Neosalvarsan is a synthetic chemotherapeutic that is an organoarsenic compound

Organoarsenic compound

Organoarsenic chemistry is the chemistry of compounds containing a chemical bond between arsenic and carbon. A few organoarsenic compounds, also called "organoarsenicals," are produced industrially with uses as insecticides, herbicides, and fungicides. In general these applications are declining in...

. It became available in 1912 and superseded the more toxic and less water-soluble salvarsan as an effective treatment for syphilis

Syphilis

Syphilis is a sexually transmitted infection caused by the spirochete bacterium Treponema pallidum subspecies pallidum. The primary route of transmission is through sexual contact; however, it may also be transmitted from mother to fetus during pregnancy or at birth, resulting in congenital syphilis...

. Because both of these arsenicals carried considerable risk of side effects, they were replaced for this indication by penicillin

Penicillin

Penicillin is a group of antibiotics derived from Penicillium fungi. They include penicillin G, procaine penicillin, benzathine penicillin, and penicillin V....

 in the 1940s.

Both salvarsan and neosalvarsan were developed in the laboratory of Paul Ehrlich

Paul Ehrlich

Paul Ehrlich was a German scientist in the fields of hematology, immunology, and chemotherapy, and Nobel laureate. He is noted for curing syphilis and for his research in autoimmunity, calling it "horror autotoxicus"...

 in Frankfurt

Frankfurt

Frankfurt am Main , commonly known simply as Frankfurt, is the largest city in the German state of Hesse and the fifth-largest city in Germany, with a 2010 population of 688,249. The urban area had an estimated population of 2,300,000 in 2010...

, Germany

Germany

Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...

. Their discoveries were the result of the first organized team effort to optimize the biological activity of a lead compound

Lead compound

A lead compound in drug discovery is a chemical compound that has pharmacological or biological activity and whose chemical structure is used as a starting point for chemical modifications in order to improve potency, selectivity, or pharmacokinetic parameters.Lead compounds are often found in...

 through systematic chemical modifications. This scheme is the basis for most modern pharmaceutical research. Both salvarsan and neosalvarsan are prodrug

Prodrug

A prodrug is a pharmacological substance administered in an inactive form. Once administered, the prodrug is metabolised in vivo into an active metabolite, a process termed bioactivation. The rationale behind the use of a prodrug is generally for absorption, distribution, metabolism, and...

s — that is, they are metabolised

Metabolism

Metabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...

 into the active drug in the body.

Structure

The structure of salvarsan, and of 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

Trimer (chemistry)

In chemistry, a trimer is a product derived from three identical precursors. Trimers are typically cyclic. Chemical compounds that often trimerise are aliphatic isocyanates and cyanic acids. Often, trimerization competes with polymerization....

 and a pentamer

Pentamer

A pentamer is a thing composed out of five sub-units.In chemistry, it applies to molecules made of five monomers.In biochemistry, it applies to macromolecules, in particular to pentameric proteins, made of five proteic sub-units....

. The revised structure features As-As single bonds, not double bonds.