Number of chiral centers in penicillin V I have often seen that in many drugs chirality plays a role. So I was trying to analyze the structure of Penicillin V.

What is number of chiral centers in the structure of penicillin V? Is the nitrogen which is  a part of the four membered ring to be counted here because I have read that the nitrogen atom without pyramidal inversion is treated as chiral. So can the nitrogen at bridgehead position be treated as chiral? Because that makes the stereocenter count 4 while on pubchem website the count is mentioned  to be 3.
Yes, here Nitrogen has to be considered as a stereocenter. Also, you can assign R and S to it. The rule is that the lone pair has the least priority and then you can assign R and S as you do for other molecules.