The synthesis of C-nucleosides has received considerable attention because of the diverse biological properties of such naturally occurring analogues as showdomycin, formycin, and oxazinomycin [2]. We have been interested recently in the synthesis for biological evaluation of C-nucleoside analogues having different substituents at the base moiety [3][4][5][6]. Substitution at the base moiety by chlorine and/or fluorine atoms is of interest because of the stability of the carbon-halogen bond in biological systems [7].
Here a series of 1-aryl-6,7-dichloro-3-/3-o-erythrofuranosylpyrazolo[3,4-b]quinoxaline analogues have been prepared and their structures and anomeric configurations were determined by NMR spectroscopy and mass spectrometry.
Condensation of 4,5-dichloro-o-phenylenediamine, D-glycero-D-gulo-heptose, and the corresponding arylhydrazine derivatives (1-4) in a conventional manner [3][4][5][6], gave the corresponding acyclic C-nucleoside analogues; 1-aryl-6,7-dichloro-3-(D-arabino-tetritol-1-yl)pyrazolo [3,4-b]quinoxalines (5-8), in good yield (85-90%). The 1H NMR spectra of compounds 5-8 showed a common spectral pattern comparable to that of unsubstituted pyrazolo [3,4-b]quinoxaline analogues [8]. The polyhydroxyalkyl chain showed three doublets corresponding to three secondary hydroxyl groups and one triplet ~' Part VI; for Part V, see ref. [1].