(S,S)-(+)-pseudoephedrine as chiral auxiliary in asymmetric acetate aldol reactions

Acyl atractyligenin and carboxyatractyligenin glycosides from Antennaria rosea subsp. confinis

Eight previously undescribed acyl atractyligenin and carboxyatractyligenin glycosides were isolated from whole Antennaria rosea subsp. confinis (Greene) R. J. Bayer (Compositae) [syn. Leontopodium leontopodioides (Willd.) Beauv. (Asteraceae)] plants and their structures were determined by spectroscopic and chemical methods. The compounds were trivially named leontopodiosides F-M. Seven of the compounds showed potent in vitro inhibitory activity toward pancreatic lipase with IC₅₀ values ranging from 3.4 to 52.5 μM, suggesting that they participate in the previously observed effect this plant has in reducing triglyceride absorption in rats.

Stereocontrolled synthesis of syn-β-Hydroxy-α-amino acids by direct aldolization of pseudoephenamine glycinamide

β-Hydroxy-α-amino acids figure prominently as chiral building blocks in chemical synthesis and serve as precursors to numerous important medicines. Reported herein is a method for the synthesis of β-hydroxy-α-amino acid derivatives by aldolization of pseudoephenamine glycinamide, which can be prepared from pseudoephenamine in a one-flask protocol. Enolization of (R,R)- or (S,S)-pseudoephenamine glycinamide with lithium hexamethyldisilazide in the presence of LiCl followed by addition of an aldehyde or ketone substrate affords aldol addition products that are stereochemically homologous with L- or D-threonine, respectively. These products, which are typically solids, can be obtained in stereoisomerically pure form in yields of 55-98 %, and are readily transformed into β-hydroxy-α-amino acids by mild hydrolysis or into 2-amino-1,3-diols by reduction with sodium borohydride. This new chemistry greatly facilitates the construction of novel antibiotics of several different classes.

Synthesis of cruentaren A

Cruentaren A, an antifungal benzolactone produced by the myxobacterium Byssovorax cruenta, is highly cytotoxic against various human cancer cell lines and a highly selective inhibitor of mitochondrial F-ATPase. A convergent and efficient synthesis of cruentaren A is reported, based upon a diastereoselective alkylation, a series of stereoselective aldol reactions utilizing Myers' pseudoephedrine propionamide, an acyl bromide mediated esterification, and a ring-closing metathesis (RCM) as the key steps. The RCM reaction was applied for the first time toward the total synthesis of cruentaren A, which led to a convergent and efficient synthesis of the natural product.

Role of pseudoephedrine as chiral auxiliary in the "acetate-type" aldol reaction with chiral aldehydes; asymmetric synthesis of highly functionalized chiral building blocks

We have studied in depth the aldol reaction between acetamide enolates and chiral α-heterosubstituted aldehydes using pseudoephedrine as chiral auxiliary under double stereodifferentiation conditions, showing that high diastereoselectivities can only be achieved under the matched combination of reagents and provided that the α-heteroatom-containing substituent of the chiral aldehyde is conveniently protected. Moreover, the obtained highly functionalized aldols have been employed as very useful starting materials for the stereocontrolled preparation of other interesting compounds and chiral building blocks such as pyrrolidines, indolizidines, and densely functionalized β-hydroxy and β-amino ketones using simple and high-yielding methodologies.

Asymmetric synthesis of both antipodes of beta-hydroxy nitriles and beta-hydroxy carboxylic acids via enzymatic reduction or sequential reduction/hydrolysis

Use of isolated carbonyl reductases in the reduction of aromatic beta-ketonitriles have completely eliminated the competing alpha-ethylation, which is often observed with whole cell biocatalysts. By choosing suitable recombinant carbonyl reductase, the reduction of beta-ketonitriles afforded (R)- or (S)-beta-hydroxy nitriles with excellent optical purity and yield. Subsequently, nitrilase-catalyzed hydrolysis of the obtained optically pure beta-hydroxy nitriles led to the corresponding beta-hydroxy carboxylic acids in high yields. More importantly, the sequential enzymatic reduction and hydrolysis could be carried out in "two-step-one-pot" fashion without the isolation of intermediates beta-hydroxy nitriles, lowering the cost and minimizing the environmental impact. This allows ready access to both antipodes of chiral beta-hydroxy nitriles and beta-hydroxy carboxylic acids of pharmaceutical importance with excellent optical purity.

Synthesis and evaluation of a new polymer-supported pseudoephedrine auxiliary for asymmetric alkylations on solid phase

A polymer-supported pseudoephedrine auxiliary linked to the support through nitrogen, has been developed for use in asymmetric alkylations on solid phase.