Strecker-Derived Methodology for Library Synthesis of N-Acylated α-Aminonitriles

The Strecker reaction is a three-component condensation of an aldehyde, an amine, and hydrogen cyanide, delivering an α-amino carbonitrile. Despite extensive investigations, the possibility to use amides instead of amines as one of the three condensation partners has been largely neglected. Nonetheless, the N-acylated α-aminocarbonitriles that are obtained in this way are of direct interest for drug discovery, because they make up a well-known class of mechanism-based inhibitors of serine- and cysteine-type hydrolases. In response, we have thoroughly explored the corresponding variant of the Strecker reaction, focusing on catalyst use, solvent, reaction time, and cyanide source. Optimized parameters were combined in a sequential one-pot protocol for which the scope was found to be compatible with library synthesis applications. Product yields ranged from 7 to 90%, and conditions were found to be mild and tolerant to a wide range of functional groups, including moieties that are typically present in druglike molecules.

Organocatalytic Asymmetric Mannich Reactions withN-Boc andN-Cbz Protected α-Amido Sulfones (Boc:tert-Butoxycarbonyl, Cbz: Benzyloxycarbonyl)

Different malonates and beta-ketoesters can react with N-tert-butoxycarbonyl- (N-Boc) and N-benzyloxycarbonyl- (N-Cbz) protected alpha-amido sulfones in an organocatalytic asymmetric Mannich-type reaction. The reaction makes use of a simple and easily obtained phase-transfer catalyst and proceeds under very mild and user-friendly conditions. The optimised protocol avoids the preparation and the isolation of the relatively unstable N-Boc and N-Cbz imines that are generated in situ from the bench-stable alpha-amido sulfones. The corresponding Mannich bases are generally obtained in good yields and enantioselectivities, and can be readily transformed into key compounds, such as optically active beta3-amino acids in one easy step. Enantioenriched N-Boc and N-Cbz protected beta-amino acids that are suitable for peptide synthesis are also available from the Mannich adducts through simple manipulations. Control experiments showed the dual role of the enolate-catalyst ion pair in this reaction, as well as the crucial role of the presence of water to achieve high enantioselectivities.

Phase Transfer Catalyzed Enantioselective Strecker Reactions of α-Amido Sulfones with Cyanohydrins

A study into the use of a chiral phase-transfer catalyst in conjunction with acetone cyanohydrin to effect the enantioselective formation of alpha-amino nitriles from alpha-amido sulfones is described. This novel catalytic asymmetric Strecker reaction is analyzed with regard to the possible mechanistic basis.

tert-Butyl (Phenylsulfonyl)alkyl- N-hydroxycarbamates: The First Class of N-(Boc) Nitrone Equivalents

[reaction: see text] tert-Butyl (phenylsulfonyl)alkyl-N-hydroxycarbamates 1 have been easily prepared from aldehydes and tert-butyl N-hydroxycarbamate in a methanol-water mixture using sodium benzenesulfinate and formic acid. These sulfones 1 behave as N-(Boc)-protected nitrones 4 in the reaction with organometallics to give N-(Boc)hydroxylamines. Some chemical transformations showing their interest as building blocks in organic synthesis are described.