[{"from": "human", "value": "Could you give me a brief overview of this molecule? [C][=C][C@H1][Branch1][O][C][C@@H1][Branch1][=Branch1][C@H1][Ring1][Branch1][C][O][O][N][C][=N][C][=C][Ring1][Branch1][N][=C][Branch1][=Branch1][N][C][Ring1][=Branch1][=O][N]"}, {"from": "gpt", "value": "The molecule is guanine substituted at the 9 position by a 4-hydroxy-3-(hydroxymethyl)-2-methylidenecyclopentyl group. A synthetic analogue of 2'-deoxyguanosine, it is a nucleoside reverse transcriptase inhibitor with selective antiviral activity against hepatitis B virus. Entecavir is phosphorylated intracellularly to the active triphosphate form, which competes with deoxyguanosine triphosphate, the natural substrate of hepatitis B virus reverse transcriptase, inhibiting every stage of the enzyme's activity, although it has no activity against HIV. It is used for the treatment of chronic hepatitis B. It has a role as an EC 2.7.7.49 (RNA-directed DNA polymerase) inhibitor and an antiviral drug. It is a member of 2-aminopurines, an oxopurine, a primary alcohol and a secondary alcohol."}]