Arsphenamine

Arsphenamine, also known as Salvarsan or compound 606, is a drug. It was introduced at the beginning of the 1910s. It was the first effective treatment for syphilis and African trypanosomiasis. This organoarsenic compound was the first modern antimicrobial {antibiotic} agent.
Arsphenamine was first synthesized in 1907 in Paul Ehrlich's lab by Alfred Bertheim. 
The antisyphilitic activity of this compound was discovered by Sahachiro Hata in 1909. He surveyed hundreds of newly synthesized organic arsenical compounds. Ehrlich thought that by screening many compounds, a drug could be discovered which would have anti-microbial activity but not kill the patient.
Ehrlich's laboratory developed a more soluble (but slightly less effective) arsenical compound, Neosalvarsan (neoarsphenamine), which was easier to prepare.