Miniblock

https://www.ebi.ac.uk/chebi/searchId.do?chebiId=CHEBI:4856
http://www.hmdb.ca/metabolites/HMDB0014333
http://www.genome.jp/dbget-bin/www_bget?drug:D07916
http://www.genome.jp/dbget-bin/www_bget?cpd:C06980
https://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=59768
https://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?sid=46506146
https://www.chemspider.com/Chemical-Structure.53916.html
http://www.bindingdb.org/bind/chemsearch/marvin/MolStructure.jsp?monomerid=50404796
https://mor.nlm.nih.gov/RxNav/search?searchBy=RXCUI&searchTerm=49737
https://www.ebi.ac.uk/chebi/searchId.do?chebiId=88206
https://www.ebi.ac.uk/chembldb/index.php/compound/inspect/CHEMBL768
http://bidd.nus.edu.sg/group/cjttd/ZFTTDDRUG.asp?ID=DAP000304
http://www.pharmgkb.org/drug/PA449500
http://www.rxlist.com/cgi/generic3/esmolol.htm
https://www.drugs.com/cdi/esmolol.html
https://en.wikipedia.org/wiki/Esmolol