Amoxicillin EP Impurity A Catalogue A536301 CAS 551-16-6 M.W 216.26 M.F C8H12N2O3S Specifications FAQs (2S,5R,6R)-6-Amino-3,3-dimethyl-7-oxo-4-thia-1-azabicyclo[3.2.0]heptane-2-carboxylic acid