4-27-00-05887 (Beilstein Handbook Reference) 4-Thia-1-azabicyclo(3.2.0)heptane-2-carboxylic acid, 3,3-dimethyl-7-oxo-6-(butylthioacetamido)- 6192-29-6 BRN 0044346 Butylmercaptomethylpenicillin Penicillin BT n-Butylthiomethylpenicillin