Celebrating the golden anniversary of the discovery of bacillosamine, the diamino sugar of a Bacillus.

Bacillosamine (2,4-diamino-2,4,6-trideoxy-d-glucose, Bac), a rare amino sugar, was discovered 50 years ago as a result of the follow-up of a chance observation made during studies of polypeptide synthesis by a Bacillus subtilis strain later renamed Bacillus licheniformis. In the following decades this amino sugar was almost completely ignored, although it was found in a number of bacterial polysaccharides and other metabolites. Recently, there has been a burst of interest in Bac when it was found to be a link glycan in eubacterial glycoproteins. In this retrospective, I review the chance discovery of Bac, its structural determination and its biosynthesis.