Example 1
Fluorenylmethyloxycarbonyl (FMOC) and Monomethoxytrityl (MMTr) protected L-lysine (15 g), N-hydroxysuccinimide (3.23 g, 1.2 eq)(Sigma-Aldrich, Cat #130672) and 1-hydroxybenzotriazole hydrate (HOBt) (˜0.19 g, 0.05 eq))(Sigma-Aldrich, Cat #711489) were added to DCM (75 mL) at room temperature (rt). The reaction mixture was then cooled in an ice bath to ˜5° C. followed by addition of N,N-Diisopropylethylamine (DIPEA) (0.30 mL, 0.075 eq.))(Sigma-Aldrich, Cat #387649) and N-(3-Dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (5.83 g, 1.3 eq.)) (Sigma-Aldrich, Cat #03450) then stirring of the resulting reaction mixture at room temperature overnight. The reaction mixture was then washed with water (45 mL×2), dried over anhydrous sodium sulfate and evaporated in vacuo. Dioxane (45 mL), 0-alanine (2.29 g, 1.1 eq.) (Sigma-Aldrich, Cat #146064), N,N-Diisopropylethylamine (DIPEA) (4.5 mL, 1.1 eq.))(Sigma-Aldrich, Cat #387649) and deionized water (22.5 mL) were then added to the resulting residue. After stirring at rt overnight, DCM (225 mL) was added and then washed with HCl/water (0.4%, 225 mL) and then water (225 mL). The organic solution was dried over anhydrous sodium sulfate and concentrated to provide crude Compound 1A. Analytical LC-MS: tR=1.93 min, m/z (ES+) found 712.5.