Quinoxaline, carbohydrate derivatives

The term C-nucleoside was only coined after isolation and characterization of the first member of this class pseudouridine, in 1975 [97ACH(ip)]. Before that, alditolyl derivatives of some heterocycles (acyclo C-nucleo-sides) were known both as natural products (alditolyl pteridines or biopterins) as well as products of syntheses (e.g., alditolyl derivatives of imidazoles, benzimidazoles, thiazoles, benzothiazoles, 1,2,3-triazoles, quinoxalines, and flavazoles) and were classified as carbohydrate derivatives of heterocyclic compounds. After isolation of pseudouridine, other naturally occurring members were successively isolated, characterized, and synthesized. It is worth mentioning that synthesis preceded isolation in two cases 9-dea-zaadenosine and pyrrolosine. Comparison with the synthetic compounds facilitated structure elucidation in one case (9-deazaadenosine) and structure reassignment in the other (pyrrolosine). 

The imine formed on hydrolysis yields o-phenylenediamine and the corresponding carbonyl compound, and, depending on the pH of the medium, can also undergo further chemical and electrochemical reactions. By this reduction of carbohydrate derivatives of quinoxaline, the corresponding deoxy saccharides would be formed. For 1,2-dihydro-2,3-dimethylquinoxaline in an alkaline medium, the decrease in the height of wave i2 and the appearance of an anodic wave, ia, with increasing pH value prove that only its protonated form is reduced to the corresponding quinoxaline derivative, whereas its nonprotonated form is capable of oxidation to the initial 2,3-dimethylquinoxaline, as shown in Scheme 13. 

Many furanones (including furanose carbohydrates) have been used as synthons with 1,2-benzenediamines to afford quinoxaline derivatives. The following examples illustrate the main types of such cyclocondensation reactions. 

The first example illustrated (Figure 1) is a quinoxaline derivative, having a four-carbon, acetylated carbohydrate chain attached to it. The... 

The discovery that 1 mole of 2-methylquinoxaline is formed from one mole of carbohydrate " led the authors to an attempt to obtain it by a method simpler than ion-exchange chromatography. " Separation of 2-methylquinoxaline from other quinoxaline derivatives was found possible by partition chromatography, but a method involving extraction with organic solvents is even more advantageous. All of the quinoxaline... 

---