# Natural Alkaloids as Antiviral Agents Against RNA Viruses: A Comprehensive and Mechanistic Review

## TL;DR

This paper reviews how natural alkaloids can act as antiviral agents against RNA viruses like influenza and coronaviruses by targeting various stages of the viral life cycle.

## Contribution

The paper provides a comprehensive and mechanistic review of alkaloids with antiviral activity against RNA viruses, distinguishing in vitro, in vivo, and in silico evidence.

## Key findings

- Alkaloids interfere with multiple stages of RNA virus life cycles, including entry, replication, and immune modulation.
- Quaternary alkaloids have unique interactions due to their ionic charge, affecting membranes and host pathways.
- Clinical translation of alkaloids is limited by incomplete mechanistic validation and poor bioavailability.

## Abstract

RNA viruses pose a persistent global threat due to their high mutation rates, zoonotic potential, and rapid adaptability. Emergence events have risen steadily, as demonstrated by major outbreaks caused by Influenza A, Ebola, Zika, and Chikungunya viruses, followed by the coronavirus epidemics of Severe Acute Respiratory Syndrome coronavirus (SARS-CoV-1) and Middle East Respiratory Syndrome Coronavirus (MERS-CoV) and culminating in the COVID-19 pandemic. These characteristics frequently compromise the durability of existing vaccines and antiviral therapies, highlighting the urgent need for new antiviral agents. Alkaloids, a structurally diverse class of nitrogen-containing natural compounds, have gained attention for their ability to interfere with multiple stages of the viral life cycle, including entry, replication, protein synthesis, and host immune modulation. To our knowledge, this review compiles all currently reported alkaloids with antiviral activity against RNA viruses and summarizes their proposed mechanisms of action, distinguishing evidence from in vitro, in vivo, and in silico studies. Quaternary alkaloids are discussed separately because their permanent ionic charge enables distinctive interactions with membranes and host pathways. Although many findings are promising, clinical translation remains limited by incomplete mechanistic validation, scarce in vivo data, suboptimal bioavailability, narrow therapeutic windows, and inconsistent experimental methodologies. To advance the field, future research should prioritize RT-qPCR–based antiviral evaluation to accurately quantify viral replication, incorporate mechanistic assays to clarify modes of action, apply structure–activity relationship (SAR) approaches for rational optimization, and expand in vivo pharmacokinetic and efficacy studies to assess therapeutic feasibility. Overall, alkaloids represent a promising yet underdeveloped reservoir for next-generation antiviral discovery against rapidly evolving RNA viruses.