Noun
isopenicillin (countable and uncountable, plural isopenicillins)
A cyclic isomer of penicillin
ACV is oxidatively cyclized (two cyclizations by a single enzyme) to bicyclic intermediate isopenicillin N by isopenicillin N synthase (IPNS) to form the penam core structure. citation Various transamidations lead to the different natural penicillins. Source: Internet
The biosynthesis of cephems branch off at isopenicillin N by an oxidative ring expansion to the cephem core. Source: Internet