Grunewald G L, Markovich K M, Sall D J
Department of Medicinal Chemistry, University of Kansas, Lawrence 66045.
J Med Chem. 1987 Dec;30(12):2191-208. doi: 10.1021/jm00395a005.
In a continuation of studies directed at characterizing the conformational basis of binding beta-phenylethylamines at the active site of phenylethanolamine N-methyltransferase (PNMT), anti-10-amino- (12) and syn-10-amino-5,6,7,8-tetrahydro-5,8-methano-9H-benzocycloheptene (13) were prepared and evaluated as substrates and inhibitors for PNMT. These conformationally defined amphetamine analogues mimic a low energy half-chair form of 2-aminotetralin (2AT). Further, in order to determine the active site binding orientation of beta-phenylethylamines bearing aryl lipophilic substituents, the aryl trifluoromethyl-substituted derivatives of 12 and 13 (20-27), as well as anti-9-amino-5-(trifluoromethyl)-(18) and anti-9-amino-6-(trifluoromethyl) benzonorbornene (19), were prepared and evaluated. The competitive inhibition displayed by the fully extended analogue 12 coupled with the uncompetitive kinetics exhibited by the folded isomer 13 supports previous findings that a fully extended side chain conformation is optimal for binding to the active site of PNMT. In addition, the fact that 12 displayed enhanced affinity as an inhibitor over its beta-phenylethylamine counterparts in the benzonorbornene and 1,4-ethanonaphthalene ring systems suggests that a half-chair conformation is preferred when 2AT analogues interact at the active site of the enzyme. This would be consistent with previous results that PNMT preferentially binds molecules with a more coplanar relationship between the aromatic ring and the amino nitrogen. The lack of activity as a substrate in 12 indicates that the negative steric interactions of the ethano bridging unit prohibits it from binding in a manner consistent with the known PNMT substrates exo-2-amino- (6) and anti-9-aminobenzonorbornene (8). Given the emergence of activity as a substrate in 20 and 21 (the 1-trifluoromethyl- and the 2-trifluoromethyl-substituted derivatives of 12), it appears that the positive interaction of the trifluoromethyl group orients these analogues in a manner in which the ethano bridge lies in regions of steric bulk tolerance. This would suggest that the region of steric intolerance has a degree of directionality. Finally, although the aromatic ring binding region of the active site of PNMT contains a large degree of lipophilic character, only specific spatial orientations between the trifluoromethyl group and the amino nitrogen of aryl trifluoromethyl-substituted beta-phenylethylamines allow both to interact simultaneously in a manner that allows the amine to bind in a region of the active site in which methylation can occur.
在旨在阐明苯乙醇胺N - 甲基转移酶（PNMT）活性位点结合β - 苯乙胺的构象基础的系列研究中，制备了反式 - 10 - 氨基 - （12）和顺式 - 10 - 氨基 - 5,6,7,8 - 四氢 - 5,8 - 亚甲基 - 9H - 苯并环庚烯（13），并将其作为PNMT的底物和抑制剂进行评估。这些构象明确的苯丙胺类似物模拟了2 - 氨基四氢萘（2AT）的低能量半椅形式。此外，为了确定带有芳基亲脂性取代基的β - 苯乙胺在活性位点的结合取向，制备并评估了12和13的芳基三氟甲基取代衍生物（20 - 27），以及反式 - 9 - 氨基 - 5 - （三氟甲基） - （18）和反式 - 9 - 氨基 - 6 - （三氟甲基）苯并降冰片烯（19）。完全伸展的类似物12表现出的竞争性抑制与折叠异构体13表现出的非竞争性动力学相结合，支持了先前的发现，即完全伸展的侧链构象对于与PNMT活性位点结合是最佳的。此外，在苯并降冰片烯和1,4 - 亚乙基萘环系统中，12作为抑制剂表现出比其β - 苯乙胺对应物更高的亲和力，这表明当2AT类似物在酶的活性位点相互作用时，半椅构象是优选的。这与先前的结果一致，即PNMT优先结合芳环和氨基氮之间具有更共面关系的分子。12作为底物缺乏活性表明，亚乙基桥连单元的负空间相互作用阻止它以与已知的PNMT底物外向 - 2 - 氨基 - （6）和反式 - 9 - 氨基苯并降冰片烯（8）一致的方式结合。鉴于20和21（12的1 - 三氟甲基 - 和2 - 三氟甲基 - 取代衍生物）作为底物出现活性，似乎三氟甲基基团的正相互作用使这些类似物以亚乙基桥位于空间容限区域的方式取向。这表明空间不容忍区域具有一定程度的方向性。最后，尽管PNMT活性位点的芳环结合区域具有很大程度的亲脂性特征，但只有芳基三氟甲基取代的β - 苯乙胺的三氟甲基基团和氨基氮之间的特定空间取向才能使两者同时以允许胺在活性位点中发生甲基化的区域结合的方式相互作用。
