Defunctionalized Lobeline Analogues: Structure−Activity of Novel Ligands for the Vesicular Monoamine Transporter
作者:Guangrong Zheng、Linda P. Dwoskin、Agripina G. Deaciuc、Seth D. Norrholm、Peter A. Crooks
DOI:10.1021/jm0501228
日期:2005.8.1
(-)-Lobeline (2R,6S,10S; 1a), an antagonist at nicotinic acetylcholine receptors (nAChRs), inhibits the neurochemical and behavioral effects of methamphetamine and inhibits dopamine transporter (DAT) and vesicular monoamine transporter (VMAT2) function. VMAT2 is a target for the development of treatments for methamphetamine abuse. Structural modification of lobeline affords the defunctionalized analogues meso-transdiene (MTD) and lobelane, which have high potency and selectivity for VMAT2. To establish the structure-activity relationships within this novel class of VMAT2 ligands, specific stereochemical forms of MTD, lobelane, and other structurally related analogues have been synthesized. These compounds have been evaluated for inhibition of [H-3]nicotine ( [H-3]NIC) binding (alpha 4 beta 2* nAChR), [H-3]methyllycaconitine ([H-3]MLA) binding (alpha 7* nAChR), and [H-3]dihydrotetrabenazine ([H-3]DTBZ) binding (VMAT2). Generally, all of these analogues had lower affinities at alpha 4 beta 2* and alpha 7* nAChRs compared to lobeline, thereby increasing selectivity for VMAT2. The following structural modifications resulted in only modest changes in affinity for VMAT2, affording analogues that were less potent than the lead compound, lobelane: (1) altering the stereochemistry at the C-2 and C-6 positions of the piperidino ring, (2) varying unsaturation in the piperidino C-2 and C-6 substituents, (3) introducing unsaturation into the piperidine ring, (4) ring-opening or eliminating the piperidine ring, and (5) removing the piperidino N-methyl group. Furthermore, incorporating a quaternary ammonium group into defunctionalized lobeline molecules in the cis-series resulted in significant loss of affinity for VMAT2, whereas only a modest change in affinity was obtained in the trans-series. The most potent (K-i = 630 nM) and VMAT2-selective compound evaluated was the N-methyl-2,6-cis-bis(naphthaleneethyl)piperidine analogue 28b (1-NAP-lobelane), in which the phenyl groups of lobelane were replaced with 1-naphthyl moieties. Thus, initial structure-activity relationship studies reveal that the most promising structural changes to the lobeline molecule that lead to enhancement of VMAT2 affinity and selectivity are defunctionalization, affording lobelane and MTD, and replacement of the phenyl rings of lobelane with other aromatic moieties that have a pi-extended structure.
(-)-Lobeline(2R,6S,10S;1a)是一种烟碱型乙酰胆碱受体(nAChRs)拮抗剂,能够抑制甲基苯丙胺的神经化学和行为效应,并抑制多巴胺转运体(DAT)和囊泡单胺转运体(VMAT2)的功能。VMAT2是开发甲基苯丙胺滥用治疗药物的目标。通过对lobeline进行结构修饰,得到了功能丧失的类似物meso-transdiene(MTD)和lobelane,它们对VMAT2具有高活性和选择性。为了建立这一新型VMAT2配体类别的结构-活性关系,研究人员合成了MTD、lobelane以及其它结构相关类似物的特定立体化学形式。这些化合物已被评估用于抑制[H-3]尼古丁([H-3]NIC)结合(α4β2* nAChR)、[H-3]甲基鲁康宁([H-3]MLA)结合(α7* nAChR)以及[H-3]二氢四苯肼([H-3]DTBZ)结合(VMAT2)的能力。总体而言,与lobeline相比,所有这些类似物在α4β2*和α7* nAChRs上的结合亲和力较低,从而提高了对VMAT2的选择性。以下是导致VMAT2亲和力变化不大,且活性低于先导化合物lobelane的结构修饰:
1. 改变哌啶环C-2和C-6位的立体化学;
2. 在哌啶C-2和C-6取代基中改变不饱和度;
3. 将不饱和引入哌啶环;
4. 开环或消除哌啶环;
5. 去除哌啶环上的N-甲基基团。
此外,在顺式系列失去功能的lobelane分子中引入季铵基团,导致对VMAT2的亲和力显著降低,而在反式系列中仅获得亲和力的小变化。评估中发现,最活跃(K-i = 630 nM)且对VMAT2选择性最高的化合物是N-甲基-2,6-顺式-双(萘乙基)哌啶类似物28b(1-NAP-lobelane),其中lobelane的苯基被1-萘基基团取代。因此,初步的结构-活性关系研究表明,对lobelane分子结构进行修饰以增强VMAT2亲和力和选择性的最有前途的变化是去功能化(得到lobelane和MTD)以及将lobelane的苯环替换为具有π扩展结构的其他芳香基团。