BH4

https://www.ebi.ac.uk/chebi/searchId.do?chebiId=CHEBI:59560
http://www.genome.jp/dbget-bin/www_bget?cpd:C00272
http://www.hmdb.ca/metabolites/HMDB0059658
http://www.genome.jp/dbget-bin/www_bget?drug:D08505
http://www.genome.jp/dbget-bin/www_bget?cpd:C00272
https://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=44257
https://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?sid=46508597
https://www.chemspider.com/Chemical-Structure.40270.html
http://www.bindingdb.org/bind/chemsearch/marvin/MolStructure.jsp?monomerid=50373697
https://mor.nlm.nih.gov/RxNav/search?searchBy=RXCUI&searchTerm=753340
https://www.ebi.ac.uk/chebi/searchId.do?chebiId=59560
https://www.ebi.ac.uk/chembldb/index.php/compound/inspect/CHEMBL1201774
https://zinc.docking.org/substances/ZINC000013585233
http://bidd.nus.edu.sg/group/cjttd/ZFTTDDRUG.asp?ID=DNC000425
http://www.pharmgkb.org/drug/PA161990676
https://www.ebi.ac.uk/pdbe-srv/pdbechem/chemicalCompound/show/H4B
https://en.wikipedia.org/wiki/Tetrahydrobiopterin