Bacimethrin (1), known as a thiamine antagonist produced by Bacillus megatherium, was isolated from Streptomyces albus and has been further characterized by NMR spectra and acetylation. A new easy three step synthesis for 1 is described. The biological activity of 1, and its mode of action were discussed. There are indications that bacimethrin inhibits the phosphorylation of 4-amino-5-hydroxymethyl-2-methylpyrimidine (Pyr-OH) during thiamine biosynthesis.