Alloxazine derivatives

Other lH-2,3-dihydro 2-oxo compounds have been prepared by more specialized routes. Reaction of quinoxaline N-oxide (61) with phenyl isocyanate gives a mixture of anilinoquinoxaline 62 and the (presumably) derived diphenyl oxo compound 63. Recently it has been shown that the alloxazine derivative (64) on treatment with di-n-butylamine undergoes a Lossen rearrangement to give the 2-oxo compound 65. Alkali treatment of compound 65 gives the 1,3-unsubstituted product 59. 

Alloxan forms an oxime (1007) which is the same compound, violuric acid, as that formed by nitrosation of barbituric acid likewise, a hydrazone and semicarbazone. Reduction of alloxan gives first alloxantin, usually formulated as (1008), and then dialuric acid (1004 R = OH) the steps are reversible on oxidation. Vigorous oxidation with nitric acid and alkaline hydrolysis both give imidazole derivatives (parabanic acid and alloxanic acid, respectively) and thence aliphatic products. Alloxan and o-phenylenediamine give the benzopteridine, alloxazine (1009) (61MI21300). 

Flavins (152), benzoamielated derivatives of lumazine (145), are implicated in a variety of photobiological processes such as photodynamic action, phototropism, phototaxis, and photosynthesis. The biologically active H form 152a of alloxazine (R = R = R = = H) is less stable in... 

Using surfactant chromophores, trans-bilayer electron transfer can also be observed, although in the absence of a mediator, the chromophore must be embedded in both surfaces of the bilayer structure. Thus, MV " in the bulk aqueous phase can be reduced by EDTA or sodium ascorbate in the inner water pools if they are separated by a bilayer consisting of 5,10,15-tris(l-methyl-pyridine)-4-yl-20-(4-stearoxyphenyl)porphinatozinc colyophilized with dipalmitoyl-L-phos-phatidylcholine (DPPC). l imilar results are obtained using surfactant derivatives of [Ru(bipy)3] and increased rates of formation are observed if mediators such as hexadecyl-viologen, 2-methyl-1,4-naphthoquinone (vitamin didodecyl- or dibutyl-alloxazine... 

The products obtained by condensation of o-phenylenediamines and alloxan and its derivatives are dependent on the pH of the reaction medium. Thus, when o-phenylenediamine hydrochloride is allowed to react with alloxan (12) in aqueous solution, alloxazine (13) is formed. ... 

Alloxazine 18 is formed by the cyclocondensation of o-phenylenediamine with alloxan (Kuhling 1891). The tautomeric isalloxazin 19 (flavin) is the parent compound of the 10-substituted derivatives. 

A few different methods of detection of an abasic site in DNA have been reported, the most common being the addition of a reagent that will occupy the space left by the missing nucleobase. The metallo-intercalator Rh(bpy)2(chrysi), where bpy is biphenyl and chrysi is chrysene-5,6-quinone diimide, is known to bind to DNA at mismatch sites where the duplex is disordered, but it will also bind at an abasic site, and has been shown to bind at abasic sites opposite both cytosine and guanine. The pteridine derivatives 6,7-dimethyllumazine and alloxazine both bind to adenine opposite to an abasic site, and both give a fluorescent signal in... 

Heterocyclic fused ring systems are found in a variety of biological compounds. The amino acid tryptophan (page 38) contains the indole nucleus, adenine and guanine (page 110) are purine derivatives and riboflavin (page 163) contains the alloxazine ring. 

Structure of the Flavins.— When riboflavin is irradiated in alcohol, a sugar, D-ribose, is split off, leaving a crystallisable residue, lumi-chrome. Alkaline hydrolysis of lumichrome yields urea and a dimethyl benzpyrazine, which suggests the presence of three rings in the original flavin, one of which has yielded the urea. This has led to the w-alloxazine formula now adopted for the lyoehromes, according to which lumichrome is the 6 7-dimethyl derivative. 

Berezovskii, V. M., L. S. Tul chinskaya, and N. A. Polyakova Alloxazine and Isoalloxazine Derivatives. XIII. Synthesis of 7-Aminoalloxazine, 7-Aminodimethyl-riboflavin, and their Derivatives. Zh. Obsh. Khim. 35, 673 (1965). 

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