Cover Picture: Organocatalytic Asymmetric Inverse‐Electron‐Demand Aza‐Diels–Alder Reaction of N ‐Sulfonyl‐1‐aza‐1,3‐butadienes and Aldehydes (Angew. Chem. Int. Ed. 51/2008)Han, Bo; Li, Jun‐Long; Ma, Chao; Zhang, Shan‐Jun; Chen, Ying‐Chun
doi: 10.1002/anie.200890263pmid: N/A
The inverse‐electron‐demand …︁ aza Diels–Alder reaction of N‐sulfonyl‐1‐aza‐1,3‐butadienes and aldehydes shown in the cover picture is explored through catalysis by an α,α‐diphenylprolinol OTMS ether salt. In their Communication on page 9971 ff., Y.‐C. Chen and co‐workers show how this simple process affords highly enantioenriched hemiaminal intermediates, which are readily converted into a diversity of chiral piperidine derivatives.
A Reverse Ozone Hole on MarsLelieveld, Jos
doi: 10.1002/anie.200804551pmid: 19012309
The Martian atmosphere accumulates ozone in the winter and destroys it in the summer—exactly opposite the situation on Earth. The large fluctuation in the ozone concentration can only be adequately described if heterogeneous reactions on ice clouds are accounted for in the chemistry–climate model.
(2.2)Paracyclophanes in Polymer Chemistry and Materials ScienceHopf, Henning
doi: 10.1002/anie.200800969pmid: 18844203
After a long period as model compounds in basic research (2.2)paracyclophanes are quickly gaining in practical importance. They can be incorporated into numerous polymeric systems in which they either lose (the so‐called Parylenes) or retain their layered structure, and they can be used for the construction of unsaturated molecular scaffolds characterized not only by conventional (lateral) π‐electron overlap but also by cofacial π‐electron interactions. Surfaces generated from and with (2.2)paracyclophanes possess interesting biological, photophysical, and optoelectronic properties.
Natural‐Product Sugar Biosynthesis and Enzymatic GlycodiversificationThibodeaux, Christopher J.; Melançon, Charles E.; Liu, Hung‐wen
doi: 10.1002/anie.200801204pmid: 19058170
Many biologically active small‐molecule natural products produced by microorganisms derive their activities from sugar substituents. Changing the structures of these sugars can have a profound impact on the biological properties of the parent compounds. This realization has inspired attempts to derivatize the sugar moieties of these natural products through exploitation of the sugar biosynthetic machinery. This approach requires an understanding of the biosynthetic pathway of each target sugar and detailed mechanistic knowledge of the key enzymes. Scientists have begun to unravel the biosynthetic logic behind the assembly of many glycosylated natural products and have found that a core set of enzyme activities is mixed and matched to synthesize the diverse sugar structures observed in nature. Remarkably, many of these sugar biosynthetic enzymes and glycosyltransferases also exhibit relaxed substrate specificity. The promiscuity of these enzymes has prompted efforts to modify the sugar structures and alter the glycosylation patterns of natural products through metabolic pathway engineering and enzymatic glycodiversification. In applied biomedical research, these studies will enable the development of new glycosylation tools and generate novel glycoforms of secondary metabolites with useful biological activity.
Reactivity of the 3,4,5‐Tridehydropyridinium Cation—An Aromatic σ,σ,σ‐TriradicalJankiewicz, Bartłomiej J.; Reece, Jennifer N.; Vinueza, Nelson R.; Nash, John J.; Kenttämaa, Hilkka I.
doi: 10.1002/anie.200802714pmid: 19006159
Seeing the sites: Reactivity studies on the σ,σ,σ‐triradical 3,4,5‐tridehydropyridinium cation by using a Fourier transform ion cyclotron resonance mass spectrometer show that bond formation first occurs at C3 for radical reactions, and at either C3 or C4 for nonradical reactions (see scheme). The isomeric 2,4,6‐tridehydropyridinium cation shows different chemical properties because of the lower reactivity of its meta‐benzyne group(s) and its greater Brønsted acidity.