Carbohydrates as chiral templates: Stereoselective Strecker synthesis of D-α-amino nitriles and acids usingO-pivaloylatedD-galactosylamine as the auxiliary

✍ Scribed by Kunz, Horst ;Sager, Wilfried ;Schanzenbach, Dirk ;Decker, Mathias

• Publisher: John Wiley and Sons
• Year: 1991
• Tongue: English
• Weight: 698 KB
• Volume: 1991
• Category: Article
• ISSN: 0947-3440
• DOI: 10.1002/jlac.1991199101117

✦ Synopsis

Abstract

The asymmetric synthesis of N‐galactosyl D‐α‐amino nitriles is accomplished by application of 2,3,4,6‐tetra‐O‐pivaloyl‐β‐D‐galactopyranosylamine (4) as the stereodifferentiating template in Strecker reactions. Aldimines 6 derived from 4 and aromatic or aliphatic aldehydes react with trimethylsilyl cyanide in 2‐propanol or tetrahydrofuran in the presence of Lewis acids, e.g. ZnCl~2~ or SnCl~4′~ to give the N‐galactosyl α‐amino nitriles 5 in high yield and with diastereomeric ratios between 6:1 and 13:1 favoring the D diastereomers. Pure D‐amino nitrile diastereomers D‐5 are obtained in high yields by recrystallization from n‐heptane. Acid‐catalyzed hydrolysis of compounds D‐5 delivers the free D‐amino acids. A mechanistic interpretation of the stereoselection observed is given in terms of stereoelectronic, steric and complexing effects exhibited by the carbohydrate.