Nomenclature of amoxicillin I am trying to understand the nomenclature of amoxicillin:



The IUPAC name that Wikipedia has given is (2S,5R,6R)-6-{[(2R)-2-amino-2-(4-hydroxyphenyl)-acetyl]amino}-3,3-dimethyl-7-oxo-4-thia-1-azabicyclo[3.2.0]heptane-24-carboxylic acid.

I think I understand most of it but I have two problems:


Why is there a 24 before the carboxylic acid? 
There is a $\ce{C=O}$ group between two nitrogens that doesn't appear in the name. I was expecting an amide, rather than amino or oxo.
To preface this, I'm not sure if this is indeed the correct IUPAC name as per the latest 2013 recommendations. It might well be, but I don't know. However, that's not crucial to your question, which is more about understanding the name that is given on Wikipedia. Here's the structure of amoxicillin:



The amide C=O is in "acetyl", which refers to the $\ce{CH3C(=O)}$ group (see e.g. acetyl chloride, $\ce{CH3COCl}$):



The '24' is probably a typo and should instead be '2'.



Following this numbering scheme you can see that the lactam C=O is in '-7-oxo'.