Molecular Engineering of Photoremovable Protecting Groups for Two-Photon Uncaging
Molecular Engineering of Photoremovable Protecting Groups for Two-Photon Uncaging
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DOI：
10.1002/anie.200803964
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发表时间：
2008-01-01
影响因子：
16.6
通讯作者：
Nicoud, Jean -Francois
中科院分区：
文献类型：
--
作者：
Gug, Sylvestre;Bolze, Frederic;Nicoud, Jean -Francois
光可拆卸保护基团已成为各种生物系统动态研究的支柱，从神经科学到遗传学，主要是因为光诱导激活与用于检测生物反应的其他技术是正交的活性分子的光化学释放通常由初始的单光子吸收过程诱导，导致释放物质的有限空间定位。为了克服这一障碍，双光子（TP）激发最近成为一种非常有前途的空间控制技术。[3,4]实际上，这种非线性光学（NLO）过程只发生在光强度最大的地方，通常是通过聚焦红外脉冲激光束。在这种情况下，激发态通过同时吸收两个低能光子（经典吸收中的红外线而不是紫外线）而产生光解反应，这也限制了激发光束的光毒性。不幸的是，为单光子光激活而开发的各种光可移动基团（“笼”）在双光子激发中表现出非常低的效率对这些发色团进行了一些化学修饰以提高它们的TP敏感性，并且还描述了新的平台。[6-10]这些方法导致了中等效率的TP笼，其释放截面（duφu）最多约为1Goeppert-Mayer （1 GM= 10À50 cm4 s photonÀ1）。然而，这个值仍然不足以用于生物学研究，因此建议的最小值为3gm本文报道了高效TP笼的设计、合成、表征及其在谷氨酸释放中的应用。在过去的十年中，优化TP吸收的发色团（TPA）成为有机化学家的一个重要目标[12,13]，并在材料[14,15]和生物[16,17]科学中得到了许多应用。这些努力导致了各种可能的方法来增加发色团或荧光团的TPA特性。研究了不同的发色团几何结构，包括线性（1D）、[18,19]平面（2D）、[20,21]和四面体（3D）[22]结构。一维TPA发色团的典型偶极结构是生物学中可用的最小系统，通常由两个电子给体或电子受体基团（D或a）通过共轭系统连接到中心核心组成。可以在中心核上添加供体或受体基团，形成四极性结构（图1）。可以通过延长共轭体系和/或增加侧基的给电子或吸电子效应来改善这种体系的TPA性质。我们最近描述了3-（2-丙基）-4 ' -甲氧基-4-硝基联苯（PMNB）笼作为谷氨酸的高效TP光耐保护基团（在800 nm处du Fu= 0.45 GM）通过对π体系的扩展，使其释放截面比已知的甲氧基硝基苯平台增大。Andraud， Baldeck及其同事提出了另一种方法，他们指出，两个弱共轭单体之间的双激子耦合可以增强低聚物的TPA截面。[24-26]我们将这一概念应用于新型线性笼化平台的分子工程。第一个设计的分子（4,4 ' -双-{8-[4-硝基-3-（2-丙基）-苯基]}- 3,3 ' -二甲氧基联苯或BNSMB，图2）由PMNB的两个乙烯链连接在一起，以利用两个单体之间可能的相互作用。在体系中引入双键以提高其在有机溶剂中的溶解度。很明显，……的增加
Photoremovable protecting groups have become a mainstay for dynamic studies in various biological systems, from neuroscience to genetics,[1] mainly because photoinduced activation is orthogonal to other techniques used to detect biological responses.[2] The photochemical release of the active molecule is usually induced by an initial one-photon absorption process, leading to a limited spatial localization of the released substance. To overcome this obstacle, twophoton (TP) excitation has recently emerged as a very promising technique to obtain spatial control.[3, 4] Indeed this nonlinear optical (NLO) process takes place only where the light intensity is at a maximum, typically by focusing an infrared pulsed laser beam. In this case, the excited state yields to the photolytic reaction by the simultaneous absorption of two low-energy photons (infrared instead of ultraviolet, in classical absorption), which also limits the phototoxicity of the excitation beam. Unfortunately, the various photoremovable groups (“cages”) that have been developed for one-photon photoactivation exhibit very low efficiency in two-photon excitation.[5] Some chemical modifications have been performed on these chromophores to improve their TP sensitivity, and new platforms have also been described.[6–10] These approaches have led to moderately efficient TP cages with uncaging cross-sections (duφu) of about 1Goeppert-Mayer (1 GM= 10À50 cm4 s photonÀ1) at best. However, this value remains insufficient for use in biological studies, for which a 3 GM minimum value has been suggested.[11] We report herein the design, synthesis, and characterization of highly efficient TP cages, and their application to glutamate photorelease. During the last decade, the optimization of chromophores for TP absorption (TPA) became an important goal for organic chemists,[12, 13] and give rise to many applications in material [14, 15] and biological [16, 17] sciences. These efforts have led to various possible approaches for increasing the TPA properties of chromophores or fluorophores. Different chromophore geometries have been investigated, with linear (1D),[18, 19] planar (2D),[20, 21] and tetrahedral (3D)[22] structures. The typical dipolar architecture of a 1D TPA chromophore, the smallest system to be useful in biology, is generally composed of two electron-donor or electron-acceptor groups (D or A) linked to a central core by conjugated systems. Donor or acceptor groups can be added on the central core to give quadrupolar architectures (Figure 1).The TPA properties of such systems can be improved by lengthening the conjugated system and/or increasing the electron-donating or-withdrawing effect of the side groups. We recently described the 3-(2-propyl)-4’-methoxy-4-nitrobiphenyl (PMNB) cage as an efficient TP photolabile protecting group for glutamate (du Fu= 0.45 GM at 800 nm).[23] Its uncaging cross-section has been increased in comparison with the well-known methoxynitrobenzyl platform by extending the π system. Another approach was proposed by Andraud, Baldeck, and co-workers, who pointed out that TPA cross-sections of oligomers can be enhanced by biexcitonic coupling between two weakly conjugated monomers.[24–26] We applied this concept to the molecular engineering of new linear caging platforms. The first designed molecule(4, 4’-bis-{8-[4-nitro-3-(2-propyl)-styryl]}-3, 3’-dimethoxybiphenyl or BNSMB, Figure2) was composed of two vinylogues of PMNB linked together to take advantage of a possible interaction between the two monomers. A double bond was introduced in the system to improve its solubility in organic solvents. Clearly, this increase in the …