Fr Francium

In this work we report on new experiments on the catalytic dehydrogenation of [H2B(μ-hpp)]2 leading to the doubly base-stabilized diborane(4) [HB(μ-hpp)]2 featuring two hpp bridges (hpp = 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidinate) under mild conditions. Several dehydrogenation (pre)catalysts were tested. The best one turned out to be Ru3(CO)12, allowing quantitative dehydrogenation already at 60 °C. Subsequently we subjected [HB(μ-hpp)]2 to reactions with S8 and disulfides (Ph2S2 and Bn2S2, Bn = benzyl). Reaction with S8 leads to oxidative insertion of one sulfur atom into the B–B bond and formation of [HB(μ-hpp)]2(μ-S). In the case of disulfides, substitution reactions leading to the doubly base-stabilized diborane(4) species [RSB(μ-hpp)]2 and HB(μ-hpp)2BSR (R = Ph or Bn) compete with sulfuration again leading to [HB(μ-hpp)]2(μ-S).Catalytic dehydrogenation of [H2B(μ-hpp)]2 leads to the doubly base-stabilized diborane(4) [HB(μ-hpp)]2. Oxidative sulfuration of the B–B bond in [HB(μ-hpp)]2 gives [HB(μ-hpp)]2(μ-S). A mixture ofsulfuration and substitution products is formed for reactions with disulfides.

Wiley Hoboken 2010, XV+459 pp., hardcover $ 195.00.—ISBN 978-0-470-22476-2

Humana Press, Totowa 2010, XIV+398 pp., hardcover $ 110.00.—ISBN 978-1-60761-534-7

The inside cover picture shows that a chemoenzymatic route to diversify aminoglycosides can light up antibacterial resistance on a microarray. The approach will allow for the identification of protein and carbohydrate substrates for acetyltransferases, which control antibacterial resistance and a host of other cellular process. More details may be found in the communication by M. D. Disney and co-workers on p. 1656 ff.

The cover picture shows a cyclic collagen binding protein, CNA35, that only becomes active after proteolytic cleavage, thereby providing a dual-specific targeting probe for imaging ECM remodeling. CNA35 consists of two domains connected through a flexible linker that bind collagen in a unique way by “wrapping” around a single collagen triple helix. Connecting the N and C termini through an MMP cleavage site yields a cyclic protein that can still form a pseudorotaxane structure that binds to the ends of loose collagen triple helices, but is topologically inhibited from binding to the majority of binding sites present in native collagen. This inhibition can be relieved through cleavage of the cyclic protein by MMP-1; this provides a new targeting strategy that integrates two different markers of ECM remodeling. For more information, see the Communication by M. Merkx et al. on p. 1665 ff. Illustration: ICMS Animation Studio, TU/e.

Threading collagen through a protein needle: The collagen-binding protein CNA35 operates by wrapping itself around the collagen triple helix. By connecting the N and C termini through an MMP recognition sequence, a dual-specific MMP-sensitive collagen-targeting ligand is obtained that can be used for imaging extracellular matrix turnover.