title: Models of molecular evolution. 2. Stereospecificity of dipeptide syntheses by means of cyanamides and carbodiimides.
abstract: Acetyl, benzyloxycarbonyl and tosyl protected DL-alanine, DL-leucine, DL-methionine, DL-phenylalanine, and DL-valine were condensed with DL-amino acid methyl esters. Cyanamide, diethylcyanamide, diisopropyl carbodiimide, dicyclohexyl carbodiimide, and N-cyclohexyl-N'-(2-morpholino ethyl) carbodiimide-N''-methotosylate served as condensing reagents. Water, methanol, and dimethylformamide were used as reaction media. The stereochemical course of these dipeptide syntheses was elucidated by means of 13C-n.m.r. spectroscopy. The formation of L-L and D-D bonds (isotactic sequences) was favoured in ca. 80% of all condensations. L-L/L-D (D-D/D-L) ratios of up to 6:1 were found.
mesh_terms: D004151:Dipeptides / Q000138:chemical synthesis*; D007202:Indicators and Reagents; D009682:Magnetic Resonance Spectroscopy; D008954:Models, Biological; D009904:Optical Rotation; D013329:Structure-Activity Relationship
chemical_list: D004151:Dipeptides; D007202:Indicators and Reagents