Breakly

https://www.ebi.ac.uk/chebi/searchId.do?chebiId=CHEBI:119915
http://www.hmdb.ca/metabolites/HMDB0014951
http://www.genome.jp/dbget-bin/www_bget?drug:D00320
https://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=3345
https://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?sid=46506372
https://www.chemspider.com/Chemical-Structure.3228.html
http://www.bindingdb.org/bind/chemsearch/marvin/MolStructure.jsp?monomerid=50008984
https://mor.nlm.nih.gov/RxNav/search?searchBy=RXCUI&searchTerm=4337
https://www.ebi.ac.uk/chebi/searchId.do?chebiId=119915
https://www.ebi.ac.uk/chembldb/index.php/compound/inspect/CHEMBL596
https://zinc.docking.org/substances/ZINC000002522669
http://bidd.nus.edu.sg/group/cjttd/ZFTTDDRUG.asp?ID=DAP000072
http://www.pharmgkb.org/drug/PA449599
http://www.guidetopharmacology.org/GRAC/LigandDisplayForward?ligandId=1626
https://www.ebi.ac.uk/pdbe-srv/pdbechem/chemicalCompound/show/7V7
http://www.rxlist.com/cgi/generic2/fentanyl.htm
https://www.drugs.com/fentanyl.html
https://en.wikipedia.org/wiki/Fentanyl