ENZYMES IN ORGANIC-CHEMISTRY .2. LIPASE-CATALYZED HYDROLYSIS OF 1-ACYLOXY-2-ARYLETHYLPHOSPHONATES AND SYNTHESIS OF PHOSPHONIC ACID ANALOGS OF L-PHENYLALANINE AND L-TYROSINE

alpha-Hydroxyphosphonates (+/-)-3, prepared by base catalysed addition of phosphites 2 to aldehydes 1, were acylated to give esters (+/-)-4. Diethyl 1-acyloxy-2-arylethylphosphonates (+/-)-4a, 4b, and 4e were hydrolysed by lipase from Aspergillus niger in a biphasic system to afford (R)-alpha-hydroxyphosphonates of low enantiomeric purity. The corresponding diisopropyl phosphonates (+/-)-4c, 4f and 4g gave (S)-alpha-hydroxyphosphonates with an ee of up to 78%, The absolute configuration of the alpha-hydroxyphosphonates was assigned by P-31 NMR spectroscopy of their (R)-MTPA-esters. (S)-3b and 3e were chemically transformed via their azides to phosphonic acid analogues of L-phenylalanine and L-tyrosine, respectively.