Sapropterin, also known as (6R)-5,6,7,8-tetrahydrobiopterin, is a drug used to reduce the symptoms of phenylketonuria (PKU), a genetic disorder that affects how the body processes protein. Here is a timeline of sapropterin's discovery based on the available information:

1. In the 1950s, scientists discovered the enzyme phenylalanine hydroxylase (PAH), which is responsible for breaking down the amino acid phenylalanine in the body [3].
2. In the 1960s, it was discovered that individuals with PKU have a deficiency in PAH, leading to a buildup of phenylalanine in the body and causing various neurological symptoms [3].
3. In the 1970s, researchers identified tetrahydrobiopterin (BH4) as a cofactor for PAH, meaning that it is necessary for the enzyme to function properly [1][3].
4. In the 1980s, it was discovered that BH4 supplementation could improve PAH activity in individuals with PKU [3].
5. In the 1990s, sapropterin, a synthetic form of BH4, was developed and tested in clinical trials [1][3].
6. In 2005, sapropterin was approved by the FDA for use in individuals with PKU [1][3].
7. In 2007, the patent for sapropterin expired, allowing for generic versions of the drug to be produced [1].

Sources:
[1] <https://www.drugpatentwatch.com/p/tradename/SAPROPTERIN>
[2] <https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4354801/>
[3] <https://en.wikipedia.org/wiki/Tetrahydrobiopterin>