STOCKHOLM (AP) — Three scientists from the United States and Denmark were jointly awarded this year’s Nobel Prize in chemistry for developing a way of “snapping molecules together” that can be used to design better medicines.

K. Barry Sharpless, Carolyn R. Bertozzi and Morten Meldal and were cited for their work on click chemistry and bioorthogonal reactions, which are used to make cancer drugs, map DNA and create materials that are tailored to a specific purpose.

Sharpless, from Scripps Research in La Jolla, previously won a Nobel Prize in 2001 and is now the fifth person to receive the award twice. He first proposed the idea for connecting molecules using chemical “buckles” around the turn of the millennium, said Aqvist.

“The problem was to find good chemical buckles,” he said. “They have to react with each other easily and specifically.”

“Barry Sharpless has had a tremendous impact on chemistry, first with his development of asymmetric synthesis and now with his elegant ‘click chemistry,’” said a quote attributed to Peter Schultz, PhD, President and CEO of Scripps Research. “His work opened whole new scientific frontiers that have had a major impact on the fields of chemistry, biology and medicine. Barry has a remarkable combination of chemical insight, uncanny intuition and real-world practicality—he is a chemist’s chemist and a wonderful colleague.”

“It’s all about snapping molecules together,” said Johan Aqvist, a member of the Royal Swedish Academy of Sciences that announced the winners Wednesday at the Karolinska Institute in Stockholm, Sweden.

Meldal, based at the University of Copenhagen, Denmark, and Sharpless, who is affiliated with Scripps Research, California, independently found the first such candidates that would easily snap together with each other but not with other molecules, leading to applications in the manufacture of medicines and polymers.

Bertozzi, who is based at Stanford University in California, “took click chemistry to a new level,” the Nobel panel said.

She found a way to make click chemistry work inside living organisms without disrupting them, establishing a new method known as bioorthogonal reactions. Such reactions are now used to explore cells, track biological processes and design experimental cancer drugs that work in a more targeted fashion.

Bertozzi said she was “absolutely stunned” to receive the prize.

“I’m still not entirely positive that it’s real, but it’s getting realer by the minute,” she said.

Last year the prize was awarded to scientists Benjamin List and David W.C. MacMillan for finding an ingenious and environmentally cleaner way to build molecules that the Nobel panel said is “already benefiting humankind greatly.”

A week of Nobel Prize announcements kicked off Monday with Swedish scientist Svante Paabo receiving the award in medicine for unlocking secrets of Neanderthal DNA that provided key insights into our immune system.

Three scientists jointly won the prize in physics Tuesday. Frenchman Alain Aspect, American John F. Clauser and Austrian Anton Zeilinger had shown that tiny particles can retain a connection with each other even when separated, a phenomenon known as quantum entanglement, that can be used for specialized computing and to encrypt information.

The awards continue with literature on Thursday. The 2022 Nobel Peace Prize will be announced on Friday and the economics award on Monday.

The prizes carry a cash award of 10 million Swedish kronor (nearly $900,000) and will be handed out on Dec. 10. The money comes from a bequest left by the prize’s creator, Swedish inventor Alfred Nobel, in 1895.