Raghavan K S, Gray D B, Scholz T H, Nemeth G A, Hussain M A
Dupont Merck Pharmaceutical Company, Experimental Station, Wilmington, Delaware 19880-0400, USA.
Pharm Res. 1996 Dec;13(12):1815-20. doi: 10.1023/a:1016076907072.
The objective was to evaluate the degradation profile of the elastase inhibitor DMP 777 and lay the foundation for formulation development.
The pKa was determined by potentiometric titration in mixed-aqueous solvents. The degradation kinetics were studied as a function of pH, buffer concentration, ionic strength, methanol concentration and temperature using a stability-indicating HPLC assay. The degradation products were identified by LC-MS, NMR, and by comparison with authentic samples.
The pKa for the protonated piperazine nitrogen was estimated to be 7.04. The pH-rate profile is described by specific acid-, water-, and specific base-catalyzed pathways. The pH of maximum stability is in the range of 4 to 4.5 where water is the principal catalyst in the reaction. Buffer catalysis, primary salt effects and medium effects were observed. The proposed mechanism for acid catalyzed degradation is the rarely observed AAL1 which involves alkyl-nitrogen heterolysis. The driving force for the reaction appears to lie in the stability of the benzylic carbocation. The proposed mechanism for base catalyzed degradation is BAC2 which involves beta-lactam ring opening. The beta-lactam ring of DMP 777, a monolactam, appears to be as reactive as that in benzylpenicillin in the KOH controlled region where a similar mechanism of hydrolysis should be operative. A contributing factor to this increased reactivity may lie in the reduced basicity of the beta-lactam nitrogen making it a good leaving group.
The degradation profile indicates that development of a solution dosage form of DMP 777 with adequate shelf-life stability at room temperature is feasible.
评估弹性蛋白酶抑制剂DMP 777的降解情况，为制剂开发奠定基础。
在混合水性溶剂中通过电位滴定法测定pKa。使用稳定性指示HPLC法研究降解动力学，考察其作为pH、缓冲液浓度、离子强度、甲醇浓度和温度的函数关系。通过LC-MS、NMR以及与标准样品比较来鉴定降解产物。
质子化哌嗪氮的pKa估计为7.04。pH-速率曲线由特定酸催化、水催化和特定碱催化途径描述。最大稳定性的pH范围为4至4.5，此时水是反应中的主要催化剂。观察到缓冲催化、一级盐效应和介质效应。酸催化降解的 proposed 机制是很少观察到的AAL1，它涉及烷基-氮杂裂解。反应的驱动力似乎在于苄基碳正离子的稳定性。碱催化降解的 proposed 机制是BAC2，它涉及β-内酰胺环开环。单内酰胺DMP 777的β-内酰胺环在KOH控制区域的反应活性似乎与苄青霉素中的β-内酰胺环相同，在该区域应存在类似的水解机制。这种反应活性增加的一个促成因素可能在于β-内酰胺氮碱性的降低，使其成为一个良好的离去基团。
降解情况表明，开发在室温下具有足够货架期稳定性的DMP 777溶液剂型是可行的。
