Successful biochemical studies of the natural products belactosin A and C and their acylated congeners have shown a β-lactonecarboxamide moiety to be a possible core structure of powerful proteasome inhibitors. As a part of further investigations, variously decorated simplified β-lactonecarboxamides have been synthesized in order to understand structure-biological activity relations in detail, to find ways of improving their biological activity and stability and to reduce the complexity of their preparation. Biological tests showed that the best compounds possess a high potential against phytopathogenic fungi in the greenhouse.

Compartmental pyrazolate‐based ligands with bis(2‐pyridinylmethyl)aminomethyl or (2‐pyridinylmethyl)[2‐(1‐methylimidazolyl)methyl]aminomethyl chelate arms have been further elaborated by attaching pivaloylamido groups to the outer pyridine rings, giving the new ligands H3L1 and H3L2. The peripheral pivaloylamido groups may serve as potential H‐bond donor or acceptor sites towards substrates in the bimetallic cavity. Protonation constants of the new ligand H3L1 as well as its nickel(II) speciation in solution have been studied by pH potentiometry, revealing pKa = 8.9 for the metal‐bound water. Based on the X‐ray crystallographic structure of [Ni2(H2L1)(H3O2)(MeCN)2](ClO4)2 (3) this pKa is rationalized in terms of two balancing effects, namely involvement of the pivaloylamido O atom in metal coordination and H‐bonding between the pivaloylamido NH group and the resulting nickel‐bound hydroxide. Complex 3 features a pyrazolate‐bridged dinickel(II) core and a bridging HO···H···OH unit within the bimetallic cavity, which is involved in multiple H‐bonding interactions.

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The cover picture shows (i) a Helicobacter pylori that produces large amounts of the enzyme urease to survive in the acidic human stomach, (ii) the urease active site, and (iii) a bioinspired bimetallic complex that features second‐shell hydrogen bonding akin to the situation in the metalloenzyme. The article by F. Meyer et al. on p. 4161 ff reports the synthesis of an elaborate new ligand scaffold that is decorated with peripheral groups for H‐bonding interactions and its speciation with nickel(II) in solution. The crystallographic structure of a dinickel(II) complex reveals a bridging HO···H···OH unit in the bimetallic cavity, which is involved in an extensive network of hydrogen bonds. Such systems might become useful for studying effects of the secondary coordination sphere in biomimetic substrate transformations.