Synthesis of (Optically Active) Sulfur-Containing Trifunctional Amino Acids by Radical Addition to (Optically Active) Unsaturated Amino Acids

Article abstract of DOI:10.1021/jo00049a041

Sulfur-based radicals, generated from R-S-H-type precursors (R = alkyl, acyl) with AIBN, smoothly add to α-allylglycines protected at none, one, or both of the amino acid functions (NH2 and/or CO2H).Sulfur-containing trifunctional amino acids were obtained in good to excellent yields (64-100 percent).The solvent used for the reaction is critical.Optimal results were obtained when both the unsaturated amino acid and RSH dissolve completely in the medium (dioxane/water or methanol/water are good solvent systems).The scope of the reaction includes α-substituted α-allylglycine derivative and derivatives as well as β-substituted β-allyl-β-amino alcohols.In the case of optically active α-allylglycine derivatives, radical addition is accompanied by a small amount of racemization, the amount depending on the type of protection and R-S-H.The products are easily optically enriched by crystallization.Addition of sulfur-based radicals to α-allylglycine is believed to be an example of a general method for synthesizing optically active trifunctional amino acids from unsaturated amino acids.