A common challenge for medicinal chemists is to reduce the pK_a of strongly basic groups' conjugate acids into a range that preserves the desired effects, usually potency and/or solubility, but avoids undesired effects like high volume of distribution (V_d), limited membrane permeation, and off-target binding to, notably, the hERG channel and monoamine receptors. We faced this challenge with a 3,4,5,6-tetrahydropyridine-2-amine scaffold harboring an amidine, a key structural component of potential inhibitors of BACE1, the rate-limiting enzyme in the production of Aβ species that make up amyloid plaques in Alzheimer's disease. In our endeavor to balance potency with desirable properties to achieve brain penetration, we introduced a diverse set of groups in beta position of the amidine that modulate logD, PSA and pK_a. Given the synthetic challenge to prepare these highly functionalized warheads, we first developed a design flow including predicted physicochemical parameters which allowed us to select only the most promising candidates for synthesis. For this we evaluated a set of commercial packages to predict physicochemical properties, which can guide medicinal chemists in their endeavors to modulate pK_a values of amidine and amine bases.

药物化学家面临的一个共同挑战是将强碱性基团的共轭酸的 pK _a降低到保持所需效果（通常是效力和/或溶解度）的范围内，但避免不希望的效果，例如高分布体积 (V _d)、有限的膜渗透和脱靶结合，尤其是 hERG 通道和单胺受体。我们使用含有脒的 3,4,5,6-四氢吡啶-2-胺支架面临这一挑战，脒是 BACE1 潜在抑制剂的关键结构成分，BACE1 是构成淀粉样蛋白斑块的 Aβ 种类产生中的限速酶在阿尔茨海默病中。在我们努力平衡效力与实现大脑穿透的理想特性的过程中，我们在脒的 β 位置引入了一组不同的基团，它们调节 logD、PSA 和 pK _a. 鉴于制备这些高度功能化弹头的合成挑战，我们首先开发了一个设计流程，包括预测的物理化学参数，这使我们能够只选择最有希望的合成候选者。为此，我们评估了一组商业软件包来预测物理化学性质，这可以指导药物化学家努力调节脒和胺碱的 pK _a值。