Megalomycin C, a macrolide antibiotic that blocks protein glycosylation and shows antiviral activity.

Megalomycin C, a natural macrolide antibiotic showed a potent antiherpetic activity. At concentrations that efficiently prevented HSV-1 multiplication, the compound had no cytotoxic or antiproliferative effects. Viral DNA and protein synthesis took place at normal levels in the presence of the antibiotic, suggesting that neither the translation of viral mRNA, nor the synthesis of viral nucleic acids was affected. The incorporation of mannose and galactosamine into viral proteins was blocked and precursor, but not mature, HSV-1 glycoproteins were detected in the presence of megalomycin C. Non-infectious HSV-1 viral particles were formed when the compound was present, but their glycoproteins were not properly glycosylated.