Large degree of racemization observed in the amide bond forming reaction on silica gel

A systematic study of racemization from the coupling of DNB-l-Leu and 3-aminopropyl silica gel with several amide coupling reagents was investigated. Significant amounts of racemization were observed from all except one coupling reagent. In comparison, similar reactions completed in homogeneous solution can be accomplished with much lower racemization and in much higher yields.