Synthesis, Cytotoxicity, and Mechanistic Evaluation of 7‐Deazapurine‐Based Neplanocin Analogues as Selective Anti‐HBV Agents

Abstract Nucleobase modifications offer a promising route for the discovery of novel antiviral compounds. The synthetic entry of 7 H ‐pyrrolo[2,3‐ d ]pyrimidine with alterations at the 4‐position has been thoroughly investigated in the search for bioactive Neplanocin analogs. A key intermediate ( 4 ) was synthesized and explored to yield a series of modified carbo‐nucleosides ( 3a – i ). Modified 7‐deazapurine has been installed to get the targeted 7‐deaza carbocyclic nucleosides with an alkyl or aryl. This was accomplished by Pd‐cross‐coupling reactions with alkyl or aryl organometallics/aryl boronic acids on 7‐deazapurines, followed by Mitsunobu coupling and deprotection to produce the final molecules ( 3a – i ). In HBV replication, the anti‐HBV activity of 3a – i was evaluated in HepG2.2.15.7 cells. Compounds 3a , 3c , 3d , 3f , 3 g , and 3i showed promise as lead compounds by exhibiting micromolar‐level activity on the HBV replicon. The tested compounds demonstrated a dose‐dependent inhibition of HBV replication, as demonstrated by the reduced secretion of HBsAg in HepG2.2.15.7 cells, in contrast to the currently approved nucleoside analogue, entecavir (ETV). These findings suggest that the mechanism of action of these analogues is distinct and likely resembles that of previously reported neplanocin derivatives (I & II), which promote the degradation of pregenomic RNA (pgRNA) via a novel pathway. Importantly, S ‐adenosylhomocysteine hydrolase (SAHase) does not appear to be involved in their antiviral activity, highlighting a unique mechanism for these neplanocin analogues in suppressing HBV replication.