beta.-Lactam antibiotics: geometrical requirements for antibacterial activities

Recent observations reveal deficiencies in the accepted theory rationalizing the biological activities of the beta-lactam antibiotics, since a study of strained carbapenem beta-lactams has shown that the observed antibacterial activities do not correlate either with the pyramidal character of the beta-lactam nitrogen atom or with the ease of base hydrolysis of the lactam amide bond. The contradiction can be reconciled by an analysis of the three-dimensional (3-D) features of a set of the representative active and inactive beta-lactam structures, which shows that highly specific 3-D recognition sites may exist in the enzymes in their recognition of the antibiotics. The identification of the geometrical requirements for antibacterial activity also reveals how it could be possible to restore antibiotic activities to inactive structures, up to now considered as devoid of any therapeutic interest.