(2S)-5-amino-2-{[(tert-butoxy)carbonyl]amino}pentanoic acid → HCID 89545117, compound

6.00 g (12.33 mmol) of the compound from example 1A was dissolved in 120 ml dichloromethane. 2.57 g (12.33 mmol) N2-(tert-Butoxycarbonyl)-L-ornithine was added. The reaction mixture was split into 6 portions. The portions were heated for 90 min in a sealed tube at 75° C. in a microwave synthesizer. The combined reaction mixture was extracted with approx. 100 ml saturated ammonium chloride solution. The aqueous phase was twice back extracted with approx. 30 ml dichloromethane each. The combined organic phases were extracted with approx. 50 ml brine and dried over sodium sulfate. The solvent was removed under reduced pressure. The raw product was dissolved in dichloromethane and chromatographed over approx. 600 ml silica gel. Solvents used were dichloromethane, dichloromethane/methanol 40/1 to dichloromethane/methanol 1/1. The product-containing fractions were combined and concentrated to dryness under reduced pressure. This gave 2.63 g (4.06 mmol, 33% of theory, 89% purity) of the desired product.