As illustrated by FIG. 5H, tyrosine benzyl ester 111 can be converted to N-acetyltyrosine benzyl ester (2) using acetic anhydride, with the hydroxy group of the tyrosine being transformed into the trifluoromethyl sufonyl derivative 113 by using phenyl bis[(trifluoromethyl)sulfonyl]amine. Compound 113 this can be coupled to vinyltributyltin in the presence of bis(triphenylphosphine)palladium dichloride and lithium chloride to give the 4-ethenylphenylalanine derivative 114. This product, on refluxing with catechol borane and further transesterification with pinanediol, gives p-boronoethyl-2-phenylalanine derivative 116. Catalytic hydrogenation affords 117, which can be further coupled to yield the desired peptide or peptidomimetic.
