The chemist Carl Djerassi was known for synthesizing progesterone, a female hormone in 1951 that is involved in the menstrual cycle and pregnancy, a development that formed the basis for oral contraceptives for women.

On the basis of this scientific achievement, he helped develop the birth control pill in cooperation with the Boston pharmacologists Gregory Pincus and John Rock.

Djerassi also contributed to synthesizing the steroid hormone cortisone, paving the way for new kinds of medical treatment for various diseases.

Carl Djerassi was born in Vienna in 1923. He was the son of a Jewish Austrian-Bulgarian couple, both doctors. Because of his Jewish origin he was forced to flee Austria when it was annexed by Adolf Hitler in 1938. Djerassi left for Bulgaria and then moved to the US, where he became an internationally renowned scientist and eventually professor emeritus at Stanford University.

Later in life, he also published poems, short stories, novels and plays. His first play, "An Immaculate Misconception" (1998), was translated into 12 languages and staged in the UK, the US, Germany, Austria, Japan and other countries.

As a famous art collector, Djerassi owned one of the most impressive collections of paintings by Paul Klee and gave about half of them to the Albertina museum in Vienna.

He died in San Francisco on Friday at the age of 91, according to a museum spokeswoman.

das/cmk (dpa, AFP)