Although the initial synthesis developed by Sheehan was not appropriate for mass production of penicillins, one of the intermediate compounds in Sheehan's synthesis was 6-aminopenicillanic acid (6-APA), the nucleus of penicillin.
While Sheehan's original method for synthesizing penicillin wasn't practical for large-scale production, a key intermediate compound from his process was 6-aminopenicillanic acid (6-APA), the fundamental building block of penicillin.