A series of structurally related antiviral antibiotics, fluvirucins A1, A2, B1, B2, B3, B4 and B5 have been isolated from the fermentation broths of five unidentified actinomycete isolates. Based on spectroscopic analysis, partial degradation experiments and 13C-enriched acetic acid-fed biosynthetic studies, their structures were elucidated to be 2.6,10-trialkyl-3(or 9)-aminoglycosyl-13-tridecanelactams.