The quinoxaline derivatives formed between dehydro-D-erythroascorbic acid (2) ando-phenylenediamine (3) were separated by preparative HPLC and their structures were analyzed by HPLC-MS, UV-vis spectrophotometry and1H NMR spectroscopy. The reaction of2with an excess amount of3in 5% aqm-phosphoric acid gave three different products, depending on the concentration of2: below 0.1 mM of2, only 3-(D-glycero-1,2-dihydroxyethyl)quinoxaline-2-carboxylic γ-lactone (4) was produced, between 0.1 to 5 mM of2, another product, 2,2′-anhydro-[2-hydroxy-3-(D-glycero-2,3-dihydroxypropanal-1-yl)quinoxaline] (5) was formed as well as4, and over 10 mM of2, the third product, 2,1′-anhydro-[2-hydroxy-4-(D-glycero-1,2-dihydroxyethyl)-1,5-benzodiazepin-3-one] (6) was formed as well as4and5, with an overall production yield over 95%. Quinoxaline6was slowly converted to4via5. Based on these results, it was concluded that all three products retain the lactone ring moiety of2, and the most stable product is4. Compounds5and6were produced with higher concentration of2, but they were unstable and slowly converted to4in aqueous solution. A possible mechanism for this conversion was proposed.