6-beta(substituted)-(S)-hydroxymethylpenicillanic acids and derivatives thereof
 Antibacterial penicillins of the formula ##STR1## or a pharmaceutically acceptable salt thereof wherein R.sup.1 is a heterocyclic group and R is hydrogen, the residue of certian carboxy protecting groups or the residue of an ester group readily hydrolyzable in vivo having activity against resistant organisms. 
Pfizer Inc.
Y C
Y02P C07D
additional inventional
Yuhpyng L.
Chen