Stereoselective Synthesis of Trisubstituted Vinyl Bromides by Addition of Alkynes to Oxocarbenium Ions.

We have developed an efficient method for the synthesis of (E)-trisubstituted vinyl bromides via a Friedel-Crafts-type addition of alkynes to oxocarbenium ions formed in situ from acetals. The success of this reaction relies on identification of MgBr·OEt as both a Lewis acid promoter and bromide source. This reaction employs simple, inexpensive starting materials and proceeds under mild conditions to allow the preparation of a range of vinyl bromide products in high yields and E:Z selectivities.

Variations in expression and release of botulinum neurotoxin in Clostridium botulinum type A strains.

In this study, we characterized the production and release of botulinum neurotoxin during growth of two Clostridium botulinum strains, Hall A and NCTC2916, of distinct gene organizations. The intra- and extracellular fractions of the bacterial cells harvested at various stages of growth were analyzed for the neurotoxin. Both strains exhibited a temporal neurotoxin gene expression; however, these two strains differ in their patterns of growth, toxin production, toxin release, and post-translational nicking.