Expanding the scope of Metal-Free enantioselective allylic substitutions: Anthrones.

The highly enantioselective asymmetric allylic alkylation of Morita-Baylis-Hillman carbonates with anthrones is presented. The reaction is simply catalyzed by cinchona alkaloid derivatives affording the final alkylated products in good yields and excellent enantioselectivities.

Solid-state NMR spin diffusion for measurement of membrane-bound peptide structure: gramicidin A.

A recently developed solid-state NMR method for measurement of depths in membrane systems is applied to gramicidin A, a membrane-bound peptide of known structure, to investigate the potential of this method. (15)N-detected, (1)H spin diffusion experiments demonstrate the resolution of the technique by measuring the 4-5 A depth differences between three (15)N-labeled backbone sites (Trp13, Val7, Gly2) in gramicidin A. We also show that (13)C-detected, (1)H spin diffusion experiments on unlabeled gramicidin A are sufficient to discriminate between the end-to-end dimer and double-helix structures of gramicidin A.

Site-directed rotational resonance solid-state NMR distance measurements probe structure and mechanism in the transmembrane domain of the serine bacterial chemoreceptor.

The serine receptor of bacterial chemotaxis is an ideal system in which to investigate the molecular mechanism of transmembrane signaling. Solid-state nuclear magnetic resonance (NMR) techniques such as rotational resonance provide a means for measuring local structure and ligand-induced structural changes in intact membrane proteins bound to native membrane vesicles. A general site-directed biosynthetic (13)C labeling strategy is used to direct the distance measurements to a specific site; the distance is measured between a unique Cys residue and a non-unique, low-abundance residue (Tyr or Phe).