Shim Joong-Youn, Welsh William J, Cartier Etienne, Edwards James L, Howlett Allyn C
Department of Basic Pharmaceutical Sciences, College of Pharmacy, University of South Carolina, Columbia, South Carolina 29208, USA.
J Med Chem. 2002 Mar 28;45(7):1447-59. doi: 10.1021/jm010267o.
N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide (SR141716; 1) is a potent and selective antagonist for the CB1 cannabinoid receptor. Using the AM1 molecular orbital method, conformational analysis of 1 around the pyrazole C3 substituent identified four distinct conformations designated Tg, Ts, Cg, and Cs. The energetic stability of these conformers followed the order Tg > Cg > Ts > Cs for the neutral (unprotonated) form of 1 and Ts > Tg > Cs > Cg for its piperidine N-protonated form. Unified pharmacophore models for the CB1 receptor ligands were developed by incorporating the protonated form of 1 into the superimposition model for the cannabinoid agonists 4-[4-(1,1-dimethylheptyl)-2-hydroxyphenyl]perhydro-2alpha,6beta-dihydroxynaphthalene (CP55244; 2) and the protonated form of (R)-2,3-dihydro-5-methyl-3-[(4-morpholinyl)methyl]pyrrolo[1,2,3-de]-1,4-benzoxazin-6-ylmethanone (WIN55212-2; 3) reported previously (Shim et al. In Rational Drug Design Symposium Series; Parrill, A. L., Reddy, M. R., Eds.; American Chemical Society: Washington, DC, 1999; pp 165-184). Values of K(i) for 1 and a series of 31 structural analogues were determined from radioligand binding analyses by competitive displacement of [3H]CP55940 from cannabinoid receptors in a rat brain membrane preparation. Comparative molecular field analysis (CoMFA) was employed to construct three-dimensional (3D)-quantitative structure-activity relationship (QSAR) models for this data set as unprotonated species assuming the Tg, Cg, and Ts conformers and for the protonated species assuming the Ts, Tg, and Cs conformers. Values of the conventional r2 and cross-validated r2 (r(cv)2) associated with these CoMFA models exceeded the threshold for statistical robustness (r2 > or = 0.90) and internal predictive ability (r(cv)2 > or = 0.50) in each of these six cases except for the protonated species assuming the Tg conformer (i.e., r2 = 0.97; r(cv)2 = 0.36). Results from conformational analyses, superimposition models, and 3D-QSAR models suggest that the N1 aromatic ring moiety of 1 dominates the steric binding interaction with the receptor in much the same way as does the C3 alkyl side chain of cannabinoid agonists and the C3 aroyl ring of the aminoalkylindole agonists. We also determined that several of the conformers considered in this study possess the proper spatial orientation and distinct electrostatic character to bind to the CB1 receptor. We propose that the unique region in space occupied by the C5 aromatic ring of 1 might contribute to conferring antagonist activity. We further propose that the pyrazole C3 substituent of 1 might contribute to conferring either neutral antagonist or inverse agonist activity, depending upon the interaction with the receptor.
N-(哌啶-1-基)-5-(4-氯苯基)-1-(2,4-二氯苯基)-4-甲基-1H-吡唑-3-甲酰胺(SR141716;1)是一种有效的CB1大麻素受体选择性拮抗剂。使用AM1分子轨道方法，对吡唑C3取代基周围的1进行构象分析，确定了四种不同的构象，分别命名为Tg、Ts、Cg和Cs。对于1的中性(未质子化)形式，这些构象体的能量稳定性顺序为Tg>Cg>Ts>Cs，而对于其哌啶N-质子化形式，顺序为Ts>Tg>Cs>Cg。通过将1的质子化形式纳入先前报道的大麻素激动剂4-[4-(1,1-二甲基庚基)-2-羟基苯基]全氢-2α,6β-二羟基萘(CP55244;2)和(R)-2,3-二氢-5-甲基-3-[(4-吗啉基)甲基]吡咯并[1,2,3-de]-1,4-苯并恶嗪-6-基甲酮(WIN55212-2;3)的质子化形式的叠加模型中，开发了CB1受体配体的统一药效团模型(Shim等人，《合理药物设计研讨会系列》;Parrill,A.L.,Reddy,M.R.编;美国化学学会:华盛顿特区，1999年;第165 - 184页)。通过在大鼠脑膜制剂中用[3H]CP55940的竞争性置换从大麻素受体的放射性配体结合分析中确定了1和一系列31种结构类似物的K(i)值。采用比较分子场分析(CoMFA)为该数据集构建三维(3D)-定量构效关系(QSAR)模型，对于未质子化物种假设为Tg、Cg和Ts构象体，对于质子化物种假设为Ts、Tg和Cs构象体。除了假设为Tg构象体(即r2 = 0.97;r(cv)2 = 0.36)的质子化物种外，与这些CoMFA模型相关的传统r2和交叉验证r2(r(cv)2)值在这六种情况中的每一种都超过了统计稳健性(r2≥0.90)和内部预测能力(r(cv)2≥0.50)的阈值。构象分析、叠加模型和三维定量构效关系模型的结果表明，1的N1芳环部分与受体的空间结合相互作用起主导作用，其方式与大麻素激动剂的C3烷基侧链和氨基烷基吲哚激动剂的C3芳酰基环非常相似。我们还确定，本研究中考虑的几种构象体具有与CB1受体结合的适当空间取向和独特的静电特征。我们提出，1的C5芳环所占据的独特空间区域可能有助于赋予拮抗剂活性。我们进一步提出，1的吡唑C3取代基可能有助于赋予中性拮抗剂或反向激动剂活性，这取决于与受体的相互作用。
