Drx 600 nmr spectrometer

The NMR spectra were recorded on the Bruker DRX-600 NMR spectrometer for ¹H- and ¹³C-NMR. EI-MS data were obtained on a Finnigan-MAT-95 mass spectrometer. Preparative isolations were performed on Agela HP P050 medium pressure column chromatography (MPCC) system (Tianjin, China). Commercial silica gel (Qing Dao Hai Yang Chemical Group Co., 300–400 mesh) was used for column chromatography. Pre-coated silica gel plates (Yan Tai Zi Fu Chemical Group Co., G60 F-254) were used for analytical thin layer chromatography (TLC). All the solvents used for column chromatography were of analytical-reagent grade.

The l-lysine and fatty acid chloride were weighed in a molar ratio of 1:2. l-lysine was added into a four-necked flask, followed by a mixture of anhydrous ethanol and deionized water (2:1, v/v). The reaction mixture was cooled in an ice-water bath under stirring. Then fatty acid chloride was added slowly via a dropping funnel. In the meantime, the pH of the reaction solution was adjusted by an aqueous sodium hydroxide solution (10 wt%) and maintained at 9–10. The reaction continued for 3 h after the dropwise addition. At last, the reaction solution was taken out and allowed to stand at room temperature for 3–4 h. After acidification with dilute hydrochloric acid, the precipitate was filtered and washed with deionized water, then rinsed with petroleum ether three times, giving a white, solid appearance the final product.
Four N^α, N^ε-diacyl-l-lysines were characterized by FT-IR, ESI-MS, and ¹H NMR measurements. IR spectra were obtained on a Nicolet iS10 FT-IR Spectrometer (Thermo Fisher Scientific, Madison, WI, USA) using KBr tablets at room temperature. ESI-MS spectra were recorded using an API3200 triple-quadrupole mass spectrometer (AB SCIEX, Redwood, CA, USA). The ¹H NMR spectra were acquired on a DRX-600 NMR spectrometer (Bruker, Ettlingen, German).