3-Amino-1 - pyrazinium

The syntheses of some pyrazolo[l,5-a]pyrazines from A-amino-pyrazinium derivatives have been described.345 Treatment of 266 R R2 = H or Me) with base gave 267, which cyclized to 268 with EP or DMAD. The A-imino derivative (270), from the interesting A-amino-pyrazinium A -oxide salt (269) gave 41 % of 271 with EP.345... 

Hofmann et al.361 have obtained evidence that glycolaldehyde can interact with e-amino groups to crosslink proteins with generation of colour due to pyrazinium radical cations (cf. CROSSPY 84) under physiological conditions. This has direct bearing on, for example, cataract formation. 

Few examples of N-amination of azines have been reported. The use of such reagents as 0-mesitylenesulfonylhydroxylamine has led to the direct synthesis of /V-aminopyridazinium, -pyrimidinium, and -pyrazinium salts (80CPB2676), and 1-aminobarbituric acids (72CPB1814), while 0-(2,4-dinitrophenyl)hydroxylamine was a useful amino-transfer reagent in the direct synthesis of 1 -amino-6-methylthio-1,2,4-triazin-4( 17/)-ones from 2-methylthio-1,2,4-triazin-5( 1H)-ones (82JHC1583). 

Most such pyrazinones have been made by primary synthesis (Chapters 1 and 2) or N-alkylation of tautomeric pyrazinones (Section 5.1.2.2). The minor route by rearrangement of alkoxypyrazines (H 184) appears to be unpresented in recent literature, but there are examples of the hydrolysis of nontautomeric iminopyrazines to corresponding pyrazinones. Thus 3-imino-4-methyl-3, 4-dihy-dro-2-pyrazinamine hydriodide (191, R = H) (i.e., 2,3-diamino-l-methyl-pyrazinium iodide) underwent hydrolysis in 2 M sodium hydroxide during 1 h at 100°C to afford 3-amino-1 -methyl-2(l//)-pyrazinonc (192, R = H) ( 40%) without any evidence of Dimroth rearrangement to 3-methylamino-2-pyrazinamine 1008 l-methyl-3-methylamino-2(l//)-pyrazinimine (191, R = Me) likewise gave 1-methyl-3-methylamino-2(l//)-pyrazinone (192, R = Me) ( 50%) 1008 and other examples have been reported.598... 

The reactions of pyrazine with sodium amide in liquid ammonia to give the anion of 2-amino-1,2-dihydropyrazine (608), and of 3-substituted 1-methylpyrazinium ions with liquid anunonia to give 3(or 5)-substituted 2-amino-1-methyl-1,2-dihydro-pyrazines (609) have been described in Section IV. 1C. Similar reactions of pyrazine with phenyllithium at —45° in tetrahydrofuran (720a) and of 1,2,5-trimethyl-pyrazinium salts in liquid ammonia with nitromethide and ethanethiolate anions (721) have been described in Section IV.2C(8). 

This effect is also shown in the proton spectra of 1-methyl-pyrazinium iodide (9), 2,4-dimethylpyrazinium (lOA), 2 amino-4-methylpyra-zinium iodide (lOB) and 1-methylquinoxalinium iodide (11) in deuterium oxide solution at 100 Me./sec.The reduction of the... 

These data demonstrate that in the reaction of the peptide, and the protein as well, crosslinking reactions lead to a strongly restricted rotation of the pyrazinium radical and to an immobilization of the radical, thus inhibiting die resolution of the EPR signal. We therefore proposed the broad singlet to represent protein-bound l,4-bis-(5-amino-5-carboxy-l-pentyl) pyrazinium... 

Figure 11. Disproportionation of CROSSPY leading to diquaternary l,4-bis-(S-amino-5-carboxy-l-pentyl)pyrazinium ions (diquats, I) and l,4-bis-(5-amino-5-carboxy-1-pentyl)-1,4-dihydropyrazirtes (II).

Molecular and crystal structure of 1-amino-X-pyrazinium mesitylenesulfonates. 

They fractionated the melanoidins by gel filtration to determine which molecular weight melanoidins were responsible for this loss. They found that aU of the fractions reacted with the sulfur-containing volatiles. Attanpts to free the melanoidin-bound volatiles through the addition of other free thiols were unsuccessful, suggesting that the sulfur compounds were not simply involved in disnlfide interchange as observed for proteins. Further work strongly supports the hypothesis that the thiols are covalently bound to pyrazinium ions which are oxidation products of l,4,-bis-(5-amino-5-carboxy-l-pentyl) pyrazinium radical ions. 

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