Nobel medicine pioneer;

Born: June 1, 1917; Died: June 13, 2012.

William S Knowles, who has died aged 95, was a long-time chemist at biotech company Monsanto who shared the Nobel Prize in chemistry.

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He retired from Monsanto in 1986 after 44 years with the company. Fifteen years later, he and two other scientists won the Nobel Prize for work that led to discoveries used to make medicines, including antibiotics, heart drugs and widely used treatment for Parkinson's disease. Monsanto said Mr Knowles's research "changed the face of modern medicine".

He was born in Massachusetts and earned a degree in chemistry from Harvard in 1939, then a graduate degree from Columbia three years later. He joined Monsanto in 1942.

In 1968, Mr Knowles found a way to produce the helpful form of the amino acid L-dopa, which is used to treat Parkinson's. He and other researchers overcame a key problem in making drugs: the molecules of many substances used as drugs come in two forms that are mirror images of each other. Only one of these is helpful.

The three men developed chemical catalysts to produce only the useful form. The resulting batches of drug are more potent and lack the side-effects the other form of the molecule would cause.