Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States.
Wolfson Department of Chemical Engineering, Technion, Israel Institute of Technology, Haifa 3200003, Israel.
Mol Pharm. 2021 Aug 2;18(8):3037-3049. doi: 10.1021/acs.molpharmaceut.1c00261. Epub 2021 Jul 8.
Stress testing of active pharmaceutical ingredients (API) is an important tool used to gauge chemical stability and identify potential degradation products. While different flavors of API stress testing systems have been used in experimental investigations for decades, the detailed kinetics of such systems as well as the chemical composition of prominent reactive species, specifically reactive oxygen species, are unknown. As a first step toward understanding and modeling API oxidation in stress testing, we investigated a typical radical "soup" solution an API is subject to during stress testing. Here we applied electronic structure calculations to automatically generate and refine a detailed chemical kinetics model, taking a fresh look at API oxidation. We generated a detailed kinetic model for a representative azobis(isobutyronitrile) (AIBN)/HO/CHOH stress-testing system with a varied cosolvent ratio (50%/50%-99.5%/0.5% vol water/methanol) for 5.0 mM AIBN and representative pH values of 4-10 at 40 °C that was stirred and open to the atmosphere. At acidic conditions, hydroxymethyl alkoxyl is the dominant alkoxyl radical, and at basic conditions, for most studied initial methanol concentrations, cyanoisopropyl alkoxyl becomes the dominant alkoxyl radical, albeit at an overall lower concentration. At acidic conditions, the levels of cyanoisopropyl peroxyl, hydroxymethyl peroxyl, and hydroperoxyl radicals are relatively high and comparable, while, at both neutral and basic pH conditions, superoxide becomes the prominent radical in the system. The present work reveals the prominent species in a common model API stress testing system at various cosolvent and pH conditions, sets the stage for an in-depth quantitative API kinetic study, and demonstrates the usage of novel software tools for automated chemical kinetic model generation and refinement.
原料药（API）的加速稳定性试验是一种用于评估化学稳定性和识别潜在降解产物的重要工具。虽然数十年来在实验研究中已经使用了不同风味的 API 加速稳定性试验系统，但这些系统的详细动力学以及主要反应性物质（特别是活性氧物种）的化学成分仍然未知。作为理解和模拟 API 在加速稳定性试验中氧化作用的第一步，我们研究了 API 在加速稳定性试验中所经历的典型自由基“汤”溶液。在这里，我们应用电子结构计算自动生成和细化详细的化学动力学模型，对 API 氧化作用进行了新的研究。我们为代表性的偶氮二异丁腈（AIBN）/HO/CHOH 加速稳定性试验系统生成了一个详细的动力学模型，该系统的共溶剂比（50%/50%-99.5%/0.5%体积水/甲醇）不同，AIBN 的浓度为 5.0 mM，研究的代表性 pH 值为 4-10，温度为 40°C，搅拌并与大气相通。在酸性条件下，羟甲基烷氧基是主要的烷氧基自由基，而在碱性条件下，对于大多数研究的初始甲醇浓度，氰基异丙基烷氧基成为主要的烷氧基自由基，尽管总体浓度较低。在酸性条件下，氰基异丙基过氧自由基、羟甲基过氧自由基和过氧氢自由基的水平相对较高且相当，而在中性和碱性 pH 条件下，超氧自由基成为体系中的主要自由基。本工作揭示了在不同共溶剂和 pH 条件下常见模型 API 加速稳定性试验系统中的主要物质，为深入的定量 API 动力学研究奠定了基础，并展示了新型软件工具在自动化学动力学模型生成和细化方面的应用。
