ABSTRACT
Synthesis of a novel 2'-deoxy-guanine carbocyclic nucleoside 4 constructed with spiro[2.4]heptane core structure in the aglycon moiety was carried out. Radical-mediated 5-exo-dig mode cyclization and following cyclopropanation proceeded efficiently to furnish the spiro alcohol 10. Subsequent Mitsunobu-type glycosylation between 13 and 14, deoxygenation of the 2'-hydroxyl group of 16 and deprotection of 17 gave the title compound 4. Compound 4 demonstrated moderate anti-HBV activity (EC50 value of 0.12 ± 0.02 µM) and no cytotoxicity against HepG2 cells was observed up to 100 µM.
Subject(s)
Antiviral Agents/chemistry , Antiviral Agents/pharmacology , Guanine/analogs & derivatives , Hepatitis B virus/drug effects , Heptanes/chemistry , Antiviral Agents/chemical synthesis , Chemistry Techniques, Synthetic , Guanine/chemical synthesis , Guanine/chemistry , Guanine/pharmacology , Structure-Activity RelationshipABSTRACT
A method for the diastereoselective synthesis of 6â³-(Z)- and 6â³-(E)-fluorinated analogues of the anti-HBV agent entecavir has been developed. Construction of the methylenecyclopentane skeleton of the target molecules has been accomplished by radical-mediated 5-exo-dig cyclization of the selenides 6 and 15 having the phenylsulfanylethynyl structure as a radical accepting moiety. In the radical reaction of the TBS-protected precursor 6, (Z)-anti-12 was formed as a major product. On the other hand, TIPS-protected 15 gave (E)-anti-12. The sulfur-extrusive stannylation of anti-12 furnished a mixture of geometric isomers of the respective vinylstannane, whereas benzoyl-protected 17 underwent the stannylation in the manner of retention of configuration. Following XeF2-mediated fluorination, introduction of the purine base and deoxygenation of the resulting carbocyclic guanosine gave the target (E)- and (Z)-3 after deprotection. Evaluation of the anti-HBV activity of 3 revealed that fluorine-substitution at the 6â³-position of entecavir gave rise to a reduction in the cytotoxicity in HepG2 cells with retention of the antiviral activity.
