不同分子量灯盏乙素-PEG酯的合成、性质及小肠吸收研究

为探讨小分子药物PEG化（PEGylation）对口服吸收的影响规律，合成了多种分子量的灯盏乙素PEG衍生物。对产物在不同条件下的理化常数、稳定性及大鼠在体小肠吸收情况进行了考察。灯盏乙素经PEG化后水溶性提高，并获得了适于口服吸收的理想的分配系数。体外试验中，该类衍生物表现出前药的特性，在pH7．4的PBS缓冲液中t1/2超过12h（37℃），而在血浆中则快速降解释放出灯盏乙素，t1／2约为1．5～3h；灯盏乙素经PEG化后，口服吸收明显增加，但PEG化物的吸收随PEG片断分子量的增大而减少。综合考虑反应收率、产物稳定性和口服吸收等情况，用于灯盏乙素修饰的PEG分子量应在400～1000 Da之间。

The Synthesis, Characterization and in Situ Intestinal Absorption of Different Molecular Weight Scutellarin-PEG Conjugates

In this report, highly water soluble esters of scutellarin with different molecular weight polyethylene glycol (PEG) were synthesized in order to improve the bioavailability of scutellarin. The physicochemical properties, the stabilities under different conditions and the in situ intestinal absorption in rats of the conjugates were investigated. By PEG modification, the greatly increased water solubility and desirable partition coefficient of scutellarin were obtained. These compounds function as prodrugs i. e. breakdown occurred in a predictable fashion: the t1/2 of them in PBS buffer at pH7.4 was above 12 h (37 degrees C) in vitro, while in plasma a rapid breakdown was observed, with a t1/2 of about 1. 5-3 h. The stabilities of the prodrugs were improved according to the increase of the molecular weight of PEG, thus, PEGylated prodrugs with desirable rates of hydrolysis could be obtained by the use of variable molecular weight PEGs. The PEGylation could enhance the absorption of scutellarin in rat intestine, and the absorption of scutellarin and its PEG conjugates by intestine was mainly via passive transport, for when the concentration was raised, the uptake did not appear saturable, and the permeability coefficient kept at an equilibrium level. When the molecular weight of PEG increased from 200 to 1000 Da, the absorption of the conjugates decreased. In conclusion, by overall consideration of the yield, stability and absorption, the present authors estimate that the PEG molecular weight used for the PEGylation of scutellarin should be within the range of 400-1 000 Da.