Neosalvarsan

Neosalvarsan is a synthetic antibiotic that is an organoarsenic compound. It became available in 1912 and superseded the more toxic and less water-soluble salvarsan as an effective treatment for syphilis. Because both of these arsenicals carried considerable risk of side-effects, they were replaced for this indication by penicillin in the 1940s.

Both salvarsan and neosalvarsan were developed in the laboratory of Paul Ehrlich in Frankfurt, Germany. Their discoveries were the result of the first organized team effort to optimize the biological activity of a lead compound through systematic chemical modifications. This scheme is the basis for most modern pharmaceutical research. Both salvarsan and neosalvarsan are prodrugs, that is to say that they are metabolised to the active drug in the body.

Structure
The structure of Salvarsan and, presumably this derivative, was once believed to feature an As=As bond as shown in the figure.. In 2005, Salvarsan was shown to be a mixture of the cyclic trimer and a pentamer. The revised structure features As-As single bonds, not double bonds.