Editing Synthesis-of-dendritic-lipid (section)

== Synthesis of&nbsp;Nα,Nδ-Bis(tert-butyl-carbamoyl)-<span style="line-height: 20.8px;">Nα,Nδ</span>-bis(3-[tert-butyl-carbamoyl-amino]propyl)ornithine (7). ==

The raw 6 (assay calculated for 100%&nbsp;yield from the previous step: 108 mmol) was dissolved in water/THF&nbsp;(5:1, v/v). Over the course of 1 h, 100 mL of 4 M NaOH and a solution<br/>of 104.2 g (477 mmol) of Boc2O (Novabiochem) in 200 mL of THF&nbsp;were added in four portions with stirring while the reaction mixture&nbsp;was kept at room temperature by cooling with a water bath. Stirring&nbsp;was continued for 6 h, and most of the THF was then evaporated. After&nbsp;addition of 600 mL of diethyl ether and 200 mL of water, the mixture&nbsp;was acidified using half-concentrated hydrochloric acid. The phases&nbsp;were separated, and the aqueous phase was extracted two more times&nbsp;with 200 mL of ether. The combined organic phases were washed twice<br/>with water, dried (Na2SO4), and evaporated. The residue was purified&nbsp;in portions of 44 g by flash chromatography on 930 g of silica gel&nbsp;using chloroform/methanol (19:1) as the eluent83 to yield 26.5 g (41mmol, 38%) of 7 as a colorless solid