(2R,3S)-N-(tert-Butyloxy)carbonyl-3-amino-2-acetoxy-4-phenylbutanal → (2S,3R,4S)-N-[(tert-Butyloxy)carbonyl]-2-amino-1-phenyl-3,4-dihydroxy-6-methylheptane

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The title compound of Step 1 was dissolved under nitrogen in 100 mL of dry THF and cooled to -70° C. To this solution was added 13 mL (26 mmol) of a 2.0M solution of isobutylmagnesium chloride in ether and the stirred mixture was allowed to warm to room temperature and stir for 2 hrs. After decomposition with MeOH/H2O the mixture was diluted with ether, washed with saturated NH4Cl solution twice and dried with magnesium sulfate and the solvents evaporated under vacuum. The residue was allowed to stand overnight in 80% MeOH--H2O containing excess ammonium hydroxide. The MeOH was stripped off and the mixture was extracted with ether. These extracts were combined, washed with water, dilute KHSO4, then dried and evaporated to give 2.36 g of a yellow glass which crystallized from 50 mL of pentane on standing overnight. The yellow-white powder obtained was recrystallized from ether-hexane and furnished the title compound (0.41g) as white, hairy needles, mp 134°-136° C., Rf (ether): single spot, 0.6. By chromatography of the mother liquors and crystallization of the appropriate fractions, an additional 0.22 g of product, mp 138°-139° C., was obtained. Anal: Calcd. for C19H31NO4 : C, 67.62; H, 9.26; N, 4.15. Found: C, 67.51; H, 9.43; N, 4.24.

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