The DNA strand-breaking activity of some dihydropyrazine derivatives, 2,3-dihydro-5,6-dimethylpyrazine (3), 2,3-dihydro-2,5,6-trimethylpyrazine (4), 2,3-dihydro-2,2,5,6-tetramethylpyrazine (5), trans-2,3-dimethyl-5,6,7,8,9, 10-hexahydroquinoxaline (6), its cis-compound (7) and the mixture of 6 and 7 (8) was tested by agarose gel electrophoresis using plasmid pBR322 ccc-DNA as a substrate. The order of DNA strand-breaking activity in the presence of Cu2+ was (7) > (8) > or = (5) > (2) > (6) > (4) > or = (1) > or = (3). 2,5-Bis(D-arabino-tetrahydroxybutyl)-2,5-dihydropyrazine (1) and 2,5-dihydro-3,6-dimethylpyrazine (2) have already been described in terms of DNA breaking activity in a previous paper. The activity was suggested to be due to the dihydropyrazine skeleton, in addition to active oxygen radicals formed in an aqueous solution. The introduction of a methyl group to the dihydropyrazine skeleton enhanced the activities of dihydropyrazine derivatives. The possible chemical basis for DNA strand breakage by dihydropyrazine derivatives, especially in the presence of Cu2+, was discussed.

Dehydrochlorination of D-glucosamine (2-amino-2-deoxy-D-glucose) hydrochloride with an anion exchange resin made its DNA breaking activity in plasmid pBR322 much higher, especially in the presence of Cu2+. The sample of anion exchanger-treated D-glucosamine hydrochloride, i.e., HCL-free D-glucosamine sample, showed an absorption maximum at 274 nm on the UV absorption spectrum in water as seen in the case of fructosazine [2,5-bis(D-arabino-tetrahydroxybutyl)pyrazine] one of the dimers of D-glucosamine. On a positive-ion fast atom bombardment (FAB) mass spectrum, the sample showed an ion peak at m/z 323 as a base peak, corresponding to dihydrofructosazine [2,5-bis(D-arabino-tetrahydroxybutyl) dihydropyrazine], which was a precursor of fructosazine, as well as those of D-glucosamine itself (m/z 180) and fructosazine (m/z 321). The DNA strand breaking activity of HCL-free D-glucosamine sample was directly proportional to the peak intensity of m/z 323 ion, while the DNA breaking activity of fructosazine was much weaker than that of HCL-free D-glucosamine sample. 2,5-Dihydro-3,6-dimethylprazine and 2,3-dihydro-5,6-dimethylpyrazine having a dihydropyrazine skeleton the same as dihydrofructosazine showed the same extent of DNA strand breaking activity as did the HCL-free D-glucosamine sample. These results indicated that dihydrofructosazine produced during the dehydrochlorination is closely involved in the DNA breaking activity of HCL-free D-glucosamine sample.

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