BRL-42715

The inhibition of the class A SHV-1 β-lactamase by 7-(tert-butoxycarbonyl)methylidenecephalosporin sulfone was examined kinetically, spectroscopically, and crystallographically. An 1.14 Å X-ray crystal structure shows that the stable acyl-enzyme, which incorporates an eight-membered ring, is a covalent derivative of Ser70 linked to the 7-carboxy group of 2-H-5,8-dihydro-1,1-dioxo-1,5-thiazocine-4,7-dicarboxylic acid. A cephalosporin-derived enzyme complex of this type is unprecedented, and the rearrangement leading to its formation may offer new possibilities for inhibitor design. The observed acyl-enzyme derives its stability from the resonance stabilization conveyed by the β-aminoacrylate (i.e., vinylogous urethane) functionality as there is relatively little interaction of the eight-membered ring with active site residues. Two mechanistic schemes are proposed, differing in whether, subsequent to acylation of the active site serine and opening of the β-lactam, the resultant dihydrothiazine fragments on its own or is assisted by an adjacent nucleophilic atom, in the form of the carbonyl oxygen of the C7 tert-butyloxycarbonyl group. This compound was also found to be a submicromolar inhibitor of the class C ADC-7 and PDC-3 β-lactamases.

This paper quantitatively investigated the contribution of molecular properties to the volume of distribution in human (Vd human) when extrapolated from preclinical animal data, and identified which molecular descriptors and animal species were essential or better for acquiring the optimal accuracy of extrapolation. First, several two‐dimensional molecular descriptors which can potentially contribute to Vd were selected to establish the model to predict Vd in humans. Then, several linear predictive models were constructed by partial least squares (PLS) using three or one animal data in combination with or without the molecular descriptors. Stepwise regression was performed to determine the important molecular descriptors. For comparison, the allometric method was also performed to estimate the Vd human from preclinical species (rat, dog and monkey) data. The predictive accuracy of PLS models was better than that obtained by the allometric method. Moreover, the predictive accuracy of these models was improved when the molecular descriptors were introduced. Interestingly, the common contributors selected were molecular weight (MW) and the negatively charged fraction value (fi‐) for any stepwise regression model concerning molecular descriptors. Additionally, the dog was a more suitable species for predicting Vd human during drug‐lead pharmacokinetic optimization. More importantly, the introduction of molecular properties could improve the predictive accuracy for the prediction of Vd human from the preclinical species, among which MW and fi‐ were the significant parameters and the latter was considered in the extrapolation process for the first time. Copyright © 2010 John Wiley & Sons, Ltd.