collecting by centrifugation followed by washing with EtOH, ether and drying at 100° in vacuo. Paper chromatography Rp 0.15 ( -PrOH, 1% aq NH3, 2 1), 0.36 ( -BuOH,AcOH, H2O, 4 1 1) and 0.47 (3% aq NH3). [Inoue and Perrin J Chem Soc 260 7962 Inoue Tetrahedron 20 243 I964 see also Blakley Biochemistry of Folic Acid and Related Pteridines North Holland Publ Co, Amsterdam 1969.]... 

For the synthesis of drosopterin, tetrahydrobiopterin, sepiapterin, 7-oxopterin and isoxanthopterin, DHN-TP is first converted to the common intermediate 6-pyruvoyl-tetrahydropterin. The biosynthesis of pteridines was studied in zebrafish in relation with the differentiation of neural crest derivatives. The key intermediate in the synthesis of 7-oxobiopterin is the sepiapterin. Pteridins are produced in xanthophores and erythrophores of fish and amphibian species. 

The excitation and emission wavelengths used for fluorescence detection in HPLC analysis are 350 and 450 nm for isoxanthopterin and 340 and 450 nm for 2,4,7-trioxopteridine, respectively." The absorption spectra of riboflavin present... 

Isoxanthopterin [529-69-1 ] Daphnla pulex EC50 (48-h) 0.47 Perry and Smith 1988... 

Pteridines are widespread in the animal kingdom, and particularly among insects (Table VI) (42). The red ants in the genera Formica, Lasius, and Rap-tiformica eontain pteridines sueh as isoxanthopterin (67) and biopterin (70) (Table VI). One of the eatecholamines, noradrenaline (133), is also detected from Formica rufa (Table VIII). 

The cabbage worm butterfly Pieris rapae crucivora and the sulfur-colored Catopsilia crocale are both found to afford the anticancer component isoxanthopterin (67) (57). In addition, isoxanthopterin (67) from the skin of the European minnow, Phoxinus phoxinus, elicits the fright reaction and hence acts as the alarm substance (52). 

The silkworm, Bombyx mori (Bombycidae), contains in various body parts simple alkylamines, tryptophan metabolites, and pteridines (Tables V, VI, and VIII). One of the pteridines, violapterin (78), is synthesized from isoxanthopterin (67) by isoxanthopterin deaminase, occurring in the larvae and adults, and is stored in situ in the larval and adult integument (80). In addition, sepiapterin deaminase in the integument of the lemon mutant silkworm catalyzes the deamination of sepiapterin (81) to 7,8-dihydro-6-lactyllumazine (79) (81). 

The end products of tryptophan metabolism in the stick insect, Carausius morosus, are the ommochromes ommin and xanthommatin (58) in the epidermis, and kynurenic acid (53) in the feces. During larval development of this insect kynurenic acid (53) is the major end product of tryptophan metabolism (Table V) (109,110). Additionally, this insect contains five pteridines (Table VI), of which leucopterin (68), xanthopterin (65), and isoxanthopterin (67) are the origin of the yellow-white color of the insect (111). 

There are a number of studies on the biosynthesis of various pteridines, i.e., xanthopterin (65), isoxanthopterin (67), erythropterin (73), leucopterin (68), and pterin (62) (509-511). The most important intermediate of the proposed biosynthetic pathway from guanosine triphosphate (GTP) (604) seems to be di-hydroneopterin triphosphate (H2-NTP) (605), however, because evidence has recently been accumulated indicating that pteridines such as biopterin (70), sepiapterin (81), and drosopterins (87) are synthesized from GTP (604) by way of H2-NTP (605) (Scheme 76) (5/2). 

In man, BH4 is degraded either nonenzymatically by side-chain cleavage to pterin or is enzymatically metabolized in the gastrointestinal tract to become a lumazine [2]. Pterin and dihydropterin are converted by xanthine dehydrogenase to isoxanthopterin and xanthopterin, respectively [3,4]. It is assumed, however, that most of the ingested BH4 is used as a cofactor (mainly for PAH in the liver) and is catabolized to nonfluorescing compounds it may even be degraded to C02 and ammonia. 

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