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Compound LS27 was prepared in a similar fashion to the preparation of intermediate LS19 employing 2-(methoxycarbonylamino)-2-(oxetan-3-yl)acetic acid (intermediate LS29) as the carboxylic acid coupling partner. The two diastereomers of LS27 were separated via preparative HPLC (Xbridge C18, 100×19 mm I.D. S-5 μm; Mobile Phase A: 95% Water-5% Acetonitrile with 10 mM ammonium acetate (pH=5); Mobile phase B: 95% Acetonitrile-5% Water with 10 mM ammonium acetate (pH=5); Isocratic 30% B for 7 min; Flow rate: 25 mL/min; UV detection: 220 nm; Sample amount: −5 mg/each injection, 300 μl sample solution in methanol (˜17 mg/mL)). Diastereomer 1: 1H NMR (500 MHz, DMSO-d6) δ ppm 0.80-0.96 (m, 6H) 1.91-2.06 (m, 6H) 2.09-2.21 (m, 3H) 3.54 (s, 3H) 3.59 (s, 3H) 3.77-3.83 (m, 2H) 3.87 (t, J=7.63 Hz, 1H) 4.06 (t, J=8.24 Hz, 1H) 4.31 (t, J=6.41 Hz, 1H) 4.43 (t, J=6.10 Hz, 1H) 4.49 (t, J=7.17 Hz, 1H) 4.51-4.57 (m, 1H) 4.80 (t, J=8.55 Hz, 1H) 5.00-5.05 (m, 1H) 5.06-5.11 (m, 1H) 7.30 (d, J=8.55 Hz, 1H) 7.50 (s, 1H) 7.58-7.89 (m, 8H) 11.77 (s, 2H). LC (Cond'n 10): RT=7.14 min; MS: Anal. Calcd. for [M+H]+ C40H48N8O7: 753.4. found 753.9. Diastereomer 2: 1H NMR (500 MHz, DMSO-d6) δ ppm 0.79-0.98 (m, 6H) 1.91-2.06 (m, 4H) 2.07-2.23 (m, 4H) 3.51-3.69 (m, 8H) 3.74-3.90 (m, 2H) 4.06 (t, J=7.48 Hz, 1H) 4.20-4.33 (m, 1H) 4.36-4.49 (m, 2H) 4.55 (s, 2H) 4.71 (s, 1H) 4.97-5.05 (m, 1H) 5.08 (s, 1H) 5.53 (s, 1H) 7.30 (d, J=7.93 Hz, 1H) 7.51 (s, 1H) 7.58-7.91 (m, 8H) 11.53 (s, 1H) 11.78 (s, 1H). LC (Cond'n 10): RT=8.79 min; MS: Anal. Calcd. for [M+H]+ C40H48N8O7: 753.4. found 753.9. Step b: A solution of methyl 2-(benzyloxycarbonylamino)-2-(oxetan-3-ylidene)acetate (intermediate LS28; Source: Moldes et al, Il Farmaco, 2001, 56, 609 and Wuitschik et al, Ang. Chem. Int. Ed. Engl, 2006, 45, 7736; 200 mg, 0.721 mmol) in ethyl acetate (7 mL) and CH2Cl2 (4.00 mL) was degassed by bubbling nitrogen for 10 min. Dimethyl dicarbonate (0.116 mL, 1.082 mmol) and Pd/C (20 mg, 0.019 mmol) were then added, the reaction mixture was fitted with a hydrogen balloon and allowed to stir at ambient temperature overnight. The reaction mixture was filtered through diatomaceous earth (Celite®) and concentrated. The residue was purified via Biotage (load with dichloromethane on 25 samplet; elute on 25S column with dichloromethane for 3CV then 0 to 5% methanol/dichloromethane over 250 mL then hold at 5% methanol/dichloromethane for 250 mL; 9 mL fractions). Fractions containing the desired product were concentrated to provide 167 mg methyl 2-(methoxycarbonylamino)-2-(oxetan-3-yl)acetate as a colorless oil which solidified on standing. 1H NMR (500 MHz, CHLOROFORM-D) δ ppm 3.29-3.40 (m, 1H) 3.70 (s, 3H) 3.74 (s, 3H) 4.55 (t, J=6.41 Hz, 1H) 4.58-4.68 (m, 2H) 4.67-4.78 (m, 2H) 5.31 (br s, 1H). MS: Anal. Calcd. for [M+H]+ C8H13NO5: 204.1. found 204.0. To methyl 2-(methoxycarbonylamino)-2-(oxetan-3-yl)acetate (50 mg, 0.246 mmol) in THF (2 mL) and Water (0.5 mL) was added lithium hydroxide monohydrate (10.33 mg, 0.246 mmol). The resultant solution was allowed to stir overnite at ambient temperature then concentrated to dryness to provide intermediate LS29 as a colorless powder. 1H NMR (500 MHz, CH3OD) δ ppm 3.38-3.50 (m, 1H) 3.67 (s, 3H) 4.28 (d, J=7.63 Hz, 1H) 4.57-4.79 (m, 4H).
