請問有大佬做過喜樹堿CPT與三光氣、2-羥乙基二硫化物在DMAP催化下生成CPT-ss-OH的反應(yīng)嘛？下面是我參考的文獻部分，反應(yīng)過程我注意了嚴(yán)格絕水，但是反應(yīng)的轉(zhuǎn)化率還是很低，比文獻提到的產(chǎn)率為80%低很多，哪位大佬能給我一些合成方面的建議和改進方法嘛？
     
               CPT (350 mg, 1 mmol) and triphosgene (110 mg, 0.34 mmol) were dispersed in anhydrous DCM (50 mL), to which, 4-dimetheylaminopyridine (DMAP) (390 mg, 3.2 mmol) was added. The mixture was stirred at room temperature for 3 h. 2-Hydroxyethyl disulfide (HEDS) (0.77 g, 5 mmol) in THF (10 mL) was added. The solution was stirred at room temperature. The reaction process was monitored by TLC and stopped after the starting material was completely consumed. The reaction solution was diluted with DCM (200 mL), and washed with HCl (pH 1, 3 × 50 mL) and then with water (3 × 50 mL). The organic phase was dried with Na2SO4. After the solvent was removed under vacuum, CPT-SS-OH was purified by silica gel column chromatography (DCM/MeOH = 50:1 v/v) to give a slight yellow solid (438 mg, yiel  80%).


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