Chemo- and biocatalytic strategies to obtain phenylisoserine, lateral chain of taxol by asymmetric reduction

Enriched ethyl 3-benzamido-2-hydroxy-3-phenylpropanoate (protected phenylisoserine), the chiral side chain of Taxol, was obtained via asymmetric reduction with transition metal-diphoshine complexes or with whole cells of non-conventional yeasts. Asymmetric hydrogenation was carried out using different approaches: hydrogenation of the tetra-substituted double bond of (E)-1-benzamido-3-ethoxy-3-oxo-1-phenylprop-1-en-2-yl ethyl oxalate 1 with Ir(I)-diphosphine complexes in the presence of TEA, hydrogenation of the carbonyl group of racemic ethyl 3-benzamido-2-oxo-3-phenylpropanoate 2 with Ru(II)-diphoshine complexes in the presence of a Lewis acid and finally a two-step enzymatic transformation of (E)-1-benzamido-3-ethoxy-3-oxo-1- phenylprop-1-en-2-yl ethyl oxalate 1 catalyzed by whole cells of yeasts bearing cell-bound esterases and dehydrogenases.