CHARACTERIZATION OF QUINOXALINE DERIVATIVES OF DEHYDRO-D-ERYTHROASCORBIC ACID

The quinoxaline derivatives formed between dehydro-D-erythroascorbic a cid (2) and o-phenylenediamine (3) were separated by preparative HPLC and their structures were analyzed by HPLC-MS, UV-vis spectrophotometr y and H-1 NMR spectroscopy. The reaction of 2 with an excess amount of 3 in 5% aq m-phosphoric acid gave three different products, depending on the concentration of 2: below 0.1 mM of 2, only lycero-1,2-dihydro xyethyl)quinoxaline-2-carboxylic gamma-lactone (4) was produced, betwe en 0.1 to 5 mM of 2, another product, (D-glycero-2,3-dihydroxypropanal -1-yl)quinoxaline] (5) was formed as well as 4, and over 10 mM of 2, t he third product, ycero-1,2-dihydroxyethyl)-1,5-benzodiazepin-3-one] ( 6) was formed as well as 4 and 5, with an overall production yield ove r 95%. Quinoxaline 6 was slowly converted to 4 via 5. Based on these r esults, ii was concluded that all three products retain the lactone ri ng moiety of 2, and the most stable product is 4. Compounds 5 and 6 we re produced with higher concentration of 2, but they were unstable and slowly converted to 4 in aqueous solution. A possible mechanism for t his conversion was proposed.