Hydrochloric Acid → (R)-6-methoxy-1,2,3,4-tetrahydronaphthalene-2-carboxylic acid

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Reaction Steps

3 g (0.0136 mol) of methyl 6-methoxy-1,2,3,4-tetrahydro-2-naphthoate are dissolved in 100 ml of tert-butanol, and 300 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 1N HCl. 1.5 g of Sigma PPL enzyme (known as porcine pancreatic lipase type II, crude, Sigma L-3126--50 U/mg using triacetin) are 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 4-5 hours, when about 22 ml of 0.25N NaOH have been consumed, sodium bicarbonate is added to the solution until the pH is 8 in order to stop the reaction by inactivation of the enzyme. Extraction is carried out with ethyl ether and the two phases are separated. The organic phase contains the unreacted ester principally of (S) configuration, which can be recovered as indicated in Example 2 below. The aqueous phase is acidified with concentrated sulfuric acid and the precipitate formed is filtered off to give 1.16 g of the title acid, which is crystallized from ethyl acetate. M.p. 130°-131° C.; [α]D20 =+57.8° (c=1.4%, CHCl3); ee 93.7% (HPLC performed under conditions (a)). This product is purer than that described in EP-A-436435, preparation (O) (i).

Provenance & Evidence