本實驗室合成D-phenylglycine-L-dopa雙胜肽先驅藥，其藥物動力學顯示具有比L-dopa較高的口服吸收外，並有較大的體內分佈體積，此可能是該雙胜肽成為腦中緩釋dopamine的原因之一。為佐證並探討D-phenylglycine是否可以成為設計緩釋先驅藥的分子，我們以人類血清白蛋白測試並比較Dphenylglycine、L-dopa和D-phenylglycine-L-dopa的蛋白質結合程度。本實驗以超過濾法分離游離藥物和蛋白質，再以高效能液相層析儀定量游離藥物。D-phenylglycine、L-dopa和D-phenylglycine-L-dopa的線性分析範圍在 0.1μg/mL-100 μg/mL之間，最低定量濃度分別為0.5 μg/mL，0.1 μg/mL及0.5 μg/mL，分析方法之再現性與可信度以同日內與異日間校正曲線之精度與準度檢定確效之（n = 3），其變異係數均小於12%，誤差均小於10%。三個化合物之回收率分別在95.4% - 98.1%、91.9 % - 98.8%及96.8% - 97.9%（n =3）。在600 μM定量濃度下，D-phenylglycine、L-dopa和D-phenylglycine-L-dopa的白蛋白結合率分別為 28.0%、8.2%及19.2%。在此濃度下，DPhenylglycine的蛋白質結合率較L-dopa高3.4倍，而且接上L-dopa之後，提高L-dopa之蛋白質結合率達2.4倍。吸附動力學的測定結果顯示，此雙胜肽與白蛋白的結合部位數（n, sites/L）比L-dopa高了5.8倍，結合常數（ka1,L/mol）比L-dopa高了3.8倍。清除率高的藥物如與D-phenylglycine化學鍵結形成先驅藥，或許可增加血漿中的蛋白質結合率而延緩清除，增長半衰期，達到緩釋的效果。

D-phenylglycine-L-dopa, a dipeptide synthesized in this laboratory for improving the oral absorption of L-dopa, showed better absorption and distribution in rats. We assumed that the extensive distribution might explain its sustained release of brain dopamine. Since protein binding is a main factor of drug distribution, we investigated the effect of D-phenylglycine on the binding of L-dopa to human serum albumin. The degree of the binding of D-phenylglycine, L-dopa and D-phenylglycine-L-dopa to serum albumin was determined. Free and bound portion of test compounds were separated with ultrafiltration method and the assay of free drug portion was conducted with reversed phase HPLC. The LOQ for D-phenylglycine, L-dopa and D-phenylglycine-L-dopa was 0.5 μg/mL, 0.1 μg/mL and 0.5 μg/mL, respectively. Assay methods were validated by determining the precision and accuracy of interday and intraday variations. The coefficient of variation (CV) was within 12% and the relative error (RE) was within 10% (n = 3). The recovery rate was 95.4% - 98.1% for D-phenylglycine, 91.9 % - 98.8% for L-dopa and 96.8% - 97.9% for D-phenylglycine-L-dopa, respectively (n = 3). D-Phenylglycine showed higher serum albumin binding than L-dopa did at various concentrations. At a concentration of 600 μM, the degree of albumin binding of D-phenylglycine, L-dopa, D-phenylglycine-L-dopa was 27.98%, 8.20% and 19.18%, respectively. The albumin binding of L-dopa at this concentration increased by 2.4 folds when chemically bound to D-phenylglycine. The number of the binding sites of L-dopa increased by 5.8 folds and the binding constant Ka1 increased by 3.8 folds when L-dopa was chemically bound to D-phenylglycine. With the affinity to serum albumin, D-phenylglycine showed its possibility as a delivery moiety for drugs with limited distribution to use the body protein as a reservoir.