Formic Acid → O-[(4-{[(2R)-1-Amino-1-oxo-3-(tritylsulfanyl)propan-2-yl]amino}-3-[(tert-butoxycarbonyl)-(methyl)amino]-4-oxobutyl)carbamoyl]-N-(tert-butoxycarbonyl)-L-tyrosine

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Reaction Steps

2.2 g (2.38 mmol) of the compound from example 8A was dissolved in 48 ml tetrahydrofuran. 1.66 ml (11.9 mmol) triethylamine, 0.45 ml (11.9 mmol) formic acid and 0.275 g (0.238 mmol) tetrakis(triphenylphosphin)palladium(0) were added. The reaction mixture was stirred over night at room temperature. The reaction was diluted with approx. 50 ml water and twice extracted with approx. 50 ml dichloromethane. The combined organic phases were extracted with brine, dried over sodium sulfate and concentrated to dryness under reduced pressure. The raw product was dissolved in dichloromethane and chromatographed over approx. 100 g silica gel. Solvents used were dichloromethane, dichloromethane/methanol 50/1 and dichloromethane/methanol 4/1. The product-containing fractions were combined and concentrated to dryness under reduced pressure. This gave 1.44 g (1.61 mmol, 68% of theory) product as a mixture of diastereomers.

Provenance & Evidence