2-Oxo-4-phenylbutyric acid → HCID 18597438, compound

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S-(2-Benzyloxycarbonylaminoethyl)-N-tert-butoxy-carbonyl-L-homocysteine (2.14 g., 0.00518 mole) and ethyl 1,2,3,4-tetrahydroisoquinoline-3-(S)-carboxylate (1.12 g., 0.00545 mole) were coupled via the procedure described in Example 5 to give 2.24 g. (72%) of ethyl N-[S-(2-benzyloxycarbonylaminoethyl)-N-tert-butoxycarbonyl-L-homocysteinyl]-1,2,3,4-tetrahydroisoquinoline-3-(S)-carboxylate (1); an oil. Compound 1 (1.10 g., 0.00183 mole) was stirred for 50 minutes at room temperature with 25 ml of trifluoroacetate acid. Concentration in vacuo gave ethyl N-[S-(2-benzyloxycarbonylaminoethyl)-L-homocysteinyl]1,2,3,4-tetrahydroisoquinoline-3-(S)-carboxylate (2) as a crude orange oil. This intermediate (2) was reductively alkylated with 2-oxo-4-phenylbutyric acid (3.00 g., 0.0068 mole) according to the procedure described in Example 5. After chromatography on an LH-20 column with methanol, 0.30 g. (25%) of ethyl N-[S-(2-benzyloxycarbonylaminoethyl)-N-(1-carboxy-3-phenylpropyl)-L-homocysteinyl]-1,2,3,4-tetrahydroisoquinoline-3-(S)-carboxylate (3) was obtained; a colorless oil.

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