Abstract

In this chapter, we reviewed the antiviral activity of natural and synthetic brassinosteroids (BRs). Brassinolide and other natural BRs such as 28-homocastasterone present a broad antiviral spectrum against RNA and DNA viruses. Since the concentration of BRs in the plant tissue is very low, isolation of these compounds from plant sources is impractical, and they had to be obtained by chemical synthesis. The antiviral activity of a group of synthetic analogues against Herpes Simplex Type 1 and 2 (HSV-1 and HSV-2), Measles (MV), Vesicular Stomatitis Virus (VSV), Polio Virus (PV) and Arena Viruses was also determined. Several of the tested compounds showed selectivity indexes 10- to 18- fold higher than ribavirin, a broad spectrum antiviral compound, for Junín Virus (JUNV), a moderate activity against HSV-1 / HSV-2 and good anti-MV, anti-PV and anti-VSV activity, with antiviral selectivity Index (SI) values also higher than ribavirin, a reference drug. Structure activity relationship Studies were performed in order to determine which stereochemistry, type and position of functional groups are needed to develop a potent and selective class of viral inhibitors. The antiviral mode of action of the BRs against HSV, JUNV and VSV was also investigated. For all assayed viruses, the antiviral compounds adversely affect virus protein synthesis and mature viral particle formation.