An Improved Synthesis of (3R)-2-(tert-Butoxycarbonyl)-7-hydroxy-1,2,3,4-tetrahydroisoquinoline-3-carboxylic Acid

An improved synthesis of (3 R)-2-( TERT-butoxycarbonyl)-7-hydroxy-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid is described wherein a modified Pictet-Spengler reaction was employed to provide 95% yield of the product with 7% racemization or less. The enantiomeric excess of the final product was improved to 99.4% via recrystallization. The overall yield of this four-step synthesis provides the title compound in 43% starting from D-tyrosine.