While geminally disubstituted α-amino acids are helix-inducing include the nucleophilic addition to (R)-or (S)-N-sulfinimines (Schemes 6-10) and other Mannich-type transformations residues in α-peptides, gem-disubstituted β-amino acids are predicted not to fit into any of the three major secondary (Schemes 19-22), stereoselective alkylations of various chiral hydropyrimidines (Schemes 11, 12, 18), of esters or amides of structures of β-peptides recognized to date [the 3 14 helix, the 12/10/12 helix, and the pleated sheet (Figure 1)]. In order to be 2-cyano-alkanoic acids (Schemes 13, 14, 16), and of Li 2 derivatives of non-racemic N-protected 3-amino-alkanoates able to synthesize and structurally identify β-peptides containing such building blocks, or consisting entirely of them, (Scheme 17), as well as sequences of reactions involving enantiopure gem-disubstituted succinic acid derivatives and a and in order to establish the chirality of secondary structures they may form, achiral and chiral gem-disubstituted β-amino
Curtius degradation (Schemes 23-26). Oligomers of the achiral gem-disubstituted compounds 1-(aminomethyl)-cyclopropane acids must be readily available. The methods of preparation of 3-amino carboxylic acids with two carbon substituents at the 2-and -cyclohexane carboxylic acid have already been shown to form 8-and 10-membered hydrogen-bonded rings, or 3-position (β 2,2 -/β 3,3 -amino acids, Figure 2) are reviewed. While there are numerous essentially classical routes to achiral respectively (Figure 5), which provide novel motifs for the possible construction of turns, links, or steps in β-peptidic and rac-β-amino acids of this type (Schemes 1-4), their EPC synthesis is currently the subject of investigations. These chains.