Sodium Hydroxide → (S)-3-(4-Hydroxy-phenyl)-2-[2-((S)-2-mercapto-3-methyl-butyrylamino)-2-methyl-propionylamino]-propionic acid

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Reaction Steps

To a solution of N-[2-(2(S)-acetylthio-3-methyl-1-oxobutylamino)-2-methyl-1-oxopropyl]-L-tyrosine ethyl ester (0.18 g, 0.39 mmol) in methanol (10 mL) is added 1N sodium hydroxide (1.55 mL, 1.55 mmol). The mixture is stirred for 5 hours and then the solvent is removed in vacuo. The residue is dissolved in water (50 mL) and washed with ethyl acetate (10 mL). The aqueous phase is acidified to pH 1 with 1N hydrochloric acid and extracted with ethyl acetate (3×50 mL). The organic phase is washed with brine, dried over magnesium sulfate and the solvent is concentrated to yield a clear oil which is crystallized from ethyl ether to give N-[2-(2(S)-mercapto-3-methyl-1-oxobutylamino)-2-methyl-1-oxopropyl]-L-tyrosine, m.p. 180°-181° C., the compound of formula II wherein R1 is 4-hydroxyphenyl, R2 and R3 are hydrogen, R4 is isopropyl, and R6 and R7 are methyl.

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