has role is protonated form of is tautomer of has functional parent 6-aminopenicillanic acid A penicillanic acid compound having a (6<i>R</i>)-amino substituent. The active nucleus common to all penicillins, it may be substituted at the 6-amino position to form the semisynthetic penicillins, resulting in a variety of antibacterial and pharmacologic characteristics. penicillanic acids 6-aminopenicillanate penicillanic acid allergen 6-aminopenicillanic acid zwitterion