A wide range of natural purine analogues was used as probe to assess the mechanism of recognition by the wild-type (WT) E. coli purine nucleoside phosphorylase (PNP) versus its Ser90Ala mutant. The results were analyzed from viewpoint of the role of the Ser90 residue and the structural features of the bases. It was found that the Ser90 residue of the PNP 1) plays an important role in the binding and activation of 8-aza-7-deazapurines in the synthesis of their nucleosides, 2) participates in the binding of α-D-pentofuranose-1-phosphates at the catalytic site of the PNP, and 3) catalyzes the dephosphorylation of intermediary formed 2-deoxy-α-D-ribofuranose-1-phosphate in the trans-2-deoxyribosylation reaction. 5-Aza-7-deazaguanine manifested excellent substrate activity for both enzymes, 8-amino-7-thiaguanine and 2-aminobenzothiazole showed no substrate activity for both enzymes. On the contrary, the 2-amino derivatives of benzimidazole and benzoxazole are substrates and are converted into the N1- and unusual N2-glycosides, respectively. 9-Deaza-5-iodoxanthine showed moderate inhibitory activity of the WT E. coli PNP, whereas 9-deazaxanthine and its 2'-deoxyriboside are weak inhibitors.
A series of 5,6-disubstituted benzimidazole nucleosides, obtained earlier, did not show any significant antiviral activity at relatively low cytotoxicity in vitro. In the course of our research we have succeeded in introducing an additional fluorine atom into the benzimidazole ring system. A new series of 4,6-difluorobenzimidazoles, bearing various groups (fluoro-, methoxy-, ethoxy-, morpholino-, and pyrrolidino-) in the 5-position of the benzene ring, have been synthesized. All these compounds proved to be substrates for recombinant E. coli purine nucleoside phosphorylase (PNP) in the transglycosylation reaction. Effective methods for the synthesis of ribo-and 2′-deoxyribonucleosides with high yields (60-90%) have been described, and the formation of regioisomeric N3-nucleosides of benzimidazoles have been detected. The biological activity of the nucleosides obtained against herpes simplex virus type 1 (HSV-1) has been elucidated. All compounds show a low cytotoxicity in the cell culture Vero E6. 4,5,6-Trifluoro-1-(β-D-ribofuranosyl)benzimidazole and 5-methoxy-4,6-difluoro-1-(β-D-2′-deoxyribofuranosyl)benzimidazole proved to inhibit completely the progression of the virus cytopathic effect (CPE) at a multiplicity of infection (MOI) of 0.01 PFU/cell.
Nucleoside analogues have long served as key chemotherapeutic drugs for treatment of viral infections and cancers. Problems associated with the development of drug resistance has led to a search for...
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