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With 1-ethyl-(3-(3-dimethylamino)propyl)-carbodiimide hydrochloride; In N,N-dimethyl-formamide; for 2h;
6'-Trifluoroacetyl-2',3-diPNZ-l-(N-Boc-3-amino-2(S)-hydroxy-propionyl)- sisomicin; To a stirring solution of N-Boc-3-amino-2(5)-hydroxy-propionic acid(1.30 g, 6.34 mmol) in DMF (14 ml) was slowly added HONB (1.14 g, 6.34 mmol) and EDC (1.21 g, 6.34 mmol) and the reaction mixture was stirred for 2 hours, when MS <n="63"/>showed complete formation of the activated ester (MS m/e [M+Na]+ calcd 389.1, found 389.1). 6'-trifluoroacetyl-2',3-diPNZ-sisomicin (4.76 g, 5.28 mmol) was then added and the reaction was allowed to stir overnight. The reaction was quenched with sat. aq. NaHCO3 (10 ml) and was extracted with EtOAc (5 x 15 mL). The combined organic layers were dried over Na2SO4, filtered and evaporated to dryness to yield a crude, which was purified by RP HPLC Method 2-Column B to yield the desired 6'- trifluoroacetyl-2',3-diPNZ-l -(N-Boc-3-amino-2(,S)-hydroxy-propionyl)-sisomicin (1.66 g, 1.52 mmol, 29% yield, >95% purity): MS m/e [M+H]+ calcd 1089.4, found 1089.2, [M+Na]+ 1111.3.
With 1-ethyl-(3-(3-dimethylamino)propyl)-carbodiimide hydrochloride; In N,N-dimethyl-formamide; for 2h;
6'-PNZ-2',3,3"-triBoc-l-(N-Boc-3-amino-2(S)-hydroxy-propionyl)-sisomicin; To a stirring solution of N-Boc-3-amino-2(5)-hydroxy-propionic acid (0.93 g, 4.53 mmol) in DMF (8 ml) was slowly added HONB (0.82 g, 4.53 mmol) and EDC (0.87 g, 4.53 mmol) and the reaction mixture was stirred for 2 hours. 6'-PNZ- 2',3,3"-triBoc-sisomicin (3.0 g, 3.23 mmol) was then added and the reaction was allowed to stir overnight. The reaction was quenched with H2O (10 ml) and was extracted with EtOAc (5 x 15 mL). The combined organic layers were dried over Na2SO4, filtered and concentrated to dryness to give the desired 6'-PNZ-2',3,3"-triBoc- l-(N-Boc-3-amino-2(,S)-hydroxy-propionyl)-sisomicin (MS m/e [M+H]+ calcd 1114.5, found 1113.9, [M+Na]+ 1136.3), which was carried through to the next step without further purification.
With 1-ethyl-(3-(3-dimethylamino)propyl)-carbodiimide hydrochloride; In tetrahydrofuran; at 0 - 20℃; for 6.33333h;Product distribution / selectivity;
6'-Trifluoroacetyl-2',3-di-PNZ-l-[(R)-3-(fer-butoxycarbonylamino)-2-hydroxy- propionyl] -sisomicin ; <n="59"/>(i?)-3-(tert-Butoxycarbonylamino)-2-hydroxypropionic acid (1.3 g, 6.3 mmol) and HONB (1.35 g, 7.5 mmol) were dissolved in THF (40 mL), the solution was cooled to 0C, and EDC (1.33 g, 6.9 mmol) was added. After 20 minutes the reaction was allowed to warm to room temperature. After 6 hours, a solution of 6'- trifluoroacetyl-2',3-di-PNZ-sisomicin (5.23 g, 5.8 mmol) in DMF (25 mL) was added, and the solution was allowed to stir overnight. The reaction was concentrated to remove the THF, and was partitioned between water and ethyl acetate. The phases were separated, and the ethyl acetate phase was washed once each with water, sat. NaHCO3, water, and brine. The ethyl acetate phase was then dried over Na2SO4, filtered, and concentrated to a residue. The residue was chromatographed by RP HPLC Method 2- Column B to give 6'-trifluoroacetyl-2',3-di-PNZ-l-[(i?)-3-(tert-butoxycarbonylamino)- 2-hydroxy-propionyl]-sisomicin as an off-white foam (1.64 g, 1.51 mmol, 24% yield): MS m/e [M+H]+ calcd 1089.4, found 1089.2.
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