Isoleucine-catalyzed direct asymmetric aldol addition of enolizable aldehydes.

Isoleucine-catalyzed direct enantioselective aldol additions between enolizable aldehydes are reported. Intermediate acetal structures dictate the configurative outcome and were supported by a hydrogen bond. This direct isoleucine-catalyzed aldol addition represents a welcome complement to both proline- and histidine-catalyzed aldol additions of enolizable aldehydes.

Stereoselective direct amine-catalyzed decarboxylative aldol addition.

A stereoselective decarboxylative aldol addition of β- and α-keto acids in the presence of catalytic amounts of amines is described. By the optional deployment of chiral enolizable aldehydes an access to enantiopure configurative defined ketopentoses, ketohexoses, or ketoheptoses is given.

Toward asymmetric aldol-Tishchenko reactions with enolizable aldehydes: access to defined configured stereotriads, tetrads, and stereopentads.

Asymmetric aldol-Tishchenko reactions of enolizable aldehydes and ketones in the presence of chiral BINOLTi(OtBu)(2)/cinchona alkaloids complexes are described. Different configurative outcomes of these reactions depend on an equilibration through a retro aldol/aldol sequence and can be influenced by the configurative architecture of substrates. The results are explained by means of transition state models and rate constants.

Catalyst-free tandem aldol condensation/Michael addition of 1,3-cyclohexanediones with enolizable aldehydes.

An efficient tandem aldol condensation/Michael addition process of unactivated aldehydes and 1,3-cyclohexanedione is described. This transformation proceeds without any catalyst at room temperature with high isolated yields. By a fine-tuning of reaction conditions an access to both the aldol condensation/Michael addition products or to the dehydrated cyclized 9-substituted 1,8-dioxo-xanthenes is given.

X-ray structures of free and leupeptin-complexed human alphaI-tryptase mutants: indication for an alpha-->beta-tryptase transition.

Tryptases alpha and beta are trypsin-like serine proteinases expressed in large amounts by mast cells. Beta-tryptase is a tetramer that has enzymatic activity, but requires heparin binding to maintain functional and structural stability, whereas alpha-tryptase has little, if any, enzymatic activity but is a stable tetramer in the absence of heparin. As shown previously, these differences can be mainly attributed to the different conformations of the 214-220 segment.

Enantioselective direct aldol-Tishchenko reaction: access to chiral stereopentads.

[reaction: see text] The aldol-Tishchenko reaction of aromatic aldehydes in the presence of titanium(IV) tertbutoxide and amino alcohols is described. When used with cinchona alkaloids, stereopentads were isolated for the first time with a high degree of diastereo- and enantioselectivity.