Hydrochloric Acid → methyl(2R,3R)-2-((tert-butyloxycarbonyl)amino)-3-((4-methylbenzyl)thio)-3-phenylpropionic acid

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The acetylated thiol 17 (500 mg, 1.4 mmol) was dissolved in methanol (2 mL) and NaOH was added (1.6 mL, 1M aqueous), followed by bromoxilene (300 mg, 1.62 mmol). After 20 min most of the starting material has disappeared (monitored by TLC). The solution was carefully neutralized with dilute HCl. The volatiles were removed in vacuo and the residue was extracted with Cl2CH2 (3×) The organic layer was washed with brine and dried over Na2SO4. The crude product was purified by flash column chromatography (silica, 5% to 20% ethyl acetate/hexane) to give the desired ester 18 (480 mg, 79%) as a white solid, which crystallized. mp 97°-98° C. (ether-hexane); [α]20D =-171.8° (c=1.05, CHCl3); 1H NMR (CDCl3).δ1.384 (s, 9H), 2.326 (s, 3H), 3.393 (d, J=13 Hz, 1H), 3.551 (d, J=13 Hz, 1H), 3.572 (s, 3H, OCH3), 4.126 (d,J=5.4 Hz, H-3), 4.630 (dd, J=8.8, 5.8 Hz, 1H, H-2), 5.220 (bd, J=8.8 Hz, 1H, H--N), 7.028-7.107 (m, 4H), 7.291-7.362 (m, 5H); 13C NMR (CDCl3).δ21.0, 28.3, 35.5, 51.6, 52.1, 57.5, 80.1, 127.8, 128.5, 128.7, 128.9, 129.2, 134.3, 136.9, 138.4, 154.7, 170.8; MS m/z 316 [M+H]+ ; Anal. Calcd for C23H29O4NS.1/4H2O: C, 65.76; H, 7.08; N, 3.33. Found: C, 65.59; H, 7.03; N, 3.36.

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