C(Cl)CCl.C1C=CC2N(O)N=NC=2C=1.CCN(C(C)C)C(C)C.[CH3:24][O:25][C:26]([CH:28]1[CH2:32][C:31]2([S:37][CH2:36][CH2:35][CH2:34][S:33]2)[CH2:30][N:29]1C(=O)C(N)C(C)(C)C)=[O:27]>C(Cl)Cl>[CH3:24][O:25][C:26]([CH:28]1[CH2:32][C:31]2([S:33][CH2:34][CH2:35][CH2:36][S:37]2)[CH2:30][NH:29]1)=[O:27]L-Boc-cyclohexyl glycine (154 mg, Bachem), EDC (115 mg), HOBt (81 mg), and DIEA (284 mg) in CH2Cl2 (1 mL) was treated with amine salt 29 (189 mg) in CH2Cl2 (2 mL) and the mixture stirred for 2 hours. The mixture was partitioned between ethyl acetate and 1.0 N HCl, the organics washed with sodium bicarbonate, 1.0 N glycine sodium salt solution, 10% potassium carbonate solution and brine then dried over sodium sulfate, filtered, and concentrated in vacuo. Purification on a plug of silica gel eluting with 30% EtOAc/hexanes afforded 221 mg (70%) of 2-[2-tert-butoxycarbonylamino-2-cyclohexyl-acetylamino)-3,3-dimethyl-butyryl]-6,10-dithia-2-aza-spiro[4.5]decane-3-carboxylic acid methyl ester 30 as a white solid.
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