Step 4:Preparation of compound 8
To a solution of 7 (200mg, 0.465mmol, 1.0 eq) in deionized water (3ml, c=0.15) was added AgCl (133mg, 0.93mmol, 2.0 eq). After addition, the reaction mixture was stirred at room temperature overnight. The suspension was then filtered and the filtrate was lyophilized to give compound 8 (141mg, yield=89.8%) as a solid. HPLC purity: at 220nm; Mass: M+1=339.4. 1H NMR (300 MHz, D2O): δ 7.117 (m, 3H), 4.056 (dd, J=8.1 Hz, 1H), 3.712~3.808 (m, 1H), 3.656 (m, J=13.2 Hz, 2H), 3.510~3.582 (m, 1H), 3.344 (m, 2H), 2.117 (s, 6H), 1.984~2.070 (m, 2H), 1.818 (m, 4H), 1.660 (m, 1H), 1.455 (m, 1H), 1.278 (t, J=7.2 Hz, 3H), 1.107 (t, 3H) ppm.