Phosphate → 5-Methoxy-1,2,3,4-tetrahydro-(2R)-2-naphthoic acid

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Reaction Steps

0.8 g (0.0036 mol) of methyl 5-methoxy-1,2,3,4-tetrahydro-2-naphthoate is dissolved in 28 ml of tert-butanol, and 80 ml of phosphate buffer at pH 7 are added to the solution prepared in this way. The pH of the solution, which rises to 7.3-7.5, is lowered to 7.1 by the addition of dilute H2SO4. 0.450 g of Sigma PPL enzyme (known as porcine pancreatic lipase type II, crude, Sigma L-3126--46 U/mg using triacetin) is added to the mixture. The pH tends to drop as the reaction progresses, but is kept constant by the addition of a 0.25N solution of NaOH, the pH being controlled by an automatic titration apparatus. After 8 hours, sodium bicarbonate is added to the solution until the pH is 7.7 in order to stop the reaction by inactivation of the enzyme. Extraction is carried out with isopropyl ether and the two phases are separated. The organic phase contains the unreacted ester principally of (S) configuration. The aqueous phase is acidified with concentrated sulfuric acid and extracted with ethyl ether, the organic phase is dried over sodium sulfate and the solvent is evaporated off under reduced pressure. The product obtained is crystallized from isopropyl ether to give 0.12 g of the title compound. M.p. 150°-152° C.; [α]D20 =+55.9° (c=1.4%, CHCl3); ee 85.6% (HPLC performed under conditions (e)).

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