1. This work is based in part on the Ph.D. thesis of Monika Konaklieva (State University of New York at Buffalo, 1997). Present address: Department of Chemistry, American University, 4400 Massachusetts Avenue, N.W., Washington, DC 20016, USA.
2. This work is based in part on the Ph.D. thesis of Rex X.-F. Ren (State University of New York at Buffalo, 1995). Present address: Department of Chemistry, Wesleyan University, Middletown, CT 06457, USA.
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5. Mechanism of action of penicillins: a proposal based on their structural similarity to acyl-D-alanyl-D-alanine.