retarpen

https://www.ebi.ac.uk/chebi/searchId.do?chebiId=CHEBI:18208
http://www.genome.jp/dbget-bin/www_bget?cpd:C05551
http://www.hmdb.ca/metabolites/HMDB0015186
http://www.genome.jp/dbget-bin/www_bget?drug:D02336
http://www.genome.jp/dbget-bin/www_bget?cpd:C05551
https://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=5904
https://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?sid=46506778
https://www.chemspider.com/Chemical-Structure.5693.html
http://www.bindingdb.org/bind/chemsearch/marvin/MolStructure.jsp?monomerid=50022787
https://mor.nlm.nih.gov/RxNav/search?searchBy=RXCUI&searchTerm=7980
https://www.ebi.ac.uk/chebi/searchId.do?chebiId=18208
https://www.ebi.ac.uk/chembldb/index.php/compound/inspect/CHEMBL29
https://zinc.docking.org/substances/ZINC000003871701
http://bidd.nus.edu.sg/group/cjttd/ZFTTDDRUG.asp?ID=DNC001109
http://www.pharmgkb.org/drug/PA450842
https://www.ebi.ac.uk/pdbe-srv/pdbechem/chemicalCompound/show/PNN
http://www.rxlist.com/cgi/generic3/pengk.htm
https://en.wikipedia.org/wiki/Benzylpenicillin