Antivirals are antimicrobial compounds that prevent viral infections or inhibit virus replication. They are either produced by living organisms or obtained through chemical synthesis. Viruses are simple in structure, consisting of a protein coat, nucleic acid, viral enzymes, and sometimes an outer envelope made of protein and phospholipid membranes. Viruses utilize cellular machinery of hosts for replication and their lifecycle could be divided into six steps, namely viral attachment, invasion, uncoating, genome (DNA/RNA) replication, assembly, and viral progeny release. Antivirals exert antiviral activity by interfering with one or more stages of the viral lifecycle.
At the initial stage of viral infection, hydrolase neuraminidase inhibitors (such as oseltamivir, zanamivir, laninamivir, peramivir) can be used to block the initial binding of the virus to cells. After attaching to host cells, the second step is viral invasion. Enfuvirtide and its series of modified peptides are a class of fusion inhibitors designed to prevent membrane fusion. Other entry inhibitors include pleconaril against non-enveloped viruses and CC-chemokine receptor 5 (CCR5) antagonist maraviroc against retrovirus. The uncoating step during viral infection is a key antiviral target. Amantadine and rimantadine are representatives of uncoating inhibitors that specifically prevent release of influenza A virus in the cells. Both drugs prevent the release of viral RNA into the cytoplasm of the infected cells by blocking the M2 proton channel.
Proteases, polymerases, reverse transcriptase, and integrases are critical enzymes for biological processes in the life cycle of viruses. Inhibition of protease activity blocks proteolytic cleavage of protein precursors, which is necessary for the production of infectious particles. Protease inhibitors share relative similarity in chemical structures, including nelfinavir, amprenavir, fosamprenavir, darunavir, saquinavir, atazanavir, indinavir, lopinavir, etc. Viral DNA and RNA polymerases are responsible for the replication and transcription of genetic materials. DNA polymerase inhibitors include acyclovir, valacyclovir, penciclovir, famciclovir, ganciclovir, valganciclovir, and so on. Viral RNA polymerase inhibitors are represented by ribavirin. Ribavirin is a broad-spectrum antiviral nucleoside that inhibits guanosine triphosphate formation and prevents viral mRNA capping. In addition, ribavirin is utilized by viral RNA-dependent RNA polymerase to cause lethal mutagenesis of the viral genome. Reverse transcriptase is an RNA-dependent DNA polymerase that used by viruses such as HIV and hepatitis B to replicate their genomes. Reverse transcriptase inhibitors are analogues of endogenous nucleosides and nucleotides, such as azidothymidine, lamivudine, cidofovir, adefovir, and tenofovir. Integrases catalyze the integration of viral DNA into the host cell genome, a critical step in viral replication. Raltegravir and elvitegravir are first-generation integrase inhibitors and dolutegravir is the second-generation integrase inhibitor.
There are many species of viruses and existing antivirals are selective toxicity against viruses. Amerigo Scientific offers a wide range of compounds against virus families such as retrovirus, herpes virus, influenza, and hepatitis.