Electrostatic and structural similarity of classical and non-classical lactam compounds

Experimental and Theoretical Studies on the Reactions of Aliphatic Imines with Isocyanates

In the context of a project aiming at the replacement of the 3-substituted β-lactam ring in classical β-lactam antibiotics by an N(3)-acyl-1,3-diazetidinone moiety, we have investigated the reaction of isocyanates with imines derived from allyl glycinate and differently substituted propionaldehydes. Imines of aromatic aldehydes with anilines have been reported to react with acyl isocyanates to give 1,3-diazetidinones or 2,3-dihydro-4H-1,3,5-oxadiazin-4-ones, via [2+2] or [4+2] cycloaddition, respectively. However, neither of these products was formed with imines derived from allyl glycinate and 2-(mono)methyl propionaldehydes. α,α-Dimethylation of the imine enabled the [4+2] cycloaddition pathway, but the desired 1,3-diazetidinone products were not observed. Surprisingly, the imines obtained from thioesters of 2,2-dimethyl 3-oxo propionic acid reacted with aryl isocyanates or with benzyl isocyanate to give 5,5-dimethyl-2,4-dioxo-6-(aryl-/alkylthio)tetrahydropyrimidines, via thiol displacement and re-addition to a putative six-membered iminium intermediate. These experimental results obtained for the reactions could be rationalized by DFT calculations. In addition, we have shown that N(3)-acyl-1,3-diazetidinone and 2,3-dihydro-4H-1,3,5-oxadiazin-4-one products can be distinguished based on experimental IR data in combination with theoretical reference spectra employing the IR spectra alignment (IRSA) algorithm. This discrimination was not possible by means of 1 H, 13 C, or 15 N NMR spectroscopy.

Molecular Modeling and Chemical Reactivity of Sanfetrinem and Derivatives

The indiscriminate use of beta-lactams has considerably diminished their efficiency as a result of bacteria developing effective defense mechanisms against them. Recent pharmaceutical research has led to the synthesis of tricyclic beta-lactam antibiotics known as "tricyclic carbapenems" or "trinems". In this work, we studied the chemical reactivity, an essential property for antibiotic action, of trinems and found it to be similar to that of cephalosporins. Also, we elucidated the interaction pattern for sanfetrinem and 4beta-methoxy trinem and compared it to that for classical beta-lactams. The behavior of both trinems was found to be similar to that of penicillin G toward Staphylococcus aureus PC1, and that of cephalothin and imipenem toward Enterobacter cloacae P99.