Hydroxycamphor-controlled S/R interconversion of amino acids

Abstract

In order to overcome the problems of complex chiral molecular structure, high molecular weight and consumption of equivalent heavy metal salts in purely chemical S/R interconversion of amino acids, a novel method for S/R interconversion of amino acids was developed by using structurally simple 2-hydroxycamphor or 3-hydroxycamphor. The reaction conditions were optimized by assessing the base, solvent and reaction temperature. Then the S/R interconversion of racemic and enantiopure amino acids with different side chains were carried out. The result shows that the best interconversion effect is obtained at 40 ℃ with potassium tert-butoxide as the base and isopropanol as the solvent. Various amino acids with fatty and aromatic side chains are well tolerated in the reactions and the S/R interconversion of amino acids can be carried out efficiently, showing excellent stereoselectivities, and the hydroxycamphors can be reused. The mechanism study shows that the high stereoselectivity of dynamic resolution is thermodynamically controlled. This method has the advantages of using structurally simple and recyclable chiral reagents, avoiding the synthesis of specific substrates from amino acids and giving good reaction conversions and stereoselectivity, which provides a novel approach for purely chemical S/R-interconversion of amino acids.

Keywords

• organic synthetic chemistry; configuration inversion; amino acids; camphor; chirality