Metallo-β-lactamases hydrolyze most β-lactam antibiotics. The lack of a successful inhibitor for them is related to the previous failure to characterize a reaction intermediate with a clinically useful substrate. Stopped-flow experiments together with rapid freeze-quench EPR and Raman spectroscopies were used to characterize the reaction of Co(II)-BcII with imipenem. These studies show that Co(II)-BcII is able to hydrolyze imipenem both in the mono- and dinuclear forms. In contrast to the situation met for penicillin, the species that accumulates during turnover is an enzyme-intermediate adduct in which the β-lactam bond has already been cleaved. This intermediate is a metal-bound anionic species, with a novel resonant structure, that is stabilized by the metal ion at the DCH or Zn2 site. This species has been characterized based on its spectroscopic features. This represents a novel, previously unforeseen intermediate, that is related to the chemical nature of carbapenems, as confirmed by the finding of a similar intermediate for meropenem. Since carbapenems are the only substrates cleaved by B1, B2 and B3 lactamases, the identification of this intermediate could be exploited as a first step towards the design of transition state based inhibitors for all three classes of metallo-β-lactamases.

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[reaction: see text] An efficient cross-metathesis on solid support for the synthesis of beta-lactam analogues of cholesterol absorption inhibitors is described. The applied strategy allows the introduction of diversity in positions 3 and 4 of the beta-lactam ring with excellent 3,4-trans selectivity and complete E selectivity at the C-3 side chain.

We have prepared immobilized olefins as models for the cross metathesis using different olefin partners in the presence of second generation Grubbs and Hoveyda-Grubbs precatalysts. We have demonstrated that solid-phase cross metathesis is strongly dependent on the degree of homodimerization of the non-immobilized olefin and the reactivity of such a homodimer. As in the homogeneous phase, the Hoveyda-Grubbs precatalyst was better for immobilized alpha,beta-unsaturated carbonyl compounds.

An efficient and high-yielding "hydrogen-free" reduction of α,β-unsaturated alkenes was carried out employing Grubbs' catalyst in a non-metathetic role and Et(3)SiH. Conditions were optimized under microwave irradiation. Application to the solid-phase organic synthesis allows a facile construction of sp(3)-sp(3) carbon bonds through a sequential cross metathesis/olefin reduction.

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